Toxicology and pharmacokinetics of DT388IL3, a fusion toxin consisting of a truncated diphtheria toxin (DT388) linked to human interleukin 3 (IL3), in cynomolgus monkeys

The fusion toxin DT388IL3 composed of the catalytic and translocation domains of diphtheria toxin (DT388) linked to interleukin-3 (IL3) was administered to 6 cynomolgus monkeys which possessed cross-reactive IL3 receptors. Groups of 2 animals (1 male and 1 female) received up to 6 every other day slow intravenous infusions of 40, 60, or 100 microg/kg DT388IL3. Monkeys given 40 or 60 microg/kg showed mild or moderate transient malaise and anorexia, respectively, without evidence of organ damage by blood tests or histopathology. Animals treated at 100 microg/kg showed severe malaise and anorexia. The female monkey had moderate to severe vasculitis in multiple tissues. Necropsies were performed on the 40 microg/kg monkeys on day 14 and the 100 microg/kg monkeys on days 6 and 7. DT388IL3 plasma half-life was approximately 30 min with a peak concentration of 0.45 microg/ml or 10,000 pM (IC50 for AML blasts treated in vitro was 6 pM). Immune responses were minimal in 4 animals tested at 12 days and 2 animals tested at 30 days post treatment with anti-DT388IL3 levels < 1 microg/ml. Bone marrow aspirates were obtained on all animals at day 19 or at necropsy and revealed myeloid suppression in the females and myeloid hyperplasia in the males irrespective of dose groups. The maximal tolerated dose of 60 microg/kg for 6 doses is markedly higher than other recombinant diphtheria toxins and provides a dose level sufficient for anti-leukemic activity in vitro and in rodent models. Thus, we propose this agent is a promising drug for AML patients.

Single administration of stem cell factor, FLT-3 ligand, megakaryocyte growth and development factor, and interleukin-3 in combination soon after irradiation prevents nonhuman primates from myelosuppression: long-term follow-up of hematopoiesis

Preservation of hematopoietic stem and progenitor cell survival is required for recovery from radiation-induced myelosuppression. We recently showed that short-term injection of antiapoptotic cytokine combinations into mice soon after lethal gamma irradiation promoted survival. The present study investigated the hematopoietic response of cynomolgus monkeys to a single dose of stem cell factor, FLT-3 ligand, megakaryocyte growth and development factor, and interleukin-3 in combination (4F, each factor given intravenously at 50 microg/kg) administered 2 hours after 5-Gy gamma irradiation. Treated monkeys (n = 4) experienced no thrombocytopenia. Only 1 in 4 displayed a transient period of neutropenia (neutrophil [ANC] count < 0.5 x 10(9)/L), whereas all irradiated controls (n = 4) experienced neutropenia (5-12 days) and thrombocytopenia (platelet [PLT] count < 20 x 10(9)/L, 5-31 days). Treated animals exhibited an impressive 2-wave PLT response that peaked at days 8 and 22 after total body irradiation (TBI). Areas under the curve (AUC) of PLTs, ANCs, white blood cells (WBCs), and red blood cells (RBCs) between days 0 and 90 were significantly higher in treated animals than in controls. Humeral bone marrow-derived clonogenic activity was significantly spared at 24 hours and 4 days after TBI in treated monkeys. No apparent impairment of the hematopoietic status and stem cell pool, in terms of long-term culture-initiating cells (LTC-ICs) and side population (SP) cells, was observed after 15 months. These results strongly suggest that the 4F cytokine combination, as a single dose regimen, could act as an emergency treatment for nuclear accident or terrorism victims.

Modulation of the sustained delivery of myelopoietin (Leridistim) encapsulated in multivesicular liposomes (DepoFoam)

Myelopoietins (MPO) are novel chimeric growth factors containing IL-3 and G-CSF receptor agonists that enhance the biological properties of both cytokines. These cytokines, like many therapeutic proteins, clear rapidly from circulation and must be administered daily to provide efficacy. Therefore, a controlled and sustained delivery system comprised of a biocompatible and biodegradable matrix, would offer important therapeutic advantages in the clinic, such as significantly reducing dose frequency and providing efficacy without toxicity. We report here the encapsulation of Leridistim (a protein from the MPO family) in multivesicular liposomes (DepoFoam) for sustained delivery, and demonstrate that a single injection of DepoFoam-encapsulated Leridistim results in elevated neutrophil counts for 10 days, in contrast to only 2 days for un-encapsulated Leridistim. Moreover, varying the lipid content of the DepoFoam matrix modulated the duration of elevated neutrophils from 2-3 to 9-10 days. The encapsulated Leridistim was released in vivo from the multivesicular liposomes in a uniform manner, consistent with its pharmacodynamic duration. Finally, a reproducible pharmacodynamic effect was observed with several batches of a DepoLeridistim formulation, indicating consistency of the manufacturing process of the DepoFoam delivery system. The capability of altering the release rates by varying the lipid composition provides maximum flexibility for controlled delivery of cytokine therapeutics.

