Cisplatin-oral microbiota synergistic role in HNSCC aggressiveness and its clinical relevance

Background: Cisplatin-based chemotherapy remains a cornerstone for treating Head and NeckSquamous Cell Carcinoma (HNSCC). However, its therapeutic success is often limited inpatients with advanced-stage disease (Stage III-IIIb). Emerging evidence indicates thatchemotherapy itself may induce or select for aggressive, therapy-resistant tumor phenotypes.Meanwhile, dysbiosis of the oral microbiota-particularly involving Fusobacterium nucleatumand Porphyromonas gingivalis-has been implicated in HNSCC progression and immuneevasion. Yet, the synergistic interplay between cisplatin treatment and oral microbial ecologyremains poorly understood. Here, we investigate whether oral microbiota enhance cisplatin-induced aggressiveness via reprogramming of cancer stem cell (CSC) phenotypes, particularlythe Tumor Stemness Defense (TSD) state, which represents an adaptive altruistic response totherapy-induced stress. Methods: Saliva samples were prospectively collected from 15 HNSCC patients prior toinitiation of cisplatin-based chemotherapy. The microbiome composition was analyzed using16S rRNA gene sequencing and targeted qPCR for F. nucleatum and P. gingivalis. In vitro,these isolates were co-cultured with SAS HNSCC cells (MOI 50:1) and treated with cisplatin(1-5 µM) for three days. Post-treatment recovery was monitored up to 14 days, withassessments of colony formation, migration, and expression of TSD-associated stemnessmarkers (EpCAM, ABCG2, HIF-2alpha, Myc, SOX2, OCT4, NANOG). Clinically, post-therapysalivary microbiota was correlated with patient outcomes and tumor hypoxia profiles. Results: Co-exposure of SAS cells to cisplatin and F. nucleatum or P. gingivalis led to theemergence of a TSD-like phenotype, characterized by elevated expression of HIF-2alpha, ABCG2,and Myc, increased clonogenic survival, and enhanced migration capacity. Thisreprogramming effect was attenuated by TLR4 inhibition. Patient saliva analysis revealed thatelevated microbial LPS load and enrichment of F. nucleatum correlated with poorchemotherapy response and higher CTC count during treatment. Conclusion : Our findings reveal that the oral microbiota synergizes with cisplatin to promotetherapy-induced adaptive stemness in HNSCC. This mechanism, involving microbialLPS/TLR4 signaling and HIF-2alpha activation, suggests that oral microbial dysbiosis may act asa co-driver of tumor evolution under chemotherapeutic stress. Targeting microbiota-chemotherapy interactions may offer a new avenue to reduce post-therapy relapse. References: 1. doi: 10.3389/fimmu.2024.1336882 2. doi: 10.3389/fimmu.2023.1198269 3 . doi:10.1620/tjem.253.249. PMID: 33840648.