Research Group of Professor Patrick Sexton, Monash Institute of Pharmaceutical Sciences

sexton main imagePatrick Sexton is Professor of Pharmacology, co-theme leader of Drug Discovery Biology and a National Health and Medical Research Principal Research Fellow within the Monash Institute of Pharmaceutical Sciences (MIPS) at Monash University, Australia. The Institute, a joint venture between the Faculty of Pharmacy and Pharmaceutical Sciences and the Faculty of Medicine, Nursing and Health Sciences, was established in 2008 and comprises the largest and most experienced group of pharmaceutical scientists in Australia.

MIPS provides vertical integration of pharmacological and pharmaceutical science research activities that enables drug investigation from discovery through to the final stages of pre-clinical development. Research at MIPS recently received the highest ranking from the ‘Excellence in Research for Australia (ERA) Initiative’, which assesses Australian Universities for research performance. The Institute concentrates its research on four major therapeutic areas: cancer, infectious diseases, CNS disorders and metabolic disease.

Patrick is a leading international researcher in the field of G protein-coupled receptors (GPCRs), particularly with respect to the allosteric modulation of receptors and the structure/function of class II (Family B) GPCRs and accessory proteins. He has published extensively on the characterization of receptors belonging to the calcitonin family of receptors. His research crosses industry and academic boundaries through the elucidation of fundamental biology and its intersection with drug-receptor interactions. Patrick has authored over 150 publications, making major contributions to the understanding of the distribution of receptors, the structural interface between peptide ligands and receptors, the modulation of receptors by accessory proteins, the detection and quantification of small molecule allosteric drug effects and ligand-biased signaling.

The Drug Discovery Biology Laboratory (DDBL), led by Patrick along with Professors Arthur Christopoulos and Roger Summers, focuses principally on G protein-coupled receptors (GPCRs), which comprise the largest family of cell surface receptor proteins and are the targets for > 30% of all currently used therapeutic drugs. Their work encompasses investigation across virtually all levels of GPCR structure/function, including understanding the modes of endogenous and exogenous ligand binding, signaling via G proteins and downstream messenger systems, interaction of receptors with regulatory accessory proteins, novel allosteric GPCR binding sites, and mathematical and molecular modeling of GPCR-ligand interactions.

A recent major paradigm shift in the understanding of drug action is the recognition of the capacity for ligand-induced signal bias that arises from the unique interactions and consequent receptor conformations that are engaged by individual drugs (Urban et al., 2007). Thus, many ligands classically considered receptor antagonists have been demonstrated to be agonists at alternate signalling pathways. Furthermore, allosteric drugs that act at sites distinct from the endogenous ligand may be particularly prone to altering the signal bias at receptors since the allosteric effect is driven by an alteration of the receptor conformation (Leach et al., 2007; Evans et al., 2010, 2011).

As a result of these findings, the DDBL has been exploring signal transduction across multiple pathways to gain insight into receptor function.  The laboratory routinely uses PerkinElmer AlphaScreen® assays (cAMP, pERK, pAkt, pGSK) to explore GPCR signaling. Figures 1 and 2 show how they have used AlphaScreen assays to monitor the intrinsic activity of small molecule modulators of the glucagon-like peptide 1 receptor and its effect on endogenous peptide signalling. These assays have allowed them to demonstrate differential efficacy and allosteric modulation across 3 different pathways (cAMP, pERK and Ca2+ mobilisation). This was further extended to demonstrate that the strength of the allosteric interaction varied for both the pathway under examination and the endogenous peptide that was assayed (Koole et al., 2010). The information obtained from such data is critical for the appropriate pre-clinical assessment of drug behaviour and for the selection of the most promising candidates to take forward.

An AlphaScreen cAMP assay to measure the interaction between oxyntomodulin and the small molecule allosteric modulator, Novo Nordisk compound 2, at the glucagon-like peptide 1 receptor. Compound 2 is a strong partial agonist of this pathway and also allosterically enhances the response to oxyntomodulin, resulting in a left shift in potency. Data adapted from Koole et al., 2010.EnlargeFigure 1: An AlphaScreen cAMP assay to measure the interaction between oxyntomodulin and the small molecule allosteric modulator, Novo Nordisk compound 2, at the glucagon-like peptide 1 receptor. Compound 2 is a strong partial agonist of this pathway and also allosterically enhances the response to oxyntomodulin, resulting in a left shift in potency. Data adapted from Koole et al., 2010.

An AlphaScreen® SureFire® pERK assay to measure the interaction between oxyntomodulin and the small molecule allosteric modulator, Novo Nordisk compound 2, at the glucagon-like peptide 1 receptor. Compound 2 is a weak partial agonist of this pathway and exhibits no allosteric modulation of the pERK response to oxyntomodulin. Data adapted from Koole et al., 2010.EnlargeFigure 2: An AlphaScreen® SureFire® pERK assay to measure the interaction between oxyntomodulin and the small molecule allosteric modulator, Novo Nordisk compound 2, at the glucagon-like peptide 1 receptor. Compound 2 is a weak partial agonist of this pathway and exhibits no allosteric modulation of the pERK response to oxyntomodulin. Data adapted from Koole et al., 2010.

The Drug Discovery Biology assays are routinely performed in 384 well plates and read in an EnVision® multilabel plate reader. The assays also have to be adapted to work with frozen cells and are readily adapted for automation. For higher throughput applications, the team use a cell::explorer™ robotic automation platform, which allows full automation of assays (Figure 3).

Figure 3: PerkinElmer cell::explorer platform operating under green light conditions for white light sensitive assays.EnlargeFigure 3: PerkinElmer cell::explorer platform operating under green light conditions for white light sensitive assays.

References

For more information on the Drug Discovery Biology Laboratory, please visit: http://www.pharm.monash.edu.au/research/mips/ddb/index.html