Despite effective antiretroviral therapy (ART), latent proviruses can reinitiate viral production upon cellstimulation or treatment interruption. The viral Tat protein enhances transcript elongation from the HIV-1promoter, controlling the switch between latency and active viral production. The block-and-lock functional cureaims at the transcriptional silencing of the viral reservoir, rendering suppressed HIV promoters extremely difficultto reactivate from latency. The Tat inhibitor, didehydro-cortistatin A (dCA) was used to prove this concept.Combining dCA with ART inhibits transcription and blocks viral rebound upon treatment interruption, as thepromoter becomes epigenetically repressed. dCA defines a novel class of drugs that can silence and maintaina transcriptionally inactive HIV promoter, offering a novel approach in the treatment of HIV. Tat is very attractive target for therapeutic intervention because: 1) is expressed early during virus replication;2) no cellular homologs; 3) Tat inhibitors block the feedback loop necessary for viral amplification; 4) epigeneticmodifications accumulate at the HIV promoter rendering reactivation less likely. Tat is also known for its role inneurotoxicity, blood-brain barrier disruption, and neuroinflammation. Thus, the immense interest in thedevelopment of Tat inhibitors to complement ART. The major hurdle towards advancing dCA into clinical trials is the cost of producing large quantities of thismolecule due to its complex structure. Additional clinical candidates, structurally distinct from dCA, that embodyequivalent bioactivity are needed in the pre-clinical pipeline. We optimized a cell-based Tat transactivation assay to use in high throughput screening (HTS), with dCA ascontrol. We combined appropriate counter-screens and a wealth of techniques to quickly discard small moleculesthat are not Tat specific. The HTS of 369,203 compounds was completed by Southern Research (SR), yieldingthree compounds, TT-44951, TT-44881 and TT-44863, with therapeutic index (TI) varying from 51.2 to 181.1and good chemical properties. In this application, we propose to perform hit validation and characterization ofchemically synthesized analogs generated by Thimble Therapeutics, during the compound progression pathway(CPP), to expand our panel of Tat inhibitors to commercialize this novel class of compounds. We propose thefollowing aims:Specific Aim 1. Validate Tat inhibitors based on disruption of Tat HIV-1 LTR transactivation.Specific Aim 2. Characterize the mechanism of action of selected hits. At the end of this study we expect to: (a) have identified small molecules that will specifically inhibitTat in cell-based assays; (b) have adequate metabolic stability and PK properties for futurepharmacological assessment in animal models and eventually in human clinical trials.
Public Health Relevance Statement: Project narrative: Development of novel Tat inhibitors
HIV transcription is regulated by the HIV Tat protein, but Tat inhibitors are not yet part of the clinical antiretroviral
ammunition despite their immense potential at shutting down particle production from infected cells and blocking
Tat toxicity. A high throughput drug screening of a total of 369,203 compounds was performed by Southern
Research yielding three strong leads. In collaboration with Thimble Therapeutics we now propose to validate
and characterize these compounds as well as improved chemically synthesized analogs generated during
compound progression pathway to expand our panel of Tat inhibitors for commercialization of this unique class
of compounds.
Project Terms: <(TNF)-α> | | | | 