Effect of dasatinib on the activity of trastuzumab in HER2-overexpressing breast cancer cells

Abstract

1084 Background: Breast cancer is the most common neoplasia in women. Although important advances in its treatment have been made along the last years, in the metastatic setting this disease remains incurable. One group of molecules involved in breast cancer genesis/progression are tyrosine kinases. HER-2 is a receptor tyrosine kinase that is overexpressed in a subset of patients with breast cancer. Targeting of HER-2 with trastuzumab a monoclonal antibody that acts on HER-2 has demonstrated clinical benefit. However, as a single agent its antitumoral activity is limited. Methods: Here we have investigated whether the action of trastuzumab, can be potentiated by dasatinib, a small molecule inhibitor that acts on several receptor and non-receptor tyrosine kinases. To this end, we have used cancer cell lines and in vivo xenografted mouse models. MTT proliferation and other apoptosis assays, biochemical and microarray experiments were performed to investigate the molecular bases of the action of the combined trastuzumab plus dasatinib treatment. Results: Combination of trastuzumab and dasatinib was synergic on breast cancer cells overexpressing HER-2, but not on cells with a normal complement of its receptor. In vivo xenograft studies confirmed the antitumoral action of this drug combination. Studies on the mechanism of action showed that this drug combination triggered apoptosis in HER-2 overexpressing cells. Apoptosis was evidenced by increased Annexin V staining, and was found to occur in a caspase-independent manner. In addition, an action of the drug combination on cell cycle could be identified, and the drugs decreased cyclins E1/2, B, and Cdk2, in addition to increasing p27. Microarray as well as biochemical analyses showed that the drug combination provoked a decrease in HER receptor phosphorylation, followed by interruption of downstream signalling. These changes resulted in alterations in the levels of proteins involved in DNA repair. Moreover, treatment with the drug combination caused a DNA damage response as evidenced by increased γH2AX. Conclusions: The effective antitumoral action of the drug combination opens new avenues for the clinical exploration of this drug combination in breast cancer patients overexpressing HER-2. No significant financial relationships to disclose.