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Absorption, Distribution, and Binding Profile of ME-401, a Potent and Selective Oral Small-Molecule Inhibitor of Phosphatidylinositol 3-Kinase δ (PI3Kδ) in Animal and B-Cell Lymphoma Models

Absorption, Distribution, and Binding Profile of ME-401, a Potent and Selective Oral... Background Phosphatidylinositol 3-kinase isoform δ (PI3Kδ) mediates multiple events in lymphocytes, including cell pro- liferation, survival, and motility. Inhibition of PI3Kδ, with downstream inhibitory effects on cell growth and survival, has been utilized to treat lymphoid malignancies. ME-401 is an oral, once-daily, selective PI3Kδ inhibitor with an optimized pharmacologic profile that is in clinical development for the treatment of B-cell malignancies. Objectives This work examined aspects of the pharmacologic profile of ME-401 in preclinical models to investigate the basis of the clinical activity of ME-401 that may differentiate it from other currently approved PI3Kδ inhibitors. Methods We determined the ME-401 blood to plasma ratios, permeability, and purified enzyme-binding kinetics. The oral bioavailability and volume of distribution of ME-401 were evaluated in various species. ME-401 concentrations in plasma and tumor and brain tissues were evaluated following oral administration in an A20 syngeneic mouse model of B-cell lymphoma. Idelalisib was used as a reference compound for the measurement of purified enzyme-binding kinetics and concentrations in plasma and tumor in the A20 syngeneic mouse model. Results Oral administration of ME-401 to dogs resulted in 79% bioavailability compared with intravenous administration. Allometric scaling from rodents, dogs, and nonhuman primates resulted in a predicted human volume of distribution at steady state of 10.75 L/kg. ME-401 was shown to distribute into the lymph in dogs and permeate into cells readily, with a human blood to plasma ratio of 1.4 and ~ 50% retention in the Caco-2 cell monolayer at 1 μM. The high binding affinity and low −11 dissociation rate of ME-401 resulted in an equilibrium dissociation constant (K ) of 3.03 × 10 M. Oral administration of ME-401 in an A20 syngeneic mouse model resulted in tumor concentrations 20–30 times higher than plasma concentrations at 4 h after the last dose. By 24 h, the tumor levels had decreased approximately 30–50% compared with levels at 4 h while remaining significantly increased relative to plasma concentrations. ME-401 was also present in brain tissue at 4 and 24 h −9 after the last dose. In comparison, the idelalisib dissociation rate was ~ 100 times higher, resulting in a K of 1.11 × 10 M. Idelalisib tumor concentrations were only approximately three times higher than plasma concentrations at 4 h, while drop- ping below the limit of quantitation in both tumor and plasma by 24 h. Conclusions These data support the capacity of ME-401 to be orally absorbed, distribute to target tissues, enter and accu- mulate in target cells, and bind to the target with high affinity to exert its mechanism of action. These characteristics underlie the high clinical potency seen in B-cell malignancies that may differentiate ME-401 from other PI3Kδ inhibitors currently approved or in development. * Ofir Moreno omoreno@meipharma.com MEI Pharma Inc., 3611 Valley Centre Drive, Suite 500, San Diego, CA 92130, USA Vol.:(0123456789) 604 O. Moreno, J. Wood activated immune cells (Raji cell line, primary basophils) Key Points with low nM 50% inhibitory concentrations even in the presence of whole blood, and activity against multiple ME-401 is an oral, once-daily, selective PI3Kδ inhibi- primary B-cell malignancies [10]. Results from a first- tor, part of a signaling pathway in cells that can become in-human study in healthy volunteers demonstrated oral hyperactive leading to tumor growth and resistance to bioavailability, linear pharmacokinetics (PK), and a half- chemotherapy. life of 28 h to support once-daily dosing. Additionally, the PK/pharmacodynamic (PD) relationship was examined In preclinical studies, ME-401 reached its target site with inhibition of basophil activation assessed via CD63 (PI3Kδ) and bound to it more tightly and longer than expression following ex vivo stimulation. Oral adminis- idelalisib, another PI3Kδ inhibitor. ME-401 bound to its tration of ME-401 resulted in 90% of maximal effective target tightly for ~ 5 h compared with ~ 2 min for idelal- concentration (EC ) at a plasma concentration of 5 ng/ isib. mL (9  nM), with trough plasma values predicted to be Oral ME-401 is well absorbed and distributed through- above the EC , using daily dosing of 60  mg [11, 12]. out the body in animal studies with concentrations in key Consequently, 60 mg/day was used as the starting dose for sites for lymphoma including lymph, plasma, lymphoma a Phase 1b dose escalation study in relapsed B-cell malig- tumor, and brain tissue. nancies, even though the maximum recommended start- ing dose (MRSD) in patients with cancer was determined to be 140 mg/day based on preclinical toxicology data. Initial results from the Phase 1b study have shown high initial overall response rates (ORRs) in relapsed follicular lymphoma (FL) and chronic lymphocytic leukemia (CLL)/ 1 Introduction small lymphocytic lymphoma (SLL) [13, 14]. To be efficacious, an oral agent must overcome the hur - Phosphatidylinositol 3-kinase (PI3K) is a lipid kinase with a dles of entering the bloodstream from the gastrointestinal catalytic subunit that exists in four different isoforms (α, β, tract, reaching the target tissues, and binding with sufficient γ, and δ). The δ isoform is highly restricted to hematopoietic affinity to exert its mechanism of action. Intracellular tar - cells and plays a key role in normal B-cell development and gets such as PI3Kδ have additional hurdles of entering the function. Once recruited to phosphorylated binding sites on target cells and establishing an effective concentration at the B-cell adapter of PI3K or on the cytoplasmic tail of the the intracellular site of action. To that end, the preclinical transmembrane protein CD19, activated PI3Kδ signaling studies presented here examined the permeability and bind- occurs via phosphorylation of the key lipid second messen- ing affinity of ME-401; oral bioavailability and volume of ger phosphatidylinositol, with resultant phosphorylation of distribution in various species; and concentrations in plasma protein kinase B (Akt), leading to the downstream phos- and tumor and brain tissues in an A20 syngeneic mouse phorylation of a variety of effector molecules (e.g., TSC1/2, model of B-cell lymphoma. Idelalisib was used as a refer- mTORC1, BAD, FOXO, GSK-3β, p27), which control cell ence compound for the measurement of purified enzyme- proliferation, survival, and motility [1, 2]. These signaling binding kinetics and plasma and tumor concentrations in the pathways are commonly hyperactive in B-cell malignancies A20 syngeneic mouse model. [3–5]. Disrupting these pathways with PI3Kδ inhibitors such as Zydelig (idelalisib), Aliqopa™ (copanlisib), and Copik- tra™ (duvelisib) has been shown to effectively treat such malignancies by inhibiting their growth and survival [5–7]. 2 Materials and Methods Although effective, these approved agents cause toxicities such as diarrhea/colitis, transaminitis, cutaneous reactions, 2.1 Animals hyperglycemia, hypertension, and pneumonitis [7–9]. These toxicities may preclude the use of these agents at their maxi- Animal studies are reported in compliance with the ARRIVE mum clinical efficacious doses, suggesting a need for novel guidelines [15, 16]. CD-1 mice were from BK Laboratory PI3K inhibitors that provide meaningful clinical benefit with Animal Co. Ltd. Sprague Dawley (SD) rats were from BK decreased toxicity. Laboratory Animal Co. Ltd and Shanghai Laboratory Ani- The primary pharmacology of the oral PI3Kδ inhibi- mal Center, CAS (Shanghai, China). Female BALB/c mice tor ME-401 has previously been characterized in several were from Charles River Laboratories (Raleigh, NC, USA). in vitro studies that demonstrated its selectivity for the δ Beagle dogs were from Marshall BioResources (Beijing, isoform, inhibition of PI3Kδ-mediated cellular activity in Preclinical Pharmacology of ME-401, a Potent and Selective PI3Kδ Inhibitor 605 China, and North Rose, NY, USA). Cynomolgus monkeys The remaining donor and receiver volumes were removed, were from Marshall BioResources (Beijing, China). and the monolayers were washed three times for 2 min each with 0.3  mL of ice-cold HBSS solution to wash excess 2.2 In Vitro Blood to Plasma Ratio, Permeability, ME-401 from the monolayers/wells and also to stop any and Binding Kinetics active processes. Cells were lysed by rinsing three times with 100 µL methanol containing 0.66 µM tolbutamide as internal 2.2.1 Blood to Plasma Ratios standard. Extracts were pooled, and 100 µL transport buffer was added to match the composition of the other samples. Blood to plasma ratios (B:Ps) were measured in fresh SD All buffer samples were quenched into 100 µL methanol and rat, beagle dog, and human (single-donor) whole blood at a 200 µL methanol containing 1 µM tolbutamide as internal concentration of 1 µM. ME-401 was incubated for 30 min standard. Allowing for dilution factors for the cell-associated at 37 °C, pH 7.4. Three replicates were carried out, and samples and the buffer samples, the final internal standard the positive markers methazolamide (B:P >>1), verapamil concentration was 0.5 µM. All samples were kept at − 20 °C (B:P ~ 1), and diclofenac (B:P < 1) were included in the for ≥ 2 h before centrifugation at 2500×g, and for 20 min at assay. 