The clinical backdrop makes the finding urgent. Surgical resection remains the only curative option for cholangiocarcinoma, yet because early-stage disease produces few symptoms, only 30 to 40 percent of patients are candidates for an operation. Even among those who undergo complete tumor removal, recurrence is common and the five-year overall survival rate falls below 40 percent. Current guidelines recommend six months of adjuvant capecitabine after curative surgery, while for advanced disease the combination of cisplatin and gemcitabine, known as CisGem, stands as the first-line standard of care. But chemotherapy resistance is high, and patients receiving CisGem experience progression-free survival and overall survival of only about 8.0 and 11.7 months, respectively. Targeted agents and immunotherapies have begun to reshape the landscape, with the IDH-1 inhibitor ivosidenib demonstrating activity in the ClarIDHy phase III trial for patients with IDH-1-mutant tumors, and pembrolizumab indicated for tumors deficient in mismatch repair proteins or showing high microsatellite instability. Still, the field suffers from a shortage of specific biomarkers and effective therapeutic targets.

CD39, also known as ectonucleoside triphosphate diphosphohydrolase 1, or ENTPD1, is a membrane-bound enzyme that hydrolyzes extracellular ATP and ADP into anti-inflammatory adenosine. It is normally expressed in organs such as the bladder, brain, lung, spleen, thymus, and placenta, primarily on endothelial and immune cells. Its abundance varies dramatically across immune populations: more than 90 percent of B lymphocytes, monocytes, and neutrophils in peripheral blood carry it, roughly 20 to 30 percent of CD4-positive T cells including memory T cells and regulatory T cells express it, fewer than 5 percent of CD8-positive T cells do, and only 2 to 5 percent of natural killer cells display it on their surface. Crucially, CD39 has been found overexpressed in a range of solid tumors, including colorectal cancer, lung cancer, pancreatic cancer, head and neck cancer, and chronic lymphocytic leukemia, and high expression has been linked to poor outcomes in clear cell renal cell carcinoma, non-small-cell lung cancers, hepatocellular carcinoma, ovarian carcinoma, and gastric cancers. Its role in cholangiocarcinoma, however, had remained unexplored until now.

To fill that gap, the researchers began with a systematic search for genes that behave abnormally in bile duct cancer. RNA sequencing of 12 paired tumor and adjacent non-tumor samples from their institution identified 3,383 upregulated and 3,258 downregulated genes. They then cross-referenced these results with RNA-seq data from the TCGA dataset, comprising 9 pairs, and a GEO dataset, also 9 pairs, and found 21 genes abnormally expressed across all three cohorts. Ten upregulated candidates were selected for validation by quantitative reverse transcription PCR in 24 paired tumor and normal tissue samples. Only one survived the scrutiny: CD39 was significantly upregulated in tumor tissue, and both RT-qPCR and western blotting confirmed that its levels were especially elevated in tumors from patients with lymph node metastasis.

The clinical significance became even clearer when the team turned to immunohistochemistry in a much larger cohort of 180 cholangiocarcinoma patients. Consistent with the molecular data, CD39 was highly expressed in tumor tissue compared with adjacent non-tumor tissue, with a P value below 0.001. Aberrant expression was also observed in patients with lymph node metastasis compared with those without, again at P < 0.001. Survival analysis revealed that patients with high CD39 expression had significantly worse overall survival, with P < 0.001. High expression correlated with a higher rate of lymph node metastasis, P = 0.007, and with more advanced TNM stage, P = 0.004. Most importantly, multivariable Cox proportional hazards regression established CD39 expression as an independent prognostic factor for overall survival, meaning its predictive power held even after accounting for other clinical variables.

Having established the correlation, the researchers moved to causation. They first profiled CD39 expression across human cholangiocarcinoma cell lines, finding it low in the RBE line and high in TFK-1, and used these two lines for gain- and loss-of-function experiments. Cell Counting Kit-8 assays showed that knocking down CD39 inhibited proliferation, while overexpressing it significantly boosted proliferative capacity. Transwell assays told a parallel story for motility: silencing CD39 suppressed the migratory and invasive abilities of TFK-1 cells, whereas forcing its expression enhanced migration and invasion in RBE cells. The pattern extended into living organisms. In cell-line-derived xenograft models using immunodeficient B-NDG mice, tumor volume and weight rose significantly when CD39 was overexpressed and fell when it was knocked down. The number of metastatic nodules in the liver increased in the overexpression group and decreased in the knockdown group, directly implicating CD39 in the metastatic spread of the disease.

