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    151

    Riv. It. Neurobiologia, 53 (3-4), 151-167, 2007

    Rassegna sintetica

    NEUROTOXICITY IN ONCOLOGY:IS NEUROPROTECTION (NP) ATTAINABLE?

    A CRITICAL REVIEW

    VIDMER SCAIOLI (), ANDREA SALMAGGI (*)

    Fondazione IRCCS Istituto Neurologico Carlo Besta, Milano;() Clinical Neurophysiology Unit; (*) Neuro-oncology Unit

    SUMMARY

    The remarkable advances in drug develompment and strategy in oncology

    have greatly contributed to improve the survival rates of cancer; hovewer

    they have also raised questions on ethics about quality of life of the patients.

    One of the emerging practical issues in cancer therapy is that neurological

    side effects represent more often one of the most common and threatening

    side effects and dose limiting factors in cancer treatment. In this review we

    have first tried to characterise the neurological side effects, either systemic

    or sporadic. The systematic side effects are represented by peripheral neu-

    ropathy and by the ocular manifestations optic neuritis and retinopathy. The

    sporadic side effects enbody a wider range of neurological manifestations

    spanning from encephalitis, to seizures, to atypical onset neuropathy and

    peripheral nervous system complications. It is worth mentioning the rele-

    vance of studying even the sporadic side effects because the search of the

    mechanisms of the pathogenetic events can reveal congenital predisposing

    factors that can be diagnosed before the beginning of the therapy and that

    can improve the strategy of treatment. Secondly, we have offered an open

    rewiev of the scoring systems, that is the either clinical, subjective or objec-

    tive ways to score the side effects and quantitative methods; the latter are

    particularly useful in order to characterise in a quantitative way the effect

    of neuroprotection. Thirdly, we have reviewed the classic, still widely used,

    drugs, responsible for the systematic or sporadic side effects. Fourthly, the

    strategy of neuroprotection has been widely analysed, together with the

    expected clinical outcome, and what is already defined and what is still in

    progress, but nonetheless deserves verification or validation.

    Key Words: Chemiotherapy, toxicity, neuroprotection, pe-

    ripheral neuropathy, optic neuropathy

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    V. SCAIOLI, A. SALMAGGI

    I n t r o d u c t i o n

    The improvement in health care systems

    and increasing needs in terms of quality

    of life, together with the ethical issues of

    dignity of death, represent nowadays one of the

    main topics in the medical treatment and strat-

    egy in oncology.

    Several drugs of proved antitumoral efficacy

    widely used in oncology have the inconvenience

    of causing some neurological complications,

    either occasionally or in a more systematic way.

    Sometimes, the neurological syndromes become

    disturbing enough so as to hamper continuation

    of treatment or the use of other drugs.

    The term neuroprotection defines the identi-

    fication of strategies to prevent or minimise,

    directly or indirectly, the neurological side

    effects of therapy.

    The possible ways by which neuroprotection

    can be achieved are:

    1. to modify the molecular conformation of the

    drug so as to maintain the antitumoral effi-

    cacy but minimise the toxic action against

    the neural tissue;

    2. to combine the drug with other(s) poten-

    tially able to exert a protective action on the

    healthy nervous tissue;

    3. to combine the drug with a vector able to

    optimize and make delivery tumor cell-

    selective.

    A fundamental step in neuroprotection is

    represented by an accurate characterisation of

    the systematic side effects of anticancer drugs;

    one of the main and best known side effects of

    antitumoural therapy is represented by periph-

    eral neuropathy (PN), as it will be reported later

    in the paper.

    With the term of systematic side effects we

    can define the appearance of a variable degree

    of clinical syndromes in most of the patients

    undergoing a given treatment.

    In this respect, the first part of the paper is

    addressed to the description of the most com-

    mon and documented neurological complica-

    tions associated with the most commonly used

    chemotherapeutic drugs.

    It is worth mentioning that, in the past, the

    characterisation of side effects was not so accu-

    rate, because the attention of oncologists was

    captured by the fight against the tumour, and lit-

    tle care was paid to the characterisation of neu-

    rological side effects. Only recently a certain

    attention has been paid to the side effects and to

    improved quality of life of the patients; on the

    other hand, in the light of increased attention

    about ethics and dignity of death, an overuse of

    treatment may be discouraged; at a certain

    point, it could be more important to stop a treat-

    ment with devastating side effects.

    Therefore, neurotoxicity remains a major

    limitation of many drugs used in cancer patients

    and their list grows steadily. On one side mag-

    netic resonance imaging and other imaging

    techniques make easier the recognition of cen-

    tral nervous system toxicity; on the other side,

    scoring procedures and clinical neurophysiology

    make it easy, and acceptable by the patients, to

    characterize peripheral nervous system toxicity.

    Synthesis and thorough clinical testing of neuro-

    protective molecules remain therefore a major

    challenge (1).

    In this context, with the term of

    Chemoprotectants we can define agents that

    have been developed to ameliorate the toxicity

    associated with cytotoxic drugs. They aim to

    provide site-specific protection for normal tis-

    sues, without compromising antitumor efficacy.

    Several chemoprotectant compounds have been

    studied in recent clinical trials. These trials

    must include sufficient dose-limiting events for

    study and assessment of both toxicity and anti-

    tumor effect.

    Major c lasses of chemioterapeut ic drugs of

    proved neurological toxic i ty

    The taxanes (paclitaxel and docetaxel) are

    highly active cytotoxic antineoplastic agents.

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    V. SCAIOLI, A. SALMAGGI

    how chemotherapy affects the nervous system

    and ultimately help develop more strategies to

    prevent drug-related neurotoxicity in cancer pa-

    tients. (13).

    The pathogenesis of central and peripheral

    nervous system neurological manifestations

    caused by anticancer agents is often poorly

    understood, and is probably multifactorial.

