Effects of imatinib on breast cancer cell biology in vitro

Abstract

3210 Background: New targeted therapies for solid tumors are currently investigated in pre-clinical and clinical studies. For Imatinib mesylate activities in inhibiting selected tyrosine kinase receptors, including PDGF-R and c-Kit, have been reported. These receptors and their downstream effectors trigger signal transduction cascades regulating processes like proliferation, differentiation and survival. Inhibition of these mechanisms could lead to growth reduction in breast cancer. Effects of Imatinib on breast cancer cell biology in vitro are evaluated. Methods: Expression patterns of PDGF-R-β and c-Κit in human breast cancer cell lines MCF-7, ZR-75–1, MDA MB 231 and T47D are detected by PCR. The IC50 of Imatinib is determined in proliferation assays and used in further experiments. Changes in PDGF-R- β phosphorylation and expression during Imatinib treatment are investigated by immunohistochemistry. In MDA MB 231 receptor activation is also detected by western blot. To investigate potential synergistic effects with cytotoxic agents, cells are treated with Imatinib combined with variable concentrations of Vinorelbine. Apoptotic effects of single Imatinib or combined with Vinorelbine are observed by TUNEL assay. Results: MCF-7 and ZR-75–1 express PDGF-R-β and c-Kit, MDA MB 231 and T47D are PDGF-R-β positive only. Imatinib mono leads to growth inhibition in breast cancer cells in a clinical tolerated dose. Combination of Imatinib and Vinorelbine shows a significantly stronger growth inhibition than Vinorelbine alone (0,5 to 6nM). TUNEL assay clearly demonstrates apoptosis in Imatinib treated breast cancer cells. Apoptosis caused by Vinorelbine can be enhanced by adding Imatinib. Immunohistochemistry shows a dose depended inhibitory effect of Imatinib on PDGF-R-β activation (phosphorylation). A change in receptor expression does not occur. In MDA MB 231 cells this data has been confirmed by western blot. Conclusions: Imatinib has an anti-proliferatory effect on breast cancer cells which is caused by inducing apoptosis and PDGF-R-β inactivation. Moreover Imatinib increases growth inhibition of vinorelbine. This may lead to new options in breast cancer therapy combining targeted and cytotoxic agents. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Novartis Novartis