Does timing matter in radiotherapy of hepatocellular carcinoma? An experimental study in mice

• Published in: Cancer medicine (Malden, MA) MA), 2021-11, Vol.10 (21), p.7712-7725
• Main Authors: Hassan, Soha A., Ali, Amira A. H., Sohn, Dennis, Flögel, Ulrich, Jänicke, Reiner U., Korf, Horst‐Werner, Gall, Charlotte
• Format: Article
• Language: English
• Subjects: Animal research; Animals; Blood Cell Count; Cancer Biology; Carcinoma, Hepatocellular - blood; Carcinoma, Hepatocellular - genetics; Carcinoma, Hepatocellular - pathology; Carcinoma, Hepatocellular - radiotherapy; Cell cycle; Cell Proliferation; Chronotherapy; Clock gene; clock genes; CLOCK Proteins - genetics; DNA Damage; Down-Regulation; Experiments; Gene Expression; Hepatocellular carcinoma; Histones - analysis; Ki-67 Antigen - analysis; Ki67; Kinases; Liver cancer; Liver Neoplasms - blood; Liver Neoplasms - genetics; Liver Neoplasms - pathology; Liver Neoplasms - radiotherapy; Magnetic resonance imaging; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Organ Culture Techniques; Period 1 protein; Period 2 protein; Radiation therapy; radiotherapy; Rhythms; Side effects; Time Factors; Tumors; γ‐H2AX
• ISSN: 2045-7634; 2045-7634
• DOI: 10.1002/cam4.4277

This study investigates whether a chronotherapeutic treatment of hepatocellular carcinoma (HCC) may improve treatment efficacy and mitigate side effects on non‐tumoral liver (NTL). HCC was induced in Per2::luc mice which were irradiated at four time points of the day. Proliferation and DNA‐double strand breaks were analyzed in irradiated and nonirradiated animals by detection of Ki67 and γ‐H2AX. Prior to whole animal experiments, organotypic slice cultures were investigated to determine the dosage to be used in whole animal experiments. Irradiation was most effective at the proliferation peaks in HCC at ZT02 (early inactivity phase) and ZT20 (late activity phase). Irradiation effects on NTL were minimal at ZT20. As compared with NTL, nonirradiated HCC revealed disruption in daily variation and downregulation of all investigated clock genes except Per1. Irradiation affected rhythmic clock gene expression in NTL and HCC at all ZTs except at ZT20 (late activity phase). Irradiation at ZT20 had no effect on total leukocyte numbers. Our results indicate ZT20 as the optimal time point for irradiation of HCC in mice at which the ratio between efficacy of tumor treatment and toxic side effects was maximal. Translational studies are now needed to evaluate whether the late activity phase is the optimal time point for irradiation of HCC in man. To elucidate whether a chronotherapeutic approach may improve the efficacy of radiotherapy for hepatocellular carcinoma (HCC) which was experimentally induced in mice by defining the optimal time point at which the HCC is more radiosensitive, while the surrounding non‐tumoral liver is more radioresistant to the damaging effects. Our results from HCC‐bearing mice irradiated at four different time points allowed us to define ZT20 (late activity phase) as an optimal time point to apply radiotherapy because of least toxicity and similar efficacy against HCC as compared to other tested ZTs. Translational studies are required to confirm the findings for HCC patients.