Multidrug Resistenz (MDR), die simultane Resistenz gegenüber strukturell und funktionell nicht-verwandten Zytostatika, stellt eine wesentliche Ursache für unzureichende Behandlungserfolge maligner Erkrankungen dar. Die inherente Resistenz bzw. Resistenzentwicklung gegenüber chemotherapeutischen Substanzen ist vor allem die Folge der Präsens und Regulation unterschiedlicher Transportproteine wie MDR1, MRP1, BCRP und MVP. In der Konsequenz kommt es zu alteriertem Influx und/oder Efflux von Zytostatika, verminderter Akkumulation und Effektivität von Chemotherapeutika. Sowohl Zytostatika als auch Zytokine zeigten modulierende Einflüsse auf die Expression der MDR-Gene MDR1, MRP1 und MVP (Kapitel 2-9). Zytostatika wie Adriamycin resultierten vorwiegend in induzierten MDR1-Expressionen, dem hauptsächlichen Interventionstarget zur Überwindung des klassischen MDR-Phänotyps. Zytokine wie TNFa führten, extern appliziert als auch durch Gentransfer, zur Chemosensitivierung der Tumorzellen, verbunden mit Down-Regulationen von MDR1 und MVP. Die Zytokin-vermittelte Überwindung des klassischen MDR-Phänotyps weist auf die Inklusion definierter Zytokine in etablierte Chemotherapieprotokolle hin, wie bereits angewendet bei der hyperthermen isolierten Extremitätenperfusion mit TNFa (Kapitel 13). Die Verwendung BCRP-spezifischer Ribozyme demonstrierte deren Potential zur Überwindung des BCRP-bedingten, atypischen MDR-Phänotyps. Darüber hinaus wurde gezeigt, dass die Expression der ABC-Transporter als auch des MVP durch Hyperthermie temperatur- und zeitabhängig induzierbar ist (Kapitel 10-13). Diese Hyperthermie-Induktion wird für MDR1 und MRP1 über den Transkriptionsfaktor YB-1 zeitnah zum Stressereignis vermittelt. In der klinischen Situation konnte anhand verfügbarer Biopsien von Kolonkarzinomen, Sarkomen und Melanomen, jeweils mittels Hyperthermie im Kontext multimodaler Behandlungsregime behandelt, kein direktes, generelles Risiko einer MDR1- oder MRP1-vermittelten, Hyperthermie-bedingten Induktion/Verstärkung einer MDR beobachtet werden. Die Analyse der Promotoren MDR-assoziierter Gene wie MDR1 und MVP zeigte deren Induzierbarkeit durch unterschiedliche Therapie-relevante Faktoren wie Zytostatika und Hyperthermie in verschiedenen in vitro- und in vivo-Modellen (Kapitel 10,14-20). Spezifische Sequenzmotive sind für die Stressfaktor-induzierte Bindung von Transkriptionsfaktoren wie YB-1 verantwortlich; Mutationen in diesen Sequenzbereichen modulierten die Induzierbarkeit (Kapitel 14,15,20). Der Einsatz Therapie-induzierbarer Promotoren unterschiedlicher MDR-Gene wie MDR1 (Kapitel 14-18) und MVP (Kapitel 19,20) erlaubt somit generell die Anpassung an etablierte Behandlungsprotokolle verschiedener Tumorentitäten. In fortführenden Arbeiten bleibt die erfolgreiche Anwendung von Therapie-induzierbaren MDR-Promotorsequenzen zur Expression therapeutisch relevanter Gene im Kontext einer Gentherapie maligner Erkrankungen zu prüfen. / Multidrug resistance, the simultaneous resistance towards structurally and functionally unrelated cytostatic drugs, still represents a major cause of cancer treatment failure. Inherent or acquired resistance against a wide variety of chemotherapeutic drugs depends mainly on the presence and regulation of different transporter proteins, such as MDR1, MRP1, BCRP, and MVP. Thus, decreased uptake and/or increased efflux, lowered net accumulation, and in consequence, less efficiency of anti-cancer drugs is the clinical hurdle to struggle with. Cytostatics as well as cytokines showed modulating effects on the expression of the MDR-associated genes MDR1, MRP1, and MVP (chapter 2-9). Cytostatics such as adriamycin resulted mainly in increased expression of the MDR1 gene, the most prominent intervention target for the reversal of the classical MDR phenotype. Cytokines such as TNFa, externally applied or by gene transfer, led to