A Dose-Escalation Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Efficacy of 2 and 4 Weeks of Twice-Daily Ocular Trabodenoson in Adults with Ocular Hypertension or Primary Open-Angle Glaucoma

Curcumin Stereoisomer, Cis-Trans Curcumin, as a Novel Ligand to A1 and A3 Adenosine Receptors

Adenosine receptors (ARs) are being explored to generate non-opioid pain therapeutics. Vanilloid compounds, curcumin, capsaicin, and vanillin possess antinociceptive properties through their interactions with the transient receptor potential channel family. However, their binding with adenosine receptors has not been well studied. The hypothesis in this study was that a vanilloid compound, cis-trans curcumin (CTCUR), binds to each of the two Gi-linked AR subtypes (A₁AR and A₃AR). CTCUR was synthesized from curcumin (CUR) using the cavitand-mediated photoisomerization technique. The cell lines transfected with the specific receptor (A₁AR or A₃AR) were treated with CTCUR or CUR and the binding was analyzed using competitive assays, confocal microscopy, and docking. The binding assays and molecular docking indicated that CTCUR had Ki values of 306 nM (A₁AR) and 400 nM (A₃AR). These values suggest that CTCUR is selective for Gi-linked ARs (A₁AR or A₃AR) over Gs-linked ARs (A_2AAR or A_2BAR), based on our previous published research. In addition, the docking showed that CTCUR binds to the toggle switch domain of ARs. Curcumin (CUR) did not exhibit binding at any of these receptors. In summary, CTCUR and other modifications of CUR can be developed as novel therapeutic ligands for the Gi-linked ARs (A₁AR and A₃AR) involved with pain and cancer.

Medical therapy for glaucoma: A review

A number of pharmacological targets are exploited to modify the parameters in the Goldmann equation and reduce the intraocular pressure (IOP). This strategy constitutes the foundation for the medical management of glaucoma, the evolution of which, until only recently, has been in relative stagnation. A burst of innovation has produced new ocular hypotensive drugs and long-acting delivery methods, including intracameral delivery, which are expanding the clinician's medical armamentarium. A number of IOP-independent neuroprotection strategies have shown strong potential in animal models of glaucoma, but translational attempts have been surprisingly limited. However, while pharmacological options are expanding, the traditional role of topical medical therapy is being challenged by selective laser trabeculoplasty, micro-invasive glaucoma surgery, and sustained delivery methods. A scientifically rigorous assessment of new treatments will be critical to empower clinicians with evidence-based information to optimise vision preservation and quality of life outcomes for their patients.

Topical Medication Therapy for Glaucoma and Ocular Hypertension

Glaucoma is one of the most common causes of blindness, thus seriously affecting people’s health and quality of life. The topical medical therapy is as the first line treatment in the management of glaucoma since it is inexpensive, convenient, effective, and safe. This review summarizes and compares extensive clinical trials on the topical medications for the treatment of glaucoma, including topical monotherapy agents, topical fixed-combination agents, topical non-fixed combination agents, and their composition, mechanism of action, efficacy, and adverse effects, which will provide reference for optimal choice of clinical medication. Fixed-combination therapeutics offer greater efficacy, reliable security, clinical compliance, and tolerance than non-fixed combination agents and monotherapy agents, which will become a prefer option for the treatment of glaucoma. Meanwhile, we also discuss new trends in the field of new fixed combinations of medications, which may better control IOP and treat glaucoma.

Drugs for the treatment of glaucoma: Targets, structure-activity relationships and clinical research

Glaucoma is the third leading cause of blindness and impairment of vision worldwide, after refractive errors and cataracts. According to the survey, the number of people with glaucoma is more than 76 million, with projections increasing to 112 million by 2040. With the coming of an aging society, the number of people suffering from glaucoma will increase day by day. Glaucoma is a heterogeneous disease characterized by damage to the head of the optic nerve and visual field. High intraocular pressure is a major risk and cause of glaucoma optic neuropathy. Therefore, drug lowering intraocular pressure therapy is still the first-line therapy in clinical practice. Here, the targets, structure-activity relationship, and clinical progress of drugs for the treatment of glaucoma are reviewed.

