Mitigating Radiation Fibrosis Through Metabolic Regulation

Abstract

Radiation fibrosis (RF), an irreversible process resulting in elevated ECM deposition following radiotherapy, affects a significant portion of head and neck cancer patients and results in substantial morbidity. No effective therapies currently exist for the treatment of RF. Studies have recently identified the involvement of metabolic dysregulation in driving onset and progression of renal and hepatic fibrosis. However, our understanding of the role of metabolic alterations in mediating RF is largely unknown. We hypothesize that metabolic deregulation plays a fundamental role in the development of RF, and as such, the effects of radiation fibrosis may be mitigated through the use of available metabolic regulating compounds. Transcriptome profiling was performed on dermal tissue sampled from head and neck cancer patients’ post-radiation therapy treatment. Pharmacogenomics analysis was performed to identify drugs in silico, followed by in vitro and in vivo validation of novel compounds in an RF model. Genomewide transcriptome profiling identified lipid oxidation and PPAR signaling, a master regulator of fatty acid oxidation (FAO), as the most significant features downregulated in RF in both humans and mice. TGF-B1, a master regulator of fibrosis, was found to mimic metabolic alterations in RF in vitro by downregulating genes in the PPAR pathway and by impairing oxidation of the fatty acid palmitate. To identify compounds that could reverse this metabolic dysregulation in RF, a pharmacogenomics analysis was performed to identify compounds that could normalize the RF transcriptome signature. Drug A was identified through this in silico approach and was shown in vitro to reverse TGF-B1-induced FAO suppression via upregulating the PPAR pathway while also decreasing TGF-B1 induced expression of pro-fibrotic proteins, collagen-1, fibronectin, and PAI-1. This effect was inhibited by the FAO inhibitor etomoxir, demonstrating that the anti-fibrotic effects of Drug A required intact FAO signaling. Further, Drug A enhanced lysosomal biogenesis and upregulated collagen-1 and fibronectin lysosomal degradation, resulting in reduced pro-fibrotic protein levels. The metabolic regulatory effects of Drug A were then validated in an RF model in vivo. Systemic administration of Drug A metabolic reprogrammed RF, resulting in FAO upregulation and reduced fibrosis severity. FAO suppression is a key feature of RF in both humans and mice. Drug A induced upregulation of the PPAR pathway and lysosomal degradation of pro-fibrotic proteins, resulting in enhanced FAO and reduced RF. Our studies suggest a fundamental role for metabolic dysregulation in RF and highlight the potential use of metabolic reprogramming compounds for the treatment of RF.