Radiotherapy's clinical impact is constrained by tumour radio-resistance and collateral intestinal injury, which can include mucosal toxicity and intestinal dysbiosis. The authors evaluated pyrogallol, a plant-derived vicinal trihydroxybenzene, for dual activity as a radiosensitizer and mucosal protector in a preclinical cancer model. The investigation aimed to connect tumour molecular responses to changes in gut microbial ecology using integrated host transcriptomics and whole-genome metagenomic sequencing.
The study used an Ehrlich ascites carcinoma (EAC) model in BALB/c mice subjected to localized linear accelerator (LINAC) irradiation at 8 Gy. Pyrogallol was administered as a co-treatment with localized irradiation. Host tumour tissues underwent transcriptomic profiling to quantify expression changes in apoptotic, proliferative, epithelial–mesenchymal transition (EMT), fibrotic, and inflammatory pathways. Paired gut metagenomic sequencing characterized radiation- and pyrogallol-associated shifts in intestinal microbial composition and ecological indices. Integrated Spearman rank correlations were used to associate host molecular markers with microbial taxa.
Co-treatment with pyrogallol significantly augmented radiotherapeutic efficacy, producing marked tumour regression relative to radiation alone. Molecular profiling demonstrated upregulation of several pro-apoptotic effectors, including Bax, Casp3, and Casp7, and activation of p53-mediated tumour suppressor pathways (Tp53, p21). Concurrent repression of the anti-apoptotic gene Bcl2 was observed, consistent with enhanced programmed cell death contributing to tumour control.
Beyond apoptosis, pyrogallol co-treatment blunted oncogenic progression at multiple levels. Markers of cell-cycle progression and proliferation such as Cdk4 and Pcna were reduced, indicating decreased tumour proliferative capacity. EMT-associated genes, including N-cadherin and vimentin, were inhibited, suggesting suppression of invasive or metastatic phenotypes. Genes involved in fibrotic remodelling—Tgfβ, Col1A1, and Fibronectin—were downregulated, and radiation-induced surges in pro-inflammatory cytokines (IL1α, Il-6, Il-12) were attenuated, indicating an anti-inflammatory and anti-fibrotic influence of pyrogallol on irradiated tissue.
Localized irradiation alone disrupted colonization resistance in the gut microbiome. The radiation-exposed microbiota showed depletion of homeostatic short-chain fatty acid (SCFA) producers and loss of Clostridium scindens, taxa typically associated with gut health. Simultaneously, pathobiont blooms were noted, including expansion of Acinetobacter baumannii and Clostridioides difficile, indicating a shift toward a dysbiotic, potentially pro-inflammatory community.
Pyrogallol co-treatment reversed aspects of radiation-associated dysbiosis via a distinct ecological shift. Although the treated animals experienced a reduction in total species richness, the intestinal niche became highly dominated by the next-generation probiotic Parabacteroides distasonis, which reached approximately 94% relative abundance (Berger–Parker index ≈ 0.94). This compositional redevelopment suggests pyrogallol drives a less diverse but potentially more protective microbial community profile after irradiation.
Integrated Spearman rank correlation analysis connected host molecular signatures and microbial taxa. Host markers of proliferation, EMT, fibrosis, and inflammation correlated positively with clusters of pathobionts (including Bacteroides caecimuris, B. faecium, and A. baumannii). In contrast, tumour regression and anti-inflammatory transcriptional patterns correlated with restriction of pathobionts and with enrichment of P. distasonis. These associations support a model in which microbial community composition aligns with, and possibly modulates, radiotherapy outcomes and host inflammatory states in this model.
In this preclinical EAC model, pyrogallol functioned as a radiosensitizer that enhanced tumour apoptosis and suppressed proliferative, EMT, fibrotic, and inflammatory programmes induced by irradiation. Simultaneously, pyrogallol remodeled the post-radiation gut microbiome from a dysbiotic, pathobiont-rich state toward dominance by Parabacteroides distasonis, a taxon associated here with anti-inflammatory and tumour-regressive host signatures. The authors propose pyrogallol as a promising adjuvant to radiotherapy that couples direct tumour-sensitizing effects with beneficial modulation of the gut microbiome.
It is important to note that this report is a preprint and has not been peer reviewed. The abstract and reported outcomes summarize transcriptomic and metagenomic findings; specific experimental details such as dosing schedules, statistical measures, timepoints, and additional protocol elements are provided in the source document but are not reproduced in full here. Further validation in peer-reviewed studies and across additional models will be required to determine translational potential and safety.