Endothelium as therapeutic target in breast and lung cancer progression: the role of nitric oxide and stemness marker ALDH1A1

Cancer is the second leading cause of death worldwide. Breast and lung cancers are highly diffused in population with a negative impact on mortality due to the high rate of dissemination and chemoresistance. The understanding of new molecular mechanisms and the introduction of new drugs are key elements in the oncology research. In cancer cells, a deregulation of metabolism and redox balance has been reported, with an increase of the detoxifying systems. High levels of reactive species may induce tumor cells to die. Many chemotherapeutic agents act in this way, shifting the balance toward an overwhelming of the endogenous scavenger systems. Nitric oxide (NO) is a Reactive Oxygen Species (ROS) member having proneoplastic and antineoplastic activity, depending on its concentration and cellular context. The first aim of this thesis was to investigate the antitumor activity of NO-donor (termed metal-nonoate) on A549 cells, a cell line representative of lung cancer. In this study, we observed cytotoxic activity of metal-nonoate and a reduction of the main hallmarks of tumor malignancy such as tumor cell clonogenicity, invasion and tumor angiogenesis. Upon NO donor treatment in A549, apoptosis pathway was activated with an upregulation of p53 and accumulation of cytochrome c. The mechanisms underlying these events were the phosphorylation of ERK1/2 and a burst of ROS production. The second part of my thesis addressed the role in tumor angiogenesis of aldehyde dehydrogenase (ALDH), a detoxifying enzyme that catalyzes the oxidation of aldehydes, a class of metabolic intermediates of tumor cell metabolism. The isoform ALDH1A1 is an important marker of breast cancer stemness. In this second study we observed a link between stemness status of breast cancer cells (MCF-7) and tumor angiogenesis, mediated by ALDH1A1. In MCF-7 overexpressing ALDH1A1, we observed a greater expression of angiogenic factors, such as HIF-1α and VEGF compared to wild type cells. In a panel of in vitro co-culture experiments, we demonstrated a promotion of endothelial cells recruitment that was dependent on VEGF expression, which was released by MCF-7 over-expressing ALDH1A1. This result was associated to in vivo tumor growth and angiogenesis in MCF-7 xenograft models, evaluated by blood flow and microvessel density (MVD). The intratumoral level of HIF-1α and VEGF was higher in MCF-7 tumor enriched of ALDH1A1, in which we also observed a greater expression of stemness markers, demonstrating a correlation between tumor stemness and tumor angiogenesis. In conclusion, our findings indicate that deregulation of tumor cell metabolism, a hallmark of cancer, is functionally linked with tumor angiogenesis and its modulation appears a promising strategy for cancer treatment.