Exploiting the anti-HIV-1 activity of acyclovir: suppression of primary and drug-resistant HIV isolates and potentiation of the activity by ribavirin

Abstract

Multiple clinical trials have demonstrated that herpes simplex virus 2 (HSV-2) suppressive therapy using acyclovir (ACV) or valacyclovir in HIV-1/HSV-2-infected persons increased the patient's survival and decreased the HIV-1 load. It has been shown that the incorporation of ACV-monophosphate into the nascent DNA chain instead of dGMP results in the termination of viral DNA elongation and directly inhibits laboratory strains of HIV-1. We evaluated here the anti-HIV activity of ACV against primary HIV-1 isolates of different clades and coreceptor specificity and against viral isolates resistant to currently used drugs, including zidovudine, lamivudine, nevirapine, a combination of nucleoside reverse transcriptase inhibitors (NRTIs), a fusion inhibitor, and two protease inhibitors. We found that, at clinically relevant concentrations, ACV inhibits the replication of these isolates in human tissues infected ex vivo. Moreover, addition of ribavirin, an antiviral capable of depleting the pool of intracellular dGTP, potentiated the ACV-mediated HIV-1 suppression. These data warrant further clinical investigations of the benefits of using inexpensive and safe ACV alone or in combination with other drugs against HIV-1, especially to complement or delay highly active antiretroviral therapy (HAART) initiation in low-resource settings.

Fig 1

Inhibition of HIV-1 replication by ACV in human lymphoid tissues. Tissue blocks (27 from each donor) were infected with HIV-1_97USNG31, HIV-1_96USNN20, HIV-1_97USNG30, or HIV-1_ME1 and treated with 3 or 30 μM ACV. Replication of HIV-1 was evaluated by p24_gag core antigen release in pooled medium bathing 27 tissue blocks using a bead-based assay. Each point represents the measurement of medium pooled from three wells, each of which contained nine tissue blocks. The anti-HIV activity of ACV was evaluated by comparing viral replication in drug-treated tissues with that in untreated donor-matched control tissues. The graph represents the typical replication kinetics of 4 to 6 experiments performed with tissues from different donors. For average replication values, see Table 1.

Fig 2

Inhibition of replication of multidrug-resistant HIV-1 clones by ACV in human lymphoid tissues. Donor-matched sets of tissue (27 blocks for each experimental condition from each of three to seven donors) were incubated with ACV (3 or 30 μM) for 12 days or used as untreated controls. Some of these sets were infected with multi-NRTI-resistant clones HIV-1_7324–4, HIV-1_10076–4, HIV-1_7303–3, HIV-1_6463–13, HIV-1_1617–1, and HIV-1_35764–2 or with the laboratory strain HIV-1_LAI.04. Replication of HIV-1 was evaluated by p24_gag core antigen release in pooled medium bathing 27 tissue blocks using a bead-based assay. The anti-HIV activity of ACV, as a percentage, was evaluated by comparing viral replication in drug-treated tissues with that in untreated donor-matched control tissues. Presented are means ± SEM of HIV-1 inhibition in 27 human tissue blocks from each of three to seven donors, relative to results for matched untreated tissues (n = 3 for HIV-1_7324–4 and HIV-1_6463–13; n = 4 for HIV-1_1617–1; n = 7 for HIV-1_10076–4, HIV-1_7303–3, HIV-1_35764–2, and HIV-1_LAI.04).

Fig 3

Potentiation of the anti-HIV-1 activity of ACV by ribavirin in human lymphoid tissue. Donor-matched tissue blocks (27 blocks from each donor) were inoculated with HIV-1_LAI.04 and treated with ACV (0.3, 3, or 10 μM) in the absence or presence of 10 μM ribavirin. Replication of HIV-1 was evaluated by p24_gag core antigen release in pooled medium bathing 27 tissue blocks using a bead-based assay. The percentage of HIV-1 inhibition was evaluated by comparing viral replication in drug-treated tissues with that in untreated donor-matched control tissues. Presented are means ± SEM of HIV-1_LAI.04 inhibition in 27 human tissue blocks from each of 6 to 10 donors, relative to results for matched untreated tissues (n = 6 for experiments performed with 0.3 μM ACV; n = 10 for experiments performed with 3 or 10 μM ACV). An asterisk denotes a statistically significant difference (P < 0.05) in HIV-1_LAI.04 inhibition between untreated and ribavirin-treated tissues.

Fig 4

Potentiation of the anti-HIV-1 activity of ACV ProTides by ribavirin in MT-4 cell culture. MT-4 cells (10⁵) infected with HIV-1_LAI.04 were cultured for 4 days in the presence of ribavirin at concentrations ranging from 1 to 20 μM and ACV ProTides at concentrations ranging from 0.01 to 50 μM. HIV replication was evaluated by p24_gag antigen release in culture medium at the end of the experiment using a bead-based assay. EC₅₀s were calculated in an experiment in which two ACV ProTides (Cf 2648 and Cf2681) were tested against HIV-1_LAI.04 as a function of different ribavirin concentrations.