chemosensitization of tumor cells, and to down regulation of MDR1 and MVP. This cytokine-mediated reversal of the classical MDR phenoype refer to the inclusion of defined cytokines into established chemotherapy protocols, as already realized by the hyperthermic isolated limb perfusion with TNFa (chapter 13). The employment of BCRP-specific ribozymes demonstrated their potential to reverse the BCRP-mediated atypical MDR phenotype. Furthermore it was shown, that the expression of the ABC transporters as well as of MVP was inducible by hyperthermia in a temperature and time-dependet manner (chapter 10-13). This hyperthermia-caused induction of MDR1 and MRP1 is mediated by the transcription factor YB-1 timely close to the stress event. However, no direct, general risk of a MDR1- or MRP1-mediated hyperthermia-caused induction/enhancement of the MDR phenotype was observed in clinical settings, analyzed by using biopsies available from colon carcinomas, sarcomas, and melanomas, which were treated with hyperthermia in the context of multimodal regimes. The analyses of promoters of the MDR-associated genes MDR1 and MVP revealed their inducibility by different therapy-related factors such as cytostatics and hyperthermia in several in vitro- and in vivo models (chapter 10,14-20). Specific sequence motifs were found to be responsible for the stress-induced binding of transcription factors; mutations within these sequence regions modulated their inducibility (chapter 14,15,20). Thus, the employment of therapy-inducible promoters of different MDR genes such as MDR1 (chapter 14-18) and MVP (chapter 19,20) allows the improvement of established treatment protocols for different tumor localizations. Based on this, the succesful use of therapy-inducible MDR promoter sequences for the expression of therapeutically relevant genes in the context of a gene therapy of cancer represents an ambitious goal for the future.

As one of the mechanisms of antibiotic resistance, bacteria use several families of membrane-embedded α-helical transporters to remove cytotoxic molecules from the cell. The small multidrug resistance protein family (SMR) is one such group of drug transporters that because of their relative small size [ca. 110 residues with four transmembrane (TM) helices] must form at the minimum dimers to efflux drugs. We have used the SMR homologue Hsmr from Halobacterium salinarum to investigate the oligomerization properties of the protein family at TM helix 4. We produced point mutations along the length of the TM4 helix in the full length Hsmr protein and assayed their dimerization and functional properties via SDS-PAGE and bacterial cell growth assays. We found that Hsmr forms functionally dependent dimers via an evolutionarily conserved 90GLxLIxxGV98 small residue heptad repeat. Upon investigation of the large hydrophobic residues in this motif by substituting each large residue to Ile, Leu, Met, Phe, and Val, we determined that Hsmr efflux function relies on an optimal level of dimerization. While some substitutions led to either decreased or increased dimer and substrate-binding strength, several Ile94 and Val98 mutants were equal to wild type dimerization levels but were nonfunctional, leading to the hypothesis of a mechanistic role at TM4 in addition to the locus of dimerization. The functionally sensitive TM4 dimer represents a potential target for SMR inhibition using a synthetic TM4 peptide mimetic. Using exponential decay measurements from a real-time cellular efflux assay, we observed the efflux decay constant was decreased by up to ~60% after treatment with the TM4 peptide inhibitor compared to control peptide treatments. Our results suggest that this approach could conceivably be used to design hydrophobic peptides for disruption of key TM-TM interactions of membrane proteins, and represent a valuable route to the discovery of new therapeutics.

