Effect of PF-04217329 a prodrug of a selective prostaglandin EP(2) agonist on intraocular pressure in preclinical models of glaucoma.

Better control of intraocular pressure (IOP) is the most effective way to preserve visual field function in glaucomatous patients. While prostaglandin FP analogs are leading the therapeutic intervention for glaucoma, new target classes also are being identified with new lead compounds being developed for IOP reduction. One target class currently being investigated includes the prostaglandin EP receptor agonists. Recently PF-04217329 (Taprenepag isopropyl), a prodrug of CP-544326 (active acid metabolite), a potent and selective EP(2) receptor agonist, was successfully evaluated for its ocular hypotensive activity in a clinical study involving patients with primary open angle glaucoma. In the current manuscript, the preclinical attributes of CP-544326 and PF-0421329 have been described. CP-544326 was found to be a potent and selective EP(2) agonist (IC(50) = 10 nM; EC(50) = 2.8 nM) whose corneal permeability and ocular bioavailability were significantly increased when the compound was dosed as the isopropyl ester prodrug, PF-04217329. Topical ocular dosing of PF-04217329 was well tolerated in preclinical species and caused an elevation of cAMP in aqueous humor/iris-ciliary body indicative of in vivo EP(2) target receptor activation. Topical ocular dosing of PF-04217329 resulted in ocular exposure of CP-544326 at levels greater than the EC(50) for the EP(2) receptor. PF-04217329 when dosed once daily caused between 30 and 50% IOP reduction in single day studies in normotensive Dutch-belted rabbits, normotensive dogs, and laser-induced ocular hypertensive cynomolgus monkeys and 20-40% IOP reduction in multiple day studies compared to vehicle-dosed eyes. IOP reduction was sustained from 6 h through 24 h following a single topical dose. In conclusion, preclinical data generated thus far appear to support the clinical development of PF-04217329 as a novel compound for the treatment of glaucoma.

Effects of p38 MAPK inhibition on early stages of diabetic retinopathy and sensory nerve function.

Purpose. p38 mitogen-activated protein kinase (MAPK) is known to play a regulatory role in inflammatory processes in disease. Inflammation has been linked also to the development of diabetic retinopathy in rodents. This study was conducted to evaluate the effect of a p38 MAPK inhibitor on the development of early stages of diabetic retinopathy in rats. Methods. Streptozotocin-diabetic rats were assigned to two groups-treated with the p38 MAPK inhibitor PHA666859 (Pfizer, New York, NY) and untreated-and compared with age-matched nondiabetic control animals. Results. At 2 months of diabetes, insulin-deficient diabetic control rats exhibited significant increases in retinal superoxide, nitric oxide (NO), cyclooxygenase (COX)-2, and leukostasis within retinal microvessels. All these abnormalities were significantly inhibited by the p38 MAPK inhibitor (25 mg/kgBW/d). At 10 months of diabetes, significant increases in the number of degenerate (acellular) capillaries and pericyte ghosts were measured in control diabetic rats versus those in nondiabetic control animals, and pharmacologic inhibition of p38 MAPK significantly inhibited all these abnormalities (all P < 0.05). This therapy also had beneficial effects outside the eye in diabetes, as evidenced by the inhibition of a diabetes-induced hypersensitivity of peripheral nerves to light touch (tactile allodynia). Conclusions. p38 MAPK plays an important role in diabetes-induced inflammation in the retina, and inhibition of p38 MAPK offers a novel therapeutic approach to inhibiting the development of early stages of diabetic retinopathy and other complications of diabetes.

L-Carnosine: multifunctional dipeptide buffer for sustained-duration topical ophthalmic formulations.

