Cannabidiol Selectively Kills Cisplatin-Resistant Head and Neck Cancer Cells in Preclinical Study

Cannabidiol, the non-psychoactive compound derived from Cannabis sativa, has shown notable antitumor activity in a cancer model that routinely defeats conventional chemotherapy. In a study published in Medical Oncology, researchers from Brazil evaluated CBD in HN13 cells, a cisplatin-resistant, HPV-negative head and neck squamous cell carcinoma line derived from the tongue. The results read like a checklist of everything an oncologist would want a drug candidate to fail at doing inside a tumor: CBD selectively killed the cancer cells, cut their migration and invasion, suppressed the matrix-degrading enzymes MMP-2 and MMP-9, nearly abolished their ability to form new colonies, shrank three-dimensional spheroids, and, when paired with cisplatin, produced a synergistic cytotoxic interaction. On the chick chorioallantoic membrane, CBD-treated tumors were significantly smaller with reduced surrounding vascular area, and the compound caused no hemorrhage, lysis, or coagulation in the vascular irritation assay. The authors emphasize that these are preclinical findings, but they argue the data justify further investigation of CBD as a potential adjunct approach, particularly in chemoresistant settings.

The stakes are high because head and neck squamous cell carcinoma remains one of the most aggressive solid tumors, arising from the mucosal epithelium of the oral cavity, sinuses, pharynx, larynx, and salivary glands. Despite advances in surgery, radiotherapy, and systemic treatments, the overall five-year survival rate hovers around fifty percent, reflecting high rates of recurrence and strong metastatic potential. The disease splits into biologically distinct subtypes based on human papillomavirus status. HPV-positive tumors are driven by the viral oncoproteins E6 and E7, which promote degradation of key regulators such as p53, Bax, pRb, and telomerase, allowing genetically damaged cells to evade death and proliferate uncontrollably. HPV-negative disease, by contrast, is primarily associated with chronic tobacco smoke and alcohol exposure, producing cumulative alterations including TP53 mutations, DNA adduct formation, aberrant methylation, and increased genomic instability. These biological differences contribute to the poorer prognosis and reduced therapeutic response observed in HPV-negative tumors, the exact subtype the new study targeted.

Standard treatment for HNSCC includes surgery, radiotherapy, and platinum-based chemotherapy, often combined with 5-fluorouracil, but these approaches are frequently limited by treatment resistance and systemic toxicity, including gastrointestinal disturbances, nephrotoxicity, immunosuppression, and reduced quality of life. For unresectable, recurrent, or metastatic disease, targeted therapies such as cetuximab and immune checkpoint inhibitors like pembrolizumab have entered clinical practice, yet their benefit remains constrained by adverse effects, resistance, and high cost. CBD has attracted attention as an alternative bioactive compound because it lacks the psychoactive effects of THC and presents a more favorable safety profile. Beyond its established use in managing chemotherapy-induced symptoms, CBD has demonstrated antiproliferative, anti-angiogenic, anti-invasive, and anti-migratory effects across multiple tumor models, including breast cancer, glioblastoma, leukemia, and prostate cancer. Mechanistically, CBD interacts with diverse molecular targets, including cannabinoid receptors CB1 and CB2, transient receptor potential vanilloid channels, peroxisome proliferator-activated receptor gamma, and G protein-coupled receptor 55, which may influence signaling pathways associated with apoptosis and autophagy. However, studies specifically addressing HPV-negative and chemoresistant HNSCC have remained limited.

