# The Effect of Dietary Fiber Compositions on the Therapeutic Outcome of Combined Radio‐ and Immunotherapy in a Preclinical Cancer Model

## TL;DR

This study shows that the type of dietary fiber can affect how well combined radiotherapy and immunotherapy work in treating colon cancer in mice.

## Contribution

The study reveals that specific fiber compositions influence the effectiveness of combined radio-immunotherapy through changes in gut microbiota and immune cell profiles.

## Key findings

- Fiber composition affected progression-free survival and gut microbiome structure in mice.
- Higher Atopobiaceae and lower Bacteroides were linked to better treatment outcomes.
- Cured mice had more CD8+ T-cells and fewer myeloid-derived suppressor cells in their spleens.

## Abstract

Several studies demonstrated curative responses of combined radio‐immunotherapy, although not standard‐of‐care for most cancers. Increased fiber intake has been associated with improved radiotherapy and immunotherapy outcomes, but fiber compositions’ impact remains unclear. This study aimed to explore whether dietary fiber composition influences the therapeutic outcome of combined radio‐immunotherapy in a preclinical cancer model. A syngeneic mouse model of colon cancer (CT26) (female BALB/cOla Hsd) was used. Mice were randomized into three groups (n = 12) of iso‐caloric diets with different fiber compositions. Five instances of local radiotherapy on tumors, combined with injections of anti‐PD‐L1, were administered over 5 and 10 days. Diets’ impact was assessed on progression‐free survival, SCFA levels in fecal and cecal samples, gut microbiome composition, and immunological profile. Progression‐free survival was different between compositions, as well as their gut microbiota community structure, at all measured time‐points. Therapeutic outcome (cure) was negatively associated with the relative abundance of Bacteroides and positively with Atopobiaceae Family. There was no association with SCFA levels. Cured mice displayed smaller spleens containing increased proportions of CD8+ T‐cells and decreased proportions of myeloid‐derived suppressor cells. Our data suggest that fiber composition may influence therapeutic outcome of combined radio‐immunotherapy treatment in vivo.

To study whether dietary fiber composition influences the therapeutic outcome of combined radio‐immunotherapy, mice were subcutaneously injected with syngeneic CT26 colon cancer cells and randomized into three groups of iso‐caloric diets with different fiber compositions. Animals were treated with local radiotherapy on tumors, combined with intraperitoneal injections of anti‐PD‐L1. Diets’ impact was assessed on progression‐free survival. Our data suggest that fiber composition may influences therapeutic outcome of combined radio‐immunotherapy treatment in vivo.