Abstract SY14-02: Regulation of kinase signaling complexes with small molecule inhibitors
Authors: Dar Arvin 
Published: August 2015

Abstract
Kinases catalyse the phosphorylation of target substrates on hydroxyl-containing residues as a means to nucleate multi-component complexes or to stabilize unique conformational states. Pseudokinases constitute a subclass of these enzymes that were originally predicted as inactive based on mutations of key conserved active site residues. Like the active kinases, pseudokinases appear to play important functional roles in signal transduction pathways and several pseudokinases have been shown to be important mediators of diseases, including cancer and diabetes.
Many pseudokinases share homology inside and outside of the kinase domain with catalytically active kinases. Examples include KSR1 and KSR2, the pseudokinase relatives within the RAF-family of kinases. And Her3, the pseudokinase member of the EGFR family. In both examples, the pseudokinase has been demonstrated to allosterically stimulate the activity of their active ancestral partners through the formation of higher-order complexes. The ability to allosterically modulate active signaling kinases appears to be a dedicated feature of several pseudokinases that overlaps or appears redundant with the ability of active kinases to modulate themselves. For example, KSR forms a high affinity dimer with RAF related kinases and this drives RAF catalytic activation. However, RAF may dimerize with itself to drive its own activation. Clinical inhibitors that bind to RAF are thought to exploit the ability of RAF to regulate itself, leading to activation, rather than inhibition, of RAF when dimeric. Similarly, Her3 dimerizes with EGFR through the formation of an asymmetric dimer, but EGFR appears able to form this dimer in the absence of Her3 as well. In this case, the clinical kinase inhibitor bosutinib, has been shown to function as an agonist through direct modulation of Her3-EGFR complexes.
Because pseudokinase function can be redundant with the scaffolding abilities of active kinases, it has been difficult to dissect their precise roles in biology using conventional genetic or biochemical techniques. Small molecules that could antagonize pseudokinase dependent activities would be valuable tools that could be used to functionally annotate the biology and therefore pharmacology of this class of proteins. In particular, direct small molecule antagonists would allow one to disable pseudokinase structure and function on very short timescales and could also provide new leads for therapeutic development. I will describe my laboratories work on developing small molecule modulators of KSR. In particular, I will describe biochemical and cell based approaches used to identify KSR antagonists and furthermore X-ray crystallographic analysis of a lead compound bound to a KSR associated complex.
Citation Format: Arvin Dar. Regulation of kinase signaling complexes with small molecule inhibitors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr SY14-02. doi:10.1158/1538-7445.AM2015-SY14-02