Venkatesh Pilla Reddy

Preclinical metabolism and disposition of SB939 (Pracinostat), an orally active histone deacetylase inhibitor, and prediction of human pharmacokinetics.

The preclinical absorption, distribution, metabolism, and excretion (ADME) properties of Pracinostat [(2E)-3-[2-butyl-1-[2-(diethylamino) ethyl]-1H-benzimidazol-5-yl]-N-hydroxyarylamide hydrochloride; SB939], an orally active histone deacetylase inhibitor, were characterized and its human pharmacokinetics (PK) was predicted using Simcyp and allometric scaling. SB939 showed high aqueous solubility with high Caco-2 permeability. Metabolic stability was relatively higher in dog and human liver microsomes than in mouse and rat. The major metabolites formed in human liver microsomes were also observed in preclinical species. Human cytochrome P450 (P450) phenotyping showed that SB939 was primarily metabolized by CYP3A4 and CYP1A2. SB939 did not significantly inhibit human CYP3A4, 1A2, 2D6, and 2C9 (>25 μM) but inhibited 2C19 (IC50 = 5.8 μM). No significant induction of human CYP3A4 and 1A2 was observed in hepatocytes. Plasma protein binding in mouse, rat, dog, and human ranged between ∼84 and 94%. The blood-to-plasma ratio was ∼1.0 in human blood. SB939 showed high systemic clearance (relative to liver blood flow) of 9.2, 4.5, and 1.5 l · h−1 · kg−1 and high volume of distribution at steady state (>0.6 l/kg) of 3.5, 1.7, and 4.2 l/kg in mouse, rat, and dog, respectively. The oral bioavailability was 34, 65, and ∼3% in mice, dogs, and rats, respectively. The predicted oral PK profile and parameters of SB939, using Simcyp and allometric scaling, were in good agreement with observed data in humans. Simcyp predictions showed lack of CYP3A4 and 2C19 drug-drug interaction potential for SB939. In summary, the preclinical ADME of SB939 supported its preclinical and clinical development as an oral drug candidate.

Physiologically Based Pharmacokinetic Model Qualification and Reporting Procedures for Regulatory Submissions: A Consortium Perspective

This work provides a perspective on the qualification and verification of physiologically based pharmacokinetic (PBPK) platforms/models intended for regulatory submission based on the collective experience of the Simcyp Consortium members. Examples of regulatory submission of PBPK analyses across various intended applications are presented and discussed. European Medicines Agency (EMA) and US Food and Drug Administration (FDA) recent draft guidelines regarding PBPK analyses and reporting are encouraging, and to advance the use and acceptability of PBPK analyses, more clarity and flexibility are warranted.

An investigation into the prediction of in vivo clearance for a range of Flavin-containing monooxygenase substrates

Flavin-containing monooxygenases (FMO) are metabolic enzymes mediating the oxygenation of nucleophilic atoms such as nitrogen, sulfur, phosphorus, and selenium. These enzymes share similar properties to the cytochrome P450 system but can be differentiated through heat inactivation and selective substrate inhibition by methimazole. This study investigated 10 compounds with varying degrees of FMO involvement to determine the nature of the correlation between human in vitro and in vivo unbound intrinsic clearance. To confirm and quantify the extent of FMO involvement six of the compounds were investigated in human liver microsomal (HLM) in vitro assays using heat inactivation and methimazole substrate inhibition. Under these conditions FMO contribution varied from 21% (imipramine) to 96% (itopride). Human hepatocyte and HLM intrinsic clearance (CLint) data were scaled using standard methods to determine the predicted unbound intrinsic clearance (predicted CLint u) for each compound. This was compared with observed unbound intrinsic clearance (observed CLint u) values back calculated from human pharmacokinetic studies. A good correlation was observed between the predicted and observed CLint u using hepatocytes (R2 = 0.69), with 8 of the 10 compounds investigated within or close to a factor of 2. For HLM the in vitro-in vivo correlation was maintained (R2 = 0.84) but the accuracy was reduced with only 3 out of 10 compounds falling within, or close to, twofold. This study demonstrates that human hepatocytes and HLM can be used with standard scaling approaches to predict the human in vivo clearance for FMO substrates.

Translational Modeling in Schizophrenia: Predicting Human Dopamine D2 Receptor Occupancy

