Taxol-induced neuropathy after nerve crush: long-term effects on regenerating axons

Peripheral neuropathy: A persisting challenge in paclitaxel-based regimes

Cumulative peripheral neuropathy (PNP) still remains a limitation to optimal treatment with paclitaxel (PAC), especially in more dose-dense schedules. This primary sensory PNP may affect the majority of patients after administration of certain cumulative dosages of PAC, while the exact mechanisms of PAC-induced PNP are not known. While a number of preclinical models revealed its vehicle Cremophor EL (CrEL) to be mainly responsible for ganglionopathy, axonopathy and demyelination, clinical data also supports a strong and independent effect of PAC itself, which is most likely based on disturbances in the microtubules in perikaryons, axons and glia cells. Indeed, clinical trials of CrEL-free formulations of PAC still report grade III neurotoxicity as dose-limiting. As treatment options of PAC-induced PNP are rare the use of specific scoring systems for screening purposes is strongly encouraged. In this report we review and discuss the pathogenesis, incidence, risk factors, diagnosis, pharmacodynamics and treatment options for PAC-induced PNP.

Chemotherapy-evoked painful peripheral neuropathy

Vincristine and paclitaxel, two of the most effective drugs in the battle against cancer, produce a dose-limiting neurotoxicity that sometimes presents as a painful peripheral neuropathy. For the first time, investigators have been able to produce these chemotherapy-evoked painful peripheral neuropathies in the laboratory rat. These new models have already begun to elucidate the causes of the neuropathic pain associated with these antineoplastic drugs, which will now make it possible to search for effective ways to prevent and treat it.

A painful peripheral neuropathy in the rat produced by the chemotherapeutic drug, paclitaxel

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.

Paclitaxel neurotoxicity: clinical and neurophysiological study of 23 patients

Paclitaxel is the prototype of a new class of chemotherapeutic agents with an antimitotic effect that is related to its ability to interfere with the microtubule system. It causes peripheral neurological toxicity by means of its activity on the axonal microtubules. To define the clinical and neurophysiological characteristics of paclitaxel neuropathy 23 patients undergoing paclitaxel therapy at a dose of 175 mg/m2 were studied. The patients were divided into two groups, with only one group receiving pretreatment with potentially neurotoxic drugs such as cisplatin and carboplatin. The results showed a high incidence of mild neurotoxicity in both groups. Treatment was discontinued due to severe neurotoxicity in only one patient pretreated with platinum-compounds. The clinical and neurophysiological data make it possible to define paclitaxel neurotoxicity as a distal axonal neuropathy with a summatory effect in patients pretreated with cisplatin; the possible reversibility of paclitaxel neurotoxicity requires further confirmation.

The effects of taxol, methylprednisolone, and 4-aminopyridine in compressive spinal cord injury: a qualitative experimental study

BACKGROUND

Taxol is a diterpene alkaloid that stimulates tubulin production in cells. It may be effective in preserving the cytoskeleton of spinal cord axons after injury.

METHODS

Thirty-nine rats were submitted to spinal cord compression. The animals were divided into three groups that received taxol (18.75 mg/m2), methylprednisolone (30 mg/kg), or 4-aminopyridine (1 mg/kg). Taxol was administered as one dose immediately after injury and two additional doses on days 14 and 21. Methylprednisolone was given as a single injection immediately postinjury. Four-aminopyridine was administered on days 25, 26, and 27. A group of nine injured animals served as a control without any treatment. Evoked potentials were recorded before, during, and 4 weeks postinjury. Behavioral tests were measured to evaluate recovery of motor function.

RESULTS

The taxol and methylprednisolone-treated animals demonstrated a significant improvement in comparison with the control group. No functional improvement was found at 1 mg/kg treatment of 4-aminopyridine in rats.

CONCLUSIONS

We conclude that taxol and methylprednisolone given shortly after the compression injury improve functional outcome after an incomplete spinal cord injury.

Taxanes: a new class of antitumor agents

Taxanes belong to a new group of antineoplastic agents with a novel mechanism of action for a cytotoxic drug. They promote microtubule assembly and stabilize the microtubules. Paclitaxel, the first agent in this group to become available, was isolated from the Pacific yew, Taxus brevifolia, in 1971. In preclinical and clinical studies, paclitaxel and its semisynthetic analog docetaxel exhibit significant antitumor activity. This review deals with the physicochemical properties, pharmacology, and results of preclinical and clinical trials of the taxanes.

