Lachnospiraceae and butyrate restrict the antitumor effect of IR. (A) GF C57BL/6 mice were fed with Lachnospiraceae and K. alysoides (TSD-26) for 1 mo, 10⁸ CFU/mouse weekly. The control group was fed the same volume of autoclaved water. Mice were injected s.c. with 10⁶ MC38 cells, and established tumors were irradiated (20 Gy) on day 10 after tumor inoculation. On day 10 after tumor inoculation, sera were collected for butyrate detection by GC/MS. A tumor growth curve is shown (n = 5/group). (B) GF C57BL/6 mice were fed HI TSD-26 weekly for 1 mo. 10⁸ CFU of TSD-26 were HI at 100°C for 30 min and fed to one mouse. The control group was fed the same volume of autoclaved water. Then the mice were injected s.c. with 10⁶ MC38 cells, and established tumors were irradiated (20 Gy) on day 10 after tumor inoculation. A tumor growth curve is shown (n = 5/group). On day 10 after tumor inoculation, sera were collected for butyrate detection by GC/MS. (C) Butyrate concentration in sera collected from A and B (control group, n = 10; TSD-26 group, n = 10; HI TSD-26 group, n = 12). Data were pooled from two independent experiments. (D) C57BL/6 mice were injected s.c. with 10⁶ MC38 cells. Established tumors were irradiated (20 Gy) on day 10 after tumor inoculation. Tumor-bearing mice were injected i.v. with 4 μmol of NaBu on days 1, 4, and 7 after IR. A tumor growth curve is shown (n = 5/group). Two-way ANOVA tests were used to analyze the tumor growth data, and unpaired t tests were used to analyze the other data. n.s., not significant; *, P < 0.05; **, P < 0.01; ****, P < 0.0001. One representative experiment (out of two experiments in A and B or three experiments in D) is shown.