Synthesis of β-Enaminonitrile-Linked 8-Methoxy-1H-Benzo[f]Chromene Moieties and Analysis of Their Antitumor Mechanisms

A series of 1H-benzo[f]chromene derivatives (4a-4q) bearing different aryl-substituted at the 1-postion were designed and synthesized via reaction of 6-methoxy-2-naphthol with a mixture of appropriate aromatic aldehydes and malononitrile under microwave conditions. The structures of the novel compounds 4b, 4c, 4f, 4g, 4i, 4l, 4m, and 4o-4q were established according to IR, 1H-NMR, 13C-NMR/13C-NMR-DEPT, and MS. The benzochromene derivative 4c with a single chlorine at meta position of phenyl ring and, to lesser extent, other benzochromenes with monohalogenated phenyl ring (4a, 4d-4f) exhibited the highest cytotoxicity against six human cancer cell lines MDA-MB-231, A549, HeLa, MIA PaCa-2, 5637, and Hep G2. Mechanisms of the cytotoxic activities of benzochromenes with monohalogenated phenyl ring (4a, 4c-4f) were further analyzed using triple-negative breast cancer cell line MDA-MB-231. Cell-cycle analysis showed accumulation of the treated cells in S phase for 4a, 4d-4f and S-G2/M phases for 4c. In vivo, 4a and 4c-4f inhibited growth, proliferation, and triggered apoptosis in preestablished breast cancer xenografts grown on the chick chorioallantoic membranes while exhibiting low systemic toxicity. Compounds 4a and 4c-4f increased levels of mitochondrial superoxide and decreased mitochondrial membrane potential resulting in initiation of apoptosis as demonstrated by caspase 3/7 activation. In addition, 4c induced general oxidative stress in cancer cells. SAR study confirmed that halogens of moderate size at meta or para positions of the pendant phenyl ring enhance the cytotoxic activity of 3-amino-1-aryl-8-methoxy-1H-benzo[f]chromene-2-carbonitriles and these compounds could serve as leads for development of novel anticancer therapies.