Department of Medical Oncology, The First Affiliated Hospital, College of Medicine, Xi'An Jiaotong University, Xi'An, China.
Prostate. 2011 Jun 1;71(8):835-45. doi: 10.1002/pros.21300. Epub 2010 Oct 28.
Glycogen synthase kinase 3 (GSK-3) has been regarded as a potential therapeutic target for multiple human cancers. We previously reported that suppression of GSK-3 activity with lithium chloride (LiCl) or small chemical inhibitors impaired cellular DNA synthesis and reduced cell proliferation in prostate cancer cells. Therefore, in this study, we extended this in vitro findings to in vivo settings in order to establish a proof of concept that inhibition of GSK-3 activity is feasible in suppressing tumor growth of prostate cancer in vivo.
In this study, we used three GSK-3 inhibitors, LiCl, TDZD-8, and L803-mts, which are structurally unrelated and non-ATP competitive. Human prostate cancer cell lines PC-3 and C4-2 were used for nude mouse xenograft models. The autochthonous transgenic prostate cancer TRAMP mice were used for testing GSK-3 inhibitor's effect on tumor development. Anti-Ki-67 and BrdU immunohistochemistry was used to determine cell proliferation. The pE2F-TA-LUC (E2F-LUC) luciferase reporter assay and gene specific small interferencing RNA technique were used to examine C/EBP involvement in GSK-3 inhibitor-induced E2F-1 suppression.
Using mouse xenograft models, we demonstrated that LiCl and TDZD-8 significantly suppressed tumor development and growth of subcutaneous xenografts derived from human prostate cancer cells. Similarly, in the TRAMP mice, TDZD-8 and L803-mts reduced the incidence and tumor burden in the prostate lobes. Consistent with our previous in vitro findings, GSK-3 inhibitors significantly reduced BrdU incorporation and Ki67-positive cells in xenograft tumors and mouse cancerous prostates compared to the control. Further analysis revealed that following GSK-3 inhibition, C/EBPα, a negative cell cycle regulator, was remarkably accumulated in xenograft tumors or in cultured prostate cancer cells. Meanwhile, knocking down C/EBPα expression abolished GSK-3 inhibition-induced suppression of E2F1 transactivation, suggesting that C/EBPα accumulation is involved in GSK-3 inhibition-induced anti-tumor effect.
Taken together, these results suggest that GSK-3 inhibition has the potential as a therapeutic strategy for prostate cancer intervention, although further pre-clinical and clinical testing are desirable.
糖原合成酶激酶 3（GSK-3）已被认为是多种人类癌症的潜在治疗靶点。我们之前的研究表明，氯化锂（LiCl）或小分子化学抑制剂抑制 GSK-3 活性会损害前列腺癌细胞的细胞 DNA 合成并减少细胞增殖。因此，在这项研究中，我们将体外研究结果扩展到体内环境，以建立抑制 GSK-3 活性在体内抑制前列腺癌肿瘤生长的概念验证。
在这项研究中，我们使用了三种 GSK-3 抑制剂，LiCl、TDZD-8 和 L803-mts，它们结构不同且不与 ATP 竞争。用人前列腺癌细胞系 PC-3 和 C4-2 建立裸鼠异种移植模型。使用同源转基因前列腺癌 TRAMP 小鼠来测试 GSK-3 抑制剂对肿瘤发展的影响。使用抗 Ki-67 和 BrdU 免疫组化来确定细胞增殖。使用 pE2F-TA-LUC（E2F-LUC）荧光素酶报告基因检测和基因特异性小干扰 RNA 技术来研究 C/EBP 参与 GSK-3 抑制剂诱导的 E2F-1 抑制。
使用小鼠异种移植模型，我们证明 LiCl 和 TDZD-8 显著抑制了源自人前列腺癌细胞的皮下异种移植物的肿瘤发生和生长。同样，在 TRAMP 小鼠中，TDZD-8 和 L803-mts 降低了前列腺叶中的发病率和肿瘤负担。与我们之前的体外研究结果一致，GSK-3 抑制剂显著减少了异种移植肿瘤和小鼠癌变前列腺中的 BrdU 掺入和 Ki67 阳性细胞。进一步的分析表明，在 GSK-3 抑制后，C/EBPα，一种负细胞周期调节剂，在异种移植肿瘤或培养的前列腺癌细胞中明显积累。同时，敲低 C/EBPα 表达消除了 GSK-3 抑制诱导的 E2F1 反式激活抑制，表明 C/EBPα 积累参与了 GSK-3 抑制诱导的抗肿瘤作用。
总之，这些结果表明 GSK-3 抑制具有作为前列腺癌干预治疗策略的潜力，尽管需要进一步的临床前和临床测试。
