The use of liquid chromatography/thermospray mass spectrometry with on-line ultraviolet diode array and radiochemical detection: characterization of the putative metabolites of U-78875 in female rat faeces

Discovery and Preclinical Characterization of BIIB091, a Reversible, Selective BTK Inhibitor for the Treatment of Multiple Sclerosis

Multiple Sclerosis is a chronic autoimmune neurodegenerative disorder of the central nervous system (CNS) that is characterized by inflammation, demyelination, and axonal injury leading to permeant disability. In the early stage of MS, inflammation is the primary driver of the disease progression. There remains an unmet need to develop high efficacy therapies with superior safety profiles to prevent the inflammation processes leading to disability. Herein, we describe the discovery of BIIB091, a structurally distinct orthosteric ATP competitive, reversible inhibitor that binds the BTK protein in a DFG-in confirmation designed to sequester Tyr-551, an important phosphorylation site on BTK, into an inactive conformation with excellent affinity. Preclinical studies demonstrated BIB091 to be a high potency molecule with good drug-like properties and a safety/tolerability profile suitable for clinical development as a highly selective, reversible BTKi for treating autoimmune diseases such as MS.

In vivo multiple metabolic pathways for a novel G protein-coupled receptor 119 agonist DS-8500a in rats: involvement of the 1,2,4-oxadiazole ring-opening reductive reaction in livers under anaerobic conditions

A 1,2,4-oxadiazole ring-containing compound DS-8500a was developed as a novel G protein-coupled receptor 119 agonist. In vivo metabolic fates of [¹⁴C]DS-8500a differently radiolabeled in the benzene ring or benzamide side carbon in rats were investigated. Differences in mass balances were observed, primarily because after the oxadiazole ring-opening and subsequent ring-cleavage small-molecule metabolites containing the benzene side were excreted in the urine, while those containing the benzamide side were excreted in the bile. DS-8500a was detected at trace levels in urine and bile, demonstrating extensive metabolism prior to urinary/biliary excretion. At least 16 metabolite structures were proposed in plasma, urine, and bile samples from rats treated with [¹⁴C]DS-8500a. Formation of a ring-opened metabolite (reduced DS-8500a) in hepatocytes of humans, monkeys, and rats was confirmed; however, it was not affected by typical inhibitors of cytochrome P450s, aldehyde oxidases, or carboxylesterases in human hepatocytes. Extensive formation of the ring-opened metabolite was observed in human liver microsomes fortified with an NADPH-generating system under anaerobic conditions. These results suggest an in vivo unique reductive metabolism of DS-8500a is mediated by human non-cytochrome P450 enzymes.

Synthesis and SAR of 1,3-thiazolyl thiophene and pyridine derivatives as potent, orally active and S1P₃-sparing S1P₁ agonists

We have previously disclosed 1,2,4-oxadiazole derivative 3 as a potent S1P(3)-sparing S1P(1) agonist. Although compound 3 exhibits potent and manageable immunosuppressive efficacy in various in vivo models, recent studies have revealed that its 1,2,4-oxadiazole ring is subjected to enterobacterial decomposition. As provisions for unpredictable issues, a series of alternative compounds were synthesized on the basis of compound 3. Extensive SAR studies led to the finding of 1,3-thiazole 24c with the EC(50) value of 3.4 nM for human S1P(1), and over 5800-fold selectivity against S1P(3). In rat on host versus graft reaction (HvGR), the ID(50) value of 24c was determined at 0.07 mg/kg. The pharmacokinetics in rat and monkey is also reported. Compared to compound 3, 24c showed excellent stability against enterobacteria.

Metabolism of [(14)C]GSK977779 in rats and its implication with the observed covalent binding

GSK977779 is a potent HM74a agonist evaluated for the treatment of dyslipidemia. The disposition and metabolism of [(14)C]GSK977779 (67.6 μmol/kg p.o.) was studied in male and female rats. The compound was well absorbed and its primary route of elimination was in the feces. Based on metabolite profiling of plasma extracts and urine and bile samples, it was demonstrated that GSK977779 was extensively metabolized in the rat by N-dealkylation, mono- and dioxygenation, reductive and oxidative cleavage of the 1,2,4-oxadiazole ring, and conjugative pathways. After plasma extraction high amounts of nonextractable radioactivity were observed, which were more pronounced in female rats. Size-exclusion chromatography and SDS gel electrophoresis indicated that the majority of the nonextractable radioactivity was covalently bound to plasma proteins. Solubilization of the plasma protein pellet followed by high-performance liquid chromatography and mass spectrometry suggested that a carboxylic acid metabolite derived from oxadiazole ring cleavage may be responsible for the observed covalent binding of the radioactivity to rat plasma proteins.

