In 2014, 1.5 million people died of TB and the infection rate totaled one-third of the world's population.
Beta-Lactams, a major class of antibiotics, can be inactivated by the Beta-lactamase enzyme. This enzyme creates drug-resistant strains of TB and other bacteria. Researchers and clinicians are adapting by developing Beta-lactamase inhibitors. Seven are currently clinically available, with Augmentin being the most commonly used. As resistance to even Augmentin grows, scientists and clinicians are moving quickly to develop new Beta-lactamase inhibitors with the help of surface plasmon resonance (SPR) to study inhibitor-enzyme binding kinetics and characteristics.
Scientists have several reasons for using SPR technology to find these important answers.
1) Direct measurement of inhibitor-enzyme interaction can be followed, making it easy to obtain kinetic information.
2) SPR is easily automated, allowing for quick and efficient data acquisition and analysis with minimal consumption of ligand and protein.
3) Highly sensitive, multichannel SPR instruments are ideally suited to finding promiscuous binders. This eliminates the challenge of using pan-assay interference compounds (PAINS).
These characteristics make SPR an excellent choice for quick and efficient fragment-based drug discovery (FBDD) screening.
Lund et al. (2016) developed one fragment inhibitor from 490 fragments for beta-lactamase OXA-48. Their protocol involved using tOXA-48 purified protein immobilized on an SPR sensor chip, using amine coupling at a concentration of 5000 RU. Meropenum was used as a positive control. The team demonstrated that the enzyme OXA-48 was still functionally viable after immobilization. Slow substrate release measurements showed that bicarbonate is essential in their running buffer. The scientists used SPR as their primary screen with positive binders checked for false positives using asecondary biochemical assay with the substrate nitrocefin. "Rule of 3" was used to confirm fragment binding which essentially states that molecular weight should be less than 300, cLogP less than 3, hydrogen bond donors and acceptors less than 3 and lastly the number of rotatable bonds should be less than 3.
Other scientists are now using SPR to study Betalactamase inhibitors. These researchers are trying to adapt current therapies to combat TB. Christopeit et al. (2015) used an orthogonal screening approach with SPR, then applied an enzyme inhibition assay to find novel inhibitors for the clinically important MBL Verona integron-encoded metallo-β-lactamase (VIM-2). The Barelier team screened a 1281 fragment library with NMR. Barelier and colleagues next used SPR technology to confirm 9 viable fragments.
These three studies are representative of SPR's viability as an investigative method for fragment based drug discovery.
Most people infected with TB will be asymptomatic; drastically increasing transmission from host to host in what is called a "super-spreader." As in the case of the early 20th century polio epidemic, international health organizations are focused on the complete elimination of TB. Until then, researchers are focused on developing and producing the cheapest and most effective antibiotics possible to combat TB. SPR is now a standard assay in fragment based drug discovery (FBDD).