Ikaros is a mutational target for lymphomagenesis in Mlh1-deficient mice

Deficiencies in DNA mismatch repair (MMR) result in replication errors within key tumor suppressor genes or oncogenes, and cause hereditary nonpolyposis colorectal cancer (HNPCC). Hematological malignancy with microsatellite instability is also associated with defective MMR, but little is known about the target genes for MMR. Here we identified Ikaros, a master transcription factor of lymphoid lineage commitment and differentiation, as a mutational target in spontaneous and radiation-induced T-cell lymphomas in Mlh1-deficient mice. Three quarters of lymphomas lacked Ikaros protein expression, which resulted from a frameshift mutation that created a stop codon. Mononucleotide repeat sequences at 1029-1034(C)6 and 1567-1572(G)6 in Ikaros were mutational hot spots with a one-base deletion occurring with a frequency of 45 and 50%, respectively. Point mutations and splicing alterations were also observed. In total, 85% of the lymphomas showed aberrations in Ikaros. The characteristic of Mlh1-deficient lymphomas is harboring of multiple mutations simultaneously in the same tumor, displaying a combination of two frameshift mutations at different repeats, frameshift and point mutations, and/or deletion mutations. This is the first report of Ikaros mutations coupled with Mlh1 deficiency in lymphomagenesis.

Effects of glycine betaine on bone marrow death and intestinal damage by gamma rays and carbon ions

In this study, we investigated the effects of glycine betaine (GB) on bone marrow death and intestinal damage by gamma rays or carbon ions. C(3)H/He female mice received an i.p.-injection of GB before or after whole-body irradiation with gamma rays or 50 keV microm(-1) carbon ions. The irradiated mice were observed to determine the mortality for 30 days after exposure. Mice were also killed at 3.5 days after the exposure to determine the intestinal damage. The numbers of crypts per transverse circumference were counted using a microscope. For the bone marrow death, GB (93 mg GB per mouse) significantly (p < 0.05) increased the percentage survival for both radiations. For the intestinal damage, GB (93 mg GB per mouse) significantly (p < 0.05) increased the crypt survival for gamma rays, but not for carbon ions. GB might be a potential protector against normal tissue damage as a side effect in radiotherapy.

Significance of fractionated irradiation for the biological therapeutic gain of carbon ions

It is well established that the RBE (relative biological effectiveness) for cell killing depends on LET (linear energy transfer), and that a maximum RBE is observed at approximately 150 keV.micron-1. However, the therapeutic gain depends on the ratio of the RBEs for the effects on the cancer cell population and the effects on normal tissues. The RBE of a given radiation quality depends not only on LET but also on dose, biological system and effect, and irradiation conditions. There is no data available to answer the question: which LET is suitable to improve the biological therapeutic gain of carbon ions? Here, three different LET values of 290 MeV/u carbon ions were selected, and the relative biological effectiveness was compared between tumour-growth retardation and skin damage using a murine transplantable tumour. Larger RBE values for tumours after than the skin type were obtained when carbon ions of intermediate LET were delivered daily for 2 to 5 fractions. The biological therapeutic gain would be high for the carbon ion SOBP if the number of fractions were correctly selected in clinical trials.

Induction of asymmetrical type of chromosomal aberrations in cultured human lymphocytes by ion beams of different energies at varying LET from HIMAC and RRC

Frequencies of asymmetrical type of chromosome aberration were scored in cultured human blood lymphocytes irradiated with carbon and neon beams. Blood cells were irradiated with various doses to establish dose response curves for chromosome aberration frequency vs. dose, and chromosome preparation was made by conventional method. Dose response curves for the per cell frequencies of the dicentrics and centric rings as well as the excess amount of acentric fragments were described for 7 different qualities (LET = 22.4, 40.0, 41.5, 69.9, 70.0, 100.0 and 150 KeV/micrometer) of carbon and neon beams with three different energies, 135, 290 and 400 MeV/u. From the analysis of those dose response curves, the maximum effect was found in the region of LET value at near 70 KeV/micrometer together with linear expression in the response from all endpoints examined. The 135 MeV/u of carbons (69.9 KeV/micrometer) and neons(70.0 KeV/micrometer) showed linear response. The 290 MeV/u of carbons (100 KeV/m) and neons (150 KeV/micrometer) showed medium effects with different shape of response, linear with a plateau and upward concavity. The 2 carbon beams (41.5 and 40 KeV/micrometer) from 2 different accelerators showed much discrepancy in the response. RBE-LET relationship was also described by comparing the coefficient alpha of the 7 different dose responses. The peak (near 70 KeV/m) was localized close to that (80 KeV/m) for the survivals of dsb repair deficient cells (Eguchi-Kasai et al. 1998), but in different position from that previously reported in many other studies (100-200 KeV/mm). Identification of the RBEmax in the present study has yet to be definitive.