Submitted by Erika Demachki (erikademachki@gmail.com) on 2016-03-03T19:34:50Z No. of bitstreams: 2 Dissertação - Ayda Luz Malaver Slamanca - 2015.pdf: 2106945 bytes, checksum: dd89c61b0a1e8fd1299227d7513b4505 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Erika Demachki (erikademachki@gmail.com) on 2016-03-03T19:36:16Z (GMT) No. of bitstreams: 2 Dissertação - Ayda Luz Malaver Slamanca - 2015.pdf: 2106945 bytes, checksum: dd89c61b0a1e8fd1299227d7513b4505 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2016-03-03T19:36:16Z (GMT). No. of bitstreams: 2 Dissertação - Ayda Luz Malaver Slamanca - 2015.pdf: 2106945 bytes, checksum: dd89c61b0a1e8fd1299227d7513b4505 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-12-04 / Clozapine (CLZ) is the antipsychotic drug of choice in treatment refractory schizophrenia (TRS), however 30% of the patients with TRS don’t have full response to treatment with CLZ, these patients are considered to have super refractory schizophrenia (SRS). The response variability to treatment with CLZ may be associated with alterations of the CLZ plasma levels promoted by 1236C>T, 2677G>T/A e 3435C>T ABCB1 gene polymorphisms. ABCB1 is a transmembrane glycoprotein of transport, which export drugs from the intracellular to the extracellular space. ABCB1 polymorphisms cause structurally and functional protein changes that influence the intracellular CLZ levels and, consequently, promoting therapy failure. This work had the aim to establish the relation between the 1236C>T, 2677G>T/A e 3435C>T ABCB1 polymorphisms and the CLZ treatment response. This study included a total of 68 patients, 34 of whom were classified as TRS (CLZ responders) and 34 as SRS (CLZ non-responders). All patients were in use of CLZ for at least one year. For the genotype test was extracted genomic DNA, following for PCR and sequencing techniques. It was not observed any differences in allelic and genotype distribution between 1236C>T, 2677G>T/A and 3435C>T polymorphisms between RS and SRS groups. The polymorphisms not influenced the CLZ dose level, and percentage of BPRS change. In the same way, the results not showed relation between age, coffee intake, smoking behaviors and ethnicity and the CLZ treatment response, however, was evidenced a higher proportion of female patients in the SRS group when compared with the TRS group. In opposite, a lower proportion of male patients was observed in the SRS than the TRS group. Taken together, the results here obtained showed no association between 12361236C>T, 2677G>T/A e 3435C>T polymorphisms of ABCB1 gene and failure to CLZ treatment. / Clozapina (CLZ) é um antipsicótico de segunda geração, indicada no tratamento de esquizofrenia refratária (ER). Apesar de ser o fármaco de escolha nestes pacientes, 30% deles não respondem satisfatoriamente à terapia com CLZ, constituindo o grupo de indivíduos portadores de esquizofrenia super-refratária (ESR). A variabilidade na resposta ao tratamento com CLZ pode estar relacionada a alterações na farmacocinética da CLZ influenciadas pelos polimorfismos 1236C>T, 2677G>T/A e 3435C>T do gene ABCB1 . ABCB1 é uma proteína transportadora de membrana, que promove a passagem de fármacos do meio intra ao extracelular. Os polimorfismos de ABCB1 podem causar mudanças estruturais ou na expressão proteica, influenciando nas concentrações intracelulares de CLZ e contribuindo para o sucesso ou o fracasso da terapia. O presente trabalho teve como objetivo avaliar a associação entre os polimorfismos 1236C>T, 2677G>T/A e 3435C>T de ABCB1 com a resposta ao tratamento à CLZ. Um total de 68 pacientes em uso de CLZ, 34 portadores de ER e 34 de ESR, foram incluídos no estudo. Os testes de genotipagem foram realizados através da extração do DNA genômico, PCR e sequenciamento. Não foi observada diferença na distribuição alélica e genotípica dos polimorfismos de ABCB1, entre os grupos ER e ESR, assim mesmo não foi observada relação entre os polimorfismos estudados com a dosagem de CLZ e a gravidade psicopatológica avaliados pela escala BPRS. Fatores como consumo de café, cigarro, idade e etnia não influenciam na resposta ao tratamento com a CLZ. Foi evidenciada maior presença de pacientes do gênero feminino no grupo ESR em relação ao grupo ER e maior presença de indivíduos do gênero masculino no grupo ER quando comparado com o grupo ESR. O conjunto dos resultados aqui obtidos demonstram que não há associação entre os polimorfismos 1236C>T, 2677G>T/A e 3435C>T do gene ABCB1 com a refratariedade ao tratamento com CLZ.