Adenosine: The common target between cancer immunotherapy and glaucoma in the eye

Adenosine, an endogenous purine nucleoside, is a well-known actor of the immune system and the inflammatory response both in physiologic and pathologic conditions. By acting upon particular, G-protein coupled adenosine receptors, i.e., A1, A2- a & b, and A3 receptors mediate a variety of intracellular and immunomodulatory actions. Several studies have elucidated Adenosine's effect and its up-and downstream molecules and enzymes on the anti-tumor response against several types of cancers. We have also targeted a couple of molecules to manipulate this pathway and get the immune system's desired response in our previous experiences. Besides, the outgrowth of the studies on ocular Adenosine in recent years has significantly enhanced the knowledge about Adenosine and its role in ocular immunology and the inflammatory response of the eye. Glaucoma is the second leading cause of blindness globally, and the recent application of Adenosine and its derivatives has shown the critical role of the adenosine pathway in its pathophysiology. However, despite a very promising background, the phase III clinical trial of Trabodenoson failed to achieve the non-inferiority goals of the study. In this review, we discuss different aspects of the abovementioned pathway in ophthalmology and ocular immunology; following a brief evaluation of the current immunotherapeutic strategies, we try to elucidate the links between cancer immunotherapy and glaucoma in order to introduce novel therapeutic targets for glaucoma.

Protection of retinal ganglion cells in glaucoma: Current status and future

Glaucoma is a neuropathic disease that causes optic nerve damage, loss of retinal ganglion cells (RGCs), and visual field defects. Most glaucoma patients have no early signs or symptoms. Conventional pharmacological glaucoma medications and surgeries that focus on lowering intraocular pressure are not sufficient; RGCs continue to die, and the patient's vision continues to decline. Recent evidence has demonstrated that neuroprotective approaches could be a promising strategy for protecting against glaucoma. In the case of glaucoma, neuroprotection aims to prevent or slow down disease progression by mitigating RGCs death and optic nerve degeneration. Notably, new pharmacologic medications such as antiglaucomatous agents, antibiotics, dietary supplementation, novel neuroprotective molecules, neurotrophic factors, translational methods such as gene therapy and cell therapy, and electrical stimulation-based physiotherapy are emerging to attenuate the death of RGCs, or to make RGCs resilient to attacks. Understanding the roles of these interventions in RGC protection may offer benefits over traditional pharmacological medications and surgeries. In this review, we summarize the recent neuroprotective strategy for glaucoma, both in clinical trials and in laboratory research.

Adenosine receptors as promising targets for the management of ocular diseases

The ocular drug discovery arena has undergone a significant improvement in the last few years culminating in the FDA approvals of 8 new drugs. However, despite a large number of drugs, generics, and combination products available, it remains an urgent need to find breakthrough strategies and therapies for tackling ocular diseases. Targeting the adenosinergic system may represent an innovative strategy for discovering new ocular therapeutics. This review focused on the recent advance in the field and described the numerous nucleoside and non-nucleoside modulators of the four adenosine receptors (ARs) used as potential tools or clinical drug candidates.

Trabodenoson on trabecular meshwork rejuvenation: a comprehensive review of clinical data

INTRODUCTION

Trabodenoson is an adenosine mimetic acting selectively at the A1 receptor (A1R) subtype, involved in multiple signaling pathways including matrix metalloproteinase (MMP-2) associated with glaucoma pathological processes. It has been developed as a Phase 3 candidate for the treatment of patients with primary open-angle glaucoma (POAG) or ocular hypertension (OH).

AREA COVERED

This review summarizes the molecular traits of Trabodenoson in intraocular pressure (IOP) regulations and provides a scientific interpretation of the Phase 2 clinical study results. This article sheds light on the root causes of the two pivotal Phase 3 clinical trial failures in patients with POAG or OH; it further highlights the discovery of MMP-2 in trabecular meshwork (TM) rejuvenation, which has strategic importance in long-term glaucoma patient care.

EXPERT OPINION

Trabodenoson is a BID glaucoma eye drop with a possible QD dose as maintenance. Its Phase 3 pivotal clinical trials failed at the wrong dose and dosing regimen because of the misinterpretation of the complex IOP results from the Phase 2 monotherapy and combination studies. The future development should focus on the TM benefits whilst unleashing its potential of neural protection through nanoparticle eye drops, medical coating, and sustained release drug delivery.

