7-Substituted 3-aryl-1,6-naphthyridine-2,7-diamines and related 2-ureas are inhibitors of fibroblast growth factor receptor-1 (FGFR-1) and vascular endothelial growth factor receptor-2 (VEGFR-2). 3-(3,5-Dimethoxyphenyl) and 3-phenyl analogues were prepared from 7-acetamido-2-tert-butylureas by alkylation with benzyl omega-iodoalkyl ethers, debenzylation, and amination, followed by selective cleavage of the 7-N-acetamide. 3-(2,6-Dichlorophenyl) analogues were prepared from the 7-fluoro-2-amine by displacement with substituted alkylamines, followed by selective acylation of the resulting substituted naphthyridine-2,7-diamines with alkyl isocyanates. The 3-(3,5-dimethoxyphenyl) derivatives were low nanomolar inhibitors of both FGFR and VEGFR and were highly selective (>100-fold) over PDGFR and c-Src. Variations in the base strength or spatial position of the 7-side chain base had only small effects on the potency (<5-fold) or selectivity (<20-fold). The 3-(2,6-dichlorophenyl)-2-urea derivatives were slightly less active against VEGFR and less selective, being more effective against PDGFR (ca. 10-fold) and c-Src (ca. 500-fold). The 3-(3,5-dimethoxyphenyl)-1,6-naphthyridines were generally more potent than the corresponding pyrido[2,3-d]pyrimidines against both VEGFR and FGFR (2- to 20-fold), with only slightly increased PDGFR and c-Src activity. The 3-(3,5-dimethoxyphenyl)-1,6-naphthyridine 2-ureas were also low nanomolar inhibitors of the growth of human umbilical vein endothelial cells (HUVECs) stimulated by serum, FGF, or VEGF, at concentrations that did not affect the growth of representative tumor cell lines, and were more (3- to 65-fold) potent than the corresponding pyrido[2,3-d]pyrimidines.

CI-994 (acetyldinaline) is an investigational anticancer drug currently in clinical trials. In preclinical safety studies in rats and dogs, CI-994 resulted in significant toxicity to bone marrow and lymphoid tissue. To determine if apoptosis was involved in CI-994 toxicity, peripheral blood lymphocytes were isolated from untreated male Wistar rats and exposed to CI-994 (1, 3, 10, or 30 μM) in vitro for up to 24 hours. Morphological and biochemical features of apoptosis were evaluated using several techniques, and lactate dehydrogenase (LDH) release was measured as an indicator of cell necrosis. No evidence of apoptosis or necrosis was detected in lymphocytes exposed to CI-994 for 4 hours. After 24 hours, concentration-dependent increases in apoptosis characterized by DNA condensation, DNA fragmentation, and/or externalization of phosphatidyl serine were seen at CI-994 concentrations as low as 1 μM and were statistically significant beginning at 10 μM. Ultrastructural analysis confirmed the presence of DNA condensation, DNA fragmentation, cell shrinkage, and membrane blebbing in cells exposed to 30 μM CI-994. After 24 hours, the percent of maximum LDH release from lymphocytes treated with 10 and 30 μM CI-994 was 7% and 15%, respectively, compared with 0% in the controls. In comparison, morphological changes of apoptosis detected by fluorescent microscopy were observed in 79% of the lymphocytes at these two concentrations. Additionally, apoptosis was seen in more than 24% of lymphocytes exposed to 1 and 3 μM CI-994, whereas maximum LDH release was less than or equal to 1% at these concentrations. These results show that apoptosis is the primary mode of cell death in rat lymphocytes exposed to CI-994 in vitro.