Two recent papers in PLoS Pathogens report that combinations of candidate latency-reversing agents can potently activate HIV production by latently infected CD4 T cells in laboratory experiments. Pairings of the PKC agonists bryostatin-1 or ingenol with the bromodomain inhibitor JQ1 were most effective, generating levels of virus production by latently infected cells similar to those achieved by maximal T cell activation. The results appear consistent with those published earlier this year by the research group of Robert Siliciano at Johns Hopkins University, and are encouraging because there had been some skepticism as to whether any latency reversing strategy could match the effects of maximal T cell activation (which is known to be too dangerous to use in people). But there are caveats: the compounds do affect T cell activation pathways and it is not yet known if they will be safe in HIV-positive individuals; currently, they are being tested (and in the case of ingenol, used topically) as cancer treatments.
The two new publications derive from independent research laboratories led by Satya Dandekar at UC Davis and Carine Van Lint at Université Libre de Bruxelles (ULB), respectively. The experimental findings are broadly consistent but involve two different variants of ingenol: ingenol-B, which has previously been reported to have latency-reversing activity, and ingenol-3-angelate (PEP005), the active component of an FDA-approved topical treatment for precancerous actinic keratosis named PICATO. The opinions of the two groups regarding which version of ingenol might be safer for systemic use in humans differ somewhat. Van Lint’s group writes:
“Importantly, ingenol-3-angelate appears to be more toxic than ing-B when orally delivered to rats and dogs (Luiz Pianowski, Kyolab, Brazil, personal communication).”
While Dandekar’s states:
“Similar to the safety of the topical application of PICATO, the systemic (intravenous) use of PEP005 in small animals (mini pig and rat model) was reported to be relatively safe, with the maximum nonlethal dose >73 μg/kg (See Assessment report of PICATO to European Medicines Agency, Sept 20, 2012). While additional safety data with systemic administration in non-human primates is needed, these existing data support further investigation of PEP005 as a potential candidate in HIV cure studies.”
Further animal model studies should help resolve this uncertainty. The UK website NHS Choices, which provides commentary on research-related stories in the mainstream media, takes a rather dim view of Dandekar’s suggestion (reported by the BBC) that the FDA-approved status of PICATO is relevant to the prospects of this approach in people with HIV, countering that “although the drug is being used on patients, it is currently just applied to the skin. The effects may be very different if the whole body is exposed to the drug, as would be required to locate hidden reservoirs of HIV.”
The other PKC agonist studied, bryostatin-1, is already being tested in HIV-positive people in a small, single-dose clinical trial in Spain supported by a biotech company named Aphios; results are pending. While some researchers have expressed concern about the potential toxicities of bryostatin-1, Van Lint’s group is more sanguine, noting that in a phase I trial in children with cancers (published in 1999) “only few patients have experienced myalgia, photophobia or eye pain.” But the report from this trial also states “toxicities of bryostatin-1 occurred days after the infusion and lasted for prolonged periods” and I think it’s fair to say that opinions about the acceptability of these types of side effects in healthy HIV-positive people are likely to vary. There are ongoing efforts to develop safer and more targeted analogs of bryostatin-1, notably those led by Paul Wender at Stanford University.
Bromodomain inhibitors are also being studied in cancer. The compound used in these studies, JQ1, has too short a half-life for human use but Van Lint and colleagues note: “Clinical trials with JQ1-derivative called TEN-010 (also called JQ2) and another BETi called GSK525762 have been initiated recently to characterize their safety, tolerability, pharmacokinetics and anti-cancer activity (clinicaltrials.gov).” Safety information from these trials will be important in determining whether studies in HIV are appropriate.
PLoS Pathog. 2015 Jul 30;11(7):e1005063. doi: 10.1371/journal.ppat.1005063. eCollection 2015 Jul.
An In-Depth Comparison of Latency-Reversing Agent Combinations in Various In Vitro and Ex Vivo HIV-1 Latency Models Identified Bryostatin-1+JQ1 and Ingenol-B+JQ1 to Potently Reactivate Viral Gene Expression.
