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Safety, Pharmacokinetics, and Pharmacodynamics of ME-401, an Oral, Potent, and Selective Inhibitor of Phosphatidylinositol 3-Kinase P110δ, Following Single Ascending Dose Administration to Healthy Volunteers

Open AccessPublished:October 26, 2018DOI:https://doi.org/10.1016/j.clinthera.2018.09.006

      Abstract

      Purpose

      ME-401 is a novel selective inhibitor of phosphatidylinositol 3 kinase p110δ, an enzyme often found overexpressed and overactive in B-cell malignancies. The current study was performed to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of single ascending oral doses of ME-401 in healthy volunteers.

      Methods

      This analysis was an open-label, nonrandomized study in healthy male volunteers. Three sequential groups were dosed. Each group received single doses of ME-401 on two occasions; the doses tested ranged from 10 to 150 mg. Blood was drawn at various time points to analyze plasma concentrations of ME-401 and inhibition of basophil activation, a marker of phosphatidylinositol 3 kinase p110δ inhibition.

      Findings

      Fifteen subjects received a single dose of ME-401 on two occasions. Three adverse events that were considered possibly related to the study drug were reported: one event of pain, one event of headache, and one event of upper abdominal pain. ME-401 exhibited dose proportionality up to 60 mg, and supra-proportional increases in exposure were observed above doses of 60 mg. In addition, there was a dose-proportional increase in the inhibition of basophil activation up to 60 mg. Mean t1/2 ranged from 9.36 to 29.23 hours across the dose range. A 60 mg dose of ME-401 approached 90% inhibition of basophil activation, and thereafter no further increase to the percent inhibition of basophil activation was observed for higher doses. Once-daily dosing of 60 mg ME-401 was forecasted to result in trough plasma levels exceeding the concentration needed for 90% inhibition of basophil activation.

      Implications

      This first-in-human study showed that ME-401 was well tolerated after single doses up to 150 mg. Pharmacologic activity was confirmed after administration of single ascending oral doses of 10 to 150 mg. ME-401 60 mg, administered once daily, was selected as the starting dose for patient studies. ClinicalTrials.gov identifier: NCT02521389.

