Developing novel pharmacological tools to probe the function of inositol monophosphatase

The purpose of the present project is to take advantage of the new methodologies and biology to identify novel modulators that can be used as tool compounds to further explore the function of inositol monophosphatase (IMPase, a highly attractive but frustratingly chemically-intractable molecular target) and test the hypothesis that inositol depletion is responsible for the therapeutic effects of lithium.
IMPase is a key enzyme involved in the phosphatidyl inositol signalling pathway. It is the putative target for the therapeutic effects of lithium in bipolar disorder and is therefore an attractive target for new drugs that retain the therapeutic effects but are devoid of the toxicity of lithium. However, this target has historically proved intractable to traditional small molecule drug discovery efforts. Nevertheless, recent advances in structure-based, fragment and virtual screening (VS) approaches coupled to chemoinformatics and insights from methods such as conformational dynamics provide new opportunities to generate inhibitors of IMPase. A particular focus will be on modulation via protein-protein interactions to inhibit either dimerization of IMPase or the recently-described IMPase-calbindin interaction.
At the UoS, the focus will be on protein biochemistry (protein expression and purification), enzymology, biophysical assays, screening of fragments and virtual screening hits and X-ray crystallography. At Janssen, the major focus will be the selection of compounds using computational and molecular modelling techniques as well as cellular assays to examine functional effects. Importantly, all these methods are in place, either generically or specifically relating to IMPase and both the UoS and Janssen have a long-standing interest in this enzyme.

The work plan is as follows:

Year 1
(UoS) Expression, purification of IMPase. Development and characterisation of an IMPase assay. Baseline X-ray crystallographic analysis of IMPase.
(Janssen) Training and evaluation of different VS techniques and selection of the preferred methodology. Firstly, structure based VS of commercially-available compounds focussing on those with predicted high CNS penetration. Secondly, we know that existing chemical libraries are not enriched with chemical matter capable of binding at the IMPase active site. Therefore recent developments in de-novo design, coupled with multifactorial genetic algorithm optimisers are highly suited to this project. Finally, hits from previous fragment screens will be used to perform ligand based VS and identify analogues with improved binding possibilities.

Year 2
(Janssen) Establish cellular assays (e.g. muscarinic M1-CHO cells) and characterise effects of lithium and further VS.
(UoS) "Wet lab" screening in the biochemical assay of virtual screening "hit" compounds. Parallel screening of an in-house library of fragments.

Year 3
(UoS) Data analysis and clustering of confirmed hits and confirmation biophysical methods (e.g. isothermal titration calorimetry, thermal shift, microscale thermophoresis) and/or X-ray crystallography. Purchase and testing of structural analogues.
(Janssen) Generation of an early pharmacophore model. Evaluation of IMPase inhibitors in cellular assays.

Year 4
(UoS) Test novel molecules to designed to improve on hits already available and further analysis (these compounds with be provided by the TDDG core resource). Write up thesis.