    A recent observation indicates that genetic

    polymorphism for methionine is a potent risk

    factor for methtrexate-induced central nervous

    system toxicity. Chronic peripheral neuropathy

    still represents a major limiting factor in a series

    of chemotherapeutic drugs, and the neuropro-

    tective effect of several older and newer agents

    is either deceptive or insufficiently proven. In

    addition to chronic neuropathy, oxaliplatine

    causes a unique acute syndrome which may

    respond to calcium plus magnesium infusion.

    Central nervous system. The most common

    neurologic complications involve acute alter-

    ations in consciousness, leukoencephalopathy,

    seizures, cerebral infarctions, paralysis, in addi-

    tion to neuropathy, and ototoxicity. Most of the

    information on toxicity comes from prospective

    reports and the adult patient population.

    Methotrexate, cyclosporin, and platinum com-

    pounds are the most frequently cited. No

    prospective studies have been done to evaluate

    chemotherapy-induced neurotoxicity in the

    pediatric population, and the exact incidence of

    such complications is unknown.

    Mostly unpredictable encephalopathy contin-

    ues to be sporadically reported even in patients

    treated systemically with conventional

    chemotherapy doses. Recently, capecitabine, a

    5-fluorouracil prodrug, has been added to the

    list. Magnetic resonance diffusion-weighted and

    fluid-attenuated inversion-recovery imaging are

    useful in demonstrating chemotherapy-induced

    central nervous system lesions.

    Peripheral Neuropathy is a dose-limiting

    side effect for a number of effective chemother-

    apeutic agents and a better understanding of

    effective mechanisms will lead to novel treat-

    ment strategies that will protect neurons with-

    out decreasing therapeutic efficacy. (14) In this

    respect, the assessment of the efficacy and neu-

    rotoxicity of various chemotherapeutic agents is

    vital, for a determination of the maximum allow-

    able dose. (14)

    The type and degree of neuropathy depend

    on the chemotherapy drug, dose-intensity, and

    cumulative dose. Disabling peripheral neuropa-

    thy has a significant negative impact on quality

    of life. Accordingly, a reliable assessment of

    chemotherapy-induced peripheral neurotoxicity

    is necessary, especially if potential neuroprotec-

    tive agents are to be investigated.

    PN can express itself either with negative or

    positive symptoms. Among the positive, painful

    paresthesia and disesthesia are the most dis-

    turbing. However, pain arises from numerous

    causes in cancer patients. On the whole, the

    neuropathic pain occurs in 1% of the population

    and is difficult to manage. Responses to single

    drugs are limited in benefit. Thirty percent will

    fail to respond altogether. (15)

    Well known to cancer care providers, but per-

    haps less well so to others, is that the main

    causes of pain in cancer patients in fact arise

    due to cancer treatments more frequently than

    due to disease itself. In this paper clinical and

    laboratory findings on the characteristics of

    chemotherapy-induced neuropathic pain are

    reviewed and a scheme for the underlying

    mechanisms is outlined. (16)

    S t e p I I c h a r a c t e r i s a t i o no f t h e s o c a l l e d s p o -

    r a d i c s i d e e f f e c t s

    Retinopathy and optic neuritis are a rela-

    tively frequent complication of medical treat-

    ments, both in cancer and in other medical

    fields, like antiepileptic drugs.

    Continuous intravenous 5 fluorouracil (5FU)

    chemotherapy may be associated with a bilater-

    al asymmetric anterior optic neuropathy (ON).

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    NEUROTOXICITY IN ONCOLOGY. A CRITICAL REVIEW

    Interestingly, a deficiency of dihydropyrimidine

    dehydrogenase (DPD) was documented.

    Patients with DPD deficiency are at increased

    risk for developing unusual and/or severe toxic-

    ity to 5FU. (17)

    A number of drugs cause ocular irritation (flu-

    orouracil, methotrexate), canalicular fibrosis

    with epiphora (fluorouracil), retinopathy

    (mitotane, tamoxifen), corneal opacities (tamox-

    ifen), cataracts (busulfan, methotrexate), and

    optic or ocular motor abnormalities (carmustine,

    vinblastine, vincristine). Based on the data in the

    National Registry of Drug-Induced Ocular Side

    Effects and the literature, adverse ocular reac-

    tions of the most commonly used chemothera-

    peutic agents have been reviewed. (18; 19)

    S t e p I I I h o w t o c h a r a c -t e r i s e t h e n e u r o l o g i c a ls i d e e f f e c t s : t h e s c o -r i n g s y s t e m s d i l e m m a

    The best way to evaluate and score the sever-

    ity of chemotherapy-induced peripheral neuropa-

    thy is still an unsettled matter; a number of scor-

    ing systems, involving both clinical and/or neuro-

    physiological testing have been employed in the

    setting of clinical research. (20-22) (23; 24)

    Two main approaches are described: the for-

    mer is based upon self-reported peripheral neu-

    ropathy and functional status (including physi-

    cal function and role function subscales), the

    latter is based upon a combination of clinical

    and neurophysiological scoring systems (total

    neuropathy score,TNS and TNSr, a reduced ver-

    sion thereof (25), ECOG score and NCI-CTC 2.0

    scores).

