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 [(s ⁴dU)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 (s ⁴dU)₃₅ preferentially binds to CD4 receptors, but not to CD48. Confocal laser scanning microscopy (CLSM) studies showed that (s ⁴dU)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.