The overall objectives of the current proposal are to define the cell type specific-regulatory mechanisms which control the expression of spermidine/spermine N1-acetyltransferase (SSAT) in human lung cancer cells and to define what role the phenotype-specific super-induction of SSAT plays in determining cellular response to a new class of antitumor polyamine analogues. This induction is at the level of both new SSAT mRNA and protein, and data demonstrate that in several non-small cell lung cancers the induction of SSAT activity can be > 1,000-fold (in some cases represents 1% total cellular protein.) The molecular probes cloned as part of the aims in the initial fiinding period of this grant will be used to examine the cell type-specific-regulation of SSAT (the rate limiting step in polyamine catabolism) at the level of transcription and translation. Understanding the regulation of this enzyme is important since cell tvpes which super-induce SSAT are killed bv the analogues. By contrast, most small cell lung cancer phenotypes do not super-induce SSAT in response to treatment and are not killed by the analogues. The differentially responding cell systems will be used as models to define the basis for the phenotype-specific response. A strategy of in vitro homologous recombination (knockout) of this X-chromosome linked gene will be used to determine if a causal link between SSAT super-induction and cytotoxicity exists. Based in part on results in the lung cancer models and the demonstration of differential sensitivity, one of the analogues, N1, N11- bis(ethyl)norspermine has recently begun clinical trials against non-small cell lung cancer and other important solid tumors. Data are consistent with the hypothesis that super-induction of SSAT plays a role in determining cell type-specific response in lung tumors. Differential induction of SSAT will be investigated for its value as a prognostic or predictive indicator of tumor response. It appears that there are many levels at which SSAT is regulated in response to the polyamine analogues. The proposed studies are designed to examine the molecular levels of control of cell responsiveness to the analogues, to gain a better understanding regarding their specific cytotoxic activity, and to define mechanisms of acquired resistance. Finally, it is projected that a more precise understanding of the tumor type-specific regulation of SSAT will aid in the development of novel antineoplastic strategies which exploit these differences.
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