The Heart's Defense Against Cancer

Introduction

Primary cardiac tumors and metastases to the heart are rare, with a reported prevalence of only approximately 0.002%, despite the highly vascularized nature of the organ. Although the mechanisms underlying this resistance to tumor growth remain poorly understood, cardiac cells largely exit the cell cycle after birth and exhibit minimal proliferative capacity in adulthood. This observation raises the possibility that the same mechanisms restricting cardiomyocyte proliferation may also suppress cancer cell growth within the heart. Interestingly, cardiac proliferative potential can be reactivated under specific conditions. For example, patients with end-stage heart failure who receive a left ventricular assist device (LVAD) experience mechanical unloading of the heart, which has been associated with increased cardiac cell proliferation. These findings suggest that mechanical load may be an important regulator of cellular proliferation, and that increasing compressive forces could potentially suppress cancer growth.

Goals of this Study

In this recent study, published in Science, the authors investigated how mechanical load inhibits cancer growth in the heart. To first determine whether tumor growth is naturally restricted in the heart, they used a genetically engineered mouse model in which systemic delivery of a Cre-expressing adenovirus activates oncogenic Kras and deletes p53 across multiple tissues, resulting in widespread tumor formation. Using this model, tumors developed in several organs, including the lung, liver, and skeletal muscle, but were notably absent from the heart.

Having established that the heart is resistant to tumorigenesis, the researchers next examined whether mechanical load contributes to this resistance. They utilized a heterotopic heart transplantation model in which a donor heart is surgically connected to the recipient mouse's carotid artery and external jugular vein. This procedure restores perfusion while eliminating the normal mechanical workload of the transplanted heart. Following injection of GFP-expressing cancer cells, the researchers observed negligible tumor growth in the native, mechanically loaded heart, whereas robust cancer cell proliferation occurred in the transplanted, mechanically unloaded heart.

The authors then confirmed these findings using an in vitro engineered cardiac tissue model composed of rat cardiomyocytes and fibroblasts anchored between adjustable metal braces that allowed mechanical load to be precisely controlled. Consistent with their transplantation experiments, unloading increased cardiac cell proliferation. Importantly, when tumor cells were incorporated into the system, mechanical unloading also promoted cancer cell proliferation.

Next, the researchers sought to identify the molecular mechanisms linking mechanical unloading to increased cell proliferation. To accomplish this, they analyzed human tumor samples from primary tumors and matched metastatic lesions, including cardiac metastases. Spatial transcriptomic analyses, which provide information on both gene expression and tissue localization, revealed enrichment of histone demethylation pathways in cardiac metastases. Further analyses demonstrated reduced levels of the repressive histone mark H3K9me3, accompanied by increased chromatin accessibility. Together, these findings suggest that mechanical changes in the cardiac environment promote histone demethylase activity, resulting in reduced H3K9me3 levels, chromatin relaxation, and altered gene expression programs.

These observations were further validated in experimental models, where unloaded hearts exhibited reduced H3K9me3 staining and a more open chromatin state compared with loaded hearts. Increased chromatin accessibility was observed at genomic regions involved in cell cycle regulation. To identify the mechanosensor responsible for translating mechanical cues into chromatin remodeling, the authors focused on components of the linker of nucleoskeleton and cytoskeleton (LINC) complex. Their results demonstrated that Nesprin-2 is a key mediator of this response. Silencing Nesprin-2 increased chromatin compaction and restored cancer cell proliferation in both in vitro and in vivo models.

This was an interesting paper that explored a well-known phenomenon that had little previous mechanistic insight. It also shows how cancer cells behave under mechanical pressure and open the door in exploring strategies outside the canonical molecular targeting.

Article title: Mechanical load inhibits cancer growth in mouse and human hearts

Article Reference: Giulio Ciucci et al., Mechanical load inhibits cancer growth in mouse and human hearts.Science392,eads9412(2026).DOI:10.1126/science.ads9412