Rosemary C. Polomano

Paclitaxel, an effective anti-neoplastic agent in the treatment of solid tumors, produces a dose-limiting painful peripheral neuropathy in a clinically significant number of cancer patients. Prior work has demonstrated paclitaxel-induced neurodegeneration and sensory loss in laboratory rodents. We describe here an experimental paclitaxel-induced painful peripheral neuropathy. Adult male rats were given four intraperitoneal injections on alternate days of vehicle or 0.5, 1.0, or 2.0 mg/kg of paclitaxel (Taxol). Behavioral tests for pain using mechanical and thermal stimuli applied to the tail and hind paws, and tests for motor performance, were taken before, during and after dosing for 22-35 days. All three doses of paclitaxel caused heat-hyperalgesia, mechano-allodynia, mechano-hyperalgesia, and cold-allodynia, but had no effect on motor performance. Neuropathic pain began within days and lasted for several weeks. We did not detect any dose-response relationship. Tests at the distal, mid, and proximal tail failed to show evidence of a length-dependent neuropathy. Vehicle control injections had no effect on any measure. No significant systemic toxicities were noted in the paclitaxel-treated animals. Light-microscopic inspection of the sciatic nerve (mid-thigh level), L4-L5 dorsal root ganglia, and dorsal and ventral roots, and the gray and white matter of the L4-L5 spinal cord, showed no structural abnormalities. Electron microscopic examination of the sciatic nerve (mid-thigh level) and the L4-L5 dorsal root ganglia and dorsal horns demonstrated no degeneration of myelinated and unmyelinated axons in the sciatic nerve and roots, but revealed endoneurial edema. This model may be useful in understanding a significant source of pain in cancer patients, and in finding ways to avoid the neurotoxicity that limits paclitaxel therapy.

Vincristine and paclitaxel, two of the most effective drugs in the battle against cancer, produce a dose-limiting neurotoxicity that sometimes presen