Protein turnover in pancreatic tumors is much higher than in normal tissues due to both unchecked proliferation and ongoing adaptive pressures. Coincident with this, normal controls on both protein synthesis and degradation are often found deregulated. Recently, the development of small molecules that block proteosomal degradation have been found to be efficacious in a number of cancers but surprisingly not in pancreatic cancer. Perhaps the reason for this is the dismal half-life of these drugs/metabolites in patients thus limiting drug efficacy to predominantly hematological malignancies. Therefore, inhibitors that possess better pharmacologic characteristics are needed. It is feared however, that increased half-life of drugs targeting the 26S proteosome will have greater systemic toxicity in a variety of potentially sensitive organs. Therefore, an ideal protein degradation antagonist would have good pharmacologic properties and would not target global protein degradation, but instead would selectively target the degradation of proteins that are key for tumor growth or therapeutic resistance. Recently, a large multi-subunit complex termed the COP9 Signalosome (CSN) that regulates cullin-dependent degradation of proteins has become of interest in tumor biology as cullins regulate multiple oncogenic pathways. Theoretically, by therapeutically targeting such a """"""""node"""""""", a large portion of the oncogenic network could be deregulated without many of the anticipated side effects generated by drugs that directly target the 26S proteosome. Recently, we have developed multiple lead compounds against the catalytic portion (CSN5) of the COP9 Signalosome (CSN). Specifically targeting CSN5 genetically or pharmacologically results in deneddylation of cullins, stabilization of their substrates, cell cycle arrest and severely compromised clonogenic growth in pancreatic adenocarcinoma cells. The same treatment in normal cells results in delayed proliferation but virtually no changes in clonogenic potential suggesting that this is a viable therapeutic paradigm. Goal: We will further examine the anti-tumorigenic effects of CSN disruption using genetic and pharmacologic testing of CSN5 both in vitro and in murine models of human lung cancers. These experiments will serve as a basis for pre-clinical trials and optimization of further therapeutics.
The COP9 Signalosome (CSN) controls the stability and function of Cullin-dependent ubiquitin E3 ligases. These ligases in turn control the stability of proteins in multiple oncogenic pathways. Using structure-based modeling, we have recently developed multiple lead CSN5 antagonists possessing specific activity toward the CSN and having significant effects on clonogenic growth. This proposal seeks to further characterize these inhibitors both in vitro and in vivo as a prelude to evaluating their efficacy in clinical trials.
|Finger, Elizabeth C; Castellini, Laura; Rankin, Erinn B et al. (2015) Hypoxic induction of AKAP12 variant 2 shifts PKA-mediated protein phosphorylation to enhance migration and metastasis of melanoma cells. Proc Natl Acad Sci U S A 112:4441-6|