Effect of alpha-difluoromethylornithine in lung metastases before and after surgery of primary adenocarcinoma tumors in mice

DFMO/eflornithine inhibits migration and invasion downstream of MYCN and involves p27Kip1 activity in neuroblastoma

Neuroblastoma (NB) is the most common extracranial pediatric tumor. NB patients over 18 months of age at the time of diagnosis are often in the later stages of the disease, present with widespread dissemination, and often possess MYCN tumor gene amplification. MYCN is a transcription factor that regulates the expression of a number of genes including ornithine decarboxylase (ODC), a rate-limiting enzyme in the biosynthesis of polyamines. Inhibiting ODC in NB cells produces many deleterious effects including G₁ cell cycle arrest, inhibition of cell proliferation, and decreased tumor growth, making ODC a promising target for drug interference. DFMO treatment leads to the accumulation of the cyclin-dependent kinase inhibitor p27^Kip1 protein and causes p27^Kip1/Rb-coupled G₁ cell cycle arrest in MYCN-amplified NB tumor cells through a process that involves p27^Kip1 phosphorylation at residues Ser10 and Thr198. While p27^Kip1 is well known for its role as a cyclin-dependent kinase inhibitor, recent studies have revealed a novel function of p27^Kip1 as a regulator of cell migration and invasion. In the present study we found that p27^Kip1 regulates the migration and invasion in NB and that these events are dependent on the state of phosphorylation of p27^Kip1. DFMO treatments induced MYCN protein downregulation and phosphorylation of Akt/PKB (Ser473) and GSK3-β (Ser9), and polyamine supplementation alleviated the DFMO-induced effects. Importantly, we provide strong evidence that p27^Kip1 mRNA correlates with clinical features and the survival probability of NB patients.

The mechanisms by which polyamines accelerate tumor spread

Increased polyamine concentrations in the blood and urine of cancer patients reflect the enhanced levels of polyamine synthesis in cancer tissues arising from increased activity of enzymes responsible for polyamine synthesis. In addition to their de novo polyamine synthesis, cells can take up polyamines from extracellular sources, such as cancer tissues, food, and intestinal microbiota. Because polyamines are indispensable for cell growth, increased polyamine availability enhances cell growth. However, the malignant potential of cancer is determined by its capability to invade to surrounding tissues and metastasize to distant organs. The mechanisms by which increased polyamine levels enhance the malignant potential of cancer cells and decrease anti-tumor immunity are reviewed. Cancer cells with a greater capability to synthesize polyamines are associated with increased production of proteinases, such as serine proteinase, matrix metalloproteinases, cathepsins, and plasminogen activator, which can degrade surrounding tissues. Although cancer tissues produce vascular growth factors, their deregulated growth induces hypoxia, which in turn enhances polyamine uptake by cancer cells to further augment cell migration and suppress CD44 expression. Increased polyamine uptake by immune cells also results in reduced cytokine production needed for anti-tumor activities and decreases expression of adhesion molecules involved in anti-tumor immunity, such as CD11a and CD56. Immune cells in an environment with increased polyamine levels lose anti-tumor immune functions, such as lymphokine activated killer activities. Recent investigations revealed that increased polyamine availability enhances the capability of cancer cells to invade and metastasize to new tissues while diminishing immune cells' anti-tumor immune functions.

Ornithine decarboxylase mRNA expression in curatively resected non-small-cell lung cancer

BACKGROUND

The effect of ornithine decarboxylase (ODC) on the pathogenesis of non-small-cell lung cancer (NSCLC) remains poorly investigated. Hence, the aim of this study was to explore the potential role of ODC mRNA expression as a prognostic biomarker in patients with curatively resected NSCLC.

PATIENTS AND METHODS

A total of 91 tumor and matching nontumorous lung tissue samples from patients with NSCLC were analyzed using a quantitative real-time reverse-transcriptase polymerase chain reaction method. The relative ODC mRNA expression was measured in tumorous and nontumorous lung tissue using beta-actin as a reference gene. Squamous cell carcinoma was found in 43 patients (47%), adenocarcinoma in 33 (36%), and large-cell carcinoma in 15 of the patients (17%). All patients' disease was R0 resected.

