Goda Katalin, Fenyvesi Ferenc, Bacsó Zsolt, Nagy Henrietta, Márián Teréz, Megyeri Attila, Krasznai Zoltán, Juhász István, Vecsernyés Miklós, Szabó Gábor
Department of Biophysics and Cell Biology, University of Debrecen, Debrecen, Hungary.
J Pharmacol Exp Ther. 2007 Jan;320(1):81-8. doi: 10.1124/jpet.106.110155. Epub 2006 Oct 18.
P-glycoprotein (Pgp) is one of the active efflux pumps that are able to extrude a large variety of chemotherapeutic drugs from the cells, causing multidrug resistance. The conformation-sensitive UIC2 monoclonal antibody potentially inhibits Pgp-mediated substrate transport. However, this inhibition is usually partial, and its extent is variable because UIC2 binds only to 10 to 40% Pgp present in the cell membrane. The rest of the Pgp molecules become recognized by this antibody only in the presence of certain substrates or modulators, including vinblastine, cyclosporine A (CsA), and SDZ PSC 833 (valspodar). Simultaneous application of any of these modulators and UIC2, followed by the removal of the modulator, results in a completely restored steady-state accumulation of various Pgp substrates (calcein-AM, daunorubicin, and 99mTc-hexakis-2-methoxybutylisonitrile), indicating near 100% inhibition of pump activity. Remarkably, the inhibitory binding of the antibody is brought about by coincubation with concentrations of CsA or SDZ PSC 833 approximately 20 times lower than what is necessary for Pgp inhibition when the modulators are applied alone. The feasibility of such a combinative treatment for in vivo multidrug resistance reversal was substantiated by the dramatic increase of daunorubicin accumulation in xenotransplanted Pgp+ tumors in response to a combined treatment with UIC2 and CsA, both administered at doses ineffective when applied alone. These observations establish the combined application of a class of modulators used at low concentrations and of the UIC2 antibody as a novel, specific, and effective way of blocking Pgp function in vivo.
P-糖蛋白（Pgp）是一种活性外排泵，能够将多种化疗药物从细胞中排出，导致多药耐药。构象敏感的UIC2单克隆抗体可能抑制Pgp介导的底物转运。然而，这种抑制通常是部分性的，其程度是可变的，因为UIC2仅与细胞膜中10%至40%的Pgp结合。其余的Pgp分子仅在某些底物或调节剂（包括长春碱、环孢素A（CsA）和SDZ PSC 833（valspodar））存在的情况下才能被该抗体识别。同时应用这些调节剂中的任何一种与UIC2，然后去除调节剂，会导致各种Pgp底物（钙黄绿素-AM、柔红霉素和99mTc-六甲基-2-甲氧基丁基异腈）的稳态积累完全恢复，表明泵活性几乎被100%抑制。值得注意的是，抗体的抑制性结合是通过与CsA或SDZ PSC 833的浓度共同孵育实现的，该浓度比单独应用调节剂抑制Pgp时所需的浓度低约20倍。对异种移植的Pgp+肿瘤联合应用UIC2和CsA进行治疗（单独应用时这两种药物的剂量均无效），结果柔红霉素在肿瘤中的积累显著增加，从而证实了这种联合治疗在体内逆转多药耐药的可行性。这些观察结果确立了低浓度使用的一类调节剂与UIC2抗体的联合应用，作为一种在体内阻断Pgp功能的新颖、特异且有效的方法。
