Comprehensive evaluation of liver microsomal cytochrome P450 3A (CYP3A) inhibition: comparison of cynomolgus monkey and human.

1. Members of the cytochrome P450 3A (CYP3A) subfamily metabolize numerous compounds and serve as the loci of drug-drug interactions (DDIs). Because of high amino acid sequence identity with human CYP3A, the cynomolgus monkey has been proposed as a model species to support DDI risk assessment. 2. Therefore, the objective of this study was to evaluate 35 known inhibitors of human CYP3A using human (HLM) and cynomolgus monkey (CLM) liver microsomes. Midazolam was employed as substrate to generate IC50 values (concentration of inhibitor rendering 50% inhibition) in the absence and presence of a preincubation (30 mins) with NADPH. 3. In the absence of preincubation, the IC50 values generated with CLM were similar to those obtained with HLM (86% within 2-fold; 100% within 3-fold difference). However, significant differences (up to 48-fold) in preincubation IC50 were observed with 17% of the compounds (raloxifene, bergamottin, nicardipine, mibefradil, ritonavir, and diltiazem). 4. Our results indicate that in most cases the cynomolgus monkey can be a viable DDI model. However, significant species differences in time-dependent CYP3A inhibition can be observed for some compounds. In the case of raloxifene, such a difference can be ascribed to a specific CYP3A4 amino acid residue.

Ultrafast mass spectrometry based bioanalytical method for digoxin supporting an in vitro P-glycoprotein (P-gp) inhibition screen.

The evaluation of interactions between drug candidates and transporters such as P-glycoprotein (P-gp) has gained considerable interest in drug discovery and development. Inhibition of P-gp can be assessed by performing bi-directional permeability studies with in vitro P-gp-expressing cellular model systems such as Caco-2 (human colon carcinoma) cells, using digoxin as a substrate probe. Existing methodologies include either assaying (3)H-digoxin with liquid scintillation counting (LSC) detection or assaying non-labeled digoxin with liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis at a speed of several minutes per sample. However, it is not feasible to achieve a throughput high enough using these approaches to sustain an early liability screen that generates more than a thousand samples on a daily basis. To address this challenge, we developed an ultrafast (9 s per sample) bioanalytical method for digoxin analysis using RapidFire™, an on-line solid-phase extraction (SPE) system, with MS/MS detection. A stable isotope labeled analog, d3-digoxin, was used as internal standard to minimize potential ionization matrix effect during the RF-MS/MS analysis. The RF-MS/MS method was more than 16 times faster than the LC-MS/MS method but demonstrated similar sensitivity, selectivity, reproducibility, linearity and robustness. P-gp inhibition results of multiple validation compounds obtained with this RF-MS/MS method were in agreement with those generated by both the LC-MS/MS method and the (3)H-radiolabel assay. This method has been successfully deployed to assess P-gp inhibition potential as an important early liability screen for drug-transporter interaction.

Discovery of 3-hydroxy-4-cyano-isoquinolines as novel, potent, and selective inhibitors of human 11ß-hydroxydehydrogenase 1 (11ß-HSD1).

Derived from the HTS hit 1, a series of hydroxyisoquinolines was discovered as potent and selective 11ß-HSD1 inhibitors with good cross species activity. Optimization of substituents at the 1 and 4 positions of the isoquinoline group in addition to the core modifications, with a special focus on enhancing metabolic stability and aqueous solubility, resulted in the identification of several compounds as potent advanced leads.

Discovery of BMS-986144, a Third-Generation, Pan-Genotype NS3/4A Protease Inhibitor for the Treatment of Hepatitis C Virus Infection.

