(W0930-02-11) Anti-inflammatory and Analgesic Effects of a Highly Selective mPGES-1 Inhibitor

Purpose: Prostaglandin E2 (PGE₂) plays a key role in inflammation. Currently available non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase (COX)-1 and/or COX-2, all with significant adverse effects. Microsomal PGE₂ synthase 1 (mPGES-1), an inducible enzyme that overproduces PGE₂, is considered a more promising target for a new type of anti-inflammatory drug without the risks associated with COX-1/2 inhibition. There have been extensive efforts to develop drugs targeting mPGES-1, but few identified potent human mPGES-1 inhibitors also potently inhibit mouse or rat mPGES-1, preventing the use of preclinical models of inflammation and pain. Our lab recently published a study in which we designed and discovered a novel compound, UK4b, capable of potently inhibiting both human mPGES-1 (IC₅₀=33 nM) and mouse mPGES-1 (IC₅₀=157 nM).¹ In the present study, we aim to demonstrate that UK4b significantly reduces PGE₂ metabolites (PGEM) in tissue samples and that UK4b has desirable potent anti-inflammatory and analgesic effects against carrageenan-induced hyperalgesia, adjuvant-induced knee joint arthritis, and postoperative hyperalgesia.

Methods: In wild-type (WT) rats, a carrageenan solution is injected subcutaneously (SC) to the plantar surface of one hind paw to induce hyperalgesia and paw edema. UK4b’s effect on paw withdrawal latency (PWL) to noxious heat and change in paw volume are assessed in both pre- and post-treatment models. At the conclusion of the study, paw tissues are collected and analyzed with a commercially available PGEM ELISA kit.

Complete Freund’s Adjuvant (CFA) is injected to one knee joint of WT rats to induce arthritis. PWL and a subjective score of limb posture, in which a higher score corresponds to worse joint pain, are recorded once daily, with UK4b administered after the arthritis develops.

In the postoperative pain (POP) model of WT mice, an incision is made to a muscle of one hind paw. UK4b’s effects on PWL and mechanical allodynia are assessed once daily in both pre- and post-treatment models.

Results: In the post-treatment model, compared to an intraperitoneal (IP) injection of 5 mg/kg oxycodone, 10 mg/kg UK4b (IP) was similarly effective in reducing carrageenan-induced hyperalgesia. When 10 mg/kg UK4b was administered SC, it was even more effective than oxycodone (5 mg/kg, IP), suggesting SC may be a better route of administration than IP for UK4b. In the pre-treatment model of carrageenan-induced hyperalgesia, 10 mg/kg UK4b (IP) was more effective than 5 mg/kg oxycodone (IP) in pain relief.

In CFA-treated groups, both doses of UK4b (5 or 10 mg/kg, IP) significantly reduced adjuvant-induced hyperalgesia and the spontaneous pain rating, compared to the vehicle control.

In the POP pre-treatment model, 20 mg/kg UK4b (SC) administration 2 hours before surgery and then once daily for 7 days blocked development of hyperalgesia and minimized allodynia. In the POP post-treatment model, all mice experienced significant hyperalgesia and allodynia 2 hours after surgery. However, on Day 1 post-surgery, PWL returned to baseline 2 hours after a dose of 20 mg/kg UK4b (SC) and remained at baseline levels throughout the duration of the study. Daily administration of 20 mg/kg UK4b continually improved allodynia.

A local SC injection of carrageenan significantly increased the concentration of PGEM in hind paw tissue. A single dose of UK4b (10 mg/kg, SC) blocked the carrageenan-induced increase in PGEM, with no significant difference between hind paw tissue in untreated and hind paw tissue from rats treated with UK4b and carrageenan.

Conclusion: Though mPGES-1 is a promising target for the development of next generation anti-inflammatory drugs, the lack of inhibitors potent against both human and mouse or rat mPGES-1 inhibitors presents a major hurdle for practical drug development. UK4b is a potent and highly selective human and mouse mPGES-1,¹ allowing us to assess its in vivo activities in WT mice or rats. A previous study revealed that UK4b significantly decreased carrageenan-stimulated PGE₂ over-production in the WT mouse air-pouch model.¹ The new animal data in this present study demonstrated for the first time that UK4b is a desirably potent anti-inflammatory and analgesic drug in three different rodent models of inflammation and pain.

Particularly, UK4b had similar efficacy as oxycodone in reducing carrageenan-induced hyperalgesia in the post-treatment model. In the pre-treatment carrageenan model, UK4b was even more effective than oxycodone in pain relief due to the potent anti-inflammatory effect of UK4b, which is consistent with the concept that opioids interfere with the perception of pain and do not target inflammation.² Of further importance is that that UK4b is ~5-fold more potent (IC₅₀ = 33 nM) against human mPGES-1 than against mouse mPGES-1 (IC₅₀ = 157 nM).¹ Hence, UK4b could be even more effective for pain relief in humans. The favorable in vivo data obtained in this study suggest that UK4b should be studied further as a promising novel non-opioid analgesic which may serve as a possible substitute of opioid drugs for pain relief and a treatment for other inflammatory diseases.

References: 1. Ding, K.; Zhou, Z.; Hou, S.; Yuan, Y.; Zhou, S.; Zheng, X.; Chen, J.; Loftin, C.; Zheng, F.; Zhan, C.-G., Structure-based discovery of mPGES-1 inhibitors suitable for preclinical testing in wild-type mice as a new generation of anti-inflammatory drugs. Scientific Reports 2018, 8 (1), 5205.
2. Dionne, R. A.; Gordon, S. M.; Moore, P. A., Prescribing Opioid Analgesics for Acute Dental Pain: Time to Change Clinical Practices in Response to Evidence and Misperceptions. Compend. Contin. Educ. Dent. 2016, 37(6), 372-378.

Acknowledgements:All the animal experiments were conducted in our animal laboratories within the University of Kentucky’s Division of Laboratory Animal Resources (DLAR) facility (PHS assurance number A3336-01; USDA number 61-R-0002; AAALAC, Intl. Unit # 13). The animal procedures used in this project were approved by the Institutional Animal Care and Use Committee (IACUC).
This work was supported in part by the funding of the Molecular Modeling and Biopharmaceutical Center (MMBC) at the University of Kentucky College of Pharmacy, National Institutes of Health (NIH) U01 HL152392 funded by NCI, NEI, NHGRI, NIDCR, the Commonwealth of Kentucky and administered by NHLBI and National Science Foundation (NSF) CHE-1111761.