4 °C. Supernatants were transferred to a microtiter plate, and substrate concentrations were assessed by liquid chromatog- 2.2.2 Caco‑2 Assay raphy–tandem mass spectroscopy (LC–MS/MS) against a matrix-matched standard curve. An assessment of the potential of ME-401 to bind to the tis- Percent recovery was calculated from the following sue culture plasticware was performed in ReadyCell 24-well equation: Transwells without cells. ME-401 (1 μM in 0.1% DMSO, SA + SB + SC recovery = × 100, N = 3) in an experimental buffer of Hank’s Balanced Salt Solution (HBSS) containing 25 mM HEPES + 5 mM glu- cose + 0.1% w/v BSA at pH 7.4 was incubated at 37 °C for where S is the amount of substrate added to the donor side, 2 h to mimic the Caco-2 experimental time course. Plastic and SA, SB, and SC are the amount of substrate in the apical binding potential was assessed by loss of ME-401 in the buffer, basolateral buffer, and cell extract, respectively, all experimental solutions at 2 h. Propranolol (10 uM) and ate- at the end of the experiment. Amounts were calculated as nolol (10 uM) were used as positive control markers for high volume (mL) × concentration (nmol/mL). and low passive permeability, respectively. Caco-2 cells in passage 63 at 24  days post-seeding 2.2.3 Purified Enzyme‑Binding Kinetics were used. Only monolayers with transepithelial electrical resistance (TEER) values of > 330 Ω/cm (taken at the start Kinase protein immobilization: An aliquot of biotinylated of the investigation and at the end of the incubations before PIK3CD/PIK3R1 (Carna Biosciences, Inc., Kobe, Japan) cell lysis to indicate the presence of an intact monolayer) was thawed, diluted to 40 µg/mL in precooled Biacore buffer were used in the investigation. The receiver buffer was the (50  mM  Tris pH  7.5, 0.05%  Tween, 150  mM  NaCl, and experimental buffer noted above. The donor buffer was the 5  mM  MgCl ), and immobilized with the biotin tag on a receiver buffer without BSA, containing the test compound Series S Sensor Chip SA. First, the streptavidin on the sen- and appropriate levels of DMSO. The ReadyCell plates were sor chip was washed three times with a washing solution washed for 1 min with 0.25-mL receiver buffer on the apical (1 M NaCl, 50 mM NaOH) for a period of 60 s with a flow side and 0.75 mL on the basolateral side, and washing was rate of 10 µL/min. Biotinylated PIK3CD/PIK3R1 was then repeated for 30 min at 37 °C with receiver buffer. The cell captured on the chip, with an aimed immobilization level of wells were then transferred to a fresh receiver plate. 8000 resonance units. Remaining streptavidin was blocked For the apical to basolateral (AB) permeability, 0.75 mL with 10 µg/mL biocytin injections to circumvent nonspecific of the receiver buffer was placed in the basolateral plate of binding of compounds to the streptavidin-bound surface. To three transwells for each concentration. Donor buffer solu- obtain a stable surface with a functional protein, the immo- tion (0.25 mL) with the test compound at pH 7.4 was added bilization procedure was performed at 4 °C. Channel 1 was to the apical compartment. For the basolateral to apical (BA) used as a reference channel to correct for buffer effects; the permeability, 0.75 mL of donor buffer solution with the test other channels were used for protein immobilization. After compound at pH 7.4 was added to the basolateral compart- immobilization, the system was buffered with Biacore buffer ment of three transwells for each concentration. Receiver containing 1% DMSO. After twice priming, a prerun was buffer solution (0.25 mL) was added to the apical compart- performed for a period of 60 min at a flow rate of 30 µL/min ment. The transwell plates were incubated at 37 °C for 2 h to obtain a stable surface. (without shaking). Samples (100 µL) were taken at 0 and 2 h. 606 O. Moreno, J. Wood Single-cycle kinetics assay: To obtain a stable signal after ChemPartner, Zhangjiang Hi-Tech Park, Pudong New Area, compound and buffer injections, the experiment was started Shanghai, China. with five start-up cycles comprising ten consecutive injec- With data from the IV PK study, the log of body weight tions with buffer performed at 22 °C. ME-401 and idelal - was plotted against the log of the apparent volume of dis- isib were dissolved in 100% DMSO to create 10-mM solu- tribution at steady state (V ), and the best-fit line by linear SS tions, which were diluted in Biacore buffer without DMSO regression was used to obtain the formulas for allometric to obtain solutions with 1% DMSO. Further dilutions were scaling of V . SS made in Biacore buffer containing 1% DMSO. This buffer was also used as running buffer during the experiments 2.3.2 Dog Lymph/Plasma PK to avoid bulk response shifts due to differences in DMSO concentration. The single-cycle kinetic experiment was per- In three male beagle dogs, a thoracic duct-to-external jugular formed at 22 °C with a compound concentration gradient of (or left subclavian, depending on individual anatomy) shunt 1–100 nM in half-log increments, a contact time of 100 s, was created in which a catheter was placed via a neck inci- and a flow rate of 30 µL/min. The dissociation period was sion into the thoracic duct at the junction of the left external 1200 s. After every single-cycle kinetics run, an extra wash jugular (or left subclavian) and axillary vein. This catheter step with 50% DMSO was performed. The kinase surface was advanced to the level of the terminal bulb of the thoracic was not washed during this step. duct and was assessed for patency by allowing the lymph to A blank run was performed before the compound range freely flow. A tip of a second catheter was placed within the was injected with five buffer injections at the same flow rate, left subclavian vein via the axillary vein. The catheters were contact time, and dissociation time as the compound runs. secured in the vessels with 2-0 silk or similar nonabsorb- This measurement was subtracted from the compound curve able suture. The catheters were connected to a three-way as a double reference to correct for surface instability. stopcock to create a “T-tube” port to allow for collection, Curve analysis: The compound curves were analyzed with and when not in use, continuous flow of lymph into the left the Biacore Evaluation Software using the method of double external jugular or subclavian vein. This system allowed for referencing. The reference channel was subtracted from the lymph to be collected by occluding the catheter leading to channel containing immobilized protein, and the reference the vein and drawing from the catheter nearest the lymph curve obtained with buffer injections was subtracted. The source. Similarly, venous blood was collected from the cath- resulting curve was fitted with the 1:1 binding model. eter within the left subclavian vein. If lymph could not be obtained because of either loss of patency or disruption of 2.3 ME‑401 Pharmacokinetics the catheter by the animal, blood was drawn from the saphe- in Non‑Tumor‑Bearing Species nous or cephalic vein. ME-401 10 mg/kg was administered by oral gavage as a 2.3.1 PK Studies Following a Single Oral or Intravenous (IV) solution in 20% vitamin E-tocopherol polyethylene glycol Dose 1000 succinate (VE-TPGS) + 80% 100 mM citrate buffer (pH 3.5). Lymph and blood samples (~ 1 and 1.5 mL, respec- The single-dose PKs of oral ME-401 were investigated in tively) were obtained pre-dose and 0.5, 1, 4, 6, 8, 24, and beagle dogs. ME-401 2 mg/kg was administered by oral 48 h post-dose. Blood was collected in K EDTA tubes, with gavage as a solution in 10% NMP/5% Solutol HS 15 + 20% the plasma separated by refrigerated centrifugation. Lymph PEG400 + 65% sterile water. The single-dose PK of IV samples also underwent refrigerated centrifugation; plasma ME-401 were investigated in CD-1 mice, SD rats, beagle and lymph samples were stored at − 80 °C until analysis. dogs, and cynomolgus monkeys. ME-401 was administered Plasma and lymph samples were analyzed for ME-401 con- IV as a solution in 10% NMP/5% Solutol HS 15 + 20% centrations by a suitably qualie fi d LC–MS/MS bioanalytical PEG400 + 65% sterile water (10 mg/kg for mice, 5 mg/kg method, with an LLOQ of 0.5 ng/mL. These experiments for rats, 2 mg/kg for dogs and monkeys). In both studies, ani- were conducted at Wake Forest Innovations, Winston-Salem, mals were fasted overnight before dosing and fed 4 h post- NC, USA (in-life) and Seventh Wave Laboratories LLC, dose. Blood samples were collected in K EDTA tubes at Chesterfield, MO, USA (Bioanalysis). pre-dose and 0.083, 0.25, 0.5, 1, 2, 4, 8, and 24 h post-dose. The plasma was separated by centrifugation and analyzed 2.4 ME‑401 and Idelalisib Tissue Distribution in A20 for ME-401 concentration by a suitably qualified LC–MS/ Syngeneic Model MS bioanalytical method, with a lower limit of quantifica- tion (LLOQ) of 1.0 ng/mL. PK parameters were estimated A20 tumor cells were obtained from ATCC and were by noncompartmental analysis with Pharsight Phoenix injected subcutaneously on the flank of 8- to 12-week-old WinNonlin software. These experiments were conducted at BALB/c mice. Body weights and tumor measurements Preclinical Pharmacology of ME-401, a Potent and Selective PI3Kδ Inhibitor 607 were recorded daily. Once tumors were 100–150  mm , high permeability marker, propranolol, showed high passive −6 pairs of matched