Ribonucleoside analogues have potential utility as anti-viral, -parasitic, -bacterial and -cancer agents. However, their clinical applications have been limited by off target effects. Development of antiviral ribonucleosides for treatment of hepatitis C virus (HCV) infection has been hampered by appearance of toxicity during clinical trials that evaded detection during preclinical studies. It is well established that the human mitochondrial DNA polymerase is an off target for deoxyribonucleoside reverse transcriptase inhibitors. Here we test the hypothesis that triphosphorylated metabolites of therapeutic ribonucleoside analogues are substrates for cellular RNA polymerases. We have used ribonucleoside analogues with activity against HCV as model compounds for therapeutic ribonucleosides. We have included ribonucleoside analogues containing 2′-C-methyl, 4′-methyl and 4′-azido substituents that are non-obligate chain terminators of the HCV RNA polymerase. We show that all of the anti-HCV ribonucleoside analogues are substrates for human mitochondrial RNA polymerase (POLRMT) and eukaryotic core RNA polymerase II (Pol II) in vitro. Unexpectedly, analogues containing 2′-C-methyl, 4′-methyl and 4′-azido substituents were inhibitors of POLRMT and Pol II. Importantly, the proofreading activity of TFIIS was capable of excising these analogues from Pol II transcripts. Evaluation of transcription in cells confirmed sensitivity of POLRMT to antiviral ribonucleosides, while Pol II remained predominantly refractory. We introduce a parameter termed the mitovir (mitochondrial dysfunction caused by antiviral ribonucleoside) score that can be readily obtained during preclinical studies that quantifies the mitochondrial toxicity potential of compounds. We suggest the possibility that patients exhibiting adverse effects during clinical trials may be more susceptible to damage by nucleoside analogs because of defects in mitochondrial or nuclear transcription. The paradigm reported here should facilitate development of ribonucleosides with a lower potential for toxicity.
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Date of publication: 15 November 2012; PLOS Pathegens
Author information: Jamie J. Arnold (1); Suresh D. Sharma (1); Joy Y. Feng (2); Adrian S. Ray (2); Eric D. Smidansky (1); Maria L. Kireeva (3); Aesop Cho (2); Jason Perry (2); Jennifer E. Vela (2); Yeojin Park (2); Yili Xu (2); Yang Tian (2); Darius Babusis (2); Ona Barauskus (2); Blake R. Peterson (4); Averell Gnatt (5); Mikhail Kashlev (3); Weidong Zhong (2); & Craig E. Cameron (1)
(1) Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, United States of America
(2) Gilead Sciences, Inc., Foster City, California, United States of America
(3) Frederick National Laboratory for Cancer Research, NCI, Frederick, Maryland, United States of America
(4) Department of Medicinal Chemistry, The University of Kansas, Lawrence, Kansas, United States of America
(5) Department of Pharmacology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America