REVIEW ARTICLE Drugs 48 (5) 667~77, 1994 OO12~667 /94/0011·0667 /S 11.00/0

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Interleukins Clinical Pharmacology and Therapeutic Use

Walter E. Aulitzky, Martin Schuler, Christian Peschel and Christoph Huber Division of Haematology, IIIrd Department of Internal Medicine, Medical School of the Johannes Gutenberg University, Mainz, Germany

Contents Summary ........... 667 1, Pharmacokinetics of Interleukins , , 668 2, Pharmacodynamics of Interleukins 669 3, Clinical Results of Interleukin Studies , 670

3,1 Interleukin-1 670 3,2 Interleukin-2 671 3,3 Interleukin-3 672 3,4 Interleukin-4 673 3,5 Interleukin-6 674 3,6 Interleukin-11 675

4, Conclusion .... 675

Summary With interleukins (lL), a new class of potential drugs has been introduced into clinical research. These signal peptides are involved in the regulation of many physiological and pathophysiological processes. IL-I, -2, -3, -4, -6 and -11 have been tested in clinical trials, The growth promoting, growth inhibiting or im­munomodulatory activities of interleukins represent the theoretical basis for large scale clinical testing, predominantly in malignant disease. Dose-dependent ef­fects on numbers of peripheral blood cells and recovery from bone marrow failure have been demonstrated for IL-I, -3, -6 and -11. Phase III trials are in progress to determine their value for clinical practice. However, investigations on the immunomodulatory activities proved to be more difficult. This is because key mechanisms for successful treatment of malignant disease by immunomodulation are not clearly defined and the methodology for assessment of immunostimula­tory effects is not well established, Besides treatment of renal cell carcinoma and malignant melanoma with IL-2, no successful trials have been reported. However, phase I clinical trials with IL-I, IL-4 and IL-6 have just been completed. Thus, it seems too early to conclude on their therapeutic potential.

Interleukins (IL) are a class of signal peptides which represent a major communication network in living organisms,lI,2] These molecules act as autocrine, paracrine and endocrine hormones and

are involved in the regulation of a variety of physiological and pathological conditions such as normal and malignant cell growth, recognition and elimination of pathogens by immune cells and in-

668 Aulitzky et al.

Table I. Pharmacokinetic data of clinically administered interleukins

Cytokine Route Serum t1;2 Concentration MTD Reference

IL-1a IV bolus NO At MTO not detectable 0.3 ~g/kg 6, 7

IL-1~ IV NO 0.1 ~g/kg 8

IL-2 IV bolus 12.9 min (a-decay) Range 650 U/ml 1 MU/kg 9, 10

85 min (~-decay) (dose-dependent)

CI Steady-state by 2h, renal Range 40 U/ml 3000 U/kg/h 9,10,11 clearance 120 ml/min (7.2 Uh) (dose-dependent)

SC/IM 30% of activity transported to 1-10% of immediate Conc 9 blood, Cm,x 90-240 min after after IV bolus injection

IP 6.3h (IP 22h) 500-fold lower than IP Conc 0.3 mg/m2 9, 12 (range IP 2800 U/ml) 8 MU/m2 13,14

Intrapleural NO NO 24 MU/m2 15

Intrathecal 4-8h (in CSF) NO NO 16

IV bolus and CI in 1 MU/m2 17 children 3 MU/m2 18

IL-3 IV bolus 23 min 15-30 ~g/L (peak) Not reached 19 (>500 ~g/m2)

4h CI 13-53 min (dose-dependent) Range 1 0-20 ~g/L Not reached 20 (dose-dependent) (>1000 ~g/m2)

SC 210min 2-1 0 ~g/L (peak) Not reached 19

IL-4 IV bolus (3 times daily) NO NO 10 ~g/kg 21

SC NO NO 5 ~g/kg 22

IL-6 SC 4.2h Range 1-2 ~g/L 10 ~g/kg (7) 23

IL-11 SC NO (Preliminary data) 50 ~g/kg 24

Abbreviations: CI = continuous infusion; Conc = concentration; Cm,x = peak plasma concentration; CSF = cerebrospinal fluid; IL = interleukin; 1M = intramuscular; IP = intraperitoneal; IV = intravenous; MTO = maximum tolerated dose; NO = not done; SC = subcutaneous; t1;2 = half-life.

flammation. The introduction of recombinant gene technology made many of these molecules avail­able in large quantities and brought up the possi­bility of large scale testing of interleukins for their therapeutic potential in a variety of malignant, in­fectious and inflammatory diseases. So far, treat­ment results have been published for IL-I, -2, -3, -4, -6 and -II.