The discovery of a pan-genotypic hepatitis C virus (HCV) NS3/4A protease inhibitor based on a P1-P3 macrocyclic tripeptide motif is described. The all-carbon tether linking the P1-P3 subsites of 21 is functionalized with alkyl substituents, which are shown to effectively modulate both potency and absorption, distribution, metabolism, and excretion (ADME) properties. The CF3Boc-group that caps the P3 amino moiety was discovered to be an essential contributor to metabolic stability, while positioning a methyl group at the C1 position of the P1' cyclopropyl ring enhanced plasma trough values following oral administration to rats. The C7-fluoro, C6-CD3O substitution pattern of the P2* isoquinoline heterocycle of 21 was essential to securing the targeted potency, pharmacokinetic (PK), and toxicological profiles. The C6-CD3O redirected metabolism away from a problematic pathway, thereby circumventing the time-dependent cytochrome P (CYP) 450 inhibition observed with the C6-CH3O prototype.

A high-throughput bioanalytical platform using automated infusion for tandem mass spectrometric method optimization and its application in a metabolic stability screen.

Liquid chromatography/tandem mass spectrometry (LC/MS/MS) is the bioanalytical method of choice to support plate-based, in vitro early ADME (Absorption, Distribution, Metabolism and Excretion) screens such as metabolic stability (Metstab) assessment. MS/MS method optimization has historically been the bottleneck in this environment, where samples from thousands of discrete compounds are analyzed on a monthly basis, mainly due to the lack of a high-quality commercially available platform to handle the necessary MS/MS method optimization steps for sample analysis by selected reaction monitoring (SRM) on triple quadrupole mass spectrometers. To address this challenge, we recently developed a highly automated bioanalytical platform by successfully integrating QuickQuan 2.0, a unique high-throughput solution featuring MS/MS method optimization by automated infusion, with a customized in-house software tool in support of a Metstab screen. In this platform, a dual-column setup running parallel chromatography was also implemented to reduce the bioanalytical cycle time for LC/MS/MS sample analysis. A set of 45 validation compounds was used to demonstrate the speed, quality and reproducibility of MS/MS method optimization, sample analysis, and data processing using this automated platform. Metstab results for the validation compounds in microsomes from multiple species (human, rat, mouse) showed good consistency within each batch, and also between batches conducted on different days. We have achieved and maintained a monthly throughput of 1300 compound assays representing 500 discrete compounds per instrument per month on this platform, and it has been used to generate metabolic stability data for more than 25 000 compounds to date with an overall success rate of more than 95%.

An automated liquid chromatography-mass spectrometry process to determine metabolic stability half-life and intrinsic clearance of drug candidates by substrate depletion.

An automated process is described for the detailed assessment of the in vitro metabolic stability properties of drug candidates in support of pharmaceutical property profiling. Compounds are incubated with liver microsomes using a robotic liquid handler. Aliquots are taken at various time points, and the resulting samples are quantitatively analyzed by liquid chromatography-mass spectrometry utilizing ion trap mass spectrometers to determine the amount of compound remaining. From these data metabolism rates can be calculated. A high degree of automation is achieved through custom software, which is employed for instrument setup, data processing, and results reporting. The assay setup is highly configurable, allowing for any combination of up to six user-selected time points, variable substrate concentration, and microsomes or other biologically active media. The data, based on relative substrate depletion, affords an estimate of metabolic stability through the calculation of half-life (t(1/2)) and intrinsic clearance, which are used to differentiate and rank order drug leads. In general, t(1/2) is the time necessary for the metabolism, following first-order kinetics, of 50% of the initial compound. Intrinsic clearance is the proportionality constant between rate of metabolism of a compound and its concentration at the enzyme site. Described here is the setup of the assay, and data from assay test compounds are presented.

Synthesis of novel ketoconazole derivatives as inhibitors of the human Pregnane X Receptor (PXR; NR1I2; also termed SXR, PAR).

