Several independent research groups have identified ingenol esters, compounds derived from the tropical shrub Euphorbia tirucalli, as potent activators of latent HIV. Papers published in the journals Virology and AIDS report that a specific semi-synthetic ingenol ester named 3-caproyl-ingenol (ING B) demonstrates the greatest promise and may represent a candidate for clinical trials. The compound appears to work by targeting the protein kinase C (PKC) pathway, similar to another known latency-reversing candidate prostratin but with less evidence of toxicity. At the International Workshop on HIV Persistence last December, Lucio Gama from Johns Hopkins University presented results from ING B studies in SIV-infected macaques indicating that the drug was safe to administer and showed activity against latent virus. Gama also offered a glimpse at preliminary data from the laboratory of Robert Siliciano suggesting that ING B potently activated latent HIV in CD4 T cells isolated from HIV-positive individuals on ART. Additional analyses are ongoing with a view to assessing if ING B can safely be advanced into human clinical trials, and whether additional modifications to the compound might enhance safety and activity.
Virology. 2014 Jul 8;462-463C:328-339. doi: 10.1016/j.virol.2014.05.033. [Epub ahead of print]
Pandeló José D, Bartholomeeusen K, da Cunha RD, Abreu CM, Glinski J, da Costa TB, Bacchi Rabay AF, Pianowski Filho LF, Dudycz LW, Ranga U, Peterlin BM, Pianowski LF, Tanuri A, Aguiar RS.
The ability of HIV to establish long-lived latent infection is mainly due to transcriptional silencing of viral genome in resting memory T lymphocytes. Here, we show that new semi-synthetic ingenol esters reactivate latent HIV reservoirs. Amongst the tested compounds, 3-caproyl-ingenol (ING B) was more potent in reactivating latent HIV than known activators such as SAHA, ingenol 3,20-dibenzoate, TNF-α, PMA and HMBA. ING B activated PKC isoforms followed by NF-κB nuclear translocation. As virus reactivation is dependent on intact NF-κB binding sites in the LTR promoter region ING B, we have shown that. ING B was able to reactivate virus transcription in primary HIV-infected resting cells up to 12 fold and up to 25 fold in combination with SAHA. Additionally, ING B promoted up-regulation of P-TEFb subunits CDK9/Cyclin T1. The role of ING B on promoting both transcription initiation and elongation makes this compound a strong candidate for an anti-HIV latency drug combined with suppressive HAART.
PLoS One. 2014 May 14;9(5):e97257. doi: 10.1371/journal.pone.0097257. eCollection 2014.
Abreu CM, Price SL, Shirk EN, Cunha RD, Pianowski LF, Clements JE, Tanuri A, Gama L.
HIV infection is not cleared by antiretroviral drugs due to the presence of latently infected cells that are not eliminated with current therapies and persist in the blood and organs of infected patients. New compounds to activate these latent reservoirs have been evaluated so that, along with HAART, they can be used to activate latent virus and eliminate the latently infected cells resulting in eradication of viral infection. Here we describe three novel diterpenes isolated from the sap of Euphorbia tirucalli, a tropical shrub. These molecules, identified as ingenols, were modified at carbon 3 and termed ingenol synthetic derivatives (ISD). They activated the HIV-LTR in reporter cell lines and human PBMCs with latent virus in concentrations as low as 10 nM. ISDs were also able to inhibit the replication of HIV-1 subtype B and C in MT-4 cells and human PBMCs at concentrations of EC50 0.02 and 0.09 µM respectively, which are comparable to the EC50 of some antiretroviral currently used in AIDS treatment. Control of viral replication may be caused by downregulation of surface CD4, CCR5 and CXCR4 observed after ISD treatment in vitro. These compounds appear to be less cytotoxic than other diterpenes such as PMA and prostratin, with effective dose versus toxic dose TI>400. Although the mechanisms of action of the three ISDs are primarily attributed to the PKC pathway, downregulation of surface receptors and stimulation of the viral LTR might be differentially modulated by different PKC isoforms.
AIDS. 2014 May 6. [Epub ahead of print]
Jiang G, Mendes EA, Kaiser P, Sankaran-Walters S, Tang Y, Weber MG, Melcher GP, Thompson GR 3rd, Tanuri A, Pianowski LF, Wong JK, Dandekar S.
OBJECTIVE: Although HAART effectively suppresses viral replication, it fails to eradicate latent viral reservoirs. The 'shock and kill' strategy involves the activation of HIV from latent reservoirs and targeting them for eradication. Our goal was to develop new approaches for activating HIV from latent reservoirs.
DESIGN: We investigated capacity of Ingenol B (IngB), a newly modified derivative of Ingenol ester that was originally isolated from a Brazilian plant in Amazon, for its capacity and mechanisms of HIV reactivation.
METHODS: Reactivation of HIV-1 by IngB was evaluated in J-Lat A1 cell culture model of HIV latency as well as in purified primary CD4 T cells from long-term HAART-treated virologically-suppressed HIV-infected individuals. The underlining molecular mechanisms of viral reactivation were investigated using flow cytometry, RT-qPCR and chromatin immunoprecipitation.
RESULTS: IngB is highly effective in reactivating HIV in J-Lat A1 cells with relatively low cellular toxicity. It is also able to reactivate latent HIV in purified CD4 T cells from HAART-treated HIV-positive individuals ex vivo. Our data show that IngB may reactivate HIV expression by both activating protein kinase Cδ-NF-κB pathway and directly inducing NF-κB protein expression. Importantly, IngB has a synergistic effect with JQ1 in latent HIV reactivation.
CONCLUSIONS: IngB is a new promising compound to activate latent HIV reservoirs. Out data suggest that formulating novel derivatives from Ingenol esters may be an innovative approach to develop new lead compounds to reactivate latent HIV.