1. Effects of Ultra-high doserate FLASH Irradiation on the Tumor Microenvironment in Lewis Lung Carcinoma: Role of Myosin Light Chain
- Author
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Cameron J. Koch, Marjan Rafat, Young Eun Kim, Billy W. Loo, Emil Schüler, Myeoung Su Kim, Jung-Min Oh, Irving L. Weissman, Hyo-Soo Kim, Hyung-Seok Choi, G-One Ahn, Seung-Hee Gwak, Peter G. Maxim, Rie von Eyben, Beom-Ju Hong, Frederik M. Lartey, and Dawit Oh
- Subjects
CD31 ,Male ,Cancer Research ,Myosin light-chain kinase ,Myosin Light Chains ,Cell ,CD8-Positive T-Lymphocytes ,Naphthalenes ,030218 nuclear medicine & medical imaging ,Histones ,03 medical and health sciences ,Carcinoma, Lewis Lung ,Mice ,0302 clinical medicine ,Western blot ,Tumor Microenvironment ,Medicine ,Animals ,Radiology, Nuclear Medicine and imaging ,Tumor microenvironment ,Radiation ,medicine.diagnostic_test ,Radiotherapy ,business.industry ,Lewis lung carcinoma ,Radiotherapy Dosage ,Azepines ,Molecular biology ,Mice, Inbred C57BL ,Platelet Endothelial Cell Adhesion Molecule-1 ,medicine.anatomical_structure ,Oncology ,Cell culture ,030220 oncology & carcinogenesis ,Blood Vessels ,business ,Reactive Oxygen Species ,Immunostaining - Abstract
Purpose To investigate whether the vascular collapse in tumors by conventional dose rate (CONV) irradiation (IR) would also occur by the ultra-high dose rate FLASH IR. Methods and Materials Lewis lung carcinoma (LLC) cells were subcutaneously implanted in mice. This was followed by CONV or FLASH IR at 15 Gy. Tumors were harvested at 6 or 48 hours after IR and stained for CD31, phosphorylated myosin light chain (p-MLC), γH2AX (a surrogate marker for DNA double strand break), intracellular reactive oxygen species (ROS), or immune cells such as myeloid and CD8α T cells. Cell lines were irradiated with CONV IR for Western blot analyses. ML-7 was intraperitoneally administered daily to LLC-bearing mice for 7 days before 15 Gy CONV IR. Tumors were similarly harvested and analyzed. Results By immunostaining, we observed that CONV IR at 6 hours resulted in constricted vessel morphology, increased expression of p-MLC, and much higher numbers of γH2AX-positive cells in tumors, which were not observed with FLASH IR. Mechanistically, MLC activation by ROS is unlikely, because FLASH IR produced significantly more ROS than CONV IR in tumors. In vitro studies demonstrated that ML-7, an inhibitor of MLC kinase, abrogated IR-induced γH2AX formation and disappearance kinetics. Lastly, we observed that CONV IR when combined with ML-7 produced some effects similar to FLASH IR, including reduction in the vasculature collapse, fewer γH2AX-positive cells, and increased immune cell influx to the tumors. Conclusions FLASH IR produced novel changes in the tumor microenvironment that were not observed with CONV IR. We believe that MLC activation in tumors may be responsible for some of the microenvironmental changes differentially regulated between CONV and FLASH IR.
- Published
- 2020