Introducing these new agents challenged clini­cal research by the extraordinary complexity of their biological activities: all ILs are pleiotropic and act on a variety of cell types. In addition, ILs can stimulate or block the production of other cytokines with similarly pleiotropic activities.[3-5] Therefore, the pharmacodynamics of interleukins are not easy to predict from preclinical data.

This review discusses pharmacological prob­lems of clinical cytokine research. In addition, the

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results of clinical trials published so far on treat­ment with interleukins are briefly summarised.

1. Pharmacokinetics of Interleukins

Studies on the pharmacokinetics of interleukins revealed similar characteristics (data and refer­ences in table I). ILs are proteins with molecular weights ranging from 15 to 28kD. They have to be administered parenterally. Studies have been pub­lished mostly on the intravenous or subcutaneous routes of administration. For IL-2, additional stud­ies on the feasibility of the inhalation, in­traperitoneal, intrapleural and intrathecal routes of administration were published.

Very short serum half-lives of less than 1 hour have been consistently reported after intravenous bolus injection. For IL-2 and IL-3, biphasic elimi­nation has been described. During the a-phase the half-lives are very short. This phase is assumed to

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Interleukins

represent distribution into the extracellular space. In addition, binding to specific receptors should influence this rapid elimination during the first hours after administration. Thereafter, more pro­longed elimination, with half-lives in the range of 1 to 2 hours, was observed. In animal models, this phase mainly represents renal elimination.l25]

After subcutaneous injection, prolonged ab­sorption has been described. Peak serum levels are in the range of I to 10% of those reported after intravenous bolus injection. In addition, the peak serum concentration is delayed and serum half-life is prolonged to approximately 4 hours. IL-2 serum concentrations were also detectable subsequent to aerosolised and intraperitoneal adrninistration.l9,26] The maximum tolerated doses (MTD) of different interleukins are highly variable and range from 0.3 /lg/kg for IL-I to 50 /lg/kg for IL-II.

In contrast to conventional drugs, pharmacoki­netic data on interleukins have not proven to be helpful for the rational design of phase II and phase III efficacy trials. In particular, serum levels of ILs correlate poorly with their biological, clinical or toxic effects. For instance, no IL-I serum levels are measurable even after administration of maximum tolerable doses of this cytokine.l6] This is probably because postreceptor effects of interleukins follow different kinetics from serum concentrations)27] Induction of the synthesis of IL-2-dependent pro­teins peaks 24 to 48 hours after injection of the cytokine, which is more than 20 hours after se­rum peak concentrations of the cytokine were reached)28] Therefore, a rational design of dosage and schedule in clinical IL trials should be based on biological rather than pharmacokinetic consid­erations.

2. Pharmacodynamics of Interleukins

Interleukins tested so far have been investigated on the basis of 2 biological properties: IL-I, -3, -6 and -11 directly and/or indirectly stimulate the growth of haemopoietic cells. IL-I, -2, -4 and -6 are considered, in addition, to be potent im­munostimulatory agents. The measurement of the growth promoting activities of interleukins on

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669

thrombopoiesis and leucopoiesis did not pose methodological problems in clinical trials. In­creases in leucocyte and thrombocyte numbers or time to recovery from bone marrow failure in­duced by cytotoxic agents are well established parameters for establishing dose-response rela­tionships of pharmacodynamic effects of these haemopoietins.

