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

Side chain effect in the modulation of αvβ3/α5β1 integrin activity via clickable isoxazoline-RGD-mimetics: development of molecular delivery systems

Construction of small molecule ligand (SML) based delivery systems has been performed starting from a polyfunctionalized isoxazoline scaffold, whose αvβ3 and α5β1 integrins' potency has been already established. The synthesis of this novel class of ligands was obtained by conjugation of linkers to the heterocyclic core via Huisgen-click reaction, with the aim to use them as "shuttles" for selective delivery of diagnostic agents to cancer cells, exploring the effects of the side chains in the interaction with the target. Compounds 17b and 24 showed excellent potency towards α5β1 integrin acting as selective antagonist and agonist respectively. Further investigations confirmed their effects on target receptor through the analysis of fibronectin-induced ERK1/2 phosphorylation. In addition, confocal microscopy analysis allowed us to follow the fate of EGFP conjugated α5β1 integrin and 17b FITC-conjugated (compound 31) inside the cells. Moreover, the stability in water solution at different values of pH and in bovine serum confirmed the possible exploitation of these peptidomimetic molecules for pharmaceutical application.

Integrins and bone metastasis: integrating tumor cell and stromal cell interactions

Integrins on both tumor cells and the supporting host stromal cells in bone (osteoclasts, new blood vessels, inflammatory cells, platelets and bone marrow stromal cells) play key roles in enhancing bone metastasis. Tumor cells localize to specific tissues through integrin-mediated contacts with extracellular matrix and stromal cells. Integrin expression and signaling are perturbed in cancer cells, allowing them to "escape" from cell-cell and cell-matrix tethers, invade, migrate and colonize within new tissues and matrices. Integrin signaling through αvβ3 and VLA-4 on tumor cells can promote tumor metastasis to and proliferation in the bone microenvironment. Osteoclast (OC) mediated bone resorption is a critical component of bone metastasis and can promote tumor growth in bone and αvβ3 integrins are critical to OC function and development. Tumors in the bone microenvironment can recruit new blood vessel formation, platelets, pro-tumor immune cells and bone marrow stromal cells that promote tumor growth and invasion in bone. Integrins and their ligands play critical roles in platelet aggregation (αvβ3 and αIIbβ3), hematopoietic cell mobilization (VLA-4 and osteopontin), neoangiogenesis (αvβ3, αvβ5, α6β4, and β1 integrin) and stromal function (osteopontin and VLA-4). Integrins are involved in the pathogenesis of bone metastasis at many levels and further study to define integrin dysregulation by cancer will yield new therapeutic targets for the prevention and treatment of bone metastasis.

Synthesis and biological evaluation of non-peptide αvβ3/α5β1 integrin dual antagonists containing 5,6-dihydropyridin-2-one scaffolds

Small constrained non-peptidic molecules consisting of a polyfunctionalized rigid core, carrying appendages corresponding to arginine and aspartic acid side chains, have been recently reported to be promising for drug development. In this work, the 5,6-dihydropyridin-2-one was envisaged as a scaffold to turn into potential integrin ligands, introducing a carboxylic acid and a basic appendage. The synthesis and the antiadhesion activity of a small library of peptidomimetics capable to recognize alpha(v)beta(3) and alpha(5)beta(1) integrins has been herein reported.

Inhibition of cancer cell adhesion by heterochiral Pro-containing RGD mimetics

In this paper, we describe the synthesis of a selected library of heterochiral d-Pro-containing RGD-peptidomimetics (RpD) and we investigate the biological activity as inhibitors of fibronectin adhesion to SK-MEL-24 tumor cells. In particular, peptides 4 and 8 showed an IC(50) in the 10(-8)M range. Despite the linear structure, the peptides tend to adopt a folded conformation in a polar environment.

Effects of HAb18G/CD147 antagonistic peptides on invasion and metastasis of HCC

AIM: To obtain the antagonistic peptides that have effect to prevent metastasis of Hepatocellular Carcinoma(HCC).

METHODS: Nine pieces of high affinity peptides (AP-1-AP-9) were obtained by pure HAb18G/CD147 antigen to panning phage displayed random peptide library. MTT assay was used to test toxicity of AP-1-AP-9 on human hepatocellular carcinoma cell (HHCC); Gelatin zymogram was used to analyze the effects of AP-1-AP-9 on activation and production of matrix metalloproteinase (MMPs); Matrigel-boyden chamber method was used to evaluate inhibitory abilities of AP-1-AP-9 on tumor cell invasion and metastasis; Inhibitory effect of AP-1-AP-9 on HHCC adhesion to extracellular matrix protein and fb cells were investigated. The influences of AP-1-AP-9 on HHCC chemotaxis migration were also tested.

RESULTS: AP-1-AP-9 has no toxicity on HHCC; AP-1, AP-6 and AP-9 could inhibit production and activation of MMP-2; the amounts of infiltrative cells in AP-1, 3, 6, 7, 8, 9 experimental groups are significantly less than that in control group (P < 0.05), and inhibition rate was 78.22%, 90.1%, 62.83%, 56.44%, 68.32%, 81.19%, respectively; AP-1-AP-9 had no effects on HHCC adhesion to matrigel and fibronectin (FN), whereas AP-3 and AP-9 could inhibit HHCC adhesion to collagen Ⅳand laminin(LN), AP-1, AP-6 and AP-9 could inhibit HHCC adhesion to fb. AP-6 could inhibit chemotaxis migration of HHCC with the inhibitory rate of 54% without statistical significance (P > 0.05).

