Background Cytokines are capable of manipulating the tumour microenvironment supporting tumour growth. Interleukin (IL)‐8 and monocyte chemoattractant protein (MCP)‐1, shown to be produced by various tumours, can negatively affect prognosis. The production of cytokines by canine mast cell tumours (MCT) has not been reported. Hypothesis/objectives We hypothesise that MCT cell lines produce IL‐8 and/or MCP‐1 in addition to other cytokines, and that their production can be modulated by the Janus kinase (JAK) inhibitor oclacitinib. This pilot study aims to investigate the production of IL‐8, MCP‐1 and nine additional cytokines in three canine MCT cell lines, and determine the effects of oclacitinib on their production. Methods and materials Reverse transcriptase‐PCR was used to detect the expression of IL‐8 and MCP‐1 mRNA in three MCT cell lines (CoMS, CM‐MC1 and VI‐MC1). The supernatant of the cell lines was evaluated for the presence of 11 cytokines [IL‐2, ‐6, ‐7, ‐8, ‐10, ‐15 and ‐18, and MCP‐1, granulocyte‐macrophage colony‐stimulating factor (GM‐CSF), interferon (IFN)γ and tumour necrosis factor (TNF)α] by enzyme‐linked immunosorbent assay (ELISA). The IC50 of oclacitinib was identified for each cell line. ELISA was performed again to compare changes in IL‐8 and MCP‐1 in treated cell lines versus untreated controls. Results Interleukin‐8 and MCP‐1 were produced by all MCT cell lines tested. Oclacitinib significantly decreased the release of IL‐8 in the CoMS cell line and of MCP‐1 in CoMS and VI‐MC1 in clinically relevant concentrations. Furthermore, oclacitinib significantly decreased the proliferation of all three cell lines. Conclusions Interleukin‐8 and MCP‐1 are produced by canine MCT cell lines. Modulation of their production is possible with oclacitinib.
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