Abstract 2808: Levels of isobutyric acid from gut butyrate-producing taxa are associated to Delta-24-RGDOX efficacy against malignant glioma

Abstract Glioblastoma (GBM) is the most aggressive malignant primary brain tumor worldwide. Current standard-of-care treatments allow for a median survival of 12 to 18 months. GBM has a poor survival prognosis, observing less than 6% of patients surviving 5 years post-diagnosis. Among recent treatment advancements, the oncolytic adenovirus Delta-24-RGDOX armed with the T-cell activator OX40L is promising. Studies have unveiled a relationship between the gut microbiome and high levels of short-chain fatty acids (SCFA), such as isobutyric and propionic acid, to immunotherapy response. Changes in the gut microbiome and metabolome associated to viroimmunotherapy efficacy remain unclear. Here, we assessed the gut microbial changes in addition to isobutyric and propionic acid levels regarding viroimmunotherapy efficacy. Immunocompetent C57BL/6 mice were intracranially implanted GL261-5 GBM cells and received intratumoral injections of PBS (control) or Delta-24-RGDOX. A naïve group with no tumor nor treatment was also included. Fecal pellets were collected at three different time points: (1) before tumor implantation, (2) before treatment, and (3) 14 days after the first dose of treatment. Genomic DNA was isolated with the QIAGEN DNeasy Powersoil Pro Kit from fecal pellets (n=75), followed by sequencing with the Illumina platform of the 16S ribosomal RNA V4 region. Quality assessment of the sequences was executed in QIITA. Bacterial community analysis with a sequencing depth of 1,470 reads, while using the taxonomic database SILVA, was followed downstream with QIIME2 and R. Metabolic profiling of SCFA of the fecal pellets was performed through Gas Chromatography. Results showed significant differences in bacterial community structure of viroimmunotherapy-treated mice with survival of >100 days compared to controls (ANOSIM p-value=0.006). Alpha diversity metrics showed significant differences in richness between the naive and tumor-implanted mice of the PBS (KW p-value=0.049) and Delta-24-RGDOX (KW p-value=0.019) groups, highlighting that tumor presence alters the gut microbiota. Additionally, viroimmunotherapy-treated mice with survival of >100 days had a significant increase of Lactobacillus and the butyrate-producing bacterias Erysipelatoclostridium and Ruminococcaceae. Also, we found significantly higher levels of isobutyric acid and lower levels of propionic acid in viroimmunotherapy-treated mice with survival of >100 days (p-value<0.05). These findings suggest that butyrate-producing bacteria coupled with higher levels of isobutyric acid may be important in the efficacy of Delta-24-RGDOX. This highlights the microbial and metabolic changes associated with oncolytic viral therapy efficacy. Sponsored by an award within The University of Puerto Rico/UT MD Anderson Cancer Center Partnership for Excellence in Cancer Research Grant (2U54CA096297-17). Citation Format: Natalie M. Meléndez-Vázquez, Xuejun Fan, Juan Fueyo, Candelaria Gomez-Manzano, Filipa Godoy-Vitorino. Levels of isobutyric acid from gut butyrate-producing taxa are associated to Delta-24-RGDOX efficacy against malignant glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2808.