Entecavir for Treatment of Hepatitis B Virus Displays No In Vitro Mitochondrial Toxicity or DNA Polymerase Gamma Inhibition

Abstract

Therapy with nucleoside reverse transcriptase inhibitors (NRTIs) can be associated with mitochondrial toxicity. In vitro studies have been used to predict the predisposition for and characterize the mechanisms causing mitochondrial toxicity. Entecavir (ETV) is an approved deoxyguanosine nucleoside for the treatment of chronic hepatitis B virus (HBV) infection that exhibits potent activity against viral reverse transcriptase. We assessed the potential for mitochondrial toxicity of ETV in long-term cultures of HepG2 hepatoma cells by measuring mitochondrial function (through lactate secretion), levels of mitochondrial DNA (mtDNA), and levels of mitochondrial proteins COX II and COX IV. Furthermore, we tested the activity of ETV-triphosphate (ETV-TP) against mitochondrial DNA polymerase ␥ (Pol ␥) in vitro. ETV concentrations as high as 100 times the maximal clinical exposure (C max ) did not affect cell proliferation, levels of lactate, mitochondrial DNA, or mitochondrial proteins throughout the 15-day culture. The lack of mitochondrial toxicity was consistent with the finding that ETV-TP was not recognized by mitochondrial DNA Pol ␥ and failed to be incorporated into DNA or inhibit the polymerase assay at the highest levels tested, 300 M. Combinations of ETV with each of the other HBV NRTI antivirals, adefovir, tenofovir, and lamivudine at 10 times their respective C max levels also failed to result in cellular or mitochondrial toxicity. In summary, cell culture and enzymatic studies yielded no evidence that would predict mitochondrial toxicity of ETV at exposure levels in excess of those expected to be achieved clinically.

In VitroMitochondrial Toxicity of Metacavir, a New Nucleoside Reverse Transcriptase Inhibitor for Treatment of Hepatitis B Virus

“…4). Consistent with previous reports (21,24), exposure of cells to ddC at 10 M resulted in significant increases in extracellular lactate levels (P Ͻ 0.001), indicating impaired mitochondrial function.…”

“…The effects of PNA and other nucleoside analogs were assessed in HepG2 cell cultures essentially as described previously (21,28). The compounds or dimethyl sulfoxide (DMSO) vehicle control was added from DMSO stocks at 1,000 times the final exposure concentration.…”

“…A large number of studies have demonstrated that AZT and dideoxycytosine (ddC) can inhibit cell proliferation, induce cytoplasmic lipid droplet accumulation, increase lactate production, and decrease the activities of mitochondrial respiratory-chain enzymes in cell culture assays (1,2,29). Therefore, AZT and ddC were two of the most commonly used reference controls for evaluation of mitochondrial toxicity (2,21,29).…”

In vivo assessment of mitochondrial toxicity of metacavir in Rhesus monkeys after three months of intravenous administration

“…However, woodchucks can carry plague and therefore are difficult to be imported into China. As a result, our study used rhesus monkeys as the sensitive animals, with an attempt to establish rhesus monkey model for mitochondrial toxicity evaluation [21][22][23][24][25] . Mitochondrial toxicities are relatively tissue-specific and drug-specific.…”

Mitochondrial myopathies caused by prolonged use of telbivudine

“…12 However, entecavir may also develop another form of myopathy. Yuan et al 13 reported a patient with entecavir-associated myopathy, in whom the muscle histopathology showed an inflammatory change, but not mitochondrial toxicity.…”