title: Dose and time dependent apoptotic response in a human melanoma cell line exposed to accelerated boron ions at four different LET.
abstract: The aim was to investigate and compare the influence of linear energy transfer (LET), dose and time on the induction of apoptosis in a human melanoma cell line exposed to accelerated light boron ((10)B) ions and photons. Cells were exposed in vitro to doses up to 6 Gy accelerated boron ions (40, 80, 125 and 160 eV nm(-1)) and up to 12 Gy photons (0.2 eV nm(-1)). The induction of apoptosis was measured up to 9 days after irradiation using morphological characterization of apoptotic cells and bodies. In parallel, measurements of cell-cycle distribution, monitored by DNA flow cytometry, and cell survival based on the clonogenic cell survival assay, were performed. In addition, the induction and repair of DNA double-strand breaks (DSB), using pulsed-field gel electrophoresis (PFGE) were studied. Accelerated boron ions induced a significant increase in apoptosis as compared with photons at all time points studied. At 1-5 h the percentage of radiation-induced apoptotic cells increased with both dose and LET. At the later time points (24-216 h) the apoptotic response was more complex and did not increase in a strictly LET-dependent manner. The early premitotic apoptotic cells disappeared at 24 h following exposure to the highest LET (160 eV nm(-1)). A postmitotic apoptotic response was seen after release of the dose-, time- and LET-dependent G2/M accumulations. The loss of clonogenic ability was dose- and LET-dependent and the fraction of un-rejoined DSB increased with increasing LET. Despite the LET-dependent clonogenic cell killing, it was not possible to measure quantitatively a LET-dependent apoptotic response. This was due to the different time course of appearance and disappearance of apoptotic cells.
authors: Department of Oncology-Pathology, Division of Medical Radiation Physics, Karolinska Institutet, Stockholm, Sweden. annelie.meijer@cck.ki.se
authors: A E
authors: AE
authors: Meijer
authors: A R-M
authors: AR
authors: Jernberg
authors: T
authors: T
authors: Heiden
authors: B
authors: B
authors: Stenerlöw
authors: L M
authors: LM
authors: Persson
authors: N
authors: N
authors: Tilly
authors: B K
authors: BK
authors: Lind
authors: M R
authors: MR
authors: Edgren
mesh_terms: D017209:Apoptosis; D001895:Boron / Q000627:therapeutic use*; D002455:Cell Division / Q000528:radiation effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000528:radiation effects; D004249:DNA Damage; D004260:DNA Repair; D016195:G2 Phase / Q000528:radiation effects; D006801:Humans; D018499:Linear Energy Transfer; D008545:Melanoma / Q000473:pathology / Q000532:radiotherapy*
chemical_list: D001895:Boron