Considerable controversy exists, however, on both utility and the optimal means to assess for immunostimulatory functions. Beneficial effects of immunostimulatory cytokines have been dem­onstrated in a variety of animal models of malig­nant and infectious diseases)29-34] However, the experimental animal tumour models used, in par­ticular, poorly reflect the biology of malignant dis­ease in humans. In addition, the crucial target func­tions for the clinical effects observed in these studies are far from clear. Although the use of gene knockout mice might provide more stringent infor­mation on critical immune effector functions in­volved in immune elimination of infectious and malignant disease, the current hypotheses for clin­ical trials might be based on misleading informa­tion. Therefore, at the beginning of a clinical trial programme for interleukins it is not clear which immunostimulatory activity of a cytokine is cru­cial for clinical success in target diseases chosen.

The second open question is how the relevant immunostimulatory functions can be measured in vivo. Most investigations have focused on assess­ment of either cell function or on the analysis of the regulation of cytokine dependent genes. Exten­sive investigations have been reported on the ef­fects of IL-2 on numbers and function of natural killer (NK) cells, T lymphocyte subsets and mye­loid cells. These IL-2 effects on haemopoietic cells have been reviewed in Drugs)35]

Most of the studies on cellular functions are re­stricted to analysis of peripheral blood cells. Im­mediately after IL-2 injection, a sharp decrease in cell numbers was reported.l 10] This reduction af­fects predominantly those cell types that are ex­pected to respond to the cytokine.l36] Most inves­tigators assume that this immediate reaction is due

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670

to increased adherence to the endothelium and/or migration into the tissues. In this context, increased expression of adhesion molecules upon stimula­tion with cytokines has been shown in various cell typesJ37]

Thus, it seems likely that cytokine-induced ac­tivation of immune cells is accompanied by their shifting into inaccessible compartments. This phe­nomenon would raise serious doubts about the dose-response relationship of cytokine effects es­tablished on the basis of peripheral blood cell data. The failure to show a reproducible and clear dose­response relationship and/or a clear correlation of immune parameters to clinical response in many clinical trials indirectly supports this view.

The second approach to measure biological re­sponse is the assessment of the induction of cyto­kine-dependent genes or measurement of cytokine­induced soluble molecules in the serum. Increased synthesis of IL-5, interferon-y (lFNy), tumour ne­crosis factor-a (TN Fa) and TNF~ has been de­scribed after administration of IL_2.l38,39] How­ever, I study measuring mRNA and protein levels of cytokines in parallel in peripheral blood cells revealed interesting differences. Whereas mRNA of the lymphocyte-cytokines IFNy and IL-2 is readily induced by IL-2 doses of as little as 50 OOOU

Table II. Clinical toxicity of interleukin-1 a l61

Toxicity Dose Maximal Dose-limiting effect WHO toxicity

grade

Fever, chills II

Myalgia, arthralgia

Headache II

Somnolence (+) I + (1 pt)

Nausea, emesis + II

Abdominal pain + III + (1 pt)

Hypotension + IV + (1 pt)

Oedema +

Cardiac ? IV +(1 pt)

Dyspnoea + III

Renal + II +

Confusion ? III + (2 pts)

Abbreviation and symbols: pt = patient; + denotes present; - denotes absent; ? denotes not sure.

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Aulitzky et al.

subcutaneously, higher doses increased in addition the synthesis of inflammatory cytokines such as TN Fa and IL-6. This increased expression of in­flammatory cytokines was accompanied by the oc­currence of toxic effects of the treatment. Measure­ments of serum levels of these cytokines did not reveal any detectable changes in these patientsJ4]

Treatment with cytokines leads not only to the induction of agonist cytokines, but also to in­creased synthesis of antagonistic proteins. Induc­tion of the IL-I receptor antagonist protein (lL­IRA) by IL-2 and IL-4 treatment has been reported.l3,21] Regulation of transforming growth factor-~ (TGF~) mRNA in peripheral blood cells was observed upon combined IFNa and IL-2 treat­ment. A dose-dependent induction of soluble IL-2 receptor protein (IL-2R) even at very low doses of IL-2 has been describedJ3]

3. Clinical Results of Interleukin Studies

3.1 Interleukin-1

A direct antiproliferative effect of IL-I against human tumour cell lines and murine tumours,[40,41] as well as an activation of effector cells[42] and induction of secondary cytokines with anti tumour or immunostimulatory potential,[43] have been demonstrated in vitro and in vivo. Further, IL-I protects and restores haemopoiesis from radiation­or chemotherapy-induced damageJ44,45] There­fore, malignant tumours and various states of bone marrow failure were studied as possible indica­tions for clinical application of this cytokine.