The mechanistic breakthrough came from co-immunoprecipitation followed by mass spectrometry. Applying stringent filters, including confidence scores of at least 100 in the mass spectrometric assays and absence from corresponding anti-sense control groups, the team identified nine candidate proteins that physically interact with CD39. Western blotting confirmed that one of them, Annexin A2, or ANXA2, specifically binds CD39. ANXA2 is a calcium-mediated phospholipid-binding protein known to regulate cell survival and communication with the extracellular environment, and it has been implicated in the metastasis of gastric, colorectal, prostate, and breast cancers. Notably, the interaction with CD39 did not change the total amount of ANXA2 in the cells; instead, it altered its phosphorylation state. Knocking down CD39 suppressed phosphorylation of ANXA2 at the tyrosine 24 residue, a modification previously linked to malignant transformation, epithelial-mesenchymal transition, tumor invasion, and metastasis.

Downstream of ANXA2, the team traced the signal into two well-known cancer-promoting programs. Gene Set Enrichment Analysis of RNA-seq data from both tumor tissue and cell lines showed that the PI3K/AKT pathway and the epithelial-mesenchymal transition, or EMT, process were significantly influenced in cases with high CD39 expression. Western blotting confirmed the bioinformatics: knocking down CD39 reduced the phosphorylation of PI3K, AKT, and mTOR at the S2448 site without changing their total protein levels, while overexpression enhanced their phosphorylation. CD39 levels also reshaped the EMT machinery, with knockdown lowering the expression of Claudin-1, Twist-1, Vimentin, and N-cadherin while raising E-cadherin, and overexpression producing the opposite pattern. The decisive proof came from a rescue experiment in which the researchers mutated the Tyr24 site of ANXA2, substituting alanine for tyrosine. This single amino acid change reversed nearly everything CD39 had done: the proliferative boost measured by CCK-8, the migratory and invasive gains seen in transwell assays, the EMT marker shifts, and the PI3K/AKT phosphorylation all collapsed once the phosphorylation site was eliminated.

The authors are candid about the limitations of their work. The study is retrospective, and the prognostic role of CD39 will need validation in a prospective multi-center cohort. The number of samples and cell lines was modest, and larger cohorts would strengthen the statistical power and generalizability of the findings. It also remains unclear exactly how the CD39/ANXA2 axis influences cholangiocarcinoma progression, and how CD39 modulates ANXA2 phosphorylation and the downstream signaling cascades requires further investigation. Even so, the convergence of evidence from human tissue, cell culture, animal models, and mechanistic biochemistry makes a compelling case. CD39 stands out as both a biomarker that could identify patients at highest risk and a therapeutic target whose blockade might starve bile duct tumors of a key growth and spread pathway. For a cancer with so few options, that dual promise is a rare and welcome development.

Subject of Research: The role of CD39 expression in the progression, metastasis, and prognosis of cholangiocarcinoma

Article Title: The aberrant expression of CD39 is associated with the dismal outcome of patients with cholangiocarcinoma

Article References: Zheng, B., Shen, S., Wang, J., Sun, W., Wan, W., Liu, J., Zhang, D., Ni, X., Suo, T., Liu, H., Ni, X., & Liu, H. (2025). The aberrant expression of CD39 is associated with the dismal outcome of patients with cholangiocarcinoma. Clinical Cancer Bulletin, 4(1), Article 1. https://doi.org/10.1007/s44272-025-00028-0

Image Credits: AI Generated

DOI: 10.1007/s44272-025-00028-0

Keywords: CD39, cholangiocarcinoma, ANXA2, PI3K/AKT signaling, EMT, phosphorylation, prognostic biomarker, biliary tract cancer, ENTPD1, metastasis, immunohistochemistry, therapeutic target

Cutaneous melanoma is the most lethal and aggressive cancer of the skin, arising from malignant transformation of melanocytes and marked by rapid proliferation, high metastatic potential, and notorious resistance to conventional therapies. The latest epidemiological estimates from the International Agency for Research on Cancer counted 331,722 new cases and 58,667 deaths worldwide in 2022, and even as targeted therapies and immunotherapies have transformed the landscape, low response rates and acquired resistance continue to frustrate effective management. That unmet need is precisely why the study’s authors turned their attention to two signaling systems increasingly recognized as vulnerabilities in tumors: purinergic signaling, the extracellular communication network built on adenosine triphosphate and its breakdown products, and the inflammatory axis involving interleukin-6 and the NLRP3 inflammasome.

