Abstract LB-285: Regulation of therapy resistance in slow-cycling cancer cells

Abstract

Abstract Tumor recurrence after chemotherapy is a major cause of patient morbidity and mortality. Recurrences are thought to be due in part to small subsets of cancer cells that are better able to survive traditional forms of chemotherapy and thus drive tumor re-growth. The ability to isolate and better characterize these therapy-resistant cells is critical for the future development of targeted therapies aimed at achieving more robust and long-lasting responses. Slow-cycling stem cells are integral components of adult epithelial tissues and are required for tissue maintenance. These slow-cycling cells are inherently resistant to traditional forms of chemotherapy that primarily target actively cycling cells. Using a novel application for the proliferation marker CFSE, we have identified populations of slow-cycling, label-retaining cells (LRCs) in primary tumors and cancer cell lines. As predicted, quiescent LRCs exhibit a multi-fold increase in chemoresistance but retain the ability to re-enter the cell cycle. We further demonstrate the innovative application of CFSE to live sort slow-cycling tumor cells and begin to explore the mechanisms behind LRC resistance and survival. Using RT-PCR and immunoblotting, we have observed consistent over-expression of the CDK5 activator, p35, in LRCs of both primary tumor xenografts and in-vitro sphere cultures. While p35 is known to play an active role in neurogenesis, cell migration, and apoptosis within the developing brain, its role in tumor biology remains unclear. Manipulation of p35 expression affects cell cycle distribution, extent of the LRC pool, and cell survival when challenged with traditional forms of chemotherapy. Additionally, we demonstrate that alterations in p35 expression alters downstream CDK5 signaling and the activation state of BCL2. Combined, our data suggest a model whereby the CDK5/p35 complex acts to slow cell cycling speed and change expression of BCL2, promoting resistance to chemotherapy. Future p35 targeting, in combination with traditional forms of chemotherapy, may help to reduce recurrence rates and increase long-term patient survival. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-285. doi:1538-7445.AM2012-LB-285