The results of phase I trials of both IL-I ~ and IL-l a monotherapy as well as in combination with chemotherapy for prophylaxis of cytopenia have been published.l6-9] IL-I appears to be a highly toxic compound and the adverse events following systemic administration of the cytokine are com­parable with that of TNF or high dose IL-2 (tables II and III). Fever, chills and other constitutional symptoms occurred in the majority of patients. In addition, hypotension, capillary leak syndrome and central nervous symptoms were observed after treatment with both IL-I a and IL-I~.

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Interleukins

Table III. Clinical toxicity of interleukin-1 ~[81

Toxicity Dose Maximal Dose-limiting

effect WHO toxicity grade

Fever, chills

Myalgia, arthralgia

Headache

Somnolence

Nausea, emesis

Abdominal pain

Hypotension + + (2 pts)

Hypertension ?

Dyspnoea

Abbreviation and symbols: pt = patient, + denotes present; - denotes absent; ? denotes not sure.

Haematological effects ofIL-l, especially dur­ing the first days of treatment, were dose-depend­ent increases of absolute leucocyte numbers. Dif­ferential counts revealed an increase of segmented neutrophils and neutrophilic bands in peripheral bloodJ6,8] Ex vivo granulocyte function tests dem­onstrated an increase or normalisation of locomo­tive and respiratory burst responses following IL-l administrationJ8,46] Platelet counts decreased dur­ing IL-l treatment at doses of 0.1 /-lg/kg or more, whereas an average increase of 70% above base­line values was observed between 1 and 2 weeks after cessation of treatment. These peripheral blood changes were in concordance with an ele­vated bone marrow cellularity observed in post­treatment aspirates, with an increase in more ma­ture myeloid cells as well as in the number of megakaryocytes. Alteration of various endocrine and metabolic parameters, especially transient hypoglycaemia, has been observed, none of them reaching clinical significance. All values returned to baseline within 3 weeks of treatmentJ6,81

No antitumour responses were found in 28 pa­tients treated with IL-l mono therapy in a phase I trialJ61 In 4 patients with severe aplastic anaemia, no significant changes in blood counts or marrow cellularity could be obtainedJ471 Administration of IL-l following myelosuppressive doses of fluoro­uracil resulted in fewer days of neutropenia; how­ever, this difference did not reach statistical signif-

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671

icanceJ81 Thrombocytopenia resulting from high dose carboplatin was significantly less severe and of shorter duration after additional treatment with IL-l at doses of 0.1 and 0.3 /-lgikg, respectively, than after chemotherapy aloneVl

3.2 Interleukin-2

The clinical application of IL-2 has been the topic of a comprehensive review published in DrugsJ351 A summary of this review is given here.

IL-2 acts as a pleiotropic mediator within the immune system, having a variety of effects via spe­cific cell surface receptors. The interaction ofIL-2 with IL-2 receptors induces proliferation and dif­ferentiation of a number of T lymphocyte subsets, and stimulates a cytokine cascade that includes various interleukins, interferons and tumour ne­crosis factors. Antitumour effects ofIL-2 appear to be mediated by its effects on natural killer, lymphokine-activated killer (LAK) and other cyto­toxic cells. In patients, the most common pharma­cological effects of IL-2 therapy appear to be eosinophilia, acute lymphopenia followed by re­bound lymphocytosis, and induction of LAK and natural killer cell activity. Increases in other cytokines have been reported, e.g. IL-3, -4, -5, and -6, TNFa and -~ and interferon-yo In vivo and in vitro effects ofIL-2 seem to be dependent to a large extent on the environment; many studies have re­ported conflicting results, perhaps due to diverse populations of effector cells, the availability of other cytokines that have synergistic or inhibitory influences, and the dosage regimens used.

