Reactivation of HIV latency by ingenol esters isolated from Euphorbia Tirucalli
During the early stages of HIV infections, the virus establishes latency in a portion of the population of infected long-lived memory cells CD4+. Such latent viral reservoirs are inaccessible to standard antiretroviral drugs and result in an inability to eradicate the infection. A reactivation of the latent virus would offer an opportunity to expose it to the action of antiretroviral drugs (HAART) and consequently lead to full elimination of the virus. We have found that esters of ingenol found in E. tirucalli act as reactivators of HIV. They were isolated by Centrifugal Partition Chromatography (FCPC Kromaton) followed by preparative HPLC and their structures were characterized by NMR as three E/Z isomers of ingenol-3-dodecatrienoate (1). We used an antiviral assay in MT-4 cells and flow cytometry studies, in the presence of 1, were to elucidate its mechanism of antiviral action. The MT-4 assay demonstrated that 1 inhibited viral replication until cellular toxicity was observed at 40µM. This molecule was able to down-regulate CD4 expression in MT-4 as well as in human PMBCs. Interestingly, this compound was also capable to activate human CD4+ cells, as shown by double marked CD4/CD38 and CD4/CD69. Nevertheless, 1 was not able to induce cellular proliferation. By acting through proviral activation and by blocking viral entrance through receptor down regulation, 1 can be used in a shock-and-kill strategy to be placed together with HAART therapy to eliminate viral reservoir.