This proposal was prompted by two recent findings by this laboratory which demonstrate the uniqueness of polyamine catabolism in human tumor cells: (1) contrary to dogma based on studies with rodent tissues, polyamine oxidation rather than polyamine acetylation appears to be the rate-limiting enzyme activity in intracellular polyamine catabolism and (2) in many human tumor cell lines, the polyamine catabolizing enzyme, spermidine/spermine N1-acetyltransferase (SSAT) displays an inducibility in response to polyamine analogs which is highly unique in its rapidity (hrs), magnitude (100 to 60,000 pmol/mg/min) and heterogeneity among cell lines. This proposal will attempt to characterize inducible polyamine metabolism in human tumor cells from mechanistic, metabolic and cellular perspectives. More specifically, we propose (a) to survey the prevalence of SSAT superinducibility among various tumor cell lines and seek a commonality for it, (b) to purify the SSAT protein from a human cell line (already accomplished for one cell line) and develop antibodies to it (underway); (c) to study the mechanistic basis for differential responsiveness to SSAT inducibility among different cell lines; (d) to evaluate the metabolic consequences of SSAT induction and its relationship to cell proliferation; (e) to examine in vivo SSAT inducibility of SSAT in human tumor zenografts and to compare it with that of normal tissues and (f) to examine polyamine catabolism in normal and neoplastic human tissue samples. The proposed studies will entail tissue culture techniques, enzyme assays, HPLC methodology, protein purification techniques, antibody development and human xenograft studies in nude mice. Ultimately, these studies are designed to determine whether inducible polyamine catabolism has relevance in monitoring or treating human malignancies.
