The research, led by João Victor Garcia de Souza and Débora Tavares de Resende e Silva of the Federal University of Fronteira Sul in Chapecó, Brazil, enrolled 40 patients undergoing surgical resection at two regional hospitals between June 2023 and December 2024. Of these, 27 tumors were classified as WHO grade 1 and 6 as WHO grade 2, while 7 cases could not be graded because pathology reports were unavailable in the electronic medical record. The cohort was predominantly female, with women making up 85 percent of participants, and the mean age was 52.9 years. Notably, two thirds of the grade 2 tumors occurred in patients aged 65 or older, a statistically significant age association, and systemic arterial hypertension was the most prevalent comorbidity in both groups.

The scientific rationale rests on the purinergic system, a signaling network that regulates cellular homeostasis through the controlled breakdown of extracellular ATP. The enzyme CD39, also known as ENTPD1, hydrolyzes ATP and ADP into AMP, after which CD73, encoded by the NT5E gene, converts AMP into adenosine. Adenosine is a potent immunosuppressive metabolite that can dampen anti-tumor T cell activity, and the CD39-CD73 axis has become a major focus of cancer immunotherapy research in gliomas and other brain tumors. Adenosine deaminase, or ADA, completes the circuit by degrading adenosine to inosine. Until now, however, these pathways had received scant attention in meningiomas, largely because the tumors are usually benign.

Using quantitative reverse transcription PCR on tumor tissue preserved in RNAlater, the researchers measured mRNA levels of ENTPD1/CD39, NT5E/CD73, CD274/PD-L1 and IL1B, normalizing expression to the ACTB reference gene with the 2^-ΔΔCt method. The results revealed a striking grade-associated pattern: NT5E/CD73 mRNA was approximately 2.15-fold higher in WHO grade 2 tumors than in grade 1, a difference that reached statistical significance, while CD274/PD-L1 and IL-1β transcripts were significantly reduced in the higher-grade tumors. CD39 mRNA, by contrast, showed no change between grades. Spearman correlation analysis found no significant relationships among the measured markers, suggesting the alterations vary independently across tumors.

Immunohistochemistry on paraffin-embedded tissue, quantified digitally with QuPath software across five representative fields per sample, validated the transcriptional findings at the protein level. CD73 immunostaining averaged 0.684 in grade 2 tumors compared with just 0.082 in grade 1, while PD-L1 staining averaged 0.211 in grade 1 versus 0.044 in grade 2. The discordance between PD-L1 mRNA and protein in grade 2 tumors, where the transcript was abundant but the protein scarce, points the authors toward post-transcriptional regulatory mechanisms, such as blocked translation or accelerated protein degradation, a phenomenon known in oncology as mRNA-protein discordance.

The team also looked beyond the tumor itself, measuring enzyme activities in peripheral blood lymphocytes isolated by Ficoll-Hypaque density gradient centrifugation. CD39 activity in hydrolyzing ATP was significantly elevated in grade 2 patients compared with healthy age- and sex-matched controls and compared with grade 1 patients, while CD73 activity in hydrolyzing AMP was higher in grade 2 than in grade 1. ADA activity was increased in both patient groups relative to controls, though it did not differ between grades. Plasma concentrations of six cytokines, including IFN-γ, TNF, IL-10, IL-6, IL-4 and IL-2, measured by cytometric bead array, showed non-significant trends toward higher values in grade 2 patients, with TNF coming closest to the significance threshold.

The authors are careful to frame these observations as hypothesis-generating rather than proof of mechanism. Because the study was cross-sectional, relied on small assay-specific subsets, sometimes numbering only four to six patients per group, and did not directly measure extracellular adenosine concentrations, adenosine receptor expression or downstream signaling, the findings cannot demonstrate adenosine-mediated immune evasion or tumor progression. The researchers also note that peripheral lymphocyte enzyme activity and circulating cytokines do not necessarily reflect what happens within the tumor microenvironment, and confounders such as hypertension, corticosteroid use and other medications may have influenced systemic measurements.

The PD-L1 result is particularly provocative because it diverges from earlier work. A 2015 study by Du and colleagues reported increased PD-L1 expression in anaplastic meningiomas, now classified as WHO grade 3, whereas the present cohort found lower PD-L1 in grade 2 tumors. The authors caution that grade 2 and grade 3 meningiomas are biologically distinct categories, and that differences in antibody clones, staining protocols, scoring thresholds and the relative abundance of neoplastic versus immune cells expressing PD-L1 can all shape immunohistochemical results. They argue that standardized, compartment-resolved analyses across larger cohorts are needed before any grade-dependent switch in immune-evasion strategy can be claimed.

The lower PD-L1 expression in higher-grade tumors also raises practical questions about therapy. Checkpoint inhibitor monotherapy relies on tumor-cell PD-L1 as both a target and a predictive biomarker, and the study’s findings suggest that such an approach may be less effective in WHO grade 2 meningiomas, where the ligand is scarce. Conversely, the consistent elevation of CD73 at both mRNA and protein levels in grade 2 tumors identifies it as a candidate grade-associated biomarker and provides a biological rationale for testing whether adenosinergic signaling differs between meningioma grades, though the authors stress that no treatment response, recurrence or survival data were analyzed.

For now, the study stands as an early map of purinergic and immune-related profiles in the most common primary brain tumor, drawn from a region of southern Brazil where agricultural employment was noted in a subset of patients, echoing prior reports linking farming and pesticide exposure to CNS tumor risk. The authors call for larger, longitudinal and mechanistic studies combining cell-type-resolved tissue analysis, direct adenosine measurements, immune phenotyping and clinical outcomes to determine whether CD73 can serve as a prognostic marker or a therapeutic target. Until then, the message is measured: CD73 rises and PD-L1 falls with meningioma grade, and understanding why could reshape how these tumors are monitored and treated.

Subject of Research: Purinergic signaling and immune checkpoint marker expression in WHO grade 1 and grade 2 meningiomas

Article Title: CD73 and PD-L1 expression in WHO grade 1 and grade 2 meningiomas: an exploratory analysis of purinergic and immune-related profiles

Article References: de Souza, J. V. G., Pretto, K. P., da Silva, L. V. G., Oenning, B. A. M., Pin, C., Menegassi, J., Franscescon, F., Chimelo, M. B., da Cunha, M. L. V., & de Resende e Silva, D. T. (2026). CD73 and PD-L1 expression in WHO grade 1 and grade 2 meningiomas: an exploratory analysis of purinergic and immune-related profiles. Journal of Neuro-Oncology, 179(2), Article 82. https://doi.org/10.1007/s11060-026-05786-y

Image Credits: AI Generated

DOI: 10.1007/s11060-026-05786-y

Keywords: meningioma, CD73, PD-L1, purinergic signaling, adenosine, tumor microenvironment, WHO grading, ectonucleotidases, immunotherapy, brain tumor, biomarker, Journal of Neuro-Oncology

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