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- Title
The SMAC mimetic BV6 sensitizes colorectal cancer cells to ionizing radiation by interfering with DNA repair processes and enhancing apoptosis.
- Authors
Hehlgans, Stephanie; Oppermann, Julius; Reichert, Sebastian; Fulda, Simone; Rödel, Claus; Rödel, Franz
- Abstract
<bold>Background: </bold>In the present study, we aimed to investigate the effect of counteracting inhibitor of apoptosis (IAP) proteins using the small molecule Second Mitochondria-derived Activator of Caspase (SMAC) mimetic BV6 in combination with ionizing radiation on apoptosis, cell cycle regulation, DNA double-strand break (DSB) repair, three-dimensional (3D) clonogenic survival and expression of IAPs in colorectal carcinoma cells.<bold>Material and Methods: </bold>Colorectal cancer cell lines (HCT-15, HT-29, SW480) were subjected to BV6 treatment (0-4 μM) with or without irradiation (2-8 Gy, single dose) followed by MTT, Caspase 3/7 activity, γH2AX/53BP1 foci assays, AnnexinV staining, cell cycle analysis, 3D colony forming assays and Western blotting (cellular IAP1 (cIAP1) and cIAP2, Survivin, X-linked IAP (XIAP)).<bold>Results: </bold>BV6 treatment decreased cell viability and significantly increased irradiation-induced apoptosis as analyzed by Caspase 3/7 activity, AnnexinV-positive and subG1 phase cells. While basal 3D clonogenic survival was decreased in a cell line-dependent manner, BV6 significantly enhanced cellular radiosensitivity of all cell lines in a concentration-dependent manner and increased the number of radiation-induced γH2AX/53BP1-positive foci. Western blot analysis revealed a markedly reduced cIAP1 expression at 4 h after BV6 treatment in all cell lines, a substantial reduction of XIAP expression in SW480 and HT-29 cells at 24 h and a slightly decreased cIAP2 expression in HCT-15 cells at 48 h after treatment. Moreover, single or double knockdown of cIAP1 and XIAP resulted in significantly increased residual γH2AX/53BP1-positive foci 24 h after 2 Gy and radiosensitization relative to control small interfering RNA (siRNA)-treated cells.<bold>Conclusion: </bold>The SMAC mimetic BV6 induced apoptosis and hampered DNA damage repair to radiosensitize 3D grown colorectal cancer cells. Our results demonstrate IAP targeting as a promising strategy to counteract radiation resistance of colorectal cancer cells.
- Subjects
PROTEIN metabolism; APOPTOSIS; CELL lines; COLON tumors; DNA; FLOW cytometry; FLUORESCENT antibody technique; GENETIC techniques; OLIGOPEPTIDES; RADIATION-sensitizing agents; RECTUM tumors; RNA; WESTERN immunoblotting; PHARMACODYNAMICS
- Publication
Radiation Oncology, 2015, Vol 10, Issue 1, p1
- ISSN
1748-717X
- Publication type
journal article
- DOI
10.1186/s13014-015-0507-4