The mixed lineage leukemia (MLL) is a histone methyltransferase that regulates the trimethylation of histone 3 lysine 4 (H3K4me3), a hallmark of transcriptionally active genes, in complex with other cofactors. Menin is an important cofactor that interacts with MLL and cooperatively regulates the methyltransferase activity of MLL complex. Through the recruitment of MLL to the promoter of p27, menin directly regulates the transcription of p27, a cyclin-dependent kinase inhibitor that is involved with cell cycle division. A recent study revealed that occupancy of menin at liver cancer-related gene promoters correlated with H3K4me3, and the knockout of menin or MLL significantly downregulated the expression of the liver cancer-driven genes. These evidences suggest that the menin-MLL complex plays an epigenetic role in promoting tumorigenesis of liver cancer through modification of H3K4, rendering menin-MLL as a potential therapeutic target. Meanwhile, the realm of natural products is an abundant source of aromatic compounds. Aromatic motifs could potentially form hydrophobic interaction with residues within the binding pocket of the menin-MLL protein-protein interface. Therefore, the coordination of aromatic motifs from natural products to transition metal complexes could potentially form effective inhibitors of the menin-MLL interaction. In this study, we identified 23 [Rho(Br-ppy)2(5,6-dmphen)](PF6) as a transition metalbased inhibitor of the menin-MLL interaction. Complex 23 carries a pyridine-like ligand (Br-ppy), and pyridine-containing compounds are found in a variety of herbal medicines, such as from Anabasis aphylla. 23 displayed promising in vitro activities in a fluorescence polarization (FP) assay with IC50 = 0.398 μM. Moreover, 23 was able to disrupt the cellular menin-MLL interaction as shown by bimolecular fluorescence complementation (BiFC) and co-immunoprecipitation (Co-IP) assays. 23 was also highly cytotoxic to hepatocellular carcinoma (HepG2) cells with an IC50 = 0.308 μM. Finally, 23 also dose-dependently downregulated the level of H3K4me3 and p27 with higher potency than MI-2, a previously reported menin-MLL inhibitor. Structureactivity relationship (SAR) studies also demonstrated that the inhibition activity of 23 is highly dependent on the presence of the rhodium(III) core. Complex 23 can, therefore, serve as useful scaffold for the future development of menin-MLL inhibitors.

MLL 是組蛋白-賴氨酸-甲基轉移酶，它通過和其他蛋白結合從而調控組蛋白 H3 賴氨酸 lysine 4 的三甲基化(H3K4me3)。H3K4me3 是轉錄活躍基因的標誌。 Menin 是其中一個重要的輔助蛋白，它通過與 MLL 結合從而參與調控 MLL 的甲 基化酶活動。P27 是一個細胞週期蛋白依賴酶抑制劑，它與細胞週期分裂有關。 研究發現，menin 通過募集 MLL 複合物到 p27 的啟動子，對 p27 的轉錄起到直 接調控作用。最近一項研究發現 menin 與肝癌相關基因啟動子的結合和 H3K4me3有重合，而且 menin和 MLL的基因敲除大大降低了肝癌相關基因的表 達。這些現象證明了 menin-MLL複合物通過調控 H3K4me3，在促進肝癌發生的 過程中扮演了改變表觀遺傳學的角色，因此使其成為治療肝癌的一個潛在靶點。 芳香化學物能和蛋白結合位點的殘基生成疏水鍵。天然產物裡面含有豐富的芳 香類化合物。芳香類化合物可與 menin-MLL 的蛋白質-蛋白質相互作用的的口 袋表面殘基生成疏水鍵。因此，從天然產物中挑選芳香類配體配合到金屬離子， 可生成潛在的 menin-MLL 抑制劑。 在本研究中，我們發現了第一個以銠為核心，並含有天然吡啶衍生物配體的 menin-MLL 抑制劑 23 [Rho(br-ppy)2(5,6-dmphen)](PF6)。吡啶類化合物在天然藥 用草藥中廣泛存在，例如無葉假木賊。23 在螢光偏振實驗中的半抑制濃度為 0.398 μM。在 BiFC 方法和 Co-IP 實驗中，23 有力地抑制抑制了 menin-MLL 的 結合。23 對肝癌細胞 HepG2 具有明顯細胞毒性，半數致死濃度為 0.308 μM。同 時，23 可劑量依賴性地降低 H3K4me3 和 p27 的水平，而且效果比已報導 meninMLL 抑制劑 MI-2 好。本研究還表明了 23 對於 menin-MLL 的抑制活性極大地依 賴銠核。因此，該研究展示了 23可作為未來發展 menin-MLL抑制劑的一個有用 的化學支架。