Effects of BMS-986094, a Guanosine Nucleotide Analogue, on Mitochondrial DNA Synthesis and Function

Use of Human iPSC-CMs in Nonclinical Regulatory Studies for Cardiac Safety Assessment

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) provide a human-relevant platform for cardiac function assessment. Alternative assays using hiPSC-CMs are increasingly being employed for regulatory decision-making. A retrospective review revealed steady use of hiPSC-CM-based in vitro assays in nonclinical studies of drug-induced cardiotoxicity in regulatory submissions to the U.S. Food and Drug Administration (FDA). Most of the hiPSC-CMs data were obtained in exploratory studies and submitted as supportive evidence in concordance with other nonclinical data. Some of those studies were used to inform clinical trial design. This article provides an overview of the use of hiPSC-CMs in regulatory applications to FDA, with a focus on the integration of human-relevant in vitro data into proarrhythmic and non-proarrhythmic risk assessment. By identifying the regulatory submissions including hiPSC-CMs data, we explore their utility and discuss their limitations for predicting human cardiac safety in clinical trials. An important take-home message is that regulatory acceptance of hiPSC-CMs data is dependent on both the context of use and accurate data interpretation.

Chronic cardiotoxicity assessment of BMS-986094, a guanosine nucleotide analogue, using human iPS cell-derived cardiomyocytes

Predicting drug-induced side effects in the cardiovascular system is very important because it can lead to the discontinuation of new drugs/candidates or the withdrawal of marketed drugs. Although chronic assessment of cardiac contractility is an important issue in safety pharmacology, an in vitro evaluation system has not been fully developed. We previously developed an imaging-based contractility assay system to detect acute cardiotoxicity using human iPS cell-derived cardiomyocytes (hiPSC-CMs). To extend the system to chronic toxicity assessment, we examined the effects of the anti-hepatitis C virus (HCV) drug candidate BMS-986094, a guanosine nucleotide analogue, which was withdrawn from phase 2 clinical trials because of unexpected contractility toxicities. Additionally, we examined sofosbuvir, another nucleotide analogue inhibitor of HCV that has been approved as an anti-HCV drug. Motion imaging analysis revealed the difference in cardiotoxicity between the cardiotoxic BMS-986094 and the less toxic sofosbuvir in hiPSC-CMs, with a minimum of 4 days of treatment. In addition, we found that BMS-986094-induced contractility impairment was mediated by a decrease in calcium transient. These data suggest that chronic treatment improves the predictive power for the cardiotoxicity of anti-HCV drugs. Thus, hiPSC-CMs can be a useful tool to assess drug-induced chronic cardiotoxicity in non-clinical settings.

Asymmetric Synthesis of 2'-C-Methyl-4'-selenonucleosides as Anti-Hepatitis C Virus Agents

In search of a new template for anti-hepatitis C virus (HCV) agents, we designed and synthesized the 2'-C-methyl-4'-selenopyrimidine and -purine nucleosides and their phosphoramidate prodrugs to replace a furanose oxygen of anti-HCV nucleos(t)ides with a selenium atom on the basis that selenium is a chemical isostere of oxygen. These nucleosides are expected to show different physicochemical properties such as better lipophilicity which might enhance the penetration across cell membranes and the conformational constraint induced by a bulky selenium atom in the sugar ring. The 2'-C-methyl-4'-selenopyrimidine and -purine nucleosides 8 and 9 were synthesized from 2-C-methyl-d-ribono-γ-lactone (14) via construction of 2-C-methyl-d-selenosugar 18 through C-4 epimerization and S_N2 cyclization with Se^2- as key steps. The key 4'-selenosugar was converted to the 2'-C-methyl-4'-selenopyrimidine and -purine nucleosides using Pummerer-type rearrangement and Vorbrüggen glycosylation, respectively. In addition, the ProTide strategy has been applied to synthesize the adenine and uracil phosphoramidate derivatives 10a and 10b to overcome the limitations associated with parent nucleosides such as inefficient conversion to their corresponding 5'-monophosphate form and poor cellular uptake. The regio- and stereochemistry of 4'-selenonucleosides were confirmed by 2D NOESY NMR spectroscopy and X-ray crystallography. None of the final pyrimidine and purine nucleosides and their prodrugs exhibited significant anti-HCV activity up to 100 μM.

