Phosphoproteomic Assessment of Therapeutic Kinases for Personalized Therapy in Castration-Resistant Prostate Cancer

Scientific Objective and Rationale: Prostate cancer is a leading cause of cancer morbidity and mortality in the United States. Early stage prostate cancer is dependent on androgens for survival. Men diagnosed with aggressive prostate cancer initially respond well to hormonal (anti-androgen) therapies resulting in tumor shrinkage, but eventually these patients develop recurrence, leading to an aggressive form of the disease termed castration-resistant prostate cancer (CRPC). The development of new anti-androgen therapies has provided some survival benefit in CRPC patients, but new treatment approaches are greatly needed. Through collaborative basic and translational research, we must advance our understanding of the biological mechanisms that drive progression to CRPC in order to develop novel therapies. As resistance to anti-androgen agents becomes more common, androgen receptor (AR) independent pathways such as kinase signaling need to be considered as new therapeutic options. Our initial analysis indicates that non-mutated signaling proteins known as kinases are significantly elevated in CRPC but not in early prostate cancer, suggesting that the activation of specific kinase signaling pathways may be important for disease progression. To identify these kinases, our group has characterized kinase activation states encompassing tyrosine, serine, and threonine kinases in lethal metastatic CRPC samples obtained at autopsy. Several druggable kinases have been identified, and importantly, the total pattern of kinases activated in each patient's tumor is often different, which underscores the heterogeneous nature of the disease and the need for patient stratification and individualized therapies. In this proposal, we plan to (1) develop a panel of kinase phosphopeptide standards that behave as surrogates for activated kinases, are targets of Food and Drug Administration-approved kinase inhibitors, and can be measured using targeted mass spectrometry approaches, (2) use targeted mass spectrometry approaches to establish robust quantitative measurements of these druggable kinases in preclinical and clinical tissues, and (3) measure the druggable kinases in clinical biopsy-sized metastatic CRPC tissues as a preliminary evaluation of patient-specific kinase activation states that may lead to personalized therapy opportunities. Clinical Applications: The measurement of several kinase activation states simultaneously using targeted mass spectrometry in preclinical and clinical tissues will uncover kinase-dependent mechanisms by which prostate cancer achieves hormone-independent growth. The results of our studies will provide a blueprint for the evaluation of a large panel of druggable, activated kinases that may lead to the identification of novel combinations of kinase activities for co-targeting in aggressive prostate cancer. Activated kinases identified from patient tumors could then be immediately targeted by available clinical kinase inhibitors as a means for personalized therapies. If this strategy proves effective, we hope to achieve broad benefits in patient-related outcomes within the next 5 years for patients with advanced prostate cancer.