Combined administration of recombinant human megakaryocyte growth and development factor and granulocyte colony-stimulating factor enhances multilineage hematopoietic reconstitution in nonhuman primates after radiation-induced marrow aplasia.

This study compared the therapeutic potential of recombinant, native versus pegylated megakaryocyte growth and development factor (rMGDF and PEG-rMGDF, respectively), as well as that of the combined administration of PEG-rMGDF and r-methionyl human granulocyte colony-stimulating factor (r-metHuG-CSF) on hematopoietic reconstitution after 700 cGy, 60Co gamma, total body irradiation in nonhuman primates. After total body irradiation, animals received either rMGDF, PEG-rMGDF, r-metHuG-CSF, PEG-rMGDF and r-metHuG-CSF or HSA. Cytokines in all MGDF protocols were administered for 21-23 d. Either rMGDF, PEG-rMGDF, or PEG-rMGDF and r-metHuG-CSF administration significantly diminished the thrombocytopenic duration (platelet count (PLT) < 20,000 per microliter)to o.25, 0, 0.5 d, respectively, and the severity of the PLT nadir (28,000, 43,000, and 30,000 per microliter, respectively) as compared with the controls (12.2 d duration, nadir 4,000 per microliter), and elicited an earlier PLT recovery. Neutrophil regeneration was augmented in all cytokine protocols and combined PEG-rMGDF and r-metHuG-CSF further decreased the duration of neutropenia compared with r-metHuG-CSF alone. These data demonstrated that the administration of PEG-rMGDF significantly induced bone marrow regeneration versus rMGDF, and when combined with r-metHuG-CSF significantly enhanced multilineage hematopoietic recovery with no evidence of lineage competition.

Organ Doses Associated with Partial-Body Irradiation with 2.5% Bone Marrow Sparing of the Non-Human Primate: A Retrospective Study.

A partial-body irradiation model with approximately 2.5% bone marrow sparing (PBI/BM2.5) was established to determine the radiation dose-response relationships for the prolonged and delayed multi-organ effects of acute radiation exposure. Historically, doses reported to the entire body were assumed to be equal to the prescribed dose at some defined calculation point, and the dose-response relationship for multi-organ injury has been defined relative to the prescribed dose being delivered at this point, e.g., to a point at mid-depth at the level of the xiphoid of the non-human primate (NHP). In this retrospective-dose study, the true distribution of dose within the major organs of the NHP was evaluated, and these doses were related to that at the traditional dose-prescription point. Male rhesus macaques were exposed using the PBI/BM2.5 protocol to a prescribed dose of 10 Gy using 6-MV linear accelerator photons at a rate of 0.80 Gy/min. Point and organ doses were calculated for each NHP from computed tomography (CT) scans using heterogeneous density data. The prescribed dose of 10.0 Gy to a point at midline tissue assuming homogeneous media resulted in 10.28 Gy delivered to the prescription point when calculated using the heterogeneous CT volume of the NHP. Respective mean organ doses to the volumes of nine organs, including the heart, lung, bowel and kidney, were computed. With modern treatment planning systems, utilizing a three-dimensional reconstruction of the NHP's CT images to account for the variations in body shape and size, and using density corrections for each of the tissue types, bone, water, muscle and air, accurate determination of the differences in dose to the NHP can be achieved. Dose and volume statistics can be ascertained for any body structure or organ that has been defined using contouring tools in the planning system. Analysis of the dose delivered to critical organs relative to the total-body target dose will permit a more definitive analysis of organ-specific effects and their respective influence in multiple organ injury.

Pharmacodynamic model of topotecan-induced time course of neutropenia.