mice received orally administered ME-401 permeability with P values > 30 × 10 cm/s, and the low app 75 mg/kg (n = 12) twice daily for 4 days. In a follow-up permeability marker, atenolol, had low passive permeability −6 study, pairs of matched mice received orally administered (< 1 × 10 cm/s). The recovery data for all positive control ME-401 (n = 12) or idelalisib (n = 12) 50 mg/kg twice daily marker conditions were acceptable as > 70%; however, the for 4 days. In both studies, ME-401 was prepared in 20% recovery for ME-401 at 1 µM was 30.3 ± 6.7% and 69 ± 5.6% VE-TPGS + 80% 100 mM citrate buffer (pH 3.5). In the sec- for AB and BA, respectively, when only the experimental ond study, idelalisib, obtained from LC Laboratories (Cat # solutions were measured. When the cell lysate was included I-7447, Lot # DLL-101), was prepared in 10% NMP/10% (thereby accounting for ME-401 associated with the cell Solutol HS 15 + 20% PEG400 in saline. Mice were given monolayer), the recovery significantly improved, with 10 mL/kg (0.2 mL/20 g mouse) of ME-401 or idelalisib 79.3 ± 5.5% for AB and 85 ± 8.5% for BA. This indicated twice daily, 4 h apart, for 4 days. In both studies, six of the that ~ 50% of the ME-401 was retained in the monolayer. mice in each group were sacrificed at 4 and 24 h after the last dose. Blood was collected in K EDTA tubes and stored on 3.1.3 Equilibrium Dissociation Constant (K ) and On/Off 2 D dry ice. Tissues were snap frozen and stored on dry ice. All Rates samples were shipped to Charles River Laboratories-Massa- chusetts for PK analysis. The plasma was separated by cen- Binding kinetics for ME-401 and idelalisib are presented trifugation. Tissue samples were analyzed against respective in Table 2. The lower dissociation rate resulted in a K of −11 homogenate curves. All samples were analyzed for ME-401 3.03 × 10 M (i.e. 30 pM) for ME-401. In comparison, the or idelalisib concentrations by a suitably qualified LC–MS/ idelalisib dissociation rate was ~ 100 times higher, resulting −9 MS bioanalytical method, with an LLOQ of 1.0 ng/mL for in a K of 1.11 × 10 M (i.e. 1110 pM). ME-401 was tightly both drugs. These experiments were conducted at Charles bound with a residence time of 5.3 h as compared to 2.3 min River Laboratories, Morrisville, NC, USA. for idelalisib. 3.2 ME‑401 Pharmacokinetics 3 Results in Non‑Tumor‑Bearing Species 3.1 In Vitro Blood to Plasma Ratio, Permeability, 3.2.1 Oral Bioavailability in Dogs and Binding Kinetics Following administration of ME-401 2 mg/kg IV in dogs, 3.1.1 ME‑401 B:P the area under the curve from time 0 to inn fi ity (AUC ) was inf 1247 ng∙h/mL. Following administration of ME-401 2 mg/ The B:P for all three of the markers was within the expected kg orally in fasted dogs, the AUC was 980 ng∙h/mL. The inf range for those compounds (Table 1). The B:P for ME-401 bioavailability of ME-401 in dogs was estimated to be 79%. was similar across the species and was measured as > 1. In human whole blood, the B:P of 1.4 indicated that ME-401 3.2.2 V from IV Dosing and Extrapolation to Human V SS SS distributes into blood cells. V from the IV single-dose experiments in CD-1 mice, SD SS 3.1.2 Caco‑2 Permeability and Percent Recovery rats, cynomolgus monkeys, and beagle dogs are presented in Table 3, and linear regression fit for allometric scaling of V SS −6 The ME-401 AB and BA P were 3.67 ± 1.37 × 10  cm/s is presented in Fig. 1. Extrapolation to a hypothetical 60-kg app −6 and 7.69 ± 1.39 × 10  cm/s, respectively. The permeabil- human resulted in a V value of 10.75 L/kg. SS ity results for the marker compounds were as expected; the Table 1 Blood to plasma ratios (mean ± SD) Table 2 Binding kinetics of ME-401 and idelalisib on PIK3CD/ PIK3R1 Compound Sprague Dawley rat Beagle dog Human Compound k (1/M·s) k (1/s) K (M) t Τ a d D ½ ME-401 1.8 ± 0.35 1.8 ± 0.35 1.4 ± 0.28 6 −5 −11 Methazolamide 150 ± 70 185 ± 140 50 ± 50 ME-401 1.72 × 10 5.20 × 10 3.03 × 10 3.7 h 5.3 h 6 −3 −9 Verapamil 1.1 ± 0.08 1.3 ± 0.13 1.1 ± 0.16 Idelalisib 6.53 × 10 7.25 × 10 1.11 × 10 1.6 min 2.3 min Diclofenac 0.8 ± 0.16 0.7 ± 0.18 0.9 ± 0.28 k association rate constant, k dissociation rate constant, K equilib- a d D SD standard deviation rium dissociation constant, t half-life, T residence time 1/2 608 O. Moreno, J. Wood 3.3 ME‑401 and Idelalisib Tissue Distribution in A20 Table 3 Preclinical intravenous single-dose pharmacokinetics Syngeneic Model Species Body weight (kg) V (L/kg) SS CD-1 mouse 0.02 5.605 The administration of ME-401 50 and 75 mg/kg twice daily Sprague Dawley rat 0.15 23.733 for 4 days resulted in tumor concentrations approximately Cynomolgus monkey 3 8 20 and 30 times higher than plasma concentrations, respec- Beagle dog 10 9.7 tively, at 4 h after the last dose (Table 4; Fig. 3). Concentra- tions within the tumor were lower at 24 h after the last dose, V apparent volume of distribution at steady state SS but higher relative to plasma, when compared to the 4-h con- centrations. In the ME-401 75-mg/kg group, concentrations in brain tissue were present at 4 and 24 h after the last dose at approximately 30% of plasma values, suggesting penetra- tion into and retention of ME-401 in the central nervous system. Administration of idelalisib 50 mg/kg twice daily for 4 days resulted in tumor concentrations approximately three times higher than plasma concentrations at 4 h after the last dose, and concentrations were below the limit of quantitation at 24 h. 4 Discussion PI3Kδ is a target for the treatment of B-cell malignancies as evidenced by the approval of the PI3K inhibitors idela- Fig. 1 Allometric relationship between volume of distribution at lisib and duvelisib for treatment of FL and CLL/SLL and steady state (V ) and body weight SS copanlisib for the treatment of FL [7–9]. However, these agents have significant toxicity; idelalisib has been shown 3.2.3 Time/Plasma Concentrations of Plasma and Lymph to cause hepatotoxicity, severe diarrhea/colitis, pneumonitis, in Dogs and intestinal perforation [8]. Copanlisib, an IV pan-PI3K inhibitor given weekly, is associated with severe hyperten- All plasma samples were collected and analyzed as planned. sion and hyperglycemia [9]. Duvelisib has been shown to However, many of the corresponding lymph samples could cause fatal and serious infections, diarrhea/colitis, cutaneous not be collected due to catheter patency. ME-401 lymph and reactions, and pneumonitis [7]. There is a need for novel plasma concentrations are plotted for each dog (Fig. 2) and PI3Kδ inhibitors with decreased toxicity profiles that pro- were above the limit of quantitation in all samples. vide durable clinical activity. Fig. 2 ME-401 concentrations in blood and lymphatic fluid following a single oral dose to male beagle dogs Preclinical Pharmacology of ME-401, a Potent and Selective PI3Kδ Inhibitor 609 Table 4 Plasma and tissue concentrations (mean ± SD) of ME-401 and idelalisib in A20 syngeneic model in BALB/c mice 4 and 24 h after the last dose Compound Plasma (ng/mL), mean ± SD (CV%) Tumor (ng/g), mean ± SD (CV%) Brain (ng/g), mean ± SD (CV%) 4 h (n = 6) 24 h (n = 6) 4 h (n = 6) 24 h (n = 6) 4 h (n = 6) 24 h (n = 6) ME-401 75 mg/kg 7225 ± 531 (7.4) 2328 ± 416 (17.9) 225,333 ± 40,582 (18) 151,500 ± 35,799 (23.6) 2603 ± 466 (17.9) 676 ± 48 (7.1) ME-401 50 mg/kg 4897 ± 467 (9.5) 420 ± 105 (25.1) 99,850 ± 18,001 (18) 48,100 ± 11,569 (24.1) NE NE Idelalisib 50 mg/kg 23.6 ± 4.81 (20.4) BLQ 61.8 ± 17.6 (28.5) BLQ NE NE BLQ below limit of quantitation of idelalisib in plasma of 1 ng/mL or 2 ng/mL after 2 × assay dilution, CV coefficient of variation, NE not evalu- ated, SD standard deviation ME-401 75 mg/kg ME-401 75 mg/kg 30000 300000 8000 25000 250000 20000 200000 15000 150000 4000 10000 100000 5000 50000 0 0 0 Plasma Tumor PlasmaBrain (a) (b) 4 hours24 hours 4 hours24 hours ME-401 50 mg/kg Idelalisib 50 mg/kg 12000 120000 80 10000 100000 8000 80000 6000 60000 40 4000 40000 2000 20000 0 0 0 Plasma Tumor PlasmaTumor (c) (d) 4 hours24 hours 4 hours Fig. 3 Plasma and tissue concentrations (mean ± SD) at 4 (n = 6) b ME-401 75  mg/kg plasma and brain concentrations. c ME-401 and 24  h (n = 6) after the last dose of ME-401 or idelalisib admin- 50  mg/kg plasma and tumor concentrations. d Idelalisib 50  mg/kg istered orally twice daily for 4  days in an A20 syngeneic model in plasma and tumor concentrations at 4 h; concentrations at 24 h were BALB/c mice. a ME-401 75 mg/kg plasma and tumor concentrations. below the limit of quantitation PI3Kδ is located inside B-cell lymphocytes, which reside Consequently, these preclinical data are used to ascertain in the bone marrow and lymphatic system. Therefore, the insights to the pharmacologic properties of ME-401. efficacy of a drug that targets PI3Kδ is governed by its We evaluated the distribution of ME-401 into cells by capacity to distribute into those tissues and cells, as well B:P and the Caco-2 cell assay. The B:P of 1.4 indicates as the potency with which it inhibits PI3Kδ function. The that ME-401 readily distributes into blood cells, reaching results of our preclinical studies demonstrate the efficiency equilibrium when approximately 60% of the drug in the and potency of ME-401 in performing these tasks. Most blood distributes into blood cells. In comparison, idelalisib of these studies were performed early in development and has a B:P of 0.5–0.7 [8, 17], suggesting it remains more served to justify advancement of ME-401 into first-in-human in the plasma rather than permeating cells as compared clinical trials. Therefore, the