RESULTS

Ornithine decarboxylase was detected in all 91 tumor and nontumorous lung tissue samples. The median tumorous expression of 9.11 (range, 0.92-155.35) was significantly elevated compared with the median ODC expression of 7.89 (range, 0.0-45.8) in nontumorous lung tissue. Ornithine decarboxylase expression levels were not associated with any clinicopathologic parameters. Using an ODC/beta-actin ratio of 10 as a cutoff, tumorous ODC (tODC) expression is a significant prognostic factor in NSCLC. The ODC ratio between tumorous and nontumorous expression was even more prognostic. Moreover, Cox proportional hazards model analysis showed ODC expression to be an independent prognostic factor.

CONCLUSION

In this study, ODC is shown to have a prognostic potential in NSCLC. Low levels of tODC expression are associated with a more aggressive tumor biology. Also, an increase of ODC mRNA expression during carcinogenesis seems to have a favorable prognostic effect. Measuring the ODC expression in patients with NSCLC could aid in further chemotherapy decisions. Our results suggest that further investigation of ODC mRNA expression in NSCLC may be warranted.

Regulation of ornithine decarboxylase during oncogenic transformation: mechanisms and therapeutic potential

The activity of ornithine decarboxylase (ODC(1)), the first enzyme in polyamine biosynthesis, is induced during carcinogenesis by a variety of oncogenic stimuli. Intracellular levels of ODC and the polyamines are tightly controlled during normal cell growth, and regulation occurs at the levels of transcription, translation and protein degradation. Several known proto-oncogenic pathways appear to control ODC transcription and translation, and dysregulation of pathways downstream of ras and myc result in the constitutive elevation of ODC activity that occurs with oncogenesis. Inhibition of ODC activity reverts the transformation of cells in vitro and reduces tumor growth in several animal models, suggesting high levels of ODC are necessary for the maintenance of the transformed phenotype. The ODC irreversible inactivator DFMO has proven to be not only a valuable tool in the study of ODC in cancer, but also shows promise as a chemopreventive and chemotherapeutic agent in certain types of malignancies.

Polyamines prevent DFMO-mediated inhibition of angiogenesis

Tumor growth mainly depend on formation of new blood vessels. DFMO (alpha-difluoromethylornithine), an inhibitor of polyamine biosynthesis, inhibits tumor growth in many animal tumors. Our investigation was to evaluate the requirement of polyamines for induction of angiogenesis by tumor cells and spleen lymphocytes from tumor-bearing mice. In this regard, we have added DFMO to cell cultures. The neovascular response induced either by tumor cells or spleen lymphocytes was completely abrogated. This inhibition could be reversed by the addition of exogenous putrescine. These findings suggest that the effect of DFMO on angiogenesis is, in part, mediated by the inhibition of polyamine biosynthesis.

Ornithine decarboxylase activity, prolactin blood levels, and estradiol and progesterone receptors in human breast cancer

Ornithine decarboxylase (ODC) activity in human breast cancer tissues was correlated with prolactinemia (Prl), estradiol and progesterone cytosol receptors (ER and PR), and histopathologic pattern. Ninety-two cases of breast cancer, six benign mammary disease, and three normal breast tissues were studied for ER, PR, and ODC. Prolactinemia was assessed in 59 cancer patients, 14 of whom showed hyper-Prl along with significantly higher ODC than in patients with normal-Prl [(20.01 +/- 6.33) 10(-2) vs (5.20 +/- 0.90) 10(-2) pmol CO2/micrograms protein/h; P less than 0.0125]. A direct correlation was found between Prl and ODC in postmenopausal women (n = 40). Prl was assayed in seven of 13 ER-PR breast cancer patients; a highly significant, direct correlation was found between Prl and ODC in this group (r = 0.934, P less than 0.0025). ODC did not correlate with ER or PR. Carcinomas with higher ODC (n = 17) had higher cellularity, lower histologic differentiation, and higher nuclear anaplasia than those in which ODC was not detectable (n = 13). In normal breast and five of six benign mammary disease tissues, ODC was not detectable. These findings suggest that ODC could be a reliable marker for prognosis.