Multidrug resistance refers to the simultaneous resistance to structurally and mechanistically unrelated cytotoxic drugs. Chronic administration of cytotoxic drugs to patients with metastatic breast cancer results in the development of multidrug resistance, thus rendering chemotherapy unsuccessful. One mechanism by which multidrug resistance is conferred is the decreased intracellular drug accumulation due to the upregulation of the ATP-binding cassette (ABC) transporters. Jadomycins are polyketide-derived natural products produced by the soil actinomycetes Streptomyces venezuelae, ISP 5230. Jadomycins exhibit anticancer, antibacterial and antifungal activities. Pilot work in our laboratory demonstrated that jadomycin B exhibited similar cytotoxic effects in drug-sensitive and drug-resistant cancer cells. We hypothesize that jadomycins are poor substrates of ABCB1, ABCC1 and ABCG2 efflux transporters, and consequently will exhibit higher intracellular accumulation, which results in improved cytotoxic efficacy over existing chemotherapeutics that are rapidly effluxed by ABC transporters. Using methyltetrazolium (MTT) cell viability assays, the cytotoxic efficacy of nine jadomycin analogues (DNV, L, B, SPhG, F, W, S, T and N) in drug-sensitive and drug-resistant MCF7 breast cancer cells was evaluated. Jadomycin B, L, S and T were found to be equally toxic to drug-sensitive and drug-resistant ABCB1, ABCC1 or ABCG2-overexpressing MCF7 breast cancer cells. The inhibition of ABCB1, ABCC1 or ABCG2 efflux transporters with verapamil, MK-571 or ko143, respectively, did not significantly augment the cytotoxic effects of jadomycin DNV, L, B and S in drug-resistant MCF7 cells, suggesting that these jadomycins are poor substrates of the targeted transporter. Furthermore, all nine jadomycin analogues did not increase the intracellular accumulation of ABCB1, ABCC1 or ABCG2 probe fluorescent substrates in HEK-293 cells, indicating that these jadomycins do not inhibit the efflux function of the transporters. We conclude that jadomycins B, L and S are effective agents in the eradication of resistant breast cancer cells grown in culture, and that the ability of specific jadomycins to retain cytotoxic efficacy in resistant cells stems from their limited interactions with ABCB1, ABCC1 or ABCG2 efflux transporters.

Regensburg, Univ., Diss., 2009.

Regensburg, Univ., Diss., 2004.

University, Diss., 2003--Frankfurt (Main).

Techn. Universiẗat, Diss., 2004--Darmstadt.

Universiẗat, Diss., 2004--Bielefeld.

Doctor of Philosophy / Biochemistry and Molecular Biophysics Interdepartmental Program / Subbaratnam Muthukrishnan / In this study, I have used dsRNA-mediated down-regulation of transcripts/proteins of several potential targets in the model beetle, Tribolium castaneum to identify a molecular target of the “chitin inhibitor”, diflubenzuron (DFB). The elytron of the red flour beetle, T. castaneum, was chosen as the model tissue for studying the mode of action of DFB and its molecular target(s). We have standardized the protocol for topical administration of DFB on precisely aged prepupae to achieve the desired level of mortality (90-95%) on day 5 of the pharate adult stage. Exposure of prepupae to DFB at 1000 ppm results in a near complete loss of chitin in the newly forming adult procuticle of the elytron and the body wall. Global analysis of transcripts by RNA Seq was carried out to look for differential expression of several critical genes of cuticle assembly in these insects compared to mock-treated controls. Interestingly, genes directly involved in the biosynthetic pathway of chitin were not among those affected by DFB. However, immunolocalization studies have shown that several proteins of chitin metabolism including chitin synthase A, which is involved in the synthesis of cuticular chitin, are present in near normal amounts but are mislocalized in DFB-treated insects. Assays for chitin synthase using elytral extracts have indicated that the enzyme preparations from DFB-treated insects are catalytically inactive. By using RNA interference and competition studies with fluorescently-tagged glibenclamide (a sulfonylurea compound) or DFB, we have identified a long-sought molecular receptor of DFB as an ABCC class transporter. DFB-treatment and RNAi of a specific ABCC-type transporter gene lead to identical phenotypes including loss of chitin, loss of laminar architecture of the cuticle, and mislocalization of CHS from its normal plasma membrane location to intracellular locations presumably by affecting vesicular transport. Further, using an in vitro chitin synthesizing system consisting of microsomes prepared from elytral tissue, which exhibits all of the hallmarks of cuticular chitin-synthesizing epidermal cells including sensitivity to DFB, further insights into the mechanistic details of how this class of insecticides inhibits chitin synthesis have been obtained.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第22729号 / 医博第4647号 / 新制||医||1046(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 武藤 学, 教授 伊達 洋至, 教授 小川 誠司 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

The PstSCAB2 complex serves the dual function of being a phosphate transporter as well as the primary sensor of phosphate for the Pho regulon. PhoU is an integral protein required for the signal from PstSCAB2 to be transmitted to PhoR. Our hypothesis is that conformational changes of PstSCAB2 during the phosphate transport process are the mechanism by which information about environmental phosphate levels are transduced to the cell. Additionally, we propose that direct protein-protein interactions between PhoU and the alternating conformations of PstSCAB2 mediate PhoU interactions with PhoR. By means of genetic and biochemical approaches, we have found substantial evidence supporting both these hypotheses.

