A new pseudo-peptide analogue of the Arg-Gly-Asp (RGD) sequence inhibits liver metastasis of colon 26-L5 carcinoma cells
Introduction
Despite the advances in diagnostic techniques for the early detection of colon cancer and the significant improvement in surgical procedures, the mortality rate of colon cancer has been increasing year after year and metastasis is one of the most frequent causes of death by cancer. The liver is the most common target of hematogeneous metastasis in gastrointestinal tract cancer, especially colon cancer, and the prognosis for cases with liver metastasis is extremely bad at present [1]. If occult micrometastases that had been already established at the time of surgery were inhibited, the prognosis of patients with colon carcinoma could be better. The suitable experimental metastatic models of colon carcinoma are necessary in the search for novel therapies for colon carcinoma. We have established a highly liver-metastatic cell line of colon 26 carcinoma (colon 26-L5) by the in vivo selection method of Fidler 2, 3.
During the metastatic cascade, metastasizing tumor cells interact with various host cells (platelets, lymphocytes, or endothelial cells) and/or extracellular matrices and basement membrane components (e.g. fibronectin and laminin) 4, 5, 6, 7. The interaction may lead to the enhancement of survival, arrest, or invasiveness of the tumor cells. Tumor interactions with host cells or components are fundamental in the metastatic cascade 5, 7, 8, 9, 10. A characteristic Arg-Gly-Asp (RGD) sequence, which was originally found within the central cell-binding domain of fibronectin, is present in a number of extracellular matrices, binds some integrins on the cell surface and contributes to cell functions including adhesion, migration and invasion 4, 5, 6, 7, 8, 9, 10. RGD-containing peptides have been reported to inhibit tumor metastasis, tumor-induced angiogenesis and tumor-elicited platelet aggregations 11, 12, 13, 14, 15. Attempts to control tumor metastasis have been carried out by using synthetic RGD-related peptides including poly(RGD) 15, 16, 17and cyclic RGDS [18]. Other related peptides such as YIGSR derived from laminin and CS1 from fibronectin have been used to inhibit tumor metastasis 19, 20, 21. We recently demonstrated that the pseudo-peptide analogue (FC-336) of the RGD sequence of fibronectin acquired a new inhibitory property of the degradation of the basement membrane by matrix metalloproteinases (MMPs) derived from tumor cells by chemical modification of original RGD-containing peptides [22]. The pseudo-peptide FC-336 caused a significant reduction of lung tumor colonies when injected with tumor cells or separately injected i.v. after tumor inoculation and it inhibited the invasion, adhesion, migration and enzymatic degradation by tumor cells in vitro [22].
To further extend our previous study, we investigated the anti-metastatic effect of the FC-336 pseudo-peptide on established liver metastasis of colon 26-L5 carcinoma cells.
Section snippets
Mice
Specific pathogen-free female BALB/c mice (7–10 weeks old) were purchased from Japan SLC (Hamamatsu, Japan). The mice were maintained in the Laboratory for Animal Experiments, Research Institute for Wakan-yaku, Toyama Medical and Pharmaceutical University, under laminar air-flow conditions.
Cells
A highly liver-metastatic cell line of colon 26 carcinoma (colon 26-L5) was obtained by the in vivo selection method of Fidler 2, 3. Colon 26-L5 cells were maintained as monolayer cultures in RPMI 1640
Effect of the pseudo-peptide on experimental liver metastasis of colon 26-L5 carcinoma cells
We first investigated the effect of RGDS tetrapeptide or FC-336 pseudo-peptide on experimental liver metastasis produced by the injection of colon 26-L5 carcinoma cells into the portal vein. Nineteen days after the injection of tumor cells with these compounds, tumor colonies in the liver were visually counted and the livers were weighed. Fig. 1Fig. 2 show that FC-336 significantly inhibited liver tumor colonization in a dose-dependent manner ranging from 1 to 5 mg/mouse and it reduced liver
Discussion
Several attempts have been made to control the mechanism involved in the cell function such as adhesion, migration and invasion of tumor cells during the metastatic process using a number of related compounds derived from adhesive molecules 11, 12, 16, 17, 18, 19, 20, 21. The RGD sequence of some adhesion molecules is recognized by several cell surface integrins 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20. We reported that the retro-peptide of the RGD sequence, Rrev-COCH2CO-D
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[25]
Acknowledgements
This work was supported in part by Grants-in-Aid for Cancer Research from the Japanese Ministry of Education, Science, Sports and Culture (Nos. 06282122 and 07273106). We thank Ms Kazuko Hayashi for her technical assistance.
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