Dual Role of Novel Ingenol Derivatives from Euphorbia tirucalli in HIV Replication: Inhibition of De Novo Infection and Activation of Viral LTR

Abstract

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.

Targeting NF-κB Signaling with Protein Kinase C Agonists As an Emerging Strategy for Combating HIV Latency

“…54 Similar findings about the effects of IngB on HIV replication in cell culture models of HIV latency were reported, but involved the use of higher concentrations of IngB, up to 1 lM. 55 Interestingly, IngB also inhibited HIV replication by suppressing the expression of CD4, CCR5, and CXCR4. However, IngB caused an increase in the expression of CD69, NF-jB, or P-TEFb proteins in CD4 + T cells at higher concentrations, raising some concerns about its potential side effects.…”

“…However, IngB caused an increase in the expression of CD69, NF-jB, or P-TEFb proteins in CD4 + T cells at higher concentrations, raising some concerns about its potential side effects. 30,54,55 Gnidimacrin and other diterpenes Gnidimacrin reactivated latent HIV LTR in U1 and ACH2 cell culture models of HIV latency at picomolar concentrations. It inhibited HIV infection of T cell lines and primary PBMCs by down-modulating the expression of HIV coreceptors CCR5 or CXCR4.…”

Molecular mechanisms of HIV latency

“…An exception is ingenol B, which was modified from other ingenols obtained from the euphorbia plant. Oral administration of ingenol B to optimally treated, infected rhesus macaques activated cells and increased levels of SIV in the periphery (86,87,89,90).…”

Progress Towards an HIV Cure: Update from the 2014 International AIDS Society Symposium

“…The first class of compounds, including prostratin, bryostatin, and ingenol, induces cellular protein kinase C (PKC) signaling leading to migration of active NF-jB into the cell nucleus, which in turn promotes initiation of HIV mRNA transcription. 15,22,23 The second class of compounds, including HMBA plus the JQ1, I-BET, and I-BET151 bromodomain and extraterminal (BET) inhibitors, all release active P-TEFb in the cell, which in turn binds the HIV Tat transcriptional activator protein to drive elongation of HIV mRNA transcripts. 24,25 Thus, both types of compounds drive different stages of HIV transcription to enhance HIV mRNA expression.…”