Putative Cancer Stem Cell Populations Research Articles

The combination of 5-Fluorouracil plus p53 pathway restoration is associated with depletion of p53-deficient or mutant p53-expressing putative colon cancer stem cells

The cancer stem cell hypothesis suggests that rare populations of tumor-initiating cells may be resistant to therapy, lead to tumor relapse and contribute to poor prognosis for cancer patients. We previously demonstrated the feasibility of p53 pathway restoration in p53-deficient tumor cell populations using small molecules including ellipticine or its derivatives. We now establish a single cell p53-regulated green fluorescent protein (EGFP)-reporter system in human DLD1 colon tumor cells expressing mutant p53 protein. We use these p53-EGFP reporter DLD1 cells to investigate the status of p53 transcriptional activity in putative colon cancer stem cell populations following exposure to p53 pathway-restoring drugs and/or classical chemotherapy. We demonstrate induction of p53-specific EGFP reporter fluorescence following overexpression of p53 family member p73 by an Adenovirus vector. We further show that p53-reporter activity is induced in DLD1 putative cancer stem cell side-populations analyzed by their Hoechst dye efflux properties following treatment with the p53 pathway restoring drug ellipticine. Combination of ellipticine with the cytotoxic agent 5-fluorouracil resulted in increased cytotoxicity as compared to either agent alone and this was associated with depletion of putative cancer stem cell populations as compared with 5-FU alone treatment. Our results support the feasibility of therapeutic targeting of mutant p53 in putative cancer stem cells as well as the potential to enhance cytotoxic chemotherapy.

Both CD133+ and CD133− subpopulations of A549 and H446 cells contain cancer‐initiating cells

Tumors have been known to contain a small population of cancer stem cells that initiate tumor growth and promote tumor spreading. CD133 alone or in combination with other markers is currently being used for identification and isolation of the putative cancer stem cell population from malignant tumors. To determine whether the CD133+ cells constitute the stem cell populations of lung cancer cells A549 and H446, CD133+ and CD133- subpopulations were sorted from A549 and H446 cells by magnetic cell separation and characterized for their in vitro stem cell-like properties. Interestingly, both the CD133+ and CD133- cells displayed similar abilities of colony formation, self-renewal, proliferation, differentiation, and invasion, as well as resistance to chemotherapy drugs. Furthermore, colony formation assays showed that more than 40% of cells in both the CD133+ cells and CD133- subpopulations could form large colonies capable of regenerating the unsorted populations and forming tumors in nude mice. These results suggest that CD133 alone cannot be used as a stem cell marker for the lung cancer cells A549 and H446, and both the CD133+ and CD133- subpopulations contain similar numbers of cancer stem cells.

Phosphatidylinositol 3-Kinase Mediates Bronchioalveolar Stem Cell Expansion in Mouse Models of Oncogenic K-ras-Induced Lung Cancer

BackgroundNon-small cell lung cancer (NSCLC) is the most common cause of cancer-related death in Western countries. Developing more effective NSCLC therapeutics will require the elucidation of the genetic and biochemical bases for this disease. Bronchioalveolar stem cells (BASCs) are a putative cancer stem cell population in mouse models of oncogenic K-ras-induced lung adenocarcinoma, an histologic subtype of NSCLC. The signals activated by oncogenic K-ras that mediate BASC expansion have not been fully defined.Methodology/Principal FindingsWe used genetic and pharmacologic approaches to modulate the activity of phosphatidylinositol 3-kinase (PI3K), a key mediator of oncogenic K-ras, in two genetic mouse models of lung adenocarcinoma. Oncogenic K-ras-induced BASC accumulation and tumor growth were blocked by treatment with a small molecule PI3K inhibitor and enhanced by inactivation of phosphatase and tensin homologue deleted from chromosome 10, a negative regulator of PI3K.Conclusions/SignificanceWe conclude that PI3K is a critical regulator of BASC expansion, supporting treatment strategies to target PI3K in NSCLC patients.

Transforming Growth Factor-β Can Suppress Tumorigenesis through Effects on the Putative Cancer Stem or Early Progenitor Cell and Committed Progeny in a Breast Cancer Xenograft Model

The transforming growth factor-beta (TGF-beta) pathway has tumor-suppressor activity in many epithelial tissues. Because TGF-beta is a potent inhibitor of epithelial cell proliferation, it has been widely assumed that this property underlies the tumor-suppressor effect. Here, we have used a xenograft model of breast cancer to show that endogenous TGF-beta has the potential to suppress tumorigenesis through a novel mechanism, involving effects at two distinct levels in the hierarchy of cellular progeny that make up the epithelial component of the tumor. First, TGF-beta reduces the size of the putative cancer stem or early progenitor cell population, and second it promotes differentiation of a more committed, but highly proliferative, progenitor cell population to an intrinsically less proliferative state. We further show that reduced expression of the type II TGF-beta receptor correlates with loss of luminal differentiation in a clinical breast cancer cohort, suggesting that this mechanism may be clinically relevant. At a molecular level, the induction of differentiation by TGF-beta involves down-regulation of Id1, and forced overexpression of Id1 can promote tumorigenesis despite persistence of the antiproliferative effect of TGF-beta. These data suggest new roles for the TGF-beta pathway in regulating tumor cell dynamics that are independent of direct effects on proliferation.