Ionizing radiation abrogates the pro-tumorigenic capacity of cancer-associated fibroblasts co-implanted in xenografts

Abstract

Cancer-associated fibroblasts (CAFs) are abundantly present in solid tumors and affect tumorigenesis and therapeutic responses. In the context of clinical radiotherapy, the impact of irradiated CAFs to treatment outcomes is largely unexplored. Aiming at improving radiotherapy efficacy, we have here explored the effect of radiation on the inherent pro-tumorigenic capacity of CAFs in animals. Ionizing radiation was delivered to cultured CAFs as single-high or fractionated doses. Tumor development was compared in mice receiving A549 lung tumor cells admixed with irradiated or control CAFs. Biological mechanisms behind tumor growth regulation were investigated by quantitative histology and immunohistochemistry. Viability assessments confirmed that irradiated CAFs are fully functional prior to implantation. However, the enhanced tumorigenic effect observed in tumors co-implanted with control CAFs was abrogated in tumors established with irradiated CAFs. Experiments to ascertain fate of implanted fibroblasts showed that exogenously administered CAFs reside at the implantation site for few days, suggesting that tumor growth regulation from admixed CAFs take place during initial tumor formation. Our work demonstrate that irradiated CAFs lose their pro-tumorigenic potential in vivo, affecting angiogenesis and tumor engraftment. This finding propose a previously unknown advantageous effect induced by radiotherapy, adding to the direct cytotoxic effects on transformed epithelial cells.

Radiation-Induced Transformation of Immunoregulatory Networks in the Tumor Stroma

“…In response to IR (1 × 18 Gy), secreted levels of CTGF from human lung CAFs are reduced 3.5-fold compared to controls, suggesting that exposure to ablative radiation doses may exert anti-fibrotic effects on CAFs ( 118 ). However, in an animal model, ex vivo irradiated CAFs (1 × 18 Gy) co-implanted with A549 tumor cells induced tumors with similar extents of collagen deposition and inflammatory cell infiltration as tumors established with non-irradiated CAFs ( 116 ).…”

“…A recent preclinical study by Li and colleagues ( 113 ) demonstrated radiation (1 × 4 Gy) to enhance the tumor-promoting effects of CAFs, an effect that was associated with increased expression of CXCL12. However, the overall tumor regulatory properties of senescent or irradiated fibroblasts remain controversial, as other studies have observed no impact of (high-dose) irradiation on the tumor enhancing effects of fibroblasts, or even loss of pro-malignant properties ( 114 – 116 ).…”

Interaction between Fibroblasts and Immune Cells Following DNA Damage Induced by Ionizing Radiation

“…In vivo models demonstrate that irradiation of CAF (iCAF) changes protumorigenic features, reducing tumor engraftment and angiogenesis [26]. For example, CAFs facilitate tumor growth when co-transplanted into athymic nude mice together with human cancer cells.…”

“…For example, CAFs facilitate tumor growth when co-transplanted into athymic nude mice together with human cancer cells. However, CAFs pretreated with either single 18 Gy or fractionated 3 × 6 Gy radiation regimens, are unable to stimulate tumor growth [26]. Of note, implanted fibroblasts, both CAFs and iCAFs, are detected only in mice during the first week following transplantation, and no longer detected during the weeks two to four, suggesting that the transplanted CAFs and iCAFs gradually die in situ during the first days of experiment [26] (Figure 1).…”

Exploring the rationale for combining ionizing radiation and immune checkpoint blockade in head and neck cancer

“…Some groups have demonstrated that CAFs appear to be highly resistant to the cytotoxic effects of IR, even at high doses (51, 52) . However, Grinde et al demonstrated that greater engraftment kinetics when CAFs were mixed with tumor cells before transplantation were abrogated when the CAFs were irradiated prior to the mixture (53) . This effect was the same between 18Gyx1 and 6Gyx3 schemas.…”