Deconstructing aqueous humor outflow - The last 50 years

Herein partially summarizes one scientist-clinician's wanderings through the jungles of primate aqueous humor outflow over the past ~45 years. Totally removing the iris has no effect on outflow facility or its response to pilocarpine, whereas disinserting the ciliary muscle (CM) from the scleral spur/trabecular meshwork (TM) completely abolishes pilocarpine's effect. Epinephrine increases facility in CM disinserted eyes. Cytochalasins and latrunculins increase outflow facility, subthreshold doses of cytochalasins and epinephrine given together increase facility, and phalloidin, which has no effect on facility, partially blocks the effect of both cytochalasins and epinephrine. H-7, ML7, Y27632 and nitric oxide - donating compounds all increase facility, consistent with a mechanosensitive TM/SC. Adenosine A1 agonists increase and angiotensin II decrease facility. OCT and optical imaging techniques now permit visualization and digital recording of the distal outflow pathways in real time. Prostaglandin (PG) F2α analogues increase the synthesis and release of matrix metalloproteinases by the CM cells, causing remodeling and thinning of the interbundle extracellular matrix (ECM), thereby increasing uveoscleral outflow and reducing IOP. Combination molecules (one molecule, two or more effects) and fixed combination products (two molecules in one bottle) simplify drug regimens for patients. Gene and stem cell therapies to enhance aqueous outflow have been successful in laboratory models and may fill an unmet need in terms of patient compliance, taking the patient out of the delivery system. Functional transfer of genes inhibiting the rho cascade or decoupling actin from myosin increase facility, while genes preferentially expressed in the glaucomatous TM decrease facility. In live NHP, reporter genes are expressed for 2+ years in the TM after a single intracameral injection, with no adverse reaction. However, except for one recent report, injection of facility-effective genes in monkey organ cultured anterior segments (MOCAS) have no effect in live NHP. While intracameral injection of an FIV. BOVPGFS-myc.GFP PGF synthase vector construct reproducibly induces an ~2 mmHg reduction in IOP, the effect is much less than that of topical PGF2⍺ analogue eyedrops, and dissipates after 5 months. The turnoff mechanism has yet to be defeated, although proteasome inhibition enhances reporter gene expression in MOCAS. Intracanalicular injection might minimize off-target effects that activate turn-off mechanisms. An AD-P21 vector injected sub-tenon is effective in 'right-timing' wound healing after trabeculectomy in live laser-induced glaucomatous monkeys. In human (H)OCAS, depletion of TM cells by saponification eliminates the aqueous flow response to pressure elevation, which can be restored by either cultured TM cells or by IPSC-derived TM cells. There were many other steps along the way, but much was accomplished, biologically and therapeutically over the past half century of research and development focused on one very small but complex ocular apparatus. I am deeply grateful for this award, named for a giant in our field that none of us can live up to.

Current and new pharmacotherapeutic approaches for glaucoma

INTRODUCTION

Glaucoma is the leading cause of irreversible blindness worldwide. Medical therapy is the main line of treatment of open-angle glaucoma (OAG) and ocular hypertension. Despite the expansion of the glaucoma lineup with the newly approved medication classes, many barriers and issues still exist with topical therapy. Novel non-topical drug delivery may address such issues, adding more options to glaucoma pharmacotherapy.

AREAS COVERED

This review outlines current topical therapies for glaucoma, in addition to new medications under trials. The issues with topical therapy, in general, are discussed, as well as the new non-topical drug delivery systems. The authors performed a comprehensive search for published studies on glaucoma medical therapy using the electronic database of PubMed and manual search for each medication and non-topical delivery options. The extra- and intraocular delivery methods and the new topical glaucoma medications under research are covered.

EXPERT OPINION

Medical management of glaucoma represents a challenge for both patients and clinicians. Noncompliance (e.g. difficulty with administering the eye drops), cost, side effects, and intraocular pressure fluctuation are the major problems with topical therapy. To overcome such barriers, research should continue in developing new medications and innovation of non-topical drug delivery systems.

Current Medical Therapy and Future Trends in the Management of Glaucoma Treatment

Glaucoma is a neurodegenerative disease characterized by progressive loss of retinal ganglion cells and their axons. Lowering of intraocular pressure (IOP) is currently the only proven treatment strategy for glaucoma. However, some patients show progressive loss of visual field and quality of life despite controlled IOP which indicates that other factors are implicated in glaucoma. Therefore, approaches that could prevent or decrease the rate of progression and do not rely on IOP lowering have gained much attention. Effective neuroprotection has been reported in animal models of glaucoma, but till now, no neuroprotective agents have been clinically approved. The present update provides an overview of currently available IOP-lowering medications. Moreover, potential new treatment targets for IOP-lowering and neuroprotective therapy are discussed. Finally, future trends in glaucoma therapy are addressed, including sustained drug delivery systems and progress toward personalized medicine.

P1 Receptor Agonists/Antagonists in Clinical Trials - Potential Drug Candidates of the Future

BACKGROUND

Adenosine mediates various physiological and pathological conditions by acting on its four P1 receptors (A1, A2A, A2B and A3 receptors). Omnipresence of P1 receptors and their activation, exert a wide range of biological activities. Thus, its modulation is implicated in various disorders like Parkinson's disease, asthma, cardiovascular disorders, cancer etc. Hence these receptors have become an interesting target for the researchers to develop potential therapeutic agents. Number of molecules were designed and developed in the past few years and evaluated for their efficacy in various disease conditions.

