Tehranolide inhibits cell proliferation via calmodulin inhibition, PDE, and PKA activation

Tehranolide, natural sesquiterpene lactone with an endoperoxide group, has been shown to inhibit cell growth in cancer cells. Tehranolide was purified from Artemisia diffusa. To detect cell viability and proliferation, MTT assay was performed. In order to determine the role of tehranolide on calmodulin (CaM) structure and activity, its effects were evaluated with fluorescence emission spectra and CaM-mediated activation of phosphodiesterase (PDE1), in comparison with artemisinin. In fact, PDE1 inhibition, cAMP accumulation, and cAMP-dependent protein kinase A (PKA) activation were examined. The inhibitory effect of tehranolide on CaM structure is more than artemisinin. The kinetic analysis of tehranolide-CaM interaction has shown that this agent competitively inhibited the activation of PDE1 without affecting Vmax. Tehranolide increased Km value in higher amounts compared with artemisinin. Moreover, tehranolide had a cytotoxic effect on K562 cell line but not on normal human lymphocytes. Additionally, PDE inhibition and consequent cAMP accumulation and PKA activity were required for inhibiting cancer cell growth by tehranolide. Our results show that tehranolide significantly reduces cell proliferation in a time and dose-dependent manner in K562 cells via CaM inhibition, following PDE inhibition, cAMP accumulation, and consequent PKA activity.