DABOs as candidates to prevent mucosal HIV transmission.

Worldwide, the heterosexual route is the prevalent mode of transmission of AIDS; therefore, demands have been raised for measures that block sexual spreading of the HIV infection. Development of microbicides for topical use may represent an efficacious alternative to condoms. Several approaches are being investigated. Besides surfactants, which directly act on the virus particle, and measures that enhance natural defence mechanisms, promising new candidates appear to be drugs that block the early steps of HIV multiplication. We describe herein a long-term assay which enables the establishment of whether the above drugs reversibly (virustatic action) or irreversibly (virucidal action) inhibit HIV-1 multiplication, thus allowing screening for effective and potent microbicides. We validated our assay with nucleoside (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs). Following a chronic treatment, the NRTIs tested (didanosine, zalcitabine, stavudine and lamivudine) simply delayed the viral breakthrough with respect to infected, untreated controls. Under the same experimental conditions, non-nucleoside reveres transcriptase inhibitors (NNRTIs), such as MKC-442, alphaAPA, nevirapine, efavirenz and 3,4-dihydro-2-alkoxy-6-benzyl-4-oxopyrimidines (DABOs) MC 1047 and MC 1220 suppressed HIV-1 replication for the entire experimental period (40 days). When cell culture samples were evaluated for the presence of infectious virus, p24 antigen and viral DNA sequences, none of them was detected up to day 40 post-infection (p.i.). Identical results were obtained after a treatment with the above NNRTIs limited to the first 4 days p.i. Under more selective experimental conditions, that is drug treatments limited to the first 4 h p.i., nevirapine and efavirenz proved to be virustatic; in fact, viral breakthrough ensued shortly after their removal from the culture medium. Conversely, DABO MC 1220 was endowed with potent virucidal activity; in fact, at 3.5 microM it was able to suppress HIV-1 multiplication in cultures acutely infected with a very high multiplicity of infection (5 CCID50/cell), thus allowing exponential cell multiplication as in uninfected cultures for the next 40 days.