The Novel PKC Activator 10-Methyl-Aplog-1 Combined with JQ1 Induced Strong and Synergistic HIV Reactivation with Tolerable Global T Cell Activation

Eliminating the HIV tissue reservoir: current strategies and challenges

BACKGROUND

Acquired immunodeficiency syndrome (AIDS) is still one of the most widespread and harmful infectious diseases in the world. The presence of reservoirs housing the human immunodeficiency virus (HIV) represents a significant impediment to the development of clinically applicable treatments on a large scale. The viral load in the blood can be effectively reduced to undetectable levels through antiretroviral therapy (ART), and a higher concentration of HIV is sequestered in various tissues throughout the body, forming the tissue reservoir - the source of viremia after interruption treatment.

METHODS

We take the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) as a guideline for this review. In June 2023, we used the Pubmed, Embase, and Scopus databases to search the relevant literature published in the last decade.

RESULTS

Here we review the current strategies and treatments for eliminating the HIV tissue reservoirs: early and intensive therapy, gene therapy (including ribozyme, RNA interference, RNA aptamer, zinc finger enzyme, transcriptional activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeats/associated nuclease 9 (CRISPR/Cas9)), 'Shock and Kill', 'Block and lock', immunotherapy (including therapeutic vaccines, broadly neutralising antibodies (bNAbs), chimeric antigen receptor T-cell immunotherapy (CAR-T)), and haematopoietic stem cell transplantation (HSCT).

CONCLUSION

The existence of an HIV reservoir is the main obstacle to the complete cure of AIDS. Choosing the appropriate strategy to deplete the HIV reservoir and achieve a functional cure for AIDS is the focus and difficulty of current research. So far, there has been a lot of research and progress in reducing the HIV reservoir, but in general, the current research is still very preliminary. Much research is still needed to properly assess the reliability, effectiveness, and necessity of these strategies.

Breaking the Silence: Regulation of HIV Transcription and Latency on the Road to a Cure

Antiretroviral therapy (ART) has brought the HIV/AIDS epidemic under control, but a curative strategy for viral eradication is still needed. The cessation of ART results in rapid viral rebound from latently infected CD4+ T cells, showing that control of viral replication alone does not fully restore immune function, nor does it eradicate viral reservoirs. With a better understanding of factors and mechanisms that promote viral latency, current approaches are primarily focused on the permanent silencing of latently infected cells ("block and lock") or reactivating HIV-1 gene expression in latently infected cells, in combination with immune restoration strategies to eliminate HIV infected cells from the host ("shock and kill"). In this review, we provide a summary of the current, most promising approaches for HIV-1 cure strategies, including an analysis of both latency-promoting agents (LPA) and latency-reversing agents (LRA) that have shown promise in vitro, ex vivo, and in human clinical trials to reduce the HIV-1 reservoir.

Biological evaluation of a phosphate ester prodrug of 10-methyl-aplog-1, a simplified analog of aplysiatoxin, as a possible latency-reversing agent for HIV reactivation

10-Methyl-aplog-1 (10MA-1), a simplified analog of aplysiatoxin, exhibits a high binding affinity for protein kinase C (PKC) isozymes with minimal tumor-promoting and pro-inflammatory activities. A recent study suggests that 10MA-1 could reactivate latent human immunodeficiency virus (HIV) in vitro for HIV eradication strategy. However, further in vivo studies were abandoned by a dose limit caused by the minimal water solubility of 10MA-1. To overcome this problem, we synthesized a phosphate ester of 10MA-1, 18-O-phospho-10-methyl-aplog-1 (phos-10MA-1), to improve water solubility for in vivo studies. The solubility, PKC binding affinity, and biological activity of phos-10MA-1 were examined in vitro, and the biological activity was comparable with 10MA-1. The pharmacokinetic studies in vivo were also examined, which suggest that further optimization for improving metabolic stability is required in the future.

Role of TLRs in HIV-1 Infection and Potential of TLR Agonists in HIV-1 Vaccine Development and Treatment Strategies

Toll-like receptors (TLRs), as a family of pattern recognition receptors, play an important role in the recognition of HIV-1 molecular structures by various cells of the innate immune system, but also provide a functional association with subsequent mechanisms of adaptive immunity. TLR7 and TLR8 play a particularly important role in the innate immune response to RNA viruses due to their ability to recognise GU-rich single-stranded RNA molecules and subsequently activate intracellular signalling pathways resulting in expression of genes coding for various biological response modifiers (interferons, proinflammatory cytokines, chemokines). The aim of this review is to summarise the most recent knowledge on the role of TLRs in the innate immune response to HIV-1 and the role of TLR gene polymorphisms in the biology and in the clinical aspects of HIV infections. In addition, the role of TLR agonists as latency reversing agents in research to treat HIV infections and as immunomodulators in HIV vaccine research will be discussed.

