Fragment-based screening: A new paradigm for ligand and target discovery.

Significant advances in fragment-based screening, including the emergence of Fully Functionalised Fragments (FFFs) and innovations in Covalent Fragment screening are providing a new paradigm for ligand and target discovery. FFFs offer some key distinct advantages over other screening modalities such as small molecules and genetic screens, including 1) An ability to access diverse chemical space employing a relatively small compound set 2) Ease of screen optimisation given there is no requirement for genetic manipulation and 3) Built-in proteomics tools to facilitate rapid target deconvolution directly in cells. Covalent fragments enable exploration of novel druggable nodes through irreversible fragment-cysteine interactions, complementing their fully functionalized counterparts. Both FFFs and Covalent fragments present the phenotypic screening community with an additional and complementary approach for disease centric target identification.

Discovery of retinoic acid receptor agonists as proliferators of cardiac progenitor cells through a phenotypic screening approach.

Identification of small molecules with the potential to selectively proliferate cardiac progenitor cells (CPCs) will aid our understanding of the signaling pathways and mechanisms involved and could ultimately provide tools for regenerative therapies for the treatment of post-MI cardiac dysfunction. We have used an in vitro human induced pluripotent stem cell-derived CPC model to screen a 10,000-compound library containing molecules representing different target classes and compounds reported to modulate the phenotype of stem or primary cells. The primary readout of this phenotypic screen was proliferation as measured by nuclear count. We identified retinoic acid receptor (RAR) agonists as potent proliferators of CPCs. The CPCs retained their progenitor phenotype following proliferation and the identified RAR agonists did not proliferate human cardiac fibroblasts, the major cell type in the heart. In addition, the RAR agonists were able to proliferate an independent source of CPCs, HuES6. The RAR agonists had a time-of-differentiation-dependent effect on the HuES6-derived CPCs. At 4 days of differentiation, treatment with retinoic acid induced differentiation of the CPCs to atrial cells. However, after 5 days of differentiation treatment with RAR agonists led to an inhibition of terminal differentiation to cardiomyocytes and enhanced the proliferation of the cells. RAR agonists, at least transiently, enhance the proliferation of human CPCs, at the expense of terminal cardiac differentiation. How this mechanism translates in vivo to activate endogenous CPCs and whether enhancing proliferation of these rare progenitor cells is sufficient to enhance cardiac repair remains to be investigated.

HEROIC: a 5-year observational cohort study aimed at identifying novel factors that drive diabetic kidney disease: rationale and study protocol.

INTRODUCTION: Diabetic kidney disease (DKD) is the leading cause of end-stage kidney disease worldwide and a major cause of premature mortality in diabetes mellitus (DM). While improvements in care have reduced the incidence of kidney disease among those with DM, the increasing prevalence of DM means that the number of patients worldwide with DKD is increasing. Improved understanding of the biology of DKD and identification of novel therapeutic targets may lead to new treatments. A major challenge to progress has been the heterogeneity of the DKD phenotype and renal progression. To investigate the heterogeneity of DKD we have set up The East and North London Diabetes Cohort (HEROIC) Study, a secondary care-based, multiethnic observational study of patients with biopsy-proven DKD. Our primary objective is to identify histological features of DKD associated with kidney endpoints in a cohort of patients diagnosed with type 1 and type 2 DM, proteinuria and kidney impairment. METHODS AND ANALYSIS: HEROIC is a longitudinal observational study that aims to recruit 500 patients with DKD at high-risk of renal and cardiovascular events. Demographic, clinical and laboratory data will be collected and assessed annually for 5 years. Renal biopsy tissue will be collected and archived at recruitment. Blood and urine samples will be collected at baseline and during annual follow-up visits. Measured glomerular filtration rate (GFR), echocardiography, retinal optical coherence tomography angiography and kidney and cardiac MRI will be performed at baseline and twice more during follow-up. The study is 90% powered to detect an association between key histological and imaging parameters and a composite of death, renal replacement therapy or a 30% decline in estimated GFR. ETHICS AND DISSEMINATION: Ethical approval has been obtained from the Bloomsbury Research Ethics Committee (REC 18-LO-1921). Any patient identifiable data will be stored on a password-protected National Health Services N3 network with full audit trail. Anonymised imaging data will be stored in a ISO27001-certificated data warehouse.Results will be reported through peer-reviewed manuscripts and conferences and disseminated to participants, patients and the public using web-based and social media engagement tools as well as through public events.

High throughput generation of a resource of the human secretome in mammalian cells.