    In an early study, the severity of chemother-

    apy-induced peripheral neuropathy (CIPN) was

    evaluated in patients treated with cisplatin- and

    paclitaxel-based chemotherapy. A reduced ver-

    sion of TNS (TNSr) was also compared. It was

    concluded that the TNS and TNSr can be used

    to assess the severity of CIPN effectively, and

    the results of this evaluation can be reliably cor-

    related with the oncologic grading of sensory

    peripheral neurotoxicity. (23)

    Later on, a multi-center study was developed

    to comparatively assess the reduced versions of

    the Total Neuropathy Score (TNS), the severity

    of chemotherapy-induced peripheral neurotoxic-

    ity (CIPN), and to compare the results with those

    obtained with common toxicity scales. (24)

    A highly significant correlation was demon-

    strated between the TNSr and the NCI-CTC 2.0

    and ECOG scores; but the TNSr evaluation was

    more accurate in view of the more extended

    score range. Also, the simpler and faster TNSc

    (based only on the clinical neurological exami-

    nation) allowed to grade accurately CIPN and

    correlated with the common toxicity scores. The

    correlation tended to be closer when the senso-

    ry items were considered, but also the TNSr

    motor items, which were not specifically investi-

    gated in any other previous study, significantly

    correlated with the results of the common toxi-

    city scales. (24; 26)

    In a recent paper, the peripheral neuropathy

    temporal course has been evaluated by means of

    the total neuropathy scoring system (TNS). The

    temporal relationships between the PN and

    paclitaxel were robustly characterised, and thus

    provide reference data and a model for testing

    the efficacy of drugs designed to provide neuro-

    protection. (27)

    Overall, while clinical self-reporting scores

    and objective evaluations with neurophyisiologi-

    cal tests may be of help in assessing peripheral

    neurotoxicity in single patients, only a combina-

    tion of these is a reliable tool in the evaluation of

    groups of patients undergoing potentially toxic

    and/or neuroprotective treatments.

    The TNS is presently the most reliable tool in

    this context, despite the need for an experi-

    enced team in its application.

    On the other hand, other scoring systems ad-

    dress neuroophtalmological systematic side-ef-

    fects, since evidence grows for a selective toxic-

    ity on these structures by new agents used in

    therapy. Also in this respect, a combination of

    both clinical and neurophysiological tests are

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    V. SCAIOLI, A. SALMAGGI

    under active investigation. Recent reports of pa-

    clitaxel treated patients have emphasised the

    clinical relevance of ophtalmological and elec-

    trophysiological evaluation and characterisation

    of neuroophtalmological manifestation. (28; 29)

    T h e s t r a t e g i e s o f n e u -r o p r o t e c t i o n

    a. Modification of the molecular structu-re of the drugThe taxanes. Paclitaxel and its semi-syn-

    thetic derivative docetaxel are potent

    chemotherapeutic agents that block tubulin

    depolymerisation, leading to the inhibition of

    microtubule dynamics and cell cycle arrest.

    Although docetaxel and paclitaxel share a mutu-

    al tubulin binding site, mechanistic and pharma-

    cological differences exist between these

    agents. For example, docetaxel has increased

    potency and an improved therapeutic index

    compared with paclitaxel, and its short 1-h infu-

    sion offers a substantial clinical advantage over

    the prolonged infusion durations required with

    paclitaxel. In clinical studies, docetaxel

    monotherapy demonstrated good response

    rates and an acceptable toxicity profile in both

    paclitaxel- and platinum-refractory ovarian can-

    cer patients. In particular, neurotoxicity - a

    dominant side effect with both paclitaxel and

    cisplatin - occurs at a low incidence with doc-

    etaxel, making docetaxel a promising agent for

    combining cisplatin and other platinum com-

    pounds. In Phase II studies, the combination of

    docetaxel with either cisplatin or carboplatin

    has yielded impressive response rates of 69-74

    and 81-87%, respectively. Furthermore, Phase

    III data suggest that docetaxel-carboplatin and

    paclitaxel-carboplatin are similarly efficacious

    with respect to progression-free survival and

    clinical response, although neurotoxicity occurs

    more frequently with the paclitaxel regimen.

    While paclitaxel-carboplatin remains the stan-

    dard treatment for the management of advanced

    ovarian cancer, docetaxel-carboplatin appears

    to be a promising alternative, particularly in

    terms of minimising the incidence and severity

    of peripheral neuropathy. (30)

    A prospective study was performed to deter-

    mine if corticosteroid co-medication reduces

    the incidence and severity of docetaxel-induced

    neuropathy. (30; 31).

    Neuropathy was evaluated by clinical sum-

    score for signs and symptoms and by measure-

    ment of the vibration perception threshold

    (VPT). The severity of neuropathy was graded

    according to the National Cancer Institutes

    Common Toxicity Criteria. The docetaxel-cis-

    platin combination chemotherapy induced a

    predominantly sensory neuropathy in 29 (53%)

    out of 55 evaluable patients. At cumulative

    doses of both cisplatin and docetaxel above 200

    mg m(-2), 26 (74%) out of 35 patients devel-

    oped a neuropathy which was mild in 15, mod-

    erate in ten and severe in one patient.

    Significant correlations were present between

    both the cumulative dose of docetaxel and cis-

    platin and the post-treatment sum-score of neu-

    ropathy (P < 0.01) as well as the post-treatment

    VPT (P < 0.01). The neurotoxic effects of this

    combination were more severe than either cis-

    platin or docetaxel as single agent at similar

    doses. (32)

    Oxaliplatin. Oxaliplatin is the only third-

    generation platinum derivative to have found a

    place in routine cancer therapy and conse-

    quentely it has become an integral part of vari-

    ous chemotherapy protocols, in advanced col-

    orectal cancer in particular (33; 34; 35). Com-

    pared with cisplatin, L-OHP has no renal toxici-

    ty, only mild hematological and gastrointestinal

    toxicity, while neurotoxicity is the limiting toxi-

    city. In addition, Oxaliplatin-containing

    chemotherapy regimens are utilized commonly

    for metastatic colorectal cancer and increasing-

    ly in the adjuvant setting following surgical re-

    section. Oxaliplatin-induced neurotoxicity con-

    sists of a rapid-onset, cold-induced, reversible

    acute sensory neuropathy and a late-onset cu-

    mulative sensory neuropathy that occurs after

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    NEUROTOXICITY IN ONCOLOGY. A CRITICAL REVIEW

    several cycles of therapy(36). In about three

    fourths of patients, neurotoxicity is reversible

    with a median time to recovery of 13 weeks af-

    ter treatment discontinuation. To date, oxali-

    platin has proven to be a safe and effective ther-

    apy for colorectal cancer and side effects have

    been easy to manage with appropriate aware-

    ness from patients and care providers. (35)

