BACKGROUND Overexpression of ATP-binding cassette (ABC) transporters, such as ABCB1 and ABCG2, has been proved to be a major trigger for multidrug resistance (MDR) in certain types of cancer. A promising approach to reverse MDR is the combined use of nontoxic and potent ABC transporters inhibitor with conventional anticancer drugs. We previously reported that FW-04-806 (conglobatin) as a novel Hsp90 inhibitor with low toxicity, capable of attenuating Hsp90/Cdc37 /clients interactions and producing antitumor action in vitro and in vivo. Our early activity screening found that FW-04-806 at non-cytotoxic concentration was able to enhance the cytotoxicity of chemotherapeutic agents on the ABCB1 overexpressing cells. Therefore, we speculated that FW-04-806 might be a promising MDR reversal agent. In the present study we further investigated its reversal effect of MDR induced by ABC transporters in vitro and in vivo. METHODS MTT assay in vitro and xenograftes in vivo were used to investigate reversal effect of FW-04-806 on MDR in ABCB1 or ABCG2 overexpressing cancer cells. To understand the mechanisms for the MDR reversal, we examined the effects of FW-04-806 on intracellular accumulation of doxorubicin (DOX, adriamycin, adr)/Rhodamine 123 (Rho 123), efflux of doxorubicin, expression levels of gene and protein of ABCB1 or ABCG2 and ATPase activity of ABCB1, and carried out molecular docking between FW-04-806 and human ABCB1. RESULTS The results indicated that FW-04-806 significantly enhanced the cytotoxicity of substrate chemotherapeutic agents on the ABCB1 or ABCG2 overexpressing cells in vitro and in vivo suggesting its reversal MDR effects. FW-04-806 increased the intracellular accumulation of DOX or Rho123 by inhibiting the efflux function of ABC transporters in MDR cells rather than in their parental sensitive cells. However, unlike other ABC transporter inhibitors, FW-04-806 had no effect on the ATPase activity nor on the expression of ABCB1 or ABCG2 on either mRNA or protein level. Molecular docking suggested that FW-04-806 may have lower affinity to the ATPase site, which was consistent with its no significant effect on the ATPase activity of ABCB1; However FW-04-806 may bind to substrate binding site in TMDs more stably than substrate anticancer drugs therefore obstruct the anticancer drugs pumped out of the cell. CONCLUSIONS FW-04-806 is a compound that has both anti-tumor and reversal MDR effects, and its antitumor clinical application is worth further study.

中文翻译：

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大环内酯二内酯化合物FW-04-806在体外和体内对ABCB1和ABCG2介导的多药耐药性的逆转作用。

背景技术已经证明，ATP结合盒（ABC）转运蛋白如ABCB1和ABCG2的过表达是某些类型癌症中多药耐药性（MDR）的主要诱因。逆转MDR的一种有前途的方法是将无毒有效的ABC转运蛋白抑制剂与常规抗癌药联合使用。我们先前曾报道FW-04-806（conglobatin）作为一种具有低毒性的新型Hsp90抑制剂，能够减弱Hsp90 / Cdc37 /客户之间的相互作用并在体内和体外产生抗肿瘤作用。我们的早期活动筛选发现，在无细胞毒性浓度的FW-04-806能够增强化学治疗剂对ABCB1过表达细胞的细胞毒性。因此，我们推测FW-04-806可能是有前途的MDR逆转代理。在本研究中，我们进一步研究了ABC转运蛋白在体外和体内对MDR的逆转作用。方法采用体外MTT法和体内异种移植物，研究FW-04-806对ABCB1或ABCG2过表达癌细胞中MDR的逆转作用。为了了解MDR逆转的机制，我们研究了FW-04-806对阿霉素（DOX，阿霉素，adr）/若丹明123（Rho 123）细胞内积累，阿霉素外排，基因和蛋白表达水平的影响。 ABCB1或ABCG2与ABCB1的ATPase活性有关，并在FW-04-806与人ABCB1之间进行了分子对接。结果结果表明，FW-04-806在体外和体内显着增强了底物化学治疗剂对ABCB1或ABCG2过表达细胞的细胞毒性，表明其逆转MDR效应。FW-04-806通过抑制ADR转运蛋白在MDR细胞而不是其亲代敏感细胞中的外排功能来增加DOX或Rho123的细胞内积累。但是，与其他ABC转运蛋白抑制剂不同，FW-04-806对mRNA或蛋白质水平上的ATPase活性或ABCB1或ABCG2的表达均无影响。分子对接表明，FW-04-806可能对ATPase位点的亲和力较低，这与其对ABCB1的ATPase活性无明显影响是一致的。然而，与底物抗癌药相比，FW-04-806可能更稳定地与TMD中的底物结合位点结合，因此阻碍了泵出细胞的抗癌药。结论FW-04-806是一种既具有抗肿瘤作用又具有逆转MDR作用的化合物，其抗肿瘤临床应用值得进一步研究。