Dans le cancer du sein non métastatique, l'approche néoadjuvante permet d'étudier les paramètres liés à la tumeur et/ou à l'hôte influençant l'efficacité des traitements. Les protéines de la famille MDR et plus particulièrement ABCB1 sont impliqués dans les mécanismes de résistance aux anthracyclines et taxanes. Les corrélations entre efficacité (réponse histologique), polymorphisme d'ABCB1 (patientes et tumeurs) et pharmacocinétique de la doxorubicine et du docétaxel ont été étudiées dans le cadre d'un essai thérapeutique. Dans cette étude, le polymorphisme de l'exon 26 d'ABCB1 (rs1045642) est le seul qui influence la pharmacocinétique du docétaxel et ceci uniquement chez les patientes non ménopausées. Les patientes porteuses du génotype CC (40%) ont une valeur moyenne de l'AUC du docétaxel statistiquement inférieure à celles porteuses des génotypes CT (45%) et TT (15%) (p<0.0001). Par ailleurs il a été constaté chez les patientes non ménopausées une corrélation statistiquement significative entre des taux d'AUC bas du docétaxel et le diplotype 2677GG-3435CC ainsi que l'haplotype 61AA-1236CC-2677GG-3435CC. Il n'a pas été trouvé de lien entre les différents polymorphismes d'ABCB1 et la pharmacocinétique de la doxorubicine. Il existe par ailleurs une relation négative entre l'AUC du docétaxel et l'obtention d'une réponse complète histologique. Il semble exister donc une valeur minimale d'AUC du docétaxel afin d'obtenir une réponse. Par ailleurs, nous avons retrouvé un lien entre réponse tumorale et le polymorphisme d'ABCB1 (génotype C3435T, TT vs CT et CC)

La surexpression de pompes d'efflux par les cellules cancéreuses permet l'élimination d'agents cytotoxiques, induisant alors une résistance à la chimiothérapie. Trois transporteurs ABC sont principalement impliqués dans cette résistance : ABCB1 (aussi appelé P-gp), ABCC1 (ou MRP1) et ABCG2 (ou BCRP, MXR, ABCP). Du fait de leur implication dans le phénotype de " MultiDrug Resistance ", il est essentiel de mieux comprendre le fonctionnement de ces transporteurs. Une étude par mutagenèse dirigée a montré que les boucles intracellulaires, ICL0 et ICL1 sont impliquées dans le transport des substrats. Deux résidus sont particulièrement intéressants : W379 qui agirait comme un filtre des substrats ; et H457 qui participerait à la reconnaissance ou à la fixation des substrats. Par ailleurs, il est important de moduler cette chimiorésistance. Dans ce contexte nous avons développé une nouvelle classe d'inhibiteurs d'ABCB1 et ABCG2 non compétitifs basés sur un motif dipeptidique. Les composés les plus efficaces, CT1347 pour ABCB1 et CT1364 pour ABCG2, s'avèrent, d'une part peu ou pas cytotoxiques à fortes concentrations, abolissent d'autre part la résistance induite par ABCB1 ou ABCG2 et se comportent comme des inhibiteurs non compétitifs du Hoechst 33342 et de la daunorubicine. De plus, CT1364 inhibe l'activité ATPasique d'ABCG2 et induit une diminution rapide de l'expression de la protéine. Enfin, les 1ers tests in vivo de ce composé montrent que l'association avec l'irinotécan ralentit la croissance des xénogreffes de petite taille chez des souris

This thesis is focused on polymorphism of MDR1 gene and related drug resistance. Resistance is caused by deletion of four nucleotids, that resulting in a frame shift and synthesis of nonfunctional transport of P-glycoprotein. The text describes a polymorphism of MDR1 (ABCB1) gene, which results in reduced resistance to drugs belonging to the group of macrocyclic lactones. It also describes inheritance of this phenomenon and it deals with the detection of mutation using PCR (polymerase chain reaction) and by fragmentation analyses. A review of literature study is a form of research solely from scientific publications. 128 dogs were included into the own analysis. The results confirmed that Collies had the highest presence of deletions (29,73 %) with a high number of carriers in the study population of dogs (54,05 %). The percentage of affected individuals in the breed of Australian Shepherd and Sheltie was significantly lower (7,32 % and 6 %), but the percentage of carriers were also high in both Australian Shepherds (34,14 %) and the breed Sheltie (48 %).

