Reversal of multidrug resistance by calcium channel blocker SR33557 without photoaffinity labeling of P-glycoprotein.
The altered pharmacology of drugs in multidrug-resistant cells (decreased accumulation and retention) appears to be mediated by a high molecular weight integral membrane protein, called P-glycogprotein (P-gp). Agents known to reverse this pleiotropic drug resistance (chemosensitizers) have been shown to interact with P-gp; and as such, the inhibition of photoaffinity labeling by P-gp probes (such as [3H]azidopine) has been proposed as a basis for mass screening of chemosensitizers. In this study, we provide direct evidence that a novel calcium channel blocker (SR33557), which was 4.5 times more potent in sensitizing P388/ADR cells to doxorubicin as compared to verapamil (while inducing a similar increase in uptake and decrease in efflux of [14C]doxorubicin, did not compete for the [3H]azidopine-binding site on P-gp, whereas verapamil did. Moreover, SR33557, which is inherently photoactivable, did not photolabel P-gp, but a 65-kDa protein did appear to be an acceptor; and this binding was displaced by diltiazem and nifedipine, but not by verapamil. Finally, the implication for the participation of a sphingomyelin/sphingosine cycle (as a potential lipid second messenger system) in the chemosensitization of P388/ADR cells was investigated. 30 microM SR33557 induced a 72% inhibition in acid lysosomal sphingomyelinase activity, a 5-fold increase in sphingosine levels, and a 75% inhibition in intracellular protein kinase C activity. Although no direct link is established between these observations and P-gp activity, further studies on a possible sphingosine-mediated regulation of P-gp may yield information on the involvement of this second messenger system in the action of SR33557.
Laboratoire de Pharmacologie et de Toxicologie Fondamentales, Centre National de la Recherche Scientifique 8221, Toulouse, France.
J P
JP
Jaffrézou
J M
JM
Herbert
T
T
Levade
M N
MN
Gau
P
P
Chatelain
G
G
Laurent
D000818:Animals; D002121:Calcium Channel Blockers / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004351:Drug Resistance; D007212:Indolizines / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D007942:Leukemia, Experimental / Q000201:enzymology / Q000473:pathology; D051379:Mice; D010627:Phenethylamines / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D015290:Second Messenger Systems; D013110:Sphingosine / Q000032:analysis; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D007212:Indolizines; D010627:Phenethylamines; D014700:Verapamil; D011493:Protein Kinase C; C059901:fantofarone; D013110:Sphingosine