Ink-Jet Printing for drug srreening on microarrays: fromcovalent approaches to in-liquid-droplets assays

Drug screening is the complex process of retrieving chemical compounds able to modulate theactivity of biological targets which are of interest for certain diseases. Conventional miniaturizeddrug screening technologies are based on robotic dispensers coupled with microwell arrays.However these devices require time and reagent consuming (micro-, nanoliter scale) instrumentaltools, liquid handling robotics and complex detectors. Here we show a low-cost and efficientdrug screening methodology based on inkjet printing for delivering molecular systems inpicoliter volumes coupled with easily-implemented detection tools for probing target-druginteraction. We firstly show up a screening platform for a model enzyme/substrate couple and weextend this approach to systems of clear interest for medicinal chemistry.The approach was initially proved with a model enzyme system like Glucose Oxidase substratecovalently linked to a functionalized silicon oxide support. On this support an enzymaticsubstrate (D-glucose)/inhibitor (D-glucal) couple was accurately dispensed. A simplecolorimetric detection method based on the production of a red quinoneimine dye in a reactioncatalyzed by Horseradish Peroxidase proved the screening capability of the microarray at thesingle spot level. Occurrence of competitive inhibition was verified at the solid-liquid interfacewith a similar behavior occurring for such system in a solution phase.Afterwards, this methodology has been extended to CYP450 enzymes like CYP3A4, one of themain targets for the phase I drug metabolism via a droplet microreactors arrays containingCYP3A4 enzyme mixed with model inhibitors (i.e. ketoconazole and erythromycin) andenzymatic chemiluminescent substrates (Luciferin- Isopropylacetate). Enzymatic activity inpicoliter liquid spots was detected by using a low cost optical method. Accordingly,bioluminescence given by D-luciferin upon reaction with oxygen in a reaction catalyzed byLuciferase enzyme leads to a production of photons that increase spot brightness which can bequantified by Charge-coupled device camera.