Role of polyamines in the growth of hormone-responsive experimental breast cancer in vivo

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.

Effects of alpha-difluoromethylornithine on local recurrence and pulmonary metastasis from MDA-MB-435 breast cancer xenografts in nude mice

We have recently shown that administration of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC), the first and rate-limiting enzyme in polyamine (PA) biosynthesis reduces pulmonary metastasis from MDA-MB-435 breast cancer xenografts in nude mice. The present experiments were designed to further explore PA involvement in breast cancer metastasis, using GFP-tagged MDA-MB-435 cells that can be tracked at the single cell level. Administration of DFMO significantly reduced the number of mice with pulmonary metastasis as well as the number of metastases per mouse. Both single-cell and multicellular metastatic deposits were similarly suppressed, thus suggesting that DFMO was inhibiting lung colonization by tumor cells rather than preventing progression of single-cell deposits to overt metastasis. DFMO administration also significantly reduced local recurrences following removal of the primary tumor. Prolongation of DFMO treatment to 14 weeks did not yield a superior antimetastatic effect beyond that provided by a 10-week course of therapy. Discontinuation of DFMO, on the other hand, was associated with local regrowth of the tumors and, possibly, recurrence of pulmonary metastasis. These data provide a rationale for testing the efficacy of anti-PA treatment within the context of adjuvant therapy of breast cancer.

Effect of alpha-difluoromethyl-ornithine on the expression and function of the epidermal growth factor receptor in human breast epithelial cells in culture

We have previously shown that ornithine decarboxylase (ODC) overexpression enhances the transforming effects of HER-2neu and epidermal growth factor (EGF) in normal MCF-10A human breast epithelial cells. Our data suggest that such potentiation may be mediated by activation of the mitogen-activated protein kinase (MAPK) pathway and, possibly, STAT signalling. To further explore the interaction between the polyamine pathway and EGF/HER-2neu signalling in this system, we inhibited endogenous ODC activity with alpha-difluoromethylornithine (DFMO) and assessed the effects of this blockade on the expression of EGF receptors (EGFR) and HER-2neu as well as activation of downstream EGF target genes. We found that DFMO administration to MCF-10A cells increased EGF-R mRNA and protein levels in a dose-response fashion, while HER-2neu expression was not affected. The effect of DFMO was mediated through polyamine depletion since it could be reversed by exogenous putrescine administration. Our results also indicated that the increase in EGFR induced by DFMO was not a non-specific consequence of inhibition of cell proliferation. The upregulated EGFRs were functional since they could be phosphorylated by EGF and they were able to promote phosphorylation of downstream signalling molecules including ERK, STAT-3, and STAT-5. We propose that physiologic levels of ODC activity may be critical for regulation of a yet undefined signalling pathway, whose blockade by DFMO leads to a compensatory increase in functional EGFR.

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.

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

The present experiments were designed to evaluate the polyamine involvement in hormonal actions on proliferation and receptor content of neoplastic tissue (hormone-responsive breast cancer) as well as on growth of normal endocrine target tissue (uterus) in the same animals. Administration of estradiol and perphenazine (to stimulate endogenous prolactin release) stimulated N-nitrosomethyl-urea (NMU)-induced rat mammary tumor growth following ovariectomy-induced tumor regression. Such hormonal activation of breast cancer growth was completely abolished by treatment with alpha-difluoromethyl-ornithine (DFMO), a specific irreversible inhibitor of ornithine decarboxylase, which lowered tumor content of polyamines. The growth inhibitory effect of DFMO was partially reversible by exogenous putrescine administration. In contrast, the rise in cytosolic content of progesterone receptors induced by hormonal treatment was not affected by suppression of tumor polyamine levels by DFMO. Similarly, DFMO administration failed to influence the hormone-induced increase in uterine weight in the same animals. Thus, our data suggest selectivity of polyamine involvement in hormone actions, which, in our experimental system, seems to be restricted to the endocrine control of neoplastic cell proliferation.

Kinetic and morphometric responses of heterogeneous populations of NMU-induced rat mammary tumor cells to hormone and antipolyamine therapy in vivo

The present experiments were designed to evaluate in vivo the differential sensitivity of tumor cell subpopulations to hormone and polyamine manipulations using the hormone-responsive N-nitrosomethyl-urea (NMU)-induced rat mammary tumor. NMU tumor bearing rats were randomly assigned to control, ovariectomy, alpha-difluoromethyl-ornithine (DFMO) administration (an inhibitor of polyamine biosynthesis), or combination treatment, and were sacrificed on day 2, 4, or 7. The proportion of different cells was estimated by morphometric analysis and their replicative activities by [3H]-thymidine autoradiography. In tumors of intact rats, the fractions of glandular, myoepithelial, and non-epithelial cells were 85.3 +/- 2.2%, 4.7 +/- 0.7%, and 9.9 +/- 1.9%, respectively. Ovariectomy induced a similar time-dependent decline in the labelling indices of each cell type (from 5% to 1%). It also decreased the fraction of glandular cells (74.9 +/- 4.5%), while increasing the fraction of myoepithelial (8.6 +/- 1.9%) and non-epithelial (16.3 +/- 3.2%) cells. DFMO exerted similar but more modest effects. DFMO-induced tumor regression was also inferior to that observed with ovariectomy. Combined ovariectomy and DFMO induced a faster and greater suppression of all labelling indices than the individual treatments, even though tumor regression was not superior to that produced by ovariectomy alone. Combination treatment also produced more profound morphologic changes, reducing the fraction of glandular cells to 64.4 +/- 3.9% and increasing that of non-epithelial cells to 26.6 +/- 4.4%. Ovariectomy and DFMO reduced height but not width of glandular cells, resulting in a modest decrease in cell volume. The combination treatment, however, significantly suppressed all three parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal control of polyamine pools in experimental breast cancer in vivo: correlation with estrogen and progesterone receptor levels

The present experiments were designed to test whether, in the hormone responsive N-nitrosomethyl-urea (NMU)-induced rat mammary tumor, polyamine levels are under hormonal control and whether they correlate with estrogen (ER) and progesterone (PgR) receptor content. We observed that tumor regression induced by ovariectomy was associated with a decline in putrescine (Pu), spermidine (Sd) and spermine (Sm). Administration of estradiol and perphenazine (to stimulate endogenous prolactin release) to castrated rats restored tumor growth and contents of Pu and Sd to control values in a time dependent fashion while Sm levels were only modestly raised. The hormonal modulation of tumor polyamine levels was particularly obvious when the treatment effects on total pools (i.e. Pu + Sd + Sm) were analyzed. No significant correlation was observed between ER and PgR and polyamines in the tumors of intact rats as well as most of the treated groups. In contrast, a highly significant correlation was observed between ER and PgR levels. We conclude that in this experimental system cellular polyamine levels are hormonally regulated but are not correlated with the ER and PgR content of the tumor.