Selectivity of polyamine involvement in hormone action on normal and neoplastic target tissues of the rat

Polyamines metabolism and breast cancer: state of the art and perspectives

Breast cancer (BC) is a common disease that generally occurs in women over the age of 50, and the risk is especially high for women over 60 years of age. One of the major BC therapeutic problems is that tumors initially responsive to chemotherapeutic approaches can progress to more aggressive forms poorly responsive to therapies. Polyamines (PAs) are small polycationic alkylamines, naturally occurring and essential for normal cell growth and development in eukaryotes. The intracellular concentration of PA is maintained within strongly controlled contents, while a dysregulation occurs in BC cells. Polyamines facilitate the interactions of transcription factors, such as estrogen receptors with their specific response element, and are involved in the proliferation of ER-negative and highly invasive BC tumor cells. Since PA metabolism has a critical role in cell death and proliferation, it represents a potential target for intervention in BC. The goal of this study was to perform a literature search reviewing the association between PA metabolism and BC, and the current evidence supporting the BC treatment targeting PA metabolism. We here describe in vitro and in vivo models, as well as the clinical trials that have been utilized to unveil the relationship between PA metabolism and BC. Polyamine pathway is still an important target for the development of BC chemotherapy via enzyme inhibitors. Furthermore, a recent promising strategy in breast anticancer therapy is to exploit the self-regulatory nature of PA metabolism using PA analogs to affect PA homeostasis. Nowadays, antineoplastic compounds targeting the PA pathway with novel mechanisms are of great interest and high social impact for BC chemotherapy.

Immunohistochemical detection of ornithine-decarboxylase in primary and metastatic human breast cancer specimens

Increased ornithine decarboxylase (ODC) activity in human breast cancer specimens has recently been shown to be an independent adverse prognostic factor for recurrence and death. Biochemical measurement of ODC, however, is not practical for routine clinical use. Furthermore, it does not take into account the heterogeneous composition of human breast cancers which contain variable proportions of epithelial and stromal elements. Therefore, we developed an immunohistochemical method for ODC determination which can be applied to formalin-fixed, paraffin-embedded tissue sections. We report here our results in a series of 30 human breast cancer samples. ODC expression was detected most consistently in the malignant epithelial component of the tumors. Twenty-seven of 30 samples stained positive with intensities ranging from 1+ to 3+. The fraction of malignant epithelial cells expressing ODC varied among specimens between 10% and > 90%. When quantitated by H-SCORE, ODC expression was significantly higher in the malignant epithelial component than in normal appearing epithelial cells and stroma admixed within the tumor. Normal mammary tissue adjacent to the cancer was available for analysis in six cases. ODC expression was absent in two (while both cancers were positive) but present in four to a degree which was overall comparable to that observed in the corresponding tumors. We believe that this technique will be useful for future studies aimed at expanding our knowledge of the role of ODC and polyamines (PA) in breast cancer biology.

GABA and hepatocellular carcinoma

Data derived from models of hepatic regeneration indicate that transient, reciprocal changes in polyamines, potent growth promoters, and gamma aminobutyric acid (GABA), an amino acid neurotransmitter with growth inhibitory properties, play important roles in enhancing and inhibiting respectively regulated hepatocyte proliferation. Based on these findings and supportive data derived from studies of human carcinoma tissues and malignant cell lines we propose that permanent increases in polyamine and decreases in GABAergic activity act in concert to contribute to the pathogenesis of hepatocellular carcinoma.

