Atrial Natriuretic Peptide as a Biomarker and Therapeutic Target in Radiation Cardiotoxicity

Background Radiation cardiotoxicity (RC) presents as acute coronary syndrome, heart failure, arrhythmias, valvulopathy and pericardial disease in the months to years after treatment.

Co-incidental dose to the heart base, where the right and left atrium chambers are located, has been linked to worse outcomes.

Atrial natriuretic peptide (ANP) is a homeostatic cardiac hormone secreted by myocytes of the atrial chamber walls that reduces myocardial fibrosis, improves ventricular contractility and triggers vasodilatation.

We hypothesise that ANP is implicated in the pathogenesis of radiation cardiotoxicity and can be leveraged both as a biomarker and a therapeutic target. Aims 1. Characterise the effect of radiation on regional cardiac and plasma ANP, and the impact of concomitant Entresto©. 2.

Evaluate the capacity of Entresto© to mitigate radiation damage according to tissue, electrocardiography, and ventricular function endpoints. 3. Explore spatial gene expression in order to understand the key features of cardiac radiobiology impacted by Entresto©.

Methods In female 12-week-old C57BL/6 mice, a CT-guided 20 Gy single-fraction irradiation will be delivered to the superior 2/3 of the heart as a 90 degree arc.

All animals will be followed up for 30 weeks following irradiation and plasma will be isolated from the blood for analysis by ELISA. Tissue levels of ANP will also be analysed by immunohistochemistry (IHC).

Functional parameters will be examined every 10 weeks, including systolic muscle function (e.g. ejection fraction and strain) and conduction abnormalities (e.g. P wave duration).

Cardiac tissue morphology 30 weeks post-irradiation will be assessed by H&E and by IHC for vasculature (CD31) and immune cells (CD45), as well as fibrosis staining (Masson’s trichrome).

Two hearts from the Entresto©-treated study arm and one heart from the radiation alone arm will be snap-frozen for spatial transcriptomics. Briefly, representative whole-heart sections will be placed on barcoded capture areas of 10X Visium slides.

Following unsupervised analyses, microscopy images will be annotated for the corresponding heart regions allowing for differential gene expression comparisons between the two study arms.

How the Results Will Be Used From our provisional data, ANP is a promising biomarker of RC and neprilysin inhibition with Entresto to maximise levels is an attractive therapeutic strategy to protect against late radiation cardiac effects.

The data from the proposed research will serve as the preliminary pre-clinical data to support a project grant including an observational clinical blood collection and co-morbidity and tumour mouse models. Evidence-depending thereafter, a phase 2 clinical trial will be considered.