Abstract 4163: Enhanced immune response according to different radiation fractionations in colorectal cancer cell lines
Authors: Byun Sang Jun , Kim Shin , Seo Incheol , Lee Hye Won , Bae Sung Uk , Baek Seong Kyu , Jeong Woon Kyung , Park Seung Gyu , Choi Euncheol 
Published: April 2023

Abstract
Background: Concurrent chemoradiation therapy is standard treatment in locally advanced rectal cancer. 5-FU is a commonly used chemotherapeutic agent, and radiotherapy is delivered with conventional or short-course fractionations. Immunotherapy is a new strategy with systemic effect, and several combinations with other treatments including surgery, chemotherapy, or radiotherapy in various sequences are evaluated. After irradiation, there is immunogenic changes in the tumor microenvironment, which is expected to improve the response of the added immunotherapy. The purpose of this study is to investigate the difference in immune response according to the radiation fractionation schedules after irradiation in various colon cancer cell lines.
Materials and Methods: The human colorectal cancer cell lines, DLD-1 and HCT116, were cultured and irradiated with total 1.8 Gy of X-rays in 10 fractions and 5 Gy of X-rays in 3 fractions using linear accelerator for 10 and 3 consecutive days. The mRNA expression levels of immune related genes including CD274, TREX1, CD74, IFNG, CALR, HMGB1, TGFB1 were evaluated using real-time PCR in 0, 3, and 7 days after irradiation.
Result: The mRNA expression levels of CD74, HMGB1 and CD274 were increased in both DLD-1 and HCT116 cell lines, and IFNG increased only in DLD-1. However, there was a difference in the increasing patterns over time between the two radiation fractionations. According to the radiation fractionation, increasement of the mRNA expression levels was more prominent in 1.8 Gy in 10 fractions than 5 Gy in 3 fractions. In addition, the radiation-resistant DLD-1 cell line showed a more marked increase in the levels of CD274 mRNA as well as other genes associated with CD274 than the radiation-sensitive HCT116 cells. Moreover, DLD-1 cell line, which is more resistant to radiation, showed more prominent elevation in CD274 mRNA level than HCT-116.
Conclusions: We could find that more fractionated irradiation schedule with smaller dose per fraction further increases the immune response. Even in radio-resistant tumor cells, better immune response could be expected after irradiation than radio-sensitive cells. It would be needed to verify the results in real tumor conditions, such as the tumor microenvironment containing immune cells and cancer-associate fibroblasts. It is also thought that studies on the appropriate time to use immunotherapeutic agent are needed.
Citation Format: Sang Jun Byun, Shin Kim, Incheol Seo, Hye Won Lee, Sung Uk Bae, Seong Kyu Baek, Woon Kyung Jeong, Seung Gyu Park, Euncheol Choi. Enhanced immune response according to different radiation fractionations in colorectal cancer cell lines. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4163.