Drug Development
Figure 3
1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08
Correlation of the hERG IC50 values obtained using the CytoPatch device with those obtained using manual patch clamp
R = 0.96901
1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 IC50 Cytopatch™ (nM)
due to blockade of the hERG ion channel. However, as more and more data becomes avail- able about drug-induced QT-prolongation, it is apparent that there is not always a correlation between hERG inhibition and QT-prolongation. There are numerous examples of false positives and false negatives in the in vitro hERG assay13-21 (Table 3). Therefore, it can be concluded that addi- tional (in vitro) assays are needed to better predict the cardiac safety profiles of compounds. The main reason for erroneous conclusions of in
vitro hERG assays is that several compounds affect ion channels other than hERG or affect multiple ion channels. Since the ventricular action potential is co- ordinated by interplay of ion channels – of which
Nav1.5, Cav1.2, Kv4.2/4.3, Kv7.1, hERG and Kir2.1 are the main ones – drug interaction with one of these other channels can affect the QT-time. To get a better cardiac safety profile of a drug candidate, screening of a compound against a panel of cell lines with overexpression of the main ion channels involved in the ventricular action potential has been proposed22. Performing such a profiling by using manual patch clamping would be too laborious for screening purposes; however, the availability of automated patch clamp platforms has made it possible to perform such a screening5. A new development is the application of induced pluripotent stem (iPS) cell-derived human car-
Drug Discovery World Spring 2013
diomyocytes. These cells express several relevant cardiac ion channels at comparable levels to pri- mary human cardiomyocytes and can be used for a total ion channel measurement. Future application of these iPS cell-derived human cardiomyocytes may give a better prediction for cardiac toxicity. Performing a total ion channel measurement is fea- sible with the automated patch clamp methods dis- cussed here.
Summary
Drug-induced QT prolongation is recognised as a major hurdle in the successful development of drug candidates. The main cause of drug-induced QT
FALSE POSITIVES hERG assay
Clomiphene Clemastine Fluoxetine Citalopram Moxifloxacin Ranolazine
False negatives hERG assay Alfuzosin Chloroquine
Table 3: Examples of drugs for which there was no correlation between inhibition in the in vitro hERG assay and QT-prolongation observed in vivo
65 VERAPAMIL
IC50 Manual Patch clamp (nM)
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80