Arginine catabolism, liver extracts and cancer.

Although it is self evident that cells will not grow in amino acid deficient medium, an observation less well appreciated is that malignant cells are particularly vulnerable to such deprivation, which can lead to their rapid demise. Indeed, the more flagrantly malignant the phenotype (anaplastic the tumor), the more susceptible the cells seem to be to deprivation. While some attempts to employ this strategy in cancer treatment have been made, the difference between normal and malignant cells should be more fully exploited as a means of selectively eliminating tumor cell populations. To be successful, information on differences between the normal and the deranged cell cycle engine and checkpoints, especially how these are affected by deprivation, is of crucial importance. Since it is only recently that the controls at restriction points have been elucidated, it is little surprise that earlier attempts to control tumor cell growth by limiting the availability of an essential amino acid have met with limited success. Studies have been sporadic and isolated, often with little more than anecdotal descriptions as far as clinical work was concerned. This review concentrates on what has been accomplished primarily in vitro and since about 1950 with regard to arginine catabolism, while recognising that other essential amino acids have also been the focus of attention by some investigators. Treatments have included medium and plasma manipulation, dietary control, enzymatic degradation, and the use of liver extracts. On some occasions, substitution of amino acid analogues has been explored. It is argued that current knowledge, combined with past experience, calls for a much closer examination of the full potential of amino acid (and specifically arginine) deprivation as a means of controlling tumor growth, with greater attention to protocols that might be used to treat human cancers.