京都大学 / 新制・課程博士 / 博士(農学) / 甲第23953号 / 農博第2502号 / 新制||農||1091(附属図書館) / 学位論文||R4||N5388(農学部図書室) / 京都大学大学院農学研究科応用生命科学専攻 / (主査)教授 木岡 紀幸, 教授 矢﨑 一史, 教授 三芳 秀人 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

In eukaryotischen Zellen sind die Lipidspezies häufig asymmetrisch zwischen den Hälften der Plasmamembran verteilt. Insbesondere Phosphatidylserin (PS) weist oft eine ausgeprägte transversale Asymmetrie auf, da es fast ausschliesslich auf die innere Hälfte der Plasmamembran beschränkt ist. In den letzten Jahren wurden mehrere Proteine diskutiert, die Lipide zwischen den Membranhälften transportieren und möglicherweise die transversale Lipidasymmetrie sowie damit verbundene Zelleigenschaften beeinflussen. Im Mittelpunkt der vorliegenden Promotion steht der Auswärtstransport fluoreszierender (C6-NBD-) Lipid-Analoga und endogener Lipide durch das Multidrug Resistance 1 P-Glycoprotein (MDR1 Pgp), das der ATP Binding Cassette (ABC) Transporter Superfamilie angehört. Interessanter Weise wird für MDR1 Pgp eine ungewöhnlich breite Substratspezifität angenommen. Das anionische Lipid PS war hier von besonderem Interesse, obgleich es in vorhergehenden Arbeiten nicht als MDR1 Pgp Substrat betrachtet wurde. Der Auswärtstransport von Phosphatidylcholin-, Phosphatidylethanolamin-, Glucosylceramid- und Sphingomyelin-Analoga durch MDR1 Pgp konnte in einer humanen Magenkarzinomlinie (EPG85-257), die MDR1 überexprimiert, mittels Fluoreszenzspektroskopie bestätigt werden. Zudem legt die verringerte Akkumulation von Diacylglycerol- und Ceramid-Analoga den Transport dieser Lipidspezies durch MDR1 Pgp nahe. Im Anschluß an die intrazelluläre Markierung mit C6-NBD-PS mittels eines neuen Verfahrens konnte der signifikant erhöhte Auswärtstransport dieses Analogons in MDR1 überexprimierenden Zellen durch Verwendung spezifischer Inhibitoren MDR1 Pgp zugeschrieben werden. In flusscytometrischen Versuchen war die Exponierung von endogenem PS auf der äusseren Membranhälfte von MDR1 überexprimierenden Zellen signifikant höher als in Kontrollzellen. Verringerung der PS-Exponierung durch einen Inhibitor von MDR1 Pgp deutet auf den Transport von endogenem PS durch MDR1 Pgp hin. Zusätzlich wurde hier der Transport von C6-NBD-PS in vier weiteren Zellinien mit verschiedener Spezies- und Gewebezugehörigkeit charakterisiert, die unterschiedliche Mengen an MDR1 Pgp synthetisieren. Wie Experimente in einer BCRP überexprimierenden EPG85-257-Sublinie nahelegen, ist ausser MDR1 Pgp möglicherweise ebenfalls der ABC Halb-Transporter Breast Cancer Resistance Protein (BCRP) am Transport von C6-NBD-PS und an der verstärkten Exponierung von endogenem PS beteiligt. / In eukaryotic cells, the lipid species are frequently distributed asymmetrically between the plasma membrane leaflets. Phosphatidylserine (PS), in particular, often exhibits a distinct transverse asymmetry, being restricted almost exclusively to the inner leaflet. In the past years, several proteins were suggested to transport lipids between the leaflets of a membrane, and to potentially influence transverse lipid asymmetry and related cell properties. This thesis focuses on outward transport of fluorescent (C6-NBD-) lipid analogs and endogenous lipids by the