Tyrosine kinase inhibitors. 14. Structure-activity relationships for methylamino-substituted derivatives of 4-[(3-bromophenyl)amino]-6-(methylamino)-pyrido[3,4-d]pyrimidine (PD 158780), a potent and specific inhibitor of the tyrosine kinase activity of receptors for the EGF family of growth factors

• Published in: Journal of medicinal chemistry 1998-02, Vol.41 (5), p.742-751
• Main Authors: Rewcastle, G W, Murray, D K, Elliott, W L, Fry, D W, Howard, C T, Nelson, J M, Roberts, B J, Vincent, P W, Showalter, H D, Winters, R T, Denny, W A
• Format: Article
• Language: English
• Subjects: 3T3 Cells; Animals; Antineoplastic Agents - chemical synthesis; Antineoplastic Agents - therapeutic use; Breast Neoplasms - drug therapy; Carcinoma, Squamous Cell - drug therapy; Carcinoma, Squamous Cell - metabolism; Enzyme Inhibitors - chemical synthesis; Enzyme Inhibitors - pharmacology; Female; Humans; Mice; Mice, Nude; Molecular Structure; Ovarian Neoplasms - drug therapy; Phosphorylation; Protein-Tyrosine Kinases - antagonists & inhibitors; Pyrimidines - chemistry; Pyrimidines - pharmacology; Receptor Protein-Tyrosine Kinases - antagonists & inhibitors; Receptor, Epidermal Growth Factor - antagonists & inhibitors; Receptor, Epidermal Growth Factor - genetics; Structure-Activity Relationship; Transfection; Tumor Cells, Cultured
• ISSN: 0022-2623
• DOI: 10.1021/jm970641d

The 4-[(3-bromophenyl)amino]pyrido[3,4-d]pyrimidine PD 158780 is a very potent in vitro inhibitor of the tyrosine kinase activity of the epidermal growth factor receptor (EGFR) (IC50 0.08 nM), and other members of the erbB family, by competitive binding at the ATP site of these signal transduction enzymes. A series of analogues of PD 158780 bearing solubilizing functions off the 6-methylamino substituent were prepared by reaction of the 6-fluoro derivatives with appropriate amine nucleophiles. These were evaluated for their ability to inhibit the tyrosine phosphorylating action of EGF-stimulated full-length EGFR enzyme and for inhibition of autophosphorylation of the EGFR in A431 human epidermoid carcinoma cells in culture. The most effective analogues were those bearing weakly basic substituents through a secondary amine linkage, which proved water-soluble (> 10 mM) and potent (IC50S generally < 1 nM). No clear SAR could be discerned for these compounds with respect to amine base strength or the distance of the cationic center from the chromophore, suggesting that 6-substituents are in a favorable area of bulk tolerance in the enzyme binding site. More distinct SAR emerged for the ability of the compounds to inhibit EGFR autophosphorylation in A431 cells, where analogues bearing lipophilic weak bases were preferred. Representative analogues were evaluated for antitumor effectiveness against four in vivo tumor models. Significant in vivo activity was observed in estrogen-dependent MCF-7 breast and A431 epidermoid tumors. Marginal activity was seen in an EGFR-transfected tumor model, suggesting that while this cell line requires EGF for clone formation in soft agar, other growth factors may be able to replace EGF in vivo. Also, no activity was seen against the SK-OV-3 ovarian cancer model, which is known to express other EGF receptor family members (although it is not clear whether these are absolutely required for growth in vivo). While substantial growth delays were seen in A431 and MCF-7 tumor models, the treated tumors remained approximately the same size throughout therapy, suggesting that the compounds are cytostatic rather than cytotoxic under these test conditions. It remains to be determined if more prolonged therapy has cytotoxic effects in vivo, resulting in net tumor cell kill.