The Role of Metabolism in Modulating Radiation Fibrosis & Lymphedema

Abstract

With the improvements in cancer diagnosis and therapy, clinical outcome has increased substantially, to the extent that by 2026, there will be >20M cancer survivors in the United States alone. The majority of survivors fare well; however, there is a significant proportion of patients who continue to experience the aftermath of their treatments such as radiation fibrosis (RF) or lymphedema. Until recently, there has been little understanding of the biological basis of RF, which is defined by the aberrant accumulation of extracellular matrix (ECM), leading to reduced tissue elasticity, and potential loss of organ function. The regulation of ECM production and degradation is a complex process, mediated through the production of a myriad of cytokines such as TGFB, and environmental conditions such as hypoxia. We have recently identified that metabolic dysregulation, and in particular, downregulation of fatty acid oxidation (FAO) is a key pathway driving the production and reducing the degradation of collagen, the predominant component of the ECM. Conversely, upregulation of PPAR signaling, a major mediator of FAO, reduced transcription of key ECM genes; whilst increasing internalization and degradation of extracellular collagen. Furthermore, CD36, a membrane transporter of long chain fatty acids, was discovered to play a critical role in regulating the trafficking of collagen and lysosomal degradation. Finally, using a pharmacogenomics approach, caffeic acid was identified to be a compound which can be systemically administered, and reduced RF in pre‐clinical models.These data, along with other reports in the literature, strongly point towards the use of metabolic drugs as a therapeutic strategy by which we can mitigate the deleterious effects of RF on cancer patients. More recently, we have also uncovered that metabolic dysregulation likely plays a similar role in the development of lymphedema, a common long‐term toxicity in women after breast cancer therapy. Finally, these findings have broad application to the increasing burden of fibrosis beyond cancer, wherein end‐stage renal, liver, cardiac, and pulmonary fibrosis accounts for up to 1/3 of the deaths around the world.Support or Funding InformationThe work is funded in part by the Canadian Institutes of Health Research, Genome Canada, the Canadian Cancer Society Research Institute, the Physicians Services Incorporated Foundation, the Harry Barberian Research Scholarship, the Mariano Elia Chair in Head and Neck Cancer Research, the Peter and Shelagh Godsoe Chair in Radiation Medicine, the Princess Margaret Cancer Centre Head and Neck Translational Program, the Princess Margaret Cancer Centre Radiation Medicine Program and the Ottawa Heart Institute Research Corporation, as well by philanthropic funding from the Jesse Rasch Foundation, the Wharton family, Joe’s Team and the Ministry of Health and Long‐Term Care.