Intracellular metabolism and potential cardiotoxicity of a β-D-2'-C-methyl-2,6-diaminopurine ribonucleoside phosphoramidate that inhibits hepatitis C virus replication

β-D-2'-C-Methyl-2,6-diaminopurine ribonucleoside (2'-C-Me-DAPN) phosphoramidate prodrug (DAPN-PD) is a selective hepatitis C virus inhibitor that is metabolized intracellularly into two active metabolites: 2'-C-Methyl-DAPN triphosphate (2'-C-Me-DAPN-TP) and 2'-C-methyl-guanosine 5'-triphosphate (2'-C-Me-GTP). BMS-986094 and IDX-184 are also bioconverted to 2'-C-Me-GTP. A phase IIb clinical trial with BMS-986094 was abruptly halted due to adverse cardiac and renal effects. Herein, we developed an efficient large scale synthesis of DAPN-PD and determined intracellular pharmacology of DAPN-PD in comparison with BMS-986094 and IDX-184, versus Huh-7, HepG2 and interspecies primary hepatocytes and human cardiomyocytes. Imaging data of drug treated human cardiomyocytes was found to be most useful in determining toxicity potential as no obvious beating rate change was observed for IDX-184 up to 50 µM up at 48 h. However, with BMS-986094 and DAPN-PD at 10 µM changes to both beat rate and rhythm were noted.

Discovery of a Series of 2'-α-Fluoro,2'-β-bromo-ribonucleosides and Their Phosphoramidate Prodrugs as Potent Pan-Genotypic Inhibitors of Hepatitis C Virus

Hepatitis C virus (HCV) nucleoside inhibitors display pan-genotypic activity, a high barrier to the selection of resistant virus, and are some of the most potent direct-acting agents with durable sustained virologic response in humans. Herein, we report, the discovery of β-d-2'-Br,2'-F-uridine phosphoramidate diastereomers 27 and 28, as nontoxic pan-genotypic anti-HCV agents. Extensive profiling of these two phosphorous diastereomers was performed to select one for in-depth preclinical profiling. The 5'-triphosphate formed from these phosphoramidates selectively inhibited HCV NS5B polymerase with no inhibition of human polymerases and cellular mitochondrial RNA polymerase up to 100 μM. Both are nontoxic by a variety of measures and display good stability in human blood and favorable metabolism in human intestinal microsomes and liver microsomes. Ultimately, a preliminary oral pharmacokinetics study in male beagles showed that 28 is superior to 27 and is an attractive candidate for further studies to establish its potential value as a new clinical anti-HCV agent.

The evolution of antiviral nucleoside analogues: A review for chemists and non-chemists. Part II: Complex modifications to the nucleoside scaffold

This is the second of two invited articles reviewing the development of nucleoside analogue antiviral drugs, written for a target audience of virologists and other non-chemists, as well as chemists who may not be familiar with the field. As with the first paper, rather than providing a chronological account, we have chosen to examine particular examples of structural modifications made to nucleoside analogues that have proven fruitful as various antiviral, anticancer, and other therapeutics. The first review covered the more common, and in most cases, single modifications to the sugar and base moieties of the nucleoside scaffold. This paper focuses on more recent developments, especially nucleoside analogues that contain more than one modification to the nucleoside scaffold. We hope that these two articles will provide an informative historical perspective of some of the successfully designed analogues, as well as many candidate compounds that encountered obstacles.

Addressing the selectivity and toxicity of antiviral nucleosides

Nucleoside and nucleotide analogs have played significant roles in antiviral therapies and are valued for their impressive potency and high barrier to resistance. They have been approved for treatment of herpes simplex virus-1, HIV, HBV, HCV, and influenza, and new drugs are being developed for the treatment of RSV, Ebola, coronavirus MERS, and other emerging viruses. However, this class of compounds has also experienced a high attrition rate in clinical trials due to toxicity. In this review, we discuss the utility of different biochemical and cell-based assays and provide recommendations for assessing toxicity liability before entering animal toxicity studies.