As one of the mechanisms of antibiotic resistance, bacteria use several families of membrane-embedded α-helical transporters to remove cytotoxic molecules from the cell. The small multidrug resistance protein family (SMR) is one such group of drug transporters that because of their relative small size [ca. 110 residues with four transmembrane (TM) helices] must form at the minimum dimers to efflux drugs. We have used the SMR homologue Hsmr from Halobacterium salinarum to investigate the oligomerization properties of the protein family at TM helix 4. We produced point mutations along the length of the TM4 helix in the full length Hsmr protein and assayed their dimerization and functional properties via SDS-PAGE and bacterial cell growth assays. We found that Hsmr forms functionally dependent dimers via an evolutionarily conserved 90GLxLIxxGV98 small residue heptad repeat. Upon investigation of the large hydrophobic residues in this motif by substituting each large residue to Ile, Leu, Met, Phe, and Val, we determined that Hsmr efflux function relies on an optimal level of dimerization. While some substitutions led to either decreased or increased dimer and substrate-binding strength, several Ile94 and Val98 mutants were equal to wild type dimerization levels but were nonfunctional, leading to the hypothesis of a mechanistic role at TM4 in addition to the locus of dimerization. The functionally sensitive TM4 dimer represents a potential target for SMR inhibition using a synthetic TM4 peptide mimetic. Using exponential decay measurements from a real-time cellular efflux assay, we observed the efflux decay constant was decreased by up to ~60% after treatment with the TM4 peptide inhibitor compared to control peptide treatments. Our results suggest that this approach could conceivably be used to design hydrophobic peptides for disruption of key TM-TM interactions of membrane proteins, and represent a valuable route to the discovery of new therapeutics.

Thesis (Ph. D.)--School of Pharmacy. University of Missouri--Kansas City, 2007. / "A dissertation in pharmaceutical science and pharmacology." Advisor: Ashim K. Mitra. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed July 16, 2008. Includes bibliographical references (leaves 231-248). Online version of the print edition.

Magister Curationis - MCur / Multidrug resistant TB (MDR-TB) is a form of TB caused by bacteria (germs) that are resistant to the usual drugs that are used to treat "normal" TB. The duration of treatment for MDR-TB is a maximum of 22 months. People with MDR-TB are treated in specialized tertiary hospitals and in out-patient clinics in the PHC facilities. The treatment includes a six months injectable phase with a wide range of TB drugs. The adverse effects of MDR-TB drugs are among the worst side effects ever reported by patients. The aim of the current study was to explore the experiences of adverse effects of MDR-TB treatment amongst patients in a primary health care facility in the Western Cape. An explorative qualitative study design was used to explore the experiences of patient with the adverse effects of MDR-TB treatment in a primary health care facility in the Western Cape. In depth interviews were conducted with 12 MDR-TB patients. Data analysis was done by using the Tesch's method of content analysis. The study revealed that participating MDR-TB patients experienced various emotional, financial, physical and social challenges. Participants explained that the experience of being on MDR-TB treatment is emotionally draining; the pain and discomfort of the adverse effect of treatment makes a person to feel anxious and depressed. Financially they depended on social grants because they had to stop working after starting treatment. They could not function well physically because of the toxic nature of the adverse effects of treatment; which resulted in fatigue, dizziness and burning sensation on the feet and hands. They were faced with a lot of stigma from the community and even family members because of their illness. The study also revealed that in spite of the challenges and obstacles the participants were all motivated to complete their treatment and get cured. It is recommended that more support structures be made available for patients who are being treated for MDRT-TB such as; psychotherapy, social support and counselling on health education. Provision needs to be made for patients who are receiving daily injection; for it to be given in their homes. Health care providers treating MDR-TB patients need to do home visits together with MDR-TB adherence counsellors, to monitor the physical wellbeing of patients at home. This will also provide patients with the platform to discuss their health concerns in a more accommodative and relaxed environment. New drug regimen with fewer tablets and less treatment duration is needed for MDR-TB.

Indiana University-Purdue University Indianapolis (IUPUI) / Human BCRP is one of the major ATP-binding cassette transporters involved in the development of multidrug resistance in cancer chemotherapy. Overexpression of BCRP in the tumor cell plasma membrane and apical membrane of the gastrointestinal tract leads to decreased intracellular accumulation of various anticancer drugs as well as reduced drug bioavailability. BCRP has been shown to exist on the plasma membrane as higher forms of homo-oligomers. In addition, the oligomerization domain of BCRP has been mapped to the carboxyl-terminal TM5-ECL3-TM6 and this truncated domain, when co-expressed with the full-length BCRP, displays a dominant inhibitory activity on BCRP function. Thus, the oligomerization of BCRP could be a promising target in reversing multidrug resistance mediated by BCRP. To further dissect the oligomerization domains of human BCRP and test the hypothesis that TM5, ECL3, and TM6 each plays a role in BCRP oligomerization and function, we engineered a series of BCRP domain-swapping constructs with alterations at TM5-ECL3-TM6 and further generated HEK293 cells stably expressing wild-type or each domain-swapping construct of BCRP. Using co-immunoprecipitation and chemical cross-linking, we found that TM5, ECL3, and TM6 all appear to partially contribute to BCRP oligomerization, which are responsible for the formation of oligomeric BCRP. However, only TM5 appears to be a major contributor to the transport activity and drug resistance mediated by BCRP, while ECL3 or TM6 is insufficient for BCRP functions. Taken together, these findings suggest that homo-oligomeric human BCRP may be formed by the interactions among TM5, ECL3 and TM6, and TM5 is a crucial domain for BCRP functions and BCRP-mediated drug resistance. These findings may further be used to explore targets for therapeutic development to reverse BCRP-mediated drug resistance and increase the bioavailability of anti-cancer drugs for better treatment of multidrug resistant cancers.

