Understanding
the transport and inhibition mechanisms of substrates
by P-glycoprotein (P-gp) is one of the important approaches in addressing
multidrug resistance (MDR). In this study, we evaluated a variety
of rhodamine derivatives as potential P-gp inhibitors targeting CmABCB1,
a P-gp homologue, with a focus on their ATPase activity. Notably,
a Q-rhodamine derivative with an o,o′-dimethoxybenzyl ester moiety (RhQ-DMB) demonstrated
superior affinity and inhibitory activity, which was further confirmed
by a drug susceptibility assay in yeast strains expressing CmABCB1.
Results from a tryptophan fluorescence quenching experiment using
a CmABCB1 mutant suggested that RhQ-DMB effectively enters
and binds to the inner chamber of CmABCB1. These findings underscore
the promising potential of RhQ-DMB as a tool for future
studies aimed at elucidating the substrate-bound state of CmABCB1.