UC Riverside

Tumorigenesis is often associated with abnormal levels of specific oncogenes, that drive proliferative and other cancer hallmark signaling events, such as for example resistance to apoptosis. Hence, modern targeted therapeutic strategies include devising agents that can suppress the function of such oncogenes, either by potent and selective inhibition, or by inducing oncogene degradation. My thesis work focused on developing novel strategies for the design of potent, selective, and irreversible anti-cancer agents. I deployed these strategies against two cancer-relevant targets, namely the protein hMcl-1, which is involved in the activation of oncogenic signaling and resistance to apoptosis in cancer cells, and the prolyl cis-trans isomerase PIN1, which stabilizes several oncogenes in cancer cells.One particularly attractive approach is the design of irreversible inhibitors, which provides a significant pharmacodynamic and pharmacokinetics advantages over reversible drugs. Indeed, in the past decade several FDA-approved therapeutics in oncology are irreversible and target a thiol group on binding site cysteine (Cys) residues. However, this target space is limited given that Cys is a relatively rare amino acid. Hence, my thesis work focused on exploring novel electrophiles that could target other more frequently occurring nucleophilic amino acids such as lysine (Lys) or histidine (His) to obtain irreversible drug candidates. A second exciting and innovative avenue to derive potent and effective agents consists in the design of ligands that, acting like “molecular crowbars”, can displace intramolecular interactions resulting in target destabilization and subsequent recognition by the ubiquitin-proteasome degradation machinery in cell. Our studies show that this novel design strategy could identify potential drug candidates that induce the degradation of the target, rather than its inhibition. Hence, similar to covalent inhibitors, those agents act irreversibly on the given target. Central to these ligand design strategies and characterizations, I deployed several biophysical techniques to guide the identification and iterative characterizations of lead candidates. Hence, the work entailed integrating iterative synthetic medicinal and combinatorial chemistry with accurate measurements of ligand binding events, binding kinetics, and thermodynamics, based on solution NMR spectroscopy, isothermal titration calorimetry, denaturation thermal shift measurements, mass spectrometry, biochemical assays, electrophoresis, and X-ray crystallography. Finally, cellular pharmacology studies with human cancer cell lines were also conducted to verify that the optimized agents act in cell with the intended mechanism. In summary, my thesis work provides not only innovative frameworks and strategies for the design of potent and selective pharmacological tools, but also resulted in possible lead candidates that could form the basis for the development of novel anti-cancer therapeutics.