ZD6474 in combination with paclitaxel and UVB irradiation enhances the antiproliferative effect and apoptosis on breast carcinoma

Abstract

Breast cancer is the leader of cancer deaths among women. Despite developments in surgery, chemotherapy and radiotherapy, the long-term survival of patients with metastatic and higher staging breast cancer has remained very low. Breast cancers and their aggressive nature are characterized by overexpression of epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR). There is a common downstream signaling molecule involved in both EGFR and VEGFR mediated pathways. There are reports that cancer cells acquired resistance to anti-EGF/EGFR therapy by increased tumor-induced angiogenesis due to the constitutive overexpression of VEGF. Hence, the inhibition of both EGFR and VEGFR signaling pathways simultaneously may provide greater benefit than blockade of either pathway alone. There are also reports that breast cancer acquired resistance to conventional chemotherapy and radiotherapy by increased phosphorylation of EGFR and VEGFR. Moreover, patients suffering from breast cancer have a poor prognosis because of a lack of effective treatment strategies. We hypothesized that inhibiting the phosphorylation of the EGFR and VEGFR by ZD6474, a dual tyrosine kinase inhibitor of EGFR and VEGFR, in combination with paclitaxel or radiation would inhibit breast cancer cell growth. We tested this hypothesis using the human breast cancer cell lines MCF-7 and MDA-MB-231. In culture, ZD6474 in combination with paclitaxel or UVB had a synergistic effect in inhibition of cell proliferation, and lowered the IC50 by 10-fold and fivefold, respectively, compared with paclitaxel/UVB alone. Flow cytometry data suggest that combination therapy of ZD6474 with paclitaxel increases apoptosis from 20% to 45% in MDA-MB-231 and from 16% to 38% in MCF-7 compared with paclitaxel alone. This is further supported by a decrease in cell cycle regulatory protein cyclin D1 and an increase in apoptosis marker poly(ADP-ribose) polymerase in combination therapy compared with paclitaxel and UVB irradiation alone. Moreover, combination therapy sensitizes the paclitaxel resistance MCF-7/PTX and MDA-MB-231/PTX. ZD6474 along with paclitaxel or radiation can therefore be used for treatment in drug-insensitive advanced breast cancers.