Rhodamine inhibitors of P-glycoprotein: an amide/thioamide "switch" for ATPase activity

J Med Chem. 2009 May 28;52(10):3328-41. doi: 10.1021/jm900253g.


We have examined 46 tetramethylrosamine/rhodamine derivatives with structural diversity in the heteroatom of the xanthylium core, the amino substituents of the 3- and 6-positions, and the alkyl, aryl, or heteroaryl group at the 9-substituent. These compounds were examined for affinity and ATPase stimulation in isolated MDR3 CL P-gp and human P-gp-His(10), for their ability to promote uptake of calcein AM and vinblastine in multidrug-resistant MDCKII-MDR1 cells, and for transport in monolayers of MDCKII-MDR1 cells. Thioamide 31-S gave K(M) of 0.087 microM in human P-gp. Small changes in structure among this set of compounds affected affinity as well as transport rate (or flux) even though all derivatives examined were substrates for P-gp. With isolated protein, tertiary amide groups dictate high affinity and high stimulation while tertiary thioamide groups give high affinity and inhibition of ATPase activity. In MDCKII-MDR1 cells, the tertiary thioamide-containing derivatives promote uptake of calcein AM and have very slow passive, absorptive, and secretory rates of transport relative to transport rates for tertiary amide-containing derivatives. Thioamide 31-S promoted uptake of calcein AM and inhibited efflux of vinblastine with IC(50)'s of approximately 2 microM in MDCKII-MDR1 cells.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / antagonists & inhibitors*
  • Adenosine Triphosphatases / drug effects
  • Adenosine Triphosphatases / metabolism*
  • Amides / chemistry
  • Amides / pharmacology*
  • Animals
  • Biological Transport
  • Cell Line
  • Dogs
  • Drug Resistance, Multiple
  • Fluoresceins / pharmacokinetics
  • Heterocyclic Compounds, 3-Ring
  • Humans
  • Kinetics
  • Protein Binding
  • Rhodamines / chemistry
  • Rhodamines / pharmacology*
  • Structure-Activity Relationship
  • Thioamides / chemistry
  • Thioamides / pharmacology*
  • Vinblastine / pharmacokinetics


  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • Amides
  • Fluoresceins
  • Heterocyclic Compounds, 3-Ring
  • Rhodamines
  • Thioamides
  • tetramethylrosamine
  • calcein AM
  • Vinblastine
  • Adenosine Triphosphatases