Blockade of the epidermal growth factor receptor signaling inhibits angiogenesis leading to regression of human renal cell carcinoma growing orthotopically in nude mice

We determined whether blockade of the epidermal growth factor-receptor (EGF-R) signaling pathway by oral administration of the EGF-R tyrosine kinase inhibitor PKI166 can inhibit angiogenesis and growth of SN12PM6 human renal cell carcinoma (HRCC) in the kidney of nude mice and whether gemcitabine can potentiate these effects. In vitro treatment of HRCC cells with PKI166 inhibited EGF-R autophosphorylation, which correlated with a decrease in expression of Bcl-xl protein and phosphorylation of signal transducers and activators of transcription, particularly signal transducers and activators of transcription 3. PKI166 also decreased expression of vascular endothelial growth factor and basic fibroblast growth factor in a dose-dependent manner. Oral administration of PKI166 or PKI166 and injected gemcitabine or gemcitabine alone beginning 7 days after implantation of SN12PM6 cells into the kidney of athymic nude mice reduced the volume of tumors by 26, 61, and 23%, respectively. In another experiment 28 days after the orthotopic implantation of SN12PM6 cells, nephrectomy was performed followed by 4 weeks of treatment. Treatment with PKI166 and, more so, PKI166 plus gemcitabine significantly inhibited lung metastasis, corresponding to a significant increase in overall length of survival. EGF-R activation was significantly blocked by therapy with PKI166 and was associated with a significant reduction in expression of vascular endothelial growth factor and interleukin-8, decreased microvessel density, decreased staining of proliferating cell nuclear antigen, and increased tumor cell apoptosis. Collectively, the data indicate that targeting activation of EGF-R on HRCC produces significant therapeutic benefits.