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The continued rise in obesity despite public education, awareness and policies indicates the need for mechanism-based therapeutic approaches to help control the disease. Our data, in conjunction with other studies, suggest an unexpected role for the polyamine catabolic enzyme spermidine/spermine-N1-acetyltransferase (SSAT) in fat homeostasis. Our previous studies showed that deletion of SSAT greatly exaggerates weight gain and that the transgenic overexpression suppresses weight gain in mice on a high-fat diet. This discovery is substantial but the underlying molecular linkages are only vaguely understood. Here, we used a comprehensive systems biology approach, on white adipose tissue (WAT), to discover that the partition of acetyl-CoA towards polyamine catabolism alters glucose homeostasis and hence, fat accumulation. Comparative proteomics and antibody-based expression studies of WAT in SSAT knockout, wild type and transgenic mice identified nine proteins with an increasing gradient across the genotypes, all of which correlate with acetyl-CoA consumption in polyamine acetylation. Adipose-specific SSAT knockout mice and global SSAT knockout mice on a high-fat diet exhibited similar growth curves and proteomic patterns in their WAT, confirming that attenuated consumption of acetyl-CoA in acetylation of polyamines in adipose tissue drives the obese phenotype of these mice. Analysis of protein expression indicated that the identified changes in the levels of proteins regulating acetyl-CoA consumption occur via the AMP-activated protein kinase pathway. Together, our data suggest that differential expression of SSAT markedly alters acetyl-CoA levels, which in turn trigger a global shift in glucose metabolism in adipose tissue, thus affecting the accumulation of body fat.

We have previously shown that the clinically relevant polyamine analog N1,N11-diethylnorspermine (DENSPM) causes rapid apoptosis in human melanoma SK-MEL-28 cells via a series of events that include mitochondrial release of cytochrome c and activation of the caspase cascade. Upstream to these events, DENSPM downregulates polyamine biosynthesis and potently upregulates polyamine catabolism at the level of spermidine/spermine N1-acetyltransferase (SSAT). In searching for downstream effectors that either contribute to or abrogate the apoptotic response, we observed that DENSPM treatment of SK-MEL-28 cells for 30 h led to cytosolic release of Smac/Diablo, a mitochondrial protein known to bind and inhibit the function of inhibitor of apoptosis proteins (IAPs). Subsequently, we found that DENSPM markedly lowered survivin and ML-IAP protein (but not XIAP) levels by 18 h via an apparently Smac/Diablo-independent pathway. Proteasome inhibitors fully prevented survivin and ML-IAP protein loss as well as apoptosis, suggesting that the proteasome-mediated degradation of survivin and ML-IAP is causally linked to the cellular outcome. We also observed that structural analogs of DENSPM which differentially induced SSAT and apoptosis lowered survivin and ML-IAP levels in a manner that correlated with enzyme activity. The linkage between IAPs and SSAT was more directly established by the finding that selective prevention of SSAT induction by small interfering RNA prevented survivin and ML-IAP loss as well as apoptosis during DENSPM treatment. Among the melanoma cell lines (SK-MEL-28, MALME-3M, A375 and LOX), survivin degradation correlated temporally with the onset of DENSPM induced apoptosis or growth inhibition. By contrast, ML-IAP degradation occurred only during rapid apoptosis seen in SK-MEL-28 cells. These data suggest a sequence of events whereby DENSPM induction of SSAT leads to loss of IAP proteins and a more fulminate apoptotic response. The findings implicate survivin and ML-IAP as important determinants of polyamine analog drug action in melanoma cells.

We tested the polyamine analog SL-11093 (3,8,13,18-tetraaza-10,11-[(E)-1,2-cyclopropyl]eicosane tetrahydrochloride) as an effective chemotherapeutic agent against human prostate cancer grown in nude mice.NCr-nu mice grafted with DU-145 human prostate tumor cells were treated i.p. with SL-11093 at 50 mg/kg q1dx5 for either three or five cycles separated by intervals of about 10-15 days.In treated animals, tumor growth remained arrested for up to 100 days with minimal animal weight loss. None of the animals died during the treatment and in one experiment two out of six animals showed no palpable tumor. SL-11093 was readily taken up by the tumors, where its levels remained elevated for about 48 h after the end of drug administration. In liver and in kidney, SL-11093 (a (alpha)N,(omega)N-bisethyl derivative) was oxidatively N-deethylated predominantly to its monoethyl and di-deethyl derivatives. In time, the monoethyl derivative was further dealkylated, with a loss of an aminobutyl chain to form an aminomethyl cyclopropyl derivative. In tumor (and in lung), N-dealkylation reactions were less evident.SL-11093 is an effective chemotherapeutic agent against a human prostate tumor xenograft grown in nude mice. The drug accumulation and slow metabolism in tumor compared to other tissues would most likely reduce systemic toxicity of the drug and contribute to a larger therapeutic window for SL-11093 as compared to other cytotoxic polyamine analogs.

Four variants of the cultured human cell line VA2 have been isolated which are resistant to the antiproliferative and antimitochondrial effects of methylglyoxal-bis(guanylhydrazone) (MGBG). Each of the four variants is two- to fivefold more sensitive to the mitochondrial protein synthesis inhibitor chloramphenicol (CAP) than wild type when grown in the absence of MGBG, and five- to tenfold more sensitive to CAP when grown in the presence of MGBG. Uptake studies demonstrate that each MGBG-resistant variant cell line is freely permeable to CAP. The in vivo rates of mitochondrial protein synthesis are significantly reduced in each of the variants whether pregrown and labeled in the presence or absence of MGBG. When cytoplasts from a cytoplasmically inherited CAP-resistant mutant are fused to an MGBG-resistant recipient cell line, cybrid clones can be isolated which are functionally resistant to low levels of CAP. With continued growth, the levels of resistance to CAP do not, however, approach the levels of resistance of the CAP-resistant donor cell line. When CAP resistance is subsequently transferred from a CAP/MGBG-resistant cybrid by enucleation and fusion to other human cell lines, then CAP-resistant cybrids can be readily selected in high levels of CAP. It is possible that the substantial decrease in mitochondrial protein synthesis observed in the variants fully accounts for their increased sensitivity to CAP, although the basis for this decreased rate of mitochondrial protein synthesis is not understood.