A low-pH culture condition enhances the radiosensitizing effect of wortmannin.
OBJECTIVE
The radiosensitizing effect of wortmannin on human tumor cells in a low-pH microenvironment was compared with that in a neutral-pH environment.


METHODS
A172 human glioblastoma cells, A549 human lung adenocarcinoma cells, and HMV-1 human melanoma cells were treated with 20 microM wortmannin 2 h before irradiation, and cell survival was examined. A low-pH microenvironment was simulated by exposing cells to low-pH culture medium for 24 h before wortmannin treatment. The effects of wortmannin on the repair of DNA double-strand breaks (dsbs) after 50-Gy irradiation in both low- and neutral-pH conditions were measured by pulsed-field gel electrophoresis. Expression of the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) in low-pH conditions was also compared with that in neutral-pH conditions by Western blot analysis.


RESULTS
The radiosensitizing effect of wortmannin was greater in low-pH cultures than in neutral-pH cultures for all cell lines. The fast-rejoining component of DNA dsb repair was inhibited more strongly in low-pH than in neutral-pH conditions, although there was little difference in DNA-PKcs expression between groups.


CONCLUSIONS
The low-pH culture condition, which was designed to mimic the microenvironment of the central tumor mass in actively proliferating solid tumors, enhanced the radiosensitizing effect of wortmannin by inhibiting the fast-rejoining component of DNA dsb repair and by prolonging the retention of nonrejoined DNA dsbs.
Department of Radiological Sciences, Ibaraki Prefectural University of Health Sciences, Ami-machi, Ibaraki, Japan.
S
S
Okada
K
K
Ono
N
N
Hamada
T
T
Inada
N
N
Kubota
D000230:Adenocarcinoma / Q000532:radiotherapy; D000730:Androstadienes / Q000494:pharmacology*; D002470:Cell Survival / Q000528:radiation effects; D003470:Culture Media / Q000737:chemistry*; D004260:DNA Repair; D004273:DNA, Neoplasm / Q000502:physiology / Q000528:radiation effects*; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D005909:Glioblastoma / Q000532:radiotherapy; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008175:Lung Neoplasms / Q000532:radiotherapy; D008545:Melanoma / Q000532:radiotherapy; D009363:Neoplasm Proteins / Q000378:metabolism; D009369:Neoplasms / Q000378:metabolism / Q000532:radiotherapy*; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D013997:Time Factors; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000528:radiation effects; D000077191:Wortmannin
D000730:Androstadienes; D003470:Culture Media; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011838:Radiation-Sensitizing Agents; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; D000077191:Wortmannin