Abstract
Purpose :
Plasma kallikrein (PKa) is a serine protease that has been implicated in diabetic macular edema. Here we investigate the effects of a novel oral PKa inhibitor KV998076 on VEGF and TNFα-induced retinal thickening and VEGF induced electroretinogram (ERG) abnormalities.
Methods :
PKa enzyme activity Effects of KV998076 on enzymatic activity of PKa were assayed in a fluorogenic assay using H-D-Pro-Phe-Arg-AFC.
Pharmacodynamics KV998076 or vehicle alone was delivered to mice s.c. at doses up to 2mg/kg/day via Alzet minipumps or by oral gavage at 50mg/kg BID. Plasma concentrations of KV998076 were determined by LC-MS/MS. Retinal thickness was measured by optical coherence tomography, at baseline and 24h post intravitreal injections of VEGF or TNFα (both at 100ng/eye) or saline vehicle. ERG A-wave and B-wave amplitudes were measured using LabChart 4.0 software.
Results :
The Ki of KV998076 for purified human PKa is 0.79nM. The inhibitor displays >500 fold selectively for PKa compared with closely related serine proteases. The IC50s of KV998076 for PKa activity in dextran sulfate (DXS) stimulated human and mouse whole plasma are 84.1nM and 85.3nM, respectively. Plasma exposure after a single gavage of 50mg/kg KV998076 (n=12 mice) was 354 ng/ml at 6h and 5.7ng/ml at 24h. Plasma samples from these mice were protected from ex vivo DXS mediated kininogen (HK) cleavage at 6hr (p=0.001) and 24hr (p=0.0383). Systemic delivery of KV998076, at 2mg/kg/day via s.c. pumps, resulted in a plasma concentration of 10.5 ± 1.3 ng/ml (n=8 mice) and the plasma was also protected from DXS stimulated HK cleavage. Infusion of KV998076 at 2, 1 and 0.5mg/kg/day s.c. reduced VEGF-stimulated edema at 24h by 79% (p=0.0003), 75.5% (p=0.0005) and 38.2% (n.s.), respectively. Abnormal ERG amplitude increases caused by VEGF at 48h post injection were ameliorated by systemic KV998076 administration; A-wave: 47.4% decrease (p=0.027); B-wave: 56.4% decrease (p=0.04). KV998076 at 2mg/kg/day s.c. also reduced TNFα induced retinal thickening by 77.2% (p=0.05). Oral delivery of KV998076 BID initiated the day before intravitreal VEGF injection, resulted in 91.3% (p<0.0001) decrease in retinal thickening (n=20 mice).
Conclusions :
Oral administration of the PKa inhibitor KV998076 may provide a therapeutic opportunity to reduce retinal edema and neuroretinal dysfunction caused by both VEGF and TNFα.
This is a 2020 ARVO Annual Meeting abstract.