CONCLUSION: HAb18G/CD147 antagonistic peptides (AP-1-AP-9) have inhibitory effects on many aspects or steps associated with metastasis of HCC, which provides avenue to explore medication for preventing metastasis of HCC.

Synthesis of RGD containing peptides and their bioactivities

RGDS, RGDV, and RGDF were used for the structural modification of YIGSR and YIGSK, the sequences involved in the development of metastasis disease. By use of a solution method, YIGSRRGDS, YIGSRRGDV, YIGSRRGDF, YIGSKRGDS, YIGSKRGDV, YIGSKRGDF, YIGSRYIGSK, and YIGSKYIGSR were prepared in good yield. The results of bioassay in vitro indicated that the target property of RGDS, RGDV, and RGDF to high affinity-receptors may be responsible for the enhanced anti-aggregation, anti-adhesion, and anti-invasion potency.

Cancer metastasis: a search for therapeutic inhibition

Failure of cancer treatment is often due to the growth of secondary, metastatic lesions in distant organs. Because initiation of metastasis is an early event in malignancy, patients often present not only with a primary tumor but also with occult metastases. Treatment of these metastases requires aggressive, systemic chemotherapy, since surgical removal of all metastatic foci is normally not feasible. However, drug toxicity caused by many of the currently used anticancer agents often limits chemotherapeutic approaches to malignant disease. In contrast, the development and use of novel cytostatic, antimetastatic agents could be less toxic and more applicable for long-term treatment in combating latent and/or residual disease. Practical intervention with such nontoxic agents has been envisioned as maintenance therapy after cytoreduction of a tumor or as a prophylactic treatment after the removal of a precancerous tumor exhibiting a genetic predisposition to a carcinomatous state. In this review, we discuss targets of the metastatic cell that may be potentially exploitable with chemotherapy, and present the current status of several novel, antimetastatic agents. Clinical evaluation of such agents will require new and appropriate clinical models for evaluating their antimetastatic efficacy. The recent successes achieved with certain proteinase inhibitors for the treatment of cancer are paving the way for the development of other therapeutic agents of this type, aimed at unique biochemical pathways associated with oncogenic behavior.

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.

Cell adhesion molecules and cancer metastasis

The adhesive interaction between tumor cells and host cells or the extracellular matrix plays a crucial role in metastasis formation. Therefore, understanding the mechanism controlling metastasis may assist in the development of antimetastatic therapy. We have used synthetic or recombinant polypeptide analogues containing the Arg-Gly-Asp (RGD) sequence found in the functional domains of fibronectin, such as poly(RGD) or CH-271, to regulate the mechanisms involved in cell adhesion during the metastatic process. Poly(RGD) inhibited experimental lung and liver metastasis effectively when coinjected i.v. with various types of tumors. In a model of spontaneous lung metastasis using the B16-BL6 melanoma, repeated administration of this polypeptide before or after surgical excision of the primary tumor resulted in a significant inhibition of tumor metastasis without affecting the growth of the primary tumor and substantially prolonged the survival time of mice. The mechanism responsible for the inhibition of tumor metastasis by the polypeptides is at least partly associated with the ability to interfere with cellular functions such as adhesiveness, motility and invasiveness in the process of metastasis. Combined treatment of the CH-271 fusion polypeptide and anticancer drugs, i.e., anti-adhesion therapy combined with chemotherapy, caused a marked inhibition of lung and liver metastasis of tumors as compared with either treatment alone or with the control. In contrast, the promotion of tumor cell interaction with immune cells via cell adhesion molecules, which differs from the anti-adhesive mechanism, may lead to the induction of anti-tumor immune responses and, consequently, to the inhibition of tumor metastasis. The transfection of the gene of the B7-1 adhesion molecule into tumor cells (B16-BL6 or K1735-M2 melanoma) resulted in the remarkable reduction of lung metastasis caused by the i.v. injection into mice. Immunization of B7-transfected tumor was effective as a tumor vaccine for preventing the metastasis of B7 negative original tumor cells. Thus, the regulation of the adhesive interaction with tumor cells may provide a new and promising approach for the control and prevention of cancer metastasis.

Differential effect of intestinal neuropeptides on invasion and migration of colon carcinoma cells in vitro

We investigated the effect of neuropeptides, which are vasoactive intestinal polypeptide (VIP), substance P, (SP), neuropeptide Y (NPY), neurokinin A (NKA), somatostatin (SOM), calcitonin gene-related peptide (CGRP), and leucine-enkephalin (L-ENK), on the invasion of murine Colon 26-L5 adenocarcinoma cells through a reconstituted basement membrane (Matrigel) using a Transwell cell culture chamber assay. VIP, SP, NPY, and L-ENK reduced invasive potential of tumor cells in a concentration-dependent manner, whereas SOM, CGRP, and NKA had no effect. Especially, VIP showed the most effective in inhibiting tumor invasion, and achieved 50% reduction at 10(-6) M. A similar effect by VIP was also observed in cell migration to fibronectin. VIP had no effect on the growth of tumor cells at the concentrations ranging from 10(-10) to 10(-6) M. The suppressed ability of the tumor cell motility by VIP (10(-6) M) was practically recovered by co-treatment with 2',5'-dideoxyadenosine, an adenylate cyclase inhibitor. These results indicate that VIP, among the neuropeptides used, could inhibit Matrigel invasion of Colon 26-L5 carcinoma cells through partial suppression of their motility, and the reduction was associated with an intracellular cAMP-mediated pathway.

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.