Identification of the Privileged Position in the Imidazo[1,2‑<i>a</i>]pyridine Ring of Phosphonocarboxylates for Development of Rab Geranylgeranyl Transferase (RGGT) Inhibitors

Members of the Rab GTPase family are master regulators of vesicle trafficking. When disregulated, they are associated with a number of pathological states. The inhibition of RGGT, an enzyme responsible for post-translational geranylgeranylation of Rab GTPases represents one way to control the activity of these proteins. Because the number of molecules modulating RGGT is limited, we combined molecular modeling with biological assays to ascertain how modifications of phosphonocarboxylates, the first reported RGGT inhibitors, rationally improve understanding of their structure–activity relationship. We have identified the privileged position in the core scaffold of the imidazo­[1,2-a]­pyridine ring, which can be modified without compromising compounds’ potency. Thus modified compounds are micromolar inhibitors of Rab11A prenylation, simultaneously being inactive against Rap1A/Rap1B modification, with the ability to inhibit proliferation of the HeLa cancer cell line. These findings were rationalized by molecular docking, which recognized interaction of phosphonic and carboxylic groups as decisive in phosphonocarboxylate localization in the RGGT binding site.Rab GTP酶家族（Rab GTPase family）成员是囊泡运输的核心调控因子。当其功能失调时，会与多种病理状态密切相关。抑制负责Rab GTP酶翻译后香叶酰香叶酰化修饰的Rab香叶酰基转移酶（Rab geranylgeranyltransferase, RGGT），是调控这类蛋白活性的可行策略之一。由于目前可用于调控RGGT的分子数量有限，我们将分子建模与生物学实验相结合，以阐明首批报道的RGGT抑制剂——膦酰羧酸类化合物（phosphonocarboxylates）的结构改造如何合理优化其构效关系。我们已确定咪唑并[1,2-a]吡啶环在核心骨架中的优势修饰位点，该位点可进行改造且不会降低化合物的活性效力。经改造后的化合物对Rab11A的异戊二烯化修饰表现出微摩尔级抑制活性，同时对Rap1A/Rap1B的修饰无影响，且能够抑制海拉（HeLa）癌细胞系的增殖。上述发现可通过分子对接分析得到合理解释：该分析确认，膦酰基与羧基的相互作用是膦酰羧酸类化合物在RGGT结合位点中精准定位的决定性因素。