Targeting rab27a with covalent inhibitors for the treatment of metastatic breast cancer
Invasion and metastases remain to date the major causes of cancer mortality around the world. Rab27A is a small GTPase that regulates vesicles trafficking and is involved in many physiological processes, e.g. melanosome transport. Being a small GTPase, Rab27A acts as a molecular switch that cycles between an inactive state (GDP bound) and an active state (GTP bound), in which this protein is able to bind to specific effectors to trigger signalling cascades in cells. Current studies suggest a role for Rab27A in exosome-mediated pre-metastatic niche promotion. Hence, interfering with Rab27A PPIs could be effective in reducing and preventing the occurrence of metastasis in cancer. Small GTPases are renowned as challenging targets and have been long considered undruggable, but the unique presence of two non-conserved cysteines in Rab27A offers a perfect starting point for the development of selective covalent inhibitors. These residues are located in the proximity of a major interaction site with a known effector of Rab27A, Slp2, therefore encouraging for targeting PPIs. A screen of covalent fragments based on the recently developed quantitative Irreversible Tethering (qIT) assay has led to the discovery of novel hits with enhanced reactivity for Rab27A against glutathione. The current project aims to (i) obtain potent Rab27A covalent inhibitors by growing hit fragments, and (ii) demonstrate selective Rab27A target engagement in cells, and efficient disruption of the PPIs of Rab27A with its main effectors. Collaboration with the CRUK Beatson Institute will provide direct access to in vivo models to validate the contribution of Rab27A to metastatic development in cancer by use of such chemical probes, whilst state-of-the-art covalent fragment know-how will be accessed for compound optimisation at the Francis Crick Institute/GSK LinkLab, enabling prompt evaluation of the therapeutic potential of optimised lead compounds that will derive from my work.