Targeting the Pim 1 Protein Kinase to Overcome Resistance to AKT Inhibitors

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DESCRIPTION (provided by applicant): The success of targeting signal transduction pathways for the development of new prostate cancer therapies has been limited to date by the subsequent development of drug resistance mechanisms. Highly activated AKT protein kinase found in almost 70% of cases of metastatic prostate cancer are an important target for therapies in this disease. Preliminary data in this proposal demonstrate that the addition of AKT inhibitors to prostate cancer cell lines induces a marked increase in cell surface receptor tyrosine kinases (RTKs) that function to limit the activity of these inhibitors by increasing cellular AKT activity. Importantly, it is also demonstrated that AKT inhibitors induce the Pim-1 protein kinase, an enzyme that has been implicated in prostate cancer initiation and progression. Investigators at the Medical University of South Carolina have discovered that knocking down Pim-1 either by siRNA or genetically engineered mouse fibroblasts will inhibit the ability of AKT inhibitors to induce RTKs. Using a small molecule Pim-1 inhibitor developed by this team of investigators, they have demonstrated that the combination of an AKT and Pim-1 inhibitor synergistically blocks prostate cancer cell growth in tissue culture and soft agar, and markedly inhibits the growth of tumors in immunosuppressed animals. These exciting results lead to the unique hypothesis that AKT inhibitor treatment causes a Pim-1-directed feedback loop that induces RTKs. Thus, the combination of an AKT and Pim inhibitor likely will synergize to kill prostate cancer. The specific aims in this proposal are to enhance the ability to target both of these pathways by: 1) understanding the mechanism by which AKT inhibitors induce Pim-1; 2) deciphering how Pim-1 modulates RTK levels and how inhibition of Pim-1 suppresses these growth factor receptors; and 3) validating this hypothesis in genetically engineered animal models and exploring the activity of this combination in killing prostate cancer grown in mice. These studies will identify RTK and induced-Pim-1 levels as intermediate markers of drug action. The proposed study designs will make use of genetically engineered cell culture models, mRNA expression analysis, chromatin immunoprecipitation, and a novel tissue recombination model. When completed, these studies will markedly accelerate the development of combination therapies with Pim and AKT inhibitors to target feedback resistance mechanisms that would control responses to single agent therapies currently under investigation for the treatment of prostate cancer.