Copper chelation reduces early collagen deposition and preserves saliva secretion in irradiated salivary glands

Radiation therapy is a first-line treatment for head and neck cancer; however, it typically leads to hyposalivation stemming from fibrosis of the salivary gland. Current strategies to restore glandular function are dependent on the presence of residual functional salivary gland tissue, a condition commonly not met in patients with extensive fibrotic coverage of the salivary gland resulting from radiation therapy. Fibrosis is defined by the pathological accumulation of connective tissue (i.e., extracellular matrix) and excessive deposition of crosslinked (fibrillar) collagen that can impact a range of tissues and given that collagen crosslinking is necessary for fibrosis formation, inhibiting this process is a reasonable focus for developing anti-fibrotic therapies. Collagen crosslinking is catalyzed by the lysyl oxidase family of secreted copper-dependent metalloenzymes, and since that copper is an essential cofactor in all lysyl oxidase family members, we tested whether localized delivery of a copper chelator into the submandibular gland of irradiated mice could suppress collagen deposition and preserve the structure and function of this organ. Our results demonstrate that transdermal injection of tetrathiomolybdate into salivary glands significantly reduced the early deposition of fibrillar collagen in irradiated mice and preserved the integrity and function of submandibular gland epithelial tissue. Together, these studies identify copper metabolism as a novel therapeutic target to control radiation induced damage to the salivary gland and the current findings further indicate the therapeutic potential of repurposing clinically approved copper chelators as neoadjuvant treatments for radiation therapy.