Submitted in fulfilment of the requirements for the Master of Health Sciences in Nursing, Durban University of Technology, 2017. / Tuberculosis (TB) is South Africa’s greatest community health problem. Nurses have a critical role in supporting patients in the TB treatment process. An estimated 480 000 new cases of Multidrug-Resistant Tuberculosis (MDR-TB) and 190 000 people died in 2014. An estimated 43 million lives were saved between 2000 and 2014 with effective diagnosis and treatment of TB. Despite these measures TB remains one of the world’s biggest threats. In an attempt to improve the practice of nurses in the prevention of MDR-TB, the knowledge of nurses with regards to the prevention of MDR-TB is essential. Aim of the Study The aim of the study was to describe the practice of the nurses in the prevention of MDR-TB and to determine whether the practice was effective in the prevention of MDR-TB. Methodology Quantitative, descriptive survey was used to conduct the study. Purposive sampling method was employed to select six primary health care clinics at uThungulu District. The target population consisted of professional nurses and enrolled nurses working in these clinics. The sample size was 122. The questionnaire was used to collect data. Descriptive statistics was used to describe the data graphically. In order to test for significant trends in the data, inferential statistics were applied. Results The findings of the study revealed that nurses were implementing measures of preventing MDR-TB like tracing of patients who interrupted TB treatment although there were inconsistencies with implementation of other measures. There were gaps related to attendance of TB courses by TB staff. Nurses were working in an overcrowded environment where it was difficult to implement measures for preventing MDR-TB. There was an increase in the workload due to the high number of patients having TB. Conclusion In this study, the majority of nurses working in primary health care clinics scored well in infection control measures with regard to practicing cough hygiene, placing patients in a well-ventilated area, collection of sputum from patients suspected of having TB and giving of health education to patients with TB and relatives but there areas that need improvement. The findings indicate knowledge gap with regard to TB. There is a need for attendance of short courses in TB, increase of staff attending to TB patients so as to cope with the workload and efficient allocation of resources. / M

Le mélanome malin (MM) est un cancer très réfractaire aux thérapies anticancéreuses, dont les vincalcaloïdes (VAs). Afin d'étudier le rôle de la GSTM1 (glutathion S-transférase 1) et la MRP1 (multidrug resistance protein 1) dans la résistance acquise du MM aux VAs, nous avons établi 4 modèles cellulaires de résistance à la vincristine (CAL1R-VCR), à la vindésine (CAL1R-VDS), à la vinorelbine (CAL1R-VRB) et à la vinflunine (CAL1R-VFL), par exposition continue de cellules du MM (CAL1-wt), pendant un an, à ces anticancéreux. L'expression d'ne GSTM1 fonctionnelle est spécifiquement observée (RT-PCR, western blot, activité GST totale) dans les cellules résistantes. Le curcumin (inhibiteur de GSTM1), la BSO (inhibiteur de synthèse de glutathion) et le MK571 (inhibiteur de MRP1), réduisent considérablement le résistance acquise à la VCR et à la VDS mais pas à la VRB ou à la VFL. Toutefois, tous ces VAs réduisent spécifiquement l'activité GSTM1. Ces données montrent l'implication différentielle de GSTM1 et MRP1 dans la résistance aux VAs. Pour déterminer les mécanismes moléculaires de cette chimiorésistance, nous avons réalisé une étude pangénomique (biopuces Affymetrix HG-U133 Plus 2.00) sur les lignées CAL1 (wt et R). Le regroupement hiérarchique (par Cluster et TreeView) des données des puces a révélé une similarité entre les profils d'expression génique de CAL1R-VRB et CAL1-wt mais aussi entre ceux de CAL1R-VCR et CAL1R-VDS. L'analyse bioinformatique (par IPA) des transcrits les plus différemment exprimés entre les lignées cellulaires, a mis en évidence 6 réseaux géniques connus pour leur rôle dans la chimiorésistance tumorale. Le programme FatiGO a révélé 3 termes biologiques sur-représentés (> 60%) dans CAL1R (ribosome, filaments