Enzastaurin inhibits ABCB1-mediated drug efflux independently of effects on protein kinase C signalling and the cellular p53 status.
The PKCβ inhibitor enzastaurin was tested in parental neuroblastoma and rhabdomyosarcoma cell lines, their vincristine-resistant sub-lines, primary neuroblastoma cells, ABCB1-transduced, ABCG2-transduced, and p53-depleted cells. Enzastaurin IC50s ranged from 3.3 to 9.5 μM in cell lines and primary cells independently of the ABCB1, ABCG2, or p53 status. Enzastaurin 0.3125 μM interfered with ABCB1-mediated drug transport. PKCα and PKCβ may phosphorylate and activate ABCB1 under the control of p53. However, enzastaurin exerted similar effects on ABCB1 in the presence or absence of functional p53. Also, enzastaurin inhibited PKC signalling only in concentrations ≥ 1.25 μM. The investigated cell lines did not express PKCβ. PKCα depletion reduced PKC signalling but did not affect ABCB1 activity. Intracellular levels of the fluorescent ABCB1 substrate rhodamine 123 rapidly decreased after wash-out of extracellular enzastaurin, and enzastaurin induced ABCB1 ATPase activity resembling the ABCB1 substrate verapamil. Computational docking experiments detected a direct interaction of enzastaurin and ABCB1. These data suggest that enzastaurin directly interferes with ABCB1 function. Enzastaurin further inhibited ABCG2-mediated drug transport but by a different mechanism since it reduced ABCG2 ATPase activity. These findings are important for the further development of therapies combining enzastaurin with ABC transporter substrates.
Institut für Medizinische Virologie, Klinikum der Goethe-Universität, Frankfurt am Main, Germany.|Centre for Molecular Processing and School of Biosciences, University of Kent, Canterbury, UK.
Martin
M
Michaelis
Institut für Medizinische Virologie, Klinikum der Goethe-Universität, Frankfurt am Main, Germany.
Florian
F
Rothweiler
Institut für Medizinische Virologie, Klinikum der Goethe-Universität, Frankfurt am Main, Germany.
Nadine
N
Löschmann
Medway School of Pharmacy, Universities of Kent and Greenwich, Chatham Maritime, Kent, UK.
Mohsen
M
Sharifi
Medway School of Pharmacy, Universities of Kent and Greenwich, Chatham Maritime, Kent, UK.
Taravat
T
Ghafourian
Institut für Medizinische Virologie, Klinikum der Goethe-Universität, Frankfurt am Main, Germany.
Jindrich
J
Cinatl
D018435:ATP Binding Cassette Transporter, Subfamily B / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D008958:Models, Molecular; D009447:Neuroblastoma / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D011493:Protein Kinase C / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D034741:RNA, Small Interfering; D012208:Rhabdomyosarcoma / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D000970:Antineoplastic Agents; D007211:Indoles; D047428:Protein Kinase Inhibitors; D034741:RNA, Small Interfering; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D011493:Protein Kinase C; C504878:enzastaurin
NSC350625; ONC201; TIC10; cancer drug