Levamisole and sodium diethyldithiocarbamate

TIPS - S e p t e m b e r 1081

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cholinergic activity of the agent leading to

Levamisole and s o d i u m d iet h yl d it h ioca rba m a t e G. Renoux LahoraUn. '

tion, the repeated although inaccurate

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th,hzolc enjoyed wide use as a broadspectrum anthelmintic, prior to a report of its effects on immune responses s. This first report initiated enthusiastic clinical investigation, as levami.~le was the first simple chemical endowed with immunoenhancing activities, and hence it opened a new field in immunotherapy. The oral administration of levami~le had a practical advantage over many other immunotherapies, as many patients prefer tablets to injections which may be painful. The results of almost a decade of publications have been summarized in recent reviews and show that ~idespread clinical testing has produced inconclusive, and contradictory evidence concerning the beneficia~ effect of the agenP ~L An analysis of the possible causes of conflicting data should help further studies and the development of active agents. Most lab~mm~ry testing involves chemotherapy-like experiments to determine whether Icvamisole is able to cure an animal of cancer or limit the incidence of turnout take. By contrast, little infiwmation i.~ obtained on the precise mechanism of levamisole action on the immune system. The pharmacology of levami~le is not taken into account seriously enough. The dos-dependent effect of levamisole on alkaline phosphatases could be the mechanism which modifies macrophage ly~somal activity in the processing of antigen, and the cause of the inhibition induced by repeated administration of the drugL Inducible aryl hydrocarbon hydroxylase is both sensitive to levamisole and genetically modulated, and the level of such liver microsomal mtmo-oxygen:tses could influcritic and the uptake of Icvami~le~s. Levamisole possesses an imidazolc moiety, the cholincrgic-like activities of which filvor, in addition to pharmacological effects on cateeholamines, augmented levels of cGMP and. therefore, the proliferation of neoplastic cells as well as lymphocytes 4. immunotherapies. The general mode of action of levami~le seems, therefore, to be a balThe les~n of levamisole ance between the increased production of I~evamisole. the/evo-isomer of 2, 3. 5, hormone-like factor(s) inducing oifferenti0-tetrahydro-6-phenylimidazo (2. I-b)- ation among the T-cell lineage s and the

The known limitations of conventional cancer therapies have provided the impetus for the utilization of agents able to mobilize immune mechanisms against ncoformed cells. At present, cancer immunotherapy goes awry because agents. mostly of bacterial origin, of half-proven activity demonstrated perhaps in unwisely chosen models, are offered to the oncologist. In turn. clinical testing is evalu:tted in lermsofsurvival rate with, apart from a few exceptions, no attempt to correlate clinic:d dala lind immunological changes. In other ~¢,rds. empiricism has preceded knowledge, a not-uncommon situation in biological sciences. A reflection on the work of pioneers in this field has led to the consensus that more information al~mt the function of the immune system and how to regulate it is required to develop agents capable of modi~,ing the immune machineu, according to the needs of the clinical situation. Immunotherapeutie agents intend to modi~' immune responses and therefore, act on the host. A therapy acting on the host and not directly against th~ intruder is outside the t radi~ional domains of pharmacology of chemotherapeutic agents, Immunopharmacology is the new di~ipline ambitiously aimed at the study of the large field of pharmacological regulation of the immune system, and ,berapeutic applications. However. immunomodifiers also need to be submitted to a classical pharmacological study, as does any other drug. I1: an agent can modify the function of a given I.vmphocyte subset, it should simultaneously inlervcnc on other cellular systems in the same way that most mediators. ht~rmones and catecholamines act ~imilarly tm different cells. ! chcmse the levamisolc story to illustrate the need for pharmacological lind immtmopharmatx~logical lesting, prior to in-depth clinical application. I should stress, however, that a similar discussion could be drawn from the trials with other

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cell proliferation. As yet, no attempt has ~ e n made to underst::nd how t h e ~ conflicting activities could interfere or intervene to modify immune function. Such lack of information renders difficult the practical use of the drug. In addi-