intermédiaires du cytosquelette, récepteurs olfactifs) tandis que l'étude fonctionnelle (invalidation génique par siRNA, test de viabilité) de GPR143, KIT et SLC45A2 (gènes interagissant avec NF-κB et CCND1 (facteurs de la chimiorésistance tumorale), très exprimés dans CAL1-wt et muets dans CAL1R) a montré la faible tendance des deux premiers à être impliqués dans la résistance aux VAs. / Malignant melanoma (MM) is a very refractory tumor to anticancer therapies, including vinca alkaloïds (VAs). To investigate the role of GSTM1 (glutathione S-transferase μ1) and MRP1 (multidrug resistance protein 1) in MM acquired resistance to VAs, we established 4 cellular models of resistance to vincristine (CAL1R-VCR), to vindesine (CAL1R-VDS), to vinorelbine (CAL1R-VRB) and to vinflunine (CAL1R-VFL), by continuous exposure of MM cells (CAL1-wt), for one year, to these anticancer agents. The expression of a functional GSTM1 is specifically observed (RT-PCR, western blot, total GST activity) in resistant cells. Curcumin (GSTM1 inhibitor), BSO (glutathione synthesis inhibitor) and MK571 (MRP1 inhibitor), considerably reduce the acquired resistance to VCR and VDS but not that to VRB or VFL. However, all these VAs specifically reduce GSTM1 activity. These data show the differential involvement of GSTM1 and MRP1 in resistance to VAs. To determine the molecular mechanisms of this chemoresistance, we performed a pangenomic study (Affymetrix HG-U133 Plus 2.00 microarrays) on the CAL1 lines (wt and R). The hierarchical clustering (by Cluster and TreeView) of array data revealed a similarity between the gene expression profiles of CAL1R-VRB and CAL1-wt, but also between those of CAL1R-VCR and CAL1R-VDS. The bioinformatic analysis (by IPA) of the most differentially expressed transcripts between cell lines, highlighted 6 gene networks known for their role in tumor chemoresistance. FatiGO program revealed 3 biological terms overrepresented (>60%) in CAL1R (ribosome, intermediate filaments of cytoskeleton, olfactory receptors), while functional study (gene invalidation by siRNA, viability test) of GPR143, KIT and SLC45A2 (genes interacting with NF-kB and CCND1 (tumor chemoresistance factors), highly expressed in CAL1-wt and mute in CAL1R) showed the weak trend of the two formers to be involved in resistance to VAs.

Die Gentherapie hat in den letzten Jahren wesentliche Entwicklungen im Vektordesign, der kontrollierte Expression sowie der Sicherheit ihrer Anwendung durchgemacht. Die Erkenntnis, dass die Tumorgentherapie allein nur in begrenztem Maße zum erhofften therapeutischen Benefit für den Patienten beitragen kann, führte zum Konzept der lokalen Gentherapie als Teil anderer, etablierter Tumortherapien. In diesem Zusammenhang wird die Gentherapie als eine moderne Option zur Steigerung der Effizienz von Chemotherapie, Strahlentherapie oder Hyperthermie verstanden. Zum Erreichen dieses Zieles ist die Etablierung Therapie-regulierbarer Vektorsysteme von besonderer Attraktivität. Im Rahmen der Strategie des lokalen Transfers therapeutischer Gene bietet inzwischen die Anwendung nicht-viraler Transfersysteme, wie z.B. in vivo-Elektrotransfer, Gene-Gun oder Jet-Injection eine klinisch applikable Technologie. Die Etablierung einer effizienten, auf der Jet-Injection basierenden nicht-viralen Transfertechnologie und die Analyse ihres Potentials für eine klinische Anwendung in einem multimodalen Therapiekonzept war ein wesentliches Ziel der Arbeit. Es wurde gezeigt, dass die Jet-Injection in tierexperimentellen Tumormodellen zur effizienten Expression der Transgene führt, dass sowohl Eindringtiefen, als auch Verteilung der Jet-Injection optimal für einen effizienten Gentransfer sind und die Höhe der Genexpression mit etablierten Gentransfer-Technologien, wie z.B. der in vivo-Lipofektion, vergleichbar ist. Basierend auf der Strategie des Einsatzes der Gentherapie in Kombination mit anderen Therapien, bestand ein weiteres Ziel der Arbeit in der Charakterisierung und Anwendung konditioneller Vektorsysteme, mit denen die Expression therapeutischer Gene durch Chemotherapie oder Hyperthermie kontrollierbar ist. Derartige Vektoren, in denen der humane Multidrug Resistenzgen 1- (mdr1) Promotor genutzt wurde, exprimierten vor allem