Effect of 5-fluorouracil on cellular response to proton beam in esophageal cancer cell lines according to the position of spread-out Bragg peak

Impacts of the STING-IFNAR1-STAT1-IRF1 pathway on the cellular immune reaction induced by fractionated irradiation

Radiotherapy (RT) combined with immune checkpoint inhibitors (ICIs) has recently produced outstanding results and is expected to be adaptable for various cancers. However, the precise molecular mechanism by which immune reactions are induced by fractionated RT is still controversial. We aimed to investigate the mechanism of the immune response regarding multifractionated, long-term radiation, which is most often combined with immunotherapy. Two human esophageal cancer cell lines, KYSE-450 and OE-21, were irradiated by fractionated irradiation (FIR) daily at a dose of 3 Gy in 5 days per week for 2 weeks. Western blotting (WB), and RNA sequencing identified type I interferon (IFN) and the STING pathway as candidates which regulate immune response by FIR. We inhibited STING, IFNAR1, STAT1 and IRF1 and investigated the effects on the immune response in cancer cells and the invasion of surrounding immune cells. We herein revealed type I IFN-dependent immune reactions and the positive feedback of STING, IRF1 and phosphorylated STAT1 induced by FIR. Knocking out STING, IFNAR1, STAT1 and IRF1 resulted in a poorer immunological response than that in wild-type cells. The STING-knockout KYSE-450 cell line exhibited significantly less invasion of peripheral blood mononuclear cells (PBMCs) than the wild-type cell line under FIR. In the analysis of STING-knockout cells and migrated PBMCs, we confirmed the occurrence of STING-dependent immune activation under FIR. In conclusion, we identified that the STING-IFNAR1-STAT1-IRF1 axis regulates immune reactions in cancer cells triggered by FIR and that the STING pathway also contributes to immune cell invasion of cancer cells.

Models for Translational Proton Radiobiology-From Bench to Bedside and Back

The number of proton therapy centers worldwide are increasing steadily, with more than two million cancer patients treated so far. Despite this development, pending questions on proton radiobiology still call for basic and translational preclinical research. Open issues are the on-going discussion on an energy-dependent varying proton RBE (relative biological effectiveness), a better characterization of normal tissue side effects and combination treatments with drugs originally developed for photon therapy. At the same time, novel possibilities arise, such as radioimmunotherapy, and new proton therapy schemata, such as FLASH irradiation and proton mini-beams. The study of those aspects demands for radiobiological models at different stages along the translational chain, allowing the investigation of mechanisms from the molecular level to whole organisms. Focusing on the challenges and specifics of proton research, this review summarizes the different available models, ranging from in vitro systems to animal studies of increasing complexity as well as complementing in silico approaches.

Retrospective analysis of neoadjuvant chemotherapy followed by surgery versus definitive chemoradiotherapy with proton beam for locally advanced esophageal squamous cell carcinoma

BACKGROUND

This is the first study to compare the long-term outcomes between neoadjuvant chemotherapy + surgery and definitive chemoradiotherapy with proton beam therapy for locally advanced esophageal squamous cell carcinoma.

METHODS

We reviewed patients with clinical stage IB-III esophageal squamous cell carcinoma (UICC 7th edition) who underwent neoadjuvant chemotherapy + surgery or definitive chemoradiotherapy with proton beam therapy (2009-2017). Overall survival, progression-free survival, and recurrence or regrowth rates were compared between the two treatment groups. Subgroup analyses of overall survival according to baseline characteristics were also performed.

RESULTS

Forty-three patients received neoadjuvant chemotherapy + surgery (median follow-up 47.4 months) and 60 received definitive chemoradiotherapy with proton beam therapy (median follow-up 51.5 months). Baseline characteristics were similar between the groups except for sex, tumor location, and cT classification. The neoadjuvant chemotherapy + surgery and definitive chemoradiotherapy with proton beam therapy groups had similar 3-year overall survival rates (73.1% and 61.7%, respectively, hazard ratio: 0.88, 95% confidence interval 0.49-1.58, p = 0.66), 3-year progression-free survival rates (46.5% and 45%, respectively, hazard ratio: 1.03, 95% confidence interval 0.62-1.70, p = 0.92), and recurrence or regrowth rates (53.5% vs. 50.0%, p = 0.84). In the subgroup analysis, favorable survival was observed after definitive chemoradiotherapy with proton beam therapy for cT1-2 disease (hazard ratio 2.58, 95% confidence interval 0.84-7.99) and after neoadjuvant chemotherapy + surgery for cT3 or higher disease (hazard ratio 0.32, 95% confidence interval 0.15-0.67, p-for-interaction = 0.002).

CONCLUSIONS

Long-term outcomes were comparable between the treatments. The choice of the treatment according to cT classification might affect survival.

PARP inhibitor olaparib sensitizes esophageal carcinoma cells to fractionated proton irradiation

Proton beam therapy (PBT) combined with chemotherapy, such as cis-diamminedichloroplatinum (II) (CDDP) and 5-fluorouracil (5-FU), has been employed as an alternative approach to improve clinical outcomes. PBT has been reported to be effective against esophageal cancer. However, apart from 5-FU and CDDP, almost no other drug has been tested in combined chemotherapy with PBT. Therefore, we investigated the effects of a poly (ADP-ribose) polymerase inhibitor on enhancing proton beam effects using esophageal cancer cell lines that exhibit resistance to radiation and CDDP. Esophageal squamous cell carcinoma cell lines OE-21 and KYSE-450 were exposed to the drugs for 1 h prior to irradiation. The cell survival curve was obtained using a clonogenic assay and the sensitizing effect ratio (SER) was calculated. The clonogenic assay was used to compare the effect of multi-fractioned irradiation between 8 Gy/1 fraction (fr) and 8 Gy/4 fr. γH2AX, Rad51, BRCA1, BRCA2 and 53BP1 foci were detected via immunofluorescence. Olaparib exhibited an SER of 1.5-1.7 on PBT. The same sensitizing effect was exhibited in multi-fractioned irradiation, and the combined use increased the expression of double-strand breaks and homologous recombination-related genes in an additive manner. Such additive effects were not observed on non-homologous end joining-related genes. We demonstrated that olaparib has a high sensitizing effect on PBT in platinum- and radiation-resistant esophageal cancer cells. Our results suggest a potential clinical application of olaparib-proton irradiation (PT) against platinum- and radiation-resistant esophageal cancer.