concentrations of ME-401 with ME-401. The Caco-2 assay indicated that ME-401 not in these studies may not reflect clinical concentrations. only permeates cells but is also retained by cells. The low 610 O. Moreno, J. Wood recovery in the Caco-2 assay prevented accurate quantitation system was evaluated by measuring drug concentration in of permeability rate; the recovery was significantly improved plasma and lymphatic fluid, following oral administration when the cell lysate was included, indicating that the low to dogs. The methodology used to collect lymphatic fluid recovery was due to retention of ME-401 inside the cells. involved surgically implanted catheters. In some cases, the Collectively, these results indicate that ME-401 exhibits a catheters became occluded, preventing collection at subse- propensity to distribute into, and accumulate inside, cells quent time points. Consequently, the lymph concentration and may account for the higher potency observed in cellular data were too sparse to calculate PK parameters with a rea- assays compared with the purified enzyme assay. It was pre- sonable degree of confidence. Nonetheless, the results were viously reported [10, 11] that the clinical half maximal effec- adequate to conclude that ME-401 readily distributes into tive concentration (EC ) of 1 nM for inhibition of activation the lymphatic system after oral administration to dogs. of peripheral blood basophils in healthy volunteers was in In the A20 syngeneic model, concentrations of ME-401 agreement with the inhibition of PI3Kδ in cellular assays in tumor tissue were approximately 20–30 times greater than (half maximal inhibitory concentration [IC ] = 0.6  nM); plasma concentrations at 4 h after the last dose; these con- the IC was 5 nM for inhibition of purified PI3Kδ enzyme. centrations remained elevated relative to plasma concentra- Kinetics of ME-401 binding to isolated, biotinylated tions 24 h after the last dose, suggesting prolonged concen- PI3Kδ immobilized on a Biacore sensor chip were measured trations in this targeted tissue. In comparison, plasma and via surface plasmon resonance and compared with binding tumor concentrations of idelalisib were significantly lower kinetics of idelalisib. The very low K of 30 pM was cou- than those of ME-401 at 4 h following the last dose. By 24 h −5 pled with a very slow off-rate of 5.20 × 10 /s, equating to after the last dose, idelalisib plasma and tumor concentra- a half-life and residence time of several hours. In contrast, tions were below the limit of quantitation. Interestingly, our idelalisib has a higher K of 1110 pM, due largely to a faster study demonstrated the distribution of ME-401 into brain −3 off-rate of 7.25 × 10 /s, equating to half-life and residence tissue at concentrations around 30% of plasma concentra- times of a few minutes. These data show that once ME-401 tions that were still measurable at 24 h, and suggests that reaches its target, it binds ~ 37 times more tightly, and future investigation into the role of ME-401 in the treatment remains on-target ~ 138 times longer, than idelalisib in vitro. of CNS lymphomas may be warranted. Although idelalisib With ME-401 accumulating in cells and binding tightly to its and ME-401 are administered to humans at different doses, target, it is possible that prolonged inhibition of PI3Kδ could potentially resulting in very different tissue concentrations, occur within the tumor or lymphoid tissue even as ME-401 these agents were tested at identical dosing regimens in the levels decrease in plasma over time. This tight binding to A20 mouse model, to enable direct comparison of the mole- PI3Kδ and its ability to readily distribute into tissue may cules’ performance attributes. Notwithstanding that ME-401 partially explain the clinical results of ME-401 of high initial plasma concentrations in our studies may not reflect clinical ORRs in early studies in FL and CLL/SLL [13, 14]. plasma concentrations, ME-401 does exhibit linear PKs in The PK profile of ME-401 was evaluated in non-tumor- mice (data not shown), indicating that drug distribution does bearing species following oral administration to dogs and IV not vary with dose. administration to mice, rats, dogs, and monkeys. The high ME-401 entered clinical trials in B-cell malignancies at oral bioavailability of 79% indicates that the drug was well a starting dose of 60 mg orally, once daily, now the recom- absorbed. Extrapolation of V from preclinical species to mended Phase 2 dose. This dose is a fraction of the predicted SS a hypothetical 60-kg human resulted in a very large V of 140-mg MRSD based on preclinical toxicology studies. It SS 645 L, which is approximately 100 times higher than blood was previously reported [11, 12] that daily oral dosing of volume and approximately 15 times higher than whole body ME-401 60 mg was expected to result in clinical plasma volume. This V is ~ 28 times larger than the 23 L reported concentrations that maintained maximal PI3Kδ inhibition. SS for idelalisib, indicating greater diffusion of ME-401 away The high in  vitro potency of ME-401, together with its from the blood and into the tissues of the body [8, 18]. capacity to distribute into target tissues and accumulate at Although the mechanism behind this large V is unclear, the site of action, could underlie the high clinical potency SS and it is beyond the scope of this work to estimate the degree in B-cell malignancies that may differentiate ME-401 from to which ME-401 distributes to extravascular tissue in other PI3Kδ inhibitors [13]. These characteristics may also humans, it is likely that ME-401 concentrations are signifi- allow ME-401 the flexibility of intermittent dosing after cantly higher in one or more extravascular tissues compared a period of continuous therapy in an effort to prevent on- with drug concentrations measured in human plasma. target immune-related adverse effects that may occur late in The capacity of ME-401 to distribute to target tissues treatment in some patients [14]. Current studies of ME-401, was evaluated in the dog lymph/plasma PK study and the as monotherapy and in combination with novel agents, are A20 syngeneic model in mice. In the lymph/plasma study, ongoing in B-cell malignancies, and future studies may the propensity for ME-401 to distribute into the lymphatic Preclinical Pharmacology of ME-401, a Potent and Selective PI3Kδ Inhibitor 611 malignancies, inhibits PI3K signaling and cellular viability. provide answers to safety and efficacy concerns that have Blood. 2011;117(2):591–4. https ://doi.org/10.1182/blood -2010- shadowed this class of agents. 03-27530 5. 6. Dreyling M, Santoro A, Mollica L, Leppa S, Follows GA, Acknowledgements The authors acknowledge Sandra Petralia, Dan Lenz G, et  al. Phosphatidylinositol 3-kinase inhibition by Gold, and David Walsey for feedback on the manuscript and the medi- copanlisib in relapsed or refractory indolent lymphoma. J cal writing assistance of Laura Jung, PharmD, of ETHOS Health Com- Clin Oncol. 2017;35(35):3898–905. https ://doi.or g/10.1200/ munications in Yardley, PA, USA, which was supported financially by JCO.2017.75.4648. MEI Pharma Inc., San Diego, CA, USA, in compliance with interna- 7. Copiktra [product insert]. Needham, MA: Verastem, Inc; 2018. tional Good Publication Practice guidelines. 8. Zydelig [product insert]. Foster City, CA: Gilead Sciences, Inc; 9. Aliqopa [product insert]. Whippany, NJ: Bayer HealthCare Phar- Compliance with Ethical Standards maceuticals, Inc; 2017. 10. O’Farrell M, Ventura R, Tai A, Tyner JW, Loriaux MM, Mahade- Funding This study was sponsored by MEI Pharma Inc. van D, et al. Preclinical characterization of PWT143, a novel selective and potent phosphatidylinositol 3-kinase delta (PI3K Conflict of interest J. Wood and O. Moreno are employees and stock- delta) inhibitor with ex-vivo activity in hematologic malignances. holders of MEI Pharma Inc. Blood. 2012;120:2907. 11. Moreno O, Butler T, Zann V, Willson A, Leung P, Connor A. Ethical approval All applicable international, national, and/or insti- Safety, pharmacokinetics, and pharmacodynamics of ME-401, tutional guidelines for the care and use of animals were followed. All an oral, potent, and selective inhibitor of phosphatidylinositol procedures performed in studies involving animals were in accordance 3-kinase P110delta, following single ascending dose administra- with the ethical standards of the institution or practice at which the tion to healthy volunteers. Clin Ther. 2018;40(11):1855–67. https studies were conducted (Charles River Institutional Animal Care and ://doi.org/10.1016/j.clint hera.2018.09.006. Use Committee ASP # 990202). 12. Zann VCA, Preston M, Leung P, Duncan D, Moreno O. Formula- tion selection and development for ME-401, an oral, potent and selective inhibitor of phosphatidylinositol 3-kinase P110δ during Open Access This article is distributed under the terms of the Crea- a first-in-human study in healthy volunteers. Denver, CO: Ameri- tive Commons Attribution-NonCommercial 4.0 International License can Association of Pharmaceutical Scientists; 2016. (http://creat iveco mmons .org/licen ses/by-nc/4.0/), which permits any 13. Soumerai JD, Pagel JM, Jagadeesh D, Salman HS, Kenkre noncommercial use, distribution, and reproduction in any medium, VP, Asch AS, et al. Initial results of a dose escalation study of provided you give appropriate credit to the original author(s) and the ME-401, a selective and structurally differentiated PI3Kδ inhibi- source, provide a link to the Creative Commons license, and indicate tor, in relapsed/refractory (R/R) follicular lymphoma (FL) and if changes were made. chronic lymphocytic leukemia (CLL)/small lymphocytic lym- phoma (SLL). Presented at Amercian Society of Clinical Oncol- ogy Annual Meeting, 1–5 June 2018, Chicago, IL (Abstract 7519). References 14. Zelenetz AD, Soumerai JD, Jagadeesh D, Reddy N, Stathis A, Asch AS, et al. 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EMEA/CHMP/324336/2014. Zydelig. 2014. 35249 2. h t t p : / / w w w.e m a . e u r o p a . e u / d o c s / e n _ G B / d o c u m e n t _ l i b r a r y / 5. Lannutti BJ, Meadows SA, Herman SE, Kashishian A, Steiner EPAR_-_Public_asses sment _r eport/human /00384 3/W C50017537 B, Johnson AJ, et  al. CAL-101, a p110delta selective phos- 9.pdf. Accessed 7 Mar 2019. phatidylinositol-3-kinase inhibitor for the treatment of B-cell http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Targeted Oncology Springer Journals

