Table 1.

Properties and limitations of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) inhibitory agents.

Inhibitor	Class	Mode of action	Properties and limitations
AS105	Pharmacologic	ATP competitive	Half maximal inhibitory concentration IC50 in the low nM range; shown to improve Ca2+ handling in isolated mouse and human cardiomyocytes. Limitations: Activity against CaMKIIα/β/γ, other off-targets, and bioavailability for in vivo delivery unknown.
GS-680	Pharmacologic	ATP competitive	IC50 of 2.3 nM for CaMKIIδ with weaker selectivity against CaMKIIα/β/γ and weak interaction with human ether-a-go-go-related gene (hERG). Shown to restore contractility and Ca2+ handling in human trabeculae from failing hearts. Limitations: Bioavailability and in vivo testing unknown and evidence of potential negative ionotropic effect reversed by isoproterenol treatment.
RA306	Pharmacologic	ATP competitive	IC50 in the 10 nM range for CaMKIIδ/γ with weaker potency against CaMKIIα/β and relatively weak inhibition against hERG, Kv4.3, Nav1.5, and Cav1.2. In vivo oral delivery restored contractility in genetic mouse model of dilated cardiomyopathy with minimal drug delivery to the brain. Limitations: Potential inhibition of other kinases associated with cardiac remodeling. Effects on electrical remodeling are not defined. Additional detail needed on acquired disease states like pressure overload.
AC3I/AIP	Peptide	Substrate competitor	IC50 of ~3 µM (AC3I) and 40 nM (AIP). Cardiac specific transgenic models shown to effectively attenuate hypertrophic remodeling, heart failure (HF), and arrhythmias. Limitations: Comprehensive screening of off-targets would be necessary for translational approaches. Existing screens show specificity for CaMKII; however, all isoforms are targeted with equal potency, mandating cardiac specific expression. Bioavailability and cell permeation nonexistent without use of viral vector delivery or potential use of novel nanoparticle delivery.
CaMKIIN	Peptide	Substrate/regulatory domain competitor	IC50 of 50 nM; however, refinement of the core peptide sequence to the most recent generation (CN19o) has enhanced specificity to CaMKII and improved the IC50 to 0.4 nM. Membrane and mitochondrial associated transgenic expression in mice reduced inflammatory signaling and mitochondrial stress following ischemic injury. Limitations: May impair CaMKII interaction with scaffolding proteins leading to disruption of kinase signaling domains. Lack of bioavailability and cell permeation, requiring viral vector or novel nanoparticle delivery.
Small interfering RNA (siRNA)/antisense oligonucleotide (ASO)/miRNA	RNAi	Degradation of mRNA, translational inhibition, or alternative splicing	Genetic knockout (KO) of CaMKII in mouse lines has led to improved cardiac performance in multiple disease models. Limitations: in vivo therapeutic delivery of RNAi-based agents has not been tested for translational application. Additional limitations include CaMKII targeting in unintended tissues from system delivery.
Ranolazine	Indirect inhibitor of CaMKII signaling	Inhibits late INa	Shown to reduce late INa and prevent hypertrophy, HF, and arrhythmias in animal models. Limitations: Clinical trials show uncertain impact preventing atrial fibrillation recurrence, ventricular tachycardia (VT)/ventricular fibrillation (VF), or improving functional cardiac output in hypertrophic cardiomyopathy.
Rycals (JTV519, S107)	Indirect inhibitor of CaMKII signaling	Stabilizes RyR2	Shown to improve Ca2+ handling and ventricular function while protecting against arrhythmias and HF development in both rodents and large animal studies. Clinical investigations performed with S107 to target RyR1 expressed in skeletal muscle for muscular dystrophy treatment
Phosphatase activators	Indirect inhibitor of CaMKII signaling	Dephosphorylation of CaMKII substrates	PP2A activator FTY720 has shown protective capability. Current trend toward phosphatase activators in cancer therapeutics may provide opportunity to examine cardiac effects. Limitations: Transgenic overexpression of phosphatase subunits has been associated with cardiac disease.