TRIACK, a Novel Irreversible High Potency Thrombin Pathway Modulator in Eye Drops Penetrates to Murine and Pig Retina

We developed two thrombin–PAR1 modulators, PARIN5 and TRIACK, with po-tential applications in retinal neuroinflammation, as candidates for topical administra-tion. Penetration of the compounds into intact pig eyes was assessed both ex-vivo and in-vivo following topical administration. Retinal penetration was evaluated by meas-uring inhibition of intrinsic thrombin activity in the neuroretina, while aqueous humour penetration was assessed by inhibition of either intrinsic or exogenously added throm-bin. Ex-vivo exposure of intact eyes to both compounds reduced thrombin activity in the neuroretina and the aqueous humour compared with controls (Neuroretina: PARIN5: 0.10 ± 0.02 vs. 0.20 ± 0.02 mU/ml, respectively, p< 0.01; TRIACK: 0.015 ± 0.009 vs. 0.27 ± 0.03 mU/ml, respectively, p< 0.0001, aqueous humour: PARIN5 2mM 0.003±0.002 mU/page 1ml vs. TRIACK:0.002±0.002 mU/ml vs. 6.9±0.03mU/ml). In-vivo topical TRIACK administration conducted in healthy, intact eyes affected neu-roretinal thrombin activity compared with the control eye (0.38 ± 0.04 vs. 0.26 ± 0.03 mU/ml, respectively, p< 0.05), with the largest effect observed in the central retina. Modulators of the thrombin–PAR1 pathway demonstrated significant penetration into pig eyes and exerted measurable biological effects on the retina. These findings support their potential development as topical eye-drop therapies for retinal diseases associated with neuroinflammation and diabetes.