Absorption, Distribution, and Binding Profile of ME-401, a Potent and Selective Oral Small-Molecule Inhibitor of Phosphatidylinositol 3-Kinase δ (PI3Kδ) in Animal and B-Cell Lymphoma Models

Moreno, Ofir; Wood, Jamie
Targeted Oncology , Volume 14 (5) – Sep 10, 2019
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Springer Journals
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Copyright © 2019 by The Author(s)
Subject
Medicine & Public Health; Oncology; Biomedicine, general
ISSN
1776-2596
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1776-260X
DOI
10.1007/s11523-019-00668-y
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Abstract

Background Phosphatidylinositol 3-kinase isoform δ (PI3Kδ) mediates multiple events in lymphocytes, including cell pro- liferation, survival, and motility. Inhibition of PI3Kδ, with downstream inhibitory effects on cell growth and survival, has been utilized to treat lymphoid malignancies. ME-401 is an oral, once-daily, selective PI3Kδ inhibitor with an optimized pharmacologic profile that is in clinical development for the treatment of B-cell malignancies. Objectives This work examined aspects of the pharmacologic profile of ME-401 in preclinical models to investigate the basis of the clinical activity of ME-401 that may differentiate it from other currently approved PI3Kδ inhibitors. Methods We determined the ME-401 blood to plasma ratios, permeability, and purified enzyme-binding kinetics. The oral bioavailability and volume of distribution of ME-401 were evaluated in various species. ME-401 concentrations in plasma and tumor and brain tissues were evaluated following oral administration in an A20 syngeneic mouse model of B-cell lymphoma. Idelalisib was used as a reference compound for the measurement of purified enzyme-binding kinetics and concentrations in plasma and tumor in the A20 syngeneic mouse model. Results Oral administration of ME-401 to dogs resulted in 79% bioavailability compared with intravenous administration. Allometric scaling from rodents, dogs, and nonhuman primates resulted in a predicted human volume of distribution at steady state of 10.75 L/kg. ME-401 was shown to distribute into the lymph in dogs and permeate into cells readily, with a human blood to plasma ratio of 1.4 and ~ 50% retention in the Caco-2 cell monolayer at 1 μM. The high binding affinity and low −11 dissociation rate of ME-401 resulted in an equilibrium dissociation constant (K ) of 3.03 × 10 M. Oral administration of ME-401 in an A20 syngeneic mouse model resulted in tumor concentrations 20–30 times higher than plasma concentrations at 4 h after the last dose. By 24 h, the tumor levels had decreased approximately 30–50% compared with levels at 4 h while remaining significantly increased relative to plasma concentrations. ME-401 was also present in brain tissue at 4 and 24 h −9 after the last dose. In comparison, the idelalisib dissociation rate was ~ 100 times higher, resulting in a K of 1.11 × 10 M. Idelalisib tumor concentrations were only approximately three times higher than plasma concentrations at 4 h, while drop- ping below the limit of quantitation in both tumor and plasma by 24 h. Conclusions These data support the capacity of ME-401 to be orally absorbed, distribute to target tissues, enter and accu- mulate in target cells, and bind to the target with high affinity to exert its mechanism of action. These characteristics underlie the high clinical potency seen in B-cell malignancies that may differentiate ME-401 from other PI3Kδ inhibitors currently approved or in development. * Ofir Moreno omoreno@meipharma.com MEI Pharma Inc., 3611 Valley Centre Drive, Suite 500, San Diego, CA 92130, USA Vol.:(0123456789) 604 O. Moreno, J. Wood activated immune cells (Raji cell line, primary basophils) Key Points with low nM 50% inhibitory concentrations even in the presence of whole blood, and activity against multiple ME-401 is an oral, once-daily, selective PI3Kδ inhibi- primary B-cell malignancies [10]. Results from a first- tor, part of a signaling pathway in cells that can become in-human study in healthy volunteers demonstrated oral hyperactive leading to tumor growth and resistance to bioavailability, linear pharmacokinetics (PK), and a half- chemotherapy. life of 28 h to support once-daily dosing. Additionally, the PK/pharmacodynamic (PD) relationship was examined In preclinical studies, ME-401 reached its target site with inhibition of basophil activation assessed via CD63 (PI3Kδ) and bound to it more tightly and longer than expression following ex vivo stimulation. Oral adminis- idelalisib, another PI3Kδ inhibitor. ME-401 bound to its tration of ME-401 resulted in 90% of maximal effective target tightly for ~ 5 h compared with ~ 2 min for idelal- concentration (EC ) at a plasma concentration of 5 ng/ isib. mL (9  nM), with trough plasma values predicted to be Oral ME-401 is well absorbed and distributed through- above the EC , using daily dosing of 60  mg [11, 12]. out the body in animal studies with concentrations in key Consequently, 60 mg/day was used as the starting dose for sites for lymphoma including lymph, plasma, lymphoma a Phase 1b dose escalation study in relapsed B-cell malig- tumor, and brain tissue. nancies, even though the maximum recommended start- ing dose (MRSD) in patients with cancer was determined to be 140 mg/day based on preclinical toxicology data. Initial results from the Phase 1b study have shown high initial overall response rates (ORRs) in relapsed follicular lymphoma (FL) and chronic lymphocytic leukemia (CLL)/ 1 Introduction small lymphocytic lymphoma (SLL) [13, 14]. To be efficacious, an oral agent must overcome the hur - Phosphatidylinositol 3-kinase (PI3K) is a lipid kinase with a dles of entering the bloodstream from the gastrointestinal catalytic subunit that exists in four different isoforms (α, β, tract, reaching the target tissues, and binding with sufficient γ, and δ). The δ isoform is highly restricted to hematopoietic affinity to exert its mechanism of action. Intracellular tar - cells and plays a key role in normal B-cell development and gets such as PI3Kδ have additional hurdles of entering the function. Once recruited to phosphorylated binding sites on target cells and establishing an effective concentration at the B-cell adapter of PI3K or on the cytoplasmic tail of the the intracellular site of action. To that end, the preclinical transmembrane protein CD19, activated PI3Kδ signaling studies presented here examined the permeability and bind- occurs via phosphorylation of the key lipid second messen- ing affinity of ME-401; oral bioavailability and volume of ger phosphatidylinositol, with resultant phosphorylation of distribution in various species; and concentrations in plasma protein kinase B (Akt), leading to the downstream phos- and tumor and brain tissues in an A20 syngeneic mouse phorylation of a variety of effector molecules (e.g., TSC1/2, model of B-cell lymphoma. Idelalisib was used as a refer- mTORC1, BAD, FOXO, GSK-3β, p27), which control cell ence compound for the measurement of purified enzyme- proliferation, survival, and motility [1, 2]. These signaling binding kinetics and plasma and tumor concentrations in the pathways are commonly hyperactive in B-cell malignancies A20 syngeneic mouse model. [3–5]. Disrupting these pathways with PI3Kδ inhibitors such as Zydelig (idelalisib), Aliqopa™ (copanlisib), and Copik- tra™ (duvelisib) has been shown to effectively treat such malignancies by inhibiting their growth and survival [5–7]. 