Purinergic signaling, first proposed in 1972, operates through P1 and P2 receptors that respond to a ladder of molecules: ATP, adenosine diphosphate, adenosine monophosphate, and adenosine. Depending on which molecules dominate the extracellular space, the same pathway can drive cell proliferation or push a cell toward apoptosis. In the tumor microenvironment, the balance tilts dangerously. Extracellular adenosine, generated in abundance, acts as a potent immunosuppressant, blunting the anti-tumor immune response. The levels of these signaling molecules are controlled largely by ectonucleotidases, membrane-bound enzymes known as CD39 and CD73, along with adenosine deaminase, which breaks adenosine down into inosine. CD39 converts ATP into ADP and AMP; CD73 then hydrolyzes AMP into adenosine. Overexpression of CD73 has been documented in pancreatic adenocarcinoma, thyroid cancer, and melanoma itself, and both CD39 and CD73 have been flagged as next-generation checkpoint targets for cancer therapy.

Against that backdrop, calcitriol offered an intriguing candidate. Previous work had shown that 1-alpha,25-dihydroxyvitamin D3 induces apoptosis in melanoma cells, enhances the anticancer effects of classical chemotherapy, inhibits proliferation and migration in breast cancer models, and can modulate IL-6 expression. Yet its mechanism of action on the purinergic system in melanoma had never been systematically explored. The research team hypothesized that calcitriol exerts a potent antineoplastic effect on cutaneous melanoma by modulating the activity and expression of ectonucleotidases, thereby rewiring the extracellular nucleotide landscape in favor of tumor cell death.

To test the hypothesis, the investigators cultured two human cutaneous melanoma cell lines, A375 and SK-MEL-28, treating them with calcitriol at 1, 10, and 50 nanomolar concentrations for 24 hours. The A375 line, which displays epithelial morphology and an invasive, metastatic profile, and SK-MEL-28, a polygonal melanoma line, were subjected to a battery of assays: MTT and fluorescence microscopy viability tests, measurements of mitochondrial transmembrane potential using the TMRE dye, detection of apoptotic bodies by acridine orange staining, wound-healing migration assays, and enzymatic quantification of ATP, ADP, and AMP hydrolysis alongside adenosine deaminase activity. Gene expression of CD39, CD73, IL-6, and NLRP3 was assessed by RT-qPCR, normalized to the housekeeping gene GAPDH and analyzed with the comparative delta-delta-CT method, with one-way ANOVA and Dunnett’s post hoc test applied throughout.

The results were striking and, in one respect, unexpectedly selective. In A375 cells, calcitriol significantly reduced viability at every concentration tested, with the MTT assay yielding P values of 0.0004 at 1 nM and below 0.0001 at 10 and 50 nM. Fluorescence microscopy independently corroborated the viability loss across all doses. Crucially, the treatment also collapsed the mitochondrial transmembrane potential of A375 cells at all concentrations, with statistical significance reaching P < 0.0001, a disruption consistent with the initiation of intrinsic apoptosis. Matching that mitochondrial signature, the treated cells showed marked nuclear fragmentation: apoptotic bodies rose significantly at all three doses, while cell counts fell in a dose-dependent manner. Wound-healing assays added another dimension, revealing that calcitriol inhibited A375 migration and wound closure at every concentration tested within just 24 hours, with P < 0.0001, a finding with obvious implications for blocking metastasis.

The SK-MEL-28 line told a different story. Calcitriol produced no significant reduction in its viability and left its mitochondrial potential untouched; at 1 nM, viability even increased slightly. The researchers point to a well-documented explanation: SK-MEL-28 cells express functionally lower levels of the vitamin D receptor than several other melanoma lines, rendering them resistant to calcitriol’s antiproliferative effects at nanomolar concentrations, with prior studies noting sensitivity only at much higher doses. The contrast between the two cell lines underscores that calcitriol’s anticancer activity depends on functional vitamin D receptor signaling, a caveat that will shape which patients might ultimately benefit from a calcitriol-based adjuvant strategy.

