Specific ActivationIn Vivoof HIV-1 by a Bromodomain Inhibitor from Monocytic Cells in Humanized Mice under Antiretroviral Therapy

Abstract

Combination antiretroviral therapy (cART) effectively suppresses HIV-1 replication and enables HIV‑infected individuals to live long, productive lives. However, the persistence of HIV-1 reservoirs of both T and myeloid cells with latent or low-replicating HIV-1 in patients under cART makes HIV-1 infection an incurable disease. Recent studies have focused on the development of strategies to activate and purge these reservoirs. Bromodomain and extraterminal domain proteins (BETs) are epigenetic readers involved in modulating gene expression. Several bromodomain inhibitors (BETi) are reported to activate viral transcription in vitro in HIV-1 latency cell lines in a P-TEFb (CDK9/cyclin T1)-dependent manner. Little is known about BETi efficacy in activating HIV-1 reservoir cells under cART in vivo. Here we report that a BETi (I-BET151) efficiently activated HIV-1 reservoirs under effective cART in humanized mice in vivo. Interestingly, I-BET151 during suppressive cART in vivo activated HIV-1 gene expression only in monocytic cells and not in CD4+ T cells. We further demonstrate that BETi preferentially enhanced HIV-1 gene expression in monocytic cells rather than in T cells and that whereas CDK9 was involved in activating HIV-1 by I-BET151 in both monocytic and T cells, CDK2 enhanced HIV-1 transcription in monocytic cells but inhibited it in T cells. Our findings reveal a role for CDK2 in differential modulation of HIV-1 gene expression in myeloid cells and in T cells and provide a novel strategy to reactivate monocytic reservoirs with BETi during cART. IMPORTANCE Bromodomain inhibitors have been reported to activate HIV-1 transcription in vitro, but their effect on activation of HIV-1 reservoirs during cART in vivo is unclear. We found that BETi (I-BET151) treatment reactivated HIV-1 gene expression in humanized mice during suppressive cART. Interestingly, I-BET151 preferentially reactivated HIV-1 gene expression in monocytic cells, but not in CD4 T cells, in cART-treated mice. Furthermore, I-BET151 significantly increased HIV-1 transcription in monocytic cells, but not in HIV-1-infected CD4 T cells, via CDK2-dependent mechanisms. Our findings suggest that BETi can preferentially activate monocytic HIV-1 reservoir cells and that a combination of reservoir activation agents targeting different cell types and pathways is needed to achieve reactivation of different HIV-1 reservoir cells during cART.

Pharmacological Activation of Non-canonical NF-κB Signaling Activates Latent HIV-1 Reservoirs In Vivo

“…Additionally, bromodomain and extraterminal domain inhibitors (BETi) are epigenetic regulators that affect HIV-1 replication by preventing positive transcription elongation factor b (P-TEFb) from interacting with BRD4, thereby allowing Tat to bind P-TEFb and mediating HIV-1 transcriptional elongation. 63 , 64 Although molecules in this class have been evaluated only preclinically for HIV-1 latency reversal, 65 different BETis are being investigated in clinical trials as cancer therapeutics. 66 Because we find that Smac mimetics can strongly synergize with a variety of epigenetic regulators, combinations of Smac mimetics with both HDACi and BETi represent potential opportunities to deliver increased latency reversal activity, while minimizing toxicities due to reduced doses of the individual drugs.…”

Modulation of BRD4 in HIV epigenetic regulation: implications for finding an HIV cure

“…In support of this, it was more recently shown that JQ1 induces dissociation of BRD4 from the repressive chromatin remodeling proteins (SWI/SNF) at the HIV LTR, thereby reversing BRD4-mediated HIV transcriptional suppression [23]. This is considered to be independent of Tat-mediated transcription elongation In addition to JQ1, several other BET inhibitors have been tested in HIV infection models with some compounds demonstrating HIV latency-reversing activities, such as UMB-136 [39], MMQO [40], OTX015 [41], and I-BET151 [42]. Mechanistically, OTX015 increases the occupancy of CDK9 at the HIV-1 LTR and activates RNAP II CTD phosphorylation, hence reactivating HIV expression [41].…”

Knowledge From London and Berlin: Finding Threads to a Functional HIV Cure

“…BET inhibitors, including JQ1, MS417, I-Bet, and I-Bet151, have reactivated HIV from latency via the action of the positive transcription elongation factor b, a subject of acetylation, in a model of HIV latency (82,122). Furthermore, I-Bet151 was investigated in humanized mice treated with suppressive cART (81). In this case, I-Bet151 did not have any observed significant toxic effect on the treated mice, and nine days after I-Bet151 initiation, HIV-1 viremia rebounded and was associated with a higher HIV-1 RNA level in different organs.…”