EFFECT OF FIALURIDINE ON REPLICATION OF MITOCHONDRIAL-DNA IN CEM CELLS AND IN HUMAN HEPATOBLASTOMA CELLS IN CULTURE

Fialuridine (FIAU) is a nucleoside analog with potent activity against hepatitis E virus in vitro and in vivo. In this report, the effect of FIAU on mitochondrial DNA (mtDNA) replication in vitro was investigat ed. CEM cells, a cell line derived from human T cells, were incubated for 6 days in up to 20 mu M FIAU. Total cellular DNA was isolated, nor malized for the number of cells, and slot hybridized to a probe specif ic for mtDNA sequences. Treatment of CEM cells with FIAU did not resul t in a dose-dependent decrease in the amount of mtDNA. In contrast, di deoxycytidine (ddC) inhibited mtDNA replication by 50% at a concentrat ion of approximately 0.1 mu M. After 6 days of incubation, both compou nds displayed a 50% toxic dose at a concentration of approximately 2 m u M in CEM cells and approximately 34 mu M in human hepatoblastoma cel ls (HepG2). In further experiments, CEM cells were incubated for 15 da ys in up to 2.5 mu M FIAU, and again, no inhibition of mtDNA was obser ved. Over a 6-day incubation, FIAU, at concentrations of up to 200 mu M, also failed to inhibit mtDNA replication in either HepG2 or HepG2 c ells which constitutively replicate duck hepatitis B virus. In contras t, ddC inhibited mtDNA replication in these cells with a 50% inhibitor y concentration of approximately 0.2 mu M over a 6-day incubation. Tre atment of cells with either FIAU or ddC resulted in a dose-dependent i ncrease in lactate levels in the cell medium, indicating that any effe ct of FIAU on mitochondrial function may not be related to inhibition of mtDNA replication on the basis of the in vitro data. Alternative ex planations for mitochondrial toxicity are considered.