In patients with metastatic renal cell carcinoma who respond poorly to conventional therapy, IL-2 therapy results in objective responses of 20% on average, with complete responses in about 5%. The duration of response varies considerably, but can be durable (> 12 months), with some patients' com­plete responses lasting for >60 months. It is un­clear at present whether higher dosage regimens improve clinical response, or whether combination therapy with other agents and/or adoptive therapy is beneficial. No controlled studies demonstrating a survival benefit are available.

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672

Patients with metastatic malignant melanoma receiving IL-2 as monotherapy show an average objective response rate of 13%; however, objective response rates increase to 30% if IL-2 is used in combination regimens. In should be noted that the different response rates observed with mono­therapy and combined treatment are not based on controlled trials.

Patients with colorectal carcinoma, ovarian cancer, bladder cancer, acute myeloid leukaemia or non-Hodgkin's lymphoma appear to achieve lower response rates to IL-2. Much research is focused upon the discovery of reliable predictors of clinical response, and upon optimum dosage schedules and methods of administration.

Adverse effects associated with IL-2 therapy can be severe, with cardiovascular, pulmonary, haematological, hepatic, neurological, endocrine, renal and/or dermatological complications fre­quently requiring doses to be withheld. Typically, these adverse reactions resolve rapidly with cessa­tion of IL-2 therapy, and may be reduced consider­ably with local or subcutaneous administration.

3.3 Interleukin-3

The rationale for the clinical investigation of IL-3 is its profound multilineage growth- and dif­ferentiation-inducing effect on early haemopoietic progenitors in vitro.[48] To date, no lineage-specific megakaryocytic growth factors have been identi­fied, the main impetus for various phase I and II trials in patients with primary and chemotherapy­induced pancytopenia is the promotion of mega­karyocyte progenitor cell proliferation by IL-3.

Generally, in phase I trials IL-3 was well toler­ated and toxicity was mild (table IV). The MTD has not been reached in several monotherapy tri­als)19,20] Haematological effects of IL-3 adminis­tration in patients with normal haemopoiesis com­prised a dose-dependent increase in leucocyte and platelet counts. Differential blood tests revealed a profound increase in eosinophils of up to 50-fold compared with baseline, and an increase in the numbers of immature leucocytes at higher dose levels. Sequential bone marrow biopsies obtained

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Aulitzky et al.

before and after IL-3 treatment demonstrated an elevation of cellularity along with increases in eo­sinophils and megakaryocytes, as well as a shift to the left in cells of the myeloid lineage) 19,49]

Erythroid and multilineage bone marrow pro­genitors increased following IL-3 therapy as well as DNA-synthesis rates of early and late granulo­cyte macrophage progenitor cells. Peripheral blood erythroid progenitors were reduced, whereas peripheral blood multilineage and granulocyte macrophage progenitor cells were increased. Peak levels were observed during IL-3 treatment com­pared with those at the end of therapy)501 Biologi­cal effects observed following IL-3 treatment were a moderate increase in acute-phase proteins C­reactive protein (CRP), fibrinogen and haptoglobin occurring simultaneously with febrile reactions. Fur­thermore, serum levels of immunoglobulin M (lgM), ~2-microglobulin and soluble IL-2R in­creased after IL-3 treatment, whereas serum levels of TNF and IL-6 as well as cell surface expression of CD 11 a-c and CD54 on monocytes remained un­changed in one studyJ191

In another trial of IL-3 administered after che­motherapy for lung cancer, serum TNF and IL-6 levels were increased after higher doses of IL-3, [51] while in a third study of patients receiving chemo­therapy for ovarian cancer only TNF serum levels were slightly elevated)52] Mild local reactions

Table IV. Clinical toxicity of interleukin·3118,19]

Toxicity Dose Maximal effect WHO

grade

Fever, chills II

Bone pain (+) III

Headache + III

Nausea, emesis (+)

Oedema

Cardiac IV

Dyspnoea III

HepatiC (+)

Flush, erythema

Dose-limiting toxicity

+(1 pt)

+(1 pt)

+(1 pt)

Abbreviation and symbols: pt = patient; + denotes present; - denotes

absent.

