Paclitaxel restores radiation-induced apoptosis in a bcl-2-expressing, radiation-resistant lymphoma cell line.
OBJECTIVE
To restore radiation-induced apoptosis in a bcl-2-expressing, radiation-resistant murine lymphoma cell line (LY-ar) by pretreatment with paclitaxel (Taxol). Because this cell line also has high intracellular levels of glutathione (GSH), reportedly due to the bcl-2 expression and involved in the cell's antioxidant functions, paclitaxel treatment was correlated with GSH levels.


METHODS
LY-ar cells were pretreated with paclitaxel and then irradiated with 5 Gy. Apoptosis was measured by DNA fragmentation 6 h later. Dose response and time course experiments were performed. Intracellular GSH levels were measured after treatment. Cell survival analysis was performed for various paclitaxel concentrations +/- 5 Gy.


RESULTS
LY-ar cells pretreated with 0 nM, 10 nM, 25 nM, and 50 nM paclitaxel for 20 h underwent apoptosis at 2%, 15%, 25%, and 22%, respectively. With the addition of 5-Gy irradiation, LY-ar cell apoptosis increased to 4%, 30%, 49%, and 57%. Maximal apoptosis was detected with a paclitaxel pretreatment time of 20 h. Intracellular GSH levels were reduced by nearly 50% with paclitaxel pretreatment. Surviving fractions (SFs) with 0 nM, 10 nM, 25 nM, and 50 nM paclitaxel and 0 Gy were 1.0, 0.50, 0.08, and 0.05, respectively. SFs with 0 nM, 10 nM, 25 nM, and 50 nM paclitaxel and 5 Gy were 0.009, 0.003, 3 x 10(-5), and 1 x 10(-5), respectively.


CONCLUSIONS
Radiation-induced apoptosis in LY-ar cells was restored by pretreatment with paclitaxel. This correlated with lowered levels of intracellular GSH. Cell survival analysis indicated that the combination of Taxol and radiation on cell killing was greater than additive.
Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA. lnnguyen@mdanderson.org
L N
LN
Nguyen
A
A
Munshi
M L
ML
Hobbs
M D
MD
Story
R D
RD
Meyn
D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D005978:Glutathione / Q000187:drug effects / Q000378:metabolism; D008223:Lymphoma / Q000378:metabolism / Q000503:physiopathology* / Q000532:radiotherapy; D051379:Mice; D009363:Neoplasm Proteins / Q000378:metabolism*; D017239:Paclitaxel / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D011836:Radiation Tolerance; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D011853:Radiobiology; D011879:Radiotherapy Dosage; D013997:Time Factors; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000528:radiation effects
D000972:Antineoplastic Agents, Phytogenic; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011838:Radiation-Sensitizing Agents; D005978:Glutathione; D017239:Paclitaxel