In vitro activity: Zidovudine pretreatment has potent anti-HIV-1 activity in the newly infected T and monocytic cells but not in chronically infected cells. Inhibition of reverse transcription by Zidovudine decreases p24 antigen levels modestly, decreased HIV-1 gag by 19-fold, and inhibits detection of 2-LTR HIV-1 DNA. Zidovudine and dideoxynucleosides deplete wild-type mitochondrial DNA levels and increase deletedmitochondrial DNA levels in cultured Kearns-Sayre syndrome fibroblasts. Zidovudine (AZT, 0.1-50 mM) has a concentration dependent suppressive effect on the growth of granulocyte-monocyte colony forming unit (CFU-GM) derived colonies. Zidovudine exposure also induces a concentration dependent suppressive effect (35-90%) on GM-CSF receptor type alpha (GM-CSFR alpha) gene expression. Zidovudine causes a much lower decrease (15-22%) on the IL-3 receptor type alpha (IL-3R alpha) message level, and has an insignificant effect on glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and c-myc message levels. Zidovudine causes a concentration-dependent inhibition in the levels of the mRNA of Epo receptors and c-fos, whereas the level of c-myc mRNA is unaffected. Zidovudine also inhibits protein kinase C (PKC) activity in a concentration- and time-dependent manner, causing 50% inhibition at 10 mM within 3 hours. Zidovudine-induced down-regulation of Epo receptors and c-fos expression coupled with inhibition of Epo receptor-mediated signal transduction through PKC are significant contributory factors to AZT-induced erythroid toxicity.

Cell Assay: Assays are performed in all cell types in the presence of titrating concentrations of ARV. 5,000 SVG, 2,500 PFA, 200,000 PBMC, or 50,000 MDM cells/well are seeded into triplicate wells of 96-well plates. Twenty-four hours later, the culture medium is removed and replaced with medium containing the ARV or DMSO (0.5% vol/vol), and equivalent TCID50 infectious units of luciferase reporter virus are added to the cells. After a 16 h incubation at 37°C, the initial viral inoculum is removed and replaced with culture medium containing the same antiretroviral drug (ARV) or DMSO (0.5% vol/vol) concentrations. At 72 h post infection, the medium is aspirated, the cells are lysed and HIV-1 infection measured using the Luciferase Assay System. Luminescence is measured using a FLUOStar Optima microplate reader. Inhibition curves and the 50% (EC50) and 90% (EC90) effective concentrations are determined by nonlinear regression analysis, using GraphPad Prism software.