妊娠滋养细胞肿瘤（GTN）是由胎盘绒毛组织发展而来的恶性肿瘤，我国发病率较高。GTN首选化疗，甲氨蝶呤（MTX）是指南推荐的一线药物，但临床不良反应多、耐药率高，增加GTN对MTX的敏感性是治疗的关键。有机阴离子转运体4（OAT4）在滋养细胞中特异性高表达，且MTX是OAT4的高亲和力底物，提示OAT4对MTX在靶细胞富集至关重要。而我们预实验发现GTN组织中OAT4表达显著低于癌旁组织和正常绒毛，且基因启动子区DNA高甲基化，DNA甲基转移酶抑制剂地西他滨显著上调GTN细胞的OAT4表达，推测GTN中OAT4表达抑制致MTX摄取不足，进而使MTX低敏并产生耐药。本项目拟阐明GTN中OAT4表达抑制的分子机理，并采用多种体内外模型探究DNA去甲基化药物能否逆转OAT4表达，增加MTX靶细胞富集，从而增敏MTX抗GTN。本研究将有助于深入理解MTX耐药机制，有望为GTN的临床治疗提供新思路。

Gestational trophoblastic neoplasia (GTN) comprises a spectrum of malignant pregnancy-related tumors, which is result from over-proliferation of trophoblasts. GTN arises more frequently in Asia including China than in North America or Europe. The main treatment for GTN is chemotherapy, and methotrexate (MTX) is the first-line drug recommended by the guidelines. However, chemotherapy resistance readily occurs and leads to treatment failure. Organic anion transporter 4 (OAT4) is specifically and highly expressed in trophoblasts, and MTX is a substrate of OAT4 with high affinity. Therefore, OAT4 plays an important role in MTX uptake in trophoblasts. Our previous study found that the expression levels of OAT4 in GTN tissues were significantly lower than that in adjacent tissues and normal chorionic villus, but the overall methylation percentage in the sequenced region were higher. In addition, decitabine (an inhibitor of DNA methyltransferase 1) significantly up-regulated the mRNA and protein levels of OAT4 in BeWo and JEG-3 cells. We speculated that the down-regulation of OAT4 in GTN resulted in insufficient MTX accumulation, thereby leading to low sensitivity and high resistance of MTX. We will investigate the molecular mechanism of OAT4 repression in GTN, and explore whether DNA demethylating agents can reverse the expression of OAT4, and increase the MTX accumulation in target cells, and obtaine synergistic anticancer effect. This study will help us understand the mechanism of MTX resistance and provide new strategies for the clinical treatment of GTN.