Pharmacodynamic measures of neutropenia, such as absolute neutrophil count at nadir and neutrophil survival fraction, may not reflect the overall time course of neutropenia. We developed a pharmacokinetic-pharmacodynamic model to describe and quantify the time course of neutropenia after administration of topotecan to children and to compare this with nonhuman primates (NHPs) as a potential preclinical model of neutropenia. Topotecan was administered as a 30-min infusion daily for 5 days, repeated every 21 days. As part of a Phase I Pediatric Oncology Group study, topotecan was administered at 1.4 and 1.7 mg/m(2)/day without filgrastim (POG), and at 1.7, 2, and 2.4 mg/m(2)/day with filgrastim (POG+G). In NHPs, topotecan was administered at 5, 10, and 20 mg/m(2)/day without filgrastim. A pharmacokinetic-pharmacodynamic model was fit to profiles of topotecan lactone plasma concentrations and neutrophil survival fraction from cycle 1 and used to calculate topotecan lactone area under the plasma concentration-versus-time curve from 0 to 120 h (AUC(LAC)) and the area between the baseline and treatment-related neutrophil survival fraction (ABC) from 0 to 700 h. The mean +/- SD neutrophil survival fraction at nadir for the POG, POG+G, and NHP groups was 0.12 +/- 0.09, 0.11 +/- 0.17, and 0.09 +/- 0.08, respectively (P > 0.05). The mean +/- SD for the ratio of ABC to AUC(LAC) for the POG and NHP groups was 1.02 +/- 0.38 and 0.16 +/- 0.09, respectively (P < 0.05). The model estimate of ABC and the ratio of ABC to AUC(LAC) in children and NHPs may better reflect sensitivity to chemotherapy-induced neutropenia.

Myelopoietin, a chimeric agonist of human interleukin 3 and granulocyte colony-stimulating factor receptors, mobilizes CD34+ cells that rapidly engraft lethally x-irradiated nonhuman primates.

Myelopoietin (MPO), a multifunctional agonist of interleukin 3 and granulocyte colony-stimulating factor (G-CSF) receptors, was evaluated for its ability to mobilize hematopoietic colony-forming cells (CFC) and CD34+ cells relative to control cytokines in normal nonhuman primates. Additionally, the engraftment potential of MPO-mobilized CD34+ cells was assessed in lethally irradiated rhesus monkeys. Normal rhesus monkeys were administered either MPO (200 microg/kg/day), daniplestim (a high-affinity interleukin 3 receptor agonist) (100 microg/kg/day), G-CSF (100 microg/kg/day), or daniplestim coadministered with G-CSF (100 microg/kg/day each), subcutaneously for 10 consecutive days. The mobilization kinetics were characterized by peripheral blood (PB) complete blood counts, hematopoietic CFC [granulocyte-macrophage CFC (GM-CFC), megakaryocyte CFC (MK-CFC)], and the immunophenotype (CD34+ cells) of PB nucleated cells prior to and on day 3 to days 7, 10, 12, and 14, and at intervals up to day 28 following initiation of cytokine administration. A single large-volume leukapheresis was conducted on day 5 in an additional cohort (n = 10) of MPO-mobilized animals. Eight of these animals were transplanted with two doses of CD34+ cells/kg. A maximum 10-fold increase in PB leukocytes (white blood cells) (from baseline 7.8-12.3 x 10(3)/microL to approximately 90 x 10(3)/microL) was observed over day 7 to day 10 in the MPO, G-CSF, or daniplestim+G-CSF cohorts, whereas daniplestim alone stimulated a less than onefold increase. A sustained, maximal rise in PB-derived GM-CFC/mL was observed over day 4 to day 10 for the MPO-treated cohort, whereas the daniplestim+G-CSF, G-CSF alone, and daniplestim alone treated cohorts were characterized by a mean peak value on days 7, 6, and 18, respectively. Mean peak values for PB-derived GM-CFC/mL were greater for MPO (5,427/mL) than for daniplestim+G-CSF (3,534/mL), G-CSF alone (3,437/mL), or daniplestim alone (155/mL) treated cohorts. Mean peak values for CD34+ cells/mL were noted within day 4 to day 5 of cytokine administration: MPO (255/microL, day 5), daniplestim+G-CSF (47/microL, day 5), G-CSF (182/microL, day 4), and daniplestim (96/microL, day 5). Analysis of the mobilization data as area under the curve indicated that for total CFCs, GM-CFC, MK-CFC, or CD34+ cells, the MPO-treated areas under the curve were greater than those for all other experimental cohorts. A single, large-volume (3.0 x blood volume) leukapheresis at day 5 of MPO administration (PB: CD34+ cell/microL = 438 +/- 140, CFC/mL = 5,170 +/- 140) resulted in collection of sufficient CD34+ cells (4.31 x 10(6)/kg +/- 1.08) and/or total CFCs (33.8 x 10(4)/kg +/- 8.34) for autologous transplantation of the lethally irradiated host. The immunoselected CD34+ cells were transfused into autologous recipients (n = 8) at cell doses of 2 x 10(6)/kg (n = 5), and 4 x 10(6)/kg (n = 3) on the day of apheresis. Successful engraftment occurred with each cell dose. The data demonstrated that MPO is an effective and efficient mobilizer of PB progenitor cells and CD34+ cells, such that a single leukapheresis procedure results in collection of sufficient stem cells for transplantation and long term engraftment of lethally irradiated hosts.

