Studies On Suramin As A Multi-functional Microbicide To Prevent HIV-1 Sexual Transmission

BACKGROUND:Acquired immunodeficiency syndrome(AIDS)is an infection disease with the deficiency of immunity caused by human immunodeficiency virus type 1(HIV-1)making serious threat to human life and health.New infection still stays at a high level worldwide and 80%of new infections acquired via sexual transmission,sexual contact remains the major mode of HIV-1 transmission.Microbicides are an effective strategy to prevent the HIV-1 transmission,but no effective microbicides have been developed so far.Semen-derived Enhancers of Viral Infection(SEVI)is one of the key reason for the failure of microbicide in clinical trials,which can significantly promote HIV-1 infection and counteract the antiviral activity of microbicides.SEVI is the best characterized amyloid fibril in semen formed by a proteolytic cleavage product of prostatic acid phosphatase,comprising amino acids 248 to 286 of the enzyme.Due to its strong positive charge,SEVI can decrease the electrostatic replusion between the negatively charged surface of virus and host cell,thus enhance HIV-1 infection.Therefore,SEVI is a key factor for microbicide to prevent HIV-1 sexual transmission.Our previous study have shown that HIV-1 entry inhibitor ADS-J1 can antagonize SEVI and display synergistic and additive effects with ARVs against HIV-1 infection in semen.However,the potential carcinogenicity of ADS-J1 hampers its clinical application.In the early stage of the screening experiment,we found a ADS-J1 analogue Suramin can inhibit the formation of SEVI fibril.Suramin is a old drug in the clinical treatment of trypanosomiasis and has strong pharmacological activities,including inhibition of protease and growth factor.In the study,we perform in-deepth the antagonistic effect of Suramin on SEVI fibril,explore its new role and evaluate its antiviral effect combined with antiretroviral drugs(ARVs).We expect to develop Suramin into a adjuvant drug in microbicide to prevent the HIV-1 sexual transmission.OBJECTIVE:We expect to elucidate the new mechanism of Suramin to prevent HIV-1 sexual transmission from different perspectives and hope to broaden the clinical usage of Suramin.Multi-effects of a candidate microbicide might provide a new viewpoint to screen future microbicide to prevent HIV-1 sexual transmission.METHODS:1.The effect of Suramin on SEVI formation or SEVI fibril was detected by Congo Red staining,transmission electron microscopy,confocal microscopy,circular dichroism spectrum,Western blot and HIV-1 infection assay.2.Antiviral effect of Suramin combined with ARVs was detected by infection assay.3.The cytotoxicity of Suramin on reproductive tract cells and lymphocytes were determined using XTT methods.Vaginal irritation test was used to evaluate safety associated with Suramin gel application,including histopathological examination,ELISA and PCNA immunostaining.4.Suramin were analysed by MD simulation with PAP248-286 to explore the inhibiting mechanism of Suramin on SEVI formation.RESULTS:1.Suramin inhibited SEVI formation by the peptide PAP248-286 in a dose dependent manner,and bind to amyloid fibrils antagonizing SEVI-mediated enhancement of HIV-1 infection.2.Combinations of Suramin with ARV-based candidate microbicides display synergistic and additive effects against HIV-1 infection in semen.The 50%combination index(CI)values of Suramin combined with these ARVs ranged from 0.233 to 0.739.3.Suramin showed little cytotoxicity in vitro to reproductive tract cells and lymphocytes detected by XTT.The CC50 of Suramin on the tested cells were more than 1000 μM,Histopathological examination showed that vaginal mucosa epithelial cells of Suramin gel group are relatively complete and lamina propria is only edema.Suramin gel did not induce an obvious inflammatory reaction.No sinificant differences in PCNA positivity were noted in the vaginal epithelial cells and stromal cells after Suramin gel administrated vaginally compared to saline control group.4.MD simulations showed that the binding models of Suramin,NF157 and NF449 were different.The molecular structure of Suramin tend to be three-dimensional and completely enveloped PAP248-286.Suramin had hydrogen bonds or hydrophobic interactions with almost all the amino acids on PAP248-286:19 hydrogen bonds and 45 hydrophobic interactions.CONCLUSIONS:1.Suramin tightly binds to PAP248-286,inhibiting its normal self-aggregation process.2.Suramin binds to amyloid fibrils and antagonizes SEVI-mediated enhancement of HIV-1 infection.3.Suramin combining with ARVs displays synergistic and additive effects against HIV-1 infection in semen and shows little cytotoxicity to reproductive tract cells and lymphocytes in vitro.Meanwhile,Suramin gel has no vaginal mucosa irritation on rabbit.