title: Drug combinations and effect parameters of zidovudine, stavudine, and nevirapine in standardized drug-sensitive and resistant HIV type 1 strains.
abstract: Reference strains of HIV-1 from the NIH AIDS Research and Reference Reagent Program, including wild-type IIIB, G762-3, and AZT resistant with RT 215T-->Y (G910-11/AZT); 67D-->N, 70K-->R, 215T-->F, 219K-->Q (G691-2/AZT); as well as nevirapine (NEV) resistant with 181Y-->C (N119/NEV); and 103K-->N, 181Y-->C (A17/NEV), were subjected to quantitative parametric efficacy analysis using AZT, stavudine (D4T), and nevirapine (NEV) singly or in combinations in MT4 or MT2 cells. The median-effect principle and combination index (CI) method of Chou-Talalay (see Ref. 26) have been used, which take into account both the potency (Dm value or EC50) and the shape of the dose-effect curve (m value). Under standardized assay conditions, G910-11 and G691-2 strains showed 600- and 7800-fold resistance to AZT, and N119 and A17 strains showed 3600- and 1000-fold resistance to NEV at the EC50 level, respectively. AZT-resistant strains exhibited slight cross-resistance to D4T. Computerized analysis indicates that IIIB gave sigmoidal dose-effect curves (m = 2.8, 3.4, and 3.1 for AZT, D4T, and NEV, respectively) whereas drug-resistant strains showed negative sigmoidicity toward the corresponding AZT or NEV, with m = 0.27-0.73. Therefore, the degrees of drug resistance are drastically different at classic EC50 and at therapeutically more relevant EC95 levels (ranging from severalfold to several log orders). Combinations of AZT+NEV and AZT+NEV+D4T showed synergism against IIIB, G762-3 (wild type) and A17/NEV, G910-11/AZT strains. D4T+NEV and AZT+D4T showed nearly additive or moderate antagonism. Synergism or additive effect leads to a favorable dose-reduction index (DRI). The present study on RT inhibitors provides quantitative assessment of the combinations of AZT, NEV, and D4T against HIV infections involving drug-sensitive and drug-resistant HIVs.
authors.affiliation: Molecular Pharmacology and Therapeutics Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
authors.forename: Q Y
authors.initials: QY
authors.lastname: Zhu
authors.forename: A
authors.initials: A
authors.lastname: Scarborough
authors.forename: B
authors.initials: B
authors.lastname: Polsky
authors.forename: T C
authors.initials: TC
authors.lastname: Chou
mesh_terms: D000998:Antiviral Agents / Q000494:pharmacology*; D002461:Cell Line, Transformed; D003602:Cytotoxicity, Immunologic; D004352:Drug Resistance, Microbial; D004359:Drug Therapy, Combination; D015658:HIV Infections / Q000188:drug therapy*; D015497:HIV-1 / Q000187:drug effects* / Q000254:growth & development; D008826:Microbial Sensitivity Tests; D019829:Nevirapine; D011725:Pyridines / Q000494:pharmacology*; D018119:Stavudine / Q000494:pharmacology*; D013601:T-Lymphocytes / Q000821:virology; D015215:Zidovudine / Q000494:pharmacology*
chemical_list: D000998:Antiviral Agents; D011725:Pyridines; D015215:Zidovudine; D019829:Nevirapine; D018119:Stavudine