Induction of the polyamine catabolic enzyme spermidine/spermine N1-acetyltransferase (SSAT) by certain polyamine analogs represents one of the most potent known gene responses attributable to an anticancer drug. The relationship of this response to antitumor activity and host toxicities has not yet been clearly established. The proposed studies build on the following observations and developments involving this novel enzyme: a) a polyamine analog currently undergoing phase 1 clinical trial (N1, N11 -diethyl-norspermine (DENSPM) is an extremely potent inducer of this enzyme; b) melanoma cells are more responsive to SSAT induction than most other tumor cell types; c) biological correlations suggest a causal linkage between analog induction of SSAT activity and in vitro and in vivo growth sensitivity of tumor cells; d) overexpression of the enzyme in transgenic animals causes striking phenotypic changes involving skin and the female reproductive tract; e) strong similarities between SSAT transgenic animals and certain other transgenics suggest a role for the enzyme in tumor promotion and f) SSAT gene expression in mouse skin and melanoma cells is markedly increased by 12-O-tetradecanoyl-13-phorbol acetate (TPA).
The Specific Aims propose: 1) to examine the cellular consequences of SSAT induction in human melanoma cells transfected with a tetracycline-inducible SSAT expression system; 2) to investigate the significance of translational control of SSAT gene expression; 3) to examine the physiological role of SSAT in tissue function using activated gene knock-out (via subcontract agreement with Dr. J. Janne's group Kuopio, Finland); 4) to utilize systems developed in aims 1-3 to study the role of SSAT in determining antitumor and toxicity responses to clinically relevant polyamine antagonists; 5) to determine via cross-breeding experiments whether SSAT overexpression renders animals more or less prone to skin carcinogenesis and 6) as a mechanistic correlate to aim 5, they propose to examine the effects of tumor promters on SSAT gene expression and the possible role of protein kinase C as a mediator of SSAT induction by both TPA and the polyamine analogs. In addition to investigating the biological significance of this unusual enzyme response, the proposed studies are designed to provide therapeutic insights and preclinical model systems for use in facilitating the ongoing clinical and preclinical development of experimental anticancer therapies targeting polyamines.
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