PROJECT SUMMARY / ABSTRACT Although next-generation androgen receptor (AR)-targeted therapies have increased survival in prostate cancer patients, recent studies reveal that exposure to these therapies result in transdifferentiation to an aggressive neuroendocrine (NE) phenotype in nearly one fifth of cases. The molecular determinants of lineage plasticity in prostate cancer are poorly understood, and there is an unmet need for non-invasive methods to study the emergence of treatment-induced lineage plasticity over time. Our team at the Massachusetts General Hospital (MGH) recently developed a novel microfluidic chip, the LPCTC-iChip, for the high-throughput isolation of circulating tumor cells (CTCs) from an entire leukapheresis product, thus providing a non-invasive alternative to serial tumor biopsies for real-time molecular profiling. In this extramural-intramural collaborative patient-centric translational research project, we propose to incorporate the LPCTC-iChip into an NCI intramural clinical trials to investigate NE transdifferentiation in prostate cancer. The overall objective of this application is to gain insight into the temporal development, molecular determinants, and clinical impact of NE transdifferentiation by analyzing CTCs in comparison to matched tumor biopsies from prostate cancer patients in a chemoimmunotherapy trial at the NIH Clinical Center. Our central hypothesis is that CTC analyses can capture the dynamic lineage state of prostate cancers during and after therapy, and that immune responses can delay the clinical impact of the NE phenotype. To attain the overall objective, the following three specific aims will be pursued: 1) Evaluate matched CTCs and metastatic biopsies from patients with heavily pre-treated metastatic castration- resistant prostate cancer for hallmarks of NE phenotype; 2) Evaluate serial CTCs in patients with metastatic castration-sensitive prostate cancer for NE transdifferentiation during therapy; and 3) Determine the association between immune responses, NE phenotype, and clinical outcomes. The LPCTC-iChip will be physically placed at the NIH Clinical Center, and serial CTCs and matched biopsies from mCRPC and mCSPC patients enrolled in the chemoimmunotherapy study of M7824+M9241+docetaxel (NCT04633252) will be analyzed for genomic, transcriptional, and protein markers of the NE phenotype. The proposed research is innovative because it utilizes a novel microfluidic device, the LPCTC-iChip, for the isolation of CTCs to interrogate a highly relevant problem in prostate cancer. The research is significant because it is expected to provide a non-invasive alternative to tissue biopsy for monitoring treatment- induced lineage plasticity, as well as provide a strong scientific framework for the design of future clinical trials to prevent and treat lethal NE phenotype prostate cancers. This intramural-extramural collaboration leverages unique resources from MGH and NCI to understand an important disease process, NE transdifferentiation, with implications for prostate cancer treatment monitoring and therapy.

PROJECT NARRATIVE The proposed research is relevant to public health because it will lead to the development of clinically useful biomarkers for therapeutic monitoring of prostate cancer, as well as a better understanding of lineage plasticity in prostate cancer. These advances are expected to ultimately lead to improvements in the treatment of patients with prostate cancer. Thus, the proposed research is relevant to the part of the NCI’s Scientific Priorities that pertains to treating cancer.