Expression of ADK-S and ADK-L Isoforms and Their Association with CD39/CD73/A2aR in Colorectal Cancer.

The level of mRNA of the long (L) and short (S) isoforms of adenosine kinase (ADK) was analyzed in patients with colorectal cancer (CRC). ADK is required to convert adenosine (ADO) to AMP. It was shown that tumor and normal colon tissues (n=13) do not differ in the level of ADK-S and ADK-L mRNA. At the same time, the level of ADK-S mRNA (tumor: p=0.0214, normal: p=0.005) in the colon tissue was lower than in the blood of CRC patients (n=20), and the level of ADK-L mRNA (tumor: p=0.007, normal: p=0.024), on the contrary, was higher. A negative correlation was found between the level of ADK-S mRNA and the level of A2aR mRNA in both tumor and normal tissues (p=0.018 and p=0.0014, respectively). In the tumor tissue, a positive correlation was shown between ADK-L and CD73 mRNA levels (p=0.017). The obtained data indicate the association ADK with the expression of CD39/CD73/A2aR in CRC patients. In this regard, the effect of recombinant ADK on the expression of CD39 and CD73 ectonucleotidase by T cells in vitro was analyzed. In a culture of peripheral blood mononuclear cells isolated from the blood of 5 healthy donors, ADK did not abolish the inhibitory effect on the expression of CD39 and CD73 by CD8+T cells in the presence of a high concentration of ATP (a source for ADO). Effects on CD39+CD4+, CD73+CD4+T cells and CD39+ Treg cells were also not found.

Relationship between the Gene Expression of Adenosine Kinase Isoforms and the Expression of CD39 and CD73 Ectonucleotidases in Colorectal Cancer.

Tumor cells have the capacity to create an adenosine-rich immunosuppressive environment, which can interfere with antitumor immunotherapy. Approaches are currently being developed with a view to suppressing the production of adenosine or its signals. Such approaches include the use of antibodies to inhibit CD39, CD73, and adenosine-receptor antagonists. However, the abundance of enzymatic pathways that control the ATP-adenosine balance, as well as the still poorly understood intracellular adenosine regulation, makes the hoped-for success unlikely. In the present study, the enzyme adenosine kinase (ADK) needed to convert adenosine to adenosine monophosphate, thereby regulating its levels, was investigated. To do so, peripheral blood samples from patients with colorectal cancer (CRC) (n = 31) were collected with blood samples from healthy donors (n = 17) used as controls. ADK gene expression levels and those of its long (ADK-L) and short (ADK-S) isoforms were measured. The relationship between the levels of ADK gene expression and that of CD39, CD73, and A2aR genes was analyzed. It turned out that in the group of CRC patients (stages III-IV), the level of ADK-L mRNA was lower (p < 0.0011) when compared to that of the control. For the first time, an average correlation was found between the level of expression of CD39 and ADK-S (r = -0.468 at p = 0.043) and between CD73 and ADK-L (r = 0.518 at p = 0.0232) in CRC patients. Flow cytometry was used to assess the content of CD39/CD73-expressing CD8+, CD4+ and Treg lymphocytes, as well as their relationship with the level of ADK gene expression in CRC patients. But no significant correlations were found.

[Expression of lymphocyte activation markers in patients with gastrointestinal tumors at different stages].

Patients with gastrointestinal tumors revealed relatively high levels of activated lymphocytes. CD25 expression at later stages was much higher than at earlier ones (I-II). A relationship between CD25, CD71 and CD95 expression was established for metastatic spread of gastrointestinal tumors as well as a correlation between CD71 and CD98 expression for favorable course. A distinct activation phenotype can be identified for peripheral blood lymphocytes in burgeoning tumor which should be taken into account in prognosis.

Expression of surface lymphocyte markers in various courses of gastrointestinal tumors.

Expression of activation antigens increased in patients with gastrointestinal tumors of various clinical courses. The count of CD25+ and CD71+ lymphocytes was high in patients with favorable course of non-progressive tumors. The increase in the expression of activation markers probably reflects adequate functional activity of the immune system in patients with tumors.