Indomethacin lowers the threshold thermal exposure for hyperthermic radiosensitization and heat-shock inhibition of ionizing radiation-induced activation of NF-kappaB.
OBJECTIVE
It is well established that salicylate and several other non-steroidal anti-inflammatory agents (NSAID), including indomethacin, can activate the heat-shock response, albeit at high concentrations. This is significant since heat shock significantly alters the cellular cytotoxic response to ionizing radiation (IR). It was previously shown that heat shock, as well as NSAIDs, inhibits IR-induced activation of NF-kappaB and that NF-kappaB protects against IR-induced cytotoxicity. Hence, it is hypothesized that pretreatment with indomethacin before heating will lower the temperature and heating times required to inhibit the activation of NF-kappaB and induce significant hyperthermic radiosensitization.


METHODS
Experiments were performed in HeLa cell lines and the DNA-binding activity was determined by EMSA. Cellular radiosensitivity was determined by clonogenic assay.


RESULTS
HeLa cells pretreated with indomethacin showed a decrease in the temperature-time combination necessary to inhibit IR-induction of NF-kappaB DNA binding. In addition, clonogenic cell survival assays using identical conditions showed an indomethacin dose-dependent enhancement of hyperthermic radiosensitization. Thus, similar concentrations of indomethacin both lowered the threshold thermal exposure to inhibit activation of NF-kappaB DNA-binding and increased the sensitivity of tumour cells to hyperthermic radiosensitization-induced cytotoxicity. In HeLa cells treated with N-alpha-tosylphenylalanyl-chloromethyl ketone (TPCK), a serine protease inhibitor that blocks activation of NF-kappaB, an increase in radiosensitivity was observed. Interestingly, no additional cell killing was observed when heat shock was added to cells treated with TPCK before IR, suggesting a possible common cytotoxic pathway.


CONCLUSIONS
The results demonstrate that indomethacin lowers the temperature-time conbination necessary to induce several physiological processes associated with the heat-shock response. Furthermore, NSAID may be potential adjuvants in improving the clinical effectiveness of hyperthermia in radiation therapy.
Locke
J E
JE
Section of Cancer Biology, Radiation Oncology Center, Institute of Radiology, Washington University School of Medicine, Saint Louis, MO, USA.
Bradbury
C M
CM
Wei
S J
SJ
Shah
S
S
Rene
L M
LM
Clemens
R A
RA
Roti Roti
J
J
Horikoshi
N
N
Gius
D
D
D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D003114:Colony-Forming Units Assay; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D006367:HeLa Cells; D000076249:Heat Shock Transcription Factors; D006358:Hot Temperature; D006801:Humans; D006979:Hyperthermia, Induced; D007213:Indomethacin / Q000494:pharmacology*; D016328:NF-kappa B / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects*; D011836:Radiation Tolerance / Q000187:drug effects*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D014108:Tosylphenylalanyl Chloromethyl Ketone / Q000494:pharmacology; D014157:Transcription Factors
D000894:Anti-Inflammatory Agents, Non-Steroidal; D004268:DNA-Binding Proteins; D000076249:Heat Shock Transcription Factors; D016328:NF-kappa B; D011838:Radiation-Sensitizing Agents; D014157:Transcription Factors; D014108:Tosylphenylalanyl Chloromethyl Ketone; D007213:Indomethacin