Hanawa Shinsuke, Mitsuhashi Akira, Shozu Makio
Department of Reproductive Medicine, Graduate School of Medicine, Chiba University, Chiba, Japan.
PLoS One. 2018 Feb 14;13(2):e0192759. doi: 10.1371/journal.pone.0192759. eCollection 2018.
Metformin, an antidiabetic drug, inhibits the endometrial cancer cell growth in vivo by improving the insulin resistance; however, its mechanism of action is not completely understood. Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase associated with insulin resistance and type 2 diabetes, and its inhibition restores the insulin resistance. This study investigated the antitumor effect of metformin on endometrial cancer with a focus on PP2A.
Metformin (1,500-2,250 mg/day) was preoperatively administered to patients with endometrial cancer for 4 to 6 weeks. Expression of the PP2A regulatory subunits, 4 (PPP2R4) and B (PP2A-B), was evaluated using real-time polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC) using paired specimens obtained before and after metformin treatment. The effect of PPP2R4 inhibition with small interfering RNA was evaluated in the endometrial cancer cell lines HEC265 and HEC1B. P values of < .05 were considered statistically significant.
Preoperative metformin treatment significantly reduced the expression of PP2A-B, as determined using IHC, and the mRNA expression of PPP2R4, as determined using RT-PCR, in the patients with endometrial cancer. However, metformin could not directly alter the PPP2R4 mRNA levels in the endometrial cancer cell lines in vitro. PPP2R4 knockdown reduced the proliferation and induced the apoptosis by activating caspases 3/7 in HEC265 and HEC1B cells.
Downregulation of the PP2A-B subunit, including PPP2R4, is an important indirect target of metformin. Inhibition of PP2A may be an option for the treatment of endometrial cancer patients with insulin resistance.
This trial is registered with UMIN-CTR (number UMIN000004852).
二甲双胍作为一种抗糖尿病药物，可通过改善胰岛素抵抗来抑制体内子宫内膜癌细胞的生长；然而，其作用机制尚未完全明确。蛋白磷酸酶2A（PP2A）是一种与胰岛素抵抗及2型糖尿病相关的丝氨酸/苏氨酸磷酸酶，抑制该酶可恢复胰岛素抵抗。本研究聚焦于PP2A，探讨二甲双胍对子宫内膜癌的抗肿瘤作用。
对子宫内膜癌患者术前给予二甲双胍（1500 - 2250毫克/天）治疗4至6周。使用实时聚合酶链反应（RT-PCR）和免疫组织化学（IHC），通过二甲双胍治疗前后获取的配对标本，评估PP2A调节亚基4（PPP2R4）和B（PP2A-B）的表达。在子宫内膜癌细胞系HEC265和HEC1B中评估小干扰RNA抑制PPP2R4的效果。P值小于0.05被认为具有统计学意义。
免疫组织化学检测显示，术前二甲双胍治疗显著降低了子宫内膜癌患者中PP2A-B的表达；实时聚合酶链反应检测表明，PPP2R4的mRNA表达也显著降低。然而，二甲双胍在体外不能直接改变子宫内膜癌细胞系中PPP2R4的mRNA水平。在HEC265和HEC1B细胞中，PPP2R4基因敲低通过激活半胱天冬酶3/7降低了细胞增殖并诱导了细胞凋亡。
包括PPP2R4在内的PP2A-B亚基下调是二甲双胍的重要间接靶点。抑制PP2A可能是治疗伴有胰岛素抵抗的子宫内膜癌患者的一种选择。
本试验已在日本大学医学情报网络临床试验注册中心（UMIN-CTR）注册（编号UMIN000004852）。
