High-throughput screening for small molecule modulators of motor protein Kinesin

A High-Throughput Cellular Screening Assay for Small-Molecule Inhibitors and Activators of Cytoplasmic Dynein-1-Based Cargo Transport

Cytoplasmic dynein-1 (hereafter dynein) is a six-subunit motor complex that transports a variety of cellular components and pathogens along microtubules. Dynein's cellular functions are only partially understood, and potent and specific small-molecule inhibitors and activators of this motor would be valuable for addressing this issue. It has also been hypothesized that an inhibitor of dynein-based transport could be used in antiviral or antimitotic therapy, whereas an activator could alleviate age-related neurodegenerative diseases by enhancing microtubule-based transport in axons. Here, we present the first high-throughput screening (HTS) assay capable of identifying both activators and inhibitors of dynein-based transport. This project is also the first collaborative screening report from the Medical Research Council and AstraZeneca agreement to form the UK Centre for Lead Discovery. A cellular imaging assay was used, involving chemically controlled recruitment of activated dynein complexes to peroxisomes. Such a system has the potential to identify molecules that affect multiple aspects of dynein biology in vivo. Following optimization of key parameters, the assay was developed in a 384-well format with semiautomated liquid handling and image acquisition. Testing of more than 500,000 compounds identified both inhibitors and activators of dynein-based transport in multiple chemical series. Additional analysis indicated that many of the identified compounds do not affect the integrity of the microtubule cytoskeleton and are therefore candidates to directly target the transport machinery.

Does altering proteasomal activity and trafficking reduce the arborization mediated specific vulnerability of SNpc dopaminergic neurons of Parkinson's disease?

Parkinson's disease (PD) is a late-onset degenerative neuronal disorder and stands second among the neurological disorders with 1% of the total world population being affected. The disease originates majorly due to compromised function of the dopaminergic (DA) neurons in the Substantia Nigra pars compacta (SNpc), but not the ventral tegmental area (VTA) region of the midbrain. The differential susceptibility for degeneration is majorly attributed to morphological, molecular, and electrophysiological heterogeneity existing in DA neurons of SNpc and VTA. Long-range axonal arborization and a higher number of synapses in SNpc DA neurons make it more vulnerable compared to VTA DA neurons. Studies have shown that a decrease in such axonal arborization places DA neurons at decreased risk in PD. The two well established underlying mechanisms are a) As arborization is an energy-demanding process, increased redistribution of mitochondria to the axonal terminals occurs to satisfy the bioenergetic requirement b) The stabilization of axon-promoting factors at the axonal tip is an essential component for enhancing the arborization process. Interfering with any of these two processes would probably alleviate the degeneration of SNpc DA neurons. To accomplish the decreased stability of arborizing factors and thereby increase the resilience of SNpc DA neurons, we hypothesize the activation of anterograde transport-dependent recruitment of proteasomes to axon terminals as one of the most favorable approaches. Understanding this putative avenue of enhancing proteasomal activity and migration to the axonal tip could provide insight into the progression of neurodegeneration in PD and possibly offer a novel therapeutic strategy.

Non-stoichiometric inhibition in integrated lead finding - a literature review

INTRODUCTION

Non-stoichiometric inhibition summarizes different mechanisms by which low-molecular weight compounds can reproducibly inhibit high-throughput screening (HTS) and other lead finding assays without binding to a structurally defined site on their molecular target. This disqualifies such molecules from optimization by medicinal chemistry, and therefore their rapid elimination from screening hit lists is essential for productive and effective drug discovery.

AREAS COVERED

This review covers recent literature that either investigates the various mechanisms behind non-stoichiometric inhibition or suggests assays and readouts to identify them. In addition, combination of the various methods to distill promising molecules out of raw primary hit lists step-by-step is considered. Emerging technologies to demonstrate target engagement in cells are also discussed.

EXPERT OPINION

Over the last few years, awareness of non-stoichiometric inhibitors within screening libraries and HTS hit lists has considerably increased, not only in the pharmaceutical industry but also in the academic drug discovery community. This has resulted in a variety of methods to detect and handle such compounds. These range from in silico approaches to flag suspicious compounds, and counterassays to measure non-stoichiometric inhibition, to biophysical methods that positively demonstrate stoichiometric binding. In addition, novel technologies to verify target engagement within cells are becoming available. While still a time- and resource-consuming nuisance, non-stoichiometric inhibitors therefore do not fundamentally jeopardize the discovery of low molecular weight lead and drug candidates. Rather, they should be viewed as a manageable issue that with appropriate expertise can be overcome through integration of the above-mentioned approaches.

Automated measurement of fast mitochondrial transport in neurons

There is growing recognition that fast mitochondrial transport in neurons is disrupted in multiple neurological diseases and psychiatric disorders. However, a major constraint in identifying novel therapeutics based on mitochondrial transport is that the large-scale analysis of fast transport is time consuming. Here we describe methodologies for the automated analysis of fast mitochondrial transport from data acquired using a robotic microscope. We focused on addressing questions of measurement precision, speed, reliably, workflow ease, statistical processing, and presentation. We used optical flow and particle tracking algorithms, implemented in ImageJ, to measure mitochondrial movement in primary cultured cortical and hippocampal neurons. With it, we are able to generate complete descriptions of movement profiles in an automated fashion of hundreds of thousands of mitochondria with a processing time of approximately one hour. We describe the calibration of the parameters of the tracking algorithms and demonstrate that they are capable of measuring the fast transport of a single mitochondrion. We then show that the methods are capable of reliably measuring the inhibition of fast mitochondria transport induced by the disruption of microtubules with the drug nocodazole in both hippocampal and cortical neurons. This work lays the foundation for future large-scale screens designed to identify compounds that modulate mitochondrial motility.