Growth factor receptors with tyrosine kinase activity mediate paracrine and autocrine growth regulation of normal and malignant cells. The epidermal growth factor receptor (EGF-R) is a tyrosine kinase transmembrane protein that is overexpressed by many epithelial malignancies[1]. RG13022, a tyrosine kinase inhibitor, inhibits the autophosphorylation reaction of the EGF-R in immunoprecipitates with an IC50 of 4 μM. RG-13022 inhibits DNA synthesis and colony formation by HER 14 cells, which are stimulated by 50 ng/mL EGF, in a dose-dependent manner. The IC50s for RG-13022 are 3 μM and 1 μM for HER 14 DNA synthesis and HER 14 colony formation, respectively. RG-13022 also suppresses DNA synthesis and colony formation by EGF-stimulated MH-85 cells in a dose-dependent manner. The IC50s for RG-13022 on MH-85 cells are 1.5 μM and 7 μM for DNA synthesis and colony formation, respectively. Nude mice implanted with MH-85 tumors manifested profound hypercalcemia, cachexia, and leukocytosis as the tumor grew. RG-13022 (400 μg/mouse/day) significantly inhibits MH-85 tumor growth in Nude Mice. Because of slower tumor growth, MH-85 tumor-bearing animals receiving injections of RG-13022 show less cachexia and hypercalcemia, eat more food, and are more active than untreated MH-85 tumor-bearing animals. RG-13022 prolongs the life span of MH-85 tumor-bearing animals as a result of suppression of tumor growth. Moreover, administration of mAb108 i.p. (1 mg/mouse/day) at 1, 5, and 10 days after MH-85 inoculation of RG-13022 (400 μg/mouse/day) for 14 days profoundly inhibits MH-85 growth in nude mice[2].
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