2 Materials and Methods Although effective, these approved agents cause toxicities such as diarrhea/colitis, transaminitis, cutaneous reactions, 2.1 Animals hyperglycemia, hypertension, and pneumonitis [7–9]. These toxicities may preclude the use of these agents at their maxi- Animal studies are reported in compliance with the ARRIVE mum clinical efficacious doses, suggesting a need for novel guidelines [15, 16]. CD-1 mice were from BK Laboratory PI3K inhibitors that provide meaningful clinical benefit with Animal Co. Ltd. Sprague Dawley (SD) rats were from BK decreased toxicity. Laboratory Animal Co. Ltd and Shanghai Laboratory Ani- The primary pharmacology of the oral PI3Kδ inhibi- mal Center, CAS (Shanghai, China). Female BALB/c mice tor ME-401 has previously been characterized in several were from Charles River Laboratories (Raleigh, NC, USA). in vitro studies that demonstrated its selectivity for the δ Beagle dogs were from Marshall BioResources (Beijing, isoform, inhibition of PI3Kδ-mediated cellular activity in Preclinical Pharmacology of ME-401, a Potent and Selective PI3Kδ Inhibitor 605 China, and North Rose, NY, USA). Cynomolgus monkeys The remaining donor and receiver volumes were removed, were from Marshall BioResources (Beijing, China). and the monolayers were washed three times for 2 min each with 0.3  mL of ice-cold HBSS solution to wash excess 2.2 In Vitro Blood to Plasma Ratio, Permeability, ME-401 from the monolayers/wells and also to stop any and Binding Kinetics active processes. Cells were lysed by rinsing three times with 100 µL methanol containing 0.66 µM tolbutamide as internal 2.2.1 Blood to Plasma Ratios standard. Extracts were pooled, and 100 µL transport buffer was added to match the composition of the other samples. Blood to plasma ratios (B:Ps) were measured in fresh SD All buffer samples were quenched into 100 µL methanol and rat, beagle dog, and human (single-donor) whole blood at a 200 µL methanol containing 1 µM tolbutamide as internal concentration of 1 µM. ME-401 was incubated for 30 min standard. Allowing for dilution factors for the cell-associated at 37 °C, pH 7.4. Three replicates were carried out, and samples and the buffer samples, the final internal standard the positive markers methazolamide (B:P >>1), verapamil concentration was 0.5 µM. All samples were kept at − 20 °C (B:P ~ 1), and diclofenac (B:P < 1) were included in the for ≥ 2 h before centrifugation at 2500×g, and for 20 min at assay. 4 °C. Supernatants were transferred to a microtiter plate, and substrate concentrations were assessed by liquid chromatog- 2.2.2 Caco‑2 Assay raphy–tandem mass spectroscopy (LC–MS/MS) against a matrix-matched standard curve. An assessment of the potential of ME-401 to bind to the tis- Percent recovery was calculated from the following sue culture plasticware was performed in ReadyCell 24-well equation: Transwells without cells. ME-401 (1 μM in 0.1% DMSO, SA + SB + SC recovery = × 100, N = 3) in an experimental buffer of Hank’s Balanced Salt Solution (HBSS) containing 25 mM HEPES + 5 mM glu- cose + 0.1% w/v BSA at pH 7.4 was incubated at 37 °C for where S is the amount of substrate added to the donor side, 2 h to mimic the Caco-2 experimental time course. Plastic and SA, SB, and SC are the amount of substrate in the apical binding potential was assessed by loss of ME-401 in the buffer, basolateral buffer, and cell extract, respectively, all experimental solutions at 2 h. Propranolol (10 uM) and ate- at the end of the experiment. Amounts were calculated as nolol (10 uM) were used as positive control markers for high volume (mL) × concentration (nmol/mL). and low passive permeability, respectively. Caco-2 cells in passage 63 at 24  days post-seeding 2.2.3 Purified Enzyme‑Binding Kinetics were used. Only monolayers with transepithelial electrical resistance (TEER) values of > 330 Ω/cm (taken at the start Kinase protein immobilization: An aliquot of biotinylated of the investigation and at the end of the incubations before PIK3CD/PIK3R1 (Carna Biosciences, Inc., Kobe, Japan) cell lysis to indicate the presence of an intact monolayer) was thawed, diluted to 40 µg/mL in precooled Biacore buffer were used in the investigation. The receiver buffer was the (50  mM  Tris pH  7.5, 0.05%  Tween, 150  mM  NaCl, and experimental buffer noted above. The donor buffer was the 5  mM  MgCl ), and immobilized with the biotin tag on a receiver buffer without BSA, containing the test compound Series S Sensor Chip SA. First, the streptavidin on the sen- and appropriate levels of DMSO. The ReadyCell plates were sor chip was washed three times with a washing solution washed for 1 min with 0.25-mL receiver buffer on the apical (1 M NaCl, 50 mM NaOH) for a period of 60 s with a flow side and 0.75 mL on the basolateral side, and washing was rate of 10 µL/min. Biotinylated PIK3CD/PIK3R1 was then repeated for 30 min at 37 °C with receiver buffer. The cell captured on the chip, with an aimed immobilization level of wells were then transferred to a fresh receiver plate. 8000 resonance units. Remaining streptavidin was blocked For the apical to basolateral (AB) permeability, 0.75 mL with 10 µg/mL biocytin injections to circumvent nonspecific of the receiver buffer was placed in the basolateral plate of binding of compounds to the streptavidin-bound surface. To three transwells for each concentration. Donor buffer solu- obtain a stable surface with a functional protein, the immo- tion (0.25 mL) with the test compound at pH 7.4 was added bilization procedure was performed at 4 °C. Channel 1 was to the apical compartment. For the basolateral to apical (BA) used as a reference channel to correct for buffer effects; the permeability, 0.75 mL of donor buffer solution with the test other channels were used for protein immobilization. After compound at pH 7.4 was added to the basolateral compart- immobilization, the system was buffered with Biacore buffer ment of three transwells for each concentration. Receiver containing 1% DMSO. After twice priming, a prerun was buffer solution (0.25 mL) was added to the apical compart- performed for a period of 60 min at a flow rate of 30 µL/min ment. The transwell plates were incubated at 37 °C for 2 h to obtain a stable surface. (without shaking). Samples (100 µL) were taken at 0 and 2 h. 606 O. Moreno, J. Wood Single-cycle kinetics assay: To obtain a stable signal after ChemPartner, Zhangjiang Hi-Tech Park, Pudong New Area, compound and buffer injections, the experiment was started Shanghai, China. with five start-up cycles comprising ten consecutive injec- With data from the IV PK study, the log of body weight tions with buffer performed at 22 °C. ME-401 and idelal - was plotted against the log of the apparent volume of dis- isib were dissolved in 100% DMSO to create 10-mM solu- tribution at steady state (V ), and the best-fit line by linear SS tions, which were diluted in Biacore buffer without DMSO regression was used to obtain the formulas for allometric to obtain solutions with 1% DMSO. Further dilutions were scaling of V . SS made in Biacore buffer containing 1% DMSO. This buffer was also used as running buffer during the experiments 2.3.2 Dog Lymph/Plasma PK to avoid bulk response shifts due to differences in DMSO concentration. The single-cycle kinetic experiment was per- In three male beagle dogs, a thoracic duct-to-external jugular formed at 22 °C with a compound concentration gradient of (or left subclavian, depending on individual anatomy) shunt 1–100 nM in half-log increments, a contact time of 100 s, was created in which a catheter was placed via a neck inci- and a flow rate of 30 µL/min. The dissociation period was sion into the thoracic duct at the junction of the left external 1200 s. After every single-cycle kinetics run, an extra wash jugular (or left subclavian) and axillary vein. This catheter step with 50% DMSO was performed. The kinase surface was advanced to the level of the terminal bulb of the thoracic was not washed during this step. duct and was assessed for patency by allowing the lymph to A blank run was performed before the compound range freely flow. A tip of a second catheter was placed within the was injected with five buffer injections at the same flow rate, left subclavian vein via the axillary vein. The catheters were contact time, and dissociation time as the compound runs. secured in the vessels with 2-0 silk or similar nonabsorb- This measurement was subtracted from the compound curve able suture. The catheters were connected to a three-way as a double reference to correct for surface instability. stopcock to create a “T-tube” port to allow for collection, Curve analysis: The compound curves were analyzed with and when not in use, continuous flow of lymph into the left the Biacore Evaluation Software using the method of double external jugular or subclavian vein. This system allowed for referencing. The reference channel was subtracted from the lymph to be collected by occluding the catheter leading to channel containing immobilized protein, and the reference the vein and drawing from the catheter nearest the lymph curve obtained with buffer injections was subtracted. The source. Similarly, venous blood was collected from the cath- resulting curve was fitted with the 1:1 binding model. eter within the left subclavian vein. If lymph could not be obtained because of either loss of patency or disruption of 2.3 ME‑401 Pharmacokinetics the catheter by the animal, blood was drawn from the saphe- in Non‑Tumor‑Bearing Species nous or cephalic vein. ME-401 10 mg/kg was administered by oral gavage as a 2.3.1 PK Studies Following a Single Oral or Intravenous (IV) solution in 20% vitamin E-tocopherol polyethylene glycol Dose 1000 succinate (VE-TPGS) + 80% 100 mM citrate buffer (pH 3.5). Lymph and blood samples (~ 1 and 1.5 mL, respec- The single-dose PKs of oral ME-401 were investigated in tively) were obtained pre-dose and 0.5, 1, 4, 6, 8, 24, and beagle dogs. ME-401 2 mg/kg was administered by oral 48 h post-dose. Blood was collected in K EDTA tubes, with gavage as a solution in 10% NMP/5% Solutol HS 15 + 20% the plasma separated by refrigerated centrifugation. Lymph PEG400 + 65% sterile water. The single-dose PK of IV samples also underwent refrigerated centrifugation; plasma ME-401 were investigated in CD-1 mice, SD rats, beagle and lymph samples were stored at − 80 °C until analysis. dogs, and cynomolgus monkeys. ME-401 was administered Plasma and lymph samples were analyzed for ME-401 con- IV as a solution in 10% NMP/5% Solutol HS 15 + 20% centrations by a