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statement that levami~le is an 'antianergic' drug s, even if the immunomodifying activity was sho~'n on normal, healthy

mice a, has contributed to a misunderstandingofthe Ix~tentiai usefulness of the agent. In spite of 'black holes' on its mode of action, the real strong need for active cancer therapy has triggered a variety of clinical trials with levamisole. Unfortunately, ;.ae majority of such test have been performed without reference to the available laboratory data. No attempts have been r~mde to determine the doses of levami,,ole active on the immune system in man, and to, use the immunoassays potentially u~ful fiw such a determination. The need for evaluating the immune status of the patient before treatment and periodically monitoring it during treatment to evaluate the effectiveness of the drug because genetic factors modulate the activity of levamisole, is recognized in few reports. As a consequence, no special attention is paid to the immunodcpression due to chronic administration which is likely t~ be linked with an increase in suppressor activities. No one cares of the warnings implicit in the evidence that levamisole c a u l s an ~::,,reased namber of tumour takes in softie murine cancers. In addition. at least in ~:l'r experience, .some 'failures" of treatmen~ ~,-i,h levami~le could be associated wirtt a~ incorrect intake of the drug, as the clinici~, has no control of the oral administration. In brief, unruly testing has led to anarchy, and conflicting results, in this regard, a recent publication ~ is all the more interesting since it shows that clinical assays based on the pattern of chemothcrapeulic trials, gives results opposite to those expected. This general situation evidences the pitfalls set by a lack of understanding of the modes of ~:tion of an agent on the immune system and other regulatory systems, As a practical result, inaccurately conducted tests may dampen the enthusiasm both for an otherwise excellent agent and for a rational, scientifically-based immunotberapy. The requirements for an augmenting agent An augmenting agent should have the following qualities: (1) no carcinogenicity or tumour enhancing influence; (2) no

IT I'S - Sepn,mh(,r i 981

antigenicity and sensitizing effects; (3) known effects on the various populations and subsets of immunocompetent cells: (4) known toxicity and pharmacological effecls. These requirements, evolved frol,q recent discoveries, would eliminate most of the inconsistencies and inconveniences. Progress in determining the molecular effects of an agent on cell function will serve as a guide for clinical trials, including therapy of turnouts in laboratory animals. Clinical testing should ignore the conventional protocols as applied to chemotherapy because augmenting agents act on the host and their eflica~' is strongly host-dependent, The reactivity of immunocompetent cells to the agent is a critical determinant of the efficacy of the immunomodificr, the activity of which is modulated by genetic factors, sex, age, nutrition and ag~ciated therapies. Therefore. a clinical protocol should definitely be based upon the relationships between clinical chaages and convenient immunoassays. Thanks to progress in clinic,~l immunology, such as monodonal antibodies tu human lymphocyte subsets, if one can develop pharmacological agents which selectively stimulate one or the other lympbocyte subsets in the mouse, it could become easier to translate these experimental data into the clinical experience. The compliance of DTC The development of sodium diethyldithiocarbamate (DTC) has resulted from such thoughts, and has emerged from the search for a synthetic, chemically-defined compound devoid of cholinergic-like effects, which are more deleterious than useful in immunotherapy ~. The pharmacology and toxicity of DTC has been studied extensivelyTM. A t high doses, above 200 mg kg -+, DTC potentiates barbital sleep, inhibits dopamine beta-hydroxylase and depresses brain norepincphrine levels. A t doses of up to 600 mg kg -~, it induces retrogade

amnesia of trained passive avoidance, and cerebral seizure activity in the rat. DTC also prevents the development of chemically-induced diabetes. As a chelating agent, DTC is used in the treatment of metal poisoning without toxic or untoward side-effects at daily doses of 30-50 mg kg-' body weight. A recent NCI Report evidences the absence of car¢inogenieity of the chemical daily administered in the feed for 104-109 weeks to rats and mice. The incidence of some spontaneous tumours was lower in

