G. Lehne et al., Growth inhibition, cytokinesis failure and apoptosis of multidrug-resistant leukemia cells after treatment with P-glycoprotein inhibitory agents, LEUKEMIA, 13(5), 1999, pp. 768-778
The multidrug transporter P-glycoprotein (Pgp), which is frequently overexp
ressed in multidrug resistant leukemia, has many proposed physiological fun
ctions including involvement in transmembraneous transport of certain growt
h-regulating cytokines. Therefore, we studied cell growth of three pairs of
drug resistant and sensitive leukemia cell lines (KG1a, K562 and HL60) exp
osed to three different inhibitors of Pgp. The resistant KG1a and K562 subl
ines, which expressed high levels of Pgp, responded to low doses of the cyc
losporin SDZ PSC 833, the cyclopeptolide SDZ 280-446, and the cyclopropyldi
benzosuberane LY335979 with a dose-dependent growth inhibition. In the resi
stant variants of KG1a and K562 cells the mean half-maximal growth inhibito
ry doses (GI(50)) of SDZ PSC 833 were 312 (SE 41) and 414 (SE 50) nM, those
of SDZ 280-446 were 685 (SE 51) and 578 (SE 54) nM, and those of LY335979
were 66 (SE 1) and 48 (SE 8) nM, respectively. Exposure to 1 mu M SDZ PSC 8
33 resulted in tetraploidization, cytokinesis failure and apoptosis of the
KG1a and K562 MDR variants. Conversely, parental cells with no or low level
s of Pgp and the non-Pgp resistant variant of HL60 cells were not receptive
to these cytotoxic effects. We conclude that inhibition of Pgp may exercis
e selective cytotoxicity in Pgp-rich leukemia cells indicating a possible t
herapeutic target in multiresistant leukemia.