Zytokingene, die die therapeutische Effizienz von Zytostatika oder der Hyperthermie verbessern. Die Zytostatika-und auch Hitze-Induzierbarkeit der mdr1-Promotor gesteuerten Genexpression konnte in verschiedenen Tumormodellen in vitro und in vivo erfolgreich demonstriert werden Diese Untersuchungen zeigten, dass eine Zytostatika-induzierte Gentherapie zu einer besseren Tumortherapie beiträgt. Die Kombinations-Experimente der konditionellen Gentherapie im Kontext einer Hyperthermie geben erste Hinweise, dass auch hier die therapeutische Effektivität in vitro und in vivo gesteigert werden kann. Im Rahmen des Konzepts der kombinierten Gen- und Chemotherapie von Tumoren ist in der Arbeit vor allem auf das chemosensitivierende Potential von Zytokinen gesetzt worden. Besonders für TNF-a, IL-2 sowie IFN-g konnte gezeigt werden, dass diese Zytokine zu einer Modulation der Expression MDR-assoziierter Gene, wie dem mdr1, MVP/LRP und auch MRP1 in der Lage sind und dadurch zur Chemosensitivierung in verschiedenen Tumormodellen führt. Diese Befunde bildeten eine wichtige Rationale für den Einsatz von Zytokingenen im Rahmen der Tumorgentherapie zur Überwindung der MDR. Gentransferexperimente mit TNF-a- und IL-2-exprimierenden Vektoren konnten analog zur Applikation rekombinanter Zytokine die Modulation der Gene mdr1 und MVP/LRP zeigen, die mit der Erhöhung der Sensitivität gegenüber Zytostatika wie Vincristin oder Adriamycin assoziiert ist. / Gene therapy has made great achievements in vector design, controlled gene expression and in safety. The fact, that gene therapy as single therapy has only limited potential for the benefit in the therapy for cancer patients, has led to the concept of local gene therapy as part of other, established therapies. In this context, gene therapy serves as a modern option to improve the efficiency of chemotherapy, radiotherapy or hyperthermia. To achieve this goal, the establishment of therapy-regulatable vectors is of particular attractiveness. For the concept of local transfer of therapeutic genes non-viral transfer systems, such as in vivo electrotransfer, gene gun or jet-injection represent clinically applicable transfer technologies. One major issue of this work was the establishment of an efficient, jet-injection based non-viral transfer technology and the analysis of its potential for clinical application in a concept of multimodal therapy. It has been shown in vivo, that efficient transgene expression can be achieved by jet-injection, that penetration and distribution of the transgene are optimal for an efficient gene transfer and that the level of gene expression is comparable to established gene transfer technologies, sch as in vivo lipofection. Based on the strategy of combination of gene therapy with other therapies, another goal of this work aimed at the characterization and utilization of conditional vector systems, by which expression of therapeutic genes is controllable by chemotherapy or hyperthermia. By such vectors, in which the human multidrug resistance gene 1 (mdr1) promoter was employed, cytokine genes were expressed, which are capable to improve the therapeutic efficacy of cytostatic drugs or of hyperthermia. The drug- and heat-inducibility of mdr1 promoter-driven gene expression has successfully been demonstrated in in vitro and n vivo tumor models. The studies have also shown, that drug-induced gene therapy leads to improved tumor treatment. Combination experiments of conditional gene therapy in the context with hyperthermia give first indication of an increased therapeutic efficiency in vitro and in vivo. For the concept of combined gene- and chemotherapy the chemosensitizing potential of cytokines was exploited. It has been shown, particularly for TNF-a, IL-2 and IFN-g, that these cytokines are capable to modulate the expression of MDR-associated genes, such as mdr1, MVP/LRP or MRP1 leading to chemosensitization in different tumor models. These observations represent an important rationale for the use of cytokine genes in gene therapy for MDR-overcoming. Gene transfer experiments with TNF- or IL-2 expressing vectors showed the modulation of mdr1 or MVP/LRP expression, associated with increased sensitivity towards cytostatic drugs, such as vincristine or adriamycin.

