BI-2536 and BI-6727, dual Polo-like kinase/bromodomain inhibitors, effectively reactivate latent HIV-1.

HIV-1 latent reservoirs harbouring silenced but replication-competent proviruses are a major obstacle against viral eradication in infected patients. The "shock and kill" strategy aims to reactivate latent provirus with latency reversing agents (LRAs) in the presence of antiretroviral drugs, necessitating the development of effective and efficient LRAs. We screened a chemical library for potential LRAs and identified two dual Polo-like kinase (PLK)/bromodomain inhibitors, BI-2536 and BI-6727 (volasertib), which are currently undergoing clinical trials against various cancers. BI-2536 and BI-6727 significantly reactivated silenced HIV-1 provirus at both the mRNA and protein level in two latently infected model cell lines (ACH2 and U1). BI-2536 dramatically reactivated transcription of latent HIV-1 provirus in peripheral blood mononuclear cells derived from infected patients. Long terminal repeat activation by the inhibitors was associated with bromodomain rather than PLK inhibition. We also found that BI-2536 synergistically activates the latent provirus in combination with SAHA, a histone deacetylase inhibitor, or the non-tumour-promoting phorbol ester prostratin. Our findings strongly suggest that BI-2536 and BI-6727 are potent LRAs for the "shock and kill" HIV-1 eradication strategy.

Therapeutic doses of irradiation activate viral transcription and induce apoptosis in HIV-1 infected cells.

The highly active antiretroviral therapy reduces HIV-1 RNA in plasma to undetectable levels. However, the virus continues to persist in the long-lived resting CD4(+) T cells, macrophages and astrocytes which form a viral reservoir in infected individuals. Reactivation of viral transcription is critical since the host immune response in combination with antiretroviral therapy may eradicate the virus. Using the chronically HIV-1 infected T lymphoblastoid and monocytic cell lines, primary quiescent CD4(+) T cells and humanized mice infected with dual-tropic HIV-1 89.6, we examined the effect of various X-ray irradiation (IR) doses (used for HIV-related lymphoma treatment and lower doses) on HIV-1 transcription and viability of infected cells. Treatment of both T cells and monocytes with IR, a well-defined stress signal, led to increase of HIV-1 transcription, as evidenced by the presence of RNA polymerase II and reduction of HDAC1 and methyl transferase SUV39H1 on the HIV-1 promoter. This correlated with the increased GFP signal and elevated level of intracellular HIV-1 RNA in the IR-treated quiescent CD4(+) T cells infected with GFP-encoding HIV-1. Exposition of latently HIV-1infected monocytes treated with PKC agonist bryostatin 1 to IR enhanced transcription activation effect of this latency-reversing agent. Increased HIV-1 replication after IR correlated with higher cell death: the level of phosphorylated Ser46 in p53, responsible for apoptosis induction, was markedly higher in the HIV-1 infected cells following IR treatment. Exposure of HIV-1 infected humanized mice with undetectable viral RNA level to IR resulted in a significant increase of HIV-1 RNA in plasma, lung and brain tissues. Collectively, these data point to the use of low to moderate dose of IR alone or in combination with HIV-1 transcription activators as a potential application for the "Shock and Kill" strategy for latently HIV-1 infected cells.

Sequence-Specific Modifications Enhance the Broad-Spectrum Antiviral Response Activated by RIG-I Agonists.

UNLABELLED: The cytosolic RIG-I (retinoic acid-inducible gene I) receptor plays a pivotal role in the initiation of the immune response against RNA virus infection by recognizing short 5'-triphosphate (5'ppp)-containing viral RNA and activating the host antiviral innate response. In the present study, we generated novel 5'ppp RIG-I agonists of varieous lengths, structures, and sequences and evaluated the generation of the antiviral and inflammatory responses in human epithelial A549 cells, human innate immune primary cells, and murine models of influenza and chikungunya viral pathogenesis. A 99-nucleotide, uridine-rich hairpin 5'pppRNA termed M8 stimulated an extensive and robust interferon response compared to other modified 5'pppRNA structures, RIG-I aptamers, or poly(I·C). Interestingly, manipulation of the primary RNA sequence alone was sufficient to modulate antiviral activity and inflammatory response, in a manner dependent exclusively on RIG-I and independent of MDA5 and TLR3. Both prophylactic and therapeutic administration of M8 effectively inhibited influenza virus and dengue virus replication in vitro. Furthermore, multiple strains of influenza virus that were resistant to oseltamivir, an FDA-approved therapeutic treatment for influenza, were highly sensitive to inhibition by M8. Finally, prophylactic M8 treatment in vivo prolonged survival and reduced lung viral titers of mice challenged with influenza virus, as well as reducing chikungunya virus-associated foot swelling and viral load. Altogether, these results demonstrate that 5'pppRNA can be rationally designed to achieve a maximal RIG-I-mediated protective antiviral response against human-pathogenic RNA viruses. IMPORTANCE: The development of novel therapeutics to treat human-pathogenic RNA viral infections is an important goal to reduce spread of infection and to improve human health and safety. This study investigated the design of an RNA agonist with enhanced antiviral and inflammatory properties against influenza, dengue, and chikungunya viruses. A novel, sequence-dependent, uridine-rich RIG-I agonist generated a protective antiviral response in vitro and in vivo and was effective at concentrations 100-fold lower than prototype sequences or other RNA agonists, highlighting the robust activity and potential clinical use of the 5'pppRNA against RNA virus infection. Altogether, the results identify a novel, sequence-specific RIG-I agonist as an attractive therapeutic candidate for the treatment of a broad range of RNA viruses, a pressing issue in which a need for new and more effective options persists.

Nucleic acid agonists for Toll-like receptor 7 are defined by the presence of uridine ribonucleotides.

Toll-like receptor 7 (TLR7) mediates innate responses by responding to viral RNA in endocytic compartments. However, the molecular pattern recognised by TLR7 and whether it differs between RNA of viral and self origin remains unclear. Here, we identify nucleic acids that act as TLR7 agonists for mouse and human cells. We show that uridine and ribose, the two defining features of RNA, are both necessary and sufficient for TLR7 stimulation, and that short single-stranded RNA (ssRNA) act as TLR7 agonists in a sequence-independent manner as long as they contain several uridines in close proximity. Consistent with the notion that TLR7 lacks specificity for sequence motifs, we show that it is triggered equally efficiently by viral or self RNA delivered to endosomes. Our results support the notion that TLR7 recognises uracil repeats in RNA and that it discriminates between viral and self ligands on the basis of endosomal accessibility rather than sequence.