A new pseudo-peptide of Arg-Gly-Asp (RGD) with inhibitory effect on tumor metastasis and enzymatic degradation of extracellular matrix

A series of pseudo-peptide analogs of the Arg-Gly-Asp (RGD) sequence of fibronectin have been synthesized, and their anti-metastatic effects in mice and inhibitory effects on tumor cell invasion in vitro have been examined. The partially modified retro pseudo-peptide of RGD, Rrev-COCH2CO-D (FC-63), was more effective in inhibiting tumor metastasis than the original RGDS peptide. Replacement of the malonyl moiety of FC-63 with a carboxyethylene linkage (Rrev-COCH2CH2-D, FC-303 ) achieved more potent inhibition of lung metastasis of melanoma cells than FC-63. Among the analogs, FC-336, a p-xylylendiamine derivative having two FC-303 moieties, showed the most potent inhibitory effect on experimental lung metastasis produced by i.v. co-injection with B16-BL6 melanoma or colon 26 M3.1 cells in a dose-dependent manner. Multiple administrations of FC-336 after tumor inoculation also showed efficient therapeutic potency against spontaneous lung metastasis of B16-BL6 melanoma in mice. Furthermore, FC-336 effectively inhibited the invasion, migration and adhesion of tumor cells in vitro, but its inhibitory effects were not more than those of RGDS peptide. Zymography analysis revealed that FC-336 inhibited the degradation of gelatin substrate by matrix metalloproteinases (MMPs) produced by tumor cells, while the RGDS peptide did not affect the enzymatic degradation. These findings indicate that the pseudo-peptides of the RGD sequence, possessing the inhibitory property of the degradation by MMPs differently from original RGD-containing peptides, may be advantageous and useful in preventing tumor metastasis.

Functional role of sialyl Lewis X and fibronectin-derived RGDS peptide analogue on tumor-cell arrest in lungs followed by extravasation

Our study demonstrates that synthetic sialyl Lewis X (SLex) as a ligand for selectins and fibronectin-derived RGDS peptide analogue [Ar(DRGDS)3] inhibits lung metastases produced by i.v. co-injection of B16-BL6 melanoma cells. To investigate the inhibitory mechanisms in a living animal, we performed positron-emission tomography (PET) analysis after i.v. injection of [2-18F]2-fluoro-2v-deoxy-D-glucose-labeled tumor cells with or without liposomal SLex or Ar(DRGDS)3. The real-time PET measurement for the first 120 min, started immediately after injection, showed that tumor-cell arrest, i.e., accumulation in the target organ (lung) was remarkably inhibited by liposomal SLex, but not inhibited by Ar(DRGDS)3 or liposomal Me-SLex, which is not recognized by selectins. In contrast, Ar(DRGDS)3 inhibited the invasion of B16-BL6 cells into reconstituted basement membrane (Matrigel) following tumor arrest, whereas SLex- or Me-SLex-entrapped liposomes did not affect tumor invasion. In the metastatic processes containing tumor-cell lodgement and arrest in the target organ followed by extravasation (invasion), SLex resulted in the inhibition of initial arrest of tumor cells, presumably tumor-endothelium interaction, while Ar(DRGDS)3 achieved inhibition of tumor invasion into basement membrane at later steps of the cascade, consequently leading to inhibition of metastasis. Thus, tumor-cell arrest in lungs in the metastatic processes must be precisely and properly controlled by different adhesion molecules at different stages, which are similar to those observed in leukocyte-endothelium interaction.

Antimetastatic activities of synthetic Arg-Gly-Asp-Ser (RGDS) and Arg-Leu-Asp-Ser (RLDS) peptide analogues and their inhibitory mechanisms

We have investigated the inhibitory effect of the N-terminal modified Arg-Gly-Asp-Ser (RGDS) analogues, AcDRGDS and AcDRLDS, on tumor cell adhesion to the components of extracellular matrix and basement membrane, and also tested the antimetastatic effect of their conjugates with trimesic acid, Ar(DRGDS)3 and Ar(DRLDS)3. AcDRGDS significantly inhibited tumor cell adhesion to fibronectin, vitronectin and RGDS substrates, but not to CS1 substrate which is a ligand for the alpha 4 beta 1 tumor surface integrin receptor. In contrast, AcDRLDS variant peptide significantly inhibited tumor cell adhesion to laminin, in addition to RGDS-mediated adhesion to fibronectin and vitronectin. AcDRLDS also inhibited tumor cell adhesion to CS1 as well as the RGDS sequence within the fibronectin molecule in a concentration-dependent manner, although the inhibitory effect was less than that of the CS1 (EILDV) peptide. Ar(DRLDS)3 inhibited the laminin- and fibronectin-mediated invasion and migration of tumor cells, whereas Ar(DRGDS)3 selectively inhibited fibronectin-mediated invasion and migration. Ar(DRGDS)3 and Ar(DRLDS)3 were much more effective in inhibiting experimental lung or liver metastases of various types of murine and human tumors than the original RGDS-containing peptides or Ar(COONa)3. Multiple administrations of Ar(DRGDS)3 or Ar(DRLDS)3 potently inhibited spontaneous lung metastasis produced by intra-footpad injection of B16-BL6 cells without affecting the primary tumor size at the time of surgical excision, as compared with RGDS peptide or untreated control. Thus, Ar(DRGDS)3 and Ar(DRLDS)3 substantially increased the exhibiting any antimetastatic effect of the peptides without direct cytotoxicity.

