AAV2sFLT01(Genzyme Corp.)

Gene therapy for the treatment of ocular neovascularization has reached clinical trial phases. The AAV2-sFLT01 construct was already evaluated in a phase 1 open-label trial administered intravitreally to patients with advanced neovascular age-related macular degeneration. SFLT01 protein functions by binding to VEGF and PlGF molecules and inhibiting their activities simultaneously. It consists of human VEGFR1/Flt-1 (hVEGFR1), a polyglycine linker, and the Fc region of human IgG1. The IgG1 upper hinge region of the sFLT01 molecule makes it vulnerable to radical attacks and prone to causing immune reactions. This study pursued two goals: (i) minimizing the immunogenicity and vulnerability of the molecule by designing a truncated molecule called htsFLT01 (hinge truncated sFLT01) that lacked the IgG1 upper hinge and lacked 2 amino acids from the core hinge region; and (ii) investigating the structural and functional properties of the aforesaid chimeric molecule at different levels (in silico, in vitro, and in vivo). Molecular dynamics simulations and molecular mechanics energies combined with Poisson-Boltzmann and surface area continuum solvation calculations revealed comparable free energy of binding and binding affinity for sFLT01 and htsFLT01 to their cognate ligands. Conditioned media from human retinal pigment epithelial (hRPE) cells that expressed htsFLT01 significantly reduced tube formation in HUVECs. The AAV2-htsFLT01 virus suppressed vascular development in the eyes of newborn mice. The htsFLT01 gene construct is a novel anti-angiogenic tool with promising improvements compared to existing treatments.

Wet age-related macular degeneration (wAMD) is characterized by the presence of choroidal neovascularization (CNV). Although there are some clinical drugs targeting vascular endothelial growth factor (VEGF) and inhibiting CNV, two major side effects limit their application, including the excessive activity of anti-VEGF and frequent intraocular injections. To explore better treatment strategies, researchers developed a hypoxic modulator retinal pigment epithelium (RPE)- specific adeno-associated virus (AAV) vector expressing endostatin to inhibit CNV. However, the mechanism of endostatin is complex. Instead, soluble fms-like tyrosine kinase-1 (sFlt-1) can inhibit VEGF-induced angiogenesis through two simple and clear mechanisms, giving rise to sequestration of VEGF and forming an inactive heterodimer with the membrane-spanning isoforms of the VEGF receptor Flt-1 and kinase insert domain-containing receptor.

In this study, we chose sFlt-1 as a safer substitute to treat wAMD by inhibiting VEGFinduced angiogenesis.

The AAV2/8-Y733F-REG-RPE-sFlt-1 vector was delivered by intravitreal injection to the eyes of mice. AAV2/8-Y733F vector is a mutant of the AAV2/8 vector, and the REG-RPE promoter is a hypoxia-regulated RPE-specific promoter. Two animal models were used to evaluate the function of the vector.

In the cobalt chloride-induced hypoxia model, the results demonstrated that the AAV2/8- Y733F-REG-RPE-sFlt-1 vector induced the expression of the sFlt-1 gene in RPE cells through hypoxia. In the laser-induced CNV model, the results demonstrated that the AAV2/8-Y733F-REG-RPE-sFlt- 1 vector reduced laser-induced CNV.

Hypoxia regulated, RPE-specific AAV vector-mediated sFlt-1 gene is a hypoxiaregulated antiangiogenic vector for wAMD.