Growth and biochemical effects of unsymmetrically substituted polyamine analogues in human lung tumor cells 1.

Three unsymmetrically substituted polyamine analogues demonstrate significant and selective antitumor effects. Each of the analogues N1-ethyl-N11-propargyl-4,8-diazaundecane (PENSpm), N1-ethyl-N11-(cyclobutyl)methyl-4,8-diazaundecane (CBENSpm), and N1-ethyl-N11-(cyclopropyl)methyl-4,8-diazaundecane (CPENSpm) is cytotoxic to a representative non-small-cell lung carcinoma line, NCI H157, while being only growth-inhibitory to a representative small-cell-lung carcinoma line, NCI H82. Cytotoxicity is accompanied by a significant increase in expression of the polyamine catabolic enzyme spermidine/spermine N1-acetyltransferase (SSAT) at the levels of activity and steady-state mRNA. These new analogues are significant both for their cell-type-specific activity and as synthetic prototypes for the addition of SSAT-activated functional groups.

Synthesis and evaluation of unsymmetrically substituted polyamine analogues as modulators of human spermidine/spermine-N1-acetyltransferase (SSAT) and as potential antitumor agents.

Spermidine/spermine-N1-acetyltransferase (SSAT), the rate-limiting step in polyamine catabolism, is critical for the interconversion and modulation of cellular polyamines. Inhibitor-initiated induction of this enzyme also appears to correlate with the sensitivity of tumor cells to a class of novel polyamine analogues, the bis(ethyl)polyamines. Thus, terminally alkylated polyamines which modulate the cellular level of SSAT could be of great value for understanding the role of this enzyme both in analogue-mediated cytotoxicity and in overall cellular polyamine metabolism. Such analogues could also become important therapeutic agents by disrupting cellular polyamine metabolism. The structure-activity relationships defining the interaction of polyamine analogues with SSAT have not been fully elucidated, and, in particular, unsymmetrically alkylated polyamines have not been synthesized and evaluated as modulators of SSAT. To this end, we now report the synthesis and preliminary biological evaluation of N1-ethyl-N11-propargyl-4,8-diazaundecane and N1-ethyl-N11-((cyclopropyl)methyl)-4,8-diazaundecane via a synthetic pathway which represents an efficient route to a variety of unsymmetrically substituted polyamine analogues. The title compounds act as effective inhibitors of isolated human SSAT and produce a differential superinduction of SSAT in situ which appears to be associated with a cell specific cytotoxic response in two human lung cancer cell lines. In so doing, these analogues exhibit promising antitumor activity against cultured human lung cancer cells.

Growth inhibition of hormone-responsive and -resistant human breast cancer cells in culture by N1, N12-bis(ethyl)spermine.

Previous studies have documented differential sensitivity of human lung cancer and melanoma cell lines to the cytotoxic effects of N1, N12-bis(ethyl)spermine (BESpm). We show here that BESpm can significantly inhibit the growth of six human breast cancer cell lines with 50% inhibitory concentration in the microM range. The degree of inhibition does not correlate with estrogen receptor status. Detailed studies with estrogen receptor-positive MCF-7 and estrogen receptor- negative Hs578t cells show a similar dose-response curve with concentrations of 1-10 microM resulting in maximal growth inhibition. Growth inhibition in both lines is associated with an 8-12-fold induction of the polyamine catabolic enzyme, spermidine/spermine N1-acetyltransferase, and a progressive decrease in intracellular polyamine levels over 6 days even though steady-state levels of BESpm are achieved within 24 h. Similar studies on WTMCF7 and AdrRMCF7 cells show that the acquisition of resistance to hormonal or doxorubicin therapy is not associated with resistance to the growth-inhibitory effects of BESpm. These results suggest that BESpm exerts similar growth-inhibitory effects against both hormone-responsive and -unresponsive human breast cancer cells, a finding which has significance for the potential use of polyamine analogues in treating human breast cancer.

Steady-state messenger RNA and activity correlates with sensitivity to N1,N12-bis(ethyl)spermine in human cell lines representing the major forms of lung cancer.

Our previous results from a limited number of cell lines have suggested that the bis(ethyl)polyamine analogues exert a phenotype-specific response in human lung cancer cells. In the present study, we have extended this work to analyze the response of the 4 major forms of human lung cancer to the polyamine analogue N1,N12-bis(ethyl)spermine (BESpm). The results suggest that non-small cell phenotypes are much more sensitive to the cytotoxic effects of BESpm than the small cell lung carcinoma phenotype. Further, there appears to be a positive association between the level of induction of the polyamine catabolic enzyme spermidine/spermine N1-acetyltransferase (SSAT) in response to the analogue and the kinetic response of cells. Specifically, cells in which SSAT activity is highly induced by BESpm are killed by the compound. Although induction of SSAT appears to occur at both the level of increased steady-state mRNA and enzyme activity, SSAT activity appears to be a better indicator of cell sensitivity to BESpm than SSAT mRNA levels. These results have significance both for the potential use of polyamine analogues in treating specific forms of human lung cancer and for understanding the regulation of SSAT at the molecular level.

Structure of the human spermidine/spermine N1-acetyltransferase gene (exon/intron gene organization and localization to Xp22.1).

The super induction of spermidine/spermine N1-acetyltransferase (SSAT), has been implicated in the cytotoxic response of human solid tumors to the bis(ethyl)polyamines. The SSAT response is a phenotype specific response and is modulated at the level of increased steady-state mRNA levels and enzyme protein. The human genomic region (4,095 bases) containing the coding sequence of SSAT has been cloned and localized to the Xp22.1 region. Primer extension analysis indicates the transcription of SSAT starts 179 bases upstream from the translational start site and appears to be under the control of a "TATA-less" promoter. The availability of this human clone will facilitate the direct functional examination of the SSAT gene.

Characterization of a full-length cDNA which codes for the human spermidine/spermine N1-acetyltransferase.

Spermidine/spermine N1-acetyltransferase is the rate-limiting enzyme in the catabolism of cellular polyamines. Using a combination of cDNA library screening and anchored PCR methodologies, a full length cDNA designated AP3/F7 corresponding to the human SSAT was cloned using RNA from the human large cell undifferentiated lung carcinoma line NCI H157. The resulting cDNA clone is 1,060 base pairs with a 513 base open reading frame coding for a 171 amino acid protein, with a predicted subunit molecular weight of 20,023. The 5' non-coding region of AP3/F7 is 165 bases and the 3' untranslated region is 382 bases with a polyadenylation site 20 bases 5' to the poly(A) tail. This full length cDNA should be an aid in the study of the regulation of spermidine/spermine N1-acetyltransferase expression and the significance of the acetyltransferase in polyamine metabolism.