Targeting Enzymes Involved in Protein Translation and Quality Control as Potential Cancer Therapeutics

Abstract

Activation of pathways resulting in an overexpression of oncoproteins, reliant on cap-dependent translation, or mutations of key proteins in a pathway can be advantageous to cancer cells but creates heightened protein quality control pressure. Because of this, there has been an interest in targeting enzymes involved in protein synthesis and protein quality control: such as the eukaryotic initiation factor, eIF4A, a DEAD-box RNA helicase involved in translation initiation, and p97, an AAA+ chaperone involved in protein quality control. Despite some successes in discovering both eIF4A and p97 inhibitors, many of these compounds have pharmacological setbacks. The work in this dissertation defines new inhibitors of eIF4A and p97 with unique mechanisms of action. As described in chapter 2, we demonstrated that a marine-derived sesquiterpene, elatol, can modulate the ATPase activity of eIF4A. We provide further evidence that this molecule inhibits cap-dependent translation. Because there is no clear consensus on the mechanism of action for elatol, we hypothesized that the mechanism of toxicity attributed to elatol is likely through inhibition of cap-dependent translation initiation by targeting eIF4A. In chapter 3, we adapted a colorimetric assay to identify natural products that modulate the ATPase activity of p97 from which withaferin A (WFA) was identified. Because proteostasis modulation can connect each of the reported modes of action of WFA, we hypothesized that the primary mode of cytotoxic action of WFA is through inhibition of protein quality control machinery. Through medicinal chemistry efforts, we were able to improve WFA's biochemical and cellular activities as well as shifting the activity toward p97 and away from the proteasome. The work described in chapter 4 reports that dehydrocurvularin (DHC) and its chlorinated analogs are covalent modifiers of p97 and that the selectivity toward p97 can be attributed, in part, to the electronic effects of the chlorines. Taken together, this work highlights the significance of targeting protein translation and quality control, by modulation of eIF4A and p97 activity respectively, as promising anticancer therapeutics.