The proteins secreted by human tissues and blood cells, the secretome, are important both for the basic understanding of human biology and for identification of potential targets for future diagnosis and therapy. Here, a high-throughput mammalian cell factory is presented that was established to create a resource of recombinant full-length proteins covering the majority of those annotated as 'secreted' in humans. The full-length DNA sequences of each of the predicted secreted proteins were generated by gene synthesis, the constructs were transfected into Chinese hamster ovary (CHO) cells and the recombinant proteins were produced, purified and analyzed. Almost 1,300 proteins were successfully generated and proteins predicted to be secreted into the blood were produced with a success rate of 65%, while the success rates for the other categories of secreted proteins were somewhat lower giving an overall one-pass success rate of ca. 58%. The proteins were used to generate targeted proteomics assays and several of the proteins were shown to be active in a phenotypic assay involving pancreatic ß-cell dedifferentiation. Many of the proteins that failed during production in CHO cells could be rescued in human embryonic kidney (HEK 293) cells suggesting that a cell factory of human origin can be an attractive alternative for production in mammalian cells. In conclusion, a high-throughput protein production and purification system has been successfully established to create a unique resource of the human secretome.

Techniques to Enable 1536-Well Phenotypic Screening.

Adaptation of phenotypic cell assays to 1536-well format brings major challenges in liquid handling for high-content assays requiring washing steps and coating of plates. In addition, problematic edge effects and reduced assay quality are frequently encountered. In this chapter, we describe the novel application of a centrifugal plate washer to facilitate miniaturization of 1536-well cell assays and a combination of techniques to reduce edge effects, all of which improved throughput and data quality. Cell assays currently limited in throughput because of cost and complex protocols may be enabled by the techniques presented in this chapter.

Enabling 1536-Well High-Throughput Cell-Based Screening through the Application of Novel Centrifugal Plate Washing.

Cell-based assays have long been important within hit discovery paradigms; however, improving the disease relevance of the assay system can positively affect the translation of small-molecule drug discovery, especially if adopted in the initial hit identification assay. Consequently, there is an increasing need for disease-relevant assay systems capable of running at large scale, including the use of induced pluripotent stem cells and donor-derived primary cells. Major hurdles to adopting these assays for high-throughput screening are the cost, availability of cells, and complex protocols. Miniaturization of such assays to 1536-well format is an approach that can reduce costs and increase throughput. Adaptation of these complex cell assays to 1536-well format brings major challenges in liquid handling for high-content assays requiring washing steps and coating of plates. In addition, problematic edge effects and reduced assay quality are frequently encountered. In this study, we describe the novel application of a centrifugal plate washer to facilitate miniaturization of a range of 1536-well cell assays and techniques to reduce edge effects, all of which improved throughput and data quality. Cell assays currently limited in throughput because of cost and complex protocols may be enabled by the techniques presented in this study.

Examining Ligand-Based Stabilization of Proteins in Cells with MEK1 Kinase Inhibitors.

In this study, we describe the evaluation of a cell-based protein stability assay using ß-galactosidase fragment complementation technology performed in two independent laboratories. The assay is based on the ability of certain ligands to bind to a protein leading to a ligand-protein complex that has a different stability than the free protein. The assay employed a prolabeled-tagged MEK1 kinase stably expressed in A549 cells and this was used to evaluate focused sets of compounds containing known MEK1inhibitors as well as a random set of compounds. An assay using a prolabeled-tagged lysine methyltransferase known as G9a expressed in A549 cells was used as a counterscreen. In one study, it was found that the majority of MEK1 inhibitors were either found as inactive (52%) or showed a selective inhibitory response (18%) in the cell-based MEK1 assay; however, eight compounds showed a specific activation response consistent with stabilization of MEK1 in cells. Examination of these stabilizing compounds showed that three of these were analogs of hypothemycin, a known covalent allosteric MEK1 inhibitor, while the remaining compounds covered one structural class. Both laboratories were able to confirm activity in the cell-based MEK1 assay for known MEK1 inhibitors and found that this activity was highly selective over the G9a counterscreen assay. Screening of a mechanism of action library containing compounds with bioactivity annotations against the cell-based MEK1 assay did not reveal any mechanisms leading to an increase in signal other than inhibitors of MEK1. This study supports that the MEK1 cellular protein stability assay is sensitive to certain MEK1 inhibitors, often noncompetitive inhibitors with respect to ATP. The cellular stability assay format could be useful to rapidly filter kinase inhibitor hit lists for allosteric kinase inhibitors and support target engagement in cells.