Role of the epithelial-to-mesenchymal transition (EMT) on circulating tumor cell (CTC) and metastasis biology in prostate cancer
Abstract
Prostate cancer is the second leading cause of cancer-related deaths in American men. Most of these deaths occur as the result of metastasis, which is associated with an epithelial-to-mesenchymal transition (EMT). EMT leads to greater migratory/invasive capacity and resistance to therapy. During metastasis and associated EMT, cancer cells shed from the primary tumor and disseminate throughout the body as circulating tumor cells (CTCs) in the bloodstream. CTCs have been correlated with increased metastatic disease, reduced survival, and therapy response/resistance. Assessing CTCs presents an opportunity to study cancer progression/treatment effectiveness from a blood test. However, outstanding questions regarding CTCs and EMT has resulted in hesitation in the clinical adoption of CTCs. This thesis aimed to gain a greater understanding of the functional role of EMT in CTC generation, detection, and metastatic behavior in prostate cancer. We converged available CTC isolation technologies to develop protocols for EMT-independent isolation and molecular analysis of CTCs in pre-clinical mouse and human samples. We compared the effectiveness of CellSearch® and Parsortix® for analyzing CTCs in prostate cancer patients and observed that both technologies were equally effective at enumerating CTCs across the clinical spectrum of prostate cancer metastasis. This resulted in identification of 24 genes whose altered expression in patient CTCs may be influencing disease progression, including several related to EMT. We then investigated how EMT affects cell morphology, phenotype, and marker expression by knockdown of the EMT-inducing transcription factor Zeb1 in mesenchymal prostate cancer cells using shRNA (Zeb1KD cells). We observed an aggressive partial (p-EMT) phenotype in Zeb1KD cells compared to controls, which was mitigated by treatment with the demethylating drug 5-azacytidine. Lastly, we identify a unique panel of p-EMT markers for aggressive disease using methylation chip analysis. This research provides the groundwork for increasing future accessibility of CTC liquid biopsies for prostate cancer patients of any disease stage and/or EMT status, thus allowing a greater number of patients to benefit from a personalized medicine approach to combating disease progression and improving outcomes.