      Key Words

      Introduction

      ME-401 is a small-molecule drug being developed for the treatment of B-cell malignancies. It is a novel, proprietary, selective inhibitor of phosphatidylinositol 3 kinase p110δ (PI3Kδ), a lipid enzyme often found overexpressed in B-cell malignancies, including follicular lymphoma, chronic lymphocytic leukemia (CLL), and diffuse large B-cell lymphoma.
      • Millis S.Z.
      • Ikeda S.
      • Reddy S.
      • Gatalica Z.
      • Kurzrock R.
      Landscape of phosphatidylinositol-3-kinase pathway alterations across 19784 diverse solid tumors.
      The PI3Kδ enzyme is an isoform of the wider PI3K group, a family of enzymes located within the lipid membrane of cells, categorized into classes IA, IB, II, and III. The PI3K p110δ isoform belongs to class IA. PI3Kδ is responsible for converting phosphatidylinositol 4, 5-bisphosphate (PIP2) into phosphatidylinositol 3, 4, 5 trisphosphate (PIP3), following activation by tyrosine kinases.
      • Stark A.
      • Sriskantharajah S.
      • Hessel E.M.
      • Okkenhaug K.
      PI3K inhibitors in inflammation, autoimmunity and cancer.
      PIP3 is a secondary messenger that mediates recruitment of protein kinase B (AKT) to the cell membrane. AKT is well known for its role in mediating cell proliferation, growth, and survival via downstream signaling such as the mechanistic target of rapamycin pathway. This setting makes PI3K/AKT an interesting target for treating malignancies. Unlike the other members of its class, PI3Kδ is not ubiquitously expressed and instead is mostly distributed on leukocytes. Preclinical studies have shown the important role that PI3Kδ plays in B-cell maturation and development, as well as in the regulation of effector and regulatory T cells.
      • Soond D.R.
      • Bjørgo E.
      • Moltu K.
      • et al.
      PI3K p110δ regulates T-cell cytokine production during primary and secondary immune responses in mice and humans.
      • Ramadani F.
      • Bolland D.J.
      • Garcon F.
      • et al.
      The PI3K isoforms p110α and p110δ are essential for Pre-B cell receptor signaling and B cell development.
      • Patton D.T.
      • Wilson M.D.
      • Rowan W.C.
      • Soond D.R.
      • Okkenhaug K.
      The PI3K p110δ regulates expression of CD38 on regulatory T cells.
      • Wentink M.
      • Dalm V.
      • Lankester A.C.
      • et al.
      Genetic defects in PI3Kδ affect B-cell differentiation and maturation leading to hypogammaglobulineamia and recurrent infections.
      • Fung-Leung W.
      Phosphoinositide 3-kinase delta (PI3Kδ) in leukocyte signaling and function.
       PI3Kδ is usually regulated by phosphatase and tensin homolog, which converts PIP3 to PIP2.
      • Brown J.S.
      • Banerji U.
      Maximising the potential of AKT inhibitors as anti-cancer treatments.
      In subjects with hematologic malignancies, PI3Kδ is commonly found to be overactivated and upregulated, with phosphatase and tensin homolog commonly underexpressed or inactivated by genetic mutation.
      • Millis S.Z.
      • Ikeda S.
      • Reddy S.
      • Gatalica Z.
      • Kurzrock R.
      Landscape of phosphatidylinositol-3-kinase pathway alterations across 19784 diverse solid tumors.
      B-cell lymphoproliferative disorders are a diverse group of malignancies, ranging from slow-growing indolent diseases, such as follicular lymphoma, to more aggressive disorders, such as diffuse large B-cell lymphoma.
      • Armitage J.O.
      • Gascoyne R.D.
      • Lunning M.A.
      • Cavalli F.
      Non-Hodgkin lymphoma.
      The combination of the anti-CD20 antibody rituximab and a chemotherapy regimen consisting of cyclophosphamide, doxorubicin, vincristine, and prednisone (commonly known as R-CHOP) is the standard of care for this disease.
      However, ∼30% of patients will relapse after an initial response to therapy.
      • Sehn L.H.
      • Gascoyne R.D.
      Diffuse large B-cell lymphoma: optimizing outcome in the context of clinical and biologic heterogeneity.
      Indolent B-cell lymphoma accounts for approximately one third of newly diagnosed cases of non-Hodgkin lymphoma, with follicular lymphoma being the most common histology. Initial chemoimmunotherapy induces an objective response in most patients, but it is not curative, and the disease recurs in nearly all patients, with the rate of disease response and duration of response decreasing with subsequent lines of therapy. More recently, small-molecule drugs that inhibit specific targets within the B-cell receptor signaling pathway, which play a key role in the survival, proliferation, adhesion, and migration of malignant B cells, have been approved for the treatment of indolent B-cell lymphoma; these include the PI3K inhibitors idelalisib and copanlisib. However, these agents are associated with severe toxicities, and copanlisib must be administered intravenously. In the European Medicines Agency's Committee for Medicinal Products for Human Use assessment report on idelalisib, it was stated that the prescribed dose of idelalisib results in clinical plasma levels that are higher than the no observable adverse effect levels (NOAELs) determined in preclinical toxicology testing. Clearly, new agents are needed that are active and well tolerated for the treatment of patients with these B-cell malignancies.
      P110δ PI3K is exceptional in that it regulates not only homeostasis and function of B cells but is also involved in the transduction of microenvironmental signals, including chemokines and cytokines derived from lymphoid tissues. The inhibition of basophil activation can be used as a biomarker for PI3Kδ inhibition (ie, a measure of ME-401 effect). The 1A class of enzymes are activated by receptor tyrosine kinases and other tyrosine kinase–coupled receptors, such as the high-affinity immunoglobulin E receptor, FCεRI.
      • Stark A.
      • Sriskantharajah S.
      • Hessel E.M.
      • Okkenhaug K.
      PI3K inhibitors in inflammation, autoimmunity and cancer.
      • Wentink M.
      • Dalm V.
      • Lankester A.C.
