A novel oral plasma kallikrein (PKal) inhibitor KV123833 blocks VEGF-mediated retinal vascular hyperpermeability in a murine model of retinal edema

Abstract

Purpose : Previous reports have implicated PKal as a VEGF-independent mediator of diabetic macular edema (DME). This study investigates the effects of an orally administered PKal inhibitor KV123833 on VEGF-induced retinal edema in mice.

Methods : PKal enzyme activity: Effects of KV123833 on enzymatic activity of PKal were assayed using H-D-Pro-Phe-Arg-AFC. Inhibitor selectivity was assessed using a panel of closely-related serine proteases.
Pharmacokinetics: Subcutaneous (s.c.) KV123833 (1.92 mg/kg/day) was administered to male C57Bl/6 mice (n=10) via micro-osmotic pumps in 10% PEG400/ 90% PBS (v/v). Oral Dosing was done at 5, 15 and 45mg/kg (p.o.) in mice (n=8 per group). Plasma concentrations of KV123833 were determined by LC-MS/MS.
Pharmacodynamics: Retinal vascular permeability (RVP) was measured in a mouse model of VEGF induced retinal edema with KV123833/vehicle given s.c. (1.92 mg/kg/day) or orally (nominally 50 mg/kg bid). RVP was measured using Evan’s blue dye permeation at 24hrs post intravitreal injections of VEGF (100ng/eye) or PBS vehicle.
Ex vivo high molecular weight kininogen (HK) assay: Effect of KV123833 on PKal activity in undiluted plasma was determined by ex vivo dextran sulfate (DXS)-induced HK cleavage measured by western blotting.

Results : KV123833 has a 3nM Ki for human plasma kallikrein and selectivity of 1000 fold over related serine proteases. The solubility of KV123833 is >500 mg/ml in aqueous and gastric fluid. Oral availability of KV123833 in rats is 36%. Infusion of KV123833 s.c. resulted in a plasma exposure of 137 ±21.6 ng/mL, (n=10). RVP in VEGF or PBS-injected eyes were 155.7 ± 26.7; n=10 and 66.8 ± 5.2 ml/g retina/hour; n=11, respectively (p= 0.0018). Subcutaneously given KV123833 decreased VEGF-induced RVP by 85.3% (79.9 ± 11.6 ml/g retina/hour; n=11, p= 0.0076). Oral dosing with KV123833 reduced VEGF-induced RVP by 86.1% p=0.028 (VEGF 183.5 ± 33.7; KV123833 & VEGF 88.5 ± 17.1; PBS 73.2 ± 17 ml/g retina/hour). Efficacious plasma exposure of drug for both s.c. and oral dosing experiments were confirmed as protection of DXS-induced HK cleavage in an ex vivo assay.

Conclusions : Oral plasma kallikrein inhibitor KV123833 blocked retinal vascular hyperpermeability induced by intravitreal VEGF. These findings suggest that oral PKal inhibitors may provide an opportunity to reduce the edematous effects of VEGF in DME.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.