A single dose of pegylated leridistim significantly improves neutrophil recovery in sublethally irradiated rhesus macaques

Leridistim, a member of the myelopoietin family of dual receptor agonists that binds interleukin-3 and G-CSF receptors, has been shown to enhance hematopoietic activity in rhesus monkeys above that observed with either cytokine alone or in combination. This study demonstrated the ability of a pegylated form of leridistim (peg-leridistim), administered s.c., as a single- or two-dose regimen separated by 4 or 7 days, to significantly improve neutrophil recovery following radiation-induced myelosuppression. Rhesus macaques were total body x-irradiated (250 kVp, TBI) to 600 cGy. Following TBI, two groups received peg-leridistim (n = 5) or leridistim (n = 4) at a dose of 600 microg/kg on day 1, while two other groups (both n = 4) received peg-leridistim at 200 microg/kg on day 1 and day 4, or day 1 and day 7. The irradiation controls (n = 7) received 0.1% autologous serum for 18 days. All peg-leridistim treatment schedules significantly improved all neutrophil-related parameters following TBI as compared with nontreated controls and were equivalent in effect when compared among themselves. Administration of a single high dose or two separate lower doses of peg-leridistim significantly improved neutrophil regeneration, in a manner equal to that of conventional daily or abbreviated every-other-day administration of leridistim in this nonhuman primate model of severe myelosuppression.

Poly(ethylene carbonate)s, part II: degradation mechanisms and parenteral delivery of bioactive agents

The degradation and drug carrier properties of poly(ethylene carbonate) (PEC) were investigated in vitro and in rats and rabbits. PEC was found to be specifically degraded in vivo and in vitro by superoxide radical anions O2-*, which are, in vivo, mostly produced by inflammatory cells. No degradation of PEC was observed in the presence of hydrolases, serum or blood. PEC is biodegraded by surface erosion without significant change in the molecular weight of the residual polymer mass. The non-hydrolytic biodegradation by cells producing O2-* is unique among the polymers used as biodegradable drug carriers. The main degradation product of PEC in aqueous systems is ethylene glycol, formed presumably by hydrolysis of ethylene carbonate. The splitting off of a five-membered ring structure from the polymer chain indicates a chain reaction mechanism for the biodegradation. PEC is a suitable drug carrier, particularly for labile drugs. Using human interleukin-3 and octreotide as model drugs, surface erosion of the PEC formulations was indicated by a 1:1 correlation between drug release and polymer mass loss.

Delivery to macrophages of interleukin 3 loaded in mouse erythrocytes

Mouse carrier erythrocytes containing 125I-interleukin 3 have been prepared and treated with band 3 crosslinking reagents. The incorporation of interleukin 3 by hypotonic treatment into mouse erythrocytes reached levels of about 15% of the interleukin 3 added to the medium being predominantly present in the cytosolic fraction (73%). Uptake fell to about 7.4% when using the same conditions but omitting hypotonic shock. The interaction of band 3 crosslinked interleukin 3 loaded erythrocytes with macrophages was also studied. A high level of incorporation of interleukin 3 into macrophages was observed either from band 3 crosslinked, interleukin 3-loaded erythrocytes or from interleukin 3 loaded erythrocytes. The observations encourage the view that the system may be able to deliver and target cytokines and other growth factors to macrophages.

Abrogation of the hematological and biological activities of the interleukin-3/granulocyte-macrophage colony-stimulating factor fusion protein PIXY321 by neutralizing anti-PIXY321 antibodies in cancer patients receiving high-dose carboplatin

This dose-escalation study was performed to evaluate the hematologic activity, biological effects, immunogenicity, and toxicity of PIXY321 (an interleukin-3/granulocyte-macrophage colony-stimulating factor fusion protein) administered after high-dose carboplatin (CBDCA) treatment. Patients with advanced cancers received CBDCA at 800 mg/m2 intravenously on day 0 of repeated 28-day cycles. In part A of the study, patients were treated with CBDCA alone during cycle 1 and then received PIXY321 on days 1 through 18 of cycle 2 and later cycles. In part B, patients received 18 days of PIXY321 beginning on day 1 of all CBDCA cycles, including cycle 1. PIXY321 was administered subcutaneously in 2 divided doses. Total doses of 135, 250, 500, 750, and 1,000 micrograms/m2/d were administered to successive cohorts of 3 to 6 patients in part A. In part B, patient groups received PIXY321 doses of 750, 1,000, and 1,250 micrograms/m2/d. The hematologic effects of PIXY321 were assessed in the first 2 cycles of therapy. Anti-PIXY321 antibody formation was assessed by enzyme-linked immunosorbent assay (ELISA) and neutralization assay. Of the 49 patients enrolled, 31 were fully evaluable for hematologic efficacy. When comparing the first B cycle (cycle B-1; with PIXY321) with the first A cycle (cycle A-1; without PIXY321), the fusion protein had no significant effect on platelet nadirs or duration of platelets less than 20,000/microL but was able to speed the time of recovery of platelet counts to 100,000/microL (15 v 20 days; P =.01). Significant improvements in neutrophil nadir and duration of ANC less than 500 were observed in cycles A-2 and B-1 (with PIXY321) as compared with cycle A-1 (without PIXY321). Initial PIXY321 prophylaxis (cycle A-2 and cycle B-1), enhanced the recovery of ANC to greater than 1,500/microL by an average of at least 8 days as compared with cycle A-1 (without PIXY321; P </=.004). However, positive PIXY321 hematologic effects were lost in the second course of PIXY321 among patients treated in part B. ELISA analysis showed that 92% of patients had developed neutralizing anti-PIXY321 antibodies by the completion of 2 PIXY321-containing cycles. The incidental action of PIXY321 to depress serum cholesterol levels was also abrogated during cycle B-2. We conclude that PIXY321 was active in speeding hematologic recovery but that neutralizing anti-PIXY321 antibody formation suppressed the hematologic and biochemical effects by the second cycle of PIXY321 administration. The immunogenicity of this fusion protein provides a cautionary warning that clinical development of bioengineered human molecules requires thorough testing for immune neutralization.