      • et al.
      Genetic defects in PI3Kδ affect B-cell differentiation and maturation leading to hypogammaglobulineamia and recurrent infections.
      • Fung-Leung W.
      Phosphoinositide 3-kinase delta (PI3Kδ) in leukocyte signaling and function.
      FCεRI is commonly found on lymphocytes, mast cells, and basophils and is directly related to the activation and degranulation of these immune cells. FCεRI is indirectly linked to the p85 subunit of PI3K enzymes via a cytosolic adaptor molecule, Gab2.
      • Hawkins P.T.
      • Stephens L.R.
      PI3K signalling in inflammation.
      • Kim M.
      • Rådinger M.
      • Gilfillan A.M.
      The multiple roles of phosphoinositide 3-kinase in mast cell biology.
      After antigen-mediated activation of the FCεRI receptor, PI3Kδ phosphorylates PIP2 into PIP3, which leads to downstream regulation of Bruton's tyrosine kinase leading to degranulation of heparin and histamine.
      • Wentink M.
      • Dalm V.
      • Lankester A.C.
      • et al.
      Genetic defects in PI3Kδ affect B-cell differentiation and maturation leading to hypogammaglobulineamia and recurrent infections.
      • Fung-Leung W.
      Phosphoinositide 3-kinase delta (PI3Kδ) in leukocyte signaling and function.
      • Kim M.
      • Rådinger M.
      • Gilfillan A.M.
      The multiple roles of phosphoinositide 3-kinase in mast cell biology.
      After degranulation, basophils present the CD63 protein on their extracellular surface.
      The preclinical primary pharmacology of ME-401 was previously characterized in a range of in vitro studies, revealing selectivity for the δ isoform, inhibition of PI3Kδ-mediated cellular activity in activated immune cells (Raji cell line, primary basophils) with low nanometer 50% inhibitory concentrations (IC50) even in the presence of whole blood, and activity against multiple primary B-cell malignancies.
      • O’Farrell M.
      • Ventura R.
      • Tai A.
      • et al.
      Preclinical characterization of PWT143, a novel selective and potent phosphatidylinositol 3 kinase delta (PI3K delta) inhibitor with ex-vivo activity in hematologic malignancies.
      Notably, ME-401 potency against PI3Kδ in cellular assays (IC50 = 0.6 nM) correlated well with inhibition of basophil activation when whole blood was incubated with ME-401 ex vivo (IC50 = 1 nM). Based on preclinical toxicokinetic data (as discussed later), it was expected that even at the doses deemed safe for healthy subjects, clinical plasma concentrations would result in significant PI3Kδ inhibition.
      The objectives of this first-in-human study were to assess the safety and the pharmacokinetic (PK) and pharmacodynamic (PD) parameters of ME-401 after administration of single ascending oral doses in healthy subjects. Although it was expected that the safety assessment from a single-dose study would not be predictive of toxicities resulting from prolonged therapy in heavily pretreated cancer patients, it is nonetheless useful for assessing any unanticipated acute toxicities of the novel molecule, which might warrant early discontinuation of development.
      The risk–benefit was fully assessed, and the drug was agreed to be acceptable for dosing in healthy volunteers. A comprehensive toxicology program, consistent with the guidance provided in the International Conference on Harmonisation (ICH) Tripartite Guideline, Nonclinical Evaluation for Anticancer Pharmaceuticals (S9), was conducted.
      • International Conference on Harmonisation
      Tripartite Guideline, Nonclinical Evaluation for Anticancer Pharmaceuticals (S9).
      Rats and dogs were the selected species for the definitive toxicology studies, based on interspecies (mice, rats, dogs, non-human primates, and human) comparison of ME-401 drug metabolism in liver microsomes, where there were no human-specific metabolites observed. The preclinical toxicology program included single- and repeat-dose exploratory toxicology studies and definitive 28-day toxicology studies conducted in rats and dogs using the clinically relevant route (oral) and schedule (daily) of administration; it also included a complete genotoxicity testing battery, as well as cardiovascular safety pharmacology studies. ME-401 was nonmutagenic and nonclastogenic/aneugenic, and no physiologically relevant effects on cardiovascular or pulmonary function were observed in conscious, freely moving telemetrized dogs at doses that were otherwise toxic to dogs in the 28-day study. Based on analyses of target organ toxicities from the rat and dog 28-day toxicology studies, it was determined that the standard laboratory assessments for a first-in-human trial in healthy subjects were adequate.
      Although ME-401 is intended for a patient population that would otherwise be eligible for an approved PI3K inhibitor (eg, idelalisib), it would be difficult to enroll those patients in a first-in-human study with a novel untested drug; an alternative (eg, more advanced) patient population would typically be used for the initial study. The intention was to use the PK and PD variables from this single-dose study to design an appropriate dosing regimen and enable a more rapid advancement into the target patient population. Although not within the scope of the present article, it was also desired to assess the sensitivity of ME-401 PK parameters to certain formulation changes.
      PD variables of ME-401 were assessed via measurement of CD63 expression by flow cytometry, following ex vivo stimulation of peripheral blood basophils with an anti- FCεRI monoclonal antibody. Inhibition of the PI3Kδ enzyme reportedly inhibits FCεRI signaling in peripheral blood basophils, measured by a reduction in CD63 expression after stimulation by anti-FCεRI antibody, and it was reported as a clinical marker of potency during the development of idelalisib.
      • Lannutti B.J.
      • Meadows S.A.
      • Herman S.E.M.
      • et al.
      CAL-101, a p110δ selective phosphatidylinositol-3-kinase inhibitor for the treatment of B-cell malignancies, inhibits PI3K signaling and cellular viability.