    Delayed neurotoxicity is a complication

    which must be considered for patients receiving

    adjuvant therapy and attempts to utilize the

    minimum effective cumulative dose of oxali-

    platin are warranted. (37)

    Various strategies have been proposed to

    prevent or treat oxaliplatin-induced neurotoxic-

    ity. The Stop-and-Go concept uses the re-

    versibility of neurologic symptoms to aim at de-

    livering higher cumulative oxaliplatin doses as

    long as the therapy is still effective. Several neu-

    romodulatory agents such as calcium-magne-

    sium infusions, antiepileptic drugs like carba-

    mazepine or gabapentin, amifostine, alpha-lipoic

    acid, and glutathione have shown promising ac-

    tivity in prophylaxis and treatment of oxali-

    platin-induced neurotoxicity. However, larger

    confirmatory trials are still lacking so that, to

    date, no evidence-based recommendation can

    be given for the prophylaxis of oxaliplatin-in-

    duced neurotoxicity. The predictability of neuro-

    toxicity associated with oxaliplatin-based thera-

    py should allow patients and doctors to develop

    strategies to manage this side effect in view of

    the individual patients clinical situation. (38)

    This side effect has been described as a tran-

    sient distal dysesthesia, enhanced by exposure

    to cold, and as a dose-related cumulative mild

    sensitive neuropathy. Two groups of patients

    (18 and 13) with advanced colorectal cancer,

    treated with median cumulative doses of L-OHP

    862 mg/m2 and 1,033.5 mg/m2, were studied. All

    the patients had been evaluated previously, dur-

    ing treatment, after discontinuation and after a

    long follow-up of 5 years to verify the incidence

    and the characteristics of the neuropathy

    induced by this antineoplastic agent. The clini-

    cal and neurophysiological examinations

    showed an acute and transient neurotoxicity

    and a cumulative dose-related sensory neuropa-

    thy in nearly all the patients. The reversibility of

    these effects was studied. Five patients contin-

    ued to manifest symptoms and signs of neuro-

    toxicity after a long follow-up, indicating per-

    sistence of this peculiar type of neuropathy(39)

    Nedaplatin. Nedaplatin (cis-diammineglyco-

    latoplatinum) can be given without hydration;

    its dose-limiting toxicity is myelosuppression, in

    particular thrombocytopenia. Although activity

    has been shown, no data from randomized com-

    parative trials are available to allow a judgement

    on its potential advantages. (33) It is worth

    mentioning that this association is of potentially

    clinical relevance given that the traditional asso-

    ciation of paclitaxel and cisplatin results in a

    cumulative neurotoxicity severe enough to

    result dose-limiting in the majority of the

    patients treated with this association (40)

    b. Combination of neuroprotective agentswith neurotoxic drugs:

    The contemporary or sequential treatment

    with a number of agents has been shown to be of

    some effectiveness in minimizing neurotoxicity.

    The goal of this approach is to keep the score of

    neurotoxicity at a level compatible with treat-

    ment continuation.

    Peripheral neuropathy (PN), associated with

    diabetes, neurotoxic chemotherapy, human

    immunodeficiency virus (HIV)/antiretroviral

    drugs, alcoholism, nutritional deficiencies,

    heavy metal toxicity, and other etiologies,

    results in significant morbidity. Conventional

    pain medications primarily mask symptoms and

    have significant side effects and addiction pro-

    files. However, a widening body of research indi-

    cates alternative medicine may offer significant

    benefit to this patient population. Alpha-lipoic

    acid, acetyl-L-carnitine, benfotiamine, methyl-

    cobalamin, and topical capsaicin are among the

    best-researched alternative options for the

    treatment of PN. Other potential nutrient or

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    V. SCAIOLI, A. SALMAGGI

    botanical therapies include vitamin E, glu-

    tathione, folate, pyridoxine, biotin, myo-inositol,

    omega-3 and -6 fatty acids, L-arginine, L-gluta-

    mine, taurine, N-acetylcysteine, zinc, magne-

    sium, chromium, and St. Johns wort. In the

    realm of physical medicine, acupuncture, mag-

    netic therapy, and yoga have been found to pro-

    vide benefit. New cutting-edge conventional

    therapies, including dual-action peptides, may

    also hold promise. (41)

    Amifostine is a pharmacological antioxidant

    used as a cytoprotectant in cancer chemothera-

    py and radiotherapy. It is thought to protect nor-

    mal tissues relative to tumor tissue against

    oxidative damage inflicted by cancer therapies

    by becoming concentrated at higher levels in

    normal tissues. The degree to which amifostine

    nevertheless accumulates in tumors and pro-

    tects them against cancer therapies has been

    debated. (42)

    Clinically relevant levels of amifostine toxici-

    ty were observed in several studies, but subcu-

    taneous administration may reduce such toxici-

    ty. Amifostine showed protection against mu-

    cositis, esophagitis, neuropathy, and other side

    effects, although protection against cisplatin-in-

    duced ototoxicity was not observed. No evi-

    dence of tumor protection was observed. (42)

    Vitamin E. Peripheral sensory neuropathy is

    the main non-haematological side-effect related

    to cisplatin chemotherapy. The strong similarity

    between clinical and neuropathological aspects

    in peripheral neuropathy induced by cisplatin

    and neurologic syndromes due to vitamin E de-

    ficiency, prompted Bove and Colleagues (43) to

    investigate the relationship between cisplatin

    neuropathy and plasmatic levels of vitamin E

    (alpha-tocopherol). In a study vitamin E levels

    were measured in the plasma of 5 patients

    (Group 1) who developed severe neurotoxicity

    after cisplatin treatment and in another group of

    5 patients (Group 2); the plasmatic levels of vi-

    tamin E were analysed before and after 2 or 4

    cycles of cisplatin treatment. The results

    showed that patients of group 1 presented low

    plasmatic levels of vitamin E and that patients of

    group 2 presented significantly lower levels of

    vitamin E after 2 or 4 cycles of cisplatin than be-

    fore treatment. These data suggest that an inad-

    equate amount of the antioxidant vitamin E due

    to cisplatin treatment could be responsible of

    the peripheral nerve damage induced by free-

    radicals. Given the lack of toxicity of vitamin E,

    we need to systematically assess the possible

    neuroprotective role of vitamin E supplementa-

    tion in patients treated with cisplatin

    chemotherapy. (43)

    The dose-limiting toxicity of the chemothera-

    peutic agent vincristine is peripheral neuropathy,

    for which there is no established therapy. (44)

    The amino acid glutamate has been pro-

    posed as a neuroprotectant for vincristine.

