Abstract 4210: Screening of kinase focused libraries for the identification of Greatwall inhibitors
Authors: Reuillon Tristan D. , Walker Sarah , Grand Darren Le , Ward Simon E. , Wahab Ben , Rajasekaran Mohan B. , Hochegger Helfrid , Oliver Antony W. 
Published: July 2017

MASTL (microtubule-associated serine/threonine kinase-like), commonly known as Greatwall (GWL), is a member of the AGC kinase family and has recently emerged as a novel cancer therapy target. GWL regulates mitotic division via phosphorylation of its known substrates ENSA and ARPP19, which upon phosphorylation act as inhibitors of the PP2A-B55δ phosphatase. Inactivation of PP2A-B55δ induces sustained activity of the CDK1-cyclin B complex, triggering mitotic entry and preventing mitotic collapse during cell division. Towards the end of mitosis, GWL inactivation is required to initiate mitotic exit. Overexpression of GWL in breast cancer cells drives oncogenic properties, such as transformation and invasions. In particular, triple negative breast cancer tumors, which are associated with a poor prognosis, overexpress GWL and are highly sensitive to GWL depletion. In addition, GWL expression has been found to be elevated in oral squamous cell carcinoma and prostate cancer tissues. A number of studies have also indicated that GWL may contribute directly to tumorigenesis, suggesting that modulation of GWL activity with small-molecule inhibitors could afford a potential new anti-cancer therapy. The precise role of GWL in cells remaining largely unexplored, the identification of a pharmacological tool would be useful to further assess the tumor-associated functions of this protein. To that end, we have recently developed and optimized a robust HTRF assay, based on a specific ENSA peptide analogue, and used it to screen kinase focused libraries, made available to us by GlaxoSmithKline and Roche. A 10.2% hit rate was achieved from the screening of the 11,000 compound set at a single concentration of 10 µM. Molecules inducing over 50% inhibition in the single point screen were subsequently tested in concentration-dependent experiments. Analysis of the IC50 generated enabled to identify molecular clusters and potential hits to initiate a medicinal chemistry campaign. A review of the literature on the selectivity of the hits identified indicated that a significant number of these molecules also had affinity for other AGC kinases and that selectivity among the AGC kinase family could be challenging to achieve. Computational studies using an in-house co-crystal structure of GWL in complex with Staurosporine and the published crystal structures of other AGC kinases will be used to design out selectivity and guide the design of inhibitors to obtain a potent chemical probe.

Citation Format: Tristan D. Reuillon, Sarah Walker, Darren Le Grand, Simon E. Ward, Ben Wahab, Mohan B. Rajasekaran, Helfrid Hochegger, Antony W. Oliver. Screening of kinase focused libraries for the identification of Greatwall inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4210. doi:10.1158/1538-7445.AM2017-4210