3055 - The Inflammatory State of the Heart at the Time of Radiotherapy may Drive Cardiotoxic vs. Therapeutic Responses

Purpose/Objective(s): Radiation therapy (RT) can improve cancer-specific outcomes, but thoracic RT can cause long-term heart toxicity. We have shown that localized heart RT (5 Gy) in models of inflammatory heart failure (HF) can improve cardiac outcomes and survival. Given these paradoxical effects, we hypothesize that differences in heart substrate characteristics at the time of RT, including altered inflammation in HF vs non-failing hearts, drive these distinct RT responses.

Materials/Methods: Male and female C57Bl6/J ACSL1TG mice, which overexpress cardiomyocyte-specific acyl-CoA synthetase causing HF induced by metabolic stress, were utilized. 6 wk old mice underwent sham, 5 or 16 Gy image-guided localized heart RT, followed by serial echocardiography at 8 and 12 wk post-RT/sham. In separate studies, non-HF C57Bl6/J wildtype (WT) mice received 5 or 16 Gy heart RT or sham with 11 mo echo performed. To characterize the inflammatory substrates in the heart, CD68 (macrophage) immunostaining, CCR2 flow cytometry, and chemokine receptor type 2 (CCR2) positron emission tomography (PET) imaging with 64Cu-DOTA-ECL1i were performed. Additionally, single-nuclear RNA sequencing (snRNA-seq) of left ventricular (LV) myocardial tissue collected from sham-treated and ACSL1TG mice was conducted, with KEGG pathway enrichment analysis performed.

Results: In the ACSL1TG HF model, we previously showed that 5 Gy heart RT improved LV ejection fraction (LVEF), decreased CCR2+ cells, and improved survival vs. sham (p<0.01). Surprisingly, 16 Gy in ACSL1TG mice also improved LVEF vs sham, with dramatic LVEF preservation at multiple time points (8 wk 37.7% vs. 52.1%, P<0.001; 12 wk 22.7% vs. 57.2%, P<0.0001). However, in non-HF WT mice, 16 Gy heart RT caused late toxicity, with significantly decreased LVEF vs sham at 11 months post-RT (68.4% vs. 59.9%, P<0.003) and increased heart CCR2+ cells by flow cytometry at 6-20 weeks post-RT. CCR2-PET imaging revealed increased cardiac CCR2+ macrophages in ACSL1TG vs WT mice at baseline (1.6% vs.1.1%, P<0.002), and immunostaining pre-RT/sham showed increased cardiac CD68+ cells in ACSL1TG vs WT mice (13.4 vs 1.1, P<0.01). In addition, LV snRNA-seq demonstrated many inflammatory pathways upregulated in ACSL1TG vs WT mice pre-RT/sham (efferocytosis, NFkB, and cytokine-receptor and chemokine pathways, Padj<1E-5). In total, these studies demonstrate a difference in the immune status of HF vs WT hearts pre-RT/sham with differences in post-RT/sham immune responses as well.

Conclusion: These studies suggest that substrate-dependent cardiac inflammatory changes may lead to disparate results of RT in failing vs non-failing hearts, highlighting the importance of considering the inflammatory substrate when evaluating RT as a therapeutic strategy for HF. The differential immune responses and macrophage profiles in normal vs failing hearts may provide insights into personalized approaches for RT treatment in HF.