Epigenetics
the most important challenge in assay development of epigenetic enzyme targets suitable for HTS applications. This was followed by reproducibili- ty/signal window and activity, then purity. Sourcing raw materials was ranked the least important challenge (Figure 7).
Main obstacles in exploiting epigenetic targets
The availability of good antibodies was ranked as the most limiting (major obstacle) in the exploita- tion of epigenetic enzyme targets today. It was closely followed by lack of known specific inhibitors; production of active protein is difficult; and then physiological substrates not yet identi- fied. Least limiting was no specific compound libraries are available (Figure 8).
Epigenetic cellular modification assays It would however be wrong to assume that all screening efforts are focused on biochemical enzyme epigenetic assays today, when in fact respondents indicated that they are spending around 50% of their effort investigating epigenet- ic cellular modification assays. Of these the most investigated today were methylation (68% investi- gating), followed by acetylation (39% investigat- ing), and then phosphorylation (24% investigat- ing). Least investigated were sumoylation (only 11% investigating) (Figure 9).
Latest developments in epigenetic drug screening
The following vendor snapshots provide addition- al details and describe some of the latest develop- ments in assays, kits, associated reagents and tools used for the screening and investigation of epige- netic target enzymes and proteins:
Active Motif (
www.activemotif.com) develops innovative tools and reagents that help researchers investigate nuclear function with par- ticular emphasis on chromatin dynamics and elu- cidating the mechanism and regulation of epige- netic events. In addition to offering validated antibodies and assays to enable the discovery and characterisation of key epigenetic processes, such as histone modification and DNA methylation Active Motif now also provides complete service solutions for the genome-wide analysis of epige- netic events, including DNA methylation, histone modification and transcriptional regulation. Active Motif offers antibody-based tools for a wide range of histone modifications as well as assays against histone modifying enzymes such as
Drug Discovery World Spring 2011 43
Figure 8: Major limitations of screening epigenetic enzyme targets
Expensive, not very specific assay kits Availability of purified enzymes Physiological substrates not yet identified Production of active protein is difficult Lack of known specific inhibitors Availability of good antibodies
Lack of follow-up cell-based assays and counter-screens
Inability to measure local versus global mark changes
Little known about protein crystal structures limits virtual screening approaches
Many assays lack ability to control for compound interference
Many compound libraries lack diversity and no hits can be identified
No specific compound libraries are available 4.97
4.61 4.71
1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 © HTStec 2011 11.00 12.00 RANKED ORDER, where 1 = least limiting (not an obstacle) and 12 = most limiting (major obstacle) 6.14 5.86 8.46
8.03 8.15 8.24
7.79 7.08 6.79
Figure 9: Most investigated epigenetic cellular modification assays
Target gene readouts Ubiquitination Phosphorylation Acetylation Methylation
Sumoylation 11% © HTStec 2011
0% 10% 20% 30% 40% 50% 60% 70% % Responding
68% 39% 24% 21% 16%
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