suitably qualie fi d LC–MS/MS bioanalytical PEG400 + 65% sterile water (10 mg/kg for mice, 5 mg/kg method, with an LLOQ of 0.5 ng/mL. These experiments for rats, 2 mg/kg for dogs and monkeys). In both studies, ani- were conducted at Wake Forest Innovations, Winston-Salem, mals were fasted overnight before dosing and fed 4 h post- NC, USA (in-life) and Seventh Wave Laboratories LLC, dose. Blood samples were collected in K EDTA tubes at Chesterfield, MO, USA (Bioanalysis). pre-dose and 0.083, 0.25, 0.5, 1, 2, 4, 8, and 24 h post-dose. The plasma was separated by centrifugation and analyzed 2.4 ME‑401 and Idelalisib Tissue Distribution in A20 for ME-401 concentration by a suitably qualified LC–MS/ Syngeneic Model MS bioanalytical method, with a lower limit of quantifica- tion (LLOQ) of 1.0 ng/mL. PK parameters were estimated A20 tumor cells were obtained from ATCC and were by noncompartmental analysis with Pharsight Phoenix injected subcutaneously on the flank of 8- to 12-week-old WinNonlin software. These experiments were conducted at BALB/c mice. Body weights and tumor measurements Preclinical Pharmacology of ME-401, a Potent and Selective PI3Kδ Inhibitor 607 were recorded daily. Once tumors were 100–150  mm , high permeability marker, propranolol, showed high passive −6 pairs of matched mice received orally administered ME-401 permeability with P values > 30 × 10 cm/s, and the low app 75 mg/kg (n = 12) twice daily for 4 days. In a follow-up permeability marker, atenolol, had low passive permeability −6 study, pairs of matched mice received orally administered (< 1 × 10 cm/s). The recovery data for all positive control ME-401 (n = 12) or idelalisib (n = 12) 50 mg/kg twice daily marker conditions were acceptable as > 70%; however, the for 4 days. In both studies, ME-401 was prepared in 20% recovery for ME-401 at 1 µM was 30.3 ± 6.7% and 69 ± 5.6% VE-TPGS + 80% 100 mM citrate buffer (pH 3.5). In the sec- for AB and BA, respectively, when only the experimental ond study, idelalisib, obtained from LC Laboratories (Cat # solutions were measured. When the cell lysate was included I-7447, Lot # DLL-101), was prepared in 10% NMP/10% (thereby accounting for ME-401 associated with the cell Solutol HS 15 + 20% PEG400 in saline. Mice were given monolayer), the recovery significantly improved, with 10 mL/kg (0.2 mL/20 g mouse) of ME-401 or idelalisib 79.3 ± 5.5% for AB and 85 ± 8.5% for BA. This indicated twice daily, 4 h apart, for 4 days. In both studies, six of the that ~ 50% of the ME-401 was retained in the monolayer. mice in each group were sacrificed at 4 and 24 h after the last dose. Blood was collected in K EDTA tubes and stored on 3.1.3 Equilibrium Dissociation Constant (K ) and On/Off 2 D dry ice. Tissues were snap frozen and stored on dry ice. All Rates samples were shipped to Charles River Laboratories-Massa- chusetts for PK analysis. The plasma was separated by cen- Binding kinetics for ME-401 and idelalisib are presented trifugation. Tissue samples were analyzed against respective in Table 2. The lower dissociation rate resulted in a K of −11 homogenate curves. All samples were analyzed for ME-401 3.03 × 10 M (i.e. 30 pM) for ME-401. In comparison, the or idelalisib concentrations by a suitably qualified LC–MS/ idelalisib dissociation rate was ~ 100 times higher, resulting −9 MS bioanalytical method, with an LLOQ of 1.0 ng/mL for in a K of 1.11 × 10 M (i.e. 1110 pM). ME-401 was tightly both drugs. These experiments were conducted at Charles bound with a residence time of 5.3 h as compared to 2.3 min River Laboratories, Morrisville, NC, USA. for idelalisib. 3.2 ME‑401 Pharmacokinetics 3 Results in Non‑Tumor‑Bearing Species 3.1 In Vitro Blood to Plasma Ratio, Permeability, 3.2.1 Oral Bioavailability in Dogs and Binding Kinetics Following administration of ME-401 2 mg/kg IV in dogs, 3.1.1 ME‑401 B:P the area under the curve from time 0 to inn fi ity (AUC ) was inf 1247 ng∙h/mL. Following administration of ME-401 2 mg/ The B:P for all three of the markers was within the expected kg orally in fasted dogs, the AUC was 980 ng∙h/mL. The inf range for those compounds (Table 1). The B:P for ME-401 bioavailability of ME-401 in dogs was estimated to be 79%. was similar across the species and was measured as > 1. In human whole blood, the B:P of 1.4 indicated that ME-401 3.2.2 V from IV Dosing and Extrapolation to Human V SS SS distributes into blood cells. V from the IV single-dose experiments in CD-1 mice, SD SS 3.1.2 Caco‑2 Permeability and Percent Recovery rats, cynomolgus monkeys, and beagle dogs are presented in Table 3, and linear regression fit for allometric scaling of V SS −6 The ME-401 AB and BA P were 3.67 ± 1.37 × 10  cm/s is presented in Fig. 1. Extrapolation to a hypothetical 60-kg app −6 and 7.69 ± 1.39 × 10  cm/s, respectively. The permeabil- human resulted in a V value of 10.75 L/kg. SS ity results for the marker compounds were as expected; the Table 1 Blood to plasma ratios (mean ± SD) Table 2 Binding kinetics of ME-401 and idelalisib on PIK3CD/ PIK3R1 Compound Sprague Dawley rat Beagle dog Human Compound k (1/M·s) k (1/s) K (M) t Τ a d D ½ ME-401 1.8 ± 0.35 1.8 ± 0.35 1.4 ± 0.28 6 −5 −11 Methazolamide 150 ± 70 185 ± 140 50 ± 50 ME-401 1.72 × 10 5.20 × 10 3.03 × 10 3.7 h 5.3 h 6 −3 −9 Verapamil 1.1 ± 0.08 1.3 ± 0.13 1.1 ± 0.16 Idelalisib 6.53 × 10 7.25 × 10 1.11 × 10 1.6 min 2.3 min Diclofenac 0.8 ± 0.16 0.7 ± 0.18 0.9 ± 0.28 k association rate constant, k dissociation rate constant, K equilib- a d D SD standard deviation rium dissociation constant, t half-life, T residence time 1/2 608 O. Moreno, J. Wood 3.3 ME‑401 and Idelalisib Tissue Distribution in A20 Table 3 Preclinical intravenous single-dose pharmacokinetics Syngeneic Model Species Body weight (kg) V (L/kg) SS CD-1 mouse 0.02 5.605 The administration of ME-401 50 and 75 mg/kg twice daily Sprague Dawley rat 0.15 23.733 for 4 days resulted in tumor concentrations approximately Cynomolgus monkey 3 8 20 and 30 times higher than plasma concentrations, respec- Beagle dog 10 9.7 tively, at 4 h after the last dose (Table 4; Fig. 3). Concentra- tions within the tumor were lower at 24 h after the last dose, V apparent volume of distribution at steady state SS but higher relative to plasma, when compared to the 4-h con- centrations. In the ME-401 75-mg/kg group, concentrations in brain tissue were present at 4 and 24 h after the last dose at approximately 30% of plasma values, suggesting penetra- tion into and retention of ME-401 in the central nervous system. Administration of idelalisib 50 mg/kg twice daily for 4 days resulted in tumor concentrations approximately three times higher than plasma concentrations at 4 h after the last dose, and concentrations were below the limit of quantitation at 24 h. 4 Discussion PI3Kδ is a target for the treatment of B-cell malignancies as evidenced by the approval of the PI3K inhibitors idela- Fig. 1 Allometric relationship between volume of distribution at lisib and duvelisib for treatment of FL and CLL/SLL and steady state (V ) and body weight SS copanlisib for the treatment of FL [7–9]. However, these agents have significant toxicity; idelalisib has been shown 3.2.3 Time/Plasma Concentrations of Plasma and Lymph to cause hepatotoxicity, severe diarrhea/colitis, pneumonitis, in Dogs and intestinal perforation [8]. Copanlisib, an IV pan-PI3K inhibitor given weekly, is associated with severe hyperten- All plasma samples were collected and analyzed as planned. sion and hyperglycemia [9]. Duvelisib has been shown to However, many of the corresponding lymph samples could cause fatal and serious infections, diarrhea/colitis, cutaneous not be collected due to catheter patency. ME-401 lymph and reactions, and pneumonitis [7]. There is a need for novel plasma concentrations are plotted for each dog (Fig. 2) and PI3Kδ inhibitors with decreased toxicity profiles that pro- were above the limit of quantitation in all samples. vide durable clinical activity. Fig. 2 ME-401 concentrations in blood and lymphatic fluid following a single oral dose to male beagle dogs Preclinical Pharmacology of ME-401, a Potent and Selective PI3Kδ Inhibitor 609 Table 4 Plasma and tissue concentrations (mean ± SD) of ME-401 and idelalisib in A20 syngeneic model in BALB/c mice 4 and 24 h after the last dose Compound Plasma (ng/mL), mean ± SD (CV%) Tumor (ng/g), mean ± SD (CV%) Brain (ng/g), mean ± SD (CV%) 4 h (n = 6) 24 h (n = 6) 4 h (n = 6) 24 h (n = 6) 4 h (n = 6) 24 h (n = 6) ME-401 75 mg/kg 7225 ± 531 (7.4) 2328 ± 416 (17.9) 225,333 ± 40,582 (18) 151,500 ± 35,799 (23.6) 2603 ± 466 (17.9) 676 ± 48 (7.1) ME-401 50 mg/kg 4897 ± 467 (9.5) 420 ± 105 (25.1) 99,850 ± 18,001 (18) 48,100 ± 11,569 (24.1) NE NE Idelalisib 50 mg/kg 23.6 ± 4.81 (20.4) BLQ 61.8 ± 17.6 (28.5) BLQ NE NE BLQ below limit of quantitation of idelalisib in plasma of 1 ng/mL or 2 ng/mL after 2 × assay dilution, CV coefficient of variation, NE not evalu- ated, SD standard deviation ME-401 75 mg/kg ME-401 75 mg/kg 30000 300000 8000 25000 250000 20000 200000 15000 150000 4000 10000 100000 5000 50000 0 0 0 Plasma Tumor PlasmaBrain (a) (b) 4 hours24 hours 4 hours24 hours ME-401 50 mg/kg Idelalisib 50 mg/kg 12000 120000 80 10000 100000 8000 80000 6000 60000 40 4000 40000 2000 20000 0 0 0 Plasma Tumor PlasmaTumor (c) (d) 4 hours24 hours 4 hours Fig. 3 Plasma and tissue concentrations (mean ± SD) at 4 (n = 6) b ME-401 75  mg/kg plasma and brain concentrations. c ME-401 and 24  h (n = 6) after the last dose of ME-401 or idelalisib admin- 50  mg/kg plasma and tumor concentrations. d Idelalisib 