Multidrug Resistance 1 P-Glycoprotein (MDR1 Pgp), a member of the ATP binding cassette (ABC) transporter superfamily. Interestingly, MDR1 Pgp has been suggested to exhibit an unusually broad substrate specificity. Here, the anionic PS was of particular concern, although previously reported not to be an MDR1 Pgp substrate. In a human gastric carcinoma cell line (EPG85-257) overexpressing MDR1, outward transport of phosphatidylcholine, phosphatidylethanolamine, glucosylceramide and sphingomyelin analogs via MDR1 Pgp was confirmed using fluorescence spectroscopy. In addition, decreased accumulation of analogs of diacylglycerol and ceramide suggest MDR1 Pgp mediated transport of these lipid species. Upon intracellular labelling with C6-NBD-PS using a novel approach, significantly increased outward transport of this analog in MDR1 overexpressing cells could be attributed to MDR1 Pgp by employing specific inhibitors. In a flow cytometry setup, the exposure of endogenous PS on the outer plasma membrane leaflet was significantly elevated in MDR1 overexpressing cells compared to controls. Reduction of PS exposure by an MDR1 Pgp inhibitor suggests transport of endogenous PS by MDR1 Pgp. Transport of C6-NBD-PS was furthermore characterized here in four additional cell lines of different species and tissue origin with varying synthesis levels of MDR1 Pgp. Besides MDR1 Pgp, the ABC half-size transporter Breast Cancer Resistance Protein (BCRP) is possibly also involved in transport of C6-NBD-PS and in increased exposure of endogenous PS, as found in a BCRP overexpressing EPG85-257 subline.

Tumorzellen entwickeln häufig Resistenzen gegen verschiedene strukturell und funktionell unabhängige Zytostatika, was als Multidrug-Resistenz (MDR) bezeichnet wird und die Hauptursache für das Scheitern einer Chemotherapie ist. Mit Hilfe von in vitro-Untersuchungen wurden erhöhte Genexpressionen der ABC-Transporter MDR1, MRP2 und BCRP als maßgebliche Resistenzfaktoren identifiziert, wie z.B. in den Magenkarzinomzellinien EPG85-257RDB (MDR1) und EPG85-257RNOV (BCRP) sowie in der Ovarialkarzinomzellinie A2780RCIS (MRP2). Ziel der Arbeit war die Entwicklung eines auf Ribozym-Technologie basierenden Therapieansatzes, welcher die Expressionen der oben genannten ABC-Transporter simultan inhibiert und dessen Anwendung zur Reversion der zellulären MDR führt. Dazu wurde ein Multitargetmultiribozym (MTMR) entwickelt, das aus in trans-aktiven Ribozymen besteht, die gegen die ABC-Transporter mRNAs gerichtet sind sowie aus in cis-spaltenden Ribozymen und aus Spacer-RNA-Sequenzen. Durch autokatalytische Spaltung in cis konnten die in trans-aktiven Ribozyme aus dem Gesamt-MTMR freigesetzt werden. Die Analyse der kinetischen Parameter des MTMRs ergab, daß die autokatalytisch entstandenen MTMR-Fragmente ihre Substrat-RNAs im Vergleich zu den korrespondierenden Monoribozymen ohne Einbuße an Effizienz spalten können. Darüber hinaus wurde die MTMR-Sequenz stabil in den drei eingangs genannten MDR-Zellinien exprimiert, was in einer signifikanten Reduktion der jeweiligen Ziel-mRNAs (97 % MDR1-, 80 % BCRP-, 96 % MRP2-mRNA) und der entsprechenden Proteine resultierte. Die Multidrug-Resistenz konnte aufgrund der MTMR-Expression