ATRA and TO-901317 inhibit HIV-1 entry and replication. A) 1G5 cells were incubated for 3 days in the presence of ATRA or TO-901317. Untreated cells (open bar) or cells treated with reconstituted water-soluble cholesterol (close bar), were then infected with HIV-1 for one hour, lysed and the amount of viral DNA was quantified by realtime PCR using R/U5 primer as described in Methods. The relative fold change of viral DNA compared to that from DMSO treatment was plotted. The results represent four independent experiments. Data are presented as mean ± the standard deviation. *p < 0.05; ** p < 0.01. B) 1G5 cells were pretreated with ATRA or TO-901317 for one day, and then infected with HIV-1 and were cultured in presence of ATRA and TO-901317. Luciferase activity was determined on 2 and 4 days after infection. The infectivity of HIV-1 was calculated by the relative fold change of luciferase on day 4 compared to that of basal level on day 2. The relative fold change compared to that of DMSO treatment was plotted. The experiment was performed in triplicates and the result is representative of two independent experiments. Data are presented as mean ± the standard deviation. ** p < 0.01 versus cells treated with DMSO.