Filgrastim for the treatment of hematopoietic acute radiation syndrome.

The U.S. Food and Drug Administration (FDA) recently approved Neupogen(®) (filgrastim) for the treatment of patients with radiation-induced myelosuppression following a radiological/nuclear incident. It is the first medical countermeasure currently approved by the FDA for this indication under the criteria of the FDA "animal rule". This article summarizes the consequences of high-dose radiation exposure, a description of the hematopoietic acute radiation syndrome (H-ARS), the use of hematopoietic growth factors in radiation accident victims and current available treatments for H-ARS with an emphasis on the use of Neupogen in this scenario.

Pegfilgrastim, a sustained-duration form of filgrastim, significantly improves neutrophil recovery after autologous marrow transplantation in rhesus macaques.

Daily administration of filgrastim decreases the duration of severe neutropenia in the clinical setting. A sustained-duration form of filgrastim, pegfilgrastim, significantly reduces scheduling protocols to a single injection per chemotherapy cycle while maintaining therapeutic efficiency. We examined the ability of a single injection of pegfilgrastim to significantly improve neutrophil recovery following autologous bone marrow transplantation (AuBMT) in rhesus macaques. On day 1, postmyeloablation (920 cGy x-irradiation) and AuBMT, animals received either 0.1% autologous serum for 18 consecutive days (n=13), or single doses of pegfilgrastim via the subcutaneous (s.c.) or intravenous (i.v.) route (300 or 100 micro g/kg), or a single dose of filgrastim at 300 micro g/kg via the s.c. or i.v. route, or filgrastim at 10 micro g/kg via the s.c. route (n=4) on a daily basis (range=days 12-17). Pharmacokinetic parameters and neutrophil recovery were assessed. A single dose of pegfilgrastim via the i.v. or s.c. route was as effective as daily filgrastim administration, resulting in significant improvement of neutrophil recovery after myeloablation and ABuMT. Effective pegfilgrastim plasma concentrations were maintained in neutropenic animals until after the onset of hematopoietic recovery. Enhanced pharmacokinetics in AuBMT cohorts are consistent with self-regulating, neutrophil-mediated clearance.

Bone marrow myelopoiesis in rats after 10%, 20%, or 30% thermal injury.

The high incidence of serious opportunistic infections that follow thermal injuries is well documented. Normal levels of functioning leukocytes are essential to the host's ability to resist infection. This study examined alterations in murine granulopoiesis after the inducement of a standardized, sublethal, third-degree burn covering 10%, 20%, or 30% of the dorsal body surface area. Significant alterations arose in peripheral leukocyte concentrations after inducement of uncomplicated thermal injury. In general, within the first day of injury, all three trauma levels produced a peripheral leukocytosis that lasted for 35 days or more. The leukocytoses that followed 20% and 30% injuries were similar and in numerous respects paralleled previously reported human peripheral responses after similar levels of thermal trauma. Differential examinations of peripheral blood demonstrated the peripheral leukocytosis to be due primarily to the influx of morphologically mature-appearing polymorphonuclear neutrophils. Premature bone marrow release did not appear to be a factor as immature polymorphonuclear neutrophils were seldom greater than 2% of polymorphonuclear neutrophil totals. Bone marrow granulopoietic activity was examined by in vitro clonal cell culture techniques and assessed over a period of 35 days after injury. Granulocyte-macrophage colony forming cells (GM-CFC), indicative of marrow progenitor cell concentrations, were significantly increased for 28 to 35 days after 10% injury and 11 to 14 days after 20% or 30% injury. Normal or increased progenitor cell concentrations and a lack of morphologically appearing premature forms suggest that the leukocytosis is the result of injury-induced alteration(s) in polymorphonuclear neutrophil margination or release mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Tropism of canine neutrophils to xanthine oxidase.