Human acute myeloblastic leukemia-ascites model using the human GM-CSF- and IL-3-releasing transgenic SCID mice

To generate an appropriate model for human acute myeloblastic leukemia (AML), we have successfully established a human hematopoietic growth factor-dependent AML cell line (TF-1 and UT-7/GM)-ascites model using human granulocyte-macrophage colony-stimulating factor (hGM-CSF)- and human interleukin 3 (hIL-3)-releasing transgenic (Tg)-SCID mice. When 1 x 10(7) cells of TF-1, a human erythroleukemia cell line, were transplanted into the peritoneum of irradiated Tg-SCID mice (TF-1 ip/Tg-SCID mice), TF-1 cells grew in both the single cell suspension form (asTF-1) and solid form in ascites and invaded various tissues: lungs, liver, pancreas, and genitals, 3-6 weeks following transplantation. Subsequently, 0.5-1 x 10(7) cells of UT-7/GM, a subline of the UT-7 human megakaryoblastic leukemia cell line, grown in the back of hGM-CSF Tg-SCID mice after subcutaneous inoculation, were transplanted into the peritoneum of other irradiated hGM-CSF Tg-SCID mice. After 4 weeks, UT-7/GM cells (asUT-7/GM) also grew in the same manner as TF-1 cells in hGM-CSF Tg-SCID mice. Analysis of the cells from the peritoneum and tissues by PCR amplifying ALU and human GM-CSF receptor beta sequences and by immunohistochemical staining using anti-human CD45 revealed that they possessed the original characteristics of the parental cells. To confirm the usefulness of this human AML-ascites model, experimental treatment of AML cells grown in these mice was carried out with a differentiation inducer, delta-aminolevulinic acid (deltaALA), which induces hemoglobin synthesis for TF-1 in vitro and is thus regarded as an anti-leukemia drug candidate. Unexpectedly, growth promotion of TF-1 cells was observed in the treated TF-1 ip/hIL-3 Tg-SCID mice without differentiation to erythroid cells after treatment with delta-ALA (5 mM) for 7 days. These results indicate that Tg-SCID mice can support the growth of human hematopoietic growth factor-dependent AML cell lines which are usually rejected by SCID mice, without modification of the parental cell characteristics. In addition, this Tg-SCID leukemia-ascites model may become a useful preclinical tool for estimation of drug efficacy in vivo, since the drug candidate which was promising in vitro did not act in the same manner in vivo.

A Phase I study of granulocyte-macrophage-colony stimulating factor/interleukin-3 fusion protein (PIXY321) following ifosfamide, carboplatin, and etoposide therapy for children with recurrent or refractory solid tumors: a report of the Children's Cancer Group

BACKGROUND

This Phase I trial was developed to determine the safety, biologic activity, and effects on hematopoietic recovery of PIXY321 following ifosfamide, carboplatin, and etoposide chemotherapy for children with recurrent or refractory solid tumors.

METHODS

Children (age < 22 years at diagnosis) received ifosfamide 1800 mg/m2/day x 5 days, carboplatin 400 mg/m2/day x 2 days, and etoposide 100 mg/m2/day x 5 days, followed by daily subcutaneous administration of PIXY321. Dose-limiting toxicity was defined as Grade IV toxicity related to PIXY321. Pharmacokinetic and endogenous cytokine production studies were conducted during Course 1, and peripheral blood (PB) progenitor cell and receptor expression studies were conducted during Course 1 when the white blood cell count recovered to > or=1000/mm3.

RESULTS

Twenty-four children received ifosfamide, carboplatin, and etoposide chemotherapy plus PIXY321, the latter at doses of 500 /g/m2/day (n=3), 750 microg/m2/day (n=6), 1000 microg/m2/day (n=9), or 500 microg/m2/twice a day (n=6). PIXY321 was well tolerated, with only 1 dose-limiting toxicity (chills, occurring at a dose of 750 microg/m2/day). The maximum tolerated dose was not reached in this study. The median days to absolute neutrophil count recovery (> or =1000/mm3) and platelet recovery (>100,000/mm3) during Course 1 following PIXY321 (1000 microg/ m2/day) were 22 days (range, 5-33 days) and 20 days (range, 5-31 days), respectively. There was a 2500, 5000, 3000, and 390% increase in PB granulocyte-macrophage colony-forming units, erythrocyte blast-forming units, granulocyte erythrocyte macrophage and megakaryocyte colony-forming units, and CD34+ cells, respectively.

CONCLUSIONS

In summary, this pediatric Phase I trial demonstrated that PIXY321 was well tolerated by children and resulted in platelet recovery a median of 20 days after ICE chemotherapy and an increase in the number of PB progenitor cells above baseline. However, based on recent negative results with PIXY321 in randomized Phase II/III trials involving adult subjects, PIXY321 is not currently available for future trials involving children.

Clinical effects and pharmacokinetics of the fusion protein PIXY321 in children receiving myelosuppressive chemotherapy

A hemopoietin with the ability to accelerate both platelet and granulocyte recovery after intensive chemotherapy would have great clinical utility. The recombinant fusion protein composed of human granulocyte-macrophage colony-stimulating factor and interleukin-3 (PIXY321), showed some promise in early adult trials. However, studies for pediatric patients are limited, and there are no systematic data on the pharmacokinetics of PIXY321 given over prolonged periods at current dosage levels.

PURPOSE

To determine the safety, clinical effects and plasma concentrations of increasing doses of PIXY321 in children treated with myelosuppressive chemotherapy.

