gs-9148 and HIV-Infections

The use of the acyclic nucleoside phosphonates, starting with (S)-HPMPA as the prototype, yielded three clinically approved antiviral drugs, cidofovir for the treatment of CMV retinitis in AIDS patients, adefovir dipivoxil for the treatment of chronic hepatitis B and tenofovir disoproxil fumarate for the treatment of HIV infections (AIDS) and HBV infections. This era has now grown to many more acyclic (and cyclic) nucleoside phosphonates (such as the "open ring" DAPy and Fd4A phosphonates) and alkoxyalkyl and phosphonoamidate prodrugs thereof, as well as new clinical applications, including new drug combination regimens for the treatment of AIDS, the chemoprophylaxis of HIV infections, and the anticancer potential against some malignant disorders.

Topics: Adenine; Antineoplastic Agents; Antiviral Agents; Cidofovir; Cytosine; Guanosine; Hepatitis B; HIV Infections; Humans; Organophosphonates; Prodrugs; Structure-Activity Relationship; Tenofovir

GS-9131 is a phosphonoamidate prodrug of the novel ribose-modified phosphonate nucleotide analog GS-9148 that demonstrates potent anti-human immunodeficiency virus type 1 (HIV-1) activity and an excellent resistance profile in vitro. Prodrug moieties were optimized for the efficient delivery of GS-9148 and its active diphosphate (DP) metabolite to lymphoid cells following oral administration. To understand the intracellular pharmacology of GS-9131, incubations were performed with various types of lymphoid cells in vitro. The intracellular accumulation and antiviral activity levels of GS-9148 were limited by its lack of cellular permeation, and GS-9131 increased the delivery of GS-9148-DP by 76- to 290-fold relative to that of GS-9148. GS-9131 activation was saturable at high extracellular concentrations, potentially due to a high-affinity promoiety cleavage step. Once inside the cells, GS-9148 was efficiently phosphorylated, forming similar amounts of anabolites in primary lymphoid cells. The levels of GS-9148-DP formed in peripheral blood mononuclear cells infected with HIV-1 were similar to that in uninfected PBMCs, and approximately equivalent intracellular concentrations of GS-9148-DP and tenofovir (TVF)-DP were required to inhibit viral replication by 90%. Once it was formed, GS-9148-DP was efficiently retained in activated CD4(+) cells, with a half-life of 19 h. In addition, GS-9131 showed a low potential for drug interactions with other adenine nucleoside/nucleotide reverse transcriptase inhibitors, based on the lack of competition for anabolism between suprapharmacologic concentrations of GS-9148 and TVF and the lack of activity of GS-9131 metabolites against purine nucleoside phosphorylase, an enzyme involved in the clearance of 2',3'-dideoxyinosine. Together, these observations elucidate the cellular pharmacology of GS-9131 and illustrate its efficient loading of lymphoid cells, resulting in a prolonged intracellular exposure to the active metabolite GS-9148-DP.

Topics: Adenine; Anti-HIV Agents; Diphosphates; Guanosine; HIV Infections; HIV-1; Humans; Leukocytes, Mononuclear; Lymphocyte Activation; Organophosphonates; Prodrugs; Reverse Transcriptase Inhibitors; Tenofovir