um 70% (A2780RCIS), 95% (257RNOV), 100% (257RDB) und die Zytostatikumsakkumulation um 90% (257RNOV-Zellen) sowie 100% (257RDB-Zellen) revertiert werden. Das MTMR stellt erstmalig ein RNA-Konstrukt dar, welches in der Lage ist, simultan mehrere unabhängige Gene funktionell auszuschalten. Es besitzt daher ein großes Potential für zukünftige gentherapeutische Ansätze. / Cancer cells are often insensible against structurally and functionally unrelated drugs that is known as multiple drug resistance (MDR) and the main cause for treatment failure. Overexpression of the ABC-transporters P-gp (ABCB1), MRP2 (ABCC2), and BCRP (ABCG2) is associated with MDR in several cancer cell lines, e.g. in the stomach carcinoma cell lines EPG85-257RDB (P-gp), EPG85-257RNOV (BCRP), and in the ovarian carcinoma cell line A2780RCIS (MRP2). We aimed the development of a novel hammerhead ribozyme-based therapeutic approach capable of simultaneous silencing of the prementioned ABC-transporters, and consequently of reversing MDR phenotypes. We designed a so-called multitarget multiribozyme (MTMR) consisting of trans-acting hammerhead ribozymes directed against the MDR1, MRP2, and BCRP transcripts, of MDR1 homologous spacer sequences, and of cis-acting ribozymes against the spacer sequences. Autocatalytic cleavage in cis excised the full-length MTMR, and released trans-acting hammerhead ribozymes. We also evaluated the catalytic features of the MTMR using large RNA target molecules. Comparison of the kinetic values of the autocatalytically derived MTMR fragments with those of corresponding mono-ribozymes demonstrated an MTMR-mediated substrate cleavage without distinct loss in catalytic efficiency. Moreover, the MTMR was stably expressed in the prementioned multidrug-resistant cancer cell lines, and decreased the targeted transcripts about 97% (MDR1), 80% (MRP2), and 96% (BCRP) as well as the corresponding protein levels, respectively. Cellular MDR could be reverted about 70% (A2780RCIS), 95% (257RNOV), and 100% (257RDB). Additionally, the MTMR reversed mitoxantrone accumulation entirely, and daunorubicin accumulation about 90% in stomach carcinoma cells, respectively. Taken together, the MTMRs capability of simultaneous silencing of multiple genes provides an effective instrument to knockdown genes of interest.

Les glioblastomes sont les tumeurs cérébrales les plus fréquentes avec une incidence en France de l'ordre de 4 nouveaux cas par an et pour 100 000 habitants (2400/ an). Le traitement standard pharmacologique des glioblastomes nouvellement diagnostiqués consiste en première ligne en une administration de témozolomide (75 mg/m2/j) pendant la radiothérapie, suivie d’une consolidation de 6 cycles. Cependant, malgré ce traitement, la médiane de survie n’est que de 15 mois et de 3 à 9 mois pour les rechutes. De nouvelles approches thérapeutiques sont donc indispensables. Parmi elles, ont été évalués le recours à d’autres chimiothérapies (irinotecan) et à l’inhibition de l’angiogénèse. L'angiogenèse est en effet un processus critique dans la progression GBM. L'inhibition de l'angiogenèse, induisant une réduction des vaisseaux sanguins, permet une diminution de l’apport des nutriments et d'oxygène à la