title: Interaction of CJY, an isoflavone, with ATPase of P-glycoprotein in doxorubicin-resistant human myelogenous leukemia (K562/DOX) cells.
abstract: OBJECTIVE
  The previous study reported CJY, an isoflavone, can reverse P-glycoprotein (P-gp)-mediated multidrug-resistance (MDR) in doxorubicin-resistant human myelogenous leukemia (K562/DOX) cells. This study will investigate the exact mechanism of CJY on P-gp.
  
  
  METHODS
  By assessment of ATPase activity, we gained further insight into the nature of the CJY interactions with P-gp. Kinetic studies on ATPase activity were applied to show the effects of Verapamil (Ver) on CJY-stimulated, CJX1 on Ver-stimulated, and CJX1 on CJY-stimulated P-gp ATPase activity. Furthermore, the combined effects of CJY with Ver, and CJY with CJX1 were also evaluated isobolographically in numerous fixed-ratio combinations of 1:1, 1:2, 1:4, 1:8, and 1:10.
  
  
  RESULTS
  The results showed that basal P-gp ATPase activity was increased by CJY with half-maximal activity concentration (Km) of 2.9±0.3 μM and the maximal ATPase activity velocity (Vmax) of 265±21 nM · min-1 · mg-1. Kinetic studies on ATPase activity showed the effects of Verapamil (Ver) on CJY-stimulated, CJX1 on Ver-stimulated, and CJX1 on CJY-stimulated P-gp ATPase activity were all non-competitive inhibition, indicating that these substrates can simultaneously but independently bind to diverse sites on P-gp. The combined effects of CJY with Ver, and CJY with CJX1 show that mixtures of both drugs at these fixed-ratios displayed synergistic interactions.
  
  
  CONCLUSIONS
  CJY, CJX1 and Ver bind P-gp on different sites. CJY could be applied combining with other P-gp inhibitors to get better reversal of multidrug resistance than it used alone.
authors.affiliation: Key Laboratory of Natural Medicine and Immune Engineering, Henan University, Kaifeng, China.
authors.forename: J
authors.initials: J
authors.lastname: Cen
authors.forename: L
authors.initials: L
authors.lastname: Liu
authors.forename: L
authors.initials: L
authors.lastname: He
authors.forename: B-S
authors.initials: BS
authors.lastname: Ji
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D017311:Amlodipine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D004317:Doxorubicin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm; D006801:Humans; D007529:Isoflavones / Q000494:pharmacology*; D020014:K562 Cells; D020112:Rhodamine 123 / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000903:Antibiotics, Antineoplastic; C504653:CJX1, amlodipine derivative; C523261:CJY compound; D007529:Isoflavones; D017311:Amlodipine; D020112:Rhodamine 123; D004317:Doxorubicin; D014700:Verapamil; D000251:Adenosine Triphosphatases