      Subjects and Methods

       Study Design

      A single-center study of single ascending doses in healthy adult volunteers was performed between June 9, 2015, and September 13, 2015, at Quotient Clinical, Nottingham, United Kingdom. The study was conducted in accordance with the clinical trial protocol, the International Conference on Harmonisation–Good Clinical Practice Guidelines, the Medicines for Human Use (Clinical Trials) Regulations (2004) and amendments (2006, 2008), and the ethical principles outlined in the World Medical Association Declaration of Helsinki and its amendments. The study was reviewed and approved by the Wales Research Ethics Committee 2 (Cardiff, United Kingdom) and the Medicines and Healthcare products Regulatory Agency. All subjects provided written informed consent before any study-related procedures were performed. Subjects were healthy men, aged 18 to 65 years, with a body mass index in the range of 18.0 to 32.0 kg/m2. Health status was determined by medical history, physical examination, and clinical laboratory test results.
      This analysis was an open-label, single ascending dose study that consisted of sequential groups (A, B, and C), comprising 3, 6, and 6 subjects, respectively (Figure 1). Each subject was administered a single dose of ME-401 on two occasions. Sentinel dosing of the first dose level in Group A was used, with the option to continue sentinel dosing for the subsequent dose levels, if appropriate. There was a minimum 7-day washout period between doses of ME-401 within each group, with the option to extend this period after a review of interim safety, tolerance, and PK data before the next dose level.
      Figure 1
      Figure 1Study outline. *Data not presented.
      Subjects were admitted 24 hours before dosing and remained at the clinical unit until 48 hours' postdose. Subjects returned for a follow-up visit, 5 to 10 days after the end of their clinical residency, following their second dose of ME-401.
      Because this study used an open-label, nonrandomized design, a randomization scheme was therefore not required. A treatment allocation list was produced before dosing with ME-401, which dictated the investigational medicinal product and dose level to be administered to each subject.

