Suppression of tumourigenicity, and induction of differentiation of the canine mammary tumour cell line MCM-B2 by sodium phenylacetate

Sodium phenylacetate inhibits the Ras/MAPK signaling pathway to induce reduction of the c-Raf-1 protein in human and canine breast cancer cells

An aromatic fatty acid, phenylacetate (PA), has been shown to have cytostatic, antitumor and cell differentiation-inducing effects on various kinds of tumors. Previously, we have demonstrated cell growth inhibition, malignant phenotype reduction and cell differentiation effects of sodium phenylacetate (NaPA) treatment in a canine mammary tumor cell line. To clarify the molecular mechanism of these effects, we examined the expression of Ras/MAPK signaling pathway-related molecules in human and canine breast cancer cell lines, and found that the level of c-Raf-1 protein was reduced by 5, 10 and 20 mM of NaPA treatments, though Ras activation was maintained. Dephosphorylation of c-Raf-1 at Serine (Ser) 259, Ser 338, and Ser 621 were also seen in NaPA-treated cells. Downstream factors in the pathway, such as mitogen-activated protein kinase/ERK kinase (MEK)1/2 and ERK1/2, showed decreased activity, and accordingly, expressions of cyclinD1, c-myc, and inactivation of p90 ribosomal S6 kinase (RSK), which are MAPK targets, were reduced. We also observed the reduction of cell-cycle-promoted molecules, such as cdc1/cdk2, cdk4, PCNA cyclin A, and cyclin B, and the increased expression of p27kip1. Furthermore, expression of an epithelial marker, E-cadherin, was increased by NaPA treatment. These results suggest that one of the molecular targets of NaPA treatment was the reduction of c-Raf-1 protein, and that its reduction results in the decrease of malignant characteristics of tumor cells through blockage of the Ras/MAPK signaling pathway.

Effects of cryopreservation and phenylacetate on biological characters of adherent LAK cells from patients with hepatocellular carcinoma

AIM: To improve the preparation of adherent lymphokine-activated killer (A-LAK) cells and to study the effects of cryopreservation and phenylacetate (PA) on biological characters of A-LAK cells.

METHODS: A-LAK cells were obtained from peripheral blood mononuclear cells (PBMCs) of the patients with hepatocellular carcinoma (HCC) by using L-phenylalanine methyl ester (PME) to deplete immunosuppressive monocytes. Proliferative activity of SMMC7721 cell line after treatment with phenylacetate (PA) was observed. A-LAK cells were treated with the supernatant of SMMC7721 cells that had been pretreated with PA. The changes of proliferation, cytotoxicity and phenotype of A-LAK cells were investigated after cryopreservation.

RESULTS: The expansion of A-LAK cells (96.79 ± 69.10 folds on Day 14) was significantly higher than that of non-adherent LAK (NA-LAK) cells (22.77 ± 13.20) as well as conventional LAK cells (4.64 ± 0.91). PA significantly suppressed the growth of SMMC7721 cells, and the inhibitor ratio was 46%. The supernatant of cultured tumor cells intensively suppressed the proliferation and cytotoxicity of A-LAK cells, but the suppressive effect of the supernatant was previously decreased after treatment with PA. Impairments in proliferation and cytotoxicity of A-LAK cells immediately after thawing of cryopreservation and recovery after reincubation with IL-2 were observed. The cytotoxicity of thawed A-LAK cells on Day 5 was significantly higher than that of fresh A-LAK before freezing (54.8% ± 10.2% vs 40.5% ± 6.4%). No significant change in the percentage of lymphocyte subsets was identified in frozen A-LAK cells as compared with that in the fresh control cells.

CONCLUSION: A-LAK cells can be simply prepared by using PME, and showed a synergistic anti-tumor effect with the combination of PA. Cryopreservation can increase the immunoactivities of A-LAK cells from the patients with hepatocellular carcinoma.