Increased glucose influx and glycogenesis in lung cancer cells surviving after irradiation

Purpose: Lung cancer is considered as one of the most frequent malignancies worldwide. Radiotherapy is the main treatment modality applied for locally advanced disease, but remnant surviving cancer tissue results in disease progression in the majority of irradiated lung carcinomas. Metabolic reprogramming is regarded as a cancer hallmark and is associated with resistance to radiation therapy. Here, we explored metabolic alterations possibly related to cancer cell radioresistance.

Materials and methods: We compared the expression of metabolism-related enzymes in the parental A549 lung cancer cell line along with two new cell lines derived from A549 cells after recovery from three (A549-IR3) and six (A549-IR6) irradiation doses with 4 Gy. Differential GLUT1 and GYS1 expression on proliferation and radioresistance were also comparatively investigated.

Results: A549-IR cells displayed increased extracellular glucose absorption, and enhanced mRNA and protein levels of the GLUT1 glucose transporter. GLUT1 inhibition with BAY-876, suppressed cell proliferation and the effect was significantly more profound on A549-IR3 cells. Protein levels of molecules associated with aerobic or anaerobic glycolysis, or the phosphate pentose pathway were similar in all three cell lines. However, glycogen synthase 1 (GYS1) was upregulated, especially in the A549-IR3 cell line, suggestive of glycogen accumulation in cells surviving post irradiation. GYS1-gene silencing repressed the proliferation capacity of A549, but this increased their radioresistance. The radio-protective effect of the suppression of proliferative activity induced by GYS1 silencing did not protect A549-IR3 cells against further irradiation.

Conclusions: These findings indicate that GYS1 activity is a critical component of the metabolism of lung cancer cells surviving after fractionated radiotherapy. Targeting the glycogen metabolic reprogramming after irradiation may be a valuable approach to pursue eradication of the post-radiotherapy remnant of disease.