REPOSITORY > RESULTS

Abstract

Cytostatics, also named anticancer drugs represent a group of pharmaceuticals that is mainly used in cancer treatment. These drugs are essentially targeting processes leading to the prevention of growth and tumour cells division via interference with the genetic material of tumour cells. However, the most commonly used cytostatics are not specific enough to target only tumour cells and they affect also normal cells of exposed humans and other organisms. Residues of cytostatics are released after human consumption into the environment, where they might affect nontarget aquatic organisms and indirectly exposed humans even at the levels of sub- to few ng/L in particular during chronic exposure. Nevertheless, ecotoxicological data that would allow evaluation of the environmental and human health risks posed by cytostatic residues released into aquatic environment are scarce. In the present thesis we focused our studies on exploring (eco)toxicity and genotoxicity of several most consumed cytostatics (i.e. 5-fluorouracil; 5-FU, cisplatin; CDDP, etoposide ; ET, imatinib mesilate; IM, cyclophosphamide; CP and ifosfamide; IF), their metabolites and transformation products towards zebrafish (Danio rerio) liver cells (ZFL) and human derived cells (human hepatoma HepG2 cells and isolated peripheral lymphocytes) in vitro as single compounds and their mixtures. The studies showed that 5-FU, CDDP, ET and IM induced genotoxic effects in both in vitro cell models which was expected for 5-FU, CDDP and ETO and is in accordance with their mechanism of therapeutic action. Surprisingly, also IM, which was developed as specific drug that acts as selective inhibitor of aberrantly expressed tyrosine kinase in certain types of cancer cells and is not classified as genotoxic, showed genotoxic activity towards nontarget cells. The analyses of the expression of DNA damage responsive genes indicated that its genotoxic activity is probably not due to direct interaction with DNA processing. This indicates that compared to other three cytostatics chronic exposure to IM probably represent a lower hazard for aquatic organisms and humans. Our studies also showed that ZFL cells are an in vitro model of choice for studying environmental pollutants. The studies of the mixtures of cytostatics demonstrated that in contrast to single drugs, which exerted genotoxic effects only at high for environment irrelevant concentrations, they affected ZFL cells at low, for environmental contamination relevant concentrations at which individual compounds are inactive. IN accordance, we showed that samples of hospital wastewaters that contained various cytostatics, their metabolites and transformation products induced ecotoxic and genotoxic effects in exposed crustaceans, plants and in ZFL cells. Furthermore, we demonstrated that certain metabolites and/or transformation products of CP and IF are even more toxic and hazardous than the parent compounds. To explore long-term adverse effects of 5-FU on aquatic organisms a two-generation toxicity study with zebrafish has been performed. In addition to standard toxicological endpoints, the induction of genotoxic effects and a whole genome gene expression profiling were performed. The results demonstrated that chronic exposure to environmentally relevant concentration of 5-FU (10 ng/L) induces histopathological changes in the liver and kidney, along with the genotoxic effects and deregulation of several DNA-damage-responsive genes and oncogenes, while classical ecotoxicological endpoints, such as survival, growth, hatching and reproduction, were not affected. Anyways, the observed genotoxicity and degenerative changes may lead to reduced fitness of fish populations, which may over long-term exposure over several generations lead to extinction of susceptible organisms even at very low concentrations of the drugs. Taken together the studies showed that certain highly consumed cytostatics do represent a risk for the environment and humans. Due to their genotoxic mechanism of action, environmental risk assessment for cytostatics should be mandatory irrespective of the predicted environmental concentrations. In addition to parental compounds, also their metabolites, transformation products and complex mixtures should be included in the environmental monitoring and risk assessments.