title: Anticancer activity of a cis-dichloridoplatinum(ii) complex of a chelating nitrogen mustard: insight into unusual guanine binding mode and low deactivation by glutathione.
abstract: A pyridine ring containing a chelating nitrogen mustard ligand bis(2-chloroethyl)pyridylmethylamine hydrochloride (L2·HCl) was synthesized from bis(2-hydroxyethyl)pyridylmethylamine (L1) on reaction with thionyl chloride. Both the ligands upon reaction with cis-[PtCl2(DMSO)2] afforded square planar complexes cis-[PtCl2(L1)] (1) and cis-[PtCl2(L2)] (2) respectively. Both the complexes were characterized by NMR, IR, UV and elemental analysis. 2 crystallized in the P21/c space group. 2 shows greater solution stability than 1 in kinetic studies by 1H NMR. Both 1 and 2 bind the model nucleobase 9-ethylguanine (9-EtG) and form multiple mono-adducts. Existence of unusual N7,O6 chelated guanine bound 2 (2e) was traced. Binding studies of 2 with glutathione (GSH) show formation of a mono-adduct cis-[PtCl(L2)SG] (2c), which transformed within a day to give an aziridinium ion of L2 (2b) after loss of L2. In vitro cytotoxicity of ligands, complexes and the clinical anticancer drug cisplatin show that 2 is the most potent against MCF-7, A549 and MIA PaCa2 exhibiting IC50 values of 12.6 ± 0.8, 18.2 ± 1.8 and 4.2 ± 1.0 μM respectively. The in vitro cytotoxicity of 2 against MCF-7, A549 and MIA PaCa2 was also probed in hypoxia and in the presence and absence of added GSH. Even in the presence of excess GSH in hypoxia, 2 exhibits significant cytotoxicity against MIA PaCa2 and MCF-7 with IC50 of 4.4 ± 0.8 and 12.5 ± 1.1 μM respectively. Metal accumulation studies by ICP-MS display greater cellular internalization of 2, than 1 and cisplatin in MCF-7 cells. 2 arrests the cell cycle at sub G1 and G2/M phases in MCF-7 whereas cisplatin exhibits S phase arrest to be dominant with increase in concentration. Complex 2 exhibits a change in mitochondrial membrane potential, caspase activity and suggests apoptotic cell death through the intrinsic pathway. Moreover it is encouraging to find that 2 also restricts angiogenesis in chick embryo.
authors.affiliation: Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur Campus, Nadia-741246, West Bengal, India. a.mukherjee@iiserkol.ac.in.
authors.forename: Subhendu
authors.initials: S
authors.lastname: Karmakar
authors.affiliation: Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur Campus, Nadia-741246, West Bengal, India. a.mukherjee@iiserkol.ac.in.
authors.forename: Kallol
authors.initials: K
authors.lastname: Purkait
authors.affiliation: Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur Campus, Nadia-741246, West Bengal, India. a.mukherjee@iiserkol.ac.in.
authors.forename: Saptarshi
authors.initials: S
authors.lastname: Chatterjee
authors.affiliation: Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur Campus, Nadia-741246, West Bengal, India. a.mukherjee@iiserkol.ac.in.
authors.forename: Arindam
authors.initials: A
authors.lastname: Mukherjee
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002614:Chelating Agents / Q000737:chemistry; D002642:Chick Embryo; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism*; D006147:Guanine / Q000737:chemistry*; D006801:Humans; D008024:Ligands; D061986:MCF-7 Cells; D008466:Mechlorethamine / Q000737:chemistry*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008744:Methylamines / Q000737:chemistry; D018919:Neovascularization, Physiologic / Q000187:drug effects; D009944:Organoplatinum Compounds / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D013237:Stereoisomerism
chemical_list: D000970:Antineoplastic Agents; D002614:Chelating Agents; D008024:Ligands; D008744:Methylamines; D009944:Organoplatinum Compounds; D008466:Mechlorethamine; D006147:Guanine; C027451:methylamine; D053148:Caspase 3; D053179:Caspase 7; D005978:Glutathione