Study On Amelioration Of Whole Abdominal Irradiation-induced Intestinal Injury In Mice By 3,3'-diindolylmethane And Study On A Role Of STAT3 In The Radiosensitivity Of Breast Cancer And Underlying Mechanisms

Intestinal injury caused by ionizing radiation is a catastrophic disease with limited effective therapies.3,3'-diindolylmethane(DIM),a potent antioxidant agent,has previously been shown to ameliorate hematopoietic injury in a murine model with total body irradiation,but its effects on ionizing radiation-induced intestinal damage are not clear.Here,we demonstrated that the administration of DIM not only protected mice against whole abdominal irradiation(WAI)-induced lethality and weight loss but also ameliorated crypt-villus structural and functional injury alteration of the small intestine.In addition,DIM significantly inhibited the WAI-induced reductions in Lgr5+ISCs and their progeny cells,including lysozyme+Paneth cells,Villin+enterocytes,and Ki67+instantaneous amplifying cells,and promoted small intestine repair.Notably,the expression of Nrf2 increased,while the number of apoptotic cells and the expression of ?H2AX decreased in the small intestines of DIM-treated mice compared to mice treated with a vehicle following WAI.In vitro,we demonstrated that DIM increased cell vitality.Moreover,these DIM-mediated alterations were related to the reduction in reactive oxygen species(ROS)levels and the increase of the expression of Nrf2 and its downstream genes HO-1 and NOQ1 in irradiated HIEC-6 cells.The DIM radioprotective effects on the intestine resulted in the restoration of the WAI-shifted gut bacteria composition in mice.Collectively,our findings demonstrate that the beneficial properties of DIM mitigate the intestinal injury caused by ionizing radiation,which provides a novel strategy for improving the therapeutic effects.Radiotherapy significantly improves the therapeutic outcomes and survival of breast cancer patients.However,the acquired resistance to this therapeutic modality is a major clinical challenge.Here we show that ionizing irradiation(IR)-induced phosphorylation of Signal transducer and activator of transcription 3(STAT3)at the Tyr705 residue and the induction of reactive oxygen species(ROS)in wild-type and radioresistant MDA-MB-231 and MDA-MB-468 triple-negative breast cancer(TNBC)cell lines.Comparing with the radiosensitive parental TNBC cells,significantly low levels of ROS and higher protein levels of pSTAT3 and Bcl-2 were observed in TNBC cells with acquired radioresistance.Moreover,knockdown of STAT3 by shRNA sensitized TNBC cells to IR.Niclosamide,a potent inhibitor of STAT3,overcame the radioresistance in TNBC cells via inhibition of STAT3 and Bcl-2 and induction of ROS.In combination with radiation,niclosamide treatment resulted in a significant increase of ROS generation and induction of apoptosis in parental and radioresistant TNBC cells in vitro and TNBC xenograft tumors in vivo.These findings demonstrate that activation of STAT3 and Bcl-2 and reduction of ROS contribute to the development of radioresistance in TNBC,and niclosamide acts as potent radiosensitizer via inhibiting STAT3 and Bcl-2 and increasing ROS generation in TNBC cells and xenograft tumors.Our findings suggest that niclosamide in combination with irradiation may offer an effective alternative approach for restoring the sensitivity of radioresistant TNBC cells to IR for improved therapeutic efficacy and outcomes.