title: Effect of pluronic P85 on ATPase activity of drug efflux transporters.
abstract: OBJECTIVE
  Pluronic block copolymers are potent sensitizers of multi-drug resistant (MDR) cancer cells. The sensitization effect by Pluronics is a result of two processes acting in concert: i) intracellular ATP depletion, and ii) inhibition of ATPase activity of drug efflux proteins. This work characterizes effects of Pluronic P85 on ATPase activities of Pgp, MRP1, and MRP2 drug efflux transport proteins and interaction of these proteins with their substrates, vinblastine, and leucotriene C4.
  
  
  METHODS
  Using membranes overexpressing Pgp, MRP1, and MRP2, the current study evaluates effects of Pluronic P85 (P85) on the kinetic parameters (Vmax, Km, Vmax/Km) of ATP hydrolysis by these ATPases.
  
  
  RESULTS
  The decreases in the maximal reaction rates (Vmax) and increases in apparent Michaelis constants (Km) for these transporters in the presence of various concentrations of P85 were observed. The mechanism of these effects may involve i) conformational changes of the transporter due to membrane fluidization and/or ii) nonspecific steric hindrance of the drug-binding sites by P85 chains embedded into cellular membranes. The extent of these alterations was increased in the row MRP1 < MRP2 << Pgp.
  
  
  CONCLUSIONS
  These data suggest that there are unifying pathways for the inhibition of Pgp and MRPs by the block copolymer. However, the effect of P85 on Pgp ATPase activity is considerably greater compared with the effects on MRP1 and MRP2 ATPases. This may be a reason for greater inhibitory effects of Pluronic in Pgp- compared with MRP-overexpressing cells.
authors.affiliation: Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, Nebraska 68198-5830, USA.
authors.forename: Elena V
authors.initials: EV
authors.lastname: Batrakova
authors.forename: Shu
authors.initials: S
authors.lastname: Li
authors.forename: Yili
authors.initials: Y
authors.lastname: Li
authors.forename: Valery Yu
authors.initials: VY
authors.lastname: Alakhov
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Kabanov
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D011060:Poloxalene / Q000378:metabolism* / Q000494:pharmacology*; D013552:Swine
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000251:Adenosine Triphosphatases; D000255:Adenosine Triphosphate; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D011060:Poloxalene; C422648:pluronic block copolymer p85