Factors affecting biological effects of metallodrugs

Antitumor metallodrugs are used in clinical treatment very often. Well known cisplatin is the most notable and the most successful representative of this group. There are a lot of drugs prepared on the basis of cisplatin and there are continuously prepared new compounds which should not have such wide spectra of side effects and nevertheless it should have the same or higher efficiency in antitumor treatment, including broader spectrum of human tumors sensitive to metallodrugs. Successfulness of new synthesized cytostatics is based on their ability of both transportation through the cell membrane and activation. Characteristic feature of many antitumor active drugs, which are prepared on the basis of heavy metals, is their direct binding to the DNA molecule. During platinum compounds binding, four types of DNA adducts (cross-links) are formed: monofunctional adduct, intrastrand and interstrand and interduplex cross-links. These bindings result in nucleic acid structure changes including bending and unwinding the DNA. Most of these damages are recognized by DNA-binding proteins and DNA-repairing enzymes. Polynuclear platinum compounds belong among newly synthesized antitumor platinum drugs. Structure of these compounds is characterised by two or three heavy metal atoms connected by more or less flexible organic chains. These drugs form intramolecular or intermolecule interstrand adducts with higher probability than mononuclear heavy metal compounds. The characteristics of newly synthesized compounds are studied in vitro and subsequently their effects on cell lines are tested. The present work deals with the effects of newly synthesized analogues of cisplatin (cis-[PtCl2(nHaza)2], nHaza is 7-azaindole-halogeno substituent) on ovarial carcinoma cell line A2780. The cytotoxicity of compounds was tested by means of MTT assay [3-(4,5-methylethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide]. It is well known that cisplatin creates intrastrand and interstrand DNA adducts, so these new analogues of cisplatin were tested with respect to creating of interstrand cross-links. Interstrand cross-links are studied because they present more serious damage of DNA. Cisplatin belongs to the most comprehensively studied therapeutics; it is known that damage of cells caused by this agent very often leads to the cell death, such as Programmed Cell Death, i.e. apoptosis. In the present work, the effect of 7-azaindole derivatives of cisplatin on induction of programmed cell death and on consequences to the cell cycle has been studied. Next part of the work has been concerned on repair mechanisms of DNA damaged by antitumor drugs and on ability of these compounds to form interduplex cross-links. Cells exert several types of DNA repair mechanisms. Damages caused by compounds on the basis of cisplatin are repaired by nucleotide excision repair (NER) mechanism. Interduplex cross-links represent minor type of DNA adducts, which can be set up mainly by polynuclear compounds. This type of cross-links is created when the molecules of DNA lie in close proximity. This feature is very common in cell nucleus during replication and recombination. Under the in vitro conditions, this environment presented in cell may be simulated by solutions containing high concentrations of ethanol and salt. All obtained results should help in future studies of another features associated with the metabolism and reactivity of antitumor platinum compounds. The main approach is to improve their pharmacological action such as reduction of inherent and acquired cancer cell resistance and minimisation of side effects.