Systemic QX-314 Reduces Bone Cancer Pain through Selective Inhibition of Transient Receptor Potential Vanilloid Subfamily 1-expressing Primary Afferents in Mice

Background: The aim of this study was to determine whether systemic administration of QX-314 reduces bone cancer pain through selective inhibition of transient receptor potential vanilloid subfamily 1 (TRPV1)-expressing afferents. Methods: A mouse model of bone cancer pain was used. The authors examined the effects of bolus (0.01 to 3 mg/kg, n = 6 to 10) and continuous (5 mg kg(-1) h(-1), n = 5) administration of QX-314 on both bone cancer pain-related behaviors and phosphorylated cyclic adenosine monophosphate response element-binding protein expression in dorsal root ganglion neurons (n = 3 or 6) and the effects of ablation of TRPV1-expressing afferents on bone cancer pain-related behaviors (n = 10). Results: The numbers of flinches indicative of ongoing pain in QX-314-treated mice were smaller than those in vehicle-treated mice at 10 min (3 mg/kg, 4 +/- 3; 1 mg/kg, 5 +/- 3 vs. 12 +/- 3; P < 0.001; n = 8 to 9), 24 h (3 +/- 2 vs. 13 +/- 3, P < 0.001), and 48 h (4 +/- 1 vs. 12 +/- 2, P < 0.001; n = 5 in each group) after QX-314 administration, but impaired limb use, weight-bearing including that examined by the CatWalk system, and rotarod performance indicative of movement-evoked pain were comparable. QX-314 selectively inhibited the increase in phosphorylated cyclic adenosine monophosphate response elementbinding protein expression in TRPV1-positive, but not in TRPV1-negative, dorsal root ganglion neurons compared to that in the case of vehicle administration (32.2 +/- 3.0% vs. 52.6 +/- 5.9%, P < 0.001; n = 6 in each group). Ablation of TRPV1expressing afferents mimicked the effects of QX-314. Conclusion: This study showed that systemic administration of QX-314 in mice inhibits some behavioral aspects of bone cancer pain through selective inhibition of TRPV1-expressing afferents without coadministration of TRPV1 agonists.