Development of proteomics-based approaches and theraputics to identify and target RET kinase protein in lethal prostate cancer

Abstract

Neuroendocrine prostate cancer (NEPC) is a subtype of metastatic castration resistant prostate cancer (mCRPC). It arises as a resistance mechanism to second generation androgen deprivation therapy (ADT). Platinum-based chemotherapy is often indicated as first-line treatment, however, they only provided minimal benefit. Therefore, there is a need to identify new therapeutic targets for NEPC and stratify patients for personalized medicine. Our lab has found that RET protein could serve as a potential therapeutic target for NEPC. RET is a receptor tyrosine kinase, which is often translocated or mutated in lung cancer and in different subsets of neuroendocrine tumors. We found that RET mRNA levels were elevated in mCRPC patients with a NEPC phenotype and in NEPC patient-derived xenografts (PDXs) compared to adenocarcinoma samples. There are two new FDA-approved RET inhibitors, and these therapies show efficacy in cancers such as papillary thyroid cancer and non-small cell lung cancer with RET fusions. We would like to expand the scope of these studies to prostate cancer and identify mCRPC patients that will potentially benefit from RET inhibition therapy. To do that, I propose using targeted mass spectrometry to identify patients with high abundance of RET protein in circulating tumor cells (CTCs). I hypothesize that liquid biopsy-based detection of RET kinase protein will aid in the stratification of patients with mCRPC. I have identified 10 candidate RET peptides that perform well on the mass spectrometer. Future studies will include evaluating these peptides for their ability to detect endogenous RET protein in pre-clinical and clinical samples. To identify new RET inhibitors, I also evaluated the effects of novel RET inhibitors on RET activity and its downstream signaling in NEPC cell line models. Novel RET inhibitors were able to reduce the activity of RET, AKT, and ERK phosphorylation. In addition, a mechanistic study also revealed the role of ASCL1 on RET in prostate cancer. These results are aimed to build the needed tools that support the hypothesis that RET is important for the survival of NEPC tumors and assessing RET expression will aid in the treatment of mCRPC/NEPC patients.