OBJECTIVES: The use of l-carnosine as an excipient in topical ophthalmic formulations containing gellan gum, a carbohydrate polymer with in-situ gelling properties upon mixing with mammalian tear fluid, was developed as a novel platform to extend precorneal duration. Specific utilisation of l-carnosine as a buffer in gellan gum carrying vehicles was characterised. METHODS: Buffer capacity was evaluated using 7.5, 13.3, and 44.2 mm l-carnosine in a pH range of 5.5-7.5. Accelerated chemical stability was determined by HPLC at l-carnosine concentrations of 5-100 mm. Combinations of 7.5 mm l-carnosine with 0.06-0.6% (w/v) gellan gum were characterised rheologically. l-Carnosine-buffered solutions of gellan gum were tested for acute topical ocular tolerance in vivo in pigmented rabbits. A unique formulation combining timolol (which lowers intraocular pressure) in l-carnosine-buffered gellan gum was compared with Timoptic-XE in normotensive dogs. KEY FINDINGS: l-Carnosine exhibited optimal pharmaceutical characteristics for use as a buffer in chronically administered topical ocular formulations. Enhancement trends were observed in solution-to-gel transition of l-carnosine-buffered vehicles containing gellan gum vs comparators. Topical tolerability of l-carnosine-buffered gellan gum formulations and lowering of intraocular pressure were equivalent with timolol and Timoptic-XE. CONCLUSIONS: Functional synergy between excipients in gellan gum formulations buffered with l-carnosine has potential for topical ocular dosage forms with sustained precorneal residence.

Ocular pharmacokinetics and hypotensive activity of PF-04475270, an EP4 prostaglandin agonist in preclinical models.

Prostaglandins are widely used to lower intraocular pressure (IOP) as part of the treatment regimen for glaucoma. While FP and EP2 agonists are known to lower IOP, we investigated the ocular hypotensive activity and ocular drug distribution of PF-04475270, a novel EP4 agonist following topical administration in normotensive Beagle dogs. PF-04475270 is a prodrug of CP-734432, which stimulated cAMP formation in HEK293 cells expressing EP4 receptor and beta-lactamase activity in human EP4 expressing CHO cells transfected with a cAMP response element (CRE) with an EC(50) of 1 nM. Prodrug conversion and transcorneal permeability were assessed in rabbit corneal homogenates and a human corneal epithelial cell (cHCE) model. The compound underwent rapid hydrolysis to CP-734432 in corneal homogenates, and exhibited good permeability in the cHCE model. The descending order of ocular exposure to CP-734432 after topical dosing of PF-04475270 in dogs was as follows: cornea > aqueous humor >or= iris/ciliary body. When administered q.d., PF-04475270 lowered IOP effectively in the dog IOP model both after single and multiple days of dosing. A maximum decrease in IOP with PF-04475270 was between 30 and 45% at 24h post-dose relative to that observed with vehicle. In conclusion, PF-04475270 is a novel ocular hypotensive compound which is bioavailable following topical dosing, effectively lowering IOP in dogs. EP4 agonists could be considered as potential targets for lowering IOP for the treatment of glaucoma and ocular hypertension.

Retinal and peripheral nerve toxicity induced by the administration of a pan-cyclin dependent kinase (cdk) inhibitor in mice.

Cyclin-dependent kinases (cdks) play a crucial role in cell cycle regulation and are considered promising targets for cancer therapy. Intravenous administration of AG-012986, a pan-cyclin-dependent kinase inhibitor (cdk(i)), resulted in unexpected retinal and peripheral nerve toxicity in mice. AG-012986 was administered daily to CD-1 or B6C3F1 mice for 5 consecutive days. Mice were euthanized 24 h after the last dose (study day 6) or after a 21-day post-dose period (study day 26). Compound related microscopic findings were seen in the sciatic nerves (axonal degeneration) of both strains and in the retina (retinal degeneration/atrophy) of CD-1 mice only after the post-dose period. Although retinal degeneration/atrophy was not detected by routine histology in mice euthanized on day 6, apoptotic retinal cells were evident at this time using TUNEL assay. To our knowledge retinal or peripheral nerve toxicity secondary to the administration of cdk(i)s has not been previously reported. Although the pathogenesis of these lesions is unclear, the toxicities may reflect the unique profile of cdk inhibition, off-target kinase inhibition or receptor binding, or metabolism/distribution properties of AG-012986. Multi-targeted-inhibitors may interfere with cdks and other kinases involved in a wide range of functions other than cell cycle regulation, which could result in unexpected toxicities that may hinder their clinical applications.