The new study began with the fundamental question of selectivity, using the MTT assay to determine half-maximal inhibitory concentrations after twenty-four hours of exposure. CBD reduced HN13 cell viability in a concentration-dependent manner, yielding an IC50 of 10 plus or minus 1.42 micromolar, while the FaDu hypopharyngeal line required 14.3 plus or minus 2.27 micromolar. When normal human lung fibroblasts (WI38) and keratinocytes (HaCaT) were treated under comparable conditions, their IC50 values rose to 27.8 and 29.5 micromolar respectively, producing selectivity indices of 2.7 and 2.8 in favor of the tumor cells. Cisplatin told a very different story. The chemotherapeutic showed an IC50 of 64.7 micromolar in HN13, a selectivity index of only 1.7 relative to fibroblasts, and, critically, marked cytotoxicity toward normal keratinocytes, with a selectivity index of 0.3, meaning the drug was actually more toxic to the normal epithelial cells than to the cancer line. This contrast underscores the lack of selectivity that limits conventional chemotherapy and suggests CBD may offer a more favorable profile, although the authors caution that therapeutic applicability requires further validation.

Having established preferential cytotoxicity, the researchers probed the tumor-associated behaviors that drive recurrence and metastasis. In Transwell invasion assays through Matrigel, ten micromolar CBD significantly inhibited HN13 cell invasion after twenty-four hours. In wound healing assays, CBD-treated cultures showed significantly reduced wound closure compared with controls, with the inhibition persisting across forty-eight and seventy-two hours; after seventy-two hours, CBD-treated cultures retained approximately sixty-six percent of the initial wound area, whereas control cells had achieved virtually complete closure. Gelatin zymography of conditioned media revealed that CBD markedly reduced gelatinolytic activity, cutting pro-MMP-9 by fifty-seven percent, active MMP-9 by seventy-seven percent, and MMP-2 by forty-five percent. These enzymes play central roles in extracellular matrix degradation, invasion, and angiogenesis, and their overexpression has been associated with aggressive behavior and poor prognosis in HNSCC. The clonogenic assay delivered perhaps the most dramatic number: CBD treatment reduced colony formation by ninety-eight percent, indicating a strong impairment of long-term proliferative capacity. In three-dimensional hanging-drop spheroids, which better recapitulate cell-cell interactions, hypoxic areas, and treatment resistance profiles of real tumors, CBD significantly inhibited spheroid growth within seventy-two hours.

At the cellular level, acridine orange/propidium iodide staining showed that CBD-treated cells exhibited features consistent with programmed cell death, including cell shrinkage, chromatin condensation, membrane blebbing, nuclear fragmentation, and the presence of acidic vesicular structures. Quantitatively, viable cells fell to six percent of the control level, while early-stage cell death rose to eighty-three percent and late-stage death to eight percent. Western blot analysis then mapped the molecular machinery behind these changes. CBD increased expression of LC3 by one hundred ninety-three percent and Beclin-2 by one hundred thirty-nine percent, proteins associated with the autophagy machinery, while reducing caspase-8 and cleaved caspase-8, suggesting modulation of extrinsic apoptotic signaling. In parallel, CBD increased cleaved caspase-3, the key executioner of apoptosis, and modulated PARP, whose cleavage is a hallmark of DNA damage-associated cell death. CBD also reduced expression of cyclin D1 by seventy-six percent, a critical regulator of G1/S cell cycle progression frequently overexpressed in HNSCC, and decreased p53 by seventy-four percent. The authors interpret the p53 finding with caution, since HPV-negative HNSCC commonly harbors mutant p53, and reduced protein levels may reflect altered stability or degradation rather than classical p53-dependent cell cycle control.

One of the most intriguing mechanistic questions concerned the role of autophagy, a process with a dual role in cancer that can either inhibit tumorigenesis or facilitate tumor cell survival. Staining with monodansylcadaverine, a marker of autophagic vacuoles, confirmed their presence after CBD treatment. When the researchers combined CBD with 3-methyladenine, a pharmacological inhibitor of autophagy-related signaling, the combination reduced LC3-II expression and significantly decreased cell viability compared with CBD alone. More tellingly, the combination increased cleavage of PARP and caspase-3, indicating enhanced apoptotic signaling. These findings suggest that the autophagy-related response associated with CBD treatment may serve a cytoprotective role in HN13 cells, helping them survive the compound’s assault, and that blocking this response could amplify the cytotoxic effect. However, the authors acknowledge an important limitation: autophagic flux was not directly assessed, so the findings should not be interpreted as definitive evidence of increased autophagic flux or autophagic cell death. Further studies using established flux assays, lysosomal inhibitors, or genetic approaches are needed to determine whether modulating autophagy can enhance CBD’s antitumor effects.

