Tongue squamous cell carcinoma (TSCC) is an aggressive malignancy with limited therapeutic options and unsatisfactory survival outcomes. However, its treatment is hampered by two major and often co-existing barriers: development of cisplatin resistance and the establishment of an immunosuppressive tumor immune microenvironment (TIME) [1,2]. Cisplatin resistance is frequently driven by tumor-intrinsic alterations such as the activation of the NF-κB signaling pathway and epithelial–mesenchymal transition (EMT), which enable cancer cells to survive genotoxic stress. At the same time, persistent antigen stimulation within the TIME leads to functional exhaustion of tumor-infiltrating CD8+ T cells, characterized by diminished cytotoxicity and upregulation of inhibitory receptors. Although these resistance mechanisms are mechanistically distinct, they clinically synergize to promote treatment failure. Therefore, therapeutic strategies that can simultaneously reverse tumor-intrinsic chemoresistance and restore antitumor immunity may offer superior and more durable clinical benefits [3,4].

In recent years, the TIME has emerged as a critical determinant of the treatment response and overall prognosis in TSCC [5]. T cells, the principal effectors of antitumor immunity, are essential both for mediating direct cytotoxicity against tumor cells and for orchestrating broader immune responses [6,7]. Nevertheless, chronic antigen exposure within the tumor milieu often results in T-cell exhaustion—characterized by reduced effector function, sustained expression of inhibitory receptors, and impaired proliferative capacity—which contributes to tumor immune evasion [8]. Checkpoint molecules, such as PD-1 and its ligand PD-L1, play pivotal roles in mediating this exhausted state [9], while immunosuppressive cytokines, like IL-10 and TGF-β, further dampen the antitumor immune response [10,11]. These factors collectively establish a suppressive TIME that not only fosters tumor progression but also undermines the efficacy of conventional chemotherapy.

Plumbagin (PLB) is a natural naphthoquinone derived from the roots of Plumbago zeylanica, a medicinal herb traditionally used in various ethnomedical systems [12]. Extensive studies have established the antitumor properties of PLB, which it primarily exhibits through its ability to inhibit tumor cell proliferation, induce apoptosis, and impede migration and invasion of tumor cells [13,14]. However, whether PLB can modulate the TIME has remained largely unexplored [15].

There is emerging evidence to show that ZW10 interactor (ZWINT) is upregulated in head-and-neck squamous cell carcinomas (HNSCCs) and is associated with chemoresistance (e.g., identified as a differentially expressed gene in HNSCC meta-analysis [16] and implicated in cisplatin resistance models in oral squamous cell carcinoma cell lines [17]). ZWINT overexpression has been reported in multiple malignancies, including hepatocellular carcinoma, where it correlates with immune infiltration and poor prognosis [18]. It has also been shown that Krüppel-like factor 2 (KLF2), a transcription factor, is critical for T-cell activation and function [19]. In healthy T cells, KLF2 maintains immune homeostasis by regulating cellular trafficking and promoting effector responses, including cytokine production and cytotoxicity [19,20]. More recently, KLF2 has been shown to play a pivotal role in suppressing CD8+ T-cell exhaustion and maintaining lineage fidelity [21]. In contrast, ZWINT, traditionally known for its role in kinetochore assembly during mitosis, has recently been implicated in cancer progression and drug resistance [22]. Although cisplatin exerts its primary cytotoxic effects through DNA damage, accumulating evidence suggests that the dysregulation of mitotic checkpoint proteins, such as ZWINT, can confer survival advantages under genotoxic stress by promoting aberrant cell-cycle progression and attenuating apoptosis [23,24]. Elevated ZWINT expression in TSCC cells is associated with cisplatin resistance, which contributes to tumor cell survival, therapy evasion, and aggressive behavior [25].

While KLF2 supports robust antitumor T-cell responses by suppressing T-cell exhaustion programs and preserving effector differentiation [21], ZWINT promotes tumor survival and chemoresistance by activating the NF-κB pathway [26]. Thus, PLB is expected to exert a dual therapeutic effect in TSCC: first, by directly sensitizing tumor cells to cisplatin through the downregulation of ZWINT and attenuation of NF-κB signaling, and second, by remodeling the TIME via stabilization of KLF2 and activation of the JAK1–STAT2 axis in T cells. This dual perspective is also supported by increasing recognition that immune activation and chemosensitization are not isolated events: effector T-cell-derived cytokines such as IFN-γ and TNF-α can suppress NF-κB–driven survival pathways in tumor cells, while the attenuation of chemoresistance-associated signaling can enhance immune-mediated cytotoxicity. Accordingly, this study investigates the integrated role of PLB in both modulating T-cell cytotoxicity and sensitizing TSCC cells to cisplatin, highlighting its potential as a dual-action chemo-immunomodulator.