Arginine deprivation therapy : tumour cell rescue
In order to evaluate arginine deprivation as a putative anticancer therapy this study investigated arginine metabolism at the molecular, cellular and whole animal levels. Firstly, a murine model for arginine deprivation was developed using the catabolic enzyme arginase to reduce the blood arginine levels in vivo. However, although the arginine levels were limiting to both host and tumour, no prolongation in survival time was noted between treated and control groups. Analysis of the L1210 lymphocytic leukaemia cells used in this study revealed their ability to recycle arginine from its precursor molecule citrulline even in the presence of the enzyme arginase indicating that the citrulline level may be as important as the arginine level to the generation of deprivation conditions in vivo. Secondly, at the cellular level a number of different immortal cell lines were analysed for their ability to utilise urea cycle intermediates in lieu of arginine in order to identify those tumour types susceptible to the therapy. Most cell lines could be classified as one of the following: Type a - can only be rescued from arginine deprivation conditions with arginine alone; Type b - can utilise arginine and argininosuccinate but not citrulline; Type c can utilise arginine and citrulline but not the intermediate argininosuccinate. This data in addition to the radiolabelled tracer data presented in this thesis supports the theory of metabolite channelling and indicates that the differential utilisation of urea cycle intermediates is not due to metabolite availability within the cell. Finally, since argininosuccinate synthetase (ASS) is the rate limiting step in the conversion of citrulline to arginine the 5' untranslated region of the ASS gene was analysed for differential expression in cell types a, b and c in order to determine if the phenotype differnces noted between the three classes were due to a genotypic difference in the expression of this gene. The region chosen for this study is the site of alternative splicing and although no quantitative or qualitative differnces were observed in either variant 1 or variant 2, three novel bands were also amplified in type c cells but not in type b cells.