Transient elevation of glycolysis confers radio-resistance by facilitating DNA repair in cells.
BACKGROUND
Cancer cells exhibit increased glycolysis for ATP production (the Warburg effect) and macromolecular biosynthesis; it is also linked with therapeutic resistance that is generally associated with compromised respiratory metabolism. Molecular mechanisms underlying radio-resistance linked to elevated glycolysis remain incompletely understood.


METHODS
We stimulated glycolysis using mitochondrial respiratory modifiers (MRMs viz. di-nitro phenol, DNP; Photosan-3, PS3; Methylene blue, MB) in established human cell lines (HEK293, BMG-1 and OCT-1). Glucose utilization and lactate production, levels of glucose transporters and glycolytic enzymes were investigated as indices of glycolysis. Clonogenic survival, DNA repair and cytogenetic damage were studied as parameters of radiation response.


RESULTS
MRMs induced the glycolysis by enhancing the levels of two important regulators of glucose metabolism GLUT-1 and HK-II and resulted in 2 fold increase in glucose consumption and lactate production. This increase in glycolysis resulted in resistance against radiation-induced cell death (clonogenic survival) in different cell lines at an absorbed dose of 5 Gy. Inhibition of glucose uptake and glycolysis (using fasentin, 2-deoxy-D-glucose and 3-bromopyruvate) in DNP treated cells failed to increase the clonogenic survival of irradiated cells, suggesting that radio-resistance linked to inhibition of mitochondrial respiration is glycolysis dependent. Elevated glycolysis also facilitated rejoining of radiation-induced DNA strand breaks by activating both non-homologous end joining (NHEJ) and homologous recombination (HR) pathways of DNA double strand break repair leading to a reduction in radiation-induced cytogenetic damage (micronuclei formation) in these cells.


CONCLUSIONS
These findings suggest that enhanced glycolysis generally observed in cancer cells may be responsible for the radio-resistance, partly by enhancing the repair of DNA damage.
Metabolic and Cell Signaling Group, Institute of Nuclear Medicine and Allied Sciences, Brig SK Mazumdar Road, New Delhi, Delhi, 110 054, India. anant@inmas.drdo.in.
Anant Narayan
AN
Bhatt
Metabolic and Cell Signaling Group, Institute of Nuclear Medicine and Allied Sciences, Brig SK Mazumdar Road, New Delhi, Delhi, 110 054, India. ankitvkc@gmail.com.
Ankit
A
Chauhan
Metabolic and Cell Signaling Group, Institute of Nuclear Medicine and Allied Sciences, Brig SK Mazumdar Road, New Delhi, Delhi, 110 054, India. suchit.khanna1985@gmail.com.
Suchit
S
Khanna
Metabolic and Cell Signaling Group, Institute of Nuclear Medicine and Allied Sciences, Brig SK Mazumdar Road, New Delhi, Delhi, 110 054, India. mahadev.kashi@gmail.com.
Yogesh
Y
Rai
Metabolic and Cell Signaling Group, Institute of Nuclear Medicine and Allied Sciences, Brig SK Mazumdar Road, New Delhi, Delhi, 110 054, India. saurabh_11may@yahoo.co.in.
Saurabh
S
Singh
Metabolic and Cell Signaling Group, Institute of Nuclear Medicine and Allied Sciences, Brig SK Mazumdar Road, New Delhi, Delhi, 110 054, India. soniravi09@rediffmail.com.
Ravi
R
Soni
Metabolic and Cell Signaling Group, Institute of Nuclear Medicine and Allied Sciences, Brig SK Mazumdar Road, New Delhi, Delhi, 110 054, India. namitaji@rediffmail.com.
Namita
N
Kalra
Metabolic and Cell Signaling Group, Institute of Nuclear Medicine and Allied Sciences, Brig SK Mazumdar Road, New Delhi, Delhi, 110 054, India. dwarakanathdrbs@gmail.com.
Bilikere S
BS
Dwarakanath
D019069:Cell Respiration; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects*; D045643:DNA Repair Enzymes / Q000378:metabolism; D004140:Dinitrophenols / Q000494:pharmacology; D006019:Glycolysis / Q000187:drug effects*; D057809:HEK293 Cells; D006801:Humans; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D011836:Radiation Tolerance
D004140:Dinitrophenols; D045643:DNA Repair Enzymes