Abstract Body: Introduction: Dose-dependent cardiotoxicity limits the efficacy of chemotherapeutic agent doxorubicin (DOX). p38δ is one of four p38 mitogen-activated protein kinase isoforms that regulate DOX-induced cardiotoxicity (DIC). p38δ genetic deletion protects female mice from DIC. In the absence of selective pharmacologic inhibitors of p38δ, docosanoic acid (DCA) conjugate-mediated delivery of chemically engineered small interfering RNA (siRNA) provides a novel avenue to achieve selective, efficient, durable, and nontoxic in vivo p38δ silencing in the heart.
Hypothesis: The selective silencing of p38δ is cardioprotective from DIC in female mice.
Methods: Following the screening of a panel of p38δ-selective siRNA sequences, the lead siRNA si-p38δ-1, with the highest silencing efficacy and potency in vitro, was identified. 15-week-old female mice were subcutaneously injected with 20 mg/kg of DCA-conjugated chemically stabilized si-p38δ-1 (n = 3) or the non-targeting control (NTC) siRNA (n = 3) twice 10 hours apart. p38δ silencing in mouse hearts was measured 14 days later by assessing mRNA and protein expression. To evaluate the effect of p38δ silencing after acute DOX treatment, the mice were administered si-p38δ-1 (n = 5) or NTC (n = 5), followed by DOX treatment (30 mg/kg) six days later. The study concluded 11 days after DOX treatment. Morbidity was assessed by assigning health scores daily. Electrocardiography, echocardiography, and optical mapping were performed to evaluate cardiac function.
Results: si-p38δ-1 led to 80% silencing of p38δ in mouse hearts 14 days after administration, without any cardiotoxic effects. si-p38δ-1-treated female mice exhibited diminished DOX-induced morbidity (p = 0.003) and were protected from developing calcium alternans (CAs) 11 days post-DOX treatment, compared to NTC-treated counterparts. Thus, DOX-induced CAs, indicative of calcium mishandling, were observed in 75% (3/4) NTC-treated mice and 0% (0/5) si-p38δ-1-treated mice.
Conclusion: Efficient and well-tolerated in vivo p38δ silencing by si-p38δ-1 in mouse hearts mitigated DOX-induced morbidity and calcium mishandling in female mice, highlighting the therapeutic potential of p38δ silencing for alleviating DIC in female cancer patients.