Inhibition of Ataxia Telangiectasia- and Rad3 -Related Function Abrogates the In Vitro and In Vivo Tumorigenicity of Human Colon Cancer Cells Through Depletion of the CD133+ Tumor-Initiating Cell Fraction§

Authors


  • Disclosure of potential conflicts of interest is found at the end of this article.

  • Author contributions: E.G.: conception and design, financial support, collection and assembly of data, data analysis and interpretation, manuscript writing, final approval of manuscript; P.C.H.: conception and design, collection and assembly of data, data analysis and interpretation, manuscript writing, final approval of manuscript; M.-T.M.: collection and assembly of data, data analysis and interpretation; J.G.M.: collection and assembly of data; A.Z.: collection and assembly of data; E.N.D.T.: data analysis and interpretation; A.P.: collection and assembly of data; C.E.: collection and assembly of data; J.W.E.: collection and assembly of data; J.R.: collection and assembly of data; B.R.-V.: provision of study material; M.H.: provision of study material; F.B.: conception and design, provision of study material; B.G.: conception, financial support; C.H.: conception and design, financial support, data analysis and interpretation, manuscript writing, final approval of manuscript. E.G. and P.C.H. contributed equally to this article.

  • §

    First published online in STEM CELLSEXPRESS February 4,2011.

Abstract

The identification of novel approaches to specifically target the DNA-damage checkpoint response in chemotherapy-resistant cancer stem cells (CSC) of solid tumors has recently attracted great interest. We show here in colon cancer cell lines and primary colon cancer cells that inhibition of checkpoint-modulating phosphoinositide 3-kinase-related (PIK) kinases preferentially depletes the chemoresistant and exclusively tumorigenic CD133+ cell fraction. We observed a time- and dose-dependent disproportionally pronounced loss of CD133+ cells and the consecutive lack of in vitro and in vivo tumorigenicity of the remaining cells. Depletion of CD133+ cells was initiated through apoptosis of cycling CD133+ cells and further substantiated through subsequent recruitment of quiescent CD133+ cells into the cell cycle followed by their elimination. Models using specific PIK kinase inhibitors, somatic cell gene targeting, and RNA interference demonstrated that the observed detrimental effects of caffeine on CSC were attributable specifically to the inhibition of the PIK kinase ataxia telangiectasia- and Rad3-related (ATR). Mechanistically, phosphorylation of CHK1 checkpoint homolog (S. pombe; CHK1) was significantly enhanced in CD133+ as compared with CD133 cells on treatment with DNA interstrand-crosslinking (ICL) agents, indicating a preferential activation of the ATR/CHK1-dependent DNA-damage response in tumorigenic CD133+ cells. Consistently, the chemoresistance of CD133+ cells toward DNA ICL agents was overcome through inhibition of ATR/CHK1-signaling. In conclusion, our study illustrates a novel target to eliminate the tumorigenic CD133+ cell population in colon cancer and provides another rationale for the development of specific ATR-inhibitors. STEM CELLS 2011;29:418–429

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