title: Caffeine eliminates gamma-ray-induced G2-phase delay in human tumor cells but not in normal cells.
abstract: It has been known for many years that caffeine reduces or eliminates the G2-phase cell cycle delay normally seen in human HeLa cells or Chinese hamster ovary (CHO) cells after exposure to X or gamma rays. In light of our recent demonstration of a consistent difference between human normal and tumor cells in a G2-phase checkpoint response in the presence of microtubule-active drugs, we examined the effect of caffeine on the G2-phase delays after exposure to gamma rays for cells of three human normal cell lines (GM2149, GM4626, AG1522) and three human tumor cell lines (HeLa, MCF7, OVGI). The G2-phase delays after a dose of 1 Gy were similar for all six cell lines. In agreement with the above-mentioned reports for HeLa and CHO cells, we also observed that the G2-phase delays were eliminated by caffeine in the tumor cell lines. In sharp contrast, caffeine did not eliminate or even reduce the gamma-ray-induced G2-phase delays in any of the human normal cell lines. Since caffeine has several effects in cells, including the inhibition of cAMP and cGMP phosphodiesterases, as well as causing a release of Ca(++) from intracellular stores, we evaluated the effects of other drugs affecting these processes on radiation-induced G2-phase delays in the tumor cell lines. Drugs that inhibit cAMP or cGMP phosphodiesterases did not eliminate the radiation-induced G2-phase delay either separately or in combination. The ability of caffeine to eliminate radiation-induced G2-phase delay was, however, partially reduced by ryanodine and eliminated by thapsigargin, both of which can modulate intracellular calcium, but by different mechanisms. To determine if caffeine was acting through the release of calcium from intracellular stores, calcium was monitored in living cells using a fluorescent calcium indicator, furaII, before and after the addition of caffeine. No calcium release was seen after the addition of caffeine in either OVGI tumor cells or GM2149 normal cells, even though a large calcium release was measured in parallel experiments with ciliary neurons. Thus it is likely that caffeine is eliminating the radiation-induced G2-phase delay through a Ca(++)-independent mechanism, such as the inhibition of a cell cycle-regulating kinase.
authors.affiliation: Department of Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523-1673, USA.
authors.forename: Mitra N
authors.initials: MN
authors.lastname: Jha
authors.forename: James R
authors.initials: JR
authors.lastname: Bamburg
authors.forename: Barbara W
authors.initials: BW
authors.lastname: Bernstein
authors.forename: Joel S
authors.initials: JS
authors.lastname: Bedford
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000037:antagonists & inhibitors; D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000037:antagonists & inhibitors; D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone / Q000494:pharmacology; D000818:Animals; D001943:Breast Neoplasms / Q000473:pathology; D002110:Caffeine / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002277:Carcinoma / Q000473:pathology; D002645:Chickens; D003703:Demecolcine / Q000494:pharmacology; D004351:Drug Resistance; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects; D016195:G2 Phase / Q000187:drug effects* / Q000528:radiation effects; D005720:Gamma Rays / Q000009:adverse effects*; D006367:HeLa Cells / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D008938:Mitosis / Q000187:drug effects / Q000528:radiation effects; D014411:Neoplastic Stem Cells / Q000166:cytology / Q000187:drug effects* / Q000528:radiation effects; D009474:Neurons / Q000187:drug effects; D010051:Ovarian Neoplasms / Q000473:pathology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011799:Quinazolines / Q000494:pharmacology; D011836:Radiation Tolerance / Q000187:drug effects; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects; D019284:Thapsigargin / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects
chemical_list: C446602:4-((3,4-(methylenedioxy)benzyl)amino)-6-methoxyquinazoline; D002121:Calcium Channel Blockers; D010726:Phosphodiesterase Inhibitors; D011799:Quinazolines; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone; D002110:Caffeine; D019284:Thapsigargin; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D003703:Demecolcine