Darcis G, Kula A, Bouchat S, Fujinaga K, Corazza F, Ait-Ammar A, Delacourt N, Melard A, Kabeya K, Vanhulle C, Van Driessche B, Gatot JS, Cherrier T, Pianowski LF, Gama L, Schwartz C, Vila J, Burny A, Clumeck N, Moutschen M, De Wit S, Peterlin BM, Rouzioux C, Rohr O, Van Lint C.
The persistence of latently infected cells in patients under combinatory antiretroviral therapy (cART) is a major hurdle to HIV-1 eradication. Strategies to purge these reservoirs are needed and activation of viral gene expression in latently infected cells is one promising strategy. Bromodomain and Extraterminal (BET) bromodomain inhibitors (BETi) are compounds able to reactivate latent proviruses in a positive transcription elongation factor b (P-TEFb)-dependent manner. In this study, we tested the reactivation potential of protein kinase C (PKC) agonists (prostratin, bryostatin-1 and ingenol-B), which are known to activate NF-κB signaling pathway as well as P-TEFb, used alone or in combination with P-TEFb-releasing agents (HMBA and BETi (JQ1, I-BET, I-BET151)). Using in vitro HIV-1 post-integration latency model cell lines of T-lymphoid and myeloid lineages, we demonstrated that PKC agonists and P-TEFb-releasing agents alone acted as potent latency-reversing agents (LRAs) and that their combinations led to synergistic activation of HIV-1 expression at the viral mRNA and protein levels. Mechanistically, combined treatments led to higher activations of P-TEFb and NF-κB than the corresponding individual drug treatments. Importantly, we observed in ex vivo cultures of CD8+-depleted PBMCs from 35 cART-treated HIV-1+ aviremic patients that the percentage of reactivated cultures following combinatory bryostatin-1+JQ1 treatment was identical to the percentage observed with anti-CD3+anti-CD28 antibodies positive control stimulation. Remarkably, in ex vivo cultures of resting CD4+ T cells isolated from 15 HIV-1+ cART-treated aviremic patients, the combinations bryostatin-1+JQ1 and ingenol-B+JQ1 released infectious viruses to levels similar to that obtained with the positive control stimulation. The potent effects of these two combination treatments were already detected 24 hours post-stimulation. These results constitute the first demonstration of LRA combinations exhibiting such a potent effect and represent a proof-of-concept for the co-administration of two different types of LRAs as a potential strategy to reduce the size of the latent HIV-1 reservoirs.
PLoS Pathog. 2015 Jul 30;11(7):e1005066. doi: 10.1371/journal.ppat.1005066. eCollection 2015 Jul.
Jiang G, Mendes EA, Kaiser P, Wong DP, Tang Y, Cai I, Fenton A, Melcher GP, Hildreth JE, Thompson GR, Wong JK, Dandekar S.
Although anti-retroviral therapy (ART) is highly effective in suppressing HIV replication, it fails to eradicate the virus from HIV-infected individuals. Stable latent HIV reservoirs are rapidly established early after HIV infection. Therefore, effective strategies for eradication of the HIV reservoirs are urgently needed. We report that ingenol-3-angelate (PEP005), the only active component in a previously FDA approved drug (PICATO) for the topical treatment of precancerous actinic keratosis, can effectively reactivate latent HIV in vitro and ex vivo with relatively low cellular toxicity. Biochemical analysis showed that PEP005 reactivated latent HIV through the induction of the pS643/S676-PKCδ/θ-IκBα/ε-NF-κB signaling pathway. Importantly, PEP005 alone was sufficient to induce expression of fully elongated and processed HIV RNAs in primary CD4+ T cells from HIV infected individuals receiving suppressive ART. Furthermore, PEP005 and the P-TEFb agonist, JQ1, exhibited synergism in reactivation of latent HIV with a combined effect that is 7.5-fold higher than the effect of PEP005 alone. Conversely, PEP005 suppressed HIV infection of primary CD4+ T cells through down-modulation of cell surface expression of HIV co-receptors. This anti-cancer compound is a potential candidate for advancing HIV eradication strategies.