Pan Xing Q, Zheng Xuan, Shi Guangfeng, Wang Huaqing, Ratnam Manohar, Lee Robert J
Division of Pharmaceutics, The Ohio State University, Columbus, Ohio 43210, USA.
Blood. 2002 Jul 15;100(2):594-602. doi: 10.1182/blood.v100.2.594.
Up-regulation of folate receptor (FR) type-beta in acute myelogenous leukemia (AML) by all-trans retinoic acid (ATRA) and its restricted normal tissue distribution makes it a potential target for therapeutic intervention. The FR-beta in peripheral blood granulocytes was unable to bind folate and appeared to have a variant GPI membrane anchor, evident from its insensitivity to phosphatidylinositol-specific phospholipase C but not nitrous acid. Granulocyte FR-beta lacked mutations, and neither deglycosylation nor detergent solubilization restored folate binding. The posttranslational modification causing its nonfunctionality was evidently absent in FR-beta from AML cells from patient marrow, which bound folate. From flow cytometric analysis of 78 AML bone marrow specimens of different subtypes, 68% expressed FR-beta, most of which were also CD34+. In model cell lines that are FR - (KG-1a, L1210, and Chinese hamster ovary [CHO]) or FR + (KG-1, L1210 JF, and recombinant CHO-FR-beta), selective FR-mediated binding and cytotoxicity was obtained using folate-coated liposomes encapsulating fluorescent calcein (f-L-calcein) and doxorubicin (f-L-DOX), respectively, which could be blocked by 1 mM free folic acid. In the FR-beta-expressing KG-1 human AML cells, treatment with ATRA further increased this specificity. In mouse ascites leukemia models generated using L1210JF or KG-1 cells, increased median survival times were obtained with f-L-DOX treatment compared to nontargeted L-DOX. In the KG-1 model, ATRA treatment increased the cure rate with f-L-DOX from 10% to 60%. The above combined data from our 2 laboratories further support the feasibility and potential usefulness of selective ATRA-facilitated liposomal drug delivery in FR-beta + AMLs.
全反式维甲酸（ATRA）可上调急性髓性白血病（AML）中β型叶酸受体（FR），且其在正常组织中的分布受限，这使其成为治疗干预的潜在靶点。外周血粒细胞中的FR-β无法结合叶酸，似乎具有变异的糖基磷脂酰肌醇（GPI）膜锚定，这从其对磷脂酰肌醇特异性磷脂酶C不敏感但对亚硝酸敏感可以明显看出。粒细胞FR-β没有突变，去糖基化和去污剂溶解均不能恢复叶酸结合。导致其无功能的翻译后修饰在来自患者骨髓的AML细胞的FR-β中显然不存在，后者能够结合叶酸。通过对78例不同亚型的AML骨髓标本进行流式细胞术分析，68%表达FR-β，其中大多数也为CD34+。在FR - （KG-1a、L1210和中国仓鼠卵巢细胞[CHO]）或FR + （KG-1、L1210 JF和重组CHO-FR-β）的模型细胞系中，分别使用包裹荧光素钙黄绿素（f-L-钙黄绿素）和阿霉素（f-L-DOX）的叶酸包被脂质体获得了选择性FR介导的结合和细胞毒性，这可被1 mM游离叶酸阻断。在表达FR-β的KG-1人AML细胞中，用ATRA处理进一步提高了这种特异性。在使用L1210JF或KG-1细胞生成的小鼠腹水白血病模型中，与非靶向的L-DOX相比，f-L-DOX处理可延长中位生存时间。在KG-1模型中，ATRA处理使f-L-DOX的治愈率从10%提高到60%。我们两个实验室的上述综合数据进一步支持了在FR-β + AML中选择性ATRA促进脂质体药物递送的可行性和潜在实用性。
