Enhancement of radiation sensitivity with BH3I-1 in non-small cell lung cancer.
BACKGROUND
Anti-apoptotic proteins, such as Bcl-2 and Bcl-xL, are frequently over-expressed in human malignancies, and this is correlated with resistance to chemotherapeutic drugs and gamma- radiation. Recently identified small organic molecules capable of inhibiting Bcl-2 and/or Bcl-xL function, may enhance radiation sensitivity of cancer cells in which they are over expressed. We examined whether specific blockade of the BH3-domain binding to Bcl-xL could sensitize cancer cells to gamma- radiation.


METHODS
Human non-small-cell lung cancer H460 cells with wild-type p53 and H1792 cells with mutant p53 were exposed to various doses of radiation and/or BH3I-1 and for different points of time to BH3I-1 treatment. XTT and clonogenic survival assays were used to evaluate the growth-inhibitory effects of the antagonist BH3I-1, ionizing radiation or both. Western blot analysis was used to examine the cellular effect of the expression of Bcl-xL, Bax, and p53. Apoptosis and cell cycle distribution were analyzed by confocal microscopy with Hoechst 33258 staining and cytochrome c, and flow cytometry, respectively.


RESULTS
BH3I-1 appeared to induce a dose- and time-dependent apoptosis in H460 and H1792 cells, regardless of p53 status. After 2 days of BH3I-1 treatment, the cells that remained attached were exposed to ionizing radiation. Followed by clonogenic assay, BH3I-1 treatment enhanced the radiation sensitivity of H1792 surviving cells with mutant p53, but not in H460 cells with wild-type p53. A transient time-dependent cell cycle blockade at G2-M phase was identified for H1792 cells without subsequent modification of cell cycle distribution.


CONCLUSIONS
These findings suggest a potential role for the small molecule inhibitor as a novel radiation sensitizer in non-small cell lung cancer.
Roa
W
W
Department of Radiation Oncology, Cross Cancer Institute, Edmonton, Alberta, Canada. wilsonro@cancerboard.ab.ca
Chen
H
H
Alexander
A
A
Gulavita
S
S
Thng
J
J
Sun
X J
XJ
Petruk
K
K
Moore
R
R
D002289:Carcinoma, Non-Small-Cell Lung / Q000532:radiotherapy*; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D053938:DNA Fragmentation / Q000187:drug effects / Q000528:radiation effects; D005434:Flow Cytometry; D006801:Humans; D007457:Iodine Radioisotopes / Q000494:pharmacology*; D008175:Lung Neoplasms / Q000532:radiotherapy*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D013844:Thiazoles / Q000494:pharmacology*; D045162:Thiazolidinediones
C503945:5-(4-bromobenzylidene)-alpha-isopropyl-4-oxo-2-thioxo-3-thazolidineacetic acid; D007457:Iodine Radioisotopes; D011838:Radiation-Sensitizing Agents; D013844:Thiazoles; D045162:Thiazolidinediones