After being administrated to humans or animals, pharmaceuticals may be metabolized by a variety of mechanisms and pathways within the body. Once these compounds and/or their metabolites are excreted, they may undergo degradation in the aquatic environment. Unfortunately, a rapid and complete mineralization cannot always be guaranteed, whereas relatively stable transformation products (TPs) may be formed. The largest part of older studies focused on investigation of the elimination kinetics of parent compounds without considering the amount and chemical structure of individual TPs. Only recently, there is an increasing trend to deliver such information. Nevertheless, since drugs are defined as significant environmental pollutants, it is not only important to elucidate their TPs, but also necessary to investigate whether these formed compounds preserve the same mode of action as the parent compound or are even more toxic. Thus, two main objectives of this thesis can be formulated. Firstly, to highlight the concern originated by metabolites and transformation products of pharmaceuticals that contaminate the environment. Hereby, the already-published knowledge on TPs within a certain selection of drugs is assessed to exemplify the number and quality of the existing information on their TPs. Secondly, to particularly investigate the fate of the antibiotic ciprofloxacin (CIP). This is done by (a) evaluating the suitability and sustainability of the photolytic decomposition as an advanced water treatment technique, (b) monitoring the course of genotoxicity of the irradiated mixtures using a battery of genotoxicity and cytoxicity in vitro assays, and (c) considering the potential genotoxicity for CIP´s individual TPs by the employment of in silico approaches using quantitative structure activity relationships (QSAR) models. This thesis based on the results and conclusions of five articles, which can be found in the appendix. A systematic literature review was conducted on the current state of knowledge on pharmaceuticals and its derivatives in the environment. Two groups, namely antibiotics and anticancer drugs, were considered more closely with respect to the availability of chemical structures for their TPs. Furthermore, the photodegradation of CIP as well as a preliminary toxicity assessment of its identified TPs were investigated in three research papers. An extensive review with a table at its core shows the existing data on 158 TPs, which already have an assigned registry number in chemical abstracts service (CAS-RN), was presented. In total, 294 TPs, identified with chemical structures in the literature, were found for 15 compounds out of the 21 that were selected as target compounds. Eleven TPs, created from CIP, were identified by high-performance liquid chromatography/high-resolution multiple-stage mass spectrometry. It was detected that the transformation of CIP mainly occurred through substitution of fluorine, defluorination, hydroxylation of the quinolone core and the breakdown of the piperazine ring. Some of the identified TPs of CIP were predicted as genotoxic by QSAR analysis, while the experimental testing for a few genotoxic and cytotoxic endpoints showed that the potential of the resultant mixtures could be primarily dependent on the concentration of residual CIP. In contrast, irradiation mixtures were neither mutagenic in the Ames Test nor genotoxic in the in vitro Micronucleus Test. It is possible that the effect of the TPs was masked by antagonistic mixture interactions and/or they were not formed at effectively concentrations. Nevertheless, all of the identified TPs of CIP still retained the core quinolone moiety, which is responsible for the biological activity. Thus, a more comprehensive assessment, encompassing more genotoxic endpoints, chemical analysis characterization and exposure analyses, needs to be conducted. Information available on TPs demonstrates that already slight changes in treatment conditions and processes result in the formation of different TPs. Nevertheless, most of the transformation products could neither be identified nor fully assessed regarding their toxicity. This, in turn, presents a major challenge for the identification and assessment of TPs. Hence, from a practical and sustainability point of view, limiting the input of pharmaceuticals into effluents as well as improving their (bio)degradability and elimination behavior, instead of only relying on advanced effluent treatments, is urgently needed. Solutions that focus on this
