Growth Factors Up-Regulate Epithelial Stem Cells: Treatment Strategies for Colorectal Cancers

Abstract

Colorectal-cancer is a leading cause of cancer deaths in United States. Accumulating evidence suggests that elevated progastrins (PG) increase the risk of colon carcinogenesis, however mechnaims involved remain ill-defined. Recently, cell-surface AnnexinA2 (CS-ANXA2) was discovered as a non-conventional receptor for progastrin. Therefore, the first goal was to examine whether ANXA2 expression is required to mediate proliferative/anti-apoptotic effects of progastrin on target cells. The studies in chapter 2, conclude that ANXA2 mediates growth effects of PG on target cells (including colonic-epithelial-cells), in vitro and in vivo, associated with up-regulation of stem/progenitor cell markers. Surprisingly, overexpression of autocrine PG in HEK-293 cells, imparted tumorigenic/metastatic potential to the cells (chapter 3). Based on these data, the second goal was to investigate the phenotypic differences between non-transformed and transformed stem cell using non-tumorigenic (HEK-C) and tumorigenic (HEK-mGAS) isogenic cells. The studies in chapter 3, conclude that transformed stem cells, unlike normal stem cells, co-express CS-ANXA2 with stem-cell-markers DCAMKL-1/CD44. Interestingly, CS-ANXA2 dictates morphology/growth characteristics of spheroidal growths, in vitro. The third goal was to identify cancer stem cell (CSC) marker(s), for developing targeted therapies against colon cancers. Since both DCAMKL-1/LGR5 have been reported as colonic CSC markers, the possible phenotypic/proliferative differences between DCAMKL-1+ve and LGR5+ve human colon CSCs was examined. Results in chapter 4 suggest that DCAMKL-1+ve cells are significantly more proliferative than either DCAMKL-1-ve or LGR5+ve stem cells. Thus targeting DCAMKL-1+ve cells may be more effective in treating/eradicating colon-cancers; this possibility was examined as part of my fourth goal. Although several therapies are currently available for treating cancers, recurrence remains a challenge. It is believed that CSCs are resistant to radiation and chemotherapeutic treatments, and are the likely cause of cancer relapse. It is therefore important to develop novel therapies which are relatively non-toxic and specifically target CSCs. Therefore the fourth goal was to examine the inhibitory efficacy of non-toxic dietary agent (Curcumin) ± RNAi against DCAMKL-1. The results in chapter 5 suggest that combination of curcumin+siRNA-DCAMKL-1 effectively attenuates growth of colon-cancer-cells in vitro and in vivo, by synergistically augmenting autophagic/apoptotic cell-death mechanisms. It is hypothesized that the combinatorial treatment will significantly reduce the risk of relapse.