2'-Chloro,2'-fluoro Ribonucleotide Prodrugs with Potent Pan-genotypic Activity against Hepatitis C Virus Replication in Culture

Pan-genotypic nucleoside HCV inhibitors display a high genetic barrier to drug resistance and are the preferred direct-acting agents to achieve complete sustained virologic response in humans. Herein, we report, the discovery of a β-d-2'-Cl,2'-F-uridine phosphoramidate nucleotide 16, as a nontoxic pan-genotypic anti-HCV agent. Phosphoramidate 16 in its 5'-triphosphate form specifically inhibited HCV NS5B polymerase with no marked inhibition of human polymerases and cellular mitochondrial RNA polymerase. Studies on the intracellular half-life of phosphoramidate 16-TP in live cells demonstrated favorable half-life of 11.6 h, suggesting once-a-day dosing. Stability in human blood and favorable metabolism in human intestinal microsomes and liver microsomes make phosphoramidate 16 a prospective candidate for further studies to establish its potential value as a new anti-HCV agent.

Structure-activity relationship analysis of mitochondrial toxicity caused by antiviral ribonucleoside analogs

Recent cases of severe toxicity during clinical trials have been associated with antiviral ribonucleoside analogs (e.g. INX-08189 and balapiravir). Some have hypothesized that the active metabolites of toxic ribonucleoside analogs, the triphosphate forms, inadvertently target human mitochondrial RNA polymerase (POLRMT), thus inhibiting mitochondrial RNA transcription and protein synthesis. Others have proposed that the prodrug moiety released from the ribonucleoside analogs might instead cause toxicity. Here, we report the mitochondrial effects of several clinically relevant and structurally diverse ribonucleoside analogs including NITD-008, T-705 (favipiravir), R1479 (parent nucleoside of balapiravir), PSI-7851 (sofosbuvir), and INX-08189 (BMS-986094). We found that efficient substrates and chain terminators of POLRMT, such as the nucleoside triphosphate forms of R1479, NITD-008, and INX-08189, are likely to cause mitochondrial toxicity in cells, while weaker chain terminators and inhibitors of POLRMT such as T-705 ribonucleoside triphosphate do not elicit strong in vitro mitochondrial effects. Within a fixed 3'-deoxy or 2'-C-methyl ribose scaffold, changing the base moiety of nucleotides did not strongly affect their inhibition constant (K_i) against POLRMT. By swapping the nucleoside and prodrug moieties of PSI-7851 and INX-08189, we demonstrated that the cell-based toxicity of INX-08189 is mainly caused by the nucleoside component of the molecule. Taken together, these results show that diverse 2' or 4' mono-substituted ribonucleoside scaffolds cause mitochondrial toxicity. Given the unpredictable structure-activity relationship of this ribonucleoside liability, we propose a rapid and systematic in vitro screen combining cell-based and biochemical assays to identify the early potential for mitochondrial toxicity.

Cardiac drug-drug interaction between HCV-NS5B pronucleotide inhibitors and amiodarone is determined by their specific diastereochemistry

Severe bradycardia/bradyarrhythmia following coadministration of the HCV-NS5B prodrug sofosbuvir with amiodarone was recently reported. Our previous preclinical in vivo experiments demonstrated that only certain HCV-NS5B prodrugs elicit bradycardia when combined with amiodarone. In this study, we evaluate the impact of HCV-NS5B prodrug phosphoramidate diastereochemistry (D-/L-alanine, R-/S-phosphoryl) in vitro and in vivo. Co-applied with amiodarone, L-ala,S_P prodrugs increased beating rate and decreased beat amplitude in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), but D-ala,R_P produgs, including MK-3682, did not. Stereochemical selectivity on emerging bradycardia was confirmed in vivo. Diastereomer pairs entered cells equally well, and there was no difference in intracellular accumulation of L-ala,S_P metabolites ± amiodarone, but no D-ala,R_P metabolites were detected. Cathepsin A (CatA) inhibitors attenuated L-ala,S_P prodrug metabolite formation, yet exacerbated L-ala,S_P + amiodarone effects, implicating the prodrugs in these effects. Experiments indicate that pharmacological effects and metabolic conversion to UTP analog are L-ala,S_P prodrug-dependent in cardiomyocytes.