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Key Concepts in Assay Development, Screening and the Properties of Lead and Candidate Compounds
Published in Venkatesan Jayaprakash, Daniele Castagnolo, Yusuf Özkay, Medicinal Chemistry of Neglected and Tropical Diseases, 2019
Automated compound handling has usually been treated separately from the liquid handling of bulk reagents for assays. Compounds are usually stored in 100% v/v DMSO as the solvent for their dissolution in microtiter plates (Chen et al. 2013, Liu et al. 2012, Popa-Burke and Russel 2014, Zaragoza-Sundqvist et al. 2009). Usually, assays will contain DMSO at concentrations in the region of 1% v/v; therefore, a 100-fold dilution of compound will need to be carried out. Thus, for an assay with a volume of 10 μl, the volume of the compound solution required will be 0.1 μl which is usually added to assay plates first. This is then followed by the addition of bulk biological reagents, e.g., in the case of a simple in vitro assay, one addition of substrate (5 μl) and a second addition of enzyme (5 μl) to initiate the reaction and a third addition (10 μl) to stop the reaction prior to reading the microtiter plate. The types of liquid handling equipment employed to dispense compounds and bulk reagents are usually kept separate as the volumes required are substantially different. Numerous technologies have been developed that are capable of reliable dispensing of sub-microlitre volumes of compounds in DMSO whilst maintaining sufficient throughput for the production of plates containing compounds for screening activities. One such example is based on capillary action using specially designed tips for fixed volume dispensing (Genomic Solutions® Hummingbird). In this case, as the same tips are re-used, they need to be washed sufficiently after each dispenses to prevent cross contamination. This washing is usually done with DMSO (the same solvent that is used to dissolve the compounds) to prevent their precipitation within the tips and blocking them. A more recent development for dispensing low volumes of solutions of DMSO is based on a contactless method using acoustic droplet ejection and is exploited by the Labcyte Echo®. As a result of the contactless dispense method, there is no need for the use of disposable tips, the need for washing is overcome, no waste DMSO is generated and compound adsorption is obviated.
Acoustic mist ionization mass spectrometry (AMI-MS) as a drug discovery platform
Published in Expert Opinion on Drug Discovery, 2019
Ian Sinclair, Gareth Davies, Hannah Semple
Since then, other work has been reported that combines acoustic droplet ejection with an open port probe developed by Oakridge with a sampling rate of 2 s per sample. Subsecond per sample analysis can be achieved by overlapping peaks and deconvoluting the spectra produced [23]. Researchers have also shown how desorption ESI (DESI) [24] and atmospheric pressure MALDI (AP-MALDI) [25], normally used for tissue imaging can be applied to reading droplet arrays, with both of these techniques being amenable to subsecond analysis.
Drug metabolic stability in early drug discovery to develop potential lead compounds
Published in Drug Metabolism Reviews, 2021
Siva Nageswara Rao Gajula, Nimisha Nadimpalli, Rajesh Sonti
In recent times, a novel advanced coupling of acoustic droplet ejection (ADE) technology, open-port interface (OPI), and electrospray ionization (ESI) MS provided fast sampling and label-free analysis. It was successfully demonstrated for rapid analysis of metabolic stability assays (Hollenbeck et al. 2020). Figure 3 displays the schematic of the ADI-OPI-MS instrument. Acoustic droplet ejection technology is used to deliver rapid, precise, and accurate nanoliter volumes of liquids on a hertz time scale (Häbe et al. 2020).
What’s happened over the last five years with high-throughput protein crystallization screening?
Published in Expert Opinion on Drug Discovery, 2018
Recently, benefiting from the rapid development of technologies such as mechanical automation, control technology, and microfluidics, researchers have developed a series of fluid manipulation technologies and devices which provide effective and reliable solutions for protein crystallization screening with HT and low consumption [23]. Generally, a sophisticated liquid-handling system is used to combine and mix the reservoir solutions and a second system sets up the sample droplets. In order to improve the liquid handling accuracy and reliability of the pipette, many companies have developed a number of automated liquid handling workstations and laboratory automation technologies to the scientific community, such as Douglas Instruments company’s Oryx systems, TTP Labtech’s mosquito series, Art Robbins Instruments’ Crystal Phoenix and Crystal Gryphon LCP, Digilab’s HoneyBee series, Tecan’s Freedom EVO workstation. Acoustic droplet ejection (ADE) using a pulse of ultrasound to move low volumes of fluids (typically nanoliters or picoliters) without any physical contact were used to improve protein crystal quality, facilitate protein crystallization, and improve HT structural biology [24]. Teplitsky and coworker described a HT method for screening up to 1728 distinct chemicals to co-position 2.5nL of protein, precipitant, and chemicals with protein crystals on a single microplate using ADE [22]. Microfluidics is a technique for manipulating fluids in microstructures on the micron scale, with conventional liquid handling volumes ranging from femtoliters to nanoliters. This technique can greatly reduce sample consumption in protein crystallization [18]. In recent years, the microfluidic technology used in HT protein crystal screening has developed rapidly, such as Formulatrix’s Formulator and Mantis, Protein BioSolutions’ Plug Maker systems. These devices are striving to increase the efficiency of the hit-identification process and/or diffraction data collection.