METHODS

A total of 39 children with relapsed or high-risk solid tumors were enrolled in this phase I/II study. PIXY321 was administered once or twice daily by subcutaneous injection in total doses of 500 to 1000 microg/m2 per day for 14 days after each course of chemotherapy with ifosfamide, carboplatin, and etoposide (ICE). Pharmacokinetic studies were performed on day 1 of the first course in 33 patients and repeated on day 14 in 13 patients (once-daily schedule only).

RESULTS

Although mild local skin reactions and fever were frequent, no dose-limiting toxicity was identified at the maximum dose studied (1000 microg/m2 per day). There were no statistically significant differences in chemotherapy-induced hematologic toxicity with increasing doses of PIXY321 or with twice-daily vs once-daily dosing. On day 1, the median PIXY321 clearance was 657 ml/min per m2 (range 77 1804 ml/min per m2) and the median half-life was 3.7 h (range 2.1-20.8 h). On day 14, clearance increased in all patients studied (median increase 63%), with a corresponding decrease in the median 12-h concentration (from 1.2 to 0.25 ng/ml). Maximum concentrations were < 1 ng/ml in 81% of patients, and only two patients had maximum plasma concentrations equivalent to those required for consistent activity in vitro.

CONCLUSIONS

The recombinant fusion protein PIXY321 proved safe in children treated with myelosuppressive ICE chemotherapy but had no demonstrable clinical benefits. The pharmacokinetic studies suggest that the observed lack of hematologic benefit may be explained by low plasma concentrations resulting from increased clearance with prolonged administration. Moreover, the significant increase in PIXY321 systemic clearance in the absence of increased circulating myeloid cells suggests that the upregulation of either extravascular compartment hematopoietic progenitor cells or nonhematopoietic cells may play an important role in controlling circulating concentrations of this unique cytokine. These findings highlight the importance of a thorough assessment of the systemic disposition of cytokines when determining the dose and schedule necessary to achieve clinical activity in patients.

Phase I trial of subcutaneous interleukin 3 in patients with refractory malignancy: hematological, immunological, and pharmacodynamic findings

We conducted a Phase I trial of s.c. recombinant human interleukin 3 (rhIL-3) to evaluate the toxicity, maximal tolerated dose, pharmacokinetics, and in vivo biological effects of this cytokine. Thirty-one patients with refractory cancer were entered into the study between November 1991 and June 1993. Therapy consisted of s.c. rhIL-3 daily for 15 days administered to cohorts of three to nine patients at dose levels of 60-4000 microgram/m2/day. Cycles were repeated at intervals of 28 days. Seventy-five cycles of rhIL-3 were administered (median, two per patient) and the maximal tolerated dose was 2000 microgram/m2/day. Toxicity was moderate, with most patients developing chills, fever, and myalgia. Dose-limiting toxicity consisted of diarrhea (two patients) and headache (one patient). Hematological effects of rhIL-3 included significant dose-related increases of WBC (P < 0.001), neutrophils (P < 0.001), and eosinophils (P < 0.001). Platelet counts and absolute lymphocyte numbers also increased. Various CD3(+) lymphocyte subsets increased; however, lytic activity (natural killer and lymphokine-activated killer) of peripheral blood lymphocytes was not enhanced. Serum levels of the soluble IL-2 receptor increased in a dose-related fashion, and IL-2-induced lymphocyte proliferation also was increased variably. Pharmacokinetic studies were performed in 13 patients, and area under the curve and maximal concentration values increased with increasing rhIL-3 dose levels (P < 0.001) and correlated with maximal changes from baseline in WBC, neutrophils, and eosinophils. rhIL-3 antibodies were detected in 8% of patients by day 29 of cycle 1 but were not neutralizing. rhIL-3 is well tolerated when administered s.c. and has reproducible hematological and immunological effects. The pleiotropic effects of this cytokine on various in vivo biological parameters were demonstrated clearly. Further studies of its immunoregulatory effects are warranted.

Acceleration of hematopoietic reconstitution with a synthetic cytokine (SC-55494) after radiation-induced bone marrow aplasia

The synthetic cytokine (Synthokine) SC-55494 is a high-affinity interleukin-3 (IL-3) receptor ligand that stimulates greater in vitro multilineage hematopoietic activity than native IL-3, while inducing no significant increase in inflammatory activity relative to native IL-3. The aim of this study was to investigate the in vivo hematopoietic response of rhesus monkeys receiving Synthokine after radiation-induced marrow aplasia. Administration schedule and dose of Synthokine were evaluated. All animals were total-body irradiated (TBI) with 700 cGy 60Co gamma radiation on day 0. Beginning on day 1, cohorts of animals (n = 5) received Synthokine subcutaneously (SC) twice daily with 25 micrograms/kg/d or 100 micrograms/kg/d for 23 days or 100 micrograms/kg/d for 14 days. Control animals (n = 9) received human serum albumin SC once daily at 15 micrograms/kg/d for 23 days. Complete blood counts were monitored for 60 days postirradiation and the durations of neutropenia (NEUT; absolute neutrophil count [ANC] < 500/microL) and thrombocytopenia (THROM; platelet count < 20,000/microL) were assessed. Synthokine significantly (P < .05) reduced the duration of THROM versus the HSA-treated animals regardless of dose or protocol length. The most striking reduction was obtained in the animals receiving 100 micrograms/kg/d for 23 days (THROM = 3.5 v 12.5 days in HSA control animals). Although the duration of NEUT was not significantly altered, the depth of the nadir was significantly lessened in all animal cohorts treated with Synthokine regardless of dose versus schedule length. Bone marrow progenitor cell cultures indicated a beneficial effect of Synthokine on the recovery of granulocyte-macrophage colony-forming units that was significantly higher at day 24 post-TBI in both cohorts treated at 25 and 100 micrograms/kg/d for 23 days relative to the control animals. Plasma pharmacokinetic parameters were evaluated in both normal and irradiated animals. Pharmacokinetic analysis performed in irradiated animals after 1 week of treatment suggests an effect of repetitive Synthokine schedule and/or TBI on distribution and/or elimination of Synthokine. These data show that the Synthokine, SC55 94, administered therapeutically post-TBI, significantly enhanced platelet recovery and modulated neutrophil nadir and may be clinically useful in the treatment of the myeloablated host.

