Preclinical evaluation of the tyrosine kinase inhibitor SU11248 as a single agent and in combination with “standard of care” therapeutic agents for the treatment of breast cancer

SU11248 is an oral multitargeted tyrosine kinase inhibitor with antitumor and antiangiogenic activities through targeting platelet-derived growth factor receptor, vascular endothelial growth factor receptor, KIT, and FLT3, the first three of which are expressed in human breast cancer and/or its supporting tissues. The purpose of the present studies was to demonstrate the potent anticancer activity of SU11248 alone or in combination with conventional cytotoxic agents against several distinct preclinical models of breast cancer. SU11248 was administered as a monotherapy to (1) mouse mammary tumor virus-v-Ha- ras mice and 7,12-dimethylbenz( a )anthracene-treated rats bearing mammary tumors and (2) mice bearing human breast cancer xenografts of s.c. MX-1 tumors and osseous metastasis of a MDA-MB-435-derived cell line (435/HAL-Luc). SU11248 was also administered in combination with docetaxel both in xenograft models and in combination with 5-fluorouracil and doxorubicin in the MX-1 model. SU11248 treatment potently regressed growth of mammary cancers in mouse mammary tumor virus-v-Ha- ras transgenic mice (82% regression) and 7,12-dimethylbenz( a )anthracene-induced mammary tumors in rats (99% regression at the highest dose; P < 0.05 for both). This agent also inhibited MX-1 tumor growth by 52%, with markedly enhanced anticancer effects when administered in combination with docetaxel, 5-fluorouracil, or doxorubicin compared with either agent alone ( P < 0.05). SU11248 treatment in combination with docetaxel effectively prolonged survival of mice, with 435/HAL-Luc cancer xenografts established in bone compared with either agent alone ( P < 0.05). These results demonstrate that SU11248 is effective in preclinical breast cancer models and suggest that it may be useful in the treatment of breast cancer in the clinic.