       Dose Selection

      The starting dose of ME-401 was selected based on the NOAEL in nonclinical toxicology studies, as prescribed by the US Food and Drug Administration’s Guidance for Industry: Estimating the Maximum Safe Starting Dose in Initial Clinical Trials for Therapeutics in Adult Healthy Volunteers.
      • Food and Drug Administration (FDA)
      Guidance for industry estimating the maximum safe starting dose in initial clinical trials for therapeutics in adult healthy volunteers.
      The NOAELS in 4-week repeat dose toxicity studies were 75 mg/kg per day (450 mg/m2) in rats (Cmax and AUC0–24 on day 28 were 409 ng/ml and 6100 ng·h/mL, respectively, in males and 732 ng/mL and 12,400 ng·h/mL in females) and 3 mg/kg per day (60 mg/m2) in dogs (combined-sex mean Cmax and AUC0–24 values on day 28 were 175 ng/mL and 1740 ng·h/mL), which correspond to human-equivalent doses (HEDs) of 12.1 mg/kg per day (rat) and 1.7 mg/kg per day (dog). Because the HED value calculated for the dog was lower than that for the rat, the dog was identified as the most sensitive species for the purpose of deriving the maximum recommended starting dose as 0.17 mg/kg per day, using a 10-fold safety factor. For an average 60-kg individual, this information translated into a starting dose of 10 mg ME-401. The HED was calculated as per the guidance document.
      Dose selection for subsequent cohorts was dependent on the safety, tolerability, and human exposure from the preceding cohort. The protocol also allowed for flexibility to dose alternate formulations of ME-401, as long as the starting dose of an untested formulation did not exceed the dose level of the previous formulation that had already been considered safe and well tolerated. Dose escalation was allowed only to a level that would not exceed the highest plasma exposure derived from the NOAEL from the 28-day repeat dose study in dogs, which is the most sensitive species.

       Pharmaceutical Development

      A powder blend in a capsule containing ME-401, filler, and buffers was developed. A bracketed capsule fill weight approach (2–60 mg) was used, with data from the lowest and highest fill weights included in the regulatory submission. This approach enabled a dose design space to be created from which any unit dose between 2 and 60 mg could be prepared. For doses >60 mg, multiple units were administered. Unit doses were only manufactured once the data from previous cohorts were available. Active pharmaceutical ingredients were provided by Patheon API Services (formerly IRIX Pharmaceuticals) on behalf of MEI Pharma.

       Safety Assessments

      Safety assessments comprised the standard battery of assessments. These assessments included adverse events, clinical laboratory tests (clinical chemistry, hematology, and urinalysis), vital signs, 12-lead ECGs, and physical examinations.

       PK Sampling and Analyses

      Blood samples were collected to assay for plasma concentrations of ME-401 before and at 0.5, 1, 1.5, 2, 3, 4, 5, 6, 8, 10, 12, 16, 24, 36, and 48 hours' postdose.
      Plasma concentrations of ME-401 were analyzed by using a validated and specific LC-MS/MS method, which used an Acquity HPLC system (Waters Corporation, Milford, Massachusetts) and an API5000 mass spectrometer (AB Sciex, Framingham, Massachusetts). Human plasma samples (50 μL) were fortified with 25 μL of warfarin internal standard working solution followed by protein precipitation with 0.1% formic acid in acetonitrile. A 50 μL aliquot of the supernatant was transferred into 400 μL of 2% formic acid in acetonitrile:water (30:70) and analyzed. The analytes were eluted by using 0.1% formic acid in acetonitrile:water (95:5) (mobile phase A) and 0.1% formic acid (aqueous) (mobile phase B), with a gradient method on a Waters BEH C8 column (2.1 × 50 mm, 1.7 μm). Selective detection was performed via multiple-reaction monitoring using electrospray ionization in positive mode. The transition monitored for ME-401 was 577 m/z > 348 m/z, and the transition monitored for warfarin was 309 m/z > 163 m/z. These transitions corresponded to the protonated ions and most abundant fragments.
      Calibration curves were constructed by using peak area ratios of the calibration standards by applying a linear weighted 1/×2 least-squares regression algorithm. The dynamic range of the assay was 0.500 to 500 ng/mL. The precision and accuracy of the assay in validation were: inter-assay precision ≤8.5 %CV (≤9.1 %CV at the lower limit of quantitation [LLOQ]), interassay accuracy ≤±3.8%RE (≤±6.2%RE at the LLOQ), intra-assay precision ≤11.5 %CV (≤11.1 %CV at the LLOQ) and intra-assay accuracy ≤±9.3 %RE (≤±14.0 %RE at the LLOQ). The stability of ME-401 in human plasma containing dipotassium EDTA has been demonstrated for up to 491 days at both –20°C and –70°C in MPI Research study 2281-005 (data on file).
      PK analysis and nonparametric superposition were performed by using standard noncompartmental methods (WinNonlin version 6.3; Certara L.P. [Pharsight], Princeton, New Jersey). Calculated PK parameters included Cmax, Tmax, AUC0–last, and AUC0–∞. Dose proportionality was assessed by using dose-adjusted Cmax, AUC0–last, and AUC0–∞. AUC calculations were performed by using the linear trapezoidal rule.

