A new curcumin derivative, HBC, interferes with the cell cycle progression of colon cancer cells via antagonization of the Ca²⁺/calmodulin function

HBC (4-{3,5-Bis-[2-(4-hydroxy-3-methoxy-phenyl)-ethyl]-4,5-dihydro-pyrazol- 1-yl}-benzoic acid) is a recently developed curcumin derivative which exhibits potent inhibitory activities against the proliferation of several tumor cell lines. In the present study, we identified Ca²⁺/calmodulin (Ca ²⁺/CaM) as a direct target protein of HBC using phage display biopanning. Ca²⁺/CaM-expressing phages specifically bound to the immobilized HBC, and the binding was Ca²⁺ dependent. Moreover, flexible docking modeling demonstrated that HBC is compatible with the binding cavity for a known inhibitor, W7, in the C-terminal hydrophobic pocket of Ca²⁺/CaM. In biological systems, HBC induced prolonged phosphorylation of ERK1/2 and activated p21^WAF1 expression, resulting in the induction of G₀/G₁ cell cycle arrest in HCT15 colon cancer cells. These results suggest that HBC inhibits the cell cycle progression of colon cancer cells via antagonizing of Ca²⁺/CaM functions.