tumeur. De manière générale, l’efficacité des traitements du glioblastome est soumise, dans un premier temps, à leur passage intra-cérébral au travers de la barrière hémato-encéphalique (BHE). L’objectif de notre travail était d’une part d’étudier l’impact de l’expression du transporteur d’efflux ABCB1 sur la distribution cérébrale du témozolomide (TMZ) et de l’irinotecan (CPT-11), et d’autre part, d’évaluer le rôle du bevacizumab (BVZ)(inhibiteur de l’angiogénèse) dans la modulation du passage intra-cérébral et intra-tumoral du TMZ et du CPT-11. A l'aide d'une étude pharmacocinétique comparative chez les souris CF1 mdr1a (+/+) et les souris CF1 mdr1a (-/-), nous avons mis en évidence un efflux actif du TMZ, du CPT-11 et de son métabolite actif le SN-38 du cerveau vers le plasma, impliquant ABCB1 au niveau de la BHE. Nous avons également démontré in vivo que le TMZ s'accumule dans la tumeur cérébrale et que le prétraitement par BVZ augmente la distribution tumorale de TMZ. En revanche, le BVZ n’a montré aucun effet sur la distribution cérébrale ou tumorale du CPT-11. Le BVZ apparaitrait donc comme un moyen intéressant d’augmenter la distribution intratumorale du TMZ. Dans ce même objectif, une collaboration initiée dans le cadre de cette thèse a permis de mettre en évidence l’intérêt de l’utilisation d’ultrasons dans l’ouverture de la BHE et l’amélioration de la distribution cérébrale des médicaments. / Glioblastomas are the most common brain tumors occurring in France with an incidence of 4 new cases per year per 100 000 population (2400/year). The gold standard pharmacological treatment of newly diagnosed glioblastoma relies on temozolomide administration (75 mg/m2/d) concomitant to radiotherapy, followed by six cycles consolidation. However, despite this treatment, the median survival is only 15 months and relapse occurs within 3 to 9 months. New therapeutic approaches are needed. Among them, other chemotherapies (irinotecan) and inhibition of angiogenesis were explored. Angiogenesis is a critical process in GBM progression. Inhibition of angiogenesis, inducing a reduction of the blood vessels, reduces supply of nutrients and oxygen to the tumor. The effectiveness of GBM treatment is subjected to intra-brain diffusion through the blood-brain barrier. The objective of this study was firstly to study the impact of efflux transporter ABCB1 brain expression on temozolomide (TMZ) and irinotecan (CPT-11) brain distribution, and secondly, to assess the role of bevacizumab (BVZ)(angiogenesis inhibitor) in the modulation of TMZ and CPT-11 brain and tumor distribution. Using a comparative pharmacokinetic study in CF1 mdr1a (+/+) and CF1 mdr1a (-/-) mice, we demonstrated an active efflux of TMZ, CPT-11 and its active metabolite SN-38 from the brain to the plasma involving ABCB1. We also demonstrated in vivo that TMZ accumulates in brain tumor and BVZ pretreatment increased TMZ tumor distribution. However no effect of BVZ on CPT-11 brain or tumor distribution was evidenced. Therefore BVZ would appear to be an interesting way to increase TMZ tumor distribution. The same objective was pursued through a different approach using ultrasound unfocused to open the BBB (Carthera collaboration).

