TNF and neoplasm: In previous studies in Ehrlich ascites and highly metastatic B16-F10 melanoma tumor cells, we found that L-Glu derived from L-Gln competitively inhibited GSH transport into mitochondria [159,169], thereby depleting selectively tumor mtGSH under in vivo conditions [159] and rendering tumor cells more susceptible to oxidative stress-induced mediators, such as TNF-α [11].