ABC-Transporter sind ein wichtiger Aspekt bei der Entwicklung von Resistenzen gegen Chemotherapeutika. Ziel dieser Studie war es, die Resistenzentwicklung in HNSCC-Zelllinien im Zusammenhang mit verschiedenen Cisplatinkozentrationen und Inkubationszeiten zu analysieren, sowie die Expression von ABC-Transportern via semi-quantitativer RT-PCR in diesen Zellen zu untersuchen. Die Zellen zeigten dabei keine relevante Resistenzentwick-lung im Sinne eines Anstiegs der IC50. Bei drei der Zelllinien konnte jedoch eine hohe intrin-sische Cisplatinresistenz beobachtet werden. Diese resistenten Zelllinien wiesen nach Inku-bation mit Cisplatin deutlich höhere Expressionswerte für TAP1, TAP2, ABCG2 sowie die ABCC-Transporterfamilie auf. Dabei zeigte sich, dass die Expression der ABCC-Familie mit zunehmender Inkubationsdauer abnahm. TAP1 in PCI-9 und PCI-68 war auch noch nach vierwöchiger Inkubation stark überexprimiert. Die initiale IC50 dieser Zelllinien lag dabei deutlich über der Plasmakonzentration von Pati-enten mit Hochdosis-Chemotherapie. Die Expression der Transporter aus der ABCC-Familie ließ die Vermutung zu, dass diese Transporter initial zur Resistenz gegen Cisplatin beitrugen, allerdings mit zunehmender Inkubationsdauer an Bedeutung verloren. Diese Annahme wurde dadurch gestützt, dass die HNSCC-Zelllinien nach einem inkubationsfreien Intervall von vier Wochen im Anschluss an die Inkubation mit Cisplatin deutliche Überexpressionen der ABCC-Transporterfamilie zeigten. Auch für Transporter (ABCG2 und TAP-Transporter), die keine Effluxfunktion für Cisplatin besitzen, konnte ein Zusammenhang der Expression mit der Resistenz der HNSCC-Zellen beobachtet werden. Der Beitrag dieser Transporter zur Resistenz von Tumorzellen könnte über deren Funktionen im Metabolismus von Tumorzel-len, deren Fähigkeiten Tumorstammzellen zu bilden und dem Efflux endogener Zellstress verursachender Substrate erklärt werden. Allerdings werden diese Transporter erst seit kur-zem mit Resistenzen gegen Cisplatin in Verbindung gebracht. Aufbauend auf diese Studie wäre eine Verifizierung der Kausalität des Resistenzmechanismus durch knock-down und Inhibition der von uns untersuchten Transporter sinnvoll. / ABC transporters are an important aspect in the development of resistance to chemotherapeutic agents. The aim of this study was to analyse the development of resistance in HNSCC cell lines in connection with different cisplatin concentrations and incubation times, as well as to investigate the expression of ABC transporters in these cells via semi-quantitative RT-PCR. The cells did not show any relevant development of resistance in the sense of an increase in the IC50. However, a high intrinsic cisplatin resistance was observed in three of the cell lines. These resistant cell lines showed significantly higher expression values for TAP1, TAP2, ABCG2 and the ABCC transporter family after incubation with cisplatin. It was shown that the expression of the ABCC family decreased with increasing incubation time. In PCI-9 and PCI-68 TAP1 was still strongly overexpressed after four weeks of incubation. The initial IC50 of these cell lines was significantly higher than the plasma concentration of patients with high-dose chemotherapy. The expression of transporters from the ABCC family led to the assumption that these transporters initially contributed to resistance to cisplatin, but lost importance with increasing incubation time. This assumption was supported by the fact that the HNSCC cell lines showed clear overexpression of the ABCC transporter family after an incubation-free interval of four weeks following incubation with cisplatin. For transporters (ABCG2 and TAP transporters) that do not have an efflux function for cisplatin, a correlation of expression with the resistance of HNSCC cells was also observed. The contribution of these transporters to the resistance of tumour cells could be explained by their functions in the metabolism of tumour cells, their ability to form tumour stem cells and the efflux of endogenous cell stress-causing substrates. However, these transporters have only recently been linked to resistance to cisplatin. Building on this study, it would be useful to verify the causality of the resistance mechanism by knocking down and inhibiting the transporters we studied.