Alkylglycerol prodrugs of phosphonoformate are potent in vitro inhibitors of nucleoside-resistant human immunodeficiency virus type 1 and select for resistance mutations that suppress zidovudine resistance

Phosphonoformate (foscarnet; PFA) is a potent inhibitor of human immunodefi ciency virus type 1 (HIV-1) reverse transcriptase (RT), but its use for the treatment of HIV-1 infection is limited by toxicity and the lack of an ora lly bioavailable formulation. Alkylglycerol-conjugated prodrugs of PFA (1-O -octadecyl-sn-glycero-3-PFA [B-PFA]) having sn-2 substituents of hydrogen ( deoxybatyl-PFA [DB-PFA]), methyl (MB-PFA), or ethyl (EB-PFA) are more-poten t inhibitors of wild-type HIV-1 in vitro than unmodified PFA and are orally bioavailable in mice. We have evaluated the activities of these compounds against a panel of nucleoside-resistant HIV-1 variants and have characteriz ed the resistant variants that emerge following in vitro selection with the prodrugs, Except for an HIV-1 variant encoding the K65R mutation in RT tha t exhibited 3.3- to 8.2-fold resistance, the nucleoside resistant viruses i ncluded in the panel were sensitive to the PFA prodrugs (<3-fold increase i n 50% inhibitory concentration), including multinucleoside-resistant varian ts encoding the Q151M complex of mutations or the T69S [SA] insert. Viruses resistant to the PFA prodrugs (> 10-fold) were selected in vitro after 15 or more serial passages of HIV-1 in MT-2 cells in escalating prodrug concen trations. Mutations detected in the resistant viruses were S117T, F160Y, an d L214F (DB-PFA); M164I and L214F (MB-PFA); and W88G and L214F (EB-PFA), Th e S117T, F160Y, and M164I mutations have not been previously identified. Ge neration of recombinant viruses encoding the single and double mutations co nfirmed their roles in prodrug resistance, including 214F, which generally increased the level of resistance. When introduced into a zidovudine (AZT)- resistant background (67N 70R 215F 219Q), the W88G, S117T, F160Y, and M164I mutations reversed AZT resistance. This suppression of AZT resistance is c onsistent with the effects of other foscarnet resistance mutations that red uce ATP-dependent removal of AZT monophosphate from terminated template pri mers. The favorable activity and resistance profiles of these PFA prodrugs warrant their further evaluation as clinical candidates.