ObjectivesTo assess the ability of a previously developed hybrid physiology-based pharmacokinetic-pharmacodynamic (PBPKPD) model in rats to predict the dopamine D2 receptor occupancy (D2RO) in human striatum following administration of antipsychotic drugs.MethodsA hybrid PBPKPD model, previously developed using information on plasma concentrations, brain exposure and D2RO in rats, was used as the basis for the prediction of D2RO in human. The rat pharmacokinetic and brain physiology parameters were substituted with human population pharmacokinetic parameters and human physiological information. To predict the passive transport across the human blood–brain barrier, apparent permeability values were scaled based on rat and human brain endothelial surface area. Active efflux clearance in brain was scaled from rat to human using both human brain endothelial surface area and MDR1 expression. Binding constants at the D2 receptor were scaled based on the differences between in vitro and in vivo systems of the same species. The predictive power of this physiology-based approach was determined by comparing the D2RO predictions with the observed human D2RO of six antipsychotics at clinically relevant doses.ResultsPredicted human D2RO was in good agreement with clinically observed D2RO for five antipsychotics. Models using in vitro information predicted human D2RO well for most of the compounds evaluated in this analysis. However, human D2RO was under-predicted for haloperidol.ConclusionsThe rat hybrid PBPKPD model structure, integrated with in vitro information and human pharmacokinetic and physiological information, constitutes a scientific basis to predict the time course of D2RO in man.

Harnessing Meta‐analysis to Refine an Oncology Patient Population for Physiology‐Based Pharmacokinetic Modeling of Drugs

Certain oncology compounds exhibit fundamental pharmacokinetic (PK) disparities between healthy and malignant conditions. Given the effects of tumor‐associated inflammation on enzyme and transporter expression, we performed a meta‐analysis of CYP‐ and transporter‐sensitive substrate clinical PK to quantitatively compare enzyme and transporter abundances between healthy volunteers (HV) and cancer patients (CP). Hepatic and intestinal CYP1A2, CYP2C19, and CYP3A4 abundance were subsequently adjusted via Simcyps sensitivity analysis tool. Of the 11 substrates we investigated, seven displayed marked exposure differences >1.25‐fold between CP and HV. Although CP studies are limited, meta‐analysis‐based reduction in CYP1A2, CYP2C19, and CYP3A4 enzyme abundances in a virtual oncology population effectively captures CP‐PK for caffeine, theophylline, midazolam, simvastatin, omeprazole, and a subset of oncology compounds. These changes allow extrapolation from HV to CP, enhancing predictive capability; therefore, conducting simulations in this CYP‐modified oncology (MOD‐CP) population provides a more relevant characterization of CP‐PK.

Development, Verification, and Prediction of Osimertinib Drug–Drug Interactions Using PBPK Modeling Approach to Inform Drug Label

Osimertinib is a potent, highly selective, irreversible inhibitor of epidermal growth factor receptor (EGFR) and T790M resistance mutation. In vitro metabolism data suggested osimertinib is a substrate of cytochrome P450 (CYP)3A4/5, a weak inducer of CYP3A, and an inhibitor of breast cancer resistance protein (BCRP). A combination of in vitro data, clinical pharmacokinetic data, and drug‐drug interaction (DDI) data of osimertinib in oncology patients were used to develop the physiologically based pharmacokinetic (PBPK) model and verify the DDI data of osimertinib. The model predicted the observed monotherapy concentration profile of osimertinib within 1.1‐fold, and showed good predictability (within 1.7‐fold) to the observed peak plasma concentration (Cmax) and area under the curve (AUC) DDI ratio changes, when co‐administered with rifampicin, itraconazole, and simvastatin, but not with rosuvastatin. Based on observed clinical data and PBPK simulations, the recommended dose of osimertinib when dosed with strong CYP3A inducers is 160 mg once daily. PBPK modeling suggested no dose adjustment with moderate and weak CYP3A inducers.

Preclinical Metabolism and Pharmacokinetics of SB1317 (TG02), a Potent CDK/JAK2/FLT3 Inhibitor

SB1317 (TG02) is a novel small molecule potent CDK/JAK2/FLT3 inhibitor. To evaluate full potential of this development candidate, we conducted drug metabolism and pharmacokinetic studies of this novel anti-cancer agent. SB1317 was soluble, highly permeable in Caco-2 cells, and showed > 99% binding to plasma from mice, dog and humans. It was metabolically stable in human and dog liver microsomes relative to mouse and rat. SB1317 was mainly metabolized by CYP3A4 and CY1A2 in vitro. SB1317 did not inhibit any of the major human CYPs in vitro except CYP2D6 (IC50=1 μM). SB1317 did not significantly induce CYP1A and CYP3A4 in human hepatocytes in vitro. The metabolic profiles in liver microsomes from preclinical species were qualitatively similar to humans. In pharmacokinetic studies SB1317 showed moderate to high systemic clearance (relative to liver blood flow), high volume of distribution ( > 0.6 L/kg), oral bioavailability of 24%, ∼ 4 and 37% in mice, rats and dogs, respectively; and extensive tissue distribution in mice. The favorable ADME of SB1317 supported its preclinical development as an oral drug candidate.

