BACKGROUND: One strategy to eliminate­­ latently infected CD4+ T-cells that persist in people living with HIV (PLWH) on suppressive antiretroviral therapy (ART) is to activate virus expression to induce immune-mediated clearance or virus induced cytolysis using latency reversing agents (LRAs). To date, evaluation of LRAs alone or in combination with antibodies or vaccination has not resulted in a substantial decrease in the frequency of infected cells or increased time to viral rebound once ART is stopped. Thus, additional strategies to kill reactivated cells are needed. Given phosphoinositide 3-kinases (PI3K) promote the survival of virus-infected cells, here we investigated whether PI3K inhibitors could be combined with LRAs to kill latently infected cells.
METHODS: We assessed the effects of three different PI3K inhibitors (IPI-443, IPI-3063 and wortmannin) alone and in combination with LRAs (romidepsin, panobinostat, JQ1 and PMA/PHA as a positive control) to determine if these pro-apoptotic agents enhanced death of HIV-infected cells using CD4+ T-cells isolated from blood from n=6 PLWH on ART.
RESULTS: We found that the histone deacetylase inhibitor romidepsin together with either IPI-443 or wortmannin PI3K inhibitor led to significant declines in the frequency of infected cells, measured as integrated HIV DNA (p=0.0312 in both cases). Both drug combinations were also synergistic (mean Bliss independence score 0.15 and 0.37, respectively). Interestingly, we found that the PI3K inhibitors alone could reactivate cell-associated HIV RNA (mean fold change of 1.43, 2.32 and 1.81, for IPI-443, IPI-3063 and wortmannin, respectively).
CONCLUSIONS: Taken together, the data suggests that sensitisation of latently infected CD4+ T-cells with pro-apoptotic compounds combined with latency reversal to drive expression of viral pro-apoptotic proteins can enhance the clearance of latently infected cells. The combination of romidepsin and select PI3K inhibitors could inhibit multiple cell survival pathways, ultimately leading to the production of ROS and an increase in pro-apoptotic molecules.

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