Date of Graduation
Doctor of Philosophy (PhD)
Brain metastasis, which frequently arises from breast cancer, lung cancer, melanoma, and colorectal cancer, remains a severely unmet medical need and its incidence continues to rise while treatment options remain palliative. To better understand the biology underlying its aggressive, incurable nature, I performed an unbiased in vivo kinome screen to identify potential driver kinases of experimental brain metastasis in a nude xenograft model using the human breast cancer cell line MDA-MB-231. Several of the kinase pools led to decreased brain metastasis-specific survival in nude mice, shortening survival time by up to 50% relative to controls. Targeted next-generation sequencing (NGS) was performed to analyze pre- and post-injection MDA-MB-231 cells, thus identifying 31 kinases that were significantly enriched in multiple animals. To validate the clinical relevance of these potential targets, kinase expression was analyzed in a collection of 32 clinical breast cancer, lung cancer, and melanoma brain metastases by RNA sequencing (RNA-seq); all but two of the kinases were expressed in brain metastases from all three types of primary tumor. Based on its enrichment in vivo and high expression in brain metastasis across cancer types, I chose to focus on PCTK1 as a potential driver. PCTK1 is expressed during spermatogenesis and neuronal differentiation but reports of its roles in cancer are limited. While overexpression of PCTK1 in MDA-MB-231 cells did not affect proliferation under routine cell culture conditions, it led to a faster rate of brain metastasis growth and thereby decreased mouse survival time by 75%. The Cancer Genome Atlas (TCGA) data analysis revealed a potential link between PCTK1 expression and glutamine metabolism and I demonstrated that the growth advantage conferred by PCTK1 was due to increased glutamine consumption by the cancer cells. Knockdown of PCTK1 in the brain metastatic HCC1954Br breast cancer cell line increased mouse survival time in an experimental brain metastasis model, indicating that PCTK1 may indeed represent a potential therapeutic target for brain metastasis. In conclusion, this study identified PCTK1 as a novel driver of brain metastasis and exposed a means of cancer cell survival in the nutrient-restricted brain.
Cancer metastasis, brain metastasis, functional genomics, in vivo screen