Title: Plumb JA, et al. The activity of verapamil as a resistance modifier in vitro in drug resistant human tumour cell lines is not stereospecific. Biochem Pharmacol. 1990 Feb 15;39(4):787-92.
Title: Perrotton T, et al. (R)- and (S)-verapamil differentially modulate the multidrug-resistant protein MRP1. J Biol Chem. 2007 Oct 26;282(43):31542-8. Epub 2007 Jul 22.