Recent studies have confirmed that the aquatic ecosystem is being polluted with an unknown cocktail of pharmaceuticals, their metabolites and/or their transformation products (TPs). Although individual pharmaceuticals are typically present at low concentrations, their continuous input into the aquatic ecosystem and their toxic and persistent presence are the major environmental concerns. Therefore, it is necessary to assess the environmental risk caused by these aquatic pollutants. Data on exposure are required for quantitative risk assessment of parent compounds and their transformation products (TPs) and/or metabolites. Such data are mostly missing, especially for TPs, because of the non-availability of TPs and very often metabolites for experimental testing. Therefore, the application of different in silico tools for qualitative risk assessment can be used. Also, the presence of these micro-pollutants (active pharmaceutical ingredients, APIs) in the aquatic cycle are increasingly seen as a challenge to the sustainable management of water resources worldwide due to ineffective effluent treatment and other measures for their input prevention. Given the poor prognosis for effluent treatment (‘end of the pipe’ approach) for input prevention of APIs in the environment, it is necessary to focus on the ‘beginning of the pipe’ strategy. The very beginning of the pipe is the molecules themselves. Therefore, novel approaches are needed like designing greener pharmaceuticals, i.e. better biodegradable ones in the aquatic environment after their release. Therefore, the present research work focused on two important topics a) assessment of the environmental risk associated with the presence of highly prescribed drugs and their TPs; b) demonstrating the feasibility of the ‘benign by design’ concept for designing biodegradable drug derivatives, which will have the better biodegradability in the environment after their release. The present thesis includes four research articles (1-4) which address these approaches. The first article is about the qualitative environmental risk assessment using the example of transformation products formed during photolysis (photo-TPs) of Diatrizoic acid (DIAT). Photolysis is the chemical reaction in which the compound is broken down by photons and often in combination with hydroxyl radicals. Photolysis is the most common abatement process of micro-pollutants in the environment. The qualitative risk assessment of DIAT and selected photo-TPs was performed by the PBT approach (i.e. Persistence, Bioaccumulation and Toxicity), using chemical analysis, experimental biodegradation test assays, QSAR models with several different toxicological endpoints and in silico read-across approaches. The second article addresses a tiered approach of implementing green and sustainable chemistry principles for theoretically designing better biodegradable and pharmacologically potent pharmaceuticals derivatives. Photodegradation process coupled with LC-MSn analysis, biodegradability testing and in silico tools such as quantitative structure-activity relationships (QSAR) analysis and molecular docking proved to be a very significant approach for the preliminary stages of designing chemical structures that would fit into the ´benign by design´ concept in the direction of green and sustainable pharmacy. Metoprolol (MTL) was used as an example. The third article was also the conceptual framework to get new drug derivatives that are biodegradable in order to tackle the global challenge of micro-pollutants in the aquatic cycle. This study increased the knowledge about the role of the attachment of certain functionalities to the parent drug molecule for its biodegradability whilst conserving drug-likeness. This approach was in the past a totally neglected issue within drug development. Atenolol (ATL), a selective β1 blocker, was selected as an example to incorporate the additional attribute such as biodegradability into its molecular structure while conserving its substructures responsible for β adrenergic receptor blocker activity. In fourth article, the concept of designing green biodegradable pharmaceuticals has been proven through expanded experimental analysis setting out from the experiences collected as described in article two and three. This study could be considered as a more extensive feasibility study of rational design of green drug derivatives. The non-selective β-blocker Propranolol (PPL) was used as an example. The risk assessment study (Article #1) contributes in enhancing the existing knowledge about the life cycle and behavior (fate) of pharmaceuticals with a special focus on photo-TPs which are generally formed during advanced effluent treatment and enter as such into the environment. Based on the obtained results, the application of the in silico tools for qualitative risk assessment analysis increased knowledge space about the environmental fate of TPs in case of their non-availability for experimental testing. The benign by design studies (Article #2-4) were based on the knowledge and experience collected during the work on DIAT. It demonstrated the feasibility of a novel approach of designing comparatively better degradable and pharmacological potent derivatives through the implementation of ´green chemistry´ principles. However, the present approach is in the juvenile stage and further knowledge has to be collected beforehand for the full implementation of this approach into drug development.