Differential mechanisms of radiosensitization by 2-deoxy-D-glucose in the monolayers and multicellular spheroids of a human glioma cell line.
In vitro studies using monolayer cultures of human tumor cell lines have shown that 2-DG selectively inhibits energy-dependent DNA repair and cellular recovery processes in cancer cells. However, monolayer cultures differ greatly from the complex environmental conditions generated in solid tumors that develop inhomogeneous hypoxic and necrotic regions. In contrast, multicellular spheroids mimic heterogeneous cellular behavior and the consequent functional characteristics of in vivo solid tumors, and serve as important in vitro model to investigate tumor biology and responses to potential therapeutic agents. The present study compares the radiomodification by 2-DG in monolayer cultures and spheroids of a human glioma cell line (BMG-1) to gain insight into the effects in solid tumors. In spheroids, the glucose consumption (2.1 p mole/cell/h) and lactate production (3.67 p mole/cell/h) was nearly 2-3 fold higher than in monolayer cells (0.83 and 1.43 p mole/cell/h respectively). Presence of 2-DG (5 mM) for 2-4 h inhibited the glucose usage and lactate production by 70% in spheroids, while a 35% reduction was observed in monolayer cells. Under these conditions, 2-DG drastically enhanced the radiation-induced cell death of spheroids (by 2-3 folds); while a 40% increase was observed in monolayer cells. Radiosensitization by 2-DG in monolayer cells was primarily due to an increase in mitotic death (23%) linked to cytogenetic damage (micronuclei), whereas a profound induction of apoptosis (40%) accounted for the sensitization in spheroids. Although the Bcl-2 and Bax levels were significantly higher in spheroids, Bcl-2/Bax ratio was similar in monolayers and spheroids. Comet assay revealed a late onset of DNA breaks in the presence of 2- DG following irradiation only in spheroids, which corroborated well with the late onset of oxidative stress. 2-DG did not induce a significant cell cycle delay in monolayers, while a transient G(2) delay was apparent in spheroids.
Khaitan
Divya
D
Institute of Nuclear Medicine and Allied Sciences, Brig. S.K. Mazumdar Marg, Delhi, India.
Chandna
Sudhir
S
Arya
M B
MB
Dwarakanath
B S
BS
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D002869:Chromosome Aberrations / Q000187:drug effects / Q000528:radiation effects; D045304:Cytochromes c / Q000378:metabolism; D004260:DNA Repair / Q000187:drug effects / Q000528:radiation effects; D003847:Deoxyglucose / Q000097:blood / Q000493:pharmacokinetics / Q000494:pharmacology*; D005910:Glioma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D019344:Lactic Acid / Q000096:biosynthesis; D051379:Mice; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011838:Radiation-Sensitizing Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D018874:Spheroids, Cellular; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D019253:Proto-Oncogene Proteins c-bcl-2; D011838:Radiation-Sensitizing Agents; D017382:Reactive Oxygen Species; D051028:bcl-2-Associated X Protein; D019344:Lactic Acid; D045304:Cytochromes c; D003847:Deoxyglucose; D005947:Glucose