Prevention of metastasis by a polyamine synthesis inhibitor in an animal bone metastasis model

Oil for the cancer engine: The cross-talk between oncogenic signaling and polyamine metabolism

The study of metabolism has provided remarkable information about the biological basis and therapeutic weaknesses of cancer cells. Classic biochemistry established the importance of metabolic alterations in tumor biology and revealed the importance of various metabolite families to the tumorigenic process. We have evidence of the central role of polyamines, small polycatonic metabolites, in cell proliferation and cancer growth from these studies. However, how cancer cells activate this metabolic pathway and the molecular cues behind the oncogenic action of polyamines has remained largely obscure. In contrast to the view of metabolites as fuel (anabolic intermediates) for cancer cells, polyamines are better defined as the oil that lubricates the cancer engine because they affect the activity of biological processes. Modern research has brought back to the limelight this metabolic pathway, providing a strong link between genetic, metabolic, and signaling events in cancer. In this review, we enumerate and discuss current views of the regulation and activity of polyamine metabolism in tumor cell biology.

The cell clone ecology hypothesis and the cell fusion model of cancer progression and metastasis (II): three pathways for spontaneous cell-cell fusion and escape from the intercellular matrix

The two-stage initiation-progression model of cancer is widely accepted. Initiation appears to result most often from accumulation of damage to the DNA expressed as multiple mutations in the phenotype. Unsymmetrical chromosome segregation during mitosis of normal or mutated cells produces aneuploid cells and also contributes to the evolution of neoplasia. However, it has been pointed out (Parris GE. Med Hypotheses 2005;65:993-4 and 2006;66:76-83) that DNA damage and loss of chromosomes are much more likely to lead the mutant clones of cells to extinction than to successful expansion (e.g., an example of Muller's Ratchet). It was argued that aneuploid neoplasia represent new parasite species that successfully evolve to devour their hosts by incorporating sex-like redistribution of chromosomes through spontaneous or virus-catalyzed cell-cell fusion into their life-cycle. Spontaneous cell-cell fusion is generally blocked by the intercellular matrix to which the cells are bound via surface adhesion molecules (frequently glycoproteins, e.g., CD44). In order for progression of matrix-contained neoplasia toward clinically significant cancer to occur, the parasite cells must escape from the matrix and fuse. Release from the matrix also allows the parasite cells to invade adjacent tissues and metastasize to remote locations. Both invasion and metastasis likely involve fusion of the migrating parasite cells with fusion-prone blast cells. There are at least three pathways through which parasite cells can be liberated from the confining matrix: (i) Their adhesion molecules may be modified (e.g., by hyper-glycosylation) so that they can no longer grip the matrix. (ii) Their adhesion molecules or matrix may be saturated with other ligands (e.g., polyamines). (iii) Their adhesion molecules may be cleaved from the cell surface or the matrix itself may be cleaved (e.g., by MMPs or ADAMs). It is hypothesized that mobilization of parasite cells and cell-cell fusion go hand-in-hand in the progression of neoplasia to clinically significant cancer through invasion and metastasis. The latency between tumor recognition and exposure to mutagens and the increased incidence of cancer with age can probably be related to slow breakdown of the intercellular matrix that provides a barrier to cell-cell fusion.

Metastatic bone disease: pathogenesis and new strategies for treatment

Bone is the third leading site of metastatic disease, after the lung and liver. Pain, pathological fractures, neurological deficits, and forced immobilization significantly decrease the quality of life of patients with bone metastasis. The development of metastasis, from the migration of malignant cells from the primary tumor to their proliferation at a distant site, involves a series of sequential steps: angiogenesis, matrix degradation, cell motility, cell attachment, and cellular proliferation. A better understanding of the pathogenesis of metastasis may be expected to lead to the development of new treatment modalities for bone metastasis. Currently, antiangiogenic agents, matrix metalloproteinase (MMP) inhibitors, and hyperthermia are some of the newer therapeutic modalities that seem to hold promise for the treatment of metastatic bone disease.

Thrombin Inhibitor, Argatroban, Prevents Tumor Cell Migration and Bone Metastasis

It is well known that malignant cells show procoagulant activity, which is associated with their metastatic potential. Thrombin, the key enzyme of the blood coagulation system, is generated around tumor cells, promoting the migration and metastasis of tumor cells. In this study, we evaluated the effect of argatroban, a specific thrombin inhibitor, on the migration and metastasis of B16BL6 melanoma cells. In vitro argatroban dose-dependently inhibited cell migration, the maximum inhibition being observed in the presence of 10 microM argatroban (p < 0.0001). In order to investigate the antimetastatic effect of the thrombin inhibitor, we used an animal model that we have reported previously. C57BL6 mice which had received a bone (femur or tibia) transplanted into the dorsal subcutis were injected with B16 melanoma cells into the left heart ventricle. Intraperitoneal injection of argatroban (9 mg/kg/day for 4 weeks) significantly reduced the number of limbs with metastatic lesions as compared to a placebo (p < 0.05). These results suggest that argatroban was associated with reduced melanoma metastases by inhibiting cell migration. Our results showed that argatroban is effective for treatment of bone metastasis.