Interaction of Zn with Losartan. Activation of Intrinsic Apoptotic Signaling Pathway in Lung Cancer Cells and Effects on Alkaline and Acid Phosphatases

Abstract

A new losartan [2-butyl-5-chloro-3-[[4-[2-(2H-tetrazol-5-yl)phenyl]phenyl]methyl]imidazol-4-yl]methanol zinc(II) complex [Zn(Los)Cl], was synthesized and characterized. The crystal structure was determined by x-ray diffraction methods. When aqueous solutions of the ligand and the metal were mixed, the known and more soluble powder [Zn(Los) 2 ].3H 2 O (ZnLos) complex has been obtained. The interactions with phosphatases showed a concerted mechanism displayed by the Zn ions and ZnLos up to 500 μM concentration: a decrease of the acid phosphatase (AcP) associated with an increase in the alkaline phosphatase (ALP) activities. The complex and ZnSO 4 showed a cytotoxic behavior on human lung A549 cancer cell line at concentrations higher than 75 μM with reactive oxygen species (ROS) generation and GSH (and GSH/GSSG ratio) depletion. Apoptotic cells were observed using terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) method, a mechanism accompanied by upregulation of BAX protein, downregulation of Bcl-XL and release of caspase-3. The BAX/Bcl-XL ratio was found to be significantly higher in cells exposure to ZnLos than cells treated with ZnSO 4 , in agreement with the higher apoptotic percentage of cells found for the complex. Cell death was found to be produced by apoptosis and no necrosis has been observed. On the contrary, losartan exerted low effects on phosphatases, produced some reduction of cancer cell viability (concentrations > 250 μM, number of apoptotic cells similar to the basal) with low ROS depletion, without alteration of the GSH/GSSG and low BAX/Bcl-XL ratios. In the MRC-5, normal lung fibroblasts cell line only ZnSO 4 at concentrations higher than 200 μM displays cytotoxic effects.