Infections arising from multidrug-resistant pathogenic bacteria are spreading rapidly throughout the world and threaten to become untreatable. The origins of resistance are numerous and complex, but one underlying factor is the capacity of bacteria to rapidly export drugs through the intrinsic activity of efflux pumps. In this work, a summary is provided of our current understanding of the structures and molecular mechanisms of multidrug efflux pumps in bacteria (Chapter 1). The emerging picture of the structure, function and regulation of efflux pumps suggests opportunities for countering their activities. Although this thesis primarily explores structure and function, it also elucidates the hidden regulatory mechanism (post-translational) behind the association of a small protein called AcrZ with the tripartite complex AcrAB/TolC, in connection with the lipid environment, and the resulting changes in the latter's functionality (Chapter 2). A regulatory role of the native membrane lipid environment as well as of small proteins for efflux pump activity have previously been hypothesised. I present the first example of a function-regulating role of the lipid cardiolipin in combination with a small protein binding partner (AcrZ) for the substrate selectivity and transport activity of an efflux pump protein (AcrB). This regulation happens through induced structural changes which have remained unseen so far. Alongside with these results, a nanodisc reconstitution method was experimentally adapted for a structure-function investigation of an efflux pump (complex) using cryo-EM (Chapter 2). Beyond some fundamental regulatory insights, hidden intrinsic transport mechanisms for some transporters have also remained to be explored and studied. The discovery of a mechanism for active influx by a prominent efflux pump model system (Chapter 3) provides hope that this phenomenon is more common amongst multidrug transporters and that it could be utilised for drug discovery purposes. This novel feature explains the contradictory findings on this transporter in the past and raises new questions about the little-known physiological role and evolution of efflux pumps. The development and evolution of antimicrobial resistance has frequently shown to be a multifactorial and fast-moving process. One of these factors is the evolution of pumps itself towards an altered functionality (e.g. towards a broader or altered substrate spectrum or higher efflux rates). Against this background, the role of key carboxylate residues for efflux-energising proton trafficking was investigated for a prominent study model of a secondary-active transporter (Chapter 4). The re-allocation and/or addition of acidic residues was demonstrated to result in the preservation of wild type activity or the generation of hyper-efflux activity, respectively. These findings suggest that rapid emergence of antimicrobial resistance could be enhanced by the 'plasticity' in the location of key carboxylate residues with a role in proton coupling. It also demonstrates the necessity of antimicrobial drug design programmes to anticipate possible trajectories of an adaptive evolution of efflux pump. The 'cryo-EM revolution' has boosted the pace at which new structural and functional insights into multidrug efflux pumps are gained. Nevertheless, in order to derive the structure of individual pump components or of a full assembly, it is sometimes necessary to identify and characterise homologues and mutants, which would allow the application of cryo-EM for obtaining near-atomic maps. Functional analyses presented in this work helped to characterise a homologue and mutants of the MacAB/TolC tripartite complex to justify the obtained protein structures and strategies for further functional characterisation (Chapter 5). Given (1) the unusual stoichiometry of a MacB dimer in complex with a hexameric membrane-fusion protein (MacA), which leads to a seeming leakiness of the assembly, and (2) the fact that substrate has to pass through a narrow aperture in the membrane-fusion protein for extrusion, it is rather surprising that MacB was previously shown to transport an entire toxin. An experimental approach was developed that could enable the structure determination of a toxin-bound full assembly of MacAB/TolC (Chapter 5). Finally, the role of multidrug efflux pumps for the evolution of multidrug resistance is yet to be studied and better explored. For instance, evolutionary trajectories of pump overexpression, as compared to those of regular expression or no expression, are unknown yet could have the potential to reveal useful insights for spread prevention and drug design. The outline of an experimental design with some preliminary validating data is presented in Chapter 6.