A SEMA3E mutant resistant to cleavage by furins (UNCL-SEMA3E) inhibits choroidal neovascularization

Abstract

Abnormal subretinal choroidal neovascularization (CNV) is a major cause of blindness in exudative age-related macular degeneration (AMD). Current anti-angiogenic treatments by VEGF sequestering agents have been successful, but a significant proportion of patients do not respond well to these treatments, and the response of others diminishes over time, suggesting that additional anti-angiogenic agents that function by separate mechanisms may be of use to such patients. We have previously found that a point mutated form of semaphorin-3E resistant to cleavage by furin like pro-protein convertases (UNCL-Sema3E) displays potent anti-angiogenic properties. We therefore determined if UNCL-Sema3E has potential as an inhibitor of CNV formation. We chose to study UNCL-Sema3E rather than wild type sema3E because unlike full length sema3E, the major p61-Sema3E peptide that is produced by cleavage of sema3E with furin like pro-protein convertases activates signal transduction mediated by the ErbB2 receptor and can promote tumor metastasis in addition to its anti-angiogenic activity. UNCL-Sema3E inhibited efficiently vascular endothelial growth factor-A (VEGF), platelet derived growth factor (PDGF) and basic fibroblast growth factor (bFGF) signaling in human umbilical vein derived endothelial cells (HUVEC) and to a lesser extent hepatocyte growth factor (HGF) signal transduction. CNV that was induced in the eyes of C57 black mice by laser photocoagulation was inhibited by 65% (P < 0.01) following a single bolus intra-vitreal injection of 5 μg UNCL-Sema3E. This inhibitory effect was similar to the inhibition produced by a single bolus intra-vitreal injection of 5 μg aflibercept. A similar inhibition of CNV was observed following the injection of UNCL-Sema3E into the eyes of Long-Evans rats. However, a higher dose of UNCL-Sema3E (125 μg), partially due to the larger volume of the vitreous cavity of rats, was required to achieve maximal inhibition of CNV. Injection of UNCL-Sema3E into eyes of healthy mice did not have any adverse effect on retinal function as assessed by optic kinetic reflex (OKR) or by electroretinogram (ERG) assays nor did UNCL-Sema3E injection affect the structure of the retina as determined using histology. To conclude, our results suggest that UNCL-Sema3E may be useful for the treatment of exudative AMD, which does not respond well to conventional anti-VEGF therapy.