Suppression of Tumor Growth and Angiogenesis by a Specific Antagonist of the Cell-Surface Expressed Nucleolin

Abstract

BackgroundEmerging evidences suggest that nucleolin expressed on the cell surface is implicated in growth of tumor cells and angiogenesis. Nucleolin is one of the major proteins of the nucleolus, but it is also expressed on the cell surface where is serves as a binding protein for variety of ligands implicated in cell proliferation, differentiation, adhesion, mitogenesis and angiogenesis.Methodology/Principal FindingsBy using a specific antagonist that binds the C-terminal tail of nucleolin, the HB-19 pseudopeptide, here we show that the growth of tumor cells and angiogenesis are suppressed in various in vitro and in vivo experimental models. HB-19 inhibited colony formation in soft agar of tumor cell lines, impaired migration of endothelial cells and formation of capillary-like structures in collagen gel, and reduced blood vessel branching in the chick embryo chorioallantoic membrane. In athymic nude mice, HB-19 treatment markedly suppressed the progression of established human breast tumor cell xenografts in nude mice, and in some cases eliminated measurable tumors while displaying no toxicity to normal tissue. This potent antitumoral effect is attributed to the direct inhibitory action of HB-19 on both tumor and endothelial cells by blocking and down regulating surface nucleolin, but without any apparent effect on nucleolar nucleolin.Conclusion/SignificanceOur results illustrate the dual inhibitory action of HB-19 on the tumor development and the neovascularization process, thus validating the cell-surface expressed nucleolin as a strategic target for an effective cancer drug. Consequently, the HB-19 pseudopeptide provides a unique candidate to consider for innovative cancer therapy.

ADAMTS-2 functions as anti-angiogenic and anti-tumoral molecule independently of its catalytic activity

“…A direct interaction between this acidic domain and ADAMTS-2 would not be surprising considering that ADAMTS-2 has affinity for the negatively charged heparin and HSPG and that the heparin-binding domain of endostatin is required for its efficient binding on the acidic domain of nucleolin. Moreover, a specific antagonist of cell-surface nucleolin reduces the phosphorylation of Erk1/2 within a few minutes and suppresses tumor growth and angiogenesis [45], two features also observed here for ADAMTS-2. The hypothesis that nucleolin is a receptor mediating the proapoptotic effect of ADAMTS-2 may seemed challenged by the observation that HEK 293-EBNA cells are not affected by ADAMTS-2 although they express nucleolin at their surface (not shown).…”

Molecular tumor targeting of gelonin by fusion with F3 peptide

“…This result appears consistent with our previous reports that gelonin is quite stable in fusions due to its structure [26,32] , which consequently contributes to the retention of its activity even after fusion with F3 peptide. To elucidate any anti-cancer targeting effects of F3-Gel or gelonin alone, for the in vitro cell experiments, we used HeLa, LnCaP, 9L, and U87 MG cancer cells because these cell lines were fully examined in other previous studies related to the F3 peptide [18,33] . In contrast to the equipotent intrinsic activity compared with unmodified gelonin in the cell-free conditions (Figure 2), in the U87 MG cell lines, F3-Gel exhibited a significantly greater ability to reduce the protein level to less than 50% than that of the gelonin ( Figure 5).…”

“…Nucleolin is known as a multifunctional DNA/RNA binding protein involved in regulation of gene transcription, chromatin remodeling, RNA metabolism, and ribosomal RNA synthesis [19] . Tumor cells with high proliferation rates are known to overexpress surface-associated nucleolins in addition to cytoplasmic and nuclear nucleolins, whereas normal cells express nucleolins in the cytoplasm and nuclear membrane [18] . Thus, surface nucleolins make tumor cells the preferential targets.…”

“…F3 is a 30-34-amino acid fragment of a high mobility group protein, HMG2N. Nucleolin is known to be highly expressed on the surface of tumor cells, whereas it is primarily expressed in the cytoplasm and nuclear membrane in normal cells, which might help to achieve selective drug targeting into the tumor site [18] . These receptor molecules expressed on the tumor cell surface are known to play an important role in facilitating the internalization of F3 peptide into tumor cells and transport into the cell nucleus.…”

RNA-binding protein nucleolin in disease

“…As explained above, the synthetic peptide HB-19 specifically antagonizes the C-terminal RGG domain of nucleolin and inhibits cell membrane-associated nucleolin function, thereby preventing the growth, angiogenesis and tumorigenicity of numerous cancer cells using different assays. 139,140 The V3 loop-mimicking pseudopeptide 5[Kpsi(CH2N)PR]-TASP binds to the cell-surface nucleolin in monocyte-derived macrophages and synergizes with the inhibitory effects of β-chemokines on HIV infection. 141 Another synthetic ligand targeting cell-surface nucleolin, N6L, also displays potent anti-tumor activities, enhances apoptosis, blocks angiogenesis and prevents tumor growth.…”