Reduction of SR Ca2+ leak and arrhythmogenic cellular correlates by SMP-114, a novel CaMKII inhibitor with oral bioavailability

  • Stefan Neef
  • Christian Mann
  • Anne Zwenger
  • Nataliya Dybkova
  • Lars S. Maier
Original Contribution


Sarcoplasmic reticulum (SR) Ca2+ leak induced by Ca2+/calmodulin-dependent protein kinase II (CaMKII) is centrally involved in atrial and ventricular arrhythmogenesis as well as heart failure remodeling. Consequently, treating SR Ca2+ leak has been proposed as a novel therapeutic paradigm, but compounds for use in humans are lacking. SMP-114 (“Rimacalib”) is a novel, orally available CaMKII inhibitor developed for human use that has already entered clinical phase II trials to treat rheumatoid arthritis. We speculated that SMP-114 might also be useful to treat cardiac SR Ca2+ leak. SMP-114 significantly reduces SR Ca2+ leak (as assessed by Ca2+ sparks) in human atrial (0.72 ± 0.33 sparks/100 µm/s vs. control 3.02 ± 0.91 sparks/100 µm/s) and failing left ventricular (0.78 ± 0.23 vs. 1.69 ± 0.27 sparks/100 µm/s) as well as in murine ventricular cardiomyocytes (0.30 ± 0.07 vs. 1.50 ± 0.28 sparks/100 µm/s). Associated with lower SR Ca2+ leak, we found that SMP-114 suppressed the occurrence of spontaneous arrhythmogenic spontaneous Ca2+ release (0.356 ± 0.109 vs. 0.927 ± 0.216 events per 30 s stimulation cessation). In consequence, post-rest potentiation of Ca2+-transient amplitude (measured using Fura-2) during the 30 s pause was improved by SMP-114 (52 ± 5 vs. 37 ± 4%). Noteworthy, SMP-114 has these beneficial effects without negatively impairing global excitation–contraction coupling: neither systolic Ca2+ release nor single cell contractility was compromised, and also SR Ca2+ reuptake, in line with resulting cardiomyocyte relaxation, was not impaired by SMP-114 in our assays. SMP-114 demonstrated potential to treat SR Ca2+ leak and consequently proarrhythmogenic events in rodent as well as in human atrial cardiomyocytes and cardiomyocytes from patients with heart failure. Further research is necessary towards clinical use in cardiac disease.


Heart failure Arrhythmias SR Ca2+ leak CaMKII 



We thank Dainippon Sumitomo Pharma for having provided SMP-114 for our experiments. The technical expertise of Felicia Radtke, Timo Schulte, and Thomas Sowa was greatly appreciated. SN receives funding from a Regensburg University ReForM B research grant and Deutsches Zentrum für Herz-Kreislauf-Forschung (DZHK B 15-014 Extern). LSM receives funding from Deutsche Forschungsgemeinschaft (MA1982/5-1).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.


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© Springer-Verlag GmbH Germany 2017

Authors and Affiliations

  1. 1.Klinik für Innere Medizin IIUniversitätsklinikum RegensburgRegensburgGermany
  2. 2.Department of Cardiology and PneumologyUniversity Medical Center GöttingenGöttingenGermany

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