    (44)

    Leukemia inhibitory factor (LIF) (45) The

    growth factor leukaemia inhibitory factor (LIF)

    has neuroprotectant activity in preclinical mod-

    els of nerve injury and degeneration and is now

    in a phase II trial in chemotherapy-induced

    peripheral neuropathy (CIPN). It is therefore

    important to ensure that LIF neither inhibits the

    antitumour activity of these drugs, nor stimu-

    lates tumour growth. (45)

    These results suggest that LIF may be safely

    used in human trials as a neuroprotectant for

    patients receiving cisplatin, paclitaxel and car-

    boplatin without concern for impairment of anti-

    tumour effect (45).

    Glutathione (36) A randomized, double-

    blind, placebo-controlled trial to assess the effi-

    cacy of glutathione (GSH) in the prevention of

    oxaliplatin-induced neurotoxicity was per-

    formed(36) The study provided evidence that

    GSH is a promising drug for the prevention of

    oxaliplatin-induced neuropathy, and that it does

    not reduce the clinical activity of oxaliplatin(36)

    Nimodipine (46) Previous randomised trial

    in patients with advanced ovarian cancer indi-

    cated a significant response and survival advan-

    tage for those receiving high-dose (100 mg/m2)

    as compared with low-dose (50 mg/m2) cis-

    platin in combination with cyclophosphamide

    (750 mg/m2). However, this was accompanied

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    NEUROTOXICITY IN ONCOLOGY. A CRITICAL REVIEW

    by more toxicity; peripheral neuropathy was

    troublesome, with 32% of patients experiencing

    > or = WHO grade 2 at the cisplatin dose of 100

    mg/m2. Nimodipine is a calcium-channel antag-

    onist that has provided protection from cis-

    platin-induced neurotoxicity in a rat model sys-

    tem.(46) These studies did not demonstrate a

    neuroprotective effect for nimodipine. The pri-

    mary efficacy variable, i.e, the neurotoxicity

    score at the end of treatment, gave a signifi-

    cantly lower mean for placebo patients than for

    nimodipine patients. (46)

    Acetyl-L-carnitine (47; 48) The hypothesis

    that acetyl-L-carnitine (ALC) may have a pro-

    tective and a curative role in chemotherapy-

    induced hyperalgesia was tested in vivo, in ani-

    mal models of cisplatin-, paclitaxel- and vin-

    cristine-induced neuropathy. In addition, the

    possible interaction between ALC and vin-

    cristine antineoplastic action was assessed.

    Chemotherapy-induced peripheral neuropathy

    (CIPN) was induced in different groups of rats.

    The effect of ALC was evaluated both when its

    administration was started together with the

    administration of anticancer drugs (preven-

    tive protocol) and when ALC administration

    was started later on during treatment (cura-

    tive protocol). The ALC treatment significantly

    prevented the lowering of the mechanical noci-

    ceptive threshold when the administration start-

    ed concomitantly and, respectively, with cis-

    platin, paclitaxel and vincristine as compared to

    each drug alone. Furthermore, when ALC

    administration was started later on during treat-

    ment, at the stage of well-established neuropa-

    thy, ALC was able to restore the mechanical

    nociceptive threshold within a few days. Finally,

    experiments indicated that ALC does not inter-

    fere with the antitumor effects of vincristine.

    Considering the absence of any satisfactory

    treatment currently available for CIPN in a clin-

    ical setting, these are important observations,

    opening up the possibility of using ALC to treat

    a wide range of patients who have undergone

    chemotherapy and developed sensory peripher-

    al neuropathy. (47; 49)

    Glutamine (44; 50; 51) In a non-randomised

    study neurologic signs and symptoms, and

    changes in nerve-conduction, were studied in 46

    consecutive patients given high-dose paclitaxel

    either with (n=17) or without (n=29) glutamine.

    Patients who received glutamine developed sig-

    nificantly less weakness (P = 0.02), less loss of

    vibratory sensation (P = 0.04) and less toe

    numbness (P = 0.004) than controls. The per

    cent change in the compound motor action

    potential (CMAP) and sensory nerve action

    potential (SNAP) amplitudes after paclitaxel

    treatment was lower in the glutamine group, but

    this finding was not statistically significant in

    these small groups. The study indicated that

    serial neurologic assessment of patient symp-

    toms and signs seemed to be a better indicator

    of a possible glutamine effect than sensory- or

    motor-nerve-conduction studies. (51)

    In another study, there were paired pre- and

    post-paclitaxel evaluations on 33 patients who

    did not receive glutamine and 12 patients who

    did. The median interval between pre- and post-

    exams was 32 days. For patients who received

    glutamine, there was a statistically significant re-

    duction in the severity of peripheral neuropathy

    as measured by development of moderate to se-

    vere dysesthesias and numbness in the fingers

    and toes (P < 0.05). The degree and incidence of

    motor weakness was reduced (56 versus 25%; P

    = 0.04) as well as deterioration in gait (85 versus

    45%; P = 0.016) and interference with activities

    of daily living (85 versus 27%; P = 0.001). Moder-

    ate to severe paresthesias in the fingers and toes

    were also reduced (55 versus 42% and 64 versus

    50%, respectively), although this value was not

    statistically significant. All of these toxicities

    were reversible over time. It was concluded that

    glutamine may reduce the severity of peripheral

    neuropathy associated with high-dose paclitaxel;

    however, results from randomized, placebo-con-

    trolled clinical trials will be needed to fully assess

    its impact, if any. Trials are currently ongoing to

    assess its efficacy for standard-dose paclitaxel in

    breast cancer and other tumors for which periph-

    eral neuropathy is the dose-limiting toxicity. (50)