The deepest technical insight, however, came from the purinergic analysis. Calcitriol left ATP hydrolysis unchanged but significantly decreased ADP hydrolysis at 1 and 10 nM, with a modest increase at 50 nM, and reduced AMP hydrolysis at 10 and 50 nM. Because CD39 and CD73 jointly convert ATP down the cascade to adenosine, dampened AMP breakdown means less substrate for adenosine production. Consistent with that logic, adenosine deaminase activity, which depends on adenosine availability, dropped sharply at 10 and 50 nM. At the gene level, calcitriol downregulated CD39 expression at 10 and 50 nM and exerted a strong suppressive effect on CD73 at those same concentrations, P < 0.0001. Together, these changes describe a coherent suppression of the AMP-to-adenosine axis, the very pathway tumors exploit to generate immunosuppressive adenosine in their microenvironment. By throttling adenosine generation, calcitriol may indirectly loosen the tumor’s grip on local immunity.

The inflammatory arm of the study completed the picture. Extracellular nucleotide signaling is intimately connected to inflammation, and both IL-6 and NLRP3 have dual, sometimes controversial roles in cancer, with evidence linking them to tumor progression, chemoresistance, immune cell infiltration, and poor prognosis in melanoma. Calcitriol significantly downregulated IL-6 expression at 10 nM and 50 nM, and produced an equally robust reduction in NLRP3 gene expression, with P < 0.0001 at both doses. Given that IL-6 targeting has been proposed to abrogate melanoma growth and progression, and that NLRP3 is increasingly viewed as a therapeutic target capable of reducing chemoresistance, these transcriptional effects suggest calcitriol acts on multiple fronts at once: killing tumor cells directly, impairing their migratory capacity, starving the immunosuppressive adenosine pathway, and calming the pro-tumoral inflammatory circuitry.

The authors are careful about scope. Their analysis covered gene expression rather than protein levels, and only two cell lines were examined, which they acknowledge as a limitation given the distinct metabolic profiles of A375 and SK-MEL-28. They also stress that while the nanomolar concentrations used appear practical for in vivo applications, safety testing is required, and future animal studies should monitor calcium levels to guard against hypercalcemia, the classic toxicity of active vitamin D compounds. Encouragingly, the adjuvant concept already has clinical footprints: calcitriol has been shown to enhance the effects of cisplatin and dacarbazine in melanoma cells, to combine favorably with the VEGFR inhibitor Cediranib, and, in a prospective phase Ib study, to be well tolerated in metastatic melanoma patients receiving high-dose encapsulated calcitriol alongside temozolomide, with no significant secondary side effects reported. Combined with prior evidence that calcitriol can sensitize melanoma cells to proton beam irradiation, the new purinergic mechanism adds a mechanistic rationale to an accumulating clinical case. If subsequent in vivo work confirms that calcitriol’s ectonucleotidase modulation translates into restored anti-tumor immunity, the sunshine vitamin’s most potent form could find itself written into the melanoma treatment algorithm.

Subject of Research: Antineoplastic effects of calcitriol on cutaneous melanoma cells via purinergic signaling modulation

Article Title: Calcitriol, the active form of vitamin D, induces cell death and purinergic signaling modulation in cutaneous melanoma cells

Article References: da Silva, G. B., Narzetti, R. A., Dallagnol, P., Ozelame, B. C., Manica, D., Ramos, V. H. M., Kempka, A. P., & Bagatini, M. D. (2026). Calcitriol, the active form of vitamin D, induces cell death and purinergic signaling modulation in cutaneous melanoma cells. Medical Oncology, 43(10), Article 288. https://doi.org/10.1007/s12032-026-03412-5

Image Credits: AI Generated

DOI: 10.1007/s12032-026-03412-5

Keywords: calcitriol, vitamin D, cutaneous melanoma, purinergic signaling, ectonucleotidases, CD39, CD73, apoptosis, mitochondrial membrane potential, IL-6, NLRP3, adjuvant therapy