Jennifer Liras

Use of immortalized human hepatocytes to predict the magnitude of clinical drug-drug interactions caused by CYP3A4 induction.

Cytochrome P4503A4 (CYP3A4) is the principal drug-metabolizing enzyme in human liver. Drug-drug interactions (DDIs) caused by induction of CYP3A4 can result in decreased exposure to coadministered drugs, with potential loss of efficacy. Immortalized hepatocytes (Fa2N-4 cells) have been proposed as a tool to identify CYP3A4 inducers. The purpose of the current studies was to characterize the effect of known inducers on CYP3A4 in Fa2N-4 cells, and to determine whether these in vitro data could reliably project the magnitude of DDIs caused by induction. Twenty-four compounds were chosen for these studies, based on previously published data using primary human hepatocytes. Eighteen compounds had been shown to be positive for induction, and six compounds had been shown to be negative for induction. In Fa2N-4 cells, all 18 positive controls produced greater than 2-fold maximal CYP3A4 induction, and all 6 negative controls produced less than 1.5-fold maximal CYP3A4 induction. Subsequent studies were conducted to determine the relationship between in vitro induction data and in vivo induction response. The approach was to relate in vitro induction data (Emax and EC50 values) with efficacious free plasma concentrations to calculate a relative induction score. This score was then correlated with decreases in area under the plasma concentration versus time curve values for coadministered CYP3A4 object drugs (midazolam or ethinylestradiol) from previously published clinical DDI studies. Excellent correlations (r2 values >0.92) were obtained, suggesting that Fa2N-4 cells can be used for identification of inducers as well as prediction of the magnitude of clinical DDIs.

Discovery of azetidinyl ketolides for the treatment of susceptible and multidrug resistant community-acquired respiratory tract infections.

Respiratory tract bacterial strains are becoming increasingly resistant to currently marketed macrolide antibiotics. The current alternative telithromycin (1) from the newer ketolide class of macrolides addresses resistance but is hampered by serious safety concerns, hepatotoxicity in particular. We have discovered a novel series of azetidinyl ketolides that focus on mitigation of hepatotoxicity by minimizing hepatic turnover and time-dependent inactivation of CYP3A isoforms in the liver without compromising the potency and efficacy of 1.

Synthesis and biological activity of piperazine-Based dual MMP-13 and TNF-α converting enzyme inhibitors

Abstract A series of novel MMP-13 and TNF-α converting enzyme inhibitors based on piperazine 2-hydroxamic acid scaffolds are described. The TACE, MMP-1 and MMP-13 activity of these inhibitors as well as the effect of substitution of the piperazine nitrogen and the P-1′ benzyloxy tailpiece is discussed. Moderate in vivo activity is observed with several members of this group.

Strategies to minimize CNS toxicity: in vitro high-throughput assays and computational modeling

Introduction: Healthy functioning of the brain is dependent on the ability of the blood–brain barrier (BBB) and other central nervous system (CNS) barriers to protect the neurocompartments from potential disruptive and damaging xenobiotic agents. In vitro high-throughput (HT) screens and computational models that assess a compounds ability to pass through or disrupt the BBB have become important tools in the identification of new well-tolerated peripheral drugs and safer chemical products such as pesticides. Leveraging these HT in vitro assays and computational BBB tools together with the current understanding of brain penetration may enable the drug discovery community to minimize access of drug candidates into the CNS compartment. Areas covered: This article reviews aspects of the most recent in vitro and computational approaches designed to provide an early assessment of a compounds ability to access the neurocompartment. This article also provides insight into using these tools to identify compounds that have restricted access to the neurocompartment. Expert opinion: The development of safer peripheral-acting medicines and chemical products can be achieved through prospective design and early assessment with HT assays of the BBB in conjunction with computational models. Exclusion or significantly reduced access of a compound to the neurocompartment will increase the odds of identifying a compound with reduced CNS-related adverse drug reactions. A holistic approach to compound design and evaluation that incorporates prospective design principles (e.g., optimization of physicochemical properties), leverages HT in vitro assays and integrates the use of BBB computational models may yield the ‘best-in-class’ peripherally acting product.