Quantitative evaluation of neutrophil chemotaxis was performed on cells obtained by hypotonic-lysis techniques from heparinized blood samples from clinically normal dogs. The techniques resulted in neutrophil recovery rates between 60 and 80%. Chemotaxis comparisons were based on cellular migration in microchambers equipped with polycarbonate membranes with 5-micron pores. Chemo-attractant comparisons were based on neutrophil migration to medium, normal canine plasma, zymosan-activated plasma, and xanthine oxidase. Cellular migration to zymosan-activated plasma in buffer (1:100 dilution) was significantly (P less than 0.001) enhanced over random baseline medium migration. Neutrophil migrations to normal canine plasma and xanthine oxidase were quantitatively less than to zymosan-activated plasma, but were equivalent to each other and significantly greater than for random migration. Migration to xanthine oxidase was maximal at concentrations near 1 U/ml within 30 minutes.

Hypermetabolic priming of canine neutrophils by 7-S nerve growth factor.

Canine circulating neutrophils, isolated by a blood lysing technique, were incubated with 7-S nerve growth factor (NGF), at final concentrations between 12.5 and 800 ng/ml, for 30 minutes at 37 C. Neutrophil cytosolic H2O2 production, measured by flow cytometry, after 7-S NGF incubation was not significantly different from that produced at 37 C (baseline temperature controls) alone. Phorbol myristate acetate (PMA; 100 ng/ml) stimulation of neutrophils produced cytosolic H2O2 concentrations almost 13 times that of baseline temperature control neutrophils. Preincubation of neutrophils with 7-S NGF (100 to 800 ng/ml, 30 minutes, 37 C) and subsequent stimulation by PMA resulted in augmented H2O2 production in excess of twice that of neutrophils treated with PMA alone, and almost 30 times that of baseline temperature controls.

Pegfilgrastim administered in an abbreviated schedule, significantly improved neutrophil recovery after high-dose radiation-induced myelosuppression in rhesus macaques.

Conventional daily administration of filgrastim is effective in reducing the duration of severe neutropenia and enhancing survival following lethal radiation, myelosuppressive cytotoxic therapy or myeloablation and stem cell transplantation. A sustained-duration form of filgrastim, pegfilgrastim has significantly simplified scheduling protocols after chemotherapy-induced neutropenia to a single injection while maintaining the therapeutic effectiveness of daily administration of filgrastim. We examined the ability of a single or double (weekly) administration of pegfilgrastim to significantly improve neutrophil recovery in a rhesus macaque model of severe radiation-induced myelosuppression. Animals were exposed to potentially lethal 6 Gy total-body X radiation. After irradiation all animals received supportive care and were administered either pegfilgrastim at 300 µg/kg on day 1 or day 1 and day 7 post exposure, or filgrastim at 10 µg/kg/day initiated on day 1 post exposure and continued daily through neutrophil recovery. Pharmacokinetic parameters and neutrophil-related values for duration of neutropenia, neutrophil nadir, time to recovery to an absolute neutrophil count ≥500/µL or ≥2000/µL, and days of antibiotic support were determined. Effective plasma concentrations of pegfilgrastim were maintained in neutropenic animals until after the onset of hematopoietic recovery, which is consistent with neutrophil-dependent properties of elimination. Administration of pegfilgrastim at day 1 and day 7 was most effective at improving neutrophil recovery compared to daily administration of filgrastim or a single injection of pegfilgrastim on day 1, after severe, radiation-induced myelosuppression in rhesus macaques.

Therapeutic efficacy of recombinant human leukemia inhibitory factor in a primate model of radiation-induced marrow aplasia.

The therapeutic efficacy of recombinant human leukemia inhibitory factor (LIF) was examined in a nonhuman primate model of radiation-induced marrow aplasia. Rhesus monkeys received 450 cGy of total-body, 1:1 mixed neutron:gamma radiation. For 23 days thereafter, each monkey received a daily subcutaneous injection of LIF or human serum albumin (HSA) at a dose of 15 micrograms/kg body weight. Complete blood counts and white blood cell differentials were monitored for 60 days postirradiation. Administration of LIF significantly decreased (P < or = .05) the duration of thrombocytopenia (platelet count < 30,000 or 20,000/microL), ie, 9.3 days or 6.3 days, respectively, versus the HSA-treated control monkeys, 12.2 days or 10.2 days, respectively. Treatment with LIF did not alter the duration of neutropenia (absolute neutrophil count < 1,000/microL) as compared with the HSA-treated control monkeys. Cytokine administration did not exacerbate the radiation-induced anemia observed in the HSA-treated control monkeys.

Combination protocols of cytokine therapy with interleukin-3 and granulocyte-macrophage colony-stimulating factor in a primate model of radiation-induced marrow aplasia.

