Abstract 6041: Fidaxomicin targets PDGFR+ cancer-associated fibroblast to restrain colorectal cancer progression

Abstract Background: Colorectal cancer (CRC) features a stroma-rich, immunosuppressive tumor microenvironment (TME) where activated fibroblasts drive tumor progression and correlate with poor prognosis. PDGFR+ cancer-associated fibroblasts (CAFs)—including PDGFRα+ inflammatory CAFs (iCAFs) and PDGFRβ+ myofibroblastic CAFs (myCAFs)—are proportionally increased and serve as key hubs of intercellular communication in CRC. High PDGFR+ CAF signatures are associated with unfavorable outcomes. Fidaxomicin, an FDA-approved oral antibiotic which selectively eliminates pathogenic Clostridioides difficile, inhibits ileal fibrosis and suppresses PDGFR expression in intestinal fibroblasts. The purpose of this study was to define the mechanisms by which PDGFR+ CAFs promote CRC progression and to evaluate the anti-tumor effects of fidaxomicin targeting PDGFR. Methods: We performed R-based analyses of datasets from human CRC and matched normal tissues to compare cellular subpopulation proportions, functional enrichment, cell-cell communication, and virtual cell states. Effects of fidaxomicin on the proliferation of CRC cells and CAFs were assessed in vitro using 2D and 3D cultures and in vivo using an orthotopic colon cancer model (MC38 co-implanted with mCAF cells). CAF-neutrophil interactions were examined through 3D co-culture, multicolor immunofluorescence, and flow cytometry. Results: Analysis of datasets from single-cell transcriptomics revealed markedly activated fibroblasts and increased monocyte-macrophage and neutrophil populations within the TME of CRCs. Tumor-enriched CAF subsets, including PDGFRα+ iCAFs and PDGFRβ+ myCAFs, expressed high levels of PDGFR and neutrophil-attracting chemokines such as CXCL1 and CXCL14. ssGSVA scores of CAF signature genes strongly correlated with poor prognosis. Treatment of CAFs with fidaxomicin significantly reduced PDGFR expression at both mRNA and protein levels, inhibited STAT3 phosphorylation, and downregulated CXCL1 and CXCL14 transcription. Moreover, oral fidaxomicin administration suppressed MC38 tumor growth. Mechanistically, fidaxomicin inhibited the transcriptional activity of the NOTCH-RBPJ-HDAC1/HDAC3 complex, leading to PDGFR downregulation and blocking PDGFR-mediated STAT3 activation and nuclear translocation that drives CXCL14 transcription and immune evasion. Conclusions: Our results demonstrate that PDGFR+ CAF subsets play a critical role in CRC progression. Fidaxomicin disrupts PDGFR+ CAF-neutrophil interactions, remodels the TME, and inhibits tumor growth. Importantly, our findings suggest a potential usage of fidaxomicin, which maintains a favorable safety profile with minimal systemic toxicity, for CRC treatment. Citation Format: Haoxiang Zhang, Xudong Zhu, Chang Li, Yinping Jiang, Yuning Zhou, B. Mark Evers, Qingding Wang. Fidaxomicin targets PDGFR+ cancer-associated fibroblast to restrain colorectal cancer progression abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6041.