The metabolic defect of methionine dependence occurs frequently in human tumor cell lines.

Methionine dependence is the inability of cells to grow when methionine (Met) is replaced by its immediate precursor homocysteine (Hcy) in the culture medium (Met-Hcy+ medium). All normal unestablished cell strains tested to date have been shown to be methionine-independent and thus grow almost as well in Met-Hcy+ medium as they do in Met+-Hcy-medium. Results presented here indicate that out of 23 cell lines derived from diverse types of human tumors, 11 do not grow at all in Met-Hcy+ medium and are absolutely methionine-dependent and 3 grow only slightly in this medium. Many of the tumor cell lines tested have little else in common other than the fact that they are methionine-dependent. The high frequency of occurrence of methionine dependence in diverse types of human tumor cells indicates that methionine dependence may be an important aspect of oncogenic transformation and therapeutically exploitable.