OBJECTIVE

The main objective is to provide an overview of new chemical entities which have crossed preclinical studies and reached clinical trials stage following their current status and future prospective.

METHODS

In this review we discuss current status of the drug candidates which have undergone clinical trials and their prospects.

RESULTS

Many chemical entities targeting various subtypes of P1 receptors are patented; twenty of them have crossed preclinical studies and reached clinical trials stage. Two of them viz adenosine and regadenoson are approved by the Food and Drug Administration.

CONCLUSION

This review is an attempt to highlight the current status, progress and probable future of P1 receptor ligands which are under clinical trials as promising novel therapeutic agents and the direction in which research should proceed with a view to come out with novel therapeutic agents.

Treatment choices for newly diagnosed primary open angle and ocular hypertension patients

Despite advances in our knowledge of the aetiology and pathophysiology of glaucoma, the sole proven, effective intervention for treating primary open-angle glaucoma (POAG) and ocular hypertension (OHT) remains lowering of intraocular pressure (IOP) to prevent further progression and visual loss. The purpose of this review is to evaluate the treatment choices available to newly diagnosed POAG and OHT patients. We review the existing literature on treatments currently available to newly diagnosed POAG and OHT patients and discuss their role in the treatment paradigm of POAG and OHT. We consider different factors that may be important when offering a choice of treatment to newly diagnosed POAG and OHT patients as well as describing new glaucoma treatments in development and future directions for treatment.

Topical Trabodenoson Is Neuroprotective in a Rodent Model of Anterior Ischemic Optic Neuropathy (rNAION)

Purpose

Nonarteritic anterior ischemic optic neuropathy (NAION) is the leading cause of sudden optic nerve-related vision loss currently without effective treatment. We evaluated the neuroprotective potential of ocular (topical) delivery of trabodenoson, a selective A₁ receptor mimetic, in a rodent model of NAION (rNAION).

Methods

Daily topical delivery of 3% trabodenoson or vehicle administered in both eyes 3 days prior to rNAION induction and for 21 days post induction. Retinal appearance and optic nerve head (ONH) edema was evaluated using spectral-domain optical coherence tomography (SD-OCT). Retinal function was evaluated before and after induction by ganzfeld electroretinography (ERG). Brn3a(+) retinal ganglion cells (RGCs) were quantified by stereology. Axonal ultrastructure was evaluated by electron microscopy.

Results

Trabodenoson-treated eyes had significantly reduced optic nerve (ON) edema compared with vehicle-treated eyes (ANOVA, P < 0.05). Electrophysiologically, there was a nonsignificant trend toward b-wave and oscillatory potential (OP) preservation in the trabodenoson-treated eyes. RGC counts were higher in trabodenoson-treated eyes compared to vehicle (74% versus 47% of the contralateral eye; two-tailed t-test; P = 0.01), as were ON axons. No overt morphologic differences in cell inflammation were observed between vehicle- and trabodenoson-treated ONHs, but trabodenoson-treated ONHs revealed increased expression of astrocyte-related neuroprotective responses.

Conclusions

Trabodenoson preserves RGCs in the rodent NAION model. While previous clinical trials focused on trabodenoson's ocular antihypertensive effect, our data suggest trabodenoson's primary target may be both the retina and ONH. Selective adenosine A₁ agonists may prove an appropriate neuroprotective adjunctive for ischemia-related ON diseases such as NAION and glaucoma.

Translational Relevance

RGC and ON neuroprotection in ischemic neuropathies may be achievable by topical administration of A₁ adenosine agonists rather than by simply relying on intraocular pressure reduction.

Historical and Current Adenosine Receptor Agonists in Preclinical and Clinical Development

Adenosine receptors (ARs) function in the body’s response to conditions of pathology and stress associated with a functional imbalance, such as in the supply and demand of energy/oxygen/nutrients. Extracellular adenosine concentrations vary widely to raise or lower the basal activation of four subtypes of ARs. Endogenous adenosine can correct an energy imbalance during hypoxia and other stress, for example, by slowing the heart rate by A₁AR activation or increasing the blood supply to heart muscle by the A_2AAR. Moreover, exogenous AR agonists, antagonists, or allosteric modulators can be applied for therapeutic benefit, and medicinal chemists working toward that goal have reported thousands of such agents. Thus, numerous clinical trials have ensued, using promising agents to modulate adenosinergic signaling, most of which have not succeeded. Currently, short-acting, parenteral agonists, adenosine and Regadenoson, are the only AR agonists approved for human use. However, new concepts and compounds are currently being developed and applied toward preclinical and clinical evaluation, and initial results are encouraging. This review focuses on key compounds as AR agonists and positive allosteric modulators (PAMs) for disease treatment or diagnosis. AR agonists for treating inflammation, pain, cancer, non-alcoholic steatohepatitis, angina, sickle cell disease, ischemic conditions and diabetes have been under development. Multiple clinical trials with two A₃AR agonists are ongoing.

