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A ruthenium(II) aquo complex [Ru(dipic)(PPh3)2(OH2)], (1 A), bearing O,N,O‐coordinated 2,6‐dipicolinate was synthesized via reaction of [Ru(PPh3)3Cl2] with 2,6‐dipicolinic acid. Crystal structure of 1 A was determined. Utilizing 1 A as a synthon, three new complexes were synthesized. Reaction of 1 A with a bidentate NHC‐ligand, viz. 1‐methyl‐3‐(2′‐pyridyl)imidazole (IMeCN), afforded [Ru(dipic)(IMeCN)(PPh3)], (2 A). Similar reactions of 1 A with two pincer ligands, viz. 2,6‐bis(1′‐methyl imidazolyl)pyridine (IMeCNC) and 2,2′;6′,2"‐terpyridine (trpy), respectively yielded [Ru(dipic)(IMeCNC)(PPh3)], (3 A) and [Ru(dipic)(trpy)(PPh3)], (3 B). Structure of 2 A was optimized by DFT method. Structures of 3 A and 3 B were determined by X‐ray crystallography. In both 3 A and 3B the 2,6‐dipicolinate ligand was found to be N,O‐coordinated with one carboxy end remaining unbound to the metal center. Anticancer property of 2 A, 3 A and 3 B was studied and compared. Cytotoxicity of 3 A, studied against three selected cancer cell lines, viz. chronic myelogenous leukemia cell line (K562), hepatocellular carcinoma cell line (HepG2) and breast adenocarcinoma cell line (MCF7), was found to be the most promising. It displayed the best activity against K562, while it did not have any appreciable effect on its normal counterpart, viz. the human peripheral blood mononuclear cells (hPBMC). The comparative cytotoxicity studies indicated that presence of the C,N,C‐coordinated pincer NHC ligand in 3 A, together with presence of the free carboxylate end of N,O‐coordinated dipic ligand, are presumably responsible for its superior cytotoxic behavior. [ABSTRACT FROM AUTHOR]

Background: Hydroxychavicol (HCH), a constituent of Piper betle leaf has been reported to exert anti-leukemic activity through induction of reactive oxygen species (ROS). The aim of the study is to optimize the oxidative stress –induced chronic myeloid leukemic (CML) cell death by combining glutathione synthesis inhibitor, buthionine sulfoximine (BSO) with HCH and studying the underlying mechanism. Materials and Methods: Anti-proliferative activity of BSO and HCH alone or in combination against a number of leukemic (K562, KCL22, KU812, U937, Molt4), non-leukemic (A549, MIA-PaCa2, PC-3, HepG2) cancer cell lines and normal cell lines (NIH3T3, Vero) was measured by MTT assay. Apoptotic activity in CML cell line K562 was detected by flow cytometry (FCM) after staining with annexinV-FITC/propidium iodide (PI), detection of reduced mitochondrial membrane potential after staining with JC-1, cleavage of caspase- 3 and poly (ADP)-ribose polymerase proteins by western blot analysis and translocation of apoptosis inducing factor (AIF) by confocal microscopy. Intracellular reduced glutathione (GSH) was measured by colorimetric assay using GSH assay kit. 2′,7′-dichlorodihydrofluorescein diacetate (DCF-DA) and 4-amino-5-methylamino-2′,7′-difluorofluorescein (DAF-FM) were used as probes to measure intracellular increase in ROS and nitric oxide (NO) levels respectively. Multiple techniques like siRNA transfection and pharmacological inhibition were used to understand the mechanisms of action. Results: Non-apoptotic concentrations of BSO significantly potentiated HCH-induced apoptosis in K562 cells. BSO potentiated apoptosis-inducing activity of HCH in CML cells by caspase-dependent as well as caspase-independent but apoptosis inducing factor (AIF)-dependent manner. Enhanced depletion of intracellular GSH induced by combined treatment correlated with induction of ROS. Activation of ROS- dependent JNK played a crucial role in ERK1/2 activation which subsequently induced the expression of inducible nitric oxide synthase (iNOS). iNOS- mediated production of NO was identified as an effector molecule causing apoptosis of CML cells. Conclusion/Significance: BSO synergizes with HCH in inducing apoptosis of CML cells through the GSH-ROS-JNK-ERK-iNOS pathway. [ABSTRACT FROM AUTHOR]

Abstract: Chlorogenic acid (Chl) has been reported to possess a wide range of biological and pharmacological properties including induction of apoptosis of Bcr-Abl+ chronic myeloid leukemia (CML) cell lines and clinical leukemia samples via inhibition of Bcr-Abl phosphorylation. Here we studied the mechanisms of action of Chl in greater detail. Chl treatment induced an early accumulation of intracellular reactive oxygen species (ROS) in Bcr-Abl+ cells leading to downregulation of Bcr-Abl phosphorylation and apoptosis. Chl treatment upregulated death receptor DR5 and induced loss of mitochondrial membrane potential accompanied by release of cytochrome c from the mitochondria to the cytosol. Pharmacological inhibition of caspase-8 partially inhibited apoptosis, whereas caspase-9 and pan-caspase inhibitor almost completely blocked the killing. Knocking down DR5 using siRNA completely attenuated Chl-induced caspase-8 cleavage but partially inhibited apoptosis. Antioxidant NAC attenuated Chl-induced oxidative stress-mediated inhibition of Bcr-Abl phosphorylation, DR5 upregulation, caspase activation and CML cell death. Our data suggested the involvement of parallel death pathways that converged in mitochondria. The role of ROS in Chl-induced death was confirmed with primary leukemia cells from CML patients in vitro as well as in vivo in nude mice bearing K562 xenografts. Collectively, our results establish the role of ROS for Chl-mediated preferential killing of Bcr-Abl+ cells. [ABSTRACT FROM AUTHOR]