ADP Detection: It’s not all about kinases

The publication of a successful RecA screen by Scott Singleton’s group at the University of North Carolina, Chapel Hill brought the total number of peer-reviewed papers referencing the Transcreener ADP Assay, BellBrook’s fluorescent ADP detection assay, to an even dozen.  Ten of these are focused on specific drug targets, half of those on enzymes other than kinases, including a carboxylase, a triphosphatase, and chaperonins (see table).  Moreover, four of the five kinase studies were focused on small molecule kinases and only one on a protein kinase.  This is exactly what he hoped for when we introduced the Transcreener ADP assay in 2006:  that people would use it to gain access to emerging drug targets, like metabolic kinases for cancer and DNA/RNA modifying enzymes for antimicrobials, that had been difficult to screen with the tools that had been developed for protein kinases.

The availability of an enabling assay can mean more than screening emerging drug targets, it can open up the exploration of new therapeutic strategies. Singleton’s RecA screen is a good example. Deleting RecA lowers antibiotic resistance rates by decreasing induced mutagenesis, intra-chromosomal recombination, and horizontal gene transfer. Singleton and others are pursuing RecA inhibitors in the hope that they might make good broad spectrum antibiotic adjuvants. However, they were limited by the sensitivity of existing assay methods like phosphate detection, which required high enzyme and ATP concentrations. This locked RecA into an inactive conformation: obviously not an ideal situation for finding inhibitors. (If this had been the case for Bcr-Abl screens, Gleevec would not have been discovered.) Using the Transcreener ADP Assay they were able to run their screen at much lower enzyme and ATP concentrations, allowing identification of inhibitors that bind to RecA in its inactive conformation.  It’s still a long way to the clinic, but without the right screening assay, there would be no possibility of developing first-in-class antibiotics targeting RecA.