Drug Development
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10 Scheel, O, Himmel, H, Rascher-Eggstein, G, Knott, T. Introduction of a modular automated voltage-clamp platform and its correlation with manual human Ether-a- go-go related gene voltage- clamp data. Assay Drug Dev Technol 2011; 9(6):600-607. 11 Stoelzle, S, Obergrussberger, A, Bruggemann, A, Haarmann, C, George, M, Kettenhofen, R et al. State-of-the-Art Automated Patch Clamp Devices: Heat Activation, Action Potentials and High Throughput in Ion Channel Screening. Front Pharmacol 2011; 2:76. 12Yang, N. Cardiac drug safety and hERG channel. T Bio/Phar Ind 2012; 1:30-35. 13 Zhang, S, Zhou, Z, Gong, Q, Makielski, JC, January, CT. Mechanism of block and identification of the verapamil binding domain to HERG potassium channels. Circ Res 1999; 84(9):989-998. 14Yuill, KH, Borg, JJ, Ridley, JM, Milnes, JT, Witchel, HJ, Paul, AA et al. Potent inhibition of human cardiac potassium (HERG) channels by the anti- estrogen agent clomiphene- without QT interval prolongation. Biochem Biophys Res Commun 2004; 318(2):556-561. 15 Ridley, JM, Milnes, JT, Hancox, JC, Witchel, HJ. Clemastine, a conventional antihistamine, is a high potency inhibitor of the HERG K+ channel. J Mol Cell Cardiol 2006; 40(1):107-118. 16 Pacher, P, Magyar, J, Szigligeti, P, Banyasz, T, Pankucsi, C, Korom, Z et al. Electrophysiological effects of fluoxetine in mammalian cardiac tissues. Naunyn Schmiedebergs Arch Pharmacol 2000; 361(1):67-73. 17 Witchel, HJ, Pabbathi, VK, Hofmann, G, Paul, AA, Hancox, JC. Inhibitory actions of the selective serotonin re-uptake inhibitor citalopram on HERG and ventricular L-type calcium currents. FEBS Lett 2002; 512(1-3):59-66.
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IC50 values was with E4031, which exhibited an 8.5-fold difference. This difference could be
explained by the use of different batches of E4031.
The correlation between the IC50 values deter- mined with the CytoPatch and those determined using manual patch clamp is depicted in Figure 3. A high correlation of 0.97 between the two meth- ods was observed representing the high data quali- ty obtained with the CytoPatch instrument.
How automated patch clamps differ Automated methods have a higher throughput than manual patch clamp methods, demand a smaller amount of test article (a few milligrams) and only require trained technicians rather than electrophysiologists to operate the devices. Based on these characteristics, the automated methods can be easily integrated in lead optimisation pro- grammes for drug development. Table 2 shows a comparison of various automated patch clamp platforms and manual patch clamping. The CytoPatch platform delivers, in comparison to the other automated patch clamp platforms, a lower throughput (approximately 20 data points per day versus up to about 100 to 1,000 data points per day for the other platforms when look- ing at hERG screening). But because the CytoPatch platform is designed with a modular concept, up to 20 devices can be connected to form one multi- channel CytoPatch instrument. Using this concept,
PATCHXPRESS (MOLECULAR DEVICES), QPATCH (SOPHION),
PATCHLINER (NANION)
Throughput Test article demand Operator Seal Glass pipette
Continuous and fast perfusion
21 CFR part 11 and GLP compliant
High Low Trained technicians Gigaseal No No No Medium Low Trained technicians Gigaseal Yes Yes Yes Low High Electrophysiologist Gigaseal Yes Yes Yes
Table 2: Comparison of the characteristics of various automated patch clamp platforms and manual patch clamping with respect to hERG screening
Drug Discovery World Spring 2013
the throughput can be increased to approximately 400 data points per day. Thus, when throughput alone is the most important criterion for selecting a patch clamp platform, the PatchXpress (Molecular Devices) or Qpatch (Sophion) plat- forms have the best characteristics.
Other characteristics such as the presence of a glass pipette, the ability to form gigaseals, fast and continuous perfusion, and 21 CFR part 11 and GLP compliancy are key criteria for measuring the quality of automated patch clamp platforms, as summarised in Table 2. All automated patch clamp devices in Table 2 have the characteristic that gigaseals are formed. In contrast to other platforms the CytoPatch does not demand fluoride buffers to enhance seal formation, which results in a more physiological model. Of the automated systems, the CytoPatch is the only system that is 21 CFR part 11 and GLP compliant, that makes use of a real glass pipette and contains a fast and continu- ous perfusion system that allows for voltage gated and ligand gated ion channels tests. Therefore the CytoPatch ensures the highest data quality and similarity with the manual patch clamp method.
Future outlook: translating in vitro safety studies into clinical QT- prolongation
The vast majority of the clinical cases of drug- induced QT-prolongation have been observed to be
CYTOPATCH
MANUAL PATCH CLAMPING
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