THE PREVENTION OF RADIATION-INDUCED MALIGNANCIES IN LI-FRAUMENI SYNDROME

Purpose:

Li-Fraumeni Syndrome (LFS) is a genetic disorder associated with a significant risk of early-onset cancer. This condition is driven by germline mutations in the TP53 gene which plays a primary role in the regulation of the radiation response. Aberrant TP53 function contributes to radiation vulnerability and a greater risk of secondary, radiation-induced malignancies. As a result, therapeutic options for LFS patients are often limited to exclude radiotherapy (RT), which may otherwise be beneficial for the treatment of primary tumours. Data from our lab demonstrate an aberrant transcriptomic response to irradiation (IR) in mutant p53 patient skin fibroblasts compared to wildtype; however, it is unknown whether reprogramming this radiation response can decrease the risk of radiation-induced malignancy in LFS. Metformin, a commonly prescribed anti-diabetic drug, is associated with lower cancer incidence and may decrease cancer-related mortality in murine LFS models. In addition to its potential anti-tumourigenicity, recent studies have shed light on the ability of metformin to prevent IR-induced damage in normal tissue; hence, we hypothesize that metformin can reprogram the radiation response to protect against radiation injury and delay the onset of radiation-induced tumours in LFS.

Materials and Methods:

To establish a murine model of radiation-induced tumours in LFS, and to investigate whether metformin can delay tumour onset in this model, whole-body or localized IR were administered to mice harboring a hotspot TP53^R172H/+mutation in the presence and absence of metformin. Serial MRI was conducted to monitor for tumour development. To understand the effect of metformin on the mutant p53 radiation response in vivo, a similar murine workflow was established and irradiated skin was collected longitudinally from untreated and metformin-treated cohorts for whole transcriptome sequencing. Sequencing data were functionally validated in a separate cohort of mice using flow cytometry. In parallel, we performed RNA sequencing on LFS patient fibroblasts to characterize the effect of metformin on the human radiation response.

Results:

We demonstrate that IR accelerates tumour onset in TP53^R172H/+ mice, and that metformin significantly delays the development of tumours within the radiation field. Moreover, transcriptomic analyses of both patient and murine samples revealed that metformin upregulates apoptosis following IR. Flow cytometry analysis of murine tumours and irradiated skin tissue validated these findings, demonstrating that metformin promotes the apoptosis-driven clearance of damaged, potentially tumourigenic cells following IR.

Conclusions:

Overall, we show that metformin delays radiation-induced tumour onset in LFS mice, and have begun to characterize the biology underpinning this reprogrammed response to IR. This study is the first to highlight metformin as a radioprotective agent in the context of germline mutant p53, with the potential to broaden RT treatment options for LFS patients.