title: Differential effects of the oncogenic BRAF inhibitor PLX4032 (vemurafenib) and its progenitor PLX4720 on ABCB1 function.
abstract: OBJECTIVE
  The clinically approved oncogenic BRAF inhibitor PLX4032 (vemurafenib) was shown to be a substrate of the ATP-binding cassette (ABC) transporter ABCB1. Here, we compared PLX4032 and its structurally closely related precursor compound PLX4720 for their interference with ABCB1 and the ABCB1-mediated compound transport using docking and cell culture experiments.
  
  
  METHODS
  For the docking study of PLX4032 and PLX4720 with ABCB1, we analysed binding of both compounds to mouse Abcb1a and to human ABCB1 using a homology model of human ABCB1 based on the 3D structure of Abcb1a. Naturally ABCB1 expressing cells including V600E BRAF-mutated and BRAF wild-type melanoma cells and cells transduced with a lentiviral vector encoding for ABCB1 were used as cell culture models. ABCB1 expression and function were studied by the use of fluorescent and cytotoxic ABCB1 substrates in combination with ABCB1 inhibitors.
  
  
  RESULTS
  Docking experiments predicted PLX4032 to interact stronger with ABCB1 than PLX4720. Experimental studies using different cellular models and structurally different ABCB1 substrates confirmed that PLX4032 interfered stronger with ABCB1 function than PLX4720. For example, PLX4032 (20 µM) induced a 4-fold enhanced rhodamine 123 accumulation compared to PLX4720 (20 µM) in ABCB1-transduced UKF-NB-3 cells and reduced the IC₅₀ for the cytotoxic ABCB1 substrate vincristine in this model by 21-fold in contrast to a 9-fold decrease induced by PLX4720.
  
  
  CONCLUSIONS
  PLX4032 exerted stronger effects on ABCB1-mediated drug transport than PLX4720. This indicates that small changes in a molecule can substantially modify its interaction with ABCB1, a promiscuous transporter that transports structurally different compounds.
authors.forename: Martin
authors.initials: M
authors.lastname: Michaelis
authors.forename: Florian
authors.initials: F
authors.lastname: Rothweiler
authors.forename: Thomas
authors.initials: T
authors.lastname: Nerreter
authors.forename: Marijke
authors.initials: M
authors.lastname: Van Rikxoort
authors.forename: Mohsen
authors.initials: M
authors.lastname: Sharifi
authors.forename: Michael
authors.initials: M
authors.lastname: Wiese
authors.forename: Taravat
authors.initials: T
authors.lastname: Ghafourian
authors.forename: Jindrich
authors.initials: J
authors.lastname: Cinatl
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D002460:Cell Line; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004359:Drug Therapy, Combination; D005434:Flow Cytometry; D006801:Humans; D007211:Indoles / Q000008:administration & dosage / Q000494:pharmacology*; D008545:Melanoma / Q000188:drug therapy; D051379:Mice; D062105:Molecular Docking Simulation; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors*; D013449:Sulfonamides / Q000008:administration & dosage / Q000494:pharmacology*; D000077484:Vemurafenib; D014750:Vincristine / Q000008:administration & dosage / Q000627:therapeutic use
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D000970:Antineoplastic Agents; D007211:Indoles; C528407:PLX 4720; D013449:Sulfonamides; D000077484:Vemurafenib; D014750:Vincristine; D048493:Proto-Oncogene Proteins B-raf; D000251:Adenosine Triphosphatases