Background:  Prostratin is a non-tumor promoting phorbol ester which inhibits de novo human immunodeficiency virus type-1 (HIV-1) infection yet up-regulates expression of latent pro-viral DNA. The lack of tumor promotion, block of viral spread, yet ability to induce latent proviral expression, suggests prostratin could serve as an inductive adjuvant therapy for patients on highly active antiretroviral therapy (HAART).

Methods:  Human PBMCs were fractionated into specific cell populations using a Miltenyi automated cell-fractionation apparatus and antibodies to specific cell surface receptors. Isolated populations of 11b+ (monocytes) and an 11b- fraction, as well as dendritic cells were treated with prostratin and assessed for morphologic changes, induction of latent HIV-1 expression by p24 antigen ELISA, and differences in cell surface receptor expression by FACS.

Results:  Prostratin, like phorbol myristic acid (PMA), induced rapid adherence of the monocyte-enriched 11b+ fraction but had no gross effect on the monocyte-depleted 11b- population. Unlike PMA, prostratin treatment of purified monocytes, washed and co-cultured with U1 cells, did not promote the expression of HIV-1, though direct addition of prostratin to U1 cells did. Prostratin also induced expression of HIV-1 from purified populations of cells derived from patient PBMCs on virally suppressive HAART. Modest down-regulation of DC-SIGN on immature monocyte-derived dendritic cells occurred after treatment with prostratin. Similar studies on blood-derived dendritic cells are underway.

Conclusions: Prostratin induces down-regulation of critical viral receptors including a modest down-regulation of DC-SIGN on immature monocyte-derived dendritic cells. Prostratin, like PMA, induces changes on 11b+ cells, consistent with accelerated activation and differentiation though, unlike PMA, does not appear to induce high levels of pro-inflammatory cytokines from treated monocytes sufficient to trigger HIV-1 expression from U1 cells. However, direct addition of prostratin induced the expression of latent HIV-1 in UI cells and purified populations of cells derived from virally suppressed, HAART patient, PBMCs. These experiments provide clues as to the nature and responsiveness of the HAART persistent viral reservoir.