Cigarette smoke induces epithelial to mesenchymal transition and increases the metastatic ability of breast cancer cells.

BACKGROUND: Recent epidemiological studies demonstrate that both active and involuntary exposure to tobacco smoke increase the risk of breast cancer. Little is known, however, about the molecular mechanisms by which continuous, long term exposure to tobacco smoke contributes to breast carcinogenesis because most previous studies have focused on short term treatment models. In this work we have set out to investigate the progressive transforming effects of tobacco smoke on non-tumorigenic mammary epithelial cells and breast cancer cells using in vitro and in vivo models of chronic cigarette smoke exposure. RESULTS: We show that both non-tumorigenic (MCF 10A, MCF-12A) and tumorigenic (MCF7) breast epithelial cells exposed to cigarette smoke acquire mesenchymal properties such as fibroblastoid morphology, increased anchorage-independent growth, and increased motility and invasiveness. Moreover, transplantation experiments in mice demonstrate that treatment with cigarette smoke extract renders MCF 10A cells more capable to survive and colonize the mammary ducts and MCF7 cells more prone to metastasize from a subcutaneous injection site, independent of cigarette smoke effects on the host and stromal environment. The extent of transformation and the resulting phenotype thus appear to be associated with the differentiation state of the cells at the time of exposure. Analysis by flow cytometry showed that treatment with CSE leads to the emergence of a CD44(hi)/CD24(low) population in MCF 10A cells and of CD44+ and CD49f + MCF7 cells, indicating that cigarette smoke causes the emergence of cell populations bearing markers of self-renewing stem-like cells. The phenotypical alterations induced by cigarette smoke are accompanied by numerous changes in gene expression that are associated with epithelial to mesenchymal transition and tumorigenesis. CONCLUSIONS: Our results indicate that exposure to cigarette smoke leads to a more aggressive and transformed phenotype in human mammary epithelial cells and that the differentiation state of the cell at the time of exposure may be an important determinant in the phenotype of the final transformed state.

Knockdown of HMGA1 inhibits human breast cancer cell growth and metastasis in immunodeficient mice.

The high mobility group A1 gene (HMGA1) has been previously implicated in breast carcinogenesis, and is considered an attractive target for therapeutic intervention because its expression is virtually absent in normal adult tissue. Other studies have shown that knockdown of HMGA1 reduces the tumorigenic potential of breast cancer cells in vitro. Therefore, we sought to determine if silencing HMGA1 can affect breast cancer development and metastatic progression in vivo. We silenced HMGA1 expression in the human breast cancer cell line MDA-MB-231 using an RNA interference vector, and observed a significant reduction in anchorage-independent growth and tumorsphere formation, which respectively indicate loss of tumorigenesis and self-renewal ability. Moreover, silencing HMGA1 significantly impaired xenograft growth in immunodeficient mice, and while control cells metastasized extensively to the lungs and lymph nodes, HMGA1-silenced cells generated only a few small metastases. Thus, our results show that interfering with HMGA1 expression reduces the tumorigenic and metastatic potential of breast cancer cells in vivo, and lend further support to investigations into targeting HMGA1 as a potential treatment for breast cancer.

Transient low doses of DNA-demethylating agents exert durable antitumor effects on hematological and epithelial tumor cells.

Reversal of promoter DNA hypermethylation and associated gene silencing is an attractive cancer therapy approach. The DNA methylation inhibitors decitabine and azacitidine are efficacious for hematological neoplasms at lower, less toxic, doses. Experimentally, high doses induce rapid DNA damage and cytotoxicity, which do not explain the prolonged time to response observed in patients. We show that transient exposure of cultured and primary leukemic and epithelial tumor cells to clinically relevant nanomolar doses, without causing immediate cytotoxicity, produce an antitumor "memory" response, including inhibition of subpopulations of cancer stem-like cells. These effects are accompanied by sustained decreases in genomewide promoter DNA methylation, gene reexpression, and antitumor changes in key cellular regulatory pathways. Low-dose decitabine and azacitidine may have broad applicability for cancer management.

A murine xenograft model of spontaneous metastases of human lung adenocarcinoma.

BACKGROUND: The flank is commonly used for primary xenografts in mice, but it is rare for these tumors to metastasize. Tail vein injection creates a pattern of metastases, but is artificial. We hypothesized that the liver is a convenient alternative xenograft site and that metastases would gradually proceed spontaneously. MATERIALS AND METHODS: Using 15 NOD.CB17-Prkdc(scid)/NcrCrl (NOD/SCID) mice, 10,000 A549 cells were xenografted into the liver while a second group of five mice were xenografted in the flank with 100,000 A549 cells as a control. Mice were euthanized and grossly dissected at 7 wk. A third group of seven mice received liver xenografts with A549 and a mouse each week was euthanized for 7 wk and evaluated. The liver, lung, and spleen were examined histologically. RESULTS: At 7 wk, 15/15 liver xenografted mice had gross primary tumor in the liver. Histologic review confirmed multiple microscopic foci of metastatic disease in all mice (15/15) throughout the lungs, mediastinal nodes, and spleen. The control group had primary tumor in the flank (4/5), but none had histologic evidence of metastases. Serially euthanized liver xenografted mice revealed evidence of a gradual spontaneous metastatic model system with the first histologic findings of micrometastases appearing in the lungs by wk 5, which became wide spread by wk 7. Splenic and mediastinal lymph node metastases developed in wk 6 and 7. CONCLUSIONS: Liver xenografting of A549 cells into NOD/SCID mice is a reliable way of developing widespread micrometastases. This model allows the study of a gradually developing solid tumor with subsequent metastatic spread.