ROCK inhibitors as novel antifibrotic strategy for glaucoma surgery.

Glaucoma is a chronic optic neuropathy which is characterized by the loss of retinal ganglion cells, resulting in irreversible visual field loss. It is the most important cause of irreversible blindness worldwide and with aging of the population the number of glaucoma patients is still expanding. Mostly the appearance of this disease is correlated with an increased intraocular pressure (IOP), due to an imbalance between aqueous humor production and outflow. Currently, lowering IOP is the main treatment modality for glaucoma. A sustained reduction of IOP can be achieved with medical therapy, laser treatment or surgical interventions. First choice treatment for glaucoma is medical therapy with IOP-lowering eye drops. Despite the fact that there are several classes of glaucoma medications available, none of them directly targets the trabecular meshwork, which represents the main outflow route in the human eye.  Experimental evidence indicates that the Rho kinase (ROCK) pathway is directly involved in the regulation of trabecular outflow. As such, targeting this pathway could potentially lead to an improved IOP control for the medical treatment of glaucoma.

            Therefore, in the first part of this PhD project we investigated the IOP-lowering potential of AMA0076, a novel locally acting ROCK inhibitor. We demonstrated that AMA0076 is a potent ROCK inhibitor with an IOP-lowering efficacy comparable to a reference ROCK inhibitor, Y-39983. While the efficacy profile of ROCK inhibitors is promising, they are associated with significant ocular hyperemia due to conjunctival vasodilatation.  However, due to its local mode of action AMA0076 induces almost no conjunctival hyperemia in contrast to Y-39983. As such, AMA0076 clearly has an improved tolerability profile with respect to hyperemia compared to other ROCK inhibitors. We also compared the IOP-lowering effect of AMA0076 to prostaglandin analogues (PGAs) because these are the most important treatment modality in the medicinal treatment of glaucoma. Our results revealed that the IOP-lowering efficacy of AMA0076 is equivalent to latanoprost in ocular normotensive rabbits. In a rabbit model of ocular hypertension, AMA0076 was even more potent in preventing IOP elevation compared to PGAs (bimatoprost and latanoprost).

            Taken together, these results indicate that ROCK inhibitors, and especially AMA0076, may be promising new candidates as novel IOP-lowering agents for the treatment glaucoma.

             Surgical intervention is an important treatment modality for glaucoma when other IOP-lowering measures (medical or laser) are inadequate. However, there is a high risk of surgical failure due to excessive subconjunctival wound healing, causing obstruction of the filtration channel by scar tissue. While the introduction of antimitotics tremendously improved surgical success, this has come at the cost of an increased risk at postoperative complications due to their nonspecific mechanism of action. Hence, there is an urgent need for novel, more specific and safer agents to prevent glaucoma filtration failure and improve surgery outcome.  In the second part of this project, we investigated the effect of ROCK inhibitor AMA0526 on the wound healing response after glaucoma filtration surgery and its subsequent effect on surgical outcome. Our in vitro results showed that the ROCK inhibitor, AMA0526, inhibited proliferation of tenon fibroblasts and fibroblast-to-myofibroblast differentiation. Using a rabbit model of glaucoma filtration surgery, we subsequently showed that postoperative treatment with the ROCK inhibitor significantly improved glaucoma filtration surgery outcome. ROCK inhibition reduced postoperative inflammation, angiogenesis and fibrosis. These results suggest that ROCK inhibitors are involved at different levels in the process of wound healing and therefore may be considered as useful agents to improve the success rate of glaucoma filtration surgery.          

Evidence from large scale clinical trials indicated that lowering IOP does not prevent glaucomatous progression in all patients and that progression can continue despite effective IOP-lowering. These inadequacies in our current treatment paradigm of this still blinding disease have encouraged research to investigate neuroprotection as an alternative treatment strategy for glaucoma. However, no neuroprotective therapy is currently available to halt glaucomatous damage. Therefore, in the last part of this project we elaborately reviewed the high potential of the Rho-ROCK pathway as a potential neuroprotective target for future management of glaucoma disease progression. Our review indicates that there is increasing evidence that ROCK inhibition can promote RGC survival, and axon regeneration, demonstrating the neuroprotective potential of ROCK inhibition for the treatment of glaucoma.

            In conclusion, in this dissertation we demonstrated that AMA0076 is a potent ROCK inhibitor with strong IOP-lowering capacity that does not induce distinct hyperemia. Secondly, we also showed that ROCK inhibition may serve as anti-scarring strategy after glaucoma filtration surgery due to its inhibitory effect on inflammation, angiogenesis and fibrosis. Furthermore, the Rho-ROCK pathway is involved in optic nerve neuroprotection. Earlier research showed that inactivation of ROCK increases survival and axon regeneration of RGCs. Considering the IOP lowering, anti-scarring and neuroprotective properties of ROCK inhibitors, targeting the Rho-ROCK pathway with selective inhibitors may be a versatile and attractive treatment option for glaucoma.