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Effects of glutathione or polyamine depletion on in vivo thermosensitization
D T Laskowitz1, G B Elion, M W Dewhirst
1Department of Pathology, Duke University Medical Center, Durham, NC 27705.
Abstract:
Investigations with the melphalan-sensitive and -resistant human rhabdomyosarcoma xenografts TE-671 and TE-671 MR were performed to examine the effect of glutathione and polyamine modulation on thermosensitivity. Regimens of intraperitoneally injected and orally administered buthionine sulfoximine were utilized to achieve glutathione depletion to 8.7% and 13% of control levels in TE-671 and TE-671 MR, respectively. Animals treated with L-buthionine-S,R-sulfoximine and 42 degrees C or 43 degrees C hyperthermia for 70 min showed no detectable growth delays beyond those observed for hyperthermia alone. Hyperthermia at 42 degrees C of disaggregated TE-671 and TE-671 MR xenografts following growth in short-term culture was performed following preincubation with buthionine sulfoximine or 0.9% saline. Buthionine sulfoximine-mediated glutathione depletion produced a significant increase in hyperthermia-induced cytotoxicity only with TE-671 MR at 43 degrees C. Polyamine depletion was achieved with a 7-day orally administered course of MDL 72.175DA [(2R,5R)-6-heptyne,5-diamine dihydrochloride], an irreversible inhibitor of ornithine decarboxylase. Although this treatment caused significant depletion of intracellular putrescine and spermidine levels, spermine levels remained relatively unaffected. No significant growth delays were observed in either xenograft line for animals treated with MDL 72.175DA or MDL 72.175DA plus hyperthermia as compared with untreated controls. These results contrast with previous work performed in vitro showing synergism between glutathione or polyamine depletion and hyperthermia, and indicate that further studies are needed.
Insights
Glutathione depletion enhanced hyperthermia
Area of Science:
- Oncology
- Cancer Research
- Pharmacology
Background:
- Rhabdomyosarcoma xenografts TE-671 and TE-671 MR are used to study melphalan sensitivity.
- Glutathione and polyamine levels influence cellular responses to therapy.
- Thermosensitivity is a potential target in cancer treatment.
Purpose of the Study:
- To investigate the impact of glutathione and polyamine modulation on the thermosensitivity of rhabdomyosarcoma xenografts.
- To determine if depleting glutathione or polyamines enhances hyperthermia efficacy in vivo.
- To compare in vivo findings with previous in vitro studies.
Main Methods:
- Glutathione depletion using L-buthionine-S,R-sulfoximine in TE-671 and TE-671 MR xenografts.
- Polyamine depletion using MDL 72.175DA, an ornithine decarboxylase inhibitor.
- Exposure of xenografts to hyperthermia (42°C or 43°C) with or without drug treatment.
- Assessment of tumor growth delays and cytotoxicity.
Main Results:
- Glutathione depletion alone did not enhance hyperthermia-induced growth delays.
- Buthionine sulfoximine-mediated glutathione depletion significantly increased hyperthermia cytotoxicity only in TE-671 MR at 43°C.
- Polyamine depletion with MDL 72.175DA did not result in significant growth delays, even with hyperthermia.
- Intracellular putrescine and spermidine levels were reduced, but spermine levels remained unchanged after polyamine depletion.
Conclusions:
- Glutathione depletion shows limited efficacy in enhancing hyperthermia treatment for rhabdomyosarcoma xenografts in vivo.
- Polyamine depletion does not appear to sensitize these xenografts to hyperthermia in the tested conditions.
- Further research is required to understand the discrepancies between in vitro and in vivo results and to optimize combination therapies.