the dosed g n m l ~ than in the corresponding control grou,~. D T C ~ as al~) h)und t o e x e r l a protective effect again~ a ~ariet~ of chemically-induced malignant turnouts. and ag;dnst ionizing radiation, in addition,

clinical "mmunothcrap.~ ol c,,nccr t,~ removing Ih¢ currcnl cn]plrl¢l,qn ~h;Lh I+¢trayed man} Icgitlmatc hope., ('limclan~ ~hould hc pro, ided ~:ilh enough data Io permit their own choice ,,| ~n DTC possesses m |li|,o atlivity against a immunomodif),mg a/zcnl, taking into number ,)f h;~clcria and parasites. account the patient slalu ~, and the other We h)und commercially as'ailable I)TC preserih~d drugs, h,r example to treat an Io hc conlaminatcd ~ilh 8-11)% o l a rcd- organ dysfunction ,~hich could t~. prc,,¢rn dish, toxic impurity. In its purified form togvlhcr ~lilh the immune dP~r(k..i Ih',~(lnstitut Mericuxl, DTC is essentiall.~ p~cs~ in clinical immtlnoh,g), ha~ alrc,ld'+ devoid of toxicity and side-effects for use ;it pro~idcd Iml~)rlanl nc~ in|lnUllo~ls,~l~,,~ t4) immunostimulam doses ((1.5-25 mg kg i). determine" cellular marker'+ and |unction At t h ¢ ~ dc~es, DTC evidences a unique Kno~ledgc on the selectl'.c cl|lcac-; of ,in influence on the immune system in induc- ;igcnt associated ~ i l h thc nlonih)rm~ }| ing the recruitment of T cells from undif- indnidual p;iticnl's immune rc~l~m~.'~ feremialed percursor cells. This influence ~hould achie~c the alm~ oi inlnlune,}thLfdp~, is medialed through the increased %vn- to treat, and c~cn curc. cancer. thesis, even in congcnitall) at h~ mic mioe. ()f Aim) it ~hould I~: ,qrc+,~cd thal hormone-like faclors acti~,e on the T-cell lherapcuticall,,-induccd moddicJtlon ,el lineage, across the species harrier +. the impaired immune sx,,tcm i+ the ultiDTC induces T cells to generate mate hope fi,r patient,, affcclcd ¢+ith enhanced levels of cytotoxic aclivily' and immum~lcficicnc-~, aut,+immunc dl,,cd'~'. resp(m.~s to alk)antigens, macrophagcs and chorale inlcction, and ~,.lhl) c,,cn ,p+_'in+,.:. mont~,'tes b) parlicipatc in delaycd-Lxpe hypersensitivi~,, resting T cells to dcvelop Reading lisl suppremiv¢ aclivities, and B cells to ~ecrel+ 1 Hrtnckcr. H , X|our,d.~-n.H T ~.n~r.,cnK X?+

antibodies of the lgG class. Thcsc activities are probably associated with an increase in the number of Lyt- 1~ T cells which Wos ide the signal for help to increase the response of other cell sub~ts when needed. DTC is devoid of direct influence on B cells, nonspecific polyclonal actisity, and in vitro augmenting effects". The agent has no sensitizing or pyrogenic influence. In contrast with other ~)-cailed immunopotcntiators, the chronic administration of DTC gives ,~ignificant responds as do single treatments. PreliminaQ phase I and phase il studies in man reveal that d o ~ s from 0.5 to 5 mg kg -~ have no influence on biochemical and hematological parameters, or non-immunological clinical signs. T h e ~ d o ~ s restore tl~e T cell mitogen-induced responses tO the Ic')el~,ol

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It seems now that the combined pharmacological and immunopharnlucological study of DTC results in consistent findings. which demonstrate its unique activity on cells of the T-cell lineage without unto~ ard side-effects, at least at immunostimulant doms. At present, other agents are being studied hy an approach similar to that used with DTC. Such an approach will ser~e

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