PGP and lymphoma: On the other hand, the p-phenoxybenzylidene derivative with the piperidine-morpholine moiety at position 2 (11, group A) was even slightly more potent than 18 to inhibit the dye-substrate efflux, while the substrate potency of 11 was significantly weaker in either the Pgp ATPase- or the PAR vs. MDR T-lymphoma cytotoxicity assays.