Survival Factor For Cancer Cells Research Articles

Osteoprotegrin and the bone homing and colonization potential of breast cancer cells

Breast cancer cells preferentially metastasize to bone, leading to the formation of primarily osteolytic lesions. Osteoprotegerin (OPG) plays multifactorial roles in the development of osteolytic bone metastases. An increase in the ratio of receptor activator of nuclear factor kappaB ligand (RANKL) to OPG increases osteoclastogenesis within the bone microenvironment. OPG also acts as a survival factor for cancer cells by protecting them from tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) mediated apoptosis. This study compares OPG production in vitro in a number of breast cancer cell lines exhibiting both differences in metastatic capacity and in preferential metastasis to bone. Our studies demonstrated that OPG expression by MDA-231, MDA-MET, and MDA-231/K cancer cells was directly correlated with bone specific homing and colonization potential but not with metastasis of cancer cells to other organs; both in IL-1 beta stimulated and control cells. We also demonstrated expression of other bone-related markers including type I collagen, osteocalcin, osteopontin, and Runx2 in these cells. However, the generally lower expression of these markers in the bone selective cell line MDA-MET suggested that increased OPG expression in the bone specific variant was not merely a consequence of enhanced osteomimicry by these cells but that it has a significant role in the metastatic process. Co-culture of breast cancer cells with osteoblastic cells (hFOB 1.19) led to an overall downregulation in OPG production, which was not affected by the bone homing and colonization potential of the cell lines, suggesting that OPG alone is not indicative of osteolytic bone activity by breast cancer cells.

Mitochondrial superoxide dismutase: a promising target for new anticancer therapies.

Compelling experimental and epidemiological evidence involves oxygen radicals in carcinogenesis, acting reactive oxygen species both as endogenous genotoxins during cell initiation and as messenger molecules in mitogenesis and in tumor promotion. Moreover, oxidants stimulate neoangiogenesis, which is a prerequisite for tumor growth. However, while several natural as well as synthetic antioxidant compounds appear to be chemopreventive in mutagenicity assays, antioxidant-based treatments for the prevention or cure of cancer have led to non-conclusive if not disappointing results. This is likely due to the fact that oxygen radicals have also a major role in the natural defences against the propagation of cancer cells, i.e. tumor cell apoptosis and immune surveillance, and mediate the beneficial cytotoxic effect of both the chemo-and radio-therapy. In recent years, the mitochondrial antioxidant enzyme, Manganous Superoxide Dismutase (MnSOD), has received a growing attention as a negative modulator of cellular apoptosis and as a survival factor for cancer cells. In fact, while overexpression of this enzyme in cancer cells decreases proliferation and tumor incidence in transgenic models, it is clear that even small amounts of this enzyme are crucial for cell resistance to inflammatory stimuli and anticancer drugs, and prevent oncogene-induced apoptosis triggered by the tumor suppressor protein p53. A previously unexpected oncogenic potential of MnSOD is also suggested by the elevated levels of this enzyme in several classes of human neoplasms, in a fashion which often correlates with the degree of their malignancy. This review focuses on the debated issue of the pro- and/or anti-tumoral effect of MnSOD, with special emphasis on recent observations suggesting that pharmacological inhibition of MnSOD may represent an effective strategy to selectively kill cancer cells and to circumvent their resistance to the commonly used anticancer treatments.

Adrenomedullin and cancer

Adrenomedullin (AM) is a pluripotent hormone with structural similarities to calcitonin gene-related peptide (CGRP), which is expressed by many tissues in the body and shows a remarkable range of effects mediated by paracrine/autocrine and possibly endocrine mechanisms. AM has been implicated as a mediator of several pathologies such as cardiovascular and renal disorders, sepsis, inflammation, diabetes and cancer, among others. AM is expressed in a variety of tumors where it aggravates several of the molecular and physiological features of malignant cells. AM has been shown to be a mitogenic factor stimulating growth in several cancer types and to encourage a more aggressive tumor phenotype. In addition, AM is an apoptosis survival factor for cancer cells and an indirect suppressor of the immune response through its binding protein, complement factor H, and regulation in expression of cytokines. AM plays an important role in environments subjected to low oxygen tensions, which is a typical feature in the proximity of solid tumors. Under these conditions, AM is upregulated through a hypoxia-inducible factor 1 (HIF-1)-dependent pathway and acts as a potent angiogenic factor promoting neovascularization. The collective findings brought together over the last years place AM as a major regulator of carcinogenesis-tumor progression and identifies its autocrine loop as a putative target for developing new strategies against human cancers.