Inhibition of tumor metastasis by Arg-Gly-Asp-Ser (RGDS) peptide conjugated with sulfated chitin derivative, SCM-chitin-RGDS

We have synthesized a new compound in which Arg-Gly-Asp-Ser (RGDS) was conjugated with 6-O-sulfated and 6-O-carboxymethyl-chitin (SCM-chitin), i.e. SCM-chitin-RGDS, and tested the inhibitory effect on lung and liver metastases of three different types of tumors in mice. SCM-chitin-RGDS was more effective for the inhibition of liver metastasis of L5178Y-ML25 lymphoma and lung metastases of colon 26 M3.1 cells than SCM-chitin, RGDS or their mixture. GRGDS peptide, however, required a higher dose (3000 micrograms) to obtain a sufficiently antimetastatic effect. Intermittent i.v. administration of SCM-chitin-RGDS before or after the i.v. inoculation of L5178Y-ML25 cells caused significant inhibition of liver metastasis as compared with the multiple administration of RGDS, SCM-chitin or untreated control. Co-injection of lymphoma cells with SCM-chitin-RGDS or multiple treatment of SCM-chitin-RGDS after tumor inoculation showed significantly enhanced survival rate. SCM-chitin-RGDS also showed the spontaneous lung metastasis produced by intrafootpad injection of B16-BL6 melanoma cells by the multiple i.v. administrations. These results demonstrate that the conjugation of RGDS peptide with SCM-chitin led to augmentation of therapeutic potential to cancer metastasis, thus implying an importance of the conjugation of cell-adhesive RGDS peptide with structurally heparin-like SCM-chitin, which possess binding ability to the heparin-binding domain of fibronectin or laminin and extremely low anticoagulant properties.

Synthetic Arg-Gly-Asp-Ser analogues of the cell recognition site of fibronectin that retain antimetastatic and anti-cell adhesive properties

Synthetic peptide analogues of the Arg-Gly-Asp-Ser (RGDS) sequence of fibronectin in which the amino acid of Gly was substituted with another one, named X, i.e. Arg-X-Asp-Ser (R-X-DS), and N-terminal modified R-X-DS have been synthesized to examine their antimetastatic effects in murine lung or liver metastasis models, as well as the inhibitory effect on tumor cell invasion, migration and adhesion in vitro. R-X-DS [X = Leu (L) or D-Leu (1)], as well as RGDS at a high dose of 3000 micrograms, significantly reduced the number of lung tumor colonies when they were co-injected with B16-BL6 melanoma. At a dose of 1000 micrograms/mouse, N-terminal modified R-X-DS, i.e. acetyl-D-R-X-DS [AcDR-X-DS: X = G, L or I], showed a more potent inhibitory effect on the lung or liver metastasis of B16-BL6 melanoma or L5178Y-ML25 lymphoma cells, respectively, as compared with RGDS or R-X-DS. AcDRLDS and AcDRIDS prevented the invasion of B16-BL6 cells into Matrigel/fibronectin- and Matrigel/laminin- coated filters, haptotactic migration, and the adhesion of the cells to both fibronectin- and laminin-coated substrates, whereas AcDRGDS inhibited only fibronectin-mediated cell functions. The intermittent i.v. administration of a water soluble vinylpolymer [poly(carboxyethylmethacrylamide), poly(CEMA)] containing R-X-DS (X = L or 1) or RGDS, following the subcutaneous inoculation of B16-BL6 cells, significantly inhibited spontaneous Jung metastasis as compared with multiple administrations of RGDS, R-X-DS or the untreated control.(ABSTRACT TRUNCATED AT 250 WORDS)

Antimetastatic effect by anti-adhesion therapy with cell-adhesive peptide of fibronectin in combination with anticancer drugs

We have investigated the therapeutic effect of CH-271 fusion polypeptide containing both cell-binding domain (C-274) and heparin-binding domain (H-271) of fibronectin in combination with anticancer drugs such as doxorubicin (DOX) or mitomycin C (MMC) on tumor metastasis of different types of tumors. CH-271 fusion polypeptide alone significantly inhibited both liver and lung metastasis when it was co-injected with L5178Y-ML25 T-lymphoma, RAW117-H10 B-lymphoma or B16-BL6 melanoma cells, and spontaneous lung metastasis of B16-BL6 melanoma cells when administered i.v. seven times before or after surgical excision of the primary tumors. Combined treatments with CH-271 and either DOX or MMC significantly inhibited liver and lung metastasis of lymphoma or melanoma cells respectively, as compared with either treatment alone or the untreated control. Administrations of CH-271 and DOX in combination substantially prolonged the survival time of mice injected i.v. with L5178Y-ML25 cells. CH-271 or DOX was effective for inhibiting the invasion of L5178Y-ML25 cells into Matrigel in a concentration-dependent manner. Our previous study has shown that CH-271-mediated inhibition of tumor invasion may be due in part to the anti-cell adhesive property without affecting the cell growth, whereas the anti-invasive effect of DOX was established to have resulted from the growth inhibition of tumor cells. Moreover, the combination of CH-271 with DOX provided a more effective inhibition of tumor invasion into Matrigel than did either alone. Thus, we have demonstrated that the combination of anti-cell adhesive CH-271 and anticancer drugs such as DOX or MMC, i.e. anti-adhesion therapy and chemotherapy, is a new approach that offers enhanced (additive) inhibitory effects on tumor metastasis and invasion.