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Interleukins

consisting of erythema and oedema were observed at the injection siteJ19]

Effects of IL-3 treatment in a phase I study of 24 patients with primary bone marrow failure (13 myelodysplastic syndrome [MDS], 8 severe aplas­tic anaemia [SAA]) were increases of neutrophils in 8 patients, of eosinophils in 6 patients, of plate­lets in 3 patients, and of reticulocytes in 2 patients. Peak values were observed within 2 to 4 weeks after initiation of treatmentJ20]

In another phase IIII trial, 9 patients with MDS and transfusion-dependent cytopenias were treated with 2 doses of IL-3. A 1.3- to 3.6-fold in­crease in leucocyte counts was observed in all pa­tients; mean absolute neutrophil counts were sig­nificantly elevated by the cytokine. In 2 of 4 severely thrombocytopenic patients, a prolonged period without platelet transfusion requirements was obtainedJ53] In some patients with MDS an increase of morphologically atypical blast cells oc­curred, which was reversible on stopping IL-3 therapyJ20,53]

Of 9 patients with aplastic anaemia treated at 2 dose levels of IL-3, an increase in platelet counts was induced in 1 and an increase in reticulocyte counts in 4 patients. Leucocytes temporarily in­creased 1.5- to 3.3-fold in 8 patientsJ54] In a study of 19 patients with small-cell lung cancer, IL-3 was administered in escalating doses after the second course of 2 different schedules of myelotoxic che­motherapy. In this setting, dose-limiting headaches were observed in 2 of 4 patients treated with 16 ~g/kg ofIL-3. There was no significant difference in leucocyte, neutrophil and platelet nadirs be­tween the courses with and without adjunctive IL-3. However, after one of the chemotherapy regimens, the median duration of neutropenia below 500 cells/~l was significantly shortened by IL-3 treat­ment. At doses of 8 ~g/kg or more, IL-3 acceler­ated leucocyte recovery, as did the cytokine at a dose of 8 ~g/kg with respect to platelet recov­eryJ51]

Effects of IL-3 on haemopoietic recovery after chemotherapy with carboplatin and cyclophosph­amide were studied as well in 20 patients with ad-

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673

vanced ovarian cancer. No difference between in­travenous and subcutaneous administration of the drug was observed. At doses of 5 ~g/kg or more, leucocyte, neutrophil and platelet recovery was significantly increased compared with control cy­cles without IL-3. Effects on reticulocyte counts were less pronounced. Significantly fewer chemo­therapy cycles with IL-3 had to be postponed be­cause of delayed bone marrow recovery than con­trol cycles without IL-3. Platelet transfusion requirements were also reduced by IL-3 therapy. However, the number of transfusions without IL-3 was too low to draw a firm conclusionJ52]

Administration of IL-3 in combination with granulocyte-macrophage colony-stimulating fac­tor (GM-CSF) following myelotoxic chemother­apy was shown to increase mobilisation of CD34+ progenitor cells as well as myeloid, erythroid and multipotential progenitor cells into the peripheral blood compared with chemotherapy aloneJ55] Whether peripheral blood progenitor cells mobil­ised with IL-3 and GM-CSF are superior to those mobilised with granulocyte colony-stimulating factor (G-CSF) or GM-CSF alone cannot be de­cided from the present literature.

Administration of IL-3 in patients undergoing autologous bone marrow transplantation resulted in substantially higher toxicity. The MTD in this setting was 2 ~g/kg. No evidence of earlier haemo­poietic recovery than in historical control patients treated with GM-CSF was observed in this phase I trialJ56]

3.4 Interleukin-4

IL-4 is an immunomodulatory cytokine pro­duced predominantly by T cells, with B cell and T cell regulatory functions. In B cells, IL-4 regulates proliferation and immunoglobulin secretion. IL-4 is involved in the induction of cytotoxic T cells and natural killer cellsJ57] Further, IL-4 has been im­plicated in the regulation of early haemopoie­sisJ58] Most of the clinical phase II studies in­tended to use IL-4 to stimulate antitumour responses.