       PD Sampling and Analyses

      Blood samples were collected for the analysis of basophil activation status. The sample collection schedule was adaptive, based on the results of emerging data from dose level 1. For 10 mg ME-401, samples were collected before and at 0.5, 1.5, and 4 hours' postdose. For all remaining dose levels, samples were collected before and 1.5, 4, and 6 hours' postdose.
      Basophil activation tests were performed on whole blood samples via flow cytometry (Flow CAST assay; Bühlmann, Schönenbuch, Switzerland). This test quantified the expression of a cell surface marker protein (CD63) at each time point. Whole blood samples were combined with a stimulation buffer and validated allergen. Staining reagent was added, containing a mixture of monoclonal anti-CD63 antibodies labeled with fluorescein isothiocyanate and antihuman chemokine receptor CCR3 antibodies labeled with phycoerythrin. CCR3 is expressed on basophils, allowing for identification and gating of basophils via flow cytometry. After activation via the allergen, basophils degranulate and express CD63 on their extracellular surface, allowing for detection via the staining reagent. A negative, predose baseline control was used to calculate the positive cell ratio, and nonstimulated cells were also measured to allow for calculation of percent inhibition of basophil activation.
      The ratio of CD63-positive (CD63pos) cells (ie, the positive cell ratio) was calculated as the percentage of CD63pos cells at each postdose time point, divided by the positive cells at predose (baseline). The percent inhibition of basophil activation was calculated as the difference in percentage of CD63pos cells between stimulated and nonstimulated samples relative to baseline. The presence of ME-401 would be expected to inhibit the process of basophil activation; it would therefore be expected that the positive cell ratio would decrease and the percent inhibition would increase. Individual plasma concentrations of ME-401 and percent inhibition of basophil activation were fitted to a simple Emax model, where E = (Emax × Cmax)/(C + EC50), to explore the relationship between concentration and effect. The Emax model was fitted by using WinNonlin version 6.3, and the fit was checked by visual inspection of predicted curve versus observed data and the residuals.

       Statistics

      This study was an exploratory trial. The numbers of subjects per cohort are consistent with common practice for this study type and were considered suitable to achieve the objectives of the study. Formal statistical analyses were performed for PK parameters Cmax, AUC0–∞, and AUC0–last to assess dose proportionality across the dose range tested (10–150 mg). The power model included terms for the natural log transformed dose fitted as a fixed effect (continuous) and subject fitted as a random effect. The estimate obtained for β (the slope of the model) is a measure of dose proportionality. Other results are presented by using descriptive summaries only.

      Results

       Subjects

      Fifteen subjects received a single dose of ME-401 on two occasions (Table I). The mean (%CV) age was 41.7 years (29.93%), and body mass index was 27.2 kg/m2 (12.92%). All subjects were white males. The doses of ME-401 studied were 10, 30, 60, 90, and 150 mg. Fourteen subjects completed the study. One subject in group B withdrew consent between period 1 and period 2 for personal reasons.
      Table ISummary of demographic data.
      Group A (N = 3)Group B (N = 6)Group C (N = 6)Total (N = 15)
      Age (years)Mean44.736.345.741.7
      SD9.312.713.512.5
      CV%2135300.3
      Height (cm)Mean176.3181.5175.7178.1
      SD1.25.43.74.9
      CV%1320.0
      Weight (kg)Mean81.192.282.786.2
      SD11.68.911.511.0
      CV%1410140.1
      BMI (kg/m2)Mean2628.126.827.2
      SD3.43.63.93.5
      CV%1313150.1
      Race (%)White3 (100)6 (100)6 (100)15 (100)
      Group A – 10 mg, 30 mg; Group B – 60 mg; Group C – 90 mg, 150 mg.

       Safety

      After a single dose of ME-401, no severe or serious adverse events were recorded. Of the total number of adverse events recorded, only 3 were considered possibly related to ME-401, reported by the same subject in group B (60 mg ME-401): one event of pain, one event of headache, and one event of upper abdominal pain. There were no clinically significant findings in laboratory assessments, vital signs, or 12-lead ECGs.