Historical and Current Adenosine Receptor Agonists in Preclinical and Clinical Development

Adenosine receptors (ARs) function in the body's response to conditions of pathology and stress associated with a functional imbalance, such as in the supply and demand of energy/oxygen/nutrients. Extracellular adenosine concentrations vary widely to raise or lower the basal activation of four subtypes of ARs. Endogenous adenosine can correct an energy imbalance during hypoxia and other stress, for example, by slowing the heart rate by A₁AR activation or increasing the blood supply to heart muscle by the A_2AAR. Moreover, exogenous AR agonists, antagonists, or allosteric modulators can be applied for therapeutic benefit, and medicinal chemists working toward that goal have reported thousands of such agents. Thus, numerous clinical trials have ensued, using promising agents to modulate adenosinergic signaling, most of which have not succeeded. Currently, short-acting, parenteral agonists, adenosine and Regadenoson, are the only AR agonists approved for human use. However, new concepts and compounds are currently being developed and applied toward preclinical and clinical evaluation, and initial results are encouraging. This review focuses on key compounds as AR agonists and positive allosteric modulators (PAMs) for disease treatment or diagnosis. AR agonists for treating inflammation, pain, cancer, non-alcoholic steatohepatitis, angina, sickle cell disease, ischemic conditions and diabetes have been under development. Multiple clinical trials with two A₃AR agonists are ongoing.

Pharmacology of Adenosine Receptors: The State of the Art

Adenosine is a ubiquitous endogenous autacoid whose effects are triggered through the enrollment of four G protein-coupled receptors: A₁, A_2A, A_2B, and A₃. Due to the rapid generation of adenosine from cellular metabolism, and the widespread distribution of its receptor subtypes in almost all organs and tissues, this nucleoside induces a multitude of physiopathological effects, regulating central nervous, cardiovascular, peripheral, and immune systems. It is becoming clear that the expression patterns of adenosine receptors vary among cell types, lending weight to the idea that they may be both markers of pathologies and useful targets for novel drugs. This review offers an overview of current knowledge on adenosine receptors, including their characteristic structural features, molecular interactions and cellular functions, as well as their essential roles in pain, cancer, and neurodegenerative, inflammatory, and autoimmune diseases. Finally, we highlight the latest findings on molecules capable of targeting adenosine receptors and report which stage of drug development they have reached.

Glaucoma Drugs in the Pipeline

Glaucoma is a chronic disease that can be challenging to treat for both patients and physicians. Most patients will require more than 1 medication over time to maintain their intraocular pressure (IOP) at a physiologically benign level. Patients may become refractory to existing compounds and many struggle with adherence to multiple topical drop regimens. The field of glaucoma therapeutics has been advancing rapidly with an emphasis on compounds comprising multiple molecules/mechanisms of action that offer additivity and are complementary to current therapeutics. Several new topical drop compounds directly targeting the trabecular meshwork (TM)/Schlemm canal/conventional outflow pathway to reduce outflow resistance have obtained US Food and Drug Administration approval in the past year. These include rho kinase inhibitors and nitric oxide donating compounds. Alternative therapies that offer long-term IOP lowering while removing the patient from the drug delivery system are moving forward in development. These include gene therapy and stem cell strategies, which could ease or eliminate the burden of topical drop self-administration for several years. Additionally, a variety of novel formulations and devices are in development that aim for controlled, steady state delivery of therapeutics over periods of months. The future of glaucoma therapy is focusing on an increase in specificity for the individual patient: their type of glaucoma; underlying mechanisms; genetic make-up; comorbid conditions; and rate of progression. Maintaining functional vision and improving patient outcomes remains the goal in glaucoma therapeutics. The current collection of novel therapeutics offers an expanded set of tools to achieve that goal.

Trabodenoson, an Adenosine Mimetic With A1 Receptor Selectivity Lowers Intraocular Pressure by Increasing Conventional Outflow Facility in Mice

Purpose

To evaluate the relationship between the IOP-lowering effect of trabodenoson and the associated structural and functional changes in the trabecular meshwork (TM).

