Purpose: Pigment epithelium-derived factor (PEDF) is a potent anti-angiogenic and tumor suppressive 50kDa protein, decreased in neovascular retinopathies, and aggressive cancers. PEDF protective activity has been localized to a 34-mer surface peptide, then 25 and 18aa fragments therein. We sought smaller practical fragments, able to be modified as prodrugs to nanocarriers, then attempted to evaluate their clinical potential in cell and animal models, and to identify their target receptor.
Methods: Truncation of the 18-25 mer fragments led to anti-angiogenic 8-10aa peptides screened by endothelial cell (EC) apoptosis after VEGF activation. Further changes identified N-terminal dicarboxylic acid (DCA) modified octa- and nonapeptides, where internal Asp to Asn residue substitution, optimized apoptotic response. Two potent small peptides (8-mer, 9-mer) by intravitreal (IVT) delivery, were tested in mouse models of choroidal neovascularization (CNV) and of ischemic retinopathy (OIR). The same peptides and cyanine dye-tagged analogs were tested against ovarian, prostate and glioma cells, also NS-1 neurons, examining apoptosis and endocytosis. The peptides were tested in tumor models and against amyloid cytotoxicity. Cell uptake of dye was examined after specific cell exposure to antibodies and free peptides.
Results: A single IVT injection of 2-4 nmol of either peptide resulted in a significant decrease in mouse CNV and in neonatal mouse OIR, with no signs of toxicity. Eye drop delivery (8mer) was effective in CNV and a prodrug nanoparticle conjugate (9mer) extended CNV protection. Peptides induced tumor cell apoptosis in both ovarian cancer in a glioma stem cells and inhibited ovarian cancer orthotopic tumor growth with QD systemic injection. They protected neural cells from apoptosis induction by amyloid peptide a,b 1-42. Brief exposure to PEDF, free peptide, and anti 67LR exposure block cyanine-peptide endocytosis in 3 cell types.
Conclusions: A small active pharmacophore was defined within the PEDF sequence (Y-D-L-Y-R-V). Optimization around ..YNLYR.. improves >100-fold on the laminin beta1 motif, YIGSR, which weakly binds non-integrin laminin receptor, 67LR. The latter plays harmful roles in angiogenesis, tumor malignancy, neuronal amyloid uptake and microbial/viral cell entry. New modifications (adipic-X-Y-N-L-Y-R-V…) yielded practical, synthetic peptides that can mitigate retinopathy and cancer growth, and protect neurons, via cell surface removal of 67LR.