Characterization of Stable Pyrazole Derivatives of Curcumin with Improved Cytotoxicity on Osteosarcoma Cell Lines

Curcumin (CUR) is a natural molecule that is unstable due to the presence of a bis-ketone. To obtain more stable derivatives in biological fluids, the bis-ketone was replaced with pyrazole or O-substituted oximes. Their stability in solution was studied by UV–visible spectrophotometry. The effects on proliferation were studied by MTT assay and/or clonogenicity assay. Induction of apoptosis was evaluated by annexin V staining and Western blot analysis. The bioavailability was obtained from the analysis of the molecular chemical–physical characteristics. The replacement of the bis-ketone with a pyrazole ring or O-substituted oximes improved the stability of all the CUR-derivative molecules. These derivatives were more stable than CUR in solution and were generally cytotoxic on a panel of cancer cell lines tested, and they promoted caspase-dependent apoptosis. Derivative 1 was the most potent in the osteosarcoma (OS) lines. With respect to CUR, this derivative showed cytotoxicity at least three times higher in the MTT assay. In addition, in the clonogenic assay, 1 maintained the activity in conditions of long treatment presumably by virtue of its improved stability in biological fluids. Notably, 1 should have improved chemical–physical characteristics of bioavailability with respect to CUR, which should allow for reaching higher blood levels than those observed in the CUR trials. In conclusion, 1 should be considered in future clinical studies on the treatment of OS, either alone or in combination with other medications currently in use.