The proteasome is a vital cellular machine that maintains protein homeostasis, which is of particular importance in multiple myeloma and possibly other cancers. Targeting proteasome 20S peptidase activity with bortezomib and carfilzomib has been widely used to treat myeloma. However, not all patients respond, and those that do eventually suffer relapse. Therefore, there is an urgent and unmet need to develop novel drugs that target proteostasis through different mechanisms. We identified quinoline-8-thiol (8TQ) as a first-in-class inhibitor of the proteasome 19S subunit Rpn11. A derivative of 8TQ, capzimin, shows >5-fold selectivity for Rpn11 over the related JAMM proteases and >2 logs less activity towards metalloenzymes. Capzimin stabilized proteasome substrates, induced an unfolded protein response, and blocked proliferation of cancer cells, including those resistant to bortezomib. Proteomic analysis revealed that capzimin stabilized a subset of polyubiquitinated substrates. Identification of capzimin offers an alternative path to develop proteasome inhibitors for cancer therapy.
Highlights d We identified an allosteric inhibitory site for an activating enzyme d The lead compound inhibits the ATP-dependent step of SUMO E1 catalysis d The compound has specificity to 1 out of 18 non-disulfide bonded Cys residues d The compound increased miR-34b and reduced c-Myc in cellular and xenograft models
The hematopoietic protein tyrosine phosphatase (HePTP) is implicated in the development of blood cancers through its ability to negatively regulate the mitogen-activated protein kinases (MAPKs) ERK1/2 and p38. Small-molecule modulators of HePTP activity may become valuable in treating hematopoietic malignancies such as T cell acute lymphoblastic leukemia (T-ALL) and acute myelogenous leukemia (AML). Moreover, such compounds will further elucidate the regulation of MAPKs in hematopoietic cells. Although transient activation of MAPKs is crucial for growth and proliferation, prolonged activation of these important signaling molecules induces differentiation, cell cycle arrest, cell senescence, and apoptosis. Specific HePTP inhibitors may promote the latter and thereby may halt the growth of cancer cells. Here, we report the development of a small molecule that augments ERK1/2 and p38 activation in human T cells, specifically by inhibiting HePTP. Structure-activity relationship analysis, in silico docking studies, and mutagenesis experiments reveal how the inhibitor achieves selectivity for HePTP over related phosphatases by interacting with unique amino acid residues in the periphery of the highly conserved catalytic pocket. Importantly, we utilize this compound to show that pharmacological inhibition of HePTP not only augments, but also prolongs activation of ERK1/2 and, especially, p38. Moreover, we present similar effects in leukocytes from mice intraperitoneally injected with the inhibitor at doses as low as 3 mg/kg. Our results warrant future studies with this probe compound that may establish HePTP as a new drug target for acute leukemic conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.