PXR, pregnane X receptor, in its activated state, is a validated target for controlling certain drug-drug interactions in humans. In this context, there is a paucity of inhibitors directed toward activated PXR. Using prior observations with ketoconazole as a PXR inhibitor, the target compound 3 was synthesized from (s)-glycidol with overall 56% yield. (+)-Glycidol was reacted with 4-bromophenol and potassium carbonate in DMF to yield the ring opened compound 6. This was then heated to reflux in benzene along with 2', 4'-difluoroacetophenone and catalytic amount of para-toluene sulfonic acid to yield 8. The resultant acetal 8 was then functionalized using Palladium chemistry to yield the target compound 3. The activity of the compound was compared with ketoconazole and UCL2158H. However, in contrast with ketoconazole (IC(50) approximately 0.020 microM; approximately 100% inhibition), 3 has negligible effects on inhibition of microsomal CYP450 (maximum approximately 20% inhibition) at concentrations >40 microM. In vitro, micromolar concentration of ketoconazole is toxic to passaged human cell lines, while 3 does not exhibit cytotoxicity up to concentrations approximately 100 microM (viability >85%). This is the first demonstration of a chemical analog of a PXR inhibitor that retains activity against activated PXR. Furthermore, in contrast with ketoconazole, 3 is less toxic in human cell lines and has negligible CYP450 activity.

An automated high throughput liquid chromatography-mass spectrometry process to assess the metabolic stability of drug candidates.

An automated high throughput process, termed the MetFast assay, is described to assess in vitro the general microsomal cytochrome P450 beta-nicotinamide adenine dinucleotide phosphate-mediated first-pass metabolic stability of potential drug candidates as a utility for pharmaceutical profiling. Utilizing robotic protocols with a multiprobe liquid handler, compounds are incubated with liver microsomes from different species. Samples are then analyzed by in-line liquid chromatography (LC)-mass spectrometry (MS) to determine the amount of compound remaining after a certain time, which allows calculation of metabolism rates. To quantitatively assess large numbers of structurally diverse compounds by LC-MS, a strategy based on an iterative two-step process was devised. Initially compounds are qualitatively analyzed by LC-ultraviolet (UV)/MS (step 1) to determine purity (UV detection) and structural integrity (MS detection). This step ensures that only correct and verified compounds with sufficient purity are being assayed to obtain reproducible high data quality. In addition, all necessary information is gathered to automatically generate specific quantitative methods for the subsequent bioanalytical analysis of metabolic stability samples by LC-UV/MS (step 2). In-house-developed, highly flexible and sophisticated data management software, termed SmartReport, is utilized for automated qualitative and quantitative LC-MS analysis set-up, data processing, and results reporting. The integration of key aspects, inherent "universal" collision-induced dissociation settings of ion trap mass spectrometers for tandem mass spectrometric scan functions utilized for compound-specific and sensitive quantitative MS methods, generic fast-LC conditions, generic MS instrument settings, and the functionality of SmartReport software resulted in an analytical process that routinely provides reproducible high-quality metabolic stability data on structurally diverse compounds. Described here is the setup of the MetFast assay, and metabolic stability data from assay validation compounds are given.

Utility of high-resolution accurate MS to eliminate interferences in the bioanalysis of ribavirin and its phosphate metabolites.

BACKGROUND: The polar nucleoside drug ribavirin (RBV) combined with IFN-α is a front-line treatment for chronic hepatitis C virus infection. RBV acts as a prodrug and exerts its broad antiviral activity primarily through its active phosphorylated metabolite ribavirin 5´-triphosphate (RTP), and also possibly through ribavirin 5´-monophosphate (RMP). To study RBV transport, diffusion, metabolic clearance and its impact on drug-metabolizing enzymes, a LC-MS method is needed to simultaneously quantify RBV and its phosphorylated metabolites (RTP, ribavirin 5´-diphosphate and RMP). In a recombinant human UGT1A1 assay, the assay buffer components uridine and its phosphorylated derivatives are isobaric with RBV and its phosphorylated metabolites, leading to significant interference when analyzed by LC-MS with the nominal mass resolution mode. RESULTS: Presented here is a LC-MS method employing LC coupled with full-scan high-resolution accurate MS analysis for the simultaneous quantitative determination of RBV, RMP, ribavirin 5´-diphosphate and RTP by differentiating RBV and its phosphorylated metabolites from uridine and its phosphorylated derivatives by accurate mass, thus avoiding interference. CONCLUSION: The developed LC-high-resolution accurate MS method allows for quantitation of RBV and its phosphorylated metabolites, eliminating the interferences from uridine and its phosphorylated derivatives in recombinant human UGT1A1 assays.