Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Schneider, C.
Effects of Novel Anticancer Therapies on Cardiac Calcium Homeostasis
Humanmedizin; [ Diplomarbeit ] Graz Medical University; 2017. pp. 80
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- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Rainer Peter
- Sedej Simon
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- Abstract:
- Background: Tyrosine-kinase inhibitors (TKIs) are widely used in cancer treatment. Despite being more targeted than conventional chemotherapy, TKIs may exhibit substantial cardiotoxicity. Here, we aim to characterise underlying alterations of cardiomyocyte calcium homeostasis caused by the TKI sorafenib in order to identify potential protective co-treatments. Methods: Intracellular calcium transients (CaTs) were assessed at room temperature using laser scanning microscopy in electrically stimulated (0.5Hz), isolated murine C57BL/6 cardiomyocytes loaded with the calcium-sensitive fluorescent dye Fluo-4/AM (1.5µM). Myocytes were superfused with sorafenib (10µM) or vehicle control (n=21 and 20 cells, respectively, 7 hearts). Isoproterenol- (10nM) and caffeine-induced (30mM) responses were measured to assess beta-adrenergic reserve and sarcoplasmic reticulum (SR) calcium content, respectively. Western blots were performed for calcium-handling proteins phospholamban (PLB) and Ca2+/calmodulin-dependent protein kinase II (CaMKII), including their phosphorylated forms pPLB S16, pPLB T17, and pCaMKII T286. Custom-made R scripts were used for CaTs and Western blot analyses, and statistical testing. Results: Sorafenib-superfused cardiomyocytes showed a progressive decrease in systolic calcium transient amplitude reaching 52±8.1% of the baseline amplitude at the maximum drug effect (p<0.001), while control cells did not show any significant difference in CaT peak amplitude over time (p=0.93). Calcium release and re-uptake kinetics were negatively altered (p<0.05) by sorafenib resulting in slower increase and decrease of CaTs, respectively. Beta-adrenergic stimulation with isoproterenol increased transient amplitude in control myocytes, which was attenuated in sorafenib-treated cells (p<0.001). Furthermore, sorafenib significantly reduced SR calcium content compared to control (p<0.05), with a trend toward prolonged decay time (Tau constant) of the caffeine-induced response (p=0.063). Western blots showed reduced phosphorylation of PLB at serine 16 and a trend towards reduced phosphorylation at threonine 17. CaMKII phosphorylation was not significantly altered. Summary: Immediate negative inotropy by sorafenib is associated with reduced SR Ca2+ load, likely due to impaired SERCA2a function caused by reduced PLB phosphorylation at serine 16 leading to a decrease of intracellular CaT peak amplitude. Furthermore, SR calcium release and re-uptake parameters are altered by sorafenib: SR calcium content is decreased and calcium release and re-uptake kinetics are slowed.