Naringenin enhances anti-proliferation effect of 1-ferrocenyl-3-(4-methylsulfonylphenyl) propen-1-one on two different cells via targeting calmodulin signaling pathway.

Background: FMSP is a synthesized ferrocene derivative with anti-cancer characteristics on tumor cells. Naringenin is a polyphenolic flavonoid with anti-tumor ability.

Methods: Cell viability and proliferation of two cancer cells and a normal cell line after treatment with these agents were determined with MTT assay. To predict the possible interaction between calmodulin (CaM) and FMSP and naringenin, docking studies were performed. By using fluorescence emission spectra, the effects of FMSP and naringenin on CaM structure and activity were studied. CaM-dependent activation of phosphodiesterase 1 (PDE1) by FMSP in relation to naringenin and their combination were compared. Effects of these compounds on PDE1 inhibition, cAMP accumulation, and cAMP-dependent protein kinase A (PKA) activation were assayed.

Results: The combination of FMSP and naringenin had more inhibitory effects on CaM structure than FMSP and naringenin alone. Results of docking analyses also confirmed efficient interaction of the two compounds with a hydrophobic pocket of calmodulin active site. Kinetic analyses of these agents' interaction with CaM showed FMSP and naringenin both competitively inhibited PDE1 activation without changing the Vmax parameter. FMSP and naringenin synergistically increased Km values at a higher level compared to FMSP or naringenin alone. The combination of these two agents also had more cytotoxic effects on cancer cells than FMSP alone.

Conclusions: It was shown that mechanism of proliferation inhibition in both cancer cells by these compounds is based on CaM and consequent PDE inhibition followed by intracellular cAMP level elevation and increased PKA activity in a dose-dependent manner.