Abstract Body: Background: Kinase inhibitors have revolutionized cancer treatment, but some exhibit cardiotoxicity. Ribociclib has been associated with an atrial fibrillation (AF) liability, but the specific pro-arrhythmic molecular interactions within cardiac tissues remain unresolved.
Research Questions: This study aimed to identify functionally-significant drug-kinase interactions in cardiac tissues over clinically-relevant ribociclib concentrations. This study further aimed to characterize potential pro-arrhythmic functional consequences of ribociclib exposure.
Methods: We comprehensively assessed kinase binding and concentration-dependent phosphorylation signaling changes in cardiac tissues using advanced phosphoproteomics strategies. Functional implications were evaluated by calcium transient measurements in isolated cardiomyocytes.
Results: Ribociclib binds CAMK2s with greater affinity than other kinases in atrial tissue (half-maximal binding: 0.45-3.36μM (95%CI) vs. >10μM). Ribociclib exposure elicits concentration-dependent phosphorylation loss in >100 cardiac proteins, including CAMK2 substrates such as the ryanodine receptor (RyR) S2813. Although a connection between CAMK2 hyperactivity and AF is established, we find that ribociclib exposure can increase the proportion of cells with spontaneous calcium releases, but specifically as an interaction effect with IP3-receptor (ITPR) activity (odds ratio: 1.88, 95%CI: [1.15 3.07]).
Conclusions: This study represents an important step in identifying the mechanisms by which kinase inhibition could broadly alter cellular phosphorylation-signaling resulting in a pro-arrhythmic liability. The ribociclib-CAMK2 interaction presents a possible atypical mechanistic link between ribociclib and atrial fibrillation via altered calcium handling (Figure 1). Understanding these mechanisms will allow for mitigating these off-target effects in future drug development.