Pharmacokinetic and pharmacodynamic studies of subcutaneously administered recombinant human interleukin-3 following chemotherapy for non-Hodgkin's lymphoma

The pharmacokinetics and the pharmacodynamic profile of subcutaneously administered recombinant human non-glycosylated interleukin-3 (rhIL-3) was studied in lymphoma patients after standard CHOP chemotherapy. 30 patients received 0.5, 1.0, 5.0, 7.5 and 10 micrograms/kg (six patients at each dose level) of rhIL-3 for 14 d. Serum rhIL-3 samples were obtained regularly, during the treatment and serially over a 24 h period on the first (cycle day 2) and the last (cycle day 15) day of rhIL-3 treatment for pharmacokinetic evaluation. Following s.c. injection on cycle day 2. the maximum rhIL-3 serum concentration ranged from 289 pg/ml (0.5 micrograms/kg) to 4690 pg/ml (10 micrograms/kg). Both the maximum serum concentration (R = 0.90. P < 0.0001) and the area under the serum concentration-time curve (R = 0.95, P < 0.0001) were related to dose. The elimination half-life T1/2 beta was 160 min for 0.5 micrograms/kg and 134 min for 10 micrograms/kg, with no apparent dose relationship. The systemic clearance of 3.0-6.0 ml/min/kg was comparable at all dose levels. No significant difference was noted between pharmacokinetic parameters on the first day of rhIL-3 and the last day of treatment, and no accumulation of the drug was noted throughout the study. The pharmacokinetic parameters correlated poorly to the clinical response of the growth factor. where dose in micrograms/kg seemed to be the most important single factor.

Pharmacodynamics of daily subcutaneous recombinant human interleukin-3 in normal volunteers

Normal volunteers received subcutaneous injections of recombinant human interleukin-3 (rhIL-3) on 4 consecutive days to characterize toxicity, pharmacokinetics, and hematopoietic effects. Dosages were 2.5, 5.0, and 7.5 micrograms/kg/day (n = 6 subjects per group). Adverse effects consisted predominantly of flu-like symptoms such as fever and headache. Mean area under the serum concentration-time curve and maximum serum concentration were linearly related to dose. Serum clearance was not apparently related to dose. Clearance increased slightly but significantly between days 1 and 4. Rapid but modest elevations in neutrophil and eosinophil counts were observed during treatment. Mean platelet counts rose modestly, peaking on day 10. Increases of CD34+ cell counts were correlated with increases of colony-forming unit-granulocyte macrophage (peak, day 7).

Interleukin-3 administration enhances human monocyte function in vivo

In addition to its haemopoietic effects, interleukin-3 (IL-3) enhances leucocyte function in vitro. In this study we examined the effects on haematological variables and monocyte function of a single IL-3 infusion in five haematologically normal individuals. There was a rapid fall in circulating monocyte (to 24 +/- 6% of pre-infusion value) and eosinophil numbers (to 3 +/- 2%) with a nadir at 30 min and gradual return to baseline over 6 h. No significant changes in monocyte expression of the adhesion molecules CD11b or L-selectin or of monocyte respiratory burst activity were detected. There was a significant increase in monocyte phagocytosis and killing of Candida after IL-3 infusion: the percentage of monocytes which had ingested Candida increased from 39 +/- 10% to 62 +/- 12% and the total number of Candida killed per 100 monocytes increased from 63 +/- 34 to 210 +/- 59 (P < 0.05 and P < 0.01 respectively). There was no inhibition of neutrophil migration into a 'skin window' site and monocyte migration was moderately enhanced (peak increase of 260 +/- 47%). These results show that IL-3 has significant effects on monocyte function in vivo and could be of use in augmenting host defence mechanisms in immunocompromised patients.

Carbohydrate does not modulate the in vivo effects of injected interleukin-3

Murine interleukin-3 (IL-3) has extensive N-linked glycosylation. Experiments were performed to determine whether the T cell-derived glycosylated IL-3 differs in its biological activity in vivo when compared with a chemically synthesized form of nonglycosylated IL-3. Groups of mice were treated by intravenous injection with identical units of IL-3 bioactivity as determined in vitro in a cell-proliferation assay. Mice that were treated with seven 5000-unit doses of either form of IL-3, given in 12-hour intervals, showed a small but significant increase in the frequency of mast cell precursor cells in the spleen and of IL-3-responsive colony-forming unit cells (CFU-C). There was no difference in potency of glycosylated and nonglycosylated IL-3. Induction, by IL-3, of histidine decarboxylase in bone marrow and spleen cells was used as a second measure for IL-3 bioactivity. Both IL-3 preparations showed good in vivo histidine decarboxylase inducing activity; however, T cell-derived glycosylated IL-3 was significantly more effective than synthetic IL-3 in inducing the enzyme histidine decarboxylase in bone marrow and in spleen cells. Pharmacokinetic studies showed that chemically synthesized IL-3 was cleared about twice as fast as the T cell-derived IL-3 and that there may be some tissue trapping of glycosylated IL-3. The shorter in vivo half-life of nonglycosylated IL-3 appears to have significant pharmacological consequences on the short-term effect of inducing histidine decarboxylase activity, but not on the effect of the long-term treatment of IL-3 on stimulating the increase of hematopoietic progenitor cells.