Paclitaxel (Taxol) induces cumulative mild neurotoxicity

Paclitaxel (Taxol), a new antineoplastic drug, has been reported to be neurotoxic at doses above 200 mg/m2 per course. It is uncertain whether neurotoxicity is related to cumulative amounts of paclitaxel. Neuropathy was prospectively assessed in 18 patients with breast cancer, receiving between two and eight courses of 135 or 175 mg/m2 of paclitaxel. Vibratory perception thresholds (VPT) and tendon reflex scores were proportionally related to the corresponding cumulative amounts of paclitaxel (P = 0.002; P = 0.0003). The amounts of paclitaxel administered between the first and last assessments (175-1225 mg/m2) were related to concomitant changes in VPT (P = 0.034). Paclitaxel had no clear neurotoxic threshold; if present, it lies below 540 mg/m2. Rather, VPT appeared to increase 0.1 micron per 400 mg/m2 over the entire range of 175-1225 mg/m2 of paclitaxel. Clinical neuropathy prevailed in 0/8 patients at screening and in 5/10 patients at the final assessment (P = 0.029). Neuropathy never exceeded grade 1. Thus, although neurotoxicity of paclitaxel is frequent and cumulative, it remains mild or subclinical up to at least 1400 mg/m2 administered over eight cycles.

Fine structural evaluation of altered Schmidt-Lanterman incisures in human sural nerve biopsies

Fine structural alterations of Schmidt-Lanterman incisures (SLI) were investigated in a series of 242 unselected sural nerve biopsies that had been examined for diagnostic purposes. The series included cases with Friedreich's ataxia, HSAN I, HMSN I-III, HMSN VI, tomaculous neuropathy, metachromatic leukodystrophy, ceroidlipofuscinosis, dysproteinemic neuropathies, and myotonic dystrophy, in addition to several neuropathies less-specifically classified as either of a predominantly demyelinating, axonal, or neuronal type. The following classification of SLI alterations is proposed: (A) abnormal inclusions; (B) changes in shape and dimension; and (C) modes of disintegration. Abnormal inclusions comprised membranous whorls, uniform and pleomorphous lysosome-like bodies, and accumulation of granular substances at the site of the major dense line, or granular deposits at the site of the intraperiod line of the myelin sheath. Variations of incisural shape and dimension included folding, dilatation, and pocket formation (compartmentalization). Disintegration at incisures comprised a fine, vesicular and a gross, vacuolar type. Various combinations of these changes were observed. The most frequent change consisted of membranous whorls, detected in SLI of 89 biopsies. They were most prominent in chloroquine neuropathy where they occurred in SLI as well as in the adaxonal and abaxonal cytoplasm of Schwann cells. Compartmentalization of the myelin sheath at incisures associated with formation of myelin loops was a frequent feature in myotonic dystrophy. It is concluded, that changes of incisural ultrastructure are sensitive indicators of human neuropathies offering clues to the type of the underlying pathomechanism.

Taxol-induced neuropathy after nerve crush: long-term effects on Schwann and endoneurial cells

The present investigation is a continuation of previous studies showing taxol-induced changes up to 4 weeks after a nerve crush. To evaluate the long-term cellular response to taxol, we have extended our morphological analysis of these changes in the taxol-treated nerve crush for up to 40 weeks after a single injection of taxol (PI). The results showed that Schwann cells exhibited a long-lasting and marked response when taxol was injected into the crushed peripheral nerve. During the first 2 months PI, taxol-induced giant axonal bulbs showed the formation of primitive nodes of Ranvier as a result of Schwann cell invaginations. The Schwann cell invaginations developed into nodes of Ranvier after 3-4 months PI together with the recovery of axonal bulbs. Ultrastructurally, cytoplasmic microtubule-related abnormalities were numerous up to 3 months PI and microtubules were seen to enclose degenerative myelin. Taxol-induced abnormalities in Schwann cells did not prevent their ability to produce myelin sheaths, although the accumulation of microtubules between myelin lamellae caused swellings of Schmidt-Lanterman incisures and paranodal myelin loops. Abnormal, extracellular collagen-like 5-nm-thin fibrils were noted closely associated with Schwann cells up to 10 weeks PI. Endoneurial cells, present as long rows without interconnections were noted in areas devoid of axonal sprouts up to 6-8 weeks PI. These cells showed marked cytoplasmic elongations and were covered by thickened basal lamina and contained several microtubule-related cytoplasmic structures, some of which have not been described previously. Taxol, when injected into crushed sciatic nerve induced a long-lasting response upon the Schwann cells with several ultrastructural abnormalities which correlate with changes in myelination and the development of nodes of Ranvier. These findings suggest that normal microtubule turnover is necessary for Schwann cells during nerve fiber regeneration.