Sehested M, Friche E, Jensen P B, Demant E J
Department of Pathology, Sundby Hospital, Copenhagen, Denmark.
Cancer Res. 1992 May 15;52(10):2874-9.
The classical multidrug resistance (MDR) phenotype is characterized by cross-resistance between a number of chemically unrelated drugs due to an increased efflux across the plasma membrane via a P-glycoprotein-mediated mechanism. The epipodophyllotoxin derivatives etoposide (VP-16) and teniposide (VM-26) are usually included among the drugs recognized by this MDR phenotype, and the MDR EHR2/DNR cell line is greater than 50-fold cross-resistant to VP-16. The steady-state accumulation of VP-16 in EHR2/DNR cells is only half that of wild-type EHR2 cells, and deprivation of energy by sodium azide surprisingly increased accumulation to a similar extent in both sublines. Efflux was rapid (halflife of 32-35 s) and similar in both sublines, while initial influx was markedly lower in the resistant cells. The temperature coefficients over 10 degrees C for VP-16 in- and efflux indicated passive transport in both sublines. In agreement with this finding, up to 10-fold molar excess (50 microM) VM-26 had no effect on VP-16 accumulation in MDR cells. VP-16 at a 100-fold molar excess inhibited azidopine photoaffinity labeling of P-glycoprotein by only 30% and vincristine binding to plasma membrane vesicles from EHR/DNR cells by 45%. However, VP-16 itself did not differentially bind to plasma membrane vesicles from EHR2 and EHR2/DNR cells. Finally, neither VP-16 accumulation nor cytotoxicity in EHR2/DNR cells were increased to the same degree as for daunorubicin and vincristine by verapamil, and the modulation was similar in wild-type and resistant cells. Thus, although VP-16 may be a substrate for P-glycoprotein, its other transport characteristics such as rapid diffusion and sensitivity to membrane perturbation in wild-type cells lessen any effect of P-glycoprotein-mediated efflux, resulting in a lack of differential modulation by verapamil. These results may be considered when planning clinical trials involving MDR modulators and epipodophyllotoxin derivatives.
经典的多药耐药（MDR）表型的特征是，由于通过P-糖蛋白介导的机制使跨质膜的外排增加，导致多种化学结构不相关的药物之间产生交叉耐药。表鬼臼毒素衍生物依托泊苷（VP-16）和替尼泊苷（VM-26）通常被认为是受这种MDR表型影响的药物，MDR EHR2/DNR细胞系对VP-16的交叉耐药性大于50倍。VP-16在EHR2/DNR细胞中的稳态蓄积量仅为野生型EHR2细胞的一半，而叠氮化钠导致的能量剥夺令人惊讶地使两个亚系中的蓄积量增加到相似程度。外排在两个亚系中都很快（半衰期为32 - 35秒）且相似，而初始内流在耐药细胞中明显较低。VP-16内流和外排在10℃以上的温度系数表明在两个亚系中均为被动转运。与此发现一致，高达10倍摩尔过量（50μM）的VM-26对MDR细胞中VP-16的蓄积没有影响。100倍摩尔过量的VP-16仅使叠氮平对P-糖蛋白的光亲和标记抑制30%，使长春新碱与EHR/DNR细胞膜囊泡的结合抑制45%。然而，VP-16本身与EHR2和EHR2/DNR细胞膜囊泡的结合没有差异。最后，维拉帕米并未使EHR2/DNR细胞中VP-16的蓄积和细胞毒性增加到与柔红霉素和长春新碱相同的程度，并且在野生型和耐药细胞中的调节作用相似。因此，尽管VP-16可能是P-糖蛋白的底物，但其其他转运特性，如在野生型细胞中的快速扩散和对膜扰动的敏感性，减轻了P-糖蛋白介导的外排的任何影响，导致维拉帕米缺乏差异调节作用。在规划涉及MDR调节剂和表鬼臼毒素衍生物的临床试验时，可能需要考虑这些结果。