Mechanistic Investigation of the Preclinical Pharmacokinetics and Interspecies Scaling of PF-05231023, a Fibroblast Growth Factor 21–Antibody Protein Conjugate

PF-05231023, a long-acting fibroblast growth factor 21 (FGF21) analog, was generated by covalently conjugating two engineered [des-His1, Ala129Cys]FGF21 molecules to a nontargeting human IgG1κ scaffold. The pharmacokinetics (PK) of PF-05231023 after i.v. and s.c. administration was evaluated in rats and monkeys using two enzyme-linked immunosorbent assays with high specificity for biologically relevant intact N termini (NT) and C termini (CT) of FGF21. Intact CT of FGF21 displayed approximately 5-fold faster systemic plasma clearance (CL), an approximately 2-fold lower steady-state volume of distribution, and at least 5-fold lower bioavailability compared with NT. In vitro serum stability studies in monkeys and humans suggested that the principal CL mechanism for PF-05231023 was degradation by serum proteases. Direct scaling of in vitro serum degradation rates for intact CT of FGF21 underestimated in vivo CL 5-fold, 1.4-fold, and 2-fold in rats, monkeys, and humans, respectively. The reduced steady-state volume of distribution and the bioavailability for intact CT relative to NT in rats and monkeys were compatible with proteolytic degradation occurring outside the plasma compartment via an unidentified mechanism. Human CL and PK profiles for intact NT and CT of FGF21 were well predicted using monkey single-species allometric and Dedrick scaling. Physiologically based pharmacokinetic models incorporating serum stability data and an extravascular extraction term based on differential bioavailability of intact NT and CT of FGF21 in monkeys improved accuracy of human PK predictions relative to Dedrick scaling. Mechanistic physiologically based pharmacokinetic models of this nature may be highly valuable for predicting human PK of fusion proteins, synthetically conjugated proteins, and other complex biologics.

Excretion, Metabolism, and Pharmacokinetics of 1-(8-(2-Chlorophenyl)-9-(4-Chlorophenyl)-9H-Purin-6-yl)-4-(Ethylamino)Piperidine-4-Carboxamide, a Selective Cannabinoid Receptor Antagonist, in Healthy Male Volunteers

The disposition of 1-(8-(2-chlorophenyl)-9-(4-chlorophenyl)-9H- purin-6-yl)-4-(ethylamino)-piperidine-4-carboxamide (CP-945,598), an orally active antagonist of the cannabinoid CB1 receptor, was studied after a single 25-mg oral dose of [14C]CP-945,598 to healthy human subjects. Serial blood samples and complete urine and feces were collected up to 672 h after dose. The mean total recovery of radioactivity was 60.1 ± 12.8 from the urine and feces, with the majority of the dose excreted in the feces. The absorption of CP-945,598 in humans was slow with Tmax at 6 h. Less than 2% of the dose was recovered as unchanged drug in the combined excreta, suggesting that CP-945,598 is extensively metabolized. The primary metabolic pathway of CP-945,598 involved N-de-ethylation to form an N-desethyl metabolite (M1), which was then subsequently metabolized by amide hydrolysis (M2), N-hydroxylation (M3), piperidine ring hydroxylation (M6), and ribose conjugation (M9). M3 was further metabolized to oxime (M4) and keto (M5) metabolites. M1, M4, and M5 were the major circulating metabolites, with AUC(0–48) values 4.7-, 1.5-, and 1.1-fold greater than that of CP-945,598. M1, M2, and M9 accounted for 5.6, 33.6, and 6.30% of the dose, respectively, in excreta. The results from in vitro experiments with recombinant isoforms suggested that the oxidative metabolism of CP-945,598 to M1 is catalyzed primarily by CYP3A4/3A5. The molecular docking study showed that the N-ethyl moiety of CP-945,598 can access to the heme iron-oxo of CYP3A4 in an energetically favored orientation. Together, these data suggest that CP-945,598 is well absorbed and eliminated largely by CYP3A4/3A5-catalyzed metabolism.

