Abstract Body: Background: Doxorubicin (DOX) is an essential anticancer agent, but it causes irreversible cardiac dysfunction. The aim of this study is to verify whether it is possible to suppress DOX-induced cardiomyopathy and improve life prognosis by stabilizing the Ryanodine receptor (RyR2) tetramer structure pharmacologically (by dantrolene) or genetically (by RyR2 V3599K mutation) in mice.
Methods and results: Using recombinant proteins, we confirmed that DOX directly binds near the calmodulin binding site and inter-domain interface of RyR2. In isolated cardiomyocytes, addition of DOX caused calmodulin dissociation from RyR2, marked Ca2+ leakage and increased oxidative stress, which were sufficiently suppressed by dantrolene or V3599K KI cardiomyocytes. Since intracellular DOX fluorescence disappeared within 7 days after administering DOX to mice, we hypothesized that myocardial protection by dantrolene would be sufficient until 7 days after completion of DOX administration. All WT mice died within 50 days after DOX administration, but the survival rate was significantly improved by continuous administration of dantrolene, and it was equally good even when dantrolene was discontinued 7 days after DOX administration. Cardiac function was also preserved in DOX cardiomyopathy model mice even if dantrolene was discontinued. We previously reported that RyR2 stabilization alleviates endoplasmic reticulum stress. Although GRP78 was known to be suppressed by DOX, DAN maintained GRP78 and suppressed apoptotic signals even in the presence of DOX.
Conclusion: Short-term concomitant use of dantrolene is extremely effective in preventing DOX cardiomyopathy by controlling Ca2+ dynamics and preserving endoplasmic reticulum stress responses, and might be a feasible therapeutic strategy.