Dissecting the intrinsic and extrinsic regulators of prostate cancer dormancy in the bonemicroenvironment.

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Project Summary / Abstract………………………………………………………………………………..…. Metastatic prostate cancer (PC) typically manifests in the skeleton. The lesions arise from disseminated tumor cells (DTCs) that often persist in a dormant state for months to decades after initial primary tumor treatment. Despite our knowledge that DTCs give rise to incurable bone metastatic PC, there remains gaps in our understanding as to the molecular mechanisms underpinning entry and reawakening from the dormancy program. Insight into those mechanisms could yield new therapeutic approaches that would prevent the metastatic relapse and ultimately death of almost 34,500 American men each year. To address this, we have developed a novel model of PC dormancy in agreement with published markers in the literature in vitro and optimized a surgical technique to study dormancy in vivo. We next performed transcriptomic sequencing on PC cells growing under normal, dormant, or reawakening conditions. Bioinformatic analysis of transcript expression and transcription factor (TF) activity revealed positive regulatory domain zinc finger region protein 16 (PRDM16) to significantly increase during entry into dormancy and decrease during exit across mouse (RM1) and human sensitive / castrate resistance cell lines (LAPC4, 22Rv1). Further, we validated PRDM16 upregulation in dormant cells on the protein level both in vitro and in vivo. Genetic silencing of PRDM16 led to a significant reduction in the ability of PC cells to enter dormancy concomitant with decreased expression of anti-apoptotic proteins including BCL-2 and increased pro-apoptotic proteins such as BIM & Noxa. Preliminary data shows that PRDM16 expression in PC cells can be induced by BMP-7 and conversely decreased by the BMP signaling antagonist, noggin, factors with known critical roles in regulating bone homeostasis. Based on our findings, we hypothesize that BMP7 induces PRDM16 expression in early skeletal DTCs, which is critical for the initiation of the dormancy program. In the F99 phase, we will identify PRDM16 transcriptome in PC dormancy and confirm BMP signaling control on its expression using genetic approaches and validation of findings in pre-clinical models. In K00 phase, we will study how aging contribute to the reawakening of dormant cancer cells in the bone microenvironment. We will identify biological and molecular determinants of cancer dormancy using Cherry-niche technology and comprehensive fluorescence-activated cell sorting (FACS), high dimensional mass cytometry, and single cell RNASeq experiments. We will then validate our findings in pre-clinical models and patient tissue sections. Findings from this work will advance our understanding of the intrinsic and extrinsic factors regulating the cancer dormancy program in skeletal metastasis in the context of aging, which is relevant to most prostate cancer patients.