472   In VitroSelection and Characterisation of HIV-1 Resistance to BCH-10618.

Z. Gu*¹, N. Nguyen-Ba¹, J. Mellors², C. Fortier¹, and M. Wainberg³.
¹BioChem Pharma, Laval, Quebec, Canada;²Univ. of Pittsburgh, PA; and³Jewish Gen. Hosp., Montreal, Quebec, Canada.

Background:BCH-10618 is a heterosubstituted nucleoside analogue ((-)-2´-deoxy-3´-oxa-4´-thiocytidine). It is a potent and selective inhibitor of HIV-1 in vitro. Since resistance to antiretroviral agents is one of the major issues in the treatment of HIV-1 infection, we investigated the potential resistance of HIV-1 to BCH-10618 in cell culture.

Methods:HIV-1_1IIIBand HIV-1_LAIwere passaged in the presence of gradually increased concentration of BCH- 10618 in MT-4 or MT-2 cells. Selected HIV-1 variants were phenotyped using BCH-10618 and other anti-HIV agents. Reverse transcriptase (RT) genotypes were determined by directly sequencing PCR products.

Results:Resistance to BCH-10618 was selected after 12 passages in MT-4 cell lines and after 20 passages in the MT-2 selection system. Genotyping reverse transcriptase of the selected strains showed that HIV-1_1IIIBhad a valine to isoleucine substitution at residue 75 of the RT (V75I); however, HIV-1_LAIshowed a lysine to arginine mutation at residue 65 of the RT (K65R). Selected viruses had a 2- to 4-fold resistance to BCH-10618. These strains remained mostly sensitive or exhibited a low level of resistance to other antiretrovirals. In addition, it was observed that development of resistance to BCH-10618 was longer than to 3TC in our selections.

Conclusion:These results indicate that BCH-10618 selected mutant HIV-1 viruses that had a low level of resistance to BCH-10618 and the currently approved antiretrovirals.