Abstract
Phosphorylation of tyrosine residues on the epidermal growth factor (EGF) receptor (EGFr) is an important early event in signal transduction, leading to cell replication for major human carcinomas. CP-358,774 is a potent and selective inhibitor of the EGFr tyrosine kinase and produces selective inhibition of EGF-mediated tumor cell mitogenesis. To assess the pharmacodynamic aspects of EGFr inhibition, we devised an ex vivo enzyme-linked immunosorbent assay for quantification of EGFr-specific tyrosine phosphorylation in human tumor tissue specimens obtained from xenografts growing s.c. in athymic mice. When coupled with pharmacokinetic analyses, this measurement can be used to describe the extent and duration of kinase inhibition in vivo. CP-358,774 is an effective, orally active inhibitor of EGFr-specific tyrosine phosphorylation (ED50 = 10 mg/kg, single dose). It has a significant duration of action, producing, on average, a 70% reduction in EGFr-associated phosphotyrosine over a 24-h period after a single 100 mg/kg dose. Inhibition of EGFr phosphotyrosine in an ex vivo assay format effectively estimates the potency and degree of inhibition of EGFr-dependent human LICR-LON-HN5 head and neck carcinoma tumor growth. Substantial growth inhibition of human tumor xenografts was achieved with p.o. doses of the compound (ED50 = 10 mg/kg q.d. for 20 days). Combination chemotherapy with cisplatin produced a significant response above that of cisplatin alone with no detectable effects on body weight or lethal toxicity. Taken together, these observations suggest that CP-358,774 may be useful for the treatment of EGFr-driven human carcinomas.
Footnotes
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Send reprint requests to: Dr. Vincent A. Pollack, Department of Genomics, Targets and Cancer Research, Pfizer Central Research, Eastern Point Road, Groton, CT 06340. E-mail:vincent_a_pollack{at}groton.pfizer.com
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↵1 Portions of this work were presented at the annual meeting of the American Association for Cancer Research, April 1997.
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↵2 Present address: Department of Chemistry, BASF Bioresearch Corp., 100 Research Dr., Worcester, MA 01605-4314.
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↵3 Address: OSI Pharmaceuticals, Inc., 106 Charles Lindbergh Blvd., Uniondale, NY 11553.
- Abbreviations:
- EGF
- epidermal growth factor
- EGFr
- epidermal growth factor receptor
- ELISA
- enzyme-linked immunosorbent assay
- HBSS
- Hanks’ balanced salt solution
- HN5
- LICR-LON-HN5 head and neck carcinoma
- Received May 18, 1999.
- Accepted August 5, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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