Oncolytic virotherapy exploits viruses that selectively infect and destroy tumour cells while sparing healthy tissue. The approach works through several mechanisms at once: direct lysis of neoplastic cells, activation of the immune system against the tumour, and reshaping of the tumour microenvironment through inflammatory responses and metabolic reprogramming. Canine distemper virus, a morbillivirus in the Paramyxoviridae family and a close relative of measles virus, has emerged as a candidate. Attenuated measles virus has already shown promise against human ovarian cancer, and the Onderstepoort vaccine strain of canine distemper virus has demonstrated inhibition of tumour growth and increased intratumoral necrosis in murine xenotransplantation models, along with immune stimulation, altered matrix metalloproteinase expression, reduced angiogenesis, and decreased cell migration.

A central unresolved question, however, is how tumour cells respond to viral treatment in different parts of a solid tumour. The centres of solid tumours are characterized by hypoxia and nutrient starvation, conditions that increase tumour aggressiveness by enhancing angiogenesis and altering metabolism. Because tumour cells react differently to treatment depending on their surroundings, a research team set out to map the transcriptional consequences of canine distemper virus infection under conditions that mimic distinct tumour zones. Their hypothesis was that both the virus and the local microenvironment would induce specific gene expression changes that could influence therapeutic efficacy.

To test this, the researchers used the canine histiocytic sarcoma cell line DH82 and a derivative line persistently infected with the Onderstepoort strain, which maintained an infection rate exceeding 90 percent to maximize the observable viral effect. The cells were cultured under three conditions: standard conditions representing the tumour periphery, hypoxia at 1 percent oxygen simulating intermediate and central regions, and serum starvation mimicking nutrient deprivation. Each condition was applied for one day, representing short-term exposure, and three days, representing prolonged exposure, and the cells were then subjected to RNA sequencing with approximately 74 million reads per sample mapped to both the canine and viral genomes.

The proliferation data already revealed that infection and environment interact. Under standard conditions, the persistently infected cells significantly outnumbered non-infected controls at both time points. Under hypoxia, cell numbers dropped dramatically in both groups, and by day 3 the infected cells were significantly fewer than the non-infected controls. Under starvation, infected cells were initially more numerous at day 1, but by day 3 their numbers had declined and no longer differed significantly from controls. These patterns suggest that viral infection heightens cellular sensitivity to environmental stress, particularly nutrient deprivation.

The transcriptomic analysis confirmed this impression on a molecular scale. Principal component analysis separated infected from non-infected cells along the first principal component, which accounted for more than half of the total variance, with culture condition and exposure duration driving further clustering. The number of differentially expressed genes varied by comparison but was consistently higher in infected cells, peaking at 3,700 genes under short-term starvation. This pronounced response indicates a rapid adaptive capacity to nutrient deprivation in infected neoplastic cells that was not observed in non-infected DH82 cells, echoing earlier findings that short-term starvation sensitizes breast cancer cells to chemotherapy and colorectal carcinoma cells to oncolytic measles virus.

Functional enrichment analysis revealed a coherent biological story. Across all conditions and time points, upregulated genes in infected cells were dominated by immune processes: defence response, response to stimuli, and pro-inflammatory signalling through pathogen-recognition receptors including Toll-like, Nod-like, and RIG-I-like receptor pathways. Chemokine signalling, JAK-STAT signalling, and pathways associated with viral infections such as influenza, measles, and herpes simplex virus were prominently enriched. The gene DDX60, which encodes a DExD/H box RNA helicase known to enhance RIG-I- and MDA5-dependent type I interferon expression, was the most upregulated gene across all conditions, positioning it as a likely key mediator of the antiviral response and, intriguingly, a molecule also associated with tumour progression and immune signalling in human pancreatic cancer.

Equally striking was what was switched off. Genes involved in circulatory system development and angiogenesis were significantly downregulated in infected cells under every condition, and the gene parvin alpha, the most downregulated across all comparisons, is known to drive tumour progression, angiogenesis, and metastasis through integrin-linked kinase-Akt-VEGF signalling. Metabolic pathways and the PI3K-Akt signalling pathway, which supports proliferation, survival, and angiogenesis across many tumour types, were also suppressed. These findings align with previous observations that canine distemper virus reduces microvessel density in histiocytic sarcoma xenografts and that oncolytic viruses can attenuate hypoxia signalling and angiogenic pathways in other cancer models.

The zone-specific comparisons added an important layer of nuance. Under hypoxia, infected cells downregulated immune-related genes while upregulating genes connected to cell movement, vasculature development, and, after prolonged exposure, cell cycle and stress response processes, a pattern consistent with hypoxia-induced immune escape that could limit virotherapy efficacy. Under starvation, the response was different: short-term exposure activated immune and chemotaxis genes while suppressing developmental and proliferative programs, and prolonged exposure upregulated cell cycle, immune, and metabolic processes while downregulating tissue development and cell adhesion. The authors note that hypoxia-induced necrosis might paradoxically enhance the antigenic potential of infected cells and promote inflammatory infiltration, as seen in xenotransplantation experiments where persistently infected cells spontaneously regressed after initial tumour formation.

Overall, the study demonstrates that canine distemper virus infection elicits conserved core effects across all simulated tumour zones, namely immune activation and angiogenesis suppression, while environmental conditions modulate the finer details of the response. The authors caution that their model relies on persistent infection, which may induce epigenetic and transcriptomic changes that would not occur after an acute therapeutic infection, limiting direct transferability to spontaneous canine tumours. Further studies using ex vivo samples from natural histiocytic sarcomas with acute infections will be needed to identify specific genes that could serve as therapeutic targets or combination partners to enhance the efficacy of canine distemper virus-based virotherapy, potentially extending beyond dogs to other malignancies.

Subject of Research: Transcriptional effects of oncolytic canine distemper virus infection in canine histiocytic sarcoma cells under hypoxic and nutrient-starved conditions

Article Title: Canine Distemper Virus‐Induced Transcriptional Modulation of Canine Histiocytic Sarcoma Cells in an In Vitro Model of Tumour Zones

Article References: Asawapattanakul, T., Schughart, K., Geffers, R., von Köckritz‐Blickwede, M., Armando, F., Baumgärtner, W., & Puff, C. (2026). Canine Distemper Virus‐Induced Transcriptional Modulation of Canine Histiocytic Sarcoma Cells in an In Vitro Model of Tumour Zones. Journal of Cellular and Molecular Medicine, 30(20), Article e71409. https://doi.org/10.1111/jcmm.71409

Image Credits: AI Generated

DOI: 10.1111/jcmm.71409

Keywords: canine distemper virus, oncolytic virotherapy, histiocytic sarcoma, tumour microenvironment, hypoxia, starvation, RNA sequencing, transcriptomics, angiogenesis, innate immunity, DDX60, veterinary oncology