Regulation of normal and cancer cells as a base for cell cycle-targeted therapy

Abstract: The majority of current treatments used for treatment of prostate cancer (PCa) and leukemia are often limited to a narrow subsets of treated patients. As such, there still remains a significant scope for gaining deeper understanding of molecular mechanisms underlying cancer metastasis for improvement of targeted treatment. Elevated expression of a cell cycle regulator cyclin A1 initiated leukemia in transgenic mice and also promoted metastasis of prostate cancer cells in xenograft mouse model. Cyclin A1/CDK1 complexes play an essential role in G2/M cell cycle transition in male germ cells. My thesis work is focused on several specific aims: i) to investigate whether promoter methylation patterns in several key cellular regulators are altered in leukemic cells; ii) to elucidate cyclin A1 function in normal hematopoietic stem and progenitor cells (HSPC) and their interaction with stem cell niches; iii) to study the role of cyclin A1 in proliferation and treatment response of cancer stem cells; iv) to study the role of CDK1, a major kinase partner of cyclin A1, in treatment response of leukemic cells. In these studies we used patient materials, cancer cell lines, and knockout and xenograft mouse models. We show that promoter methylation patterns are changed in several key genes, in particular p16 in leukemic cells compared to their normal counterparts, and that such epigenetic changes are also associated with treatment response to therapeutic drugs. Next, we show that cyclin A1 function is required for HSPC to home to and interact with niche regions under steady state condition and upon γ-irradiation treatment. The regulation of HSPC numbers and their interaction with the niches by cyclin A1 are critical for protection of the bone marrow from injury. We further show that the introduction of cyclin A1 overexpression promotes expansion of ALDH-positive population representing cancer stem cells in cell lines, increase their ability to form tumor spheres in vitro, and to metastasize in xenograft mice. Overexpression of cyclin A1 reduced sensitivity of ALDH-positive population within PCa cells to avastin and docetaxel combination treatment. Finally, we show that cyclin A1 associated CDK1 and its associated network proteins in particular RARγ are responsible for cell cycle progression through G0/G1 and G2/M phases. CDK1 and RARγ function are required to facilitate ATRA-effect on leukemic cells. Our findings unravel cellular mechanism underlying proliferation and survival of normal stem cells and cancer stem cells under steady state condition and upon treatment. Our novel findings shield light for designing novel treatment strategies to overcome drug-resistance of cancer cells.