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    Corticosteroid Two groups of patients treat-

    ed with docetaxel in subsequent cohorts were

    prospectively analyzed for neurotoxicity. Group

    A consisted of 38 patients with a variety of solid

    tumors, who were treated in studies before cor-

    ticosteroid co-medication was recommended,

    while 49 female patients in group B with

    metastatic breast cancer were treated after co-

    medication with corticosteroids was introduced

    as a routine. Neuropathy was evaluated by a

    clinical sum-score for symptoms and signs, and

    by measurement of the vibration perception

    threshold (VPT). The severity of neuropathy

    was graded according to NCI Common Toxicity

    Criteria. In 42% of patients of group A and in

    65% of patients of group B a mainly mild neu-

    ropathy was documented. There was no statisti-

    cally significant difference in neurotoxicity

    between group A and B. The cumulative dose of

    docetaxel showed a significant correlation with

    post-treatment scores of VPT, sensory sum-

    score, grade of paresthesias, and grade of neu-

    rosensory and neuromotor toxicity.

    Corticosteroid co-medication does not reduce

    the development of docetaxel-related neuropa-

    thy. (31)

    Melatonin (52) Experimental data have

    suggested that the pineal hormone melatonin

    (MLT) may counteract chemotherapy-induced

    myelosuppression and immunosuppression. In

    addition, MLT has been shown to inhibit the

    production of free radicals, which play a part in

    mediating the toxicity of chemotherapy. A

    study was therefore performed in an attempt to

    evaluate the influence of MLT on chemotherapy

    toxicity. The study involved 80 patients with

    metastatic solid tumors who were in poor clini-

    cal condition (lung cancer: 35; breast cancer:

    31; gastrointestinal tract tumors: 14). Lung can-

    cer patients were treated with cisplatin and

    etoposide, breast cancer patients with mitox-

    antrone, and gastrointestinal tract tumor

    patients with 5-fluorouracil plus folates.

    Patients were randomised to receive

    chemotherapy alone or chemotherapy plus MLT

    (20 mg/day p.o. in the evening).

    Thrombocytopenia was significantly less fre-

    quent in patients concomitantly treated with

    MLT. Malaise and asthenia were also significant-

    ly less frequent in patients receiving MLT.

    Finally, stomatitis and neuropathy were less

    frequent in the MLT group, albeit without sta-

    tistically significant differences. Alopecia and

    vomiting were not influenced by MLT. This pilot

    study seems to suggest that the concomitant

    administration of the pineal hormone MLT dur-

    ing chemotherapy may prevent some

    chemotherapy-induced side-effects, particular-

    ly myelosuppression and neuropathy.

    Evaluation of the impact of MLT on chemother-

    apy efficacy will be the aim of future clinical

    investigations(52)

    N-acetyl-cisteine (53) Although adding

    oxaliplatin to fluorouracil and leucovorin in

    adjuvant chemotherapy for colon cancer may

    improve disease-free survival, grade 3-4 sensory

    neuropathy also increases. To determine

    whether oral N-acetylcysteine is neuroprotec-

    tive against oxaliplatin-induced neuropathy, a

    pilot study was undertaken. Fourteen stage III

    colon cancer patients with 4 or more regional

    lymph nodes metastasis (N2 disease) receiving

    adjuvant biweekly oxaliplatin (85 mg/m(2)) plus

    weekly fluorouracil boluses and low-dose leu-

    covorin were randomized to oral N-acetylcys-

    teine (1,200 mg) (arm A) or placebo (arm B).

    Clinical neurological and electrophysiological

    evaluations were performed at baseline and

    after 4, 8, and 12 treatment cycles. Treatment-

    related toxicity was evaluated based on National

    Cancer Institute (NCI) Criteria. After four

    cycles of chemotherapy, seven of nine patients

    in arm B and two of five in arm A experienced

    grade 1 sensory neuropathy. After eight cycles,

    five experienced sensory neuropathy (grade 2-4

    toxicity) in arm B; none in arm A (p

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    incidence of oxaliplatin-induced neuropathy in

    colon cancer patients receiving oxaliplatin-

    based adjuvant chemotherapy. (53)

    Calcium and magnesium infusion. Infu-

    sions of oxalate chelators Ca/Mg seem to reduce

    incidence and intensity of acute oxaliplatin-in-

    duced symptoms and might delay cumulative

    neuropathy, especially in 85 mg/m(2) oxaliplatin

    dosage. (54; 54) (54).

    Erythropoietin (55) In addition to its well-

    known erythropoetic effect, erythropoietin

    (EPO) has also been shown to be neuroprotec-

    tive in various animal models. In contrast to

    EPO, carbamylated EPO (CEPO) does not bind

    to the EPO receptor on UT7 cells or have any

    haematopoietic/proliferative activity on these

    cells. In vivo studies in mice and rats showed

    that even high doses of CEPO for long periods

    are not erythropoietic. However, in common

    with EPO, CEPO does inhibit the apoptosis

    associated with glutamate toxicity in hippocam-

    pal cells. Like EPO, CEPO is neuroprotective in

    a wide range of animal models of neurotoxicity:

    middle cerebral artery occlusion model of

    ischaemic stroke, sciatic nerve compression,

    spinal cord depression, experimental autoim-

    mune encephalomyelitis and peripheral diabetic

    neuropathy. To date, EPO and CEPO have been

    exciting developments in the quest for the treat-

    ment of various types of neurotoxicity. The

    development of CEPO should continue. (55)

    c. Medical treatment of peripheral ner-vous system neurotoxicity

    A few antiepileptic drugs are acquiring

    increasing popularity for non-epileptic syn-

    dromes, and particularly for the treatment of

    painful neuropathy (56) (57); namely

    gabapentin (58), topiramate, venlafaxine and

    pregabalin (56) (57). As a matter of fact, for

    decades, antiepileptic drugs (AEDs) have been

    used to treat a variety of nonepileptic conditions

    such as chronic pain, psychiatric disorders, and

    movement disorders.

