Abstract #1276: Methionine induces cell cycle arrest selectively in LNCaP and MCF-7 cells but not in colon cancer cells or untransformed breast, prostate, and colon cells.

Methionine, an essential amino acid, is not only fundamental for protein synthesis, but also as a major donor of methyl group for DNA methylation and because of its involvement in the initiation of translation. We previously showed that methionine potently inhibits proliferation of breast and prostate cancer cell lines, concomitant with modification of p53 which suggesting anti-cancer potential. The mechanisms underlying interactions of p53 with the cell cycle in response to methionine remain unknown. We aimed 1) to determine whether cell growth inhibitory effects of methionine are limited to breast and prostate cancer cells and selective for cancer cells; 2) to assess effects methionine on cell cycle and apoptosis; and 3) to explore mechanisms of the possible involvement of p53 in these methionine effects. The following human cell lines were treated with methionine (5mg/ml) for 72 hrs: MCF-7 breast cancer cells, LNCaP prostate cancer cells, and LS-174 colon cancer cells, all of which express wild-type p53, DU-145 prostate cancer cells and SW480 colon cancer cells, both of which express inactive mutated p53, and immortalized but untransformed NCM-460 colon cells, MCF-10A breast cells, and BPH-1 prostate cells. Cell cycle effects of methionine were assessed by flow cytometry and effects on expression of p53, MDM2, and HAUSP and on caspase 3 cleavages were evaluated by Western analysis. Caspase 3 expression was also evaluated using immunofluorescence and flow cytometry. Methionine caused cell cycle arrest at G1 of both MCF-7 and LNCaP cells, but had no effect on cell cycle parameters of LS-174 cells and of untransformed MCF-10A, BPH-1, and NCM-460 cells. In contrast, methionine induced S growth arrest of DU-145 containing mutated p53. Apoptotic rates were generally very low (2.1%), regardless of treatment, but methionine slightly increased apoptotic rates in BPH-1 cells (5.2%) and reduced apoptosis in normal colon NCM-460 cells (1.6%) which had highest apoptotic rates when untreated (7.4%). Methionine did not alter caspase 3 cleavage in LNCaP. In association with cell cycle arrest at G1 in LNCaP and MCF-7 cells, methionine treatment resulted in appearance of a 67 Kd modified form of p53 when probed with the Pab1801 antibody and over-expression of MDM2 and decreased HAUSP expression. In conclusion, methionine at a pharmacological but non-apoptosis-inducing concentration of 5 mg/ml causes cell cycle arrest at G1 in LNCaP and MCF-7 prostate and breast cancer cells, but not in untransformed prostate and breast cell lines or benign and malignant colon cells. DU-145 with inactive, mutated p53 was growth arrested at S. Also, these results may suggest methionine-induced ubiquitination of p53, possibly mediated by MDM2 and HAUSP. Thus, methionine may have therapeutic benefit because of its growth inhibitory effects selectively in prostate and breast cancer cells.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 1276.