PROJECT SUMMARY/ABSTRACT
In accordance with RFA-AI-19-072, Novel Therapeutics Directed to Intracellular HIV Targets, we propose using
targeted protein degradation (TPD) against the essential HIV reverse transcriptase (RT). The RFA states
“Controlling protein function by controlling intracellular protein levels has evolved as a promising and novel
therapeutic strategy. This can be achieved by the targeted degradation of intracellular proteins thru the ubiquitin-
proteasome pathway.” Heterobifunctional targeted protein degraders (TPDs) are being actively pursued as
enhancers of proteasomal destruction of proteins specifically associated with several cancers. Such agents offer
advantages over traditional occupancy-based inhibitors including a unique catalytic mechanism of action, greater
target selectivity, and a reduced probability for resistance development. Surprisingly, this promising therapeutic
modality has only recently been applied to antiviral drug discovery through a successful Telapravir-based TPD
effective against the wild type and resistant forms of the HCV protease. Analysis of reported HIV-1 drug-bound
structures suggests that the essential viral RT should be readily adaptable to targeted protein degradation. The
potent and clinically used HIV-1 RT inhibitor (RTI), Rilpivirine (RPV) binds the RT site in Gag-Pol and also
allosterically inhibits p66/p51 RT function by binding the non-nucleoside-RTI (NNRTI) Binding Pocket
(NNIBP) on the p66 subunit. RPV is amenable to conjugation with linkers and ubiquitin E3 ligase recruiting
ligands to serve in the design and preparation of prototype HIV-1 RT TPDs. The OBJECTIVE of this study is to
show proof-of-concept of a new inhibitory mechanism by which HIV-1 RT can be targeted for degradation,
impairing HIV infectivity and replication. Importantly, due to TPDs’ unique mechanism of action, even a low-
affinity RT/TPD interaction will likely lead to effective target degradation. Thus, we pose the HYPOTHESIS that
RPV-based TPDs will not only augment inhibition against HIV-1 with RTI-sensitive RT but will remain effective
against RTI-resistant RT variants. Ultimately, this approach can reduce resistance development and potentially
extend regimen lifetimes in the fight against HIV disease. The objective of AIM 1 is to design and prepare RPV-
based TPDs built on state-of-the-art computational methods and predictive physicochemical properties currently
accepted for in vivo active TPDs. In AIM 2, we will screen the two series of TPDs for antiviral activity in
complementary in vitro models of HIV-1 single-round infection (in the TZM-bl assay), and of replication (in primary
CD4+ T lymphocytes). The IMPACT of the discovery of targeted HIV-1 RT degraders that limit infectivity and
replication through a mechanism distinct from occupancy-based HIV-1 RTIs will be the identification of agents
that are effective against RTI-resistant HIV strains and that limit RTI susceptibility to viral resistance
development. Grandly, this research will demonstrate that TPD approaches can be superior in the treatment of
HIV disease and will set the stage for the advancement of TPDs against other HIV targets with improvements in
the prevention of resistance development and with concomitant enhanced clinical treatment outcomes.
