Search

Methionine addiction is a fundamental and general hallmark of cancer discovered by us almost a half-century ago [Proc Natl Acad Sci U S A 73 (1976) 1523-1527]. Methionine addiction is defined as the requirement, specific for cancer cells of all types, for exogenous methionine despite the normal ability to synthesize methionine from homocysteine. The methionine addiction of cancer is termed the Hoffman-effect, analogous to the Warburg-effect of the high glucose requirement of cancer cells. Methionine addiction is due to excess transmethylation reactions resulting in high methionine flux in cancer cells, which causes them to selectively arrest under methionine restriction due to depletion of free methionine and S-adenosyl methionine. Recently we have shown methionine-addicted cancer cells over-methylate histone H3 lysine marks which are not over-methylated in normal cells or in low-malignancy methionine-independent revertants derived from methionine-addicted cancer cells. In the present report, we show that in patient-derived xenograft (PDX) mouse models of the most common soft tissue sarcomas: myxofibrosarcoma, undifferentiated pleomorphic sarcoma (UPS) and liposarcoma, histone H3K4me3 and H3K9me3 are super over-methylated compared to normal muscle tissue. This new result is discussed along with our previous reports, regarding the potential of histone H3 over-methylation as a basis of malignancy.

Methionine addiction is a fundamental and general hallmark of cancer and is an area of current intense interest. Methionine addiction results from the overuse of methionine by cancer cells for excess transmethylation reactions. In order to identify excess transmethylation reactions in cancer and further understand the basis of methionine addiction, we compared the histone H3 lysine methylation status between methionine-addicted cancer cells, normal cells and rare revertants of methionine-addicted cancer cells which regained methionine independence and lost malignancy. The levels of H3K4me3, H3K9me3 and H3K36me3 were strongly elevated in methionine-addicted cancer cells in vitro compared to methionine-independent revertants isolated from the cancer cells. Tumorigenicity and experimental metastatic potential in nude mice were highly reduced in the methionine-independent revertants compared to the parental cells. Our previous studies showed that methionine restriction (MR) selectively arrests methionine-addicted cancer cells due to loss of histone H3 lysine methylation which was stable in normal cells under MR. Our previous and present results suggest that overmethylation of histone H3 lysine is linked with methionine addiction of cancer, required for the growth of cancer cells in vitro and in vivo, and necessary for malignancy as the histone lysine overmethylation disappears when the methionine-addicted cells revert to methionine independence and reduced malignancy. Methionine addiction has revealed fundamental molecular changes necessary for malignancy and presents great potential as a pan-cancer therapeutic target.