EXPRESSION OF THE BIOCHEMICAL DEFECT OF METHIONINE DEPENDENCE IN FRESH PATIENT TUMORS IN PRIMARY HISTOCULTURE

Methionine dependence is a metabolic defect that occurs in many human tumor cell lines but not normal in unestablished cell strains. Methion ine-dependent tumor cell lines are unable to proliferate and arrest in the late S/G2 phase of the cell cycle when methionine is replaced by its immediate precursor homocysteine in the culture medium (MET-HCY+ m edium). However, it is not known whether methionine dependence occurs in fresh patient tumors as it does in cell lines. In order to determin e whether methionine dependence occurs in fresh patient tumors as well as in cell lines we took advantage of the technique of sponge-gel-sup ported histoculture to grow tumors directly from surgery. We then meas ured nuclear DNA content by image analysis to determine the cell cycle position in MET-HCY+ compared to MET+HCY- medium in 21 human patient tumors. Human tumor cell lines found to be methionine dependent by cel l count were used as positive controls and were found to have marked r eduction of cells in G1 compared to total cells in the cell cycle in M ET-HCY+ medium with respect to the G1: total cell ratio in MET+HCY- me dium. Therefore late cell cycle arrest was used as a marker of methion ine dependence for histocultured patient tumors. We found that 5 human tumors of 21, including tumors of the colon, breast, ovary, prostate, and a melanoma, were methionine dependent based on cell cycle analysi s. These data on fresh human tumors indicate that methionine dependenc e may frequently occur in the cancer patient population. Implications for potential therapy based on methionine dependence are discussed.