    Venlafaxine (Efexor; Wyeth Lederle), a

    serotoninergic-like anti-depressant, and Topira-

    mate (Topamax; Jansen Cilag), a new anti-

    epileptic drug, shares some evidence of clinical

    activity in the treatment of neuropathic pain.

    Several anti-cancer agents have neurosensory

    toxicity as limiting toxicity of their repeated ad-

    ministration and one of the most recent and

    most widely used is oxaliplatin. No medication is

    presently known to be active against oxaliplatin

    permanent neurosensory toxicity. It has been

    observed that venlafaxine hydrochloride or low-

    dose topiramate could be active against the per-

    manent neuropathy-related symptoms of oxali-

    platin. Both agents allowed pain relief and a sig-

    nificant autonomy improvement so to further

    encourage venlafaxine hydrochloride and topi-

    ramate for the treatment of permanent anti-can-

    cer chemotherapy-induced neuropathies. (57)

    Gabapentin (Neurontin, Pfizer Canada Inc)

    and pregabalin (Lyrica, Pfizer Canada Inc)

    were initially developed as antiepileptic drugs

    and unlike conventional AEDs used to treat

    nonepileptic disorders (e.g., carbamazepine,

    phenytoin, valproate) gabapentin offers the

    advantages of low toxicity and a favorable side-

    effect profile. The largest area of nonepileptic

    use of gabapentin is neuropathic pain, in which

    it has demonstrated efficacy in treatment of

    postherpetic neuralgia, diabetic neuropathy,

    and trigeminal neuralgia. It has also been report-

    ed effective as therapy for several psychiatric

    disorders, most notably bipolar disorder. In

    addition, review of the published literature

    reveals the usefulness of gabapentin in move-

    ment disorders, migraine prophylaxis, and

    cocaine dependence. Future clinical studies will

    provide further insight into the range of condi-

    tions for which gabapentin is effective (58). In

    addition, they were later discovered to be effec-

    tive in the treatment of neuropathic pain, creat-

    ing a relatively novel class of analgesic drugs

    even useful for treating a wide range of neuro-

    logic and psychiatric conditions. Although its

    exact mechanism of action has yet to be deter-

    mined, gabapentin is likely to have multiple

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    effects. Laboratory evidence suggests that both

    gabapentin and pregabalin can inhibit hyperal-

    gesia and allodynia evoked by a variety of neural

    insults, including peripheral trauma, diabetes

    and chemotherapy. Current opinion suggests

    these antinociceptive effects occur because of

    drug interaction with the alpha2-delta subunit

    of voltage-gated calcium channels. Early com-

    parative trials and pooled estimates from meta-

    analyses suggest that analgesic efficacy of

    gabapentin and pregabalin is perhaps slightly

    lower than that of tricyclic antidepressants or

    opioids. However, the most attractive aspects of

    these two drugs include their tolerability, lack of

    serious toxicity and ease of use. Future research

    efforts are warranted to fully understand the

    mechanism of action of these drugs, to clearly

    characterize the safety and efficacy of

    gabapentin and pregabalin in all clinical neuro-

    pathic pain syndromes, and to further explore

    the role of these drugs in the rational polyphar-

    macy of neuropathic pain. (56)

    d. modification of the sensitivity of thetumor to the action of the drug

    Recent developments in the treatment of

    cancer have involved the use of cellular thera-

    pies by the use of carrier cells infected with

    viruses able to interfere with survival/replication

    of cancer cells. The refinements of this

    approach could lead in prospective to minimisa-

    tion of damage to healthy tissues. (59)

    C o n c l u s i o n

    Survival rates for adults and children with

    cancer have increased dramatically over the past

    few decades. Development of new chemothera-

    peutic agents and the expanded use of older

    agents have had a major impact on this celebrat-

    ed improvement. Recent advances in the devel-

    opment and administration of chemotherapy for

    malignant diseases have been rewarded with

    prolonged survival rates. The cost of progress

    has come at a price and the nervous system is

    frequently the target of chemotherapy-induced

    neurotoxicity. Unlike more immediate toxicities

    that affect the gastrointestinal tract and bone

    marrow, chemotherapy-induced neurotoxicity is

    frequently delayed in onset and may progress

    over time. In the peripheral nervous system, the

    major brunt of the toxicity is directed against the

    peripheral nerve, resulting in chemotherapy-in-

    duced peripheral neuropathy (CIPN).

    Chemotherapy can have, however, significant

    toxicity on the central nervous system. Most of

    the information on toxicity comes from prospec-

    tive reports and the adult patient population.

    Methotrexate, cyclosporin, and platinum com-

    pounds are the most frequently cited. It is worth

    mentioning, however, that in spite of more ex-

    haustive studies performed in adults, no

    prospective studies have been done to evaluate

    chemotherapy-induced neurotoxicity in the pe-

    diatric population, and the exact incidence of

    such complications is unknown. Such investiga-

    tion is greatly needed, as it may lead to a better

    understanding of how chemotherapy affects the

    nervous system and ultimately help develop

    more strategies to prevent drug-related neuro-

    toxicity in pediatric cancer patients. (60)

    Chemotherapeutic agents used to treat

    haematologic and solid tumors target a variety

    of structures and functions in the peripheral

    nervous system, including the neuronal cell

    body, the axonal transport system, the myelin

    sheath, and glial support structures. Each agent

    exhibits a spectrum of toxic effects unique to its

    mechanism of toxic injury, and recent study in

    this field has yielded clearer ideas on how to

    mitigate injury. Combined with the call for a

    greater recognition of the potentially devastat-

    ing ramifications of CIPN on quality of life, basic

    and clinical researchers have begun to investi-

    gate therapy to prevent neurotoxic injury.

