Activated Polyamine Catabolism Depletes Acetyl-CoA Pools and Suppresses Prostate Tumor Growth in TRAMP Mice

Abstract

The enzyme spermidine/spermine N 1 -acetyltransferase (SSAT) regulates the catabolism and export of intracellular polyamines. We have previously shown that activation of polyamine catabolism by conditional overexpression of SSAT has antiproliferative consequences in LNCaP prostate carcinoma cells. Growth inhibition was causally linked to high metabolic flux arising from a compensatory increase in polyamine biosynthesis. Here we examined the in vivo consequences of SSAT overexpression in a mouse model genetically predisposed to develop prostate cancer. TRAMP (transgenic adenocarcinoma of mouse prostate) female C57BL/6 mice carrying the SV40 early genes (T/t antigens) under an androgen-driven probasin promoter were cross-bred with male C57BL/6 transgenic mice that systemically overexpress SSAT. At 30 weeks of age, the average genitourinary tract weights of TRAMP mice were ϳ4 times greater than those of TRAMP/SSAT bigenic mice, and by 36 weeks, they were ϳ12 times greater indicating sustained suppression of tumor outgrowth. Tumor progression was also affected as indicated by a reduction in the prostate histopathological scores. By immunohistochemistry, SV40 large T antigen expression in the prostate epithelium was the same in TRAMP and TRAMP/SSAT mice. Consistent with the 18-fold increase in SSAT activity in the TRAMP/SSAT bigenic mice, prostatic N 1 -acetylspermidine and putrescine pools were remarkably increased relative to TRAMP mice, while spermidine and spermine pools were minimally decreased due to a compensatory 5-7-fold increase in biosynthetic enzymes activities. The latter led to heightened metabolic flux through the polyamine pathway and an associated ϳ70% reduction in the SSAT cofactor acetylCoA and a ϳ40% reduction in the polyamine aminopropyl donor S-adenosylmethionine in TRAMP/SSAT compared with TRAMP prostatic tissue. In addition to elucidating the antiproliferative and metabolic consequences of SSAT overexpression in a prostate cancer model, these findings provide genetic support for the discovery and development of specific small molecule inducers of SSAT as a novel therapeutic strategy targeting prostate cancer.

Potent Modulation of Intestinal Tumorigenesis in Apcmin/+ Mice by the Polyamine Catabolic Enzyme Spermidine/Spermine N1-acetyltransferase

“…Although the basis for this phenomenon is unknown, it is likely manifested during gestation because there were no noticeable increases in postnatal mortality. Normal Mendelian segregation of genotypes was observed previously in a cross of SSAT transgenic and TRAMP mice (13,19). The deficiency of MIN/SSAT-tg progeny in the current cross may be related to the report of Jacoby et al (26,27), who observed that treatment with the ODC inhibitor a-difluoromethylornithine during embryonic development is selectively lethal to fetuses bearing a heterozygous mutation in the Apc gene.…”

“…This provocative finding suggests quite clearly that high levels of SSAT expression can exert tumor-suppressive effects. However, in contrast to expectations, polyamine pools were not significantly depleted by SSAT in either LNCaP cells or in prostate tumors of TRAMP mice (13,19). Rather, the antitumor effect seems to be directly related to a compensatory up-regulation of polyamine biosynthesis in response to SSAT overproduction.…”

“…Extending this finding to an in vivo system, we recently reported that cross-breeding SSAToverexpressing transgenic mice with prostate cancer-predisposed TRAMP [transgenic adenocarcinoma of mouse prostate; ref. (18)] mice inhibits tumor outgrowth (19). This provocative finding suggests quite clearly that high levels of SSAT expression can exert tumor-suppressive effects.…”

The Effect of Difluoromethylornithine on Decreasing Prostate Size and Polyamines in Men: Results of a Year-Long Phase IIb Randomized Placebo-Controlled Chemoprevention Trial

“…Gupta et al (18) showed marked reduction in weight and volume of the prostate as well as metastasis in the group treated with 1% DFMO. Another group reported on the manipulation of polyamines in the transgenic adenocarcinoma mouse prostate model by overexpression of spermidine/spermine N1-acetyltransferase, which regulates the catabolism and export of intracellular polyamines (19). The transgenic adenocarcinoma mouse prostate/spermidine/spermine N 1-acetyltransferase animals had smaller weights of their prostates at 30 and 36 weeks and better histologic scores.…”

Spermidine: a physiological autophagy inducer acting as an anti-aging vitamin in humans?

“…The net cytosolic spermidine content further depends on its catabolism, which is mainly driven by acetylation and subsequent oxidation [29–31], but also on its uptake from the extracellular space and its excretion by the cell. This may be mediated by membrane transporters such as the ones operating in yeast and bacteria [32], but could also involve endocytosis/exocytosis processes.…”