Suppression of P-glycoprotein expression by antipsychotics trifluoperazine in adriamycin-resistant L1210 mouse leukemia cells.

Multidrug resistance (MDR) to unrelated chemotherapeutic drugs can be mediated by overexpression of P-glycoprotein (P-gp), the mdr gene product. Trifluoperazine (TFP), a phenothiazine derivative antipsychotics, is known to reverse MDR of tumor cell lines by blocking P-gp efflux function. In the present study, we evaluated the effect of TFP on the expression of P-gp in multidrug-resistant L1210/Adr mouse leukemic cell lines, which are characterized by overexpession of P-gp. We found that TFP induced the downregulation of P-gp protein and mdr1b mRNA in a dose- and time-dependent manner in L1210/Adr cells. TFP reduction of mdr1b mRNA was paralleled by transcriptional suppression of the mdr1b promoter. Moreover, TFP restored the adriamycin-induced apoptosis in L1210/Adr cells. These results suggest that TFP may have utility as an adjuvant in the therapy of leukemia for the reversal of P-gp-dependent MDR as well as for the management of psychological symptoms in the cancer patients.