Perhaps the most clinically relevant result emerged from the combination experiments. Because cisplatin resistance in HNSCC involves mechanisms such as enhanced DNA damage repair, cell cycle checkpoint activation, and adaptive survival signaling, strategies that increase chemotherapy sensitivity are particularly valuable. The researchers pretreated HN13 cells with cisplatin for five hours to sensitize them, then added CBD for twenty-four hours, analyzing the interaction with CompuSyn software, which generates combination index values where values below one indicate synergism, one indicates an additive effect, and values above one indicate antagonism. The best synergistic combinations were cisplatin at five micromolar combined with CBD at ten micromolar, yielding a combination index of 0.6, and cisplatin at twenty-five micromolar with CBD at ten micromolar, yielding 0.8. These results suggest that pairing CBD with cisplatin could allow a reduction in the cisplatin dose while maintaining cytotoxic efficacy, potentially reducing the systemic toxicity that limits conventional chemotherapy. The authors stress that further preclinical studies are needed to determine whether lower cisplatin doses can maintain antitumor efficacy while reducing toxicity in mammalian models.

The in vivo relevance was explored using the chick chorioallantoic membrane assay, a rapid and cost-effective platform for early-stage evaluation, though the authors note it lacks the immune and stromal complexity of mammalian models, which remain the gold standard for validation. In the CAM model, CBD significantly reduced tumor size compared with controls and reduced the vascular area surrounding tumors, while junction number and vessel length were not significantly altered, suggesting a selective effect on vascular density consistent with previously reported anti-angiogenic effects of CBD. Vascular safety was assessed using the Hen’s Egg Test-Chorioallantoic Membrane assay, in which CBD did not induce hemorrhage, vascular lysis, or coagulation and was classified as practically non-irritating, with an irritation score of 0.57, comparable to the negative and vehicle controls, in stark contrast to the strong irritant response produced by one percent sodium dodecyl sulfate, which scored 18.79. The authors also note a translational caveat: the ten micromolar CBD concentration used in vitro corresponds to approximately 3145 nanograms per milliliter, higher than the mean maximum plasma concentration of 1003 nanograms per milliliter reported in healthy individuals receiving a twenty milligram per kilogram oral dose under high-fat meal conditions. Future studies incorporating mammalian models, three-dimensional tumor systems, and mechanistic analyses of receptor involvement and autophagic flux are required to define CBD’s translational potential in chemoresistant HNSCC.

Subject of Research: Effects of cannabidiol on cisplatin-resistant HPV-negative head and neck squamous cell carcinoma cells

Article Title: Cannabidiol impairs tumor-associated behaviors and modulates apoptosis- and autophagy-related pathways in cisplatin-resistant head and neck squamous cell carcinoma

Article References: de Melo, E. S. A., Almeida, J. M. D., Pires, A. C., & Ribeiro, R. I. M. A. (2026). Cannabidiol impairs tumor-associated behaviors and modulates apoptosis- and autophagy-related pathways in cisplatin-resistant head and neck squamous cell carcinoma. Medical Oncology, 43(11), Article 360. https://doi.org/10.1007/s12032-026-03480-7

Image Credits: AI Generated

DOI: 10.1007/s12032-026-03480-7

Keywords: cannabidiol, head and neck squamous cell carcinoma, cisplatin resistance, apoptosis, autophagy, HPV-negative tumors, matrix metalloproteinases, combination index, chorioallantoic membrane model, preclinical study, impairs, tumor-associated