       PK Results

      After single doses of 10 to 150 mg administered in the fasted state, ME-401 was absorbed slowly with median Tmax occurring at 5 hours. The range of Tmax values varied from 1.5 to 6.0 hours (Table II).
      Table IISummary of ME-401 PK parameters.
      TmaxCmaxAUC0–lastAUC0–infHalf-Life
      hng/mLh·ng/mLh·ng/mLh
      Group AN33322
      10 mgGeometric meanNC1.6118.224.99.36
      Median51.6420.629.811.99
      CV%
      Range is presented for Tmax in lieu of CV%.
      (5.00–6.00)
      Range is presented for Tmax in lieu of CV%.
      8.970.5106.8138.8
      Group AN33333
      30 mgGeometric meanNC3.8977.311729.23
      Median54.497296.629.6
      CV%
      Range is presented for Tmax in lieu of CV%.
      (5.00–6.00)
      Range is presented for Tmax in lieu of CV%.
      66.850.144.738.1
      Group BN66666
      60 mgGeometric meanNC9.3916223427.78
      Median59.5416223427.2
      CV%
      Range is presented for Tmax in lieu of CV%.
      (4.98–6.00)
      Range is presented for Tmax in lieu of CV%.
      32.232.621.636.2
      Group CN66655
      90 mgGeometric meanNC13.629946627.56
      Median514.333652224.8
      CV%
      Range is presented for Tmax in lieu of CV%.
      (3.00–6.00)
      Range is presented for Tmax in lieu of CV%.
      44.136.644.746.6
      Group CN66666
      150 mgGeometric meanNC34.865493928.09
      Median540.7775110026.27
      CV%
      Range is presented for Tmax in lieu of CV%.
      (1.50–6.02)
      Range is presented for Tmax in lieu of CV%.
      55.261.862.231.1
      NC – Not Calculated.
      Range is presented for Tmax in lieu of CV%.
      Exposure generally increased proportionally with dose increments up to 60 mg (Figure 2). A supra-proportional increase in exposure was observed for doses >60 mg. Mean Cmax (%CV) values for each dose level were 1.61 ng/mL (8.9%), 3.89 ng/mL (66.8%), 9.39 ng/mL (32.2%), 13.6 ng/mL (44.1%), and 34.8 ng/mL (55.2%), respectively. Mean AUC0–last (%CV) values for each dose level were 18.2 ng·h/mL (70.5%), 77.3 ng·h/mL (50.1%), 162 ng · h/mL (32.6%), 299 ng·h/mL (36.6%), and 654 ng·h/mL (61.8%) (Table II, Figure 3, Figure 4).
      Figure 2
      Figure 2Mean ± SD ME-401 plasma concentrations versus time plot (semi-log).
      Figure 3
      Figure 3Cmax as a function of dose. Slope = 0.23 (95% CI, 0.14–0.33).
      Figure 4
      Figure 4AUC0–∞ as a function of dose. Slope = 6.78 (95% CI, 4.89–8.72).
      Mean t1/2 ranged from 9.36 to 29.23 hours (%CV ranged from 31.1% to 138.8%) across the dose range.
      Dose proportionality was assessed for the parameters Cmax, AUC0–∞, and AUC0–last. The results for Cmax values confirmed dose proportionality across the dose range of 10 to 150 mg. In contrast, assessment of AUC0–∞ and AUC0–last (last time point for the 10 mg dose was 36 hours, and 48 hours for doses 30–150 mg) did not show dose proportionality. For results to be consistent with dose proportionality, the slope of the dose proportionality model (β) should be close to 1.0, and the 90% CI should include 1.0. The estimates for β and the 90% CIs were 1.1 (0.9–1.3), 1.3 (1.1–1.6), and 1.3 (1.1–1.5) for Cmax, AUC0–∞, and AUC0–last, respectively.

       PD Results

      After single oral doses of 10, 30, 60, 90, and 150 mg ME-401, inhibition of basophil activation, as measured by the difference in percentage of CD63pos between stimulated and nonstimulated control cells, was observed for all dose levels. The only exception was the 0.5 hour postdose time point for the 10 mg dose level, for which no inhibition was observed (Table III).
      Table IIISummary of pharmacodynamic data.
      ME-401 Dose LevelTime PointPositive Cell Ratio %, Mean (SD)Inhibition %, Mean (SD)
      10 mg (n = 3)Baseline100
      0.5 h postdose100.57 (2.37)0.41 (2.55)
      1.5 h postdose87.50 (3.34)13.58 (3.68)
      4 h postdose57.34 (14.63)45.12 (16.82)
      30 mg (n = 3)Baseline100
      1.5 h postdose49.79 (33.88)51.46 (34.13)
      4 h postdose32.94 (20.52)69.32 (20.15)
      6 h postdose33.25 (17.58)68.68 (17.50)
      60 mg (n = 6)Baseline100
      1.5 h postdose53.86 (33.39)46.43 (33.31)
      4 h postdose13.78 (7.96)87.17 (7.93)
      6 h postdose11.22 (7.33)89.87 (7.17)
      90 mg (n = 6)Baseline100
      1.5 h postdose22.06 (9.90)80.52 (11.52)
      4 h postdose19.73 (12.07)74.54 (5.37)
      6 h postdose20.00 (10.71)76.38 (1.99)
      150 mg (n = 6)Baseline1000
      1.5 h postdose21.48 (15.80)84.73 (14.19)
      4 h postdose18.67 (14.90)86.74 (12.64)
      6 h postdose15.63 (13.72)86.56 (14.05)
      Inhibition approaching 90% was observed at the 60 mg dose level at 4 and 6 hours postdose. A dose-related response in percent inhibition was observed up to the 60 mg dose level. Thereafter, as the dose increased (90 and 150 mg), no further increases in percent inhibition were observed. In addition, the percent inhibition for the 90 and 150 mg doses was similar across all time points (Table III).
      Based on the fitted Emax model, a 90% effective concentration (EC90) was determined to be 5 ng/mL (Figure 5). Data from the PK analysis were modeled by using nonparametric superposition to predict the steady-state plasma concentrations after single daily doses of the intended therapeutic regimen of oral dosing. The data forecasted that once-daily dosing of 60 mg ME-401 would result in trough plasma concentrations exceeding the EC90 (Figure 6).
      Figure 5
      Figure 5Percent inhibition of basophil activation, corrected for baseline, as a function of ME-401 plasma concentration.
      Figure 6
      Figure 6Simulated steady-state plasma concentration-time profiles for ME-401 after daily oral administration of 30, 60 and 90 mg strength in capsules.

