Cancer stem cells (CSCs) represent a subpopulation of cancer cells that are believed to initiate and drive cancer progression. In animal models, xenotransplanted CSCs have demonstrated the ability to produce tumors. Since their initial isolation in blood cancers, CSCs have been identified in various solid human cancers, including oral squamous cell carcinoma (OSCC). In addition to their tumorigenic properties, dysregulated stem-cell-related signaling pathways—Wnt family member (Wnt), neurogenic locus notch homolog protein (Notch), and hedgehog—have been shown to endow CSCs with characteristics like self-renewal, phenotypic plasticity, and chemoresistance, contributing to recurrence and treatment failure. Consequently, CSCs have become targets for new therapeutic agents, with some currently in different phases of clinical trials. Notably, small molecule inhibitors of the hedgehog signaling pathway, such as vismodegib and glasdegib, have been approved for the treatment of basal cell carcinoma and acute myeloid leukemia, respectively. Other strategies for eradicating CSCs include natural compounds, nano-drug delivery systems, targeting mitochondria and the CSC microenvironment, autophagy, hyperthermia, and immunotherapy. Despite the extensive documentation of CSCs in OSCC since its first demonstration in head and neck (HN) SCC in 2007, none of these novel pharmacological approaches have yet entered clinical trials for OSCC patients. This narrative review summarizes the in vivo and in vitro evidence of CSCs and CSC-related signaling pathways in OSCC, highlighting their role in promoting chemoresistance and immunotherapy resistance. Additionally, it addresses methodological challenges and discusses future research directions to improve experimental systems and advance CSC studies.

Cancer is one of the most common causes of death in the developed world, with one-third of people diagnosed with cancer during their lifetime. Oral cancer commonly occurs involving the buccal mucosa (cheeks), tongue, floor of the mouth and lip. It is one of the most devastating and disfiguring of malignancies. Morinda citrifolia L., commonly known as ‘noni’, belongs to the Rubiaceae family. It is native to the Pacific islands, Hawaii, Caribbean, Asia and Australia. The plant displays broad curative effects in pharmacological studies. Damnacanthal (DAM) and Nordamnacanthal (NDAM), anthraquinone compounds isolated from the roots of Morinda citrifolia L., has been used for the treatment of several chronic diseases including cancer. The objectives of this study were to evaluate cytotoxicity, morphological changes, cell death mode (apoptosis/necrosis), and cell migration induced by DAM and NDAM on the most common type of oral cancer, oral squamous cell carcinoma (OSCC)cells. Anti-proliferative effects of these compounds against OSCC cell lines were determined by MTT assay. The mode of cell death was analysed by phase contrast and fluorescent microscopy as well as flow cytometry. In addition, cell migration was assessed. The results showed that DAM and NDAM exerted cytotoxicity against OSCC cells with IC50 values of 1.9 to >30 μg/ml after 72 h treatment. Maximum growth inhibition among the tested cell lines for both compounds was observed in H400 cells, and thus it was selected for further study. The study demonstrated inhibition of H400 OSCC cell proliferation, marked apoptotic morphological changes, induction of early apoptosis, and inhibition of cell migration by DAM and NDAM. Therefore, this information suggests that these compounds from noni have potential for used as anti tumor agents for oral cancer therapy.

Cancer stem cells (CSCs) are key drivers of heterogeneity, recurrence, and therapy resistance in oral squamous cell carcinoma (OSCC). CD44, CD133, ALDH, and BMI1 have been highlighted as clinically relevant CSC markers, yet no single marker sufficiently defines CSC identity. This study aims to explore computationally CSC heterogeneity in Asian-derived ORL cell lines (ORL-48, ORL-115, ORL-174, ORL-214). Unsupervised clustering of single-cell qPCR datasets revealed enrichment of quadruple-positive (CD44⁺/CD133⁺/ALDH1A1⁺/BMI1⁺) subsets, alongside smaller heterogeneous fractions. PhenoGraph clustering and viSNE analyses of arcsinh-transformed flow cytometry datasets independently confirmed dominant CD44⁺ and BMI1⁺ fractions, smaller CD133⁺ and ALDH⁺ subsets, and rare CSC-enriched multi-marker clusters consistent with the single-cell qPCR analysis. In addition, sphere formation assays further validated the presence of self-renewing CSC-like populations across all lines. As this work was designed as an exploratory study, analyses were performed once per cell line without replicates; future studies will incorporate independent validations.

Cancer stem cell (CSC) persistence drives recurrence and therapy resistance in oral squamous cell carcinoma (OSCC), but what keeps cells locked in this stem-like state is poorly understood. In this narrative review, we propose that CSC state is sustained not by any single pathway but by joint dysregulation of three interacting cell-biological systems: membrane potential (V_mem), communication between neighbouring cells through gap junctional intercellular communication (GJIC), and the Hippo–YAP pathway. We argue that these systems act together on one common point—the YAP protein, retained in the nucleus—which switches on a SOX2-centred stemness gene programme and stabilises a self-reinforcing CSC state. Drawing on evidence from cancer genomics, developmental bioelectricity, connexin biology, and OSCC-specific studies, we reconstruct how membrane depolarisation, loss of gap junction coupling, FAT1 mutation, and Hippo pathway inactivation could converge on persistent nuclear YAP, and how betel quid—the principal risk factor across South and Southeast Asia—may engage all three systems at once. Because the model holds that each input reinforces the others, it predicts that targeting several together should displace CSC state more durably than targeting any one alone. We set out the testable predictions this framework generates.