Quantitative Translational Analysis of Brain Kynurenic Acid Modulation via Irreversible Kynurenine Aminotransferase II Inhibition

Kynurenic acid (KYNA) plays a significant role in maintaining normal brain function, and abnormalities in KYNA levels have been associated with various central nervous system disorders. Confirmation of its causality in human diseases requires safe and effective modulation of central KYNA levels in the clinic. The kynurenine aminotransferases (KAT) II enzyme represents an attractive target for pharmacologic modulation of central KYNA levels; however, KAT II and KYNA turnover kinetics, which could contribute to the duration of pharmacologic effect, have not been reported. In this study, the kinetics of central KYNA-lowering effect in rats and nonhuman primates (NHPs, Cynomolgus macaques) was investigated using multiple KAT II irreversible inhibitors as pharmacologic probes. Mechanistic pharmacokinetic-pharmacodynamic analysis of in vivo responses to irreversible inhibition quantitatively revealed that 1) KAT II turnover is relatively slow [16–76 hours’ half-life (t1/2)], whereas KYNA is cleared more rapidly from the brain (<1 hour t1/2) in both rats and NHPs, 2) KAT II turnover is slower in NHPs than in rats (76 hours vs. 16 hours t1/2, respectively), and 3) the percent contribution of KAT II to KYNA formation is constant (∼80%) across rats and NHPs. Additionally, modeling results enabled establishment of in vitro-in vivo correlation for both enzyme turnover rates and drug potencies. In summary, quantitative translational analysis confirmed the feasibility of central KYNA modulation in humans. Model-based analysis, where system-specific properties and drug-specific properties are mechanistically separated from in vivo responses, enabled quantitative understanding of the KAT II-KYNA pathway, as well as assisted development of promising candidates to test KYNA hypothesis in humans.

Discovery of Potent and Selective Periphery-Restricted Quinazoline Inhibitors of the Cyclic Nucleotide Phosphodiesterase PDE1

We disclose the discovery and X-ray cocrystal data of potent, selective quinazoline inhibitors of PDE1. Inhibitor ( S)-3 readily attains free plasma concentrations above PDE1 IC50 values and has restricted brain access. The racemic compound 3 inhibits >75% of PDE hydrolytic activity in soluble samples of human myocardium, consistent with heightened PDE1 activity in this tissue. These compounds represent promising new tools to probe the value of PDE1 inhibition in the treatment of cardiovascular disease.

Gamma-secretase modulators demonstrate similar exposure-response relationship in the rat and guinea pig

Background: Compounds that modulate g -secretase (GSMs) activity to selectively lower brain Ab42 have been pursued as potential therapies for individuals with Alzheimer’s disease. The Ab sequence in humans and guinea pigs is identical but differs from that in rat. To probe the pharmacodynamic (PD) effects of GSMs, the guinea pig seems to be a reasonable model; however, rat is the preferred species since pharmacokinetic (PK) and safety characterization is conducted in the rat. Therefore, it is critical to understand whether the exposure-response relationship of GSMs vary between the rat and guinea pig. Methods:We completed comprehensive time-course studies for measurement of compound concentrations and Ab levels in the plasma, cerebrospinal fluid (CSF), and brain in the rat and guinea pig. Each species was administered with two structurally distinct GSMs, GSM67 and GSM09. The data enabled a PK/PDmodel, which accounts for the synthesis as well as clearance of Ab, to derive an intrinsic PK/PD relationship that was devoid of confounds from PK or Ab turnover. Results: GSM67 and GSM09 significantly reduced Ab42 in a dose-dependent fashion in the plasma, CSF, and brain in the rat and guinea pig. For all three compartments, the intrinsic PK/PD relationship for Ab42 lowering was similar between these two species. Conclusions: Our quantitative PK/PD analysis support utilizing the rat as a suitable model for preclinical profiling of GSMs. Moreover, the quantitative approach described here can be used for further assessment of PK/PD translatability across species.