The Use of the Selective Imidazoline I1 Receptor Agonist Carbophenyline as a Strategy for Neuropathic Pain Relief: Preclinical Evaluation in a Mouse Model of Oxaliplatin-Induced Neurotoxicity

Abstract

Anti-cancer therapy based on the repeated administration of oxaliplatin is limited by the development of a disabling neuropathic syndrome with detrimental effects on the patient's quality of life. The lack of effective pharmacological approaches calls for the identification of innovative therapeutic strategies based on new targets. We focused our attention on the imidazoline I₁ receptor (I₁-R) and in particular on the selective I₁-R agonist 2-(1-([1,1'-biphenyl]-2-yl)propan-2-yl)-4,5-dihydro-1H-imidazole) (carbophenyline). The purpose of this work was the preclinical evaluation of the efficacy of carbophenyline on oxaliplatin-induced neuropathic pain in mice. Carbophenyline, acutely per os administered (0.1-10 mg kg^-1), induced a dose-dependent anti-hyperalgesic effect that was completely blocked by the pre-treatment with the I₁-R antagonist 3 or the I₁/α₂ receptor antagonist efaroxan, confirming the I₁-R-dependent mechanism. Conversely, pre-treatment with the I₂-R antagonist BU224 did not block the anti-nociceptive effect evoked by carbophenyline. Repeated oral administrations of carbophenyline (1 mg kg^-1) for 14 days, starting from the first day of oxaliplatin injection, counteracted the development of neuropathic pain in all behavioral tests (cold plate, Von Frey, and paw pressure tests) carried out 24 h after the last carbophenyline treatment on days 7 and 14. In the dorsal horn of the spinal cord, carbophenyline significantly decreased the oxaliplatin-induced astrocyte activation detected by immunofluorescence staining by the specific labelling with GFAP antibody. In conclusion, carbophenyline showed anti-neuropathic properties both after acute and chronic treatment with preventive effect against oxaliplatin-induced astrocyte activation in the spinal cord. Therefore, I₁-R agonists emerge as a new class of candidates for the management of oxaliplatin-induced neuropathic pain.

Keywords: Imidazoline I1 receptor agonist; astrocytes; carbophenyline; chemotherapy-induced neuropathic pain; oxaliplatin.

Fig. 1

Chemical structures of compounds 1–4, sharing a common bioversatile scaffold

Fig. 2

Effect of acute carbophenyline administrations on pain behavior induced by oxaliplatin. Pain threshold to (a) a non-noxious thermal stimulus (cold plate test), (b) to a noxious mechanical stimulus (paw pressure test) and (c) to a non-noxious mechanical stimulus (Von Frey test) were measured. Oxaliplatin (2.4 mg kg⁻¹, i.p.) was administered for 2 weeks (10 injections). Starting from day 14, carbophenyline was acutely per os administered (0.1–10 mg kg⁻¹) and measurements assessed before and 15, 30, 45, 60 min after injection. Control animals were treated with vehicles. Each value represents the mean ± S.E.M. of 10 animals per group performed in 2 experimental sets. Statistical analysis is one-way ANOVA followed by Bonferroni’s post hoc comparison. ^^P < 0.01 vs vehicle + vehicle; **P < 0.01 vs oxaliplatin + vehicle

Fig. 3

Study of carbophenyline pharmacodynamic profile. Pain was induced by repeated treatment with oxaliplatin. The hypersensitivity to a cold stimulus was measured by the cold plate test. Carbophenyline was administered per os at 10 mg kg⁻¹. The I₁ receptor antagonist 3 (10 mg kg⁻¹), the I₁/α₂ receptor antagonist efaroxan (10 mg kg⁻¹) and the I₂ receptor antagonist BU224 (3 mg kg⁻¹) were p.o. administered 15 min before carbophenyline; measurements were assessed before and 15, 30, 45, 60 min after carbophenyline injection. Control animals were treated with vehicles. Each value represents the mean ± S.E.M. of 10 animals per group performed in 2 experimental sets. Statistical analysis is one-way ANOVA followed by Bonferroni’s post hoc comparison. ^^P < 0.01 vs vehicle + vehicle; **P < 0.01 vs oxaliplatin + vehicle; °°P < 0.01 vs oxaliplatin + carbophenyline

Fig. 4

Effects of repeated administration of carbophenyline against pain induced by oxaliplatin. Pain threshold to a non-noxious thermal stimulus as measured by the cold plate test (a). Sensitivity to a noxious mechanical stimulus as measured by the paw pressure test (b). Pain threshold to a non-noxious mechanical stimulus as measured by the Von Frey test (c). Behavioral tests were performed on days 7 and 14 after the beginning of oxaliplatin and carbophenyline administrations, 24 h after the last treatment. Oxaliplatin (2.4 mg kg⁻¹, i.p.) was administered for 2 weeks (10 injections) whereas carbophenyline (1 mg kg⁻¹, p.o.) was daily administered, starting from day 1 of oxaliplatin injection. Control animals were treated with vehicles. Each value represents the mean ± S.E.M. of 10 animals per group performed in 2 experimental sets. Statistical analysis is one-way ANOVA followed by Bonferroni’s post hoc comparison. ^^P < 0.01 vs vehicle + vehicle; **P < 0.01 vs oxaliplatin + vehicle

Fig. 5

Astrocytic profile in the spinal cord. The effect of repeated treatment with carbophenyline (1 mg kg⁻¹) was evaluated in oxaliplatin-treated mice on day 14. The number of GFAP-positive cells was measured in the dorsal horn of the L4–L5 spinal cord. Transverse sections of spinal cord imaged with × 20 objective (scale bar = 50 μm); insert shows morphological characteristics of a representative astrocytic cell. Histograms show the quantitative analysis of GFAP fluorescence intensity. Each value represents the mean of 6 mice, performed by analyzing 4 independent fields for both sides of the dorsal horn of the lumbar spinal cord. Statistical analysis is one-way ANOVA followed by Bonferroni’s post hoc comparison. ^^P < 0.05 vs vehicle + vehicle; **P < 0.01 vs oxaliplatin + vehicle