Impact of DNA repair and reactive oxygen species levels on radioresistance in pancreatic cancer.

Purpose: Radioresistance in pancreatic cancer patients remains a critical obstacle to overcome. Understanding the molecular mechanisms underlying radioresistance may achieve better response to radiotherapy and thereby improving the poor treatment outcome. The aim of the present study was to elucidate the mechanisms leading to radioresistance by detailed characterization of isogenic radioresistant and radiosensitive cell lines.
Methods: The human pancreatic cancer cell lines, Panc-1 and MIA PaCa-2 were repeatedly exposed to radiation to generate radioresistant (RR) isogenic cell lines. The surviving cells were expanded, and their radiosensitivity was measured using colony formation assay. Tumor growth delay after irradiation was determined in a mouse pancreatic cancer xenograft model. Gene and protein expression were analyzed using RNA sequencing and Western blot, respectively. Cell cycle distribution and apoptosis (Caspase 3/7) were measured by FACS analysis. Reactive oxygen species generation and DNA damage were analyzed by detection of CM-H ₂ DCFDA and γH2AX staining, respectively. Transwell chamber assays were used to investigate cell migration and invasion.
Results: The acquired radioresistance of RR cell lines was demonstrated in vitro and validated in vivo. Ingenuity pathway analysis of RNA sequencing data predicted activation of cell viability in both RR cell lines. RR cancer cell lines demonstrated greater DNA repair efficiency and lower basal and radiation-induced reactive oxygen species levels. Migration and invasion were differentially affected in RR cell lines.
Conclusions: Our data indicate that repeated exposure to irradiation increases the expression of genes involved in cell viability and thereby leads to radioresistance. Mechanistically, increased DNA repair capacity and reduced oxidative stress might contribute to the radioresistant phenotype.
Competing Interests: Declaration of Competing Interest Prof. Combs reports grants from Deutsche Forschungsgemeinschaft, non-financial support from Deutsches Konsortium für Translationale Krebsforschung, during the conduct of the study; personal fees and non-financial support from Roche, personal fees and non-financial support from AstraZeneca, personal fees and non-financial support from Medac, personal fees and nonfinancial support from Dr. Sennewald Medizintechnik, personal fees and non-financial support from Elekta, personal fees and non-financial support from Accuray, personal fees and nonfinancial support from BMS, personal fees and non-financial support from Brainlab, personal fees and non-financial support from Daiichi Sankyo, personal fees and non-financial support from Icotec, outside the submitted work.
(Copyright © 2021 The Author(s). Published by Elsevier B.V. All rights reserved.)