Vanhoefer U, Cao S, Minderman H, Toth K, Skenderis B S, Slovak M L, Rustum Y M
Department of Experimental Therapeutics, Grace Cancer Drug Center and Department of Surgical Oncology, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
Clin Cancer Res. 1996 Dec;2(12):1961-8.
Intracellular glutathione (GSH) has been implicated as a regulatory determinant of multidrug resistance protein (MRP) function. The objective of the present study was to evaluate in vivo the ability of d,l-buthionine-(S,R)-sulfoximine (d,l-BSO), a potent inhibitor of GSH biosynthesis, to reverse MRP-mediated drug resistance to doxorubicin. Athymic nude mice (nu/nu) bearing advanced parental human fibrosarcoma HT1080 and MRP-expressing HT1080/DR4 tumors were treated with the maximum tolerated dose of doxorubicin (10 mg/kg, i. v. push). This therapy produced an overall response rate of 50% (20% complete response and 30% partial response) in mice bearing parental HT1080 xenografts, whereas no significant antitumor activity against HT1080/DR4 tumors was observed. Treatment of mice bearing HT1080 and HT1080/DR4 xenografts with a continuous i.v. infusion of nontoxic doses of d,l-BSO (300 and 600 mg/kg/day) produced a 60% reduction of GSH plasma levels and greater than 95% reduction in GSH tumor levels in both parental and multidrug-resistant tumors; however, this treatment possessed no in vivo antitumor activity by itself. Under these treatment conditions, a combination of d,l-BSO with the maximum tolerated dose of doxorubicin administered at 24 h during a 48-h i.v. infusion of d,l-BSO completely restored the response of MRP-expressing HT1080/DR4 tumors to doxorubicin (overall response rate, 63%; complete response rate, 38%) with no potentiation of host toxicity. The d,l-BSO-induced in vivo reversal of MRP-mediated drug resistance correlated in vitro with the restoration of intracellular doxorubicin retention in cultured HT1080/DR4 cells. Depletion of GSH by d,l-BSO in drug-sensitive HT1080 tumors that do not express MRP did not alter the in vivo response to doxorubicin. Using the same treatment schedule, dose, and administration of doxorubicin with and without d,l-BSO in nude mice bearing P-170 glycoprotein-expressing A2780/Dx5 tumors, no potentiation of the therapeutic index of doxorubicin was found, demonstrating the in vivo selectivity of d, l-BSO-induced GSH depletion on MRP-function. The data reported herein indicate that in vivo function of MRP as a mediator of doxorubicin resistance requires the presence of sufficient GSH pools. d,l-BSO may provide an example of an effective in vivo modulator of MRP-mediated drug resistance.
细胞内谷胱甘肽（GSH）被认为是多药耐药蛋白（MRP）功能的调节决定因素。本研究的目的是在体内评估GSH生物合成的强效抑制剂d，l-丁硫氨酸-（S，R）-亚砜胺（d，l-BSO）逆转MRP介导的对阿霉素耐药性的能力。用阿霉素的最大耐受剂量（10mg/kg，静脉推注）治疗携带晚期亲本人类纤维肉瘤HT1080和表达MRP的HT1080/DR4肿瘤的无胸腺裸鼠（nu/nu）。该疗法在携带亲本HT1080异种移植物的小鼠中产生了50%的总体反应率（20%完全缓解和30%部分缓解），而未观察到对HT1080/DR4肿瘤有显著的抗肿瘤活性。用无毒剂量的d，l-BSO（300和600mg/kg/天）持续静脉输注治疗携带HT1080和HT1080/DR4异种移植物的小鼠，在亲本和多药耐药肿瘤中，血浆GSH水平降低了60%，肿瘤GSH水平降低了95%以上；然而，这种治疗本身在体内没有抗肿瘤活性。在这些治疗条件下，在48小时静脉输注d，l-BSO的24小时期间，将d，l-BSO与阿霉素的最大耐受剂量联合使用，完全恢复了表达MRP的HT1080/DR4肿瘤对阿霉素反应（总体反应率63%；完全反应率38%），且未增强宿主毒性。d，l-BSO在体内诱导的MRP介导的耐药性逆转在体外与培养的HT1080/DR4细胞中细胞内阿霉素保留的恢复相关。在不表达MRP的药物敏感HT1080肿瘤中，d，l-BSO消耗GSH并未改变对阿霉素的体内反应。在携带表达P-170糖蛋白的A2780/Dx5肿瘤的裸鼠中，使用相同的治疗方案、剂量以及阿霉素有无d，l-BSO的给药方式，未发现阿霉素治疗指数的增强，这证明了d，l-BSO诱导的GSH消耗对MRP功能的体内选择性。本文报道的数据表明，MRP作为阿霉素耐药性介质的体内功能需要足够的GSH储备。d，l-BSO可能是MRP介导的耐药性的一种有效的体内调节剂实例。