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

ABCB1, a member of the ATP binding cassette (ABC) transporter family, hydrolyses ATP as energy source for the translocation of substrate chemicals across the cell membrane. ABCB1-like transporters are found in all studied species. Typically, these transporters are abundant in tissues that separate compartments of the body such as the blood-brain barrier. Among the ABC transporters the ABCB1-like transporter proteins are of particular interest because they accept a broad variety of substrates and are therefore able to confer multidrug resistance (MDR) and multixenobiotic resistance (MXR) in wildlife, respectively. Inhibitors of the ABCB1-like transporter function can cause chemosensitisation, i.e. accumulation and increased sensitivity of organisms towards potentially harmful (natural/man-made) ABCB1-like substrate chemicals. In zebrafish (Danio rerio) Abcb4 was identified as functionally homologous to ABCB1. The aim of this study was to further characterise Danio rerio Abcb4 and to provide a database to approach the question to what extent ABCB1-like transporter related functions/effects are of ecotoxicological relevance. Main objectives are whether and how known ABCB1 ATPase stimulators and inhibitors interact with Abcb4 ATPase activity; to what extent ABCB1 ATPase assay data are transferable to Abcb4 ATPase assay data; and whether and how environmental chemicals interact with Danio rerio Abcb4 ATPase activity. In this study we established a test system – the ATPase assay with recombinant Danio rerio Abcb4 – to study the interaction of chemicals with the ATPase activity of the transporter protein. To relate obtained data to data for the well-known Homo sapiens ABCB1 and because available data for Homo sapiens ABCB1 were not in all cases suitable for a comparison, the ATPase assay with recombinant ABCB1 was adapted accordingly. Chemicals were tested up to concentrations in the range of their water solubilities to modulate basal and stimulator co-treated Abcb4 and/or ABCB1 ATPase activities. ATPase stimulators are often transported substrates. However, lipophilic compounds stimulating the transporter ATPase activity are not or little transported by transporter action. Therefore, experiments revealing whether compounds are translocated by transporters chemical interference with the transporter protein will not be indicated. Chemicals inhibiting the stimulator (here verapamil) co-treated ATPase activity compete with the verapamil to stimulate ATPase activity or are non-competitive inhibitors. When tested individually, these chemicals can be stimulators or inhibitors of basal ATPase activity, or do not interact with basal ATPase activity. ATPase inhibitors mitigate ATPase activity and ABCB1-like transporter mediated translocation of substrate chemicals. Obtained ATPase assay data were analysed with regard to concentrations at half-maximal effects (EC50s) and effect strengths (percent modulation). ATPase assays with recombinant Abcb4 (at 27 °C) are comparable to ABCB1 ATPase assay data obtained at 37 °C. Danio rerio Abcb4 seems less temperature-sensitive than ABCB1. Calculated activation energies for Abcb4 ATPase activities (40.75 kJ/mol for basal ATPase activity) were up to half as high as those for ABCB1 ATPase activities (81.61 kJ/mol for basal ATPase activity). Larger activation energies were previously proposed to be indicative for larger conformational rearrangements and hence possibly smaller rearrangements take place in Abcb4 compared to ABCB1. Known standard modulators of Homo sapiens ABCB1 ATPase activity interacted specifically with Danio rerio Abcb4 ATPase actitiy. The EC50s of the tested chemicals – 16 of 17 tested chemiacals interacted with the ABCB1 and the Abcb4 ATPase activity – ranged from 0.09 to 296 µM for ABCB1 and from 0.14 to 171 µM for Abcb4. Qualitative ATPase assay data for ABCB1, as interaction or not, seems transferable to Danio rerio Abcb4. Furthermore, when aligning amino acid sequences of mammalian ABCB1 transporter proteins and Danio rerio Abcb4 and comparing ABCB1 residues known to bind to (lipophilic) chemicals no obvious hints were found that chemical binding to Abcb4 is certainly different from ABCB1. Twenty-five of 33 studied environmental chemicals modulated the Abcb4 ATPase activity as stimulators and/or inhibitors. Stimulation of basal Abcb4 ATPase activity was lower for environmental chemicals than for known standard modulators. EC50s of environmental chemicals ranged from below 10 to 357 µM. Effects by environmental chemicals on Abcb4 ATPase activity with EC50s close to their water solubilities may be rather unspecific. The results of this work underline that Abcb4 function is of ecotoxicological importance as on the one hand several environmental chemicals were identified to inhibit Abcb4 ATPase activity – likely acting as chemosensitisers, while on the other hand chemicals stimulating basal ATPase activity suggest that these chemicals are possibly transported. A number of environmental chemicals also inhibited the basal Abcb4 ATPase activity. Especially non-transported inhibitors of the basal Abcb4 ATPase activity would be of ecotoxicological relevance as organisms (here Danio rerio) exposed to these chemicals would not be protected by Abcb4 mediated multixenobiotic resistance and were moreover threatened by chemosensitisation. Future studies should systematically elucidate under which circumstances chemicals are apparently net transported by ABCB1-like transporters and relate these findings to concentrations of environmental chemicals and ABCB1-like transporter protein abundance in wildlife.