In-vivo and in-vitro impact of high-dose rate radiotherapy using flattening-filter-free beams on the anti-tumor immune response.

INTRODUCTION: Modern accelerators have the "flattening filter-free" (FFF) technique to deliver RT with a moderate high-dose rate, currently used in limited clinical indications. No scientifically established data are currently available on the possible effects of this high dose rate on the anti-tumor immune response. We therefore propose here to study these effects in a preclinical CT26 murine colorectal tumor model. MATERIAL AND METHODS: In-vitro, CT26 cells were irradiated on a Varian TrueBeam® linac at 3 different dose rates (4; 12 or 24 Gy/min) using the FFF mode. Activation of the anti-tumor immune response was evaluated by the analysis of induction of genes of the type I interferon pathway by RT-qPCR, and by the study of the induction of immunogenic death biomarkers. In-vivo, an efficacy study of RT delivering 16.5 Gy at 2 different dose rates was performed in immunocompetent Balb/c mice carrying CT26 syngeneic tumors, as well as an immunomonitoring analysed by flow cytometry and a transcriptomic analysis using RNA sequencing. Statistical analyzes were performed using non-parametric tests. RESULTS: In-vitro, no significant influence of an increase in FFF dose rate was shown for the induction of genes of the type I interferon pathway as well as for the studied immunogenic death markers (HMGB1 secretion). In-vivo, no difference in terms of tumor growth retardation between the 2 dose rates used was demonstrated, as well as for the composition of immune cell infiltrates within tumor microenvironment and the expression of immune checkpoints in immunomonitoring and RNAseq. CONCLUSION: In this study involving the CT26 model, no influence of a moderate high dose rate in FFF technique on the anti-tumor immune response was demonstrated, which would make studies of associations between RT and checkpoint inhibitors fit with this technique of RT. However, further explorations using other cellular models seem to be of interest.

Hypolipemic and potential antiatherosclerotic properties of diprophyllinyl-4-benzyloxybenzoate.

To assess the hypolipemic and antiatherosclerotic activity of diprophyllinyl-4-benzyloxybenzoate guinea-pigs were kept on a high-lipid diet alone or with the tested compound for 21 days, and rabbits--for 3 months. It was found that diprophyllinyl-4-benzyloxybenzoate displays a distinct hypolipemic activity, particularly with respect to cholesterol, both in guinea-pigs and rabbits. It also depresses the cholesterol and the trigliceride content in liver homogenates and shows a tendency to normalize the low-density-lipoprotein fraction in guinea-pigs, as well as cholesterol of the high-density lipoprotein fraction, and malon dialdehyde in rabbits. The area of intima covered with atheromatous plaques was smaller in rabbits receiving the high-lipid diet with diprophyllinyl-4-benzyloxybenzoate than in those receiving that diet alone.

Study on the antioxidant properties of pollen extracts.

The study on the antioxidant and hypolipidemic effect of pollen extracts (Cernitins) was conducted in male mongrel rabbits and Wistar rats. The animals were fed a high-fat diet (HFD) composed of cholesterol, coconut oil and cholic acid, and received pollen extracts (Cernitins) orally (the rabbits over a period of 12 weeks and the rats over a period of 2 weeks). The levels of malondialdehyde (MDA) as an indication of the degree of peroxidation and lipids (cholesterol, triglyceride, separation of lipoproteins into fractions) were measured. The study demonstrated the reduction of MDA concentrations under the influence of Cernitins, suggesting their antioxidant properties. Total cholesterol and triglyceride content was also decreased.