Tumor suppressive activities of solvatochromic 3,3’‐azadimethylene dinaphthospiropyran in colon cancer model

Spiropyrans have been extensively investigated because of their thermo- and photochromic characteristics, but their biotherapeutic properties have not been explored much. We report anti-proliferative properties of a novel 3,3'-azadimethylene dinaphthospiropyran 11. Dibenzospiropyrans and dinaphthospiropyrans were synthesized by a simple and expedient method using acid-catalyzed aldol condensation of salicylaldehyde and 2-hydroxy-1-naphthaldehyde, respectively, with cyclic ketones. Together with structural elucidation by 2D NMR and X-ray crystallography studies, we provide a putative mechanism for their formation. Compound 11 showed solvatochromism and exhibited altered spectral characteristics depending on the pH. In acidic conditions, 11 remains in open form, whereas upon alkalinization it reverts back to closed form. Based on the in vitro anti-proliferative activity in H441, HCT-116, MiaPaCa-2, and Panc-1 cancer cell lines, 11 was submitted to further investigation. It reduced HCT116 colonosphere formation and demonstrated induction of caspase cascade, suggesting apoptosis. In vitro proliferation assays also suggested that HCl and trifluoroacetate salts of 11 are more effective. Treatment of mice carrying HCT-116 xenografts with 11 (5 µg/day, intraperitoneal for 3 weeks) suppressed tumor growth by 62%. Overall, the results reveal a new series of structurally complex, but relatively easy to synthesize molecules of which compound 11 represents a lead for anticancer development.