Methods

Six independent cohorts of young and aged mice were exposed to three different topical once-a-day formulations of trabodenoson and eyes were compared to those treated with placebo drops. IOP was measured daily just before drug administration using rebound tonometry. Outflow facility was measured in enucleated eyes. Flow patterns and morphology of conventional outflow tissues were monitored using tracer beads and standard histology, respectively. In parallel, three-dimensional human TM tissue constructs (3D-HTM) were grown and used in experiments to test effect of trabodenoson on the expression of collagen IV, fibronectin, matrix metalloproteinase (MMP)-2 and MMP-14 plus MMP-2 activity.

Results

Topical administration of trabodenoson significantly lowered IOP on every day tested, up to 7 days. After 2 days of treatment, outflow facility increased by 26% in aged mice and 30% overall (young and aged mice), which was significantly different from vehicle (P < 0.05). Outflow facility was 15% higher than controls after 7 days of treatment (P = 0.07). While gross morphology was not affected by treatment, the intensity of tracer bead distribution increased by day 7 (P = 0.05). Parallel experiments in 3D-HTM showed that trabodenoson treatment significantly increased MMP-2 activity and MMP-14 abundance, while decreasing fibronectin and collagen IV expression.

Conclusions

Trabodenoson alters ECM turnover by TM cells and increases conventional outflow facility, which accounts for its ability to lower IOP in young and aged mice.

iDrugs and iDevices Discovery Research: Preclinical Assays, Techniques, and Animal Model Studies for Ocular Hypotensives and Neuroprotectants

Discovery ophthalmic research is centered around delineating the molecular and cellular basis of ocular diseases and finding and exploiting molecular and genetic pathways associated with them. From such studies it is possible to determine suitable intervention points to address the disease process and hopefully to discover therapeutics to treat them. An investigational new drug (IND) filing for a new small-molecule drug, peptide, antibody, genetic treatment, or a device with global health authorities requires a number of preclinical studies to provide necessary safety and efficacy data. Specific regulatory elements needed for such IND-enabling studies are beyond the scope of this article. However, to enhance the overall data packages for such entities and permit high-quality foundation-building publications for medical affairs, additional research and development studies are always desirable. This review aims to provide examples of some target localization/verification, ocular drug discovery processes, and mechanistic and portfolio-enhancing exploratory investigations for candidate drugs and devices for the treatment of ocular hypertension and glaucomatous optic neuropathy (neurodegeneration of retinal ganglion cells and their axons). Examples of compound screening assays, use of various technologies and techniques, deployment of animal models, and data obtained from such studies are also presented.

New pharmacotherapy for the treatment of glaucoma

INTRODUCTION

Glaucoma is the second leading cause of blindness in the world and current pharmacotherapies for glaucoma have remained relatively unchanged (with the exception of fixed combinations of previously available medications) since the mid-1990s with the development of prostaglandin analogues. Now, with both new formulations and new classes of medications with novel mechanisms of action, the medical therapy of glaucoma may be heralding a new dawn in medical management. Areas covered: This review outlines new topical therapies for intraocular pressure (IOP) lowering treatment, in addition to new formulations, preservative-free options, and advances in glaucoma medical therapy delivery. We performed a comprehensive search for published studies for glaucoma medical therapy using the electronic database PubMed. A manual search for each therapy or delivery system was also performed. Expert commentary: These advances in glaucoma therapy have the potential to overcome many barriers to glaucoma's medical care, particularly in terms of adherence. However, both time and research are needed to prove the relative efficacy and safety of these new pharmacotherapies and products, helping us decide their role in the treatment of elevated intraocular pressure. We are hopeful that these new developments in therapy may bring more options for glaucoma medical therapy.

Effect of Cromakalim Prodrug 1 (CKLP1) on Aqueous Humor Dynamics and Feasibility of Combination Therapy With Existing Ocular Hypotensive Agents

Purpose

Cromakalim prodrug 1 (CKLP1) is a water-soluble ATP-sensitive potassium channel opener that has shown ocular hypotensive properties in ex vivo and in vivo experimental models. To determine its mechanism of action, we assessed the effect of CKLP1 on aqueous humor dynamics and in combination therapy with existing ocular hypotensive agents.

Methods

Outflow facility was assessed in C57BL/6 mice by ex vivo eye perfusions and by in vivo constant flow infusion following CKLP1 treatment. Human anterior segments with no trabecular meshwork were evaluated for effect on pressure following CKLP1 treatment. CKLP1 alone and in combination with latanoprost, timolol, and Rho kinase inhibitor Y27632 were evaluated for effect on intraocular pressure in C57BL/6 mice and Dutch-belted pigmented rabbits.

