title: Enhanced characterization of contractility in cardiomyocytes during early drug safety assessment.
abstract: We sought to investigate whether drug-induced changes in contractility were affected by pacing rates that represent the range of heart rates encountered in vivo. Using the cell geometry measurement system (IonOptix), we paced dog cardiomyocytes at different cycle lengths (CLs) of 2000, 1000, 500, and 333.3 ms, before and after exposure to 13 inotropic drugs. Time course data using vehicle control (0.1% dimethyl sulfoxide (DMSO)) demonstrated stability of the system at all CLs tested. Seven positive inotropes (eg isoproterenol) exerted rate-dependent increases in sarcomere shortening (Sarc. short.; maximal effect at a CL of 333.3 ms [0.1 µM isoproterenol increased Sarc. short. by 41.1% and 145.9% at 2000 and 333.3 ms, respectively]). Omecamtiv mecarbil showed an atypical profile (increased Sarc. short. at 2000 ms [106.9%] and decreased at 333.3 ms [IC(50) = 0.64 µM]). Four negative inotropes (eg flecainide) showed rate-independent inhibition of Sarc. short. (IC(50)s: 3.3 µM [2000 ms] versus 2.3 µM [333.3 ms]). The remaining negative inotropes, verapamil, and BTS (N-benzyl-p-toluene sulphonamide) produced an increase (IC(50)s: 3.9 µM [2000 ms] versus 0.043 µM [333.3ms]) and decrease (IC(50)s: 18.3 µM [2000 ms] versus 34.0 µM [333.3 ms]) in potency, respectively. Negative inotropes (eg flecainide, BTS, and verapamil) decreased the area of the Ca(2+) transient versus Sarc. short. hysteresis loop, although rate dependency was seen with verapamil only. Positive inotropes (eg isoproterenol and levosimendan) induced a rate-dependent increase in the area, however Omecamtiv mecarbil increased and decreased the area at CLs of 2000 and 333.3 ms, respectively. Thus, the use of different pacing rates may improve the detection of inotropes in early drug discovery and illustrate the potential for finger-printing different mechanisms of action.
authors.affiliation: *Translational Safety, Drug Safety and Metabolism and Discovery Sciences, Innovative Medicines and Early Development, AstraZeneca R&D, Macclesfield SK10 4TG, UK.
authors.forename: Larissa
authors.initials: L
authors.lastname: Butler
authors.affiliation: *Translational Safety, Drug Safety and Metabolism and Discovery Sciences, Innovative Medicines and Early Development, AstraZeneca R&D, Macclesfield SK10 4TG, UK.
authors.forename: Caroline
authors.initials: C
authors.lastname: Cros
authors.affiliation: *Translational Safety, Drug Safety and Metabolism and Discovery Sciences, Innovative Medicines and Early Development, AstraZeneca R&D, Macclesfield SK10 4TG, UK.
authors.forename: Karen L
authors.initials: KL
authors.lastname: Oldman
authors.affiliation: *Translational Safety, Drug Safety and Metabolism and Discovery Sciences, Innovative Medicines and Early Development, AstraZeneca R&D, Macclesfield SK10 4TG, UK.
authors.forename: Alex R
authors.initials: AR
authors.lastname: Harmer
authors.affiliation: *Translational Safety, Drug Safety and Metabolism and Discovery Sciences, Innovative Medicines and Early Development, AstraZeneca R&D, Macclesfield SK10 4TG, UK.
authors.forename: Amy
authors.initials: A
authors.lastname: Pointon
authors.affiliation: *Translational Safety, Drug Safety and Metabolism and Discovery Sciences, Innovative Medicines and Early Development, AstraZeneca R&D, Macclesfield SK10 4TG, UK.
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Pollard
authors.affiliation: *Translational Safety, Drug Safety and Metabolism and Discovery Sciences, Innovative Medicines and Early Development, AstraZeneca R&D, Macclesfield SK10 4TG, UK najah.abigerges@astrazeneca.com.
authors.forename: Najah
authors.initials: N
authors.lastname: Abi-Gerges
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002304:Cardiac Pacing, Artificial; D002316:Cardiotonic Agents / Q000494:pharmacology*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D056966:Excitation Contraction Coupling / Q000187:drug effects*; D005260:Female; D006339:Heart Rate; D009200:Myocardial Contraction / Q000187:drug effects*; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D012518:Sarcomeres / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors
chemical_list: D002316:Cardiotonic Agents; D002118:Calcium
keywords: cardiac safety; cardiomyocyte; drug discovery and development; hysteresis loop; inotropy; pacing rate