The use of 96-well Scintiplates to facilitate definitive metabolism studies for drug candidates

Semi-quantitative analysis of the drug-related components in biological samples collected during definitive metabolism studies using radiolabelled drug candidates is commonly achieved by HPLC profiling, using either on-line radiochemical detection or off-line liquid scintillation counting (LSC) following collection of the HPLC eluent into vials. However, although the use of LSC with vials has high sensitivity, the approach is time-consuming, laborious and destructive, whilst on-line detection methods are inappropriate for samples with low-levels of radioactivity (commonly the case with plasma samples). The use of 96-well microtitre plates (Scintiplates) for fraction collection during HPLC profiling provides a sensitive, effective and efficient alternative method for the semi-quantitative analysis of radiolabelled components in biological samples. Furthermore, the approach is non-destructive, such that subsequent identification of the isolated components can be achieved. Although the Scintiplate methodology is not appropriate for the analysis of excreta samples, where quenching of the radiochemical signal by endogenous components was observed, the approach was demonstrated to be valid for the relative quantification of [14C]-labelled material in plasma samples for all species investigated. In addition, good sensitivity was observed, with a counting efficiency of 79% for [14C], such that a drug-related component accounting for 10-15 dpm is quantifiable. The utility of the methodology for profiling circulating metabolites was demonstrated by the analysis of a rat plasma sample following oral administration of [14C]-UK-349,862. The Scintiplate approach and subsequent mass spectrometric analysis resulted in the relative quantitation and specific characterisation of circulating metabolites accounting for 93% of the total plasma radioactivity.

Metabolic, idiosyncratic toxicity of drugs: overview of the hepatic toxicity induced by the anxiolytic, panadiplon

Preclinical drug safety evaluation studies, typically conducted in two or more animal species, reveal and define dose-dependent toxicities and undesirable effects related to pharmacological mechanism of action. Idiosyncratic toxic responses are often not detected during this phase in development due to their relative rarity in incidence and differences in species sensitivity. This paper reviews and discusses the metabolic idiosyncratic toxicity and species differences observed for the experimental non-benzodiazepine anxiolytic, panadiplon. This compound produced evidence of hepatic toxicity in Phase 1 clinical trial volunteers that was not predicted by rat, dog or monkey preclinical studies. However, subsequent studies in Dutch-belted rabbits revealed a hepatic toxic syndrome consistent with a Reye's Syndrome-like idiosyncratic response. Investigations into the mechanism of toxicity using rabbits and cultured hepatocytes from several species, including human, provided a sketch of the complex pathway required to produce hepatic injury. This pathway includes drug metabolism to a carboxylic acid metabolite (cyclopropane carboxylic acid), inhibition of mitochondrial fatty acid beta-oxidation, and effects on intermediary metabolism including depletion of glycogen and disruption of glucose homeostasis. We also provide evidence suggesting that the carboxylic acid metabolite decreases the availability of liver CoA and carnitine secondary to the formation of unusual acyl derivatives. Hepatic toxicity could be ameliorated by administration of carnitine, and to a lesser extent by pantothenate. These hepatocellular pathway defects, though not directly resulting in cell death, rendered hepatocytes sensitive to secondary stress, which subsequently produced apoptosis and hepatocellular necrosis. Not all rabbits showed evidence of hepatic toxicity, suggesting that individual or species differences in any step along this pathway may account for idiosyncratic responses. These differences may be roughly applied to other metabolic idiosyncratic hepatotoxic responses and include variations in drug metabolism, effects on mitochondrial function, nutritional status, and health or underlying disease.

Use and value of metabolism databases

A key objective during drug discovery is to ensure selection of lead compounds for development that have the optimum pharmacodynamic profile without undesirable toxicity. Metabolism plays a key role in determining the biological activity of compounds in vivo, and is therefore an important factor to consider during the discovery phase. The ability to predict the biotransformation pathways for specific chemical structures provides the opportunity to implement structural modifications that might advantageously modify these processes. Potentially valuable tools include knowledge databases that contain searchable information on the known metabolites of existing compounds and databases that are designed to predict the metabolites.

Disruption of mitochondrial activities in rabbit and human hepatocytes by a quinoxalinone anxiolytic and its carboxylic acid metabolite

The quinoxalinone anxiolytic, panadiplon, was dropped from clinical development due to unexpected hepatic toxicity in human volunteers. Subsequent experimental studies in rabbits demonstrated a hepatic toxicity that resembled Reye's syndrome. In the present studies, we examined the effects of panadiplon and a metabolite, cyclopropane carboxylic acid (CPCA) on hepatic mitochondrial activities in vitro and ex vivo. Acute inhibition of beta-oidation of [14C]palmitate was observed in rabbit and human hepatocyte suspensions incubated with 100 microM panadiplon. Panadiplon (30 microM) also reduced mitochondrial uptake of rhodamine 123 (R123) in cultured rabbit and human, but not rat hepatocytes, following 18 h exposure. CPCA also impaired beta-oxidation and R123 uptake in rabbit and human hepatocytes. R123 uptake and beta-oxidation in cells from some donors was not impaired by either agent, and cell death was not observed in any experiment. Hepatocytes isolated from panadiplon-treated rabbits had reduced palmitate beta-oxidation rates and inhibited mitochondrial R123 uptake; R123 uptake remained inhibited until 48-72 h in culture. Rabbit mitochondrial respiration experiments revealed a slightly lower ratio of ATP formed/oxygen consumed in panadiplon-treated animals: direct exposure of normal rabbit liver mitochondria to panadiplon did not have this effect. Hepatocytes isolated from panadiplon-treated rabbits showed reduced respiratory control ratios and lower oxygen consumption compared to controls. Our results indicate that panadiplon induces a mitochondrial dysfunction in the liver, and suggest that this dysfunction may be attributed to the carboxylic acid metabolite.