Results

CKLP1 lowered episcleral venous pressure (control: 8.9 ± 0.1 mm Hg versus treated: 6.2 ± 0.1 mm Hg, P < 0.0001) but had no detectable effect on outflow facility, aqueous humor flow rate, or uveoscleral outflow. Treatment with CKLP1 in human anterior segments without the trabecular meshwork resulted in a 50% ± 9% decrease in pressure, suggesting an effect on the distal portion of the conventional outflow pathway. CKLP1 worked additively with latanoprost, timolol, and Y27632 to lower IOP, presumably owing to combined effects on different aspects of aqueous humor dynamics.

Conclusions

CKLP1 lowered intraocular pressure by reducing episcleral venous pressure and lowering distal outflow resistance in the conventional outflow pathway. Owing to this unique mechanism of action, CKLP1 works in an additive manner to lower intraocular pressure with latanoprost, timolol, and Rho kinase inhibitor Y27632.

Topical treatment of glaucoma: established and emerging pharmacology

INTRODUCTION

Glaucoma is a collection of optic neuropathies consisting of retinal ganglion cell death and corresponding visual field loss. Glaucoma is the leading cause of irreversible vision loss worldwide and is forecasted to precipitously increase in prevalence in the coming decades. Current treatment options aim to lower intraocular pressure (IOP) via topical or oral therapy, laser treatment to the trabecular meshwork or ciliary body, and incisional surgery. Despite increasing use of trabecular laser therapy, topical therapy remains first-line in the treatment of most forms of glaucoma. Areas covered: Novel glaucoma therapies are a long-standing focus of investigational study. More than two decades have passed since the last United States Food and Drug Administration (FDA) approval of a topical glaucoma drug. Here, the authors review established topical glaucoma drops as well as those currently in FDA phase 2 and 3 clinical trial, nearing clinical use. Expert opinion: Current investigational glaucoma drugs lower IOP, mainly through enhanced trabecular meshwork outflow. Although few emerging therapies show evidence of retinal ganglion cell and optic nerve neuroprotection in animal models, emerging drugs are focused on lowering IOP, similar to established medicines.

Manipulating ocular endothelial tight junctions: Applications in treatment of retinal disease pathology and ocular hypertension

Protein levels of endothelial tight-junctions of the inner retinal microvasculature, together with those of Schlemm's canal, can be readily manipulated by RNA interference (RNAi), resulting in the paracellular clefts between such cells to be reversibly modulated. This facilitates access to the retina of systemically-deliverable low molecular weight, potentially therapeutic compounds, while also allowing potentially toxic material, for example, soluble Amyloid-β1-40, to be removed from the retina into the peripheral circulation. The technique has also been shown to be highly effective in alleviation of pathological cerebral oedema and we speculate that it may therefore have similar utility in the oedematous retina. Additionally, by manipulating endothelial tight-junctions of Schlemm's canal, inflow of aqueous humour from the trabecular meshwork into the Canal can be radically enhanced, suggesting a novel avenue for control of intraocular pressure. Here, we review the technology underlying this approach together with specific examples of clinical targets that are, or could be, amenable to this novel form of genetic intervention.

Targeting Schlemm's Canal in the Medical Therapy of Glaucoma: Current and Future Considerations

Schlemm’s canal (SC) is a unique, complex vascular structure responsible for maintaining fluid homeostasis within the anterior segment of the eye by draining the excess of aqueous humour. In glaucoma, a heterogeneous group of eye disorders afflicting approximately 60 million individuals worldwide, the normal outflow of aqueous humour into SC is progressively hindered, leading to a gradual increase in outflow resistance, which gradually results in elevated intraocular pressure (IOP). By and large available antiglaucoma therapies do not target the site of the pathology (SC), but rather aim to decrease IOP by other mechanisms, either reducing aqueous production or by diverting aqueous flow through the unconventional outflow system. The present review first outlines our current understanding on the functional anatomy of SC. It then summarizes existing research on SC cell properties; first in the context of their role in glaucoma development/progression and then as a target of novel and emerging antiglaucoma therapies. Evidence from ongoing research efforts to develop effective antiglaucoma therapies targeting SC suggests that this could become a promising site of future therapeutic interventions.

New classes of glaucoma medications

PURPOSE OF REVIEW

To discuss recent advances in the medical management of glaucoma and to highlight future medical therapies currently in development.

RECENT FINDINGS

In 1996, latanoprost (Xalatan) was approved in the United States as a new chemical entity and new class (prostaglandin analogs) for the topical treatment of ocular hypertension and glaucoma. In the period from the late 1990s-2010s, while there were additional new chemical entities, fixed dose combinations, and formulation improvements, there were no new classes of ocular hypotensive medications approved worldwide. We summarize new pharmacological treatments that are currently in clinical trials - new classes, new molecules and new delivery systems.