50  mg/kg istered orally twice daily for 4  days in an A20 syngeneic model in plasma and tumor concentrations at 4 h; concentrations at 24 h were BALB/c mice. a ME-401 75 mg/kg plasma and tumor concentrations. below the limit of quantitation PI3Kδ is located inside B-cell lymphocytes, which reside Consequently, these preclinical data are used to ascertain in the bone marrow and lymphatic system. Therefore, the insights to the pharmacologic properties of ME-401. efficacy of a drug that targets PI3Kδ is governed by its We evaluated the distribution of ME-401 into cells by capacity to distribute into those tissues and cells, as well B:P and the Caco-2 cell assay. The B:P of 1.4 indicates as the potency with which it inhibits PI3Kδ function. The that ME-401 readily distributes into blood cells, reaching results of our preclinical studies demonstrate the efficiency equilibrium when approximately 60% of the drug in the and potency of ME-401 in performing these tasks. Most blood distributes into blood cells. In comparison, idelalisib of these studies were performed early in development and has a B:P of 0.5–0.7 [8, 17], suggesting it remains more served to justify advancement of ME-401 into first-in-human in the plasma rather than permeating cells as compared clinical trials. Therefore, the concentrations of ME-401 with ME-401. The Caco-2 assay indicated that ME-401 not in these studies may not reflect clinical concentrations. only permeates cells but is also retained by cells. The low 610 O. Moreno, J. Wood recovery in the Caco-2 assay prevented accurate quantitation system was evaluated by measuring drug concentration in of permeability rate; the recovery was significantly improved plasma and lymphatic fluid, following oral administration when the cell lysate was included, indicating that the low to dogs. The methodology used to collect lymphatic fluid recovery was due to retention of ME-401 inside the cells. involved surgically implanted catheters. In some cases, the Collectively, these results indicate that ME-401 exhibits a catheters became occluded, preventing collection at subse- propensity to distribute into, and accumulate inside, cells quent time points. Consequently, the lymph concentration and may account for the higher potency observed in cellular data were too sparse to calculate PK parameters with a rea- assays compared with the purified enzyme assay. It was pre- sonable degree of confidence. Nonetheless, the results were viously reported [10, 11] that the clinical half maximal effec- adequate to conclude that ME-401 readily distributes into tive concentration (EC ) of 1 nM for inhibition of activation the lymphatic system after oral administration to dogs. of peripheral blood basophils in healthy volunteers was in In the A20 syngeneic model, concentrations of ME-401 agreement with the inhibition of PI3Kδ in cellular assays in tumor tissue were approximately 20–30 times greater than (half maximal inhibitory concentration [IC ] = 0.6  nM); plasma concentrations at 4 h after the last dose; these con- the IC was 5 nM for inhibition of purified PI3Kδ enzyme. centrations remained elevated relative to plasma concentra- Kinetics of ME-401 binding to isolated, biotinylated tions 24 h after the last dose, suggesting prolonged concen- PI3Kδ immobilized on a Biacore sensor chip were measured trations in this targeted tissue. In comparison, plasma and via surface plasmon resonance and compared with binding tumor concentrations of idelalisib were significantly lower kinetics of idelalisib. The very low K of 30 pM was cou- than those of ME-401 at 4 h following the last dose. By 24 h −5 pled with a very slow off-rate of 5.20 × 10 /s, equating to after the last dose, idelalisib plasma and tumor concentra- a half-life and residence time of several hours. In contrast, tions were below the limit of quantitation. Interestingly, our idelalisib has a higher K of 1110 pM, due largely to a faster study demonstrated the distribution of ME-401 into brain −3 off-rate of 7.25 × 10 /s, equating to half-life and residence tissue at concentrations around 30% of plasma concentra- times of a few minutes. These data show that once ME-401 tions that were still measurable at 24 h, and suggests that reaches its target, it binds ~ 37 times more tightly, and future investigation into the role of ME-401 in the treatment remains on-target ~ 138 times longer, than idelalisib in vitro. of CNS lymphomas may be warranted. Although idelalisib With ME-401 accumulating in cells and binding tightly to its and ME-401 are administered to humans at different doses, target, it is possible that prolonged inhibition of PI3Kδ could potentially resulting in very different tissue concentrations, occur within the tumor or lymphoid tissue even as ME-401 these agents were tested at identical dosing regimens in the levels decrease in plasma over time. This tight binding to A20 mouse model, to enable direct comparison of the mole- PI3Kδ and its ability to readily distribute into tissue may cules’ performance attributes. Notwithstanding that ME-401 partially explain the clinical results of ME-401 of high initial plasma concentrations in our studies may not reflect clinical ORRs in early studies in FL and CLL/SLL [13, 14]. plasma concentrations, ME-401 does exhibit linear PKs in The PK profile of ME-401 was evaluated in non-tumor- mice (data not shown), indicating that drug distribution does bearing species following oral administration to dogs and IV not vary with dose. administration to mice, rats, dogs, and monkeys. The high ME-401 entered clinical trials in B-cell malignancies at oral bioavailability of 79% indicates that the drug was well a starting dose of 60 mg orally, once daily, now the recom- absorbed. Extrapolation of V from preclinical species to mended Phase 2 dose. This dose is a fraction of the predicted SS a hypothetical 60-kg human resulted in a very large V of 140-mg MRSD based on preclinical toxicology studies. It SS 645 L, which is approximately 100 times higher than blood was previously reported [11, 12] that daily oral dosing of volume and approximately 15 times higher than whole body ME-401 60 mg was expected to result in clinical plasma volume. This V is ~ 28 times larger than the 23 L reported concentrations that maintained maximal PI3Kδ inhibition. SS for idelalisib, indicating greater diffusion of ME-401 away The high in  vitro potency of ME-401, together with its from the blood and into the tissues of the body [8, 18]. capacity to distribute into target tissues and accumulate at Although the mechanism behind this large V is unclear, the site of action, could underlie the high clinical potency SS and it is beyond the scope of this work to estimate the degree in B-cell malignancies that may differentiate ME-401 from to which ME-401 distributes to extravascular tissue in other PI3Kδ inhibitors [13]. These characteristics may also humans, it is likely that ME-401 concentrations are signifi- allow ME-401 the flexibility of intermittent dosing after cantly higher in one or more extravascular tissues compared a period of continuous therapy in an effort to prevent on- with drug concentrations measured in human plasma. target immune-related adverse effects that may occur late in The capacity of ME-401 to distribute to target tissues treatment in some patients [14]. Current studies of ME-401, was evaluated in the dog lymph/plasma PK study and the as monotherapy and in combination with novel agents, are A20 syngeneic model in mice. In the lymph/plasma study, ongoing in B-cell malignancies, and future studies may the propensity for ME-401 to distribute into the lymphatic Preclinical Pharmacology of ME-401, a Potent and Selective PI3Kδ Inhibitor 611 malignancies, inhibits PI3K signaling and cellular viability. provide answers to safety and efficacy concerns that have Blood. 2011;117(2):591–4. https ://doi.org/10.1182/blood -2010- shadowed this class of agents. 03-27530 5. 6. Dreyling M, Santoro A, Mollica L, Leppa S, Follows GA, Acknowledgements The authors acknowledge Sandra Petralia, Dan Lenz G, et  al. Phosphatidylinositol 3-kinase inhibition by Gold, and David Walsey for feedback on the manuscript and the medi- copanlisib in relapsed or refractory indolent lymphoma. J cal writing assistance of Laura Jung, PharmD, of ETHOS Health Com- Clin Oncol. 2017;35(35):3898–905. https ://doi.or g/10.1200/ munications in Yardley, PA, USA, which was supported financially by JCO.2017.75.4648. 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Ethical approval All applicable international, national, and/or insti- Safety, pharmacokinetics, and pharmacodynamics of ME-401, tutional guidelines for the care and use of animals were followed. All an oral, potent, and selective inhibitor of phosphatidylinositol procedures performed in studies involving animals were in accordance 3-kinase P110delta, following single ascending dose administra- with the ethical standards of the institution or practice at which the tion to healthy volunteers. Clin Ther. 2018;40(11):1855–67. https studies were conducted (Charles River Institutional Animal Care and ://doi.org/10.1016/j.clint hera.2018.09.006. Use Committee ASP # 990202). 12. Zann VCA, Preston M, Leung P, Duncan D, Moreno O. Formula- tion selection and development for ME-401, an oral, potent and selective inhibitor of phosphatidylinositol 3-kinase P110δ during Open Access This article is distributed under the terms of the Crea- a first-in-human study in healthy volunteers. 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