The overall objectives of the current proposal are to investigate the regulation of the spermidine/spermine N1-acetyltransferase (SSAT) in human lung cancer cells and to determine what role the induction of SSAT (the first and rate limiting enzyme in the back conversion pathway in polyamine metabolism) may play in determining the sensitivity of various lung tumor cell types to polyamine analogues. Specifically, the proposed studies are designed to extend preliminary results which indicate that the differential induction of SSAT in the various phenotypes of human lung cancers may, in part, determine their specific response to the bis(ethyl) polyamine analogues. The human large cell lung carcinoma line, NCI H157, responds to treatment with N1, N12-bis(ethyl) spermine (BESpm) in a frank cytotoxic manner. This cellular behavior is accompanied by a profound induction of SSAT to >1,700-fold over baseline. This is in direct contrast to results in the human small cell lung cancer line, NCI H82, which is only minimally growth inhibited by BESpm, and responds with a <7-fold induction of SSAT. These two cell types will be used as models to further investigate the mechanisms underlying the differential induction of SSAT and to determine if the induction of this enzyme is critical to the observed cytotoxicity in the responsive cell types. Further, since preliminary studies indicate that the unusually high induction of SSAT observed in the large cell is due almost entirely to new protein synthesis, which in turn is based primarily on new mRNA synthesis, the large cell NCI H157 will be used, after induction with BESpm, to provide mRNA for the construction of an expression library to be used in cloning of the SSAT gene. Once cloned, probes to this gene will be utilized to investigate, further, the mechanisms of regulation for induction of the enzyme by natural polyamines and the polyamine analogues. The above studies should provide significant information to aid in the future design and development of specific agents to exploit subtle differences in polyamine metabolism between cell types to provide useful agents in the treatment of human cancers.
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