TGF-B3 Dependent Modification of Radiosensitivity in Reporter Cells Exposed to Serum from Whole-Body Low Dose-Rate Irradiated Mice

Abstract

Prior findings in vitro of a TGF-β3 dependent mechanism induced by low dose-rate irradiation and resulting in increased radioresistance and removal of low dose hyper-radiosensitivity (HRS) was tested in an in vivo model. DBA/2 mice were given whole-body irradiation for 1 h at low dose-rates (LDR) of 0.3 or 0.03 Gy/h. Serum was harvested and added to RPMI (4% mouse serum and 6% bovine serum).This medium was transferred to reporter cells (T-47D breast cancer cells or T98G glioblastoma cells). The response to subsequent challenge irradiation of the reporter cells was measured by the colony assay. While serum from unirradiated control mice had no effect on the radiosensitivity in the reporter cells, serum from mice given 0.3 Gy/h or 0.03 Gy/h for 1 h removed HRS and also increased survival in response to doses up to 5 Gy. The effect lasted for at least 15 months after irradiation. TGF-β3 neutralizer added to the medium containing mouse serum inhibited the effect. Serum from mice given irradiation of 0.3 Gy/h for 1 h and subsequently treated with iNOS inhibitor 1400W did not affect radiosensitivity in reporter cells; neither did serum from the unirradiated progeny of mice given 1h LDR whole-body irradiation.

Low-Dose-Rate Irradiation for 1 Hour Induces Protection Against Lethal Radiation Doses but Does Not Affect Life Span of DBA/2 Mice

“…In our previous studies, we found that radioprotective effects were seen in reporter cells exposed to serum from primed mice even when the serum was harvested up to 15 months after priming irradiation. 24 In both cases, involvement of TGF-b3 and iNOS activity was demonstrated, 23,24,26 which makes it tempting to speculate that TGF-b3 and iNOS activity may play a role in the adaptive effect observed in Figures 1 and 2. However, this remains to be further investigated.…”

“…26 In the experiments with reporter cells exposed to serum from irradiated mice, the effect was also seen for 3 cGy/h. 24 The effect seems thus to be dose independent as long as the dose rate is within a certain window and the irradiation time is long enough. Our data confirm that the used priming dose induced similar mechanisms in mice as in human cell cultures.…”

“…The effect of the serum was seen to depend on TGF-β3 during reporter cell exposure and on inducible nitric oxide synthase (iNOS) activity in the mice before the serum was harvested. 24 …”

“…The effect of the serum was seen to depend on TGF-b3 during reporter cell exposure and on inducible nitric oxide synthase (iNOS) activity in the mice before the serum was harvested. 24 In the light of these results, we wondered if the mechanisms activated in the mouse body by the priming dose could not only protect reporter cells against a challenge dose but perhaps even improve the mouse survival after a whole-body, lethal challenge dose (LD 50 ). We conclude that whole-body preirradiation with 30 cGy/h protects DBA/2 mice against a subsequent single whole-body LD 50 (9-9.5 Gy) challenge dose, but it does not affect the life span of mice not given a challenge dose.…”

Differential miRNA expression profiling reveals miR-205-3p to be a potential radiosensitizer for low- dose ionizing radiation in DLD-1 cells

“…This LDHRS phenomenon appears as an opportunity to decrease the IR doses used in RT [ 9 , 11 , 15 , 24 – 26 ], decreasing toxicity and side effects of conventional therapy. In addition, it was reported that serum from 0.3–0.03 Gy irradiated DBA/2 mice allowed an increased radioresistance and viability of non-irradiated breast and glioblastoma cell lines [ 27 ], which suggested that exposure to low doses IR would also diminish bystander effect of RT.…”