Specific overexpression of 15-lipoxygenase in endothelial cells promotes cancer cell death in an in vivo Lewis lung carcinoma mouse model.

Purpose: Lipoxygenases (LOX) have been implicated in carcinogenesis, however both pro- and anti-carcinogenic effects have been reported in different cancer models. Using transgenic mice, which specifically overexpress human 15-lipoxygenase (ALOX15) in endothelial cells (EC), we previously demonstrated significant inhibition of tumor development. In the Lewis lung carcinoma (LLC) model, the primary tumor developed similarly in both wild type (WT) and ALOX15 overexpressing mice. However, metastases development was significantly inhibited in the transgenic mice. Here, we explored the molecular basis for the anti-metastatic effect of endothelial cell specific ALOX15 overexpression.

Materials/methods: We used ALOX15 overexpressing mice, and in-vitro cell model to evaluate the molecular effect of ALOX15 on EC and LLC cells.

Results: When LLC cells were injected in WT and ALOX15 overexpressing mice, we observed a higher degree of apoptosis and necrosis in primary and metastatic tumors of ALOX15 overexpressing animals. These anti-carcinogenic and anti-metastatic effects were paralleled by augmented expression of cyclin-dependent kinase inhibitor 1A (CDKN1A; p21) and of the peroxisome proliferators-activated receptor (PPAR)γ and by downregulation of the steady state concentrations of connexin26 mRNA. Consistent with these in vivo effects, ALOX15 overexpression in LLC and HeLa cancer cells in vitro significantly reduced cell viability in culture. In contrast, similar treatment of non-cancerous B2B epithelial cells did not impact cell viability.

Conclusions: Taken together, our data suggests that endothelial cell specific overexpression of ALOX15 promotes apoptosis and necrosis in primary and metastatic tumors in mice, by upregulation of P21 and PPARγ expression in adjacent cancer cells.