以小分子探针研究靶向PI3K亚型抑制前列腺癌转移的作用和多重分子机理

PI3K (phosphatidylinositol 3-kinase), which consists of 4 isoforms with respective functions, is known to play important roles in cell growth, etc. Advanced prostate cancer is currently not yet curable due to a high rate of metastasis. Favorable antitumor efficacy of targeting PI3K in various solid tumors has been well reported while the anti-metastatic effect remains unknown yet. Our previous study indicated that a pan-PI3K inhibitor which targets all the 4 isoforms of PI3K had potential anti-metastatic effect on prostate cancer via blocking migratin of prostate cancer cells, and inhibiting tumor angiogenesis. Interestingly, our rencent study showed that inhibition against PI3K beta isoform decreased metastatic ability of prostate cancer cells, far more than that againt other 3 respective isoforms did. Therefore, we predict that PI3K beta might play a predominant role in the metastasis of prostate cancer, and targeting PI3K beta might inhibit prostate cancer metastasis via two mechanisms: inhibition of cancer cell migration, adhesion and invasion by downregulating p-Girdin, p-integrin and MMPs, all of which are located downstream of PI3K; and inhibition of tumor angiogenesis via blocking secretion of VEGF by cancer cells. To demonstrate our prediction, we will investigate the anti-metastatic effects of targeting PI3K isofoms on various models in vitro and in vivo with small-molecule probes, by using multiple approaches such as Western blot and ELISA. Our study is expected to demonstrate that PI3K beta is an important molecular target for prostate cancer metastasis, providing a new strategy for the therapy of prostate cancer.

PI3K是一个与细胞生长等密切相关的脂激酶家族，包括4种亚型，其功能有所不同。前列腺癌易转移，尚无有效药物。靶向PI3K为癌症治疗的研究热点，但关于抗前列腺癌转移未见报道。我们的前期工作证明了同时抑制PI3K 4种亚型具有抗前列腺癌转移作用。本课题预实验又显示与其它亚型相比，靶向PI3K beta 亚型具有更显著的抑制前列腺癌细胞的迁移等作用。为此我们假设beta亚型可能在前列腺癌转移中占主导地位，靶向PI3K beta亚型可能通过抑制癌细胞的迁移侵袭和抗血管生成两种机理而产生抗前列腺癌转移作用。为验证此假设，我们通过建立体内外各种前列腺癌转移模型，利用特异性靶向各种PI3K亚型的小分子探针,采用免疫印迹及ELISA等手段从抗癌细胞迁移和抗血管生成两方面系统研究靶向PI3K亚型抗前列腺癌转移的作用和机理。本研究将证明PI3K beta亚型为前列腺癌转移的重要靶点，为前列腺癌治疗提供新的思路。

前列腺癌在我国发病率逐年上升，严重危害国民健康。由于被诊断时常已发生转移，抑制前列腺癌转移成为治疗的关键。本课题研究靶向抑制PI3K亚型对前列腺癌转移的作用及其分子机理，以分别靶向PI3Kα、β、δ和γ亚型的特异性抑制剂BYL719、TGX221、IC87114以及AS252424为小分子探针，利用Transwell小室迁移实验研究靶向抑制PI3K各亚型对PC3和DU145细胞迁移的影响，分别计算其IC50(以DU145为例，BYL719：8.27 µM, TGX221：0.05 µM，IC87114：3.52 µM，AS252424：29.98 µM)，并与酶水平抑制活性的IC50值(BYL719：0.0046 µM, TGX221：0.005 µM, IC87114：0.5 µM, AS252424: 0.033 µM)进行比较，发现PI3Kβ及δ亚型抑制剂的相对迁移抑制活性较强、PI3Kα及γ亚型抑制剂的相对迁移抑制活性较弱；利用Transwell小室侵袭实验得到了类似的结果，提示PI3Kβ及δ亚型在前列腺癌细胞转移中起关键作用，而PI3Kα及γ亚型亚型对前列腺癌细胞转移似乎不重要。PI3Kβ及δ亚型抑制剂可显著降低PC3和DU145细胞Akt及下游蛋白Integrinβ1的磷酸化水平，这可能与其抗转移作用有关。利用siRNA技术分别对PC3和DU145细胞中PI3Kβ及δ亚型降表达后两种细胞的迁移能力显著降低，进一步证明了两种亚型对前列腺癌细胞的迁移是必须的；利用前列腺癌骨转移模型结合microCT检测技术研究PI3Kβ抑制剂GSK2636771及δ亚型抑制剂CAL101对体内前列腺癌转移的影响，发现与对照组相比两给药组动物骨小梁厚度、骨小梁数量、骨体积分数以及骨密度均有不同程度增加，而骨小梁分离度显著下降，提示给药两种抑制剂靶向PI3Kβ或δ亚型后抑制了骨转移导致的骨质疏松；同时HE染色结果表明给药组发生浸润和转移的癌细胞数量显著降低、TRAP染色表明给药组破骨细胞数目显著减少，这些结果均提示靶向PI3Kβ及δ亚型具有显著的体内抗前列腺癌效果。因此本课题阐明了在前列腺癌转移中起关键作用的PI3K亚型为β和δ亚型，证明了靶向此两种亚型的抗前列腺癌转移效果，为前列腺癌治疗提供了新的思路。