We describe an on-flow zonal affinity-based chromatography assay to screen ligands for the nucleoside diphosphate kinase B enzyme (NME2) from Homo sapiens. For the first time, we have covalently immobilized NME2 on the surface of an open fused silica capillary reactor (NME2-ICER) and placed the reactor before the analytical column, which resulted in a two-dimensional liquid chromatography-based system. We evaluated the pH effect on immobilized NME2 activity and carried out steady-state kinetic studies to compare free and immobilized NME2. Steady-state kinetic studies with the substrates adenosine 5’-triphosphate di(tris) salt dihydrate (ATP) and guanosine 5’-diphosphate sodium salt (GDP) resulted in apparent Michaelis-Menten constant values of 1136 and 713 mmol L-1, respectively. The ping-pong catalysis mechanism and substrate specificity were preserved after NME2 immobilization. By employing a reference inhibitor, (-)-epicatechin gallate (ECG), we verified the potential application of this method in NME2 ligand screening and NME2 inhibitor identification. The half maximum inhibitory concentration (IC50) for ECG was 161.3 ± 1.0 μmol L-1.

The methodology developed in this study through the acquisition of fingerprint chromatograms by liquid chromatography-diode array detector (LC-DAD), aided by principal component analysis, made it possible to assess, in a rational way, the chemical differences between six accessions of Lippia alba and to verify the influence of the method of extraction, the seasonality and the individuality of each accession on chemical composition of its extracts. Among all extracts analyzed against cancer cell lines, eight of them showed to be more promising against a human leukemia cell line (HL-60), displaying cell growth inhibition percentage ranging between 40.0 and 52.0%. In the inhibitory activity assays against acetylcholinesterase enzyme, all extracts showed weak inhibitory effect, with highlight only for six of them, which displayed inhibition ranging between 27.0 and 32.0%.