Short Pigment Epithelial-Derived Factor-Derived Peptide Inhibits Angiogenesis and Tumor Growth

Abstract

Purpose: Pigment epithelial-derived factor (PEDF) is a potent angiogenesis inhibitor with multiple other functions, some of which enhance tumor growth. Our previous studies mapped PEDF antiangiogenic and prosurvival activities to distinct epitopes. This study was aimed to determine the minimal fragment of PEDF, which maintains antiangiogenic and antitumor efficacy. Experimental Design: We analyzed antigenicity, hydrophilicity, and charge distribution of the angioinhibitory epitope (the 34-mer) and designed three peptides covering its COOH terminus, P14, P18, and P23. We analyzed their ability to block endothelial cell chemotaxis and induce apoptosis in vitro and their antiangiogenic activity in vivo. The selected peptide was tested for the antitumor activity against mildly aggressive xenografted prostate carcinoma and highly aggressive renal cell carcinoma. To verify that P18 acts in the same manner as PEDF, we used immunohistochemistry to measure PEDF targets, vascular endothelial growth factor receptor 2, and CD95 ligand expression in P18-treated vasculature. Results: P14 and P18 blocked endothelial cell chemotaxis; P18 and P23 induced apoptosis. P18 showed the highest IC 50 and blocked angiogenesis in vivo : P23 was inactive and P14 was proangiogenic. P18 increased the production of CD95 ligand and reduced the expression of vascular endothelial growth factor receptor 2 by the endothelial cells in vivo. In tumor studies, P18 was more effective in blocking the angiogenesis and growth of the prostate cancer than parental 34-mer; in the renal cell carcinoma, P18 strongly decreased angiogenesis and halted the progression of established tumors. Conclusions: P18 is a novel and potent antiangiogenic biotherapeutic agent that has potential to be developed for the treatment of prostate and renal cancer.Angiogenesis (the formation of new capillaries from established ones) is a necessary prerequisite for the exponential tumor growth. Angiogenesis is regulated by the balance between positive and negative regulators, inhibitors and stimuli, in the tumor microenvironment also termed angiogenic switch: in the normal tissue, the prevalence of inhibitors maintains vascular quiescence, whereas, in tumors, the balance is tipped in favor of the stimuli (1). Angiogenic switch can be flipped back to the ''off position'' by sequestering angiogenic stimuli with appropriate neutralizing antibodies, by blocking their signaling receptors using small-molecule inhibitors, or by employing natural antiangiogenic molecules. The advent of therapies targeting proangiogenic vascular endothelial growth factor (VEGF) and platelet-derived growth factor-BB or their receptors (Avastin, sunitinib, and sorafenib; refs. 2,3) underscores the therapeutic value of antiangiogenics but also highlights the possibility of overcoming the withdrawal of a single angiogenic factor (4). Studies of past two decades suggest that natural inhibitors of angiogenesis act as endothelial-specific tumor suppressors (5); their specificity for remodeling endothelium...

Pigment epithelium-derived factor inhibits caveolin-induced interleukin-8 gene expression and proliferation of human prostate cancer cells

“…There is accumulating evidence that overexpression of Cav promotes tumor growth and metastasis of prostate cancer via diverse pathways (3)(4)(5)(6), while PEDF may protect against the progression of prostate cancer, via anti-angiogenic, anti-inflammatory and proapoptotic effects (17)(18)(19). To the best of our knowledge, the present study demonstrated for the first time that treatment with 1 or 10 nM PEDF significantly inhibited the Cav-induced increase in IL-8 mRNA expression in PC-3 (17).…”

“…PEDF has been identified as a highly effective inhibitor of angiogenesis in cell culture models as well as in animal models (11,12). Furthermore, studies have demonstrated that PEDF blocks cytokine-induced and vascular endothelial growth factor-induced angiogenesis and inflammatory reactions, inhibits tumor growth and induces apoptosis in tumors, including prostate cancer (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24). Our group has recently demonstrated that PEDF binds to Cav and blocks its pro-inflammatory effects in endothelial cells (25).…”

Pigment Epithelium-Derived Factor – An Angiostatic Factor with a Broader Function in Melanoma

“…In a more recent study, smaller regions of 34-mer epitope (named P14, P18 and P23, according to their respective length) were tested for angioinhibitory activity in vitro and in vivo. P14 and P23 display antiangiogenic activity in vitro (both blocking endothelial chemotaxis, and inducing apoptosis in the case of P23), but not in vivo; while P18 is a more potent antiangiogenic peptide than 34-mer in prostate cancer, being able to block bFGF and VEGF-dependent angiogenesis in the in vivo cornea neovascularisation assay (Mirochnik et al, 2009). Another study by Ek and colleagues identified other small peptides with antitumoral activity in an orthotopic osteosarcoma model.…”

Regulation of MT1-MMP and MMP-2 by the Serpin PEDF: a Promising New Target for Metastatic Cancer

“…Essentially, PEDF has been determined to be the most potent endogenous angiogenic inhibitor in the body with the ability to prohibit neovascularization in the cornea, as well as endothelial cell growth, tumour proliferation and cancer metastasis [17,20]. Furthermore, PEDF has also been found to promote neuronal survival and cellular differentiation [21,22]. …”