INHIBITION OF THE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-I INTEGRASE BY GUANOSINE QUARTET STRUCTURES

An oligonucleotide (T30177) composed entirely of deoxyguanosine and th ymidine has previously been shown to fold upon itself in the presence of potassium into a highly stable four-stranded DNA structure containi ng two stacked deoxyguanosine quarters (G4s). T30177 also protects hos t cells from the cytopathic effects of human immunodeficiency virus ty pe 1 (HIV-1). We report that this G4 oligonucleotide is the most poten t inhibitor of HIV-1 integrase identified to date, with IC50 values in the nanomolar range. Both the number of quarters formed and the seque nce of the loops between the quartets are important for optimal activi ty. T30177 binds to HIV-1 integrase without being processed and blocks the binding of the normal viral DNA substrate to the enzyme. The norm al DNA substrate was not able to compete off T30177 binding to HIV-1 i ntegrase, indicating a tight binding of G4s to the enzyme. Experiments with truncated HIV-1 integrases indicate that the N-terminal region c ontaining a putative zinc finger is required for inhibition by T30177 and that T30177 binds better to full-length or deletion mutant integra ses containing the zinc finger region than to a deletion mutant consis ting of only the central catalytic domain. The N-terminal region of in tegrase alone is able to bind efficiently to T30177, but not the linea r viral DNA substrate, in the presence of zinc. Hence, G4s represent t he first class of compounds that inhibit HIV-1 integrase by interactin g with the enzyme N-terminal domain, The greater inhibitory potency of T30177 in buffer containing magnesium versus manganese suggests that divalent metal ion coordination along the phosphodiester backbone may play a role in the inhibitory activity. T30177 inhibited HIV-2 integra se with similar potency as HIV-1 but inhibited feline and simian immun odeficiency virus integrases at higher concentrations, suggesting sele ctivity can be achieved. We propose that novel AIDS therapies could be based upon guanosine quartets as inhibitors of HIV-I integrase.