Single cytokine therapy with granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-3 (IL-3) has been shown to be effective in decreasing the respective periods of neutropenia and thrombocytopenia following radiation- or drug-induced marrow aplasia. The combined administration of IL-3 and GM-CSF in normal primates suggested that a sequential protocol of IL-3 followed by GM-CSF would be more effective than that of GM-CSF alone in producing neutrophils (PMN). We investigated the therapeutic efficacy of two combination protocols, the sequential and coadministration of recombinant human IL-3 and GM-CSF relative to respective single cytokine therapy, and delayed GM-CSF administration in sublethally irradiated rhesus monkeys. Monkeys irradiated with 450 cGy (mixed fission neutron:gamma radiation) received either IL-3, GM-CSF, human serum albumin (HSA), or IL-3 coadministered with GM-CSF for days 1 through 21 consecutively postexposure, or IL-3 or HSA for days 1 through 7 followed by GM-CSF for days 7 through 21. All cytokines and HSA were injected subcutaneously at a total dose of 25 micrograms/kg/d, divided twice daily. Complete blood counts (CBC) and platelet (PLT) counts were monitored over 60 days postirradiation. The respiratory burst activity of the PMN was assessed flow cytometrically, by measuring hydrogen peroxide (H2O2) production. Coadministration of IL-3 and GM-CSF reduced the average 16-day period of neutropenia and antibiotic support in the control animals to 6 days (P = .006). Similarly, the average 10-day period of severe thrombocytopenia, which necessitated PLT transfusion in the control animals, was reduced to 3 days when IL-3 and GM-CSF were coadministered (P = .004). The sequential administration of IL-3 followed by GM-CSF had no greater effect on PMN production than GM-CSF alone and was less effective than IL-3 alone in reducing thrombocytopenia. PMN function was enhanced in all cytokine-treated animals.

Aminophylline induced oxidative metabolism in isolated canine polymorphonuclear leukocytes.

Adenosine reportedly mediates myocardial and skeletal blood flow, bronchoconstriction, and cellular production of toxic oxygen radicals. Cellular effects of adenosine can be antagonized by the methylxanthines, which are widely used in the clinical treatment of obstructive airway diseases. Methylxanthine compounds such as aminophylline and theophylline inhibit the cyclic nucleotide phosphodiesterase of smooth muscle, reversing pathogenic states of bronchoconstriction. Recent techniques in flow cytometry allow examination of individual cells for the electrophysiological and metabolic cellular side effects of methylxanthine therapy. We report that the flow cytometric examination of isolated canine peripheral neutrophils, in the presence of therapeutic concentrations of aminophylline resulted in small but significant membrane depolarization and almost fivefold increases in baseline cytosolic H202 levels. If aminophylline is capable of direct in vitro activation of isolated canine neutrophils it may have the capacity to potentiate neutrophil activation in vivo: indirectly by competing with circulating modifiers, such as adenosine, for cell surface receptor sites and directly by the induction of toxic oxygen radicals as demonstrated here. H202 induction by aminophylline and other xanthine derivatives may become clinically important in instances of vascular occlusion, stasis, or instances of reperfusion where neutrophils may become activated. In an activated state, neutrophils could contribute to pathogenicity and tissue damage by indiscriminantly releasing oxygen-reactive species.

Therapeutic efficacy of recombinant interleukin-6 (IL-6) alone and combined with recombinant human IL-3 in a nonhuman primate model of high-dose, sublethal radiation-induced marrow aplasia.

Using a nonhuman-primate model of radiation-induced bone marrow aplasia, we examined whether the single, concomitant, or sequential administration of recombinant human interleukin-3 (IL-3) and IL-6 would promote bone marrow regeneration measured by an increase in circulating platelets (PLT) and neutrophils (PMN). Rhesus monkeys were irradiated at 450 cGy and were randomly assigned to one of five treatment protocols, receiving IL-6; IL-3; combined IL-6 and IL-3; sequential IL-3 and IL-6; or human serum albumin (HSA) as a control. Cytokines or HSA were administered at total dosages of 15 micrograms/kg/day. Complete blood counts and white blood cell differentials were monitored for 60 days postirradiation. Both IL-3 and IL-6 significantly enhanced the regeneration of PLTs and decreased the duration of thrombocytopenia (P = .005) without affecting PMN recovery. The radiation-induced anemia that was observed in the HSA-treated controls was less severe and resolved more quickly in the IL-6 treated animals. Sequential IL-3/IL-6 significantly increased the production of PLTs when compared with the HSA-treated controls (P = .003) and monkeys receiving concomitant IL-3/IL-6 (P = .041) but did not alter PMN levels significantly (P = .80). Coadministration of IL-6 and IL-3 did not enhance PLT but improved PMN recovery over IL-6 alone. In this primate model of marrow aplasia, IL-6 significantly enhanced the regeneration of PLTs but had no significant effect on PMN production, and did not exacerbate radiation-induced anemia. Furthermore, the use of sequentially administered IL-3 and IL-6 may improve PLT recovery as compared with concurrent IL-3/IL-6 administration, although this protocol is not significantly different in effect than either cytokine alone.

