ABSTRACT
A new tetrafunctional dinuclear platinum complex trans,trans-[{PtCl2(NH3)}2(piperazine)] with sterically rigid linking group was designed, synthesized and characterized. In this novel molecule, the DNA-binding features of two classes of the platinum compounds with proven antitumor activity are combined, namely trans oriented bifunctional mononuclear platinum complexes with a heterocyclic ligand and polynuclear platinum complexes. DNA-binding mode of this new complex was analyzed by various methods of molecular biology and biophysics. The complex coordinates DNA in a unique way and interstrand and intrastrand cross-links are the predominant lesions formed in DNA in cell-free media and in absence of proteins. An intriguing aspect of trans,trans-[{PtCl2(NH3)}2(piperazine)] is that, using a semi-rigid linker, interstrand cross-linking is diminished relative to other dinuclear platinum complexes with flexible linking groups and lesions that span several base pairs, such as tri- and tetrafunctional adducts, become unlikely. In addition, in contrast to the inability of trans,trans-[{PtCl2(NH3)}2(piperazine)] to cross-link two DNA duplexes, the results of the present work convincingly demonstrate that this dinuclear platinum complex forms specific DNA lesions which can efficiently cross-link proteins to DNA. The results substantiate the view that trans,trans-[{PtCl2(NH3)}2(piperazine)] or its analogues could be used as a tool for studies of DNA properties and their interactions or as a potential antitumor agent. The latter view is also corroborated by the observation that trans,trans-[{PtCl2(NH3)}2(piperazine)] is a more effective cytotoxic agent than cisplatin against human tumor ovarian cell lines.
Subject(s)
DNA/metabolism , Piperazines/chemistry , Platinum Compounds/chemistry , Platinum/chemistry , Animals , Antineoplastic Agents/chemistry , Antineoplastic Agents/pharmacology , Base Sequence , Cattle , Cell Line, Tumor , Cisplatin/chemistry , Cisplatin/metabolism , Cisplatin/pharmacology , Cross-Linking Reagents/chemistry , Cross-Linking Reagents/pharmacology , DNA/chemistry , DNA/genetics , DNA Adducts/chemistry , DNA, Superhelical/metabolism , DNA-Binding Proteins/metabolism , Female , Humans , Inhibitory Concentration 50 , Kinetics , Ligands , Magnetic Resonance Spectroscopy , Models, Chemical , Molecular Sequence Data , Molecular Structure , Ovarian Neoplasms/drug therapy , Ovarian Neoplasms/pathology , Piperazine , Platinum Compounds/chemical synthesis , Polarography , Spectrometry, Fluorescence , Temperature , Transcription, GeneticABSTRACT
Replacement of one ammine in clinically ineffective trans-[PtCl2(NH3)2] (transplatin) by a planar N-heterocycle, thiazole, results in significantly enhanced cytotoxicity. Unlike 'classical' cisplatin {cis-[PtCl2(NH3)2]} or transplatin, modification of DNA by this prototypical cytotoxic transplatinum complex trans-[PtCl2(NH3)(thiazole)] (trans-PtTz) leads to monofunctional and bifunctional intra or interstrand adducts in roughly equal proportions. DNA fragments containing site-specific bifunctional DNA adducts of trans-PtTz were prepared. The structural distortions induced in DNA by these adducts and their consequences for high-mobility group protein recognition, DNA polymerization and nucleotide excision repair were assessed in cell-free media by biochemical methods. Whereas monofunctional adducts of trans-PtTz behave similar to the major intrastrand adduct of cisplatin [J. Kasparkova, O. Novakova, N. Farrell and V. Brabec (2003) Biochemistry, 42, 792-800], bifunctional cross-links behave distinctly differently. The results suggest that the multiple DNA lesions available to trans-planaramine complexes may all contribute substantially to their cytotoxicity so that the overall drug cytotoxicity could be the sum of the contributions of each of these adducts. However, acquisition of drug resistance could be a relatively rare event, since it would have to entail resistance to or tolerance of multiple, structurally dissimilar DNA lesions.
Subject(s)
Antineoplastic Agents/toxicity , Cross-Linking Reagents/toxicity , DNA Adducts/chemistry , Organoplatinum Compounds/toxicity , Thiazoles/toxicity , Antineoplastic Agents/chemistry , Cisplatin/chemistry , Cisplatin/toxicity , Cross-Linking Reagents/chemistry , DNA/biosynthesis , DNA Adducts/metabolism , DNA Repair , High Mobility Group Proteins/metabolism , Nucleic Acid Conformation , Organoplatinum Compounds/chemistry , Thiazoles/chemistryABSTRACT
Piroxicam (=Hpir) is a non-steroidal anti-inflammatory and an anti-arthritic drug. VO(2+), Mn(2+), Fe(3+), MoO(2)(2+) and UO(2)(2+) complexes with deprotonated piroxicam have been prepared and characterized with the use of infrared, UV-Vis, nuclear magnetic resonance and electron paramagnetic resonance spectroscopies. The experimental data suggest that piroxicam acts as a deprotonated bidentate ligand in all complexes and is coordinated to the metal ion through the pyridine nitrogen and the amide oxygen. Molecular mechanics calculations in the gas state have been performed in order to propose a model for the Fe(3+), VO(2+) and MoO(2)(2+) complexes. Potential anticancer cytostatic and cytotoxic effects of piroxicam complexes with VO(2+), Mn(2+) and MoO(2)(2+) on human promyelocytic leukemia HL-60 cells have been investigated. Among all complexes, only VO(pir)(2)(H(2)O) clearly induces apoptosis after 24-h incubation, whereas piroxicam induces apoptosis after 57-h incubation.