SUMMARY

Although challenges in medical treatment of glaucoma exist, particularly in patient adherence, medical therapy remains the first line treatment for almost all glaucoma patients. Few new medications for glaucoma therapy are currently available for our patients, but multiple drugs with novel mechanisms of action, new formulations, and new delivery mechanisms are currently in development.

Novel Pharmacologic Candidates for Treatment of Primary Open-Angle Glaucoma

Primary open-angle glaucoma (OAG) affects approximately 45 million people worldwide and more than 2.5 million people aged 40 years or older in the United States. Pharmacologic treatment for glaucoma is directed towards lowering intraocular pressure (IOP) to slow disease progression and delay visual field loss. Current medical treatment options for the lowering of IOP include the following classes of topical medications: beta-adrenergic antagonists, alpha-adrenergic agonists, cholinergic agonists, carbonic anhydrase inhibitors, and prostaglandin analogs. Issues with existing drugs include failure to achieve target IOP with monotherapy, drug-related side effects, and low patient compliance with multiple daily administration of eye drops. In recent years, the scientific and medical community has seen encouraging development of novel classes of drugs for primary OAG, the majority of which lower IOP by targeting the trabecular meshwork outflow pathway to increase aqueous humor outflow. Among the most promising new pharmacologic candidates are rho kinase inhibitors including ripasudil (K-115), netarsudil (AR-13324), and AMA0076; adenosine receptor agonists including trabodenoson (INO-8875); and modified prostaglandin analogs including latanoprostene bunod (LBN, BOL-303259-X) and ONO-9054. This study aims to systematically review and summarize the most recent developments in clinical trials for new pharmacologic options for the treatment of primary open-angle glaucoma.

Latanoprostene bunod ophthalmic solution 0.024% for IOP lowering in glaucoma and ocular hypertension

INTRODUCTION

Intraocular pressure (IOP)-lowering has been demonstrated to slow the progression or onset of visual field loss in open-angle glaucoma (OAG) or ocular hypertension (OHT). Pharmacological lowering of IOP is the most common initial intervention in patients with OAG or OHT, however, many patients will require more than one therapy to achieve target IOP. Latanoprostene bunod is a novel nitric oxide (NO)-donating prostaglandin F2α analog for the reduction of IOP. Areas covered: Current knowledge concerning the mechanism of action of latanoprostene bunod is presented. Additionally, clinical safety and efficacy data from published Phase 1 (KRONUS), Phase 2 (VOYAGER, CONSTELLATION) and Phase 3 (APOLLO, LUNAR, JUPITER) studies are reviewed. Expert opinion: Latanoprostene bunod is a dual mechanism, dual pathway molecule, consisting of latanoprost acid, which is known to enhance uveoscleral (unconventional) outflow by upregulating matrix metalloproteinase expression and remodeling of the ciliary muscle's extracellular matrix, linked to an NO-donating moiety, which enhances trabecular meshwork/Schlemm's canal (conventional) outflow by inducing cytoskeletal relaxation via the soluble guanylyl cyclase-cyclic guanosine monophosphate (sGC-cGMP) signaling pathway. Latanoprostene bunod 0.024% solution applied topically once daily appears more effective in reducing IOP in OHT and OAG subjects than either latanoprost or timolol, with a side effect profile similar to that of latanoprost.

The exit strategy: Pharmacological modulation of extracellular matrix production and deposition for better aqueous humor drainage

Primary open angle glaucoma (POAG) is an optic neuropathy and an irreversible blinding disease. The etiology of glaucoma is not known but numerous risk factors are associated with this disease including aging, elevated intraocular pressure (IOP), race, myopia, family history and use of steroids. In POAG, the resistance to the aqueous humor drainage is increased leading to elevated IOP. Lowering the resistance and ultimately the IOP has been the only way to slow disease progression and prevent vision loss. The primary drainage pathway comprising of the trabecular meshwork (TM) is made up of relatively large porous beams surrounded by extracellular matrix (ECM). Its juxtacanalicular tissue (JCT) or the cribriform meshwork is made up of cells embedded in dense ECM. The JCT is considered to offer the major resistance to the aqueous humor outflow. This layer is adjacent to the endothelial cells forming Schlemm's canal, which provides approximately 10% of the outflow resistance. The ECM in the TM and the JCT undergoes continual remodeling to maintain normal resistance to aqueous humor outflow. It is believed that the TM is a major contributor of ECM proteins and evidence points towards increased ECM deposition in the outflow pathway in POAG. It is not clear how and from where the ECM components emerge to hinder the normal aqueous humor drainage. This review focuses on the involvement of the ECM in ocular hypertension and glaucoma and the mechanisms by which various ocular hypotensive drugs, both current and emerging, target ECM production, remodeling, and deposition.