Potent inhibition of HIV-1 entry by (s4dU)35

We have previously reported the potent in vitro HIV-1 anti-reverse transcriptase activity of a 35-mer of 4-thio-deoxyuridylate [(s4dU)35]. In efforts to define its activity in a more physiological system, studies were carried out to determine the stage of viral infection that this compound mediates its anti-viral effect. Results of the studies reported herein show that (s4dU)35 is nontoxic and is capable of inhibiting both single and multi-drug resistant HIV strains (IC50: 0.8-25.4 μg/ml) in vitro. Besides its previously reported anti-RT activity, (s4dU)35 mediated its antiviral action by preventing virus attachment (IC50: 0.002-0.003 μg/ml), and was stable in vitro and slowly degraded by DNAses. Competition studies and fluorescence resonance energy transfer (FRET) experiments indicated that (s4dU)35 preferentially binds to CD4 receptors, but not to CD48. Confocal laser scanning microscopy (CLSM) studies showed that (s4dU)35 did not penetrate into the cells and colocalized with cell surface thioredoxin. Our studies identify (s4dU)35 as a potential novel HIV entry inhibitor that may have utility as either a systemic antiretroviral or as a preventing agent for HIV transmission.