      Discussion

      Idelalisib, an orally bioavailable and selective PI3Kδ inhibitor, was approved by the US Food and Drug Administration in 2014 for the treatment of patients with relapsed CLL, follicular lymphoma, and small lymphocytic lymphoma (SLL). However, the drug has significant toxicity, including hepatotoxicity, severe diarrhea, pneumonitis, colitis, and intestinal perforation.
      • Coutré S.E.
      • Barrientos J.C.
      • Brown J.R.
      • et al.
      Management of adverse events associated with idelalisib treatment: expert panel opinion.
      Copanlisib, a pan-PI3K inhibitor, was approved by the US Food and Drug Administration in 2017 for the treatment of relapsed follicular lymphoma but requires weekly infusions and has unique toxicities associated with its PI3Kα inhibition, such as severe hypertension and hyperglycemia.
      • Dreyling M.
      • Santoro A.
      • Mollica L.
      • et al.
      Phosphatidylinositol 3-kinase inhibition by copanlisib in relapsed or refractory indolent lymphoma.
      Therefore, an opportunity exists for a drug with an improved therapeutic window. ME-401 represents such a drug and is currently in a Phase Ib dose escalation study in patients with recurrent CLL, SLL, or follicular lymphoma.
      • Soumerai J.D.
      • Pagel J.M.
      • Jagadeesh D.
      • et al.
      Initial results of a dose escalation study of a selective and structurally differentiated PI3Kδ inhibitor, ME-401, in relapsed/refractory (R/R) follicular lymphoma (FL) and chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL).
      Because ME-401 was developed for an oncology indication, the more common route into clinical development would be to move directly into dosing within a patient group. The decision to conduct the first-in-human study in healthy volunteers was driven by the need to rapidly identify the appropriate dose and schedule to enable swift advancement into the target patient population. Consequently, the design of this first-in-human study was novel. The minimum number of subjects possible to achieve the study objectives were included (a large database of information in healthy subjects would be of limited value) and there was no placebo (causality of adverse events was unlikely to halt development, due to a higher risk–benefit relationship being acceptable for oncology indications).
      ME-401 was well tolerated after single doses up to 150 mg. All treatment-emergent adverse events deemed related to ME-401 were recorded by the same subject in the 60 mg dose group (Group B), were mild in nature, and had resolved by the end of the study. There were no clinically significant changes in laboratory parameters, and no clinically significant changes in vital signs or ECGs were recorded for any subject. No subject reached the subject withdrawal criteria based on QTcF prolongation or safety laboratory tests. It should be noted that these results may not predict the expected adverse events in patients undergoing continuous daily therapy.
      ME-401 was slowly absorbed, with a median Tmax occurring at 5 hours. The mean elimination t1/2 was 26.09 hours. A shorter t1/2 was observed in subjects administered 10 mg single doses in Group A. This outcome is likely due to plasma levels that were below the limit of quantitation and were obtained from the terminal time points used in the estimation (Table II).
      Exposure generally increased in a proportional manner across dose levels 10 to 60 mg. Formal statistical analysis confirmed Cmax dose proportionality but not for AUC0–last. Supra-proportionality seemed to occur from the 60 mg dose upward. This outcome could be due to a saturation of efflux transporters in the gut wall or a clearance mechanism, although the terminal t1/2 was similar over the dose range of 30 to 150 mg (Figure 2, Figure 3, Figure 4, Table II).
      The late Tmax is indicative of slow absorption, which is often attributed to poor drug substance solubility. However, the fact that sub-proportional exposure was not observed suggests that, at the doses tested, exposure was not limited by solubility.
      The impact of PI3Kδ inhibition on basophil activation had been reported previously and provided a convenient method of measuring the PD effect. The PI3Kδ inhibitory activity of ME-401 was assessed by the basophil activation test, a flow cytometry–based functional assay that assesses the degree of cell activation after ex vivo stimulation. Basophils in blood samples, collected at specific time points during the study, were stimulated to express CD63, the cell surface marker protein. Expression of this marker was quantified to provide a summary of the positive cell ratio and the percent inhibition of basophil activation as measured by a difference between percent stimulated and nonstimulated control.
      As expected, the ratio of positive cells compared with baseline decreased with time, and percent inhibition of basophil activation generally increased with time, as plasma concentrations of drug increased toward Tmax, after single doses of ME-401. Inhibition of basophil activation was observed for all dose levels, with the greatest mean decrease recorded for 60 mg (Table III). Approximately 90% inhibition of basophil activation was achieved for the 60 mg dose level at both 4 and 6 hours' postdose. At 10 and 30 mg, inhibition was observed but to a lesser extent. Levels of inhibition were recorded at 90 mg and 150 mg that were similar to the 60 mg dose. These data indicate that increasing the dose above 60 mg does not increase the inhibitory effect. This conclusion seems to be consistent with the literature on other PI3Kδ inhibitors, which indicates that, although activation of basophils is primarily through the PI3Kδ-mediated pathway, there are PI3Kδ-independent pathways that can also lead to activation and degranulation
      • Kim M.
      • Rådinger M.
      • Gilfillan A.M.
      The multiple roles of phosphoinositide 3-kinase in mast cell biology.
      (Figure 2).
      From the fitted Emax model, the concentrations of ME-401 estimated to yield 50% and 90% (ie, EC50 and EC90 respectively) of the maximum effect (Emax, 91.6%) were 0.572 and 5.15 ng/mL, respectively (0.99 and 8.93 nM) (Figure 5). This clinical EC50 is in agreement with the preclinical inhibition of PI3Kδ in cellular assays (IC50 = 0.6 nM) and inhibition of basophil activation when whole blood was incubated with ME-401 ex vivo (IC50 = 1 nM).
      The modeled PK data predict that single daily doses of 60 mg would maintain plasma levels above the established EC90, at steady state (Figure 6). Consequently, a dosing regimen of 60 mg ME-401, administered once daily, was selected as the starting dose for the subsequent dose escalation Phase Ib study in patients with relapsed follicular lymphoma and CLL/SLL. The clinical plasma levels from single daily doses of 60 mg were also projected to be below the NOAELs from the preclinical toxicology studies. Preliminary results of this Phase Ib study indicated that ME-401 was active in relapsed follicular lymphoma and CLL/SLL, with an overall response rate of 90% in 30 evaluable patients, and that doses >60 mg did not improve efficacy; these findings confirm that the dose of 60 mg identified in the healthy volunteer study was also the recommended dose for Phase II trials.
      • Soumerai J.D.
      • Pagel J.M.
      • Jagadeesh D.
      • et al.
      Initial results of a dose escalation study of a selective and structurally differentiated PI3Kδ inhibitor, ME-401, in relapsed/refractory (R/R) follicular lymphoma (FL) and chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL).
      The dose of 60 mg once daily is substantially lower than the maximum recommended starting dose (MRSD) for ME-401 in patients with cancer. The MRSD calculated from the preclinical toxicology data is 140 mg/d according to the MRSD algorithm typically used for patients with advanced cancer (International Conference on Harmonisation (ICH) Tripartite Guideline, Nonclinical Evaluation for Anticancer Pharmaceuticals (S9)).
      • International Conference on Harmonisation
      Tripartite Guideline, Nonclinical Evaluation for Anticancer Pharmaceuticals (S9).
      Therefore, compared with the more common approach of conducting the first-in-human-trial in patients with cancer, the performance of this first-in-human study in healthy volunteers afforded more rapid advancement into the target patient population.

      Conclusions

      This first-in-human study has shown that ME-401 is well tolerated after single doses up to 150 mg. Pharmacologic activity was confirmed after administration of single ascending oral doses of 10 mg to 150 mg. A 60 mg dose of ME-401, administered once daily, was selected as the starting dose for a Phase Ib study evaluating ME-401 in relapsed follicular lymphoma and CLL/SLL (NCT02914938).

      Acknowledgments

      This study was funded by MEI Pharma, Inc. The authors thank the team at LGC Ltd for bioanalytical method validation and sample analysis during the conduct of the study.
      Mr. Willson wrote the initial draft. Dr. Moreno, Mr. Butler, Dr. Zann, Dr. Leung, and Dr. Connor contributed to study design and supervised the study. All authors contributed to writing and review of the manuscript, and all authors read and approved the manuscript.

      Conflicts of Interest

      Dr. Moreno is an employee of MEI Pharma, Inc. Mr. Butler was an employee of MEI Pharma, Inc. when the study was conducted. The study was conducted at Quotient Sciences, Ltd (formerly Quotient Clinical, Ltd.). Mr. Willson, Dr. Zann and Dr. Connor are employees of Quotient Sciences, Ltd. Dr. Leung was an employee of Quotient Sciences, Ltd. when the study was conducted.

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