The involvement of the noradrenergic system in the antinociceptive effect of cucurbitacin D on mice with paclitaxel-induced neuropathic pain

Paclitaxel (sold under the brand name Taxol) is a chemotherapeutic drug that is widely used to treat cancer. However, it can also induce peripheral neuropathy, which limits its use. Although several drugs are used to attenuate neuropathy, no optimal treatment is available to date. In this study, the effect of cucurbitacins B and D on paclitaxel-induced neuropathic pain was assessed. Multiple paclitaxel injections (a cumulative dose of 8 mg/kg, i. p.) induced cold and mechanical allodynia from days 10 to 21 in mice, and the i. p. administration of 0.025 mg/kg of cucurbitacins B and D attenuated both allodynia types. However, as cucurbitacin B showed a more toxic effect on non-cancerous (RAW 264.7) cells, further experiments were conducted with cucurbitacin D. The cucurbitacin D dose-dependently (0.025, 0.1, and 0.5 mg/kg) attenuated both allodynia types. In the spinal cord, paclitaxel injection increased the gene expression of noradrenergic (α (1)-and α (2)-adrenergic) receptors but not serotonergic (5-HT(1A) and (3)) receptors. Cucurbitacin D treatment significantly decreased the spinal α (1)- but not α (2)-adrenergic receptors, and the amount of spinal noradrenaline was also downregulated. However, the tyrosine hydroxylase expression measured via liquid chromatography in the locus coeruleus did not decrease significantly. Finally, cucurbitacin D treatment did not lower the anticancer effect of chemotherapeutic drugs when co-administered with paclitaxel in CT-26 cell-implanted mice. Altogether, these results suggest that cucurbitacin D could be considered a treatment option against paclitaxel-induced neuropathic pain.