Xanthine oxidase potentiation of reactive oxygen intermediates in isolated canine peripheral neutrophils.

Oxygen-derived free radicals are believed to contribute to reperfusion injury based, in part, upon results conferred by the pharmacologic administration of allopurinol. Allopurinol inhibits xanthine oxidase (XO) activity in ischemic tissues. The possible role of XO as a pathologic mediator prompted examination of its effects on isolated peripheral canine neutrophils. In contrast to neutrophils alone, or following stimulation with phorbol myristate acetate (PMA), it was determined that XO affected both the membrane potential and the metabolism significantly. Membrane potential assay showed that at 5-10 min, PMA depolarized 89-96% of the canine neutrophils between 32-48%. Incubation with 0.5 U/ml XO involved fewer cells (54-86%), but at substantially increased cellular depolarization levels (76-90%). Metabolic assay showed that XO concentrations as low as 0.124 U induced significant cellular H2O2 production compared with temperature controls. At 0.25-0.5 U XO/10(6) cells, cytosolic H2O2 increases were almost three times those of PMA.

Recombinant human megakaryocyte growth and development factor stimulates thrombocytopoiesis in normal nonhuman primates.

Megakaryocyte growth and development factor (MGDF) is a novel cytokine that binds to the c-mpl receptor and stimulates megakaryocyte development in vitro and in vivo. This report describes the ability of recombinant human (r-Hu) MGDF to affect megakaryocytopoiesis in normal nonhuman primates. r-HuMGDF was administered subcutaneously to normal, male rhesus monkeys once per day for 10 consecutive days at dosages of 2.5, 25, or 250 micrograms/kg of body weight. Bone marrow and peripheral blood were assayed for clonogenic activity and peripheral blood counts were monitored. Circulating platelet counts increased significantly (P < .05) for all doses within 6 days of r-HuMGDF administration and reached maximal levels between day 12 and day 14 postcytokine administration. The 2.5, 25.0, and 250.0 micrograms/kg/d doses elicited peak mean platelet counts that were 592%, 670%, and 449% of baseline, respectively. Bone marrow-derived clonogenic data showed significant increases in the concentration of megakaryocyte (MEG)-colony-forming unit (CFU) and granulocyte-erythroid-macrophage-megakaryocyte (GEMM)-CFU, whereas that of granulocyte-macrophage (GM)-CFU and burst-forming unit-erythroid (BFU-e) remained unchanged during the administration of r-HuMGDF. These data show that r-HuMGDF is a potent stimulator of thrombocytopoiesis in the normal nonhuman primate.

Promegapoietin-1a, an engineered chimeric IL-3 and Mpl-L receptor agonist, stimulates hematopoietic recovery in conventional and abbreviated schedules following radiation-induced myelosuppression in nonhuman primates.

Promegapoietin-1a (PMP-1a), a multifunctional agonist for the human interleukin 3 and Mpl receptors, was evaluated for its ability to stimulate hematopoietic reconstitution in nonhuman primates following severe radiation-induced myelosuppression. Animals were total body x-irradiated (250 kVp) to 600 cGy total midline tissue dose. PMP-1a was administered s.c. in several protocols: A) daily (50 microg/kg) for 18 days; B) nine doses (5 microg/kg) every other day for 3 weeks; C) a single high dose (100 microg/kg) at 20 hours, or D) a single high dose (100 microg/kg) at 1 hour following TBI. The irradiation controls received 0.1% autologous serum for 18 consecutive days. Hematopoietic recovery was assessed by bone marrow clonogenic activity, peripheral blood cell nadirs, duration of cytopenias, time to recovery to cellular thresholds, and requirements for clinical support. PMP-1a, irrespective of administration schedule, significantly improved all platelet-related parameters: thrombocytopenia was eliminated, the severity of platelet nadirs was significantly improved, and recovery of platelet counts to > or =20,000/miccrol was significantly reduced in all PMP-1a-treated cohorts. As a consequence, all PMP-1a-treated cohorts were transfusion-independent. Neutrophil regeneration was augmented in all treatment schedules. Additionally, all PMP-1a-treated cohorts showed an improvement in red blood cell nadir and recovery. PMP-1a in conventional or abbreviated schedules induced significant thrombopoietic regeneration relative to the control cohort, whereas significant improvement in neutrophil recovery was schedule-dependent in radiation-myelosuppressed nonhuman primates.