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674

Table V. Clinical toxicity of interleukin-4[21)

Toxicity Dose Maximal Dose-limiting effect WHO toxicity

grade

Fever + II

Headache III + (1 pt)

Fatigue + Oedema + II

Hypotension + Dyspnoea + III + (1 pt)

Renal + Hyponatraemia + III + (1 pt)

CNS II

Diarrhoea + III + (2 pts)

Nasal congestion

Abbreviation and symbols: pt = patient; + denotes present; - denotes absent.

The toxic adverse effects oflL-4 identified dur­ing phase I trials were of similar quality, but in general were less severe than after treatment with high dose IL-2 or IL-l (table V). In vivo adminis­tration of IL-4 led to an average decrease in abso­lute lymphocyte counts by 67% and to an increase of 20% in haematocrit compared with baseline val­ues. Biological responses oflL-4 treatment include a marked elevation oflL-l RA levels and a modest rise of serum CRP levels, whereas TNF and IL-l ~ levels remain unchanged. The only consistent al­teration of cell surface markers following IL-4 therapy is a decrease in CD 16+ monocytes and an elevation of human leucocyte antigen (HLA) class II expression on monocytes. Quantitative immuno­globulin levels decreased, while soluble CD23 lev­els increased during each course of IL-4 treat­mentVl,22] In a recent phase II trial, no objective responses were observed in 16 patients with refrac­tory multiple myeloma treated with 5 /-lg/kg/day of IL-4.[59]

3.5 Interleukin-6

IL-6 is produced by a wide variety of cells in­cluding monocytes, lymphocytes and epithelial cells. It is a co-stimulator of T cell immunity and induces antibody secretion by B cells. In addition, by induction of acute phase proteins it may be in-

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Aulitzky et a/.

volved in critical control mechanisms of infectious diseases and inflammation)60] Antitumour effects of IL-6 administration have been reported in vivo)34] Furthermore, IL-6 plays a role in the reg­ulation of growth of various haemopoietic and non­haemopoietic cells. IL-6 stimulates the prolifera­tion of early, immature haemopoietic cells. In contrast to other haemopoietic growth factors, a more pronounced thrombopoietic activity was hypothesised from preclinical data.[61] Therefore, the study of both anti tumour and haemopoietic ef­fects of IL-6 provided a rationale for clinical test­ing of this cytokine.

In several clinical phase I and phase 1111 studies IL-6 has been applied alone or in conjunction with myelotoxic chemotherapy. Of note are conflicting results regarding the MTD of subcutaneous bolus injections of IL-6, which report MTDs ranging from 1 /-lg/kg to 25 /-lg/kg)23,62,63] Toxicity of clin­ical IL-6 administration is summarised in table VI.

The main haematological effect of IL-6 in vivo is a significant increase in platelet counts of 200%. A biphasic course of platelet counts is frequently observed. During IL-6 treatment, platelet counts initially decrease, but rise 1 to 2 weeks after cessa­tion of IL-6 treatment above pretreatment values. This increase was clearly dose-dependent: IL-6 dosages of 10 /-lg/kg/day or more produced signif­icantly higher peak platelet counts than lower doses. Bone marrow biopsies revealed no signifi­cant effect on numbers of megakaryocytes. There-

Table VI. Clinical toxicity of interleukin-6[23)

Toxicity

Fever. chills

Headache

Fatigue

Nausea

Anaemia

Renal

HepatiC

Cardiac

Dose effect

+

+

+

Maximal WHO grade

III

Dose-limiting toxicity

+(1 pt)

+ (1 pt)

Abbreviation and symbols: pt = patient; + denotes present; - denotes absent.

