title: Structure-activity relationship studies of propafenone analogs based on P-glycoprotein ATPase activity measurements.
abstract: Propafenone analogs (PAs) were previously identified as potent inhibitors of P-glycoprotein (Pgp)-mediated toxin efflux. For this as well as other classes of Pgp inhibitors, lipophilicity as well as hydrogen bond acceptor strength are important determinants of biological activity. The question as to whether a direct interaction between PA-type modulators and Pgp takes place was addressed by means of Pgp ATPase measurements and transport studies. Propafenone-type modulators stimulated ATPase activity up to 2-fold over basal activity in a concentration-dependent biphasic manner. Within a series of structural homologs, Ka values of ATPase stimulation strongly correlated with lipophilicity. Analogs containing a quaternary nitrogen stimulated Pgp ATPase activity with lesser efficacy, while Ka values were somewhat higher when compared to corresponding tertiary analogs. Transport studies performed in inside-out plasma membrane (I/O) vesicles demonstrated that analogs containing a tertiary nitrogen rapidly associated with the biomembrane. Quaternary analogs, which are restricted by a permanent positive charge in transiting the plasma membrane by diffusion, accumulated in Pgp containing I/O vesicles in an ATP-dependent and cyclosporin A-inhibitable manner, which identified them as Pgp substrates. Identical structure-activity relationships were found in either Pgp ATPase stimulation experiments in I/O vesicles or in toxin efflux inhibition studies using intact cells. Therefore, differences in membrane transit are not responsible for the observed structure-activity relationships.
authors.affiliation: Institute of Medical Chemistry, University of Vienna, Austria.
authors.forename: D
authors.initials: D
authors.lastname: Schmid
authors.forename: G
authors.initials: G
authors.lastname: Ecker
authors.forename: S
authors.initials: S
authors.lastname: Kopp
authors.forename: M
authors.initials: M
authors.lastname: Hitzler
authors.forename: P
authors.initials: P
authors.lastname: Chiba
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D011405:Propafenone / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D020112:Rhodamine 123 / Q000378:metabolism; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D020112:Rhodamine 123; D011405:Propafenone; D000251:Adenosine Triphosphatases