Slow-Cycling, Treatment-Resistant Cancer Stem Cells of Colorectal Cancer.
Michal Kamionek, Nathan Moore, Karen Dresser, Stephen Lyle. University of Massachusetts Medical School, Worcester
Background: Cancer stem cells are a subpopulation of cancer cells with stem cell properties that are thought to drive tumor growth, resistance to therapy and recurrence. One important property of normal adult stem cells is their quiescent, slow-cycling nature that helps them survive chemotherapy and radiotherapy. This property may also allow cancer stem cells to survive current treatment regimens and consequently leads to recurrence. Our study was designed to isolate slow-cycling cancer cells, identify key regulatory genes and determine cancer stem cell survival after chemo- and radiotherapy.
Design: Colon cancer cell line (HCT116) and primary cancer tissue was labeled with the metabolically activated dye, Carboxyfluorescin succinimidly ester (CFSE), and injected into immunocompromised mice to generate tumor xenografts. After 2-4 weeks of chase period xenograft tissues were harvested and labeled CFSE-positive and negative cells were isolated by fluorescence-activated cell sorting (FACS). RNA was harvested and used for RNA expression analysis. Several genes showed consistent up-regulation in quiescent cancer stem cells among the different tumors. Twenty specimens of colorectal cancer, status post chemo- and radiotherapy, paired with pretreatment initial biopsy were selected from the surgical pathology files of the Dept. of Pathology. Selected blocks with most representative cancer sample and pretreatment biopsy were examined by immunohistochemistry for expression of up-regulated genes p16 and CDK5R1, as well as described stem cell markers, CD44 and CD24. Dworak tumor regression rate was recorded for each post-treatment specimen to determine association of regression with protein expression.
Results: There was an increased population of cancer cells showing expression of p16 and CDK5R1 in residual, post-treatment tumors compared with pretreatment biopsies. No significant changes were observed in expression of purported stem cell surface markers CD44 and CD24. Tumors with low Dworak regression scores tended to have higher expression of p16 in the pretreatment biopsy while tumors with extensive regression showed lower initial staining and increased staining of residual tumor cells.
Conclusions: Expression levels of p16 and CDK5R1 are up-regulated in slow-cycling, CFSE-label retaining cancer stem cells. There is enrichment of p16 and CDK5R1-positive cancer cells after chemo- and radiotherapy suggesting that these genes may enhance the chemo-/radio-resistance of cancer stem cells.
Wednesday, March 2, 2011 9:30 AM
Poster Session V # 40, Wednesday Morning