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Interleukins

fore, a true thrombopoietic effect of IL-6 was pos­tulated to be responsible for the haematological changes)23,62]

Leucocyte counts and differentials remained unaffected by IL-6 treatment, whereas a dose­dependent decrease of about 20% in numbers of erythrocytes and haemoglobin was observed. Anaemia necessitating erythrocyte transfusions was noted at higher dosages in some patients)23] Within 1 week after cessation of IL-6 treatment, red blood cell counts returned to pretreatment val­ues.

When used after cytotoxic chemotherapy, IL-6 was reported to reduce the severity of thrombo­cytopenia without affecting the severity of anae­mia)62] Coadministration of low doses of IL-6 with G-CSF or GM-CSF was well tolerated)64,65] A dose-related induction of the acute-phase pro­teins CRP, fibrinogen and haptoglobin was ob­served within 24 hours after IL-6 administra­tion)23,62] No increase in bone marrow plasma cells or peripheral blood B cells was noted, and there were no qualitative or quantitative changes in immunoglobulin patterns. Total lymphocyte counts and CD4+/CD8+ ratio remained unchanged at all dose levels of IL-6 tested. An increased ex­pression of intercellular adhesion molecule-l (ICAM-l) and of the low affinity IL-2 receptor (IL-2R a-chain) were observed. No objective anti­tumour responses were achieved in 11 patients treated in a phase I monotherapy trial)23]

3.6 Interleukin-ll

IL-ll is a haemopoietic growth factor stimulat­ing thrombopoiesis and early haemopoietic pro­genitor cells)66] Only preliminary data of a phase I study of IL-ll have been published,l24] Dose es­calation was performed starting from 10 to 75 Ilg/kg/day as daily subcutaneous injections for 12 days following myelosuppressive chemotherapy. So far, 12 women with breast cancer have entered the study. Mean nadir platelet counts were mark­edly higher in patients receiving IL-ll in dosages of 25 Ilg/kg/day or more, whereas nadir leucocyte counts were similar to those seen in patients re-

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675

ceiving the lower dosages. As after administration of IL-6, a mean decrease of 20% in haemoglobin levels was observed at day 3, which resolved im­mediately after completion of IL-ll therapy. Scin­tigraphic analyses indicate an expansion of plasma volume as the underlying cause of this phenome­non.[67]

Coadministration of IL-ll and G-CSF was free of significant adverse effects and it effectively ac­celerated myeloid recovery. Reversible grade 2 oedema, fatigue and myalgias were observed in all patients at the 75 Ilg/kg/day dose level. Bone mar­row biopsies revealed a significant increase of megakaryocyte numbers following doses of 50 Ilg/kg/day or higher despite only a modest increase in marrow cellularity. A grade 1 to 2 increase in marrow fibrosis was observed, suggesting an ef­fect ofIL-ll on marrow stromal cell elements)68]

4. Conclusion

Although none of the interleukins has definitely proven its clinical value in randomised clinical tri­als, these substances represent a group of diverse biological compounds with promising clinical ac­tivities of potential therapeutic benefit. Early phase I and II trials of the haemopoietins IL-l, IL-3, IL-6 and IL-ll clearly demonstrated both their ca­pability to enhance numbers of peripheral blood cells and to accelerate recovery after intensive che­motherapy. Phase III trials are in progress to deter­mine their role in the clinic.

With the exception of IL-2 in metastasising re­nal cell cancer and malignant melanoma, no poten­tial indications have been identified so far for ap­plication of interleukins as immunostimulatory agents. Most of the clinical trials used randomly selected high dose regimens close to the maximum tolerable doses. In addition, phase I and phase II trials of interleukins studied predominantly pa­tients with advanced malignancies. It remains to be answered whether treatment with immuno­stimulatory cytokines will be more successful tar­geting nonmalignant conditions such as autoim­mune or infectious diseases or using biologically active low dose regimens rather than MTD. How-

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ever, due to the complexity of their pharmacody­namic properties, progress in this field will require a close collaboration of clinical researchers and ba­sic scientists.

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Correspondence and reprints: Dr W.E. Aulitzky, Division of Haematology, IIIrd Department of Internal Medicine, University Hospital Mainz, Langenbeckstrasse 1, 55131 Mainz, Germany.

Drugs 48 (5) 1994