pkh-26 and Carcinoma

Radiotherapy is the most successful nonsurgical treatment for nasopharyngeal carcinoma (NPC). Despite this, the prognosis remains poor. Although NPCs initially respond well to a full course of radiation, recurrence is frequent. The cancer stem cell (CSC) hypothesis provides a framework for explaining the discrepancy between the response of NPC to therapy and the poor survival rate. In this study, a stem cell-like subpopulation (PKH26+) was identified in NPC cell lines using a label-retention technique. PKH26+ cells were enriched for clonogenicity, sphere formation, side-population cells, and resistance to radiotherapy. Using genomic approaches, we show that the proto-oncogene c-MYC (MYC) regulates radiotolerance through transcriptional activation of CHK1 (CHEK1) and CHK2 (CHEK2) checkpoint kinases through direct binding to the CHK1 and CHK2 promoters. Overexpression of c-MYC in the PKH26+ subpopulation leads to increased expression of CHK1 and CHK2 and subsequent activation of the DNA-damage-checkpoint response, resulting in radioresistance. Furthermore, loss of CHK1 and CHK2 expression reverses radioresistance in PKH26+ (c-MYC high expression) cells in vitro and in vivo. This study elucidates the role of the c-MYC-CHK1/CHK2 axis in regulating DNA-damage-checkpoint responses and stem cell characteristics in the PKH26+ subpopulation. Furthermore, these data reveal a potential therapeutic application in reversal of radioresistance through inhibition of the c-MYC-CHK1/CHK2 pathway.

Topics: Animals; Carcinoma; Cell Line, Tumor; Checkpoint Kinase 1; Checkpoint Kinase 2; DNA Damage; DNA Repair; Female; Humans; Mice; Nasopharyngeal Carcinoma; Nasopharyngeal Neoplasms; Neoplastic Stem Cells; Organic Chemicals; Protein Kinases; Protein Serine-Threonine Kinases; Proto-Oncogene Mas; Proto-Oncogene Proteins c-myc; Radiation Tolerance

Solid tumors appear to contain a subpopulation of cells (tumor-initiating cells, TICs) that not only drives and sustains tumor growth, but is possibly responsible for recurrence. We isolated, after enzymatic digestion of primary ovarian carcinoma samples, a subpopulation of cells propagating as non-adherent spheres in medium suitable for tumor stem cells. These cells were able to self-renew in vitro, as suggested by PKH-26 staining studies, were tumorigenic and acquired an epithelial morphology when grown in FBS-supplemented medium, losing their tumorigenic potential. Interestingly, the tumorigenic potential of PKH-26 (high) - and PKH-26 (neg) -sorted cells was similar. These TIC-enriched cultures showed higher levels of genes involved in stemness than differentiated cells derived from them and were more resistant to the cytotoxic effects of some drugs but equally sensitive to others. The higher level of ABCG2 efflux pump could explain increased resistance to taxol and VP16, and higher levels of genes involved in nucleotide excision repair partially explain the resistance to cisplatin. These cells express mesenchymal markers, and epithelial transition could be induced when cultured in differentiating conditions, with a loss of invasive potential. These data suggest that ovarian cancer is a stem cell disease and should help elucidate the role of these cells in the aggressive phenotype of this tumor and find new therapeutic strategies to reduce resistance to current chemotherapeutic drugs.

Topics: Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Carcinoma; Cell Differentiation; Cell Survival; Cisplatin; Drug Resistance, Neoplasm; Epithelial-Mesenchymal Transition; Etoposide; Female; Fluorescent Antibody Technique, Indirect; Humans; Mesenchymal Stem Cells; Neoplasm Proteins; Neoplastic Stem Cells; Organic Chemicals; Ovarian Neoplasms; Paclitaxel; Tumor Cells, Cultured