Leridistim, a chimeric dual G-CSF and IL-3 receptor agonist, enhances multilineage hematopoietic recovery in a nonhuman primate model of radiation-induced myelosuppression: effect of schedule, dose, and route of administration.

Leridistim is from the myelopoietin family of proteins, which are dual receptor agonists of the human interleukin-3 and G-CSF receptor complexes. This study investigated the effect of dosage, administration route, and schedule of leridistim to stimulate multilineage hematopoietic recovery in total body irradiated rhesus monkeys. Animals were x-irradiated on day 0 (600 cGy, 250 kVp) and then received, on day 1, leridistim s.c. in an abbreviated, every-other-day schedule at 200 microg/kg, or daily at 50 microg/kg, or i.v. daily or every-other-day schedules at 200 microg/kg dose. Other cohorts received G-CSF (Neupogen((R)) [Filgrastim]) in an every-other-day schedule at 100 microg/kg/day, or autologous serum (0.1%) s.c. daily. Hematopoietic recovery was assessed by bone marrow clonogenic activity, peripheral blood cell nadirs, duration of cytopenias, time to recovery to cellular thresholds, and requirements for clinical support. Leridistim, administered s.c. every other day, or i.v. daily, significantly improved neutrophil, platelet, and lymphocyte nadirs, shortened the respective durations of cytopenia, hastened trilineage hematopoietic recovery, and reduced antibiotic and transfusion requirements. A lower dose of leridistim administered daily s.c. enhanced recovery of neutrophil and platelet parameters but did not affect lymphocyte recovery relative to controls. Leridistim, a novel engineered hematopoietic growth factor administered at the appropriate dose, route and schedule, stimulates multilineage hematopoietic reconstitution in radiation-myelosuppressed nonhuman primates.

Myelopoietin, an engineered chimeric IL-3 and G-CSF receptor agonist, stimulates multilineage hematopoietic recovery in a nonhuman primate model of radiation-induced myelosuppression.

Myelopoietins (MPOs) constitute a family of engineered, chimeric molecules that bind and activate the IL-3 and G-CSF receptors on hematopoietic cells. This study investigated the in vivo hematopoietic response of rhesus monkeys administered MPO after radiation-induced myelosuppression. Animals were total body irradiated (TBI) in 2 series, with biologically equivalent doses consisting of either a 700 cGy dose of Cobalt-60 ((60)Co) gamma-radiation or 600 cGy, 250 kVp x-irradiation. First series: On day 1 after 700 cGy irradiation, cohorts of animals were subcutaneously (SC) administered MPO at 200 microg/kg/d (n = 4), or 50 microg/kg/d (n = 2), twice daily, or human serum albumin (HSA) (n = 10). Second series: The 600 cGy x-irradiated cohorts of animals were administered either MPO at 200 microg/kg/d, in a daily schedule (n = 4) or 0.1% autologous serum (AS), daily, SC (n = 11) for 23 days. MPO regardless of administration schedule (twice a day or every day) significantly reduced the mean durations of neutropenia (absolute neutrophil count [ANC] < 500/microL) and thrombocytopenia (platelet < 20,000/microL) versus respective control-treated cohorts. Mean neutrophil and platelet nadirs were significantly improved and time to recovery for neutrophils (ANC to < 500/microL) and platelets (PLT < 20,000/microL) were significantly enhanced in the MPO-treated cohorts versus controls. Red cell recovery was further improved relative to control-treated cohorts that received whole blood transfusions. Significant increases in bone marrow-derived clonogenic activity was observed by day 14 after TBI in MPO-treated cohorts versus respective time-matched controls. Thus, MPO, administered daily was as effective as a twice daily schedule