    In recent years, oxaliplatin-based chemother-

    apy protocols, particularly oxaliplatin in combi-

    nation with infusional 5-fluorouracil/leucovorin,

    have emerged as the standard of care in first-

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    and second-line therapy of advanced-stage col-

    orectal cancer. Although oxaliplatin by itself has

    only mild hematologic and gastrointestinal side

    effects, its clinically dominating toxicity affects

    the peripheral sensory nervous system in the

    form of 2 distinct types of neurotoxicity, an acute

    sensory neuropathy and a chronic, cumulative

    sensory neuropathy resembling that caused by

    cis-platin and completely reversible. Various

    strategies have been proposed to prevent or

    treat oxaliplatin-induced neurotoxicity.

    Chemoprotectants are agents that have been

    developed to ameliorate the toxicity associated

    with cytotoxic drugs and to provide site-specific

    protection for normal tissues, without compro-

    mising antitumor efficacy. Several chemoprotec-

    tant compounds have been studied in recent

    clinical trials. These trials must include suffi-

    cient dose-limiting events for study and assess-

    ment of both toxicity and antitumor effect.

    Preliminary studies have shown promise for

    some agents including glutamine, glutathione,

    vitamin E, acetyl-L-carnitine, calcium, and mag-

    nesium infusions, but final recommendations

    await prospective confirmatory studies. (60)

    The stop-and-go concept uses the pre-

    dictability and reversibility of neurologic symp-

    toms to allow patients to stay on an oxaliplatin-

    containing first-line therapy for a prolonged

    period. Several neuromodulatory agents such as

    calcium-magnesium infusions; antiepileptic

    drugs like carbamazepine, gabapentin, and ven-

    lafaxine; amifostine; a-lipoic acid; and glu-

    tathione have demonstrated some activity in the

    prophylaxis and treatment of oxaliplatin-

    induced acute neuropathy.

    However, randomized trials demonstrating a

    prophylactic or therapeutic effect on oxaliplatins

    cumulative neurotoxicity are still lacking. The

    predictability of neurotoxicity associated with

    oxaliplatin-based therapy should allow patients

    and doctors to develop strategies to manage this

    side effect in view of the individual patients clin-

    ical situation. This is of increasing importance,

    because the addition of bevacizumab to FOLFOX

    will conceivably further prolong the progression-

    free survival achieved with FOLFOX so that neu-

    rotoxicity and not tumor progression could be-

    come the dominating treatment-limiting issue in

    the first-line therapy of advanced colorectal can-

    cer. (61)

    A more specific clinical problem is represent-

    ed by the treatment of the neuropathic pain and

    new drugs and treatment algorithms in the man-

    agement of neuropathic pain have been pro-

    posed. New information on opioids (tramadol

    and buprenorphine) suggests benefits in the

    management of neuropathic pain and has

    increased interest in their use earlier in the

    course of illness. Newer antidepressants, selec-

    tive noradrenaline and serotonin reuptake

    inhibitors (SNRIs and SSRIs) have evidence for

    benefit and reduced toxicity without an eco-

    nomic disadvantage compared to tricyclic anti-

    depressants (TCAs). Pregabalin and gabapentin

    are effective in diabetic neuropathy and pos-

    therpetic neuralgia. Treatment paradigms are

    shifting from sequential single drug trials to

    multiple drug therapies. Evidence is needed to

    justify this change in treatment approach. Drug

    choices are now based not only on efficacy but

    also on toxicity and drug interactions. For this

    reason, SNRIs and gabapentin/pregabalin have

    become popular though efficacy is not better

    than for TCAs (15).

    A future avenue of investigation includes the

    identification of patients at higher risk for the

    development of peripheral neuropathy and cen-

    tral nervous system toxicity (17) based on their

    genotype. Identification of these higher-risk

    patients may enable us to devise prevention

    strategies prior to the onset of this potentially

    debilitating complication. (62)

    With their significant impact on quality of life,

    neurotoxicity treatment and prevention are be-

    coming increasingly important issues in the care

    of patients with cancer (63); physicians should

    be aware of the potential harmful effects of pre-

    scribed therapies as well as of the therapeutic

    tools in the overall management of their pa-

    tients.

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    165

    Indirizzo:

    Vidmer Scaioli

    Fondazione IRCCS Istituto

    Neurologico C. Besta Milano

    Via Celoria 11 - 20133 Milano

    Tel.:+390224942-2275

    e-mail: [email protected]

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    167

    Cisplatin, Oxaliplatin, Concomitant

    administration

    Reduced incidence

    of retinopathy

    Fair

    Table 4.

    Neuroprotective Chemo- Strategy Expected result * Strength

    agent therapeutic drug of evidence

    Vit E

    Oxaliplatin Concomitant

    administration

    Reduced incidence

    of sensory positive

    symptoms

    GoodN-acetyl-cisteine

    Various

    Oxaliplatin

    Various

    Pretreatment

    Concomitant

    Concomitant

    Reduced severity of PN

    Delayed cumulative toxicity

    Delayed cumulative toxicity

    Weak

    Fair

    Fair

    Erythropoietin

    Chelants Ca/Mg

    Melatonin

    Various Subsequent;

    Concomitant

    Reduced severity;

    Post-chemotherapy

    treatment

    GoodAntiepileptic

    drugs

    Various Concomitant /

    Subsequent

    treatment

    Increased tolerability GoodGabapentin;

    pregabalin