Preclinical pharmacology of lumiracoxib: a novel selective inhibitor of cyclooxygenase-2

Abstract

1. This manuscript presents the preclinical profile of lumiracoxib, a novel cyclooxygenase-2 (COX-2) selective inhibitor. 2. Lumiracoxib inhibited purified COX-1 and COX-2 with K(i) values of 3 and 0.06 microM, respectively. In cellular assays, lumiracoxib had an IC(50) of 0.14 microM in COX-2-expressing dermal fibroblasts, but caused no inhibition of COX-1 at concentrations up to 30 microM (HEK 293 cells transfected with human COX-1). 3. In a human whole blood assay, IC(50) values for lumiracoxib were 0.13 microM for COX-2 and 67 microM for COX-1 (COX-1/COX-2 selectivity ratio 515). 4. Lumiracoxib was rapidly absorbed following oral administration in rats with peak plasma levels being reached between 0.5 and 1 h. 5. Ex vivo, lumiracoxib inhibited COX-1-derived thromboxane B(2) (TxB(2)) generation with an ID(50) of 33 mg kg(-1), whereas COX-2-derived production of prostaglandin E(2) (PGE(2)) in the lipopolysaccharide-stimulated rat air pouch was inhibited with an ID(50) value of 0.24 mg kg(-1). 6. Efficacy of lumiracoxib in rat models of hyperalgesia, oedema, pyresis and arthritis was dose-dependent and similar to diclofenac. However, consistent with its low COX-1 inhibitory activity, lumiracoxib at a dose of 100 mg kg(-1) orally caused no ulcers and was significantly less ulcerogenic than diclofenac (P<0.05). 7. Lumiracoxib is a highly selective COX-2 inhibitor with anti-inflammatory, analgesic and antipyretic activities comparable with diclofenac, the reference NSAID, but with much improved gastrointestinal safety.

Figure 1

Chemical structure of compounds studied in this report.

Figure 2

Inhibition of COX-1 and COX-2 in cell-based assays. Human HEK 293 cells stably expressing human COX-1, and human dermal fibroblasts, stimulated with IL-1β to induce COX-2, were pretreated with compounds for 30 min and then arachidonic acid was added to generate PGE₂ production. Each concentration of compound was tested in quadruplicate and normalised to percent inhibition. The results were pooled from a series of experiments (lumiracoxib, n=7 experiments; diclofenac, n=7; celecoxib, n=2; naproxen, n=2). Results shown are mean percent inhibition (±s.e.m.) for COX-1 and COX-2.

Figure 3

In vitro inhibition of COX-1 and COX-2 in human blood assays. Results shown are mean percent inhibition (±s.e.m.) for COX-1 and COX-2. The IC₅₀ values are presented in Table 2. TxB₂ production was stimulated with the addition of A23187 (50 μM) and assessed after 1 h incubation; PGE₂ production was induced with LPS (10 μg ml⁻¹) and assessed after overnight incubation. Prostanoid production was normalised to percent inhibition and the results from a number of donors were pooled (lumiracoxib, n=52 donors; diclofenac, n=52; celecoxib, n=14; naproxen, n=15).

Figure 4

Concentrations of lumiracoxib and diclofenac in plasma of rats following a single oral administration of a 5 mg kg⁻¹ dose. Results are expressed as means±s.e.m. (n=4). Samples were processed through a C₁₈ reverse-phase HPLC column, and the plasma levels were determined by LC/MS/MS.

Figure 5

Inhibition of ex vivo COX-1-dependent TxB₂ and in vivo COX-2-dependent PGE₂ in rat. Results shown are mean percent inhibition (±s.e.m.) for serum TxB₂ (n=5–6 rats per dose) or air pouch PGE₂ (n=9–12 rats per dose). TxB₂ levels were determined ex vivo by radioimmunoassay of extracts from clotted blood sampled from rats 4 h after dosing. COX-2 activity was assessed by measuring PGE₂ concentration in LPS-stimulated dorsal air pouches 4 h after dosing.

Figure 6

In vivo anti-inflammatory efficacy of lumiracoxib and diclofenac. Inflammation, hyperalgesia and pyresis were induced as described in the Methods section. Percent inhibition of (a) carrageenan-induced paw oedema measured 4 h after dosing (mean from two experiments, n=6 rats per treatment group in each experiment), (b) hyperalgesia 1 h after dosing (mean from three experiments, n=6 rats per treatment group in each experiment) and (c) pyresis 2 h after dosing (mean from four experiments, n=3 rats per treatment group in each experiment). The values shown are mean percent inhibition (±s.e.m.) for lumiracoxib and diclofenac.

Figure 7

Effects of lumiracoxib and diclofenac treatment on clinical severity of adjuvant-induced arthritis. (a) Rats were injected with M. tuberculosis and arranged into groups of equal severity on day 14. Rats were treated daily with lumiracoxib or diclofenac for 4 consecutive days. Values represent the mean percent inhibition (±s.e.m.) of paw volume 24 h after the final dose of compounds (mean from two experiments, n=4 rats per treatment group in each experiment). (b) Rats were injected with adjuvant on day 1 and treated with lumiracoxib or diclofenac (both at 2 mg kg⁻¹) once daily from day 12 until termination of the experiment. Arthritis and normal control rats were given vehicle alone. Paw volumes were measured periodically during the course of disease. Values shown are mean volumes±s.e.m. (mean from four experiments, n=6 rats per treatment group in each experiment).