In vitro evaluation of the inhibition and induction potential of olaparib, a potent poly(ADP-ribose) polymerase inhibitor, on cytochrome P450

Abstract 1.u2003In vitro studies were conducted to evaluate potential inhibitory and inductive effects of the poly(ADP-ribose) polymerase (PARP) inhibitor, olaparib, on cytochrome P450 (CYP) enzymes. Inhibitory effects were determined in human liver microsomes (HLM); inductive effects were evaluated in cultured human hepatocytes. 2.u2003Olaparib did not inhibit CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2D6 or CYP2E1 and caused slight inhibition of CYP2C9, CYP2C19 and CYP3A4/5 in HLM up to a concentration of 100u2009μM. However, olaparib (17–500u2009μM) inhibited CYP3A4/5 with an IC50 of 119u2009μM. In time-dependent CYP inhibition assays, olaparib (10u2009μM) had no effect against CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6 and CYP2E1 and a minor effect against CYP3A4/5. In a further study, olaparib (2–200u2009μM) functioned as a time-dependent inhibitor of CYP3A4/5 (KI, 72.2u2009μM and Kinact, 0.0675u2009min−1). Assessment of the CYP induction potential of olaparib (0.061–44u2009μM) showed minor concentration-related increases in CYP1A2 and more marked increases in CYP2B6 and CYP3A4 mRNA, compared with positive control activity; however, no significant change in CYP3A4/5 enzyme activity was observed. 3.u2003Clinically significant drug–drug interactions due to olaparib inhibition or induction of hepatic or intestinal CYP3A4/5 cannot be excluded. It is recommended that olaparib is given with caution with narrow therapeutic range or sensitive CYP3A substrates, and that prescribers are aware that olaparib may reduce exposure to substrates of CYP2B6.

Erratum to: Translational Modeling in Schizophrenia: Predicting Human Dopamine D₂ Receptor Occupancy

Erratum to: Pharm Res n nDOI 10.1007/s11095-015-1846-4 n n nThere occurred two errors in the above manuscript (Pharm Res. 2015 Dec 30 [Epub ahead of print]). The correct information is as follows: n n nThe differential equations in Appendix 2 should read: n ndAbv/dt=CLbv/Vplasma∗Aplasma−CLbv/Vbv∗Abv−CLbev/Vbv∗fuplasma∗Abv+CLbev/Vbev∗fubrain∗Abev+CLeff/Vbev∗fubrain∗AbevdAbev/dt=CLbev/Vbv∗fuplasma∗Abv−CLbev/Vbev∗fubrain∗Abev−CLeff/Vbev∗fubrain∗Abev−CLst/Vbev∗fubrain∗Abev+CLst/Vstf∗fubrain∗AstfdAstf/dt=CLst/Vbev∗fubrain∗Abev−CLst/Vstf∗fubrain∗Astf−kon∗fubrain∗Astf∗Bmax−CB+koff∗AstbdAstb/dt=kon∗fubrain∗Astf∗Bmax−CB−koff∗Astb n n n n nTable III should read: n n n nTable III n nIn vitro, in vivo and ex vivo values estimates used in the human D2RO predictive model.

The brain-penetrant clinical ATM inhibitor AZD1390 radiosensitizes and improves survival of preclinical brain tumor models

Preclinical data highlight AZD1390 as a potentially powerful new therapy to enhance brain tumor patient responses to radiotherapy. Poor survival rates of patients with tumors arising from or disseminating into the brain are attributed to an inability to excise all tumor tissue (if operable), a lack of blood-brain barrier (BBB) penetration of chemotherapies/targeted agents, and an intrinsic tumor radio-/chemo-resistance. Ataxia-telangiectasia mutated (ATM) protein orchestrates the cellular DNA damage response (DDR) to cytotoxic DNA double-strand breaks induced by ionizing radiation (IR). ATM genetic ablation or pharmacological inhibition results in tumor cell hypersensitivity to IR. We report the primary pharmacology of the clinical-grade, exquisitely potent (cell IC50, 0.78 nM), highly selective [>10,000-fold over kinases within the same phosphatidylinositol 3-kinase–related kinase (PIKK) family], orally bioavailable ATM inhibitor AZD1390 specifically optimized for BBB penetration confirmed in cynomolgus monkey brain positron emission tomography (PET) imaging of microdosed 11C-labeled AZD1390 (Kp,uu, 0.33). AZD1390 blocks ATM-dependent DDR pathway activity and combines with radiation to induce G2 cell cycle phase accumulation, micronuclei, and apoptosis. AZD1390 radiosensitizes glioma and lung cancer cell lines, with p53 mutant glioma cells generally being more radiosensitized than wild type. In in vivo syngeneic and patient-derived glioma as well as orthotopic lung-brain metastatic models, AZD1390 dosed in combination with daily fractions of IR (whole-brain or stereotactic radiotherapy) significantly induced tumor regressions and increased animal survival compared to IR treatment alone. We established a pharmacokinetic-pharmacodynamic-efficacy relationship by correlating free brain concentrations, tumor phospho-ATM/phospho-Rad50 inhibition, apoptotic biomarker (cleaved caspase-3) induction, tumor regression, and survival. On the basis of the data presented here, AZD1390 is now in early clinical development for use as a radiosensitizer in central nervous system malignancies.