N-methyl-D-aspartate type glutamate receptors in cancer cell lines

N-methyl-D-aspartate receptors (NMDAR) are ionotropic glutamate receptors, which were originally discovered in the central nervous system. Recently functional NMDARs have been described in certain tumors (like NSCLC, melanoma etc.). Therefore we aimed to examine potential functions of NMDARs in various cancer cell lines.
Human gastric (MKN7), colon (CACO2) and invasive ductal breast (MCF7) adenocarcinoma cell lines were used for the experiments. Our laboratory previously specified NMDAR subunit expression in the above mentioned cell lines at mRNA and protein level. The next step was to examine metabolic activity and proliferation changes after treatments with NMDAR agonists and antagonists. Metabolic activity was measured by MTT assay, and 3H-thymidine incorporation assay was used for examining proliferation. Results were evaluated by Tukey’s HSD one-way ANOVA test.
We found in every investigated cell line, that administration either of a selective NR1 subunit antagonist, DAP5 (20 µM) or an NMDAR glycine binding site antagonist, DCKA (10 µM) for 48 hours caused significant increases of metabolic activity (n=12, p≤0.05). On the contrary, the addition of the agonists (glutamate (20 µM), NMDA (20 µM), glycine (10 µM)) or the NR2B subunit antagonist Ifenprodil (20 µM) did not result in any significant changes. Although the administration of the specific glycine receptor (GlyR) antagonist, strychnine (5 µM) solely did not result in any changes in MTT assays, but in combination with glycine or glycine+glutamate it significantly increased metabolic activity in all cell lines. 3H-thymidine incorporation assays were also performed after similar 48-hour incubations with the above mentioned chemicals. 3H-thymidine was added to each sample for 16 hours. Detailed evaluation and statistical analysis of the results is in progress.
These findings suggest that metabolic activity of the investigated adenocarcinoma cell lines is sensitive to GlyR and certain NMDAR inhibition. It implies that NMDAR functions as well as GlyRs may influence survival of the investigated cancer cells suggesting that NMDARs and GlyRs could become interesting new targets for cancer treatment.
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