The ingenol-based protein kinase C agonist GSK445A is a potent inducer of HIV and SIV RNA transcription

Activation of the NF-κB signaling pathway by Protein Kinase C (PKC) agonists is a potent mechanism for human immunodeficiency virus (HIV) latency disruption in vitro. However, significant toxicity risks and the lack of evidence supporting their activity in vivo have limited further evaluation of PKC agonists as HIV latency-reversing agents (LRA) in cure strategies. Here we evaluated whether GSK445A, a stabilized ingenol-B derivative, can induce HIV/simian immunodeficiency virus (SIV) transcription and virus production in vitro and demonstrate pharmacological activity in nonhuman primates (NHP). CD4⁺ T cells from people living with HIV and from SIV⁺ rhesus macaques (RM) on antiretroviral therapy (ART) exposed in vitro to 25 nM of GSK445A produced cell-associated viral transcripts as well as viral particles at levels similar to those induced by PMA/Ionomycin, indicating that GSK445A can potently reverse HIV/SIV latency. Importantly, these concentrations of GSK445A did not impair the proliferation or survival of HIV-specific CD8⁺ T cells, but instead, increased their numbers and enhanced IFN-γ production in response to HIV peptides. In vivo, GSK445A tolerability was established in SIV-naïve RM at 15 μg/kg although tolerability was reduced in SIV-infected RM on ART. Increases in plasma viremia following GSK445A administration were suggestive of increased SIV transcription in vivo. Collectively, these results indicate that GSK445A is a potent HIV/SIV LRA in vitro and has a tolerable safety profile amenable for further evaluation in vivo in NHP models of HIV cure/remission.

Antiretroviral therapy (ART) is not a definitive cure for HIV infection, in part, because the virus is able to integrate its genetic material in the host cell and remain in a dormant but fully replication-competent form during ART. These latently-infected cells can persist for long periods of time and remain hidden from the host’s immune system. If ART is stopped, the virus can reactivate from this pool of infected cells and resume HIV replication and disease progression. As such, finding and eliminating cells with latent HIV infection is priority for HIV cure research. One approach is to use compounds referred to as latency-reversing agents, that can induce HIV reactivation during ART. The goal of this approach is to facilitate elimination of infected cells by the virus itself once it reactivates or by the host’s immune system, once virus induction renders the cells detectable by the immune system, while also preventing the virus from infecting new cells due to the continued presence of ART. In this study we report on the activity of a novel latency-reversing agent called GSK445A, a potent activator of the enzyme protein kinase C (PKC). We show that GSK445A can induce HIV and simian immunodeficiency virus (SIV) latency reversal in vitro and has a tolerable saftey profile in nonhuman primates that should permit further testing of this PKC-agonist in strategies to cure HIV.

Histone deacetylase inhibition reduces deleterious cytokine release induced by ingenol stimulation

Latency reversing agents (LRAs), such as protein kinase C (PKC) agonists, constitute a promising strategy for exposing and eliminating the HIV-1 latent reservoir. PKC agonists activate NF-κB and induce deleterious pro-inflammatory cytokine production. Adjuvant pharmacological agents, such as ruxolitinib, a JAK inhibitor, have previously been combined with LRAs to reduce deleterious pro-inflammatory cytokine secretion without inhibiting HIV-1 reactivation in vitro. Histone deacetylase inhibitors (HDACi) are known to dampen pro-inflammatory cytokine secretion in the context of other diseases and synergize with LRAs to reactivate latent HIV-1. This study investigates whether a panel of epigenetic modifiers, including HDACi, could dampen PKC-induced pro-inflammatory cytokine secretion during latency reversal. We screened an epigenetic modifier library for compounds that reduced intracellular IL-6 production induced by the PKC agonist Ingenol-3,20-dibenzoate. We further tested the most promising epigenetic inhibitor class, HDACi, for their ability to reduce pro-inflammatory cytokines and reactivate latent HIV-1 ex vivo. We identified nine epigenetic modulators that reduced PKC-induced intracellular IL-6. In cells from aviremic individuals living with HIV-1, the HDAC1-3 inhibitor, suberohydroxamic acid (SBHA), reduced secretion of pro-inflammatory cytokines TNF-α, IL-5, IL-2r, and IL-17 but did not significantly reactivate latent HIV-1 when combined with Ingenol-3,20-dibenzoate. Combining SBHA and Ingenol-3,20-dibenzoate reduces deleterious cytokine production during latency reversal but does not induce significant viral reactivation in aviremic donor PBMCs. The ability of SBHA to reduce PKC-induced pro-inflammatory cytokines when combined with Ingenol-3,20-dibenzoate suggests SBHA can be used to reduced PKC induced pro-inflammatory cytokines but not to achieve latency reversal in the context of HIV-1.