Thrombin as a survival factor for cancer cells: thrombin activation in malignant effusions in vivo and inhibition of idarubicin-induced cell death in vitro.

The aim of the experiments shown here, is to demonstrate exemplarily that thrombin can be a survival factor for malignant cells. Activation of the coagulation system has been examined in patients with acute myeloid leukemia (AML) and non-Hodgkin lymphoma (NHL) before and after chemotherapy as well as in malignant effusions of heavily pretreated patients with solid tumors. Thrombin receptor expression (PAR-I) has been examined on HL-60 cells; the effect ofthrombin on the proliferation of the cells and inhibition of apoptosis induction by idarubicin has been shown. Using fibrinopeptide A as an indirect parameter for thrombin activation, we found elevated levels in patients with AML and NHL before and a significant 2-fold increase after chemotherapy (p < 0.02 for the AML group; p < 0.0006 for the NHL group). Apparently, this does not only affect patients with hematological diseases, but also with solid tumors. In order to find out if the tumor cells directly activate thrombin, we examined malignant effusions of patients with different solid tumors. Comparing prothrombin fragment 1 + 2 in ascites and pleural effusions with the patients' serum levels, we found it significantly increased in all cases (mean of 1.96 +/- 0.5 nmol/l in the serum vs. 12.1 +/- 3.6 nmol/l in effusions; p < 0.001). The majority of patients presented elevated serum levels. Additionally, we incubated HL-60 cells (human promyelocytic leukemia) with thrombin prior to treatment with idarubicin. Expression of thrombin receptor (PAR-1) could be verified by FACS-analysis using a monoclonal antibody. HL-60 cells responded with increased proliferation to thrombin exposure with concentrations between 0.3 and 3 U/ml. This effect could be abolished by the addition of hirudin, demonstrating thrombin specificity. In these concentrations, thrombin was able to abrogate the induction of apoptosis by idarubicin completely (p < 0.005). Here we give evidence for the role of thrombin as a resistance factor for tumor cells towards chemotherapy. In the light of the fact that thrombin is regularly activated in cancer patients, these findings indicate that thrombin is a clinically relevant cellular resistance factor. A number of pre-clinical and clinical studies imply that inhibition of the coagulation system, e.g. by low-molecular weight heparins or warfarin, increases the effect of chemotherapy.

Fatty acid oxidation and signaling in apoptosis.

It is well established that fatty acid metabolites of cyclooxygenase, lipoxygenase (LOX), and cytochrome P450 are implicated in essential aspects of cellular signaling including the induction of programmed cell death. Here we review the roles of enzymatic and non-enzymatic products of polyunsaturated fatty acids in controlling cell growth and apoptosis. Also, the spontaneous oxidation of polyunsaturated fatty acids yields reactive aldehydes and other products of lipid peroxidation that are potentially toxic to cells and may also signal apoptosis. Significant conflicting data in terms of the role of LOX enzymes are highlighted, prompting a re-evaluation of the relationship between LOX and prostate cancer cell survival. We include new data showing that LNCaP, PC3, and Du145 cells express much lower levels of 5-LOX mRNA and protein compared with normal prostate epithelial cells (NHP2) and primary prostate carcinoma cells (TP1). Although the 5-LOX activating protein inhibitor MK886 killed these cells, another 5-LOX inhibitor AA861 hardly showed any effect. These observations suggest that 5-LOX is unlikely to be a prostate cancer cell survival factor, implying that the mechanisms by which LOX inhibitors induce apoptosis are more complex than expected. This review also suggests several mechanisms involving peroxisome proliferator activated receptor activation, BCL proteins, thiol regulation, and mitochondrial and kinase signaling by which cell death may be produced in response to changes in non-esterified and non-protein bound fatty acid levels. Overall, this review provides a context within which the effects of fatty acids and fatty acid oxidation products on signal transduction pathways, particularly those involved in apoptosis, can be considered in terms of their overall importance relative to the much better studied protein or peptide signaling factors.