Polyamine profiles and growth properties of ornithine decarboxylase overexpressing MCF-7 breast cancer cells in culture

To determine the direct influence of the polyamine (PA) pathway on breast cancer phenotype, we employed a transfection approach to induce overexpression of the PA biosynthetic enzyme ornithine decarboxylase (ODC) in the hormone-responsive MCF-7 breast cancer cell line. Using a modified calcium phosphate method and an ODC cDNA coding for a truncated and more stable enzyme, we were able to achieve a moderate to marked degree of ODC overexpression (up to 150-fold) in a transient transfection system. ODC-overexpressing MCF-7 cells exhibited a selective increase in cellular putrescine content, while the levels of spermidine and spermine remained unaffected. Under defined culture conditions, overexpression of ODC resulted in a consistent but modest increase in [3H]thymidine incorporation into DNA which was similar in the presence and absence of 17-beta-estradiol, TGF-alpha, and IGF-I. In the presence of serum, the effect of ODC overexpression on basal [3H]-thymidine incorporation into DNA was inconsistent, possibly as a result of subtle differences in culture conditions. Overall, our results support the hypothesis that activation of the PA biosynthetic pathway may confer a growth advantage to breast cancer cells.

Role of polyamines in the growth of hormone-responsive and -resistant human breast cancer cells in nude mice

Recent in vitro data suggest that at least some hormone-independent breast cancer cells exhibit increased polyamine biosynthesis and resistance to antipolyamine therapy. To address this issue under conditions of in vivo growth, we tested the antiproliferative effect of the polyamine synthetic inhibitor alpha-difluoromethyl-ornithine (DFMO) on hormone-dependent (MCF-7) and -independent (MDA-MB-231, BT-20) breast cancer cell lines growing in nude mice. We observed that DFMO significantly inhibited the growth of established tumors to a similar extent in all cell lines, even though tumor regression was only observed with MCF-7 cells. DFMO, while inhibiting E2-supported MCF-7 breast cancer growth, did not inhibit E2-stimulated progesterone receptor synthesis. Cellular levels of polyamines were highest in MCF-7 cells and lowest in the BT-20 cell line. Tumor content of spermidine was similarly suppressed by DFMO treatment in the 3 cell lines, while the spermine level was unaffected. Cellular putrescine levels were suppressed in MCF-7 and BT-20 cells. Administration of DFMO prior to implantation of fragments of MCF-7 or MDA-MB-231 tumors in nude mice significantly inhibited tumor development to a similar extent. The action of DFMO seemed to be predominantly tumoristatic since new tumors develop in some mice upon discontinuation of the drug. We conclude that the hormone-independent breast cancer cell lines tested do not exhibit increased polyamine biosynthesis or resistance to antipolyamine therapy when grown in vivo in nude mice.

Polyamine involvement in the secretion and action of TGF-alpha in hormone sensitive human breast cancer cells in culture

These experiments were designed to test polyamine (PA) involvement in the secretion and action of transforming growth factor alpha (TGF-alpha) in hormone responsive MCF-7 breast cancer cells in liquid culture. At the same time, we evaluated the influence of culture conditions (with serum vs. serum depleted) and subclonality of MCF-7 cells on PA involvement in estrogen (E2) and TGF-alpha stimulated cell proliferation. Despite inducing a profound suppression of cellular PA levels and inhibiting basal and E2-stimulated growth, administration of the PA synthesis inhibitor alpha-difluoromethylornithine (DFMO) did not influence either basal or E2-induced TGF-alpha secretion. In the same experiments, on the other hand, addition of DFMO completely blocked the growth stimulatory effect of exogenous TGF-alpha. However, when the culture conditions were changed to serum-free medium, TGF-alpha and E2-induced cell proliferation was affected modestly or not at all by DFMO administration, despite similar suppression of cellular ornithine decarboxylase (ODC) activity and PA levels. In addition, different clones of MCF-7 cells differed in their sensitivity to the antiproliferative effect of DFMO as well as in basal levels of ODC activity and PA. We conclude that PAs are not involved in basal or E2-stimulated TGF-alpha secretion in MCF-7 breast cancer cells. On the other hand, PAs do seem to be important mediators of TGF-alpha and E2-induced breast cancer cell proliferation, though the degree of such involvement appears to be influenced by serum factors and clonal variability of MCF-7 cells.