Recombinant human interleukin-3: pharmacokinetics after intravenous and subcutaneous bolus injection and effects on granulocyte kinetics

The pharmacokinetics of E. coli derived recombinant human interleukin-3 (rhIL-3) was studied following intravenous (i.v.) and subcutaneous (s.c.) bolus injection of rhIL-3. After i.v. bolus injection in eight patients, serum peak levels of 34.5-135.0 ng/ml were reached, followed by a rapid decline with a t1/2 alpha of 17 +/- 2 min and a t1/2 beta of 59 +/- 7 min. After s.c. bolus injection in five patients, the absorption was more prolonged with peak serum levels reached at 2.8 +/- 0.4 h. Elimination was also more protracted, and serum base-line levels were reached at 14-24 h. The immediate effect of rhIL-3 on peripheral white blood cells was less pronounced and more variable than previously found for G- or GM-CSF. Following i.v. administration, neutrophils showed a moderate drop to median 64% of initial values (range 42-85%) at median 30 min after injection (range 15-60 min) followed by an increase at 24 h to 69-288% of initial values. Eosinophils dropped to a median nadir of 34% and then gradually increased to maximum values in the range 135-720% at 18-24 h. The effect of rhIL-3 was further examined following i.v. injection of autologous 111Indium-labelled granulocytes in six patients. In steady state, i.v. injection of rhIL-3 caused a moderate drop in 111Indium activity of peripheral blood within 20 min without tendency to subsequent recovery. No change occurred in the activity recorded over the lungs and liver. The activity over the spleen decreased moderately in two patients. These results are strikingly different from those previously obtained after i.v. injection of rhGM-CSF.

Pharmacokinetics of recombinant human interleukin 3 administered subcutaneously and by continuous intravenous infusion in patients after chemotherapy for ovarian cancer

Twenty chemotherapy-naive patients with ovarian carcinoma received 1, 5, 10, or 15 micrograms/kg/day (five patients per dose step) of recombinant human interleukin 3 (rhIL-3) over 7 days after carboplatin/cyclophosphamide in Cycles 1 and 3. Patients received rhIL-3 by continuous i.v. infusion or once daily s.c. injection in Cycle 1 and the alternate route in Cycle 3. Plasma rhIL-3 samples were obtained once daily on Days 1 to 6 and serially over a 24-h period on Day 7 for pharmacokinetic assessment of s.c. and i.v. administered rhIL-3 in 16 and 17 patients, respectively. Concentrations were assayed by a time-resolved fluorescence sandwich immunoassay. Pharmacokinetic parameters were derived by noncompartmental methods. Mean steady-state concentrations during continuous i.v. infusion ranged from 117 pg/ml (1 microgram/kg/day) to 2217 pg/ml (15 micrograms/kg/day) and were linearly related to dose (r = 0.87, P < 0.001). When dose normalized, the mean steady-state concentrations were comparable at all doses. The total-body clearance was approximately 4 to 5 ml/min/kg. Elimination half-life (t1/2 i.v.) could be assessed for the 5- to 15-micrograms/kg/day dose levels and was 53, 41, and 26 min for the 5-, 10-, and 15-micrograms dose levels, respectively (not significant between dose levels). Following s.c. injection, the maximum rhIL-3 plasma concentration ranged from 206 pg/ml (1 microgram/kg/day) to 6930 pg/ml (15 micrograms/kg/day). Both the maximum measured plasma concentration (r = 0.89, P < 0.0001) and the area under the plasma concentration/time curve (r = 0.93, P < 0.0001) were related to dose. Dose-normalized values were comparable over the entire dose range. Elimination t1/2s.c. was 4.8 h at the 1-microgram dose level and roughly half this time for the 5- to 15-micrograms/kg/day dose levels. The systemic clearance of approximately 5 to 6 ml/min/kg was comparable at all dose levels. Based on trough levels of the 7-day s.c. course, no rhIL-3 accumulation occurred. Bioavailability of s.c. administered rhIL-3 was nearly 100%. No correlation between creatinine clearance and pharmacokinetic parameters of rhIL-3 could be demonstrated. Since there was also no difference in hematological efficacy between the two routes of rhIL-3 administration, we conclude that the s.c. route of administration appears to have no disadvantages over the i.v. route and may facilitate its clinical application.

Pharmacokinetic basis for optimal hemopoietic effectiveness of homologous IL-3 administered to rhesus monkeys

To design an interleukin-3 (IL-3) administration schedule for optimal hemopoietic effectiveness, serum half-life (t1/2) was determined after intravenous (i.v) and subcutaneous (s.c.) bolus injections. The initial t1/2 in serum after i.v. injection was about 10 minutes and the terminal t1/2 close to 2 hours. Subcutaneous administration resulted in plateau levels after 2 to 4 hours, while the apparent terminal t1/2 was similar to that after i.v. infusion. The bioavailability of IL-3 following subcutaneous administration was only about 40% of that following i.v. administration. Hemopoietic effects of continuous i.v. infusion of IL-3 was then compared to s.c. administration in either one, two, or three daily injections. Doses chosen ranged from 1 to 30 micrograms/kg per day. In agreement with the more limited bioavailability of IL-3 following s.c. administration, continuous i.v. infusion was much more effective in stimulating hemopoiesis than s.c. administration. Two or three daily s.c. injections did not improve the hemopoietic response compared to a single s.c. injection, which is in agreement with the apparent terminal t1/2 of 101 min. It is concluded that IL-3 is more effective by continuous i.v. infusion than by subcutaneous administration.

Enhancement of the biologic effects of interleukin-3 in vivo by anti-interleukin-3 antibodies

Interleukin-3 (IL-3) has been shown to be a promising agent in the stimulation of bone marrow regeneration following myeloablative therapy. The biologic half-life of this agent is very short (5 to 15 minutes), which limits the effectiveness of low-dose therapy. Here we show that the biologic effects of low-dose IL-3 in mice may be enhanced by concurrent use of polyclonal anti-IL-3 antibodies. The biologic effects of IL-3 in vivo were enhanced dramatically by the combination of the cytokine and polyclonal rabbit anti-IL-3 antibodies, which recognized a peptide comprising the first 29 amino acids of the IL-3 molecule. Enhancing effects were not apparent in vitro, where weak neutralizing properties were observed for these antibodies. The mechanism of this enhancement by the antibody appears to be via a ninefold reduction in the total-body clearance of the cytokine in vivo. The apparent volumes of distribution for IL-3 and for the IL-3/antibody complex were surprisingly similar and exceeded the expected intravascular volume. The prolonged biologic half-life of IL-3 was reproducibly associated with a threefold to fivefold increase in splenic mast-cell precursors over levels observed in mice treated with IL-3 alone; increases in the numbers of mature mucosal-type mast cells in the spleen, but not in the jejunum or lung; increases in IL-3-dependent colony-forming unit-cell in the spleen; and an apparent redistribution of mast cells away from the bone marrow. These experiments demonstrate that antibodies to a cytokine can enhance the biologic activity of that cytokine in vivo.

Anti-cytokine antibodies as carrier proteins. Prolongation of in vivo effects of exogenous cytokines by injection of cytokine-anti-cytokine antibody complexes

Anti-cytokine antibodies that block interactions between cytokines and cytokine receptors have been used to inhibit endogenous cytokine function. However, injection of mice with mixtures of IL-4 and either of two neutralizing anti-IL-4 mAb, at a cytokine/anti-cytokine mAb molar ratio of approximately 2:1, enhances and prolongs in vivo IL-4 activity, as measured by induction of increased spleen cell Ia expression. Although splenocyte Ia expression returns to baseline two days after mice are injected with free IL-4, soluble IL-4-anti-IL-4 mAb complexes still induce several-fold increases in Ia expression 3 days after injection. Complexes that contain as little as 400 ng of IL-4 have considerable in vivo stimulatory activity, and a maximal effect on splenocyte Ia expression is induced by injection of 2 micrograms of complexed IL-4. The stimulatory effect of IL-4-containing complexes on splenocyte Ia expression can be blocked by increasing the ratio of anti-IL-4 mAb to IL-4, by injection of anti-IL-4R mAb, and by in vivo aggregation of the complexes. Complexes of IL-4 with a non-neutralizing anti-IL-4 mAb do not have increased IL-4 agonist activity in vivo. These observations are most consistent with the possibility that neutralizing anti-IL-4 mAb act as carrier proteins that increase the in vivo half-life of IL-4 by preventing its excretion, and possibly, by preventing modification of its active site. The enhanced agonist effect of IL-4-anti-IL-4 mAb complexes is not unique; complexes of IL-3 with a neutralizing anti-IL-3 mAb have a greatly increased ability, compared with free IL-3, to stimulate mucosal mastocytosis, and complexes of IL-7 with a neutralizing anti-IL-7 mAb have a greatly increased ability, compared with free IL-7 or IL-7 complexed with a non-neutralizing anti-IL-7 mAb, to stimulate an increase in pre-B cell number. These observations suggest that complexes of cytokines and neutralizing anti-cytokine mAb may provide a generally useful way to increase the magnitude and duration of cytokine effects in vivo.

Phase I study of recombinant human interleukin-3 in patients with bone marrow failure

Interleukin-3 (IL-3) is a T-cell-derived colony-stimulating factor (CSF) whose primary targets include relatively early, multipotential, hematopoietic progenitor cells. In this trial, we treated 24 patients with recombinant human IL-3 given by a daily 4-hour intravenous infusion for 28 days. The dose levels were 30, 60, 125, 250, 500, 750, and 1,000 micrograms/m2/d. At least three patients were entered at every dose level. Each participant suffered from bone marrow failure, with the underlying diagnosis being myelodysplastic syndrome (13 patients), aplastic anemia (eight patients), or aplasia after prolonged high-dose chemotherapy (three patients) for multiple myeloma, breast cancer, or acute myelogenous leukemia. Most patients tolerated therapy well, with the most frequent side effects being low-grade fever and headaches. Hematopoietic changes included modest increases in neutrophil counts (eight patients), eosinophil counts (six patients), platelet counts (three patients), and reticulocyte counts (two patients). An increase in blasts occurred in one patient who had refractory anemia with excess blasts in transformation and was reversible once IL-3 was discontinued. In addition, one patient with chronic myelomonocytic leukemia showed an increase in monocytes (and granulocytes). Progression to acute leukemia did not occur. Pharmacokinetic analyses showed a rapid clearance with a mean half-life of 18.8 minutes at the 60 micrograms/m2/d dose, and 52.9 minutes at the 250 micrograms/m2/d dose. Serum concentrations of 10 to 20 ng/mL of IL-3 were achievable at the 250 micrograms/m2/d dose. Our observations indicate that recombinant human IL-3 can be given safely at doses of 1,000 micrograms/m2/d or less. In addition, on the basis of preclinical data and the biologic activity observed in this study, further trials of this molecule, alone and in combination with other growth factors, are warranted in patients with pancytopenia.

Clinical effects of recombinant human interleukin-3

Interleukin-3 (IL-3) is a glycoprotein belonging to the hematopoietic growth factor family that in preclinical in vitro and in vivo studies has exhibited a multilineage activity. Phase I/II trials with recombinant human IL-3 (rhIL-3) expressed in yeast are being done in patients with advanced malignancies as well as in patients with bone marrow failure states. Subcutaneous administration of rhIL-3 at dosages between 30 and 500 micrograms/m2 for 15 consecutive days has resulted in a dose-dependent increase in platelet counts as well as in a substantial increase in the number of circulating neutrophils, eosinophils, monocytes, and lymphocytes in patients with advanced malignancies but normal hematopoiesis. Erythropoiesis is less stimulated with an increase in hemoglobin concentration only in a minority of patients. In patients with secondary hematopoietic failure due to prolonged chemo-/radiotherapy or bone marrow infiltration by tumor cells, treatment with rhIL-3 leads to a clinically significant restoration of hematopoiesis, especially of thrombopoiesis and granulopoiesis. rhIL-3 has also been shown to improve neutrophil and platelet counts in patients with myelodysplastic syndromes, while improvement of hematopoiesis is rarely observed in patients with severe aplastic anemia with the presently used treatment schedules. Adverse effects of rhIL-3 are minor at the clinically used dosages and include fever, bone pain, headache, and stiffness of the neck. Transient thrombocytopenia has been observed in a few patients with myelodysplastic syndrome or aplastic anemia treated at dosages of 250-500 micrograms/m2. rhIL-3 is a multilineage hematopoietic cytokine with promising effects on platelet and neutrophil counts and special usefulness in patients with secondary hematopoietic failure.

Effect of dexamethasone on IL-1 and IL-3-LA release by unstimulated human mononuclear cells

The effect of dexamethasone on the in vitro release of IL-1 and IL-3-LA by human unstimulated mononuclear cells was studied. The drug elicited a dose-dependent effect on the production of both interleukins. In addition, a time course effect of dexamethasone on IL-3-LA was demonstrated. It appeared after 5 min of incubation, reached a maximal level after 15 min, and remained at that level after 24 h. The drug also caused a dose-dependent inhibitory effect on the ability of human mononuclear cells to incorporate [3H] uridine. The inhibitory effect of dexamethasone on these interleukins may serve as a partial explanation of the susceptibility to infection in patients treated with corticosteroids.

Granulocyte-macrophage colony-stimulating factor regulation in murine T cells and its relation to cyclosporin A

The coordinated expression of the hematopoietic growth factors, interleukin 3 (IL3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) in activated T cells suggests common synthetic pathways. However, cyclosporin A (CsA) appears to differentially effect the synthesis of these two lymphokines. When the supernatants from the concanavalin A-stimulated thymoma EL-4 or the T-cell hybrid 2B4 were assayed on the GM-CSF/IL3-dependent PT-18 and on the IL3-dependent DA-1 cell lines, IL3 activity could not be detected following CsA treatment, but substantial growth activity, which was identified as GM-CSF, was observed on the PT-18 cell line. CsA did not affect the kinetics of GM-CSF release, but inhibited the release of IL3 over a period of 40 h after the cells were stimulated and treated with CsA. In addition, CsA could be added up to 1 h after stimulation of the cells without affecting GM-CSF activity but inhibiting completely the IL3 activity. To substantiate the inability of CsA to inhibit GM-CSF activity, GM-CSF gene expression was evaluated. By Northern analysis GM-CSF mRNA was not inhibited by doses of CsA up to 1 microgram/ml. The data reveal that CsA can dissociate between the production of IL3 and GM-CSF, suggesting that these two CSFs are regulated by different mechanisms.

Specific binding, internalization, and degradation of human recombinant interleukin-3 by cells of the acute myelogenous, leukemia line, KG-1

We have studied the interaction of 35S-labeled recombinant IL-3 with the acute myelogenous leukemia cell line, KG-1. 35S-IL-3 bound to these cells in a time dependent, saturable, and specific manner at 4 degrees C. Scatchard transformation of binding isotherms demonstrated the existence of a small number (200) of binding sites, with an apparent dissociation constant of 70-105 pM. After a temperature shift from 4 degrees C to 37 degrees C, surface-bound 35S-IL-3 was rapidly internalized and processed into a trichloroacetic acid soluble form that was released into the medium. Experiments to address the specificity of the IL-3 binding site revealed that neither human IL-2, M-CSF, erythropoietin, transferrin, bovine insulin, nor murine nerve growth factor compete with IL-3 for binding to KG-1 cells. Both human and gibbon recombinant IL-3 and, surprisingly, human recombinant GM-CSF effectively competed the binding of the labeled IL-3 to these cells at 4 degrees C. The competition by GM-CSF was found to be concentration dependent, but much higher concentrations were required to achieve the levels obtained with IL-3. These results suggest that GM-CSF may also interact with the high-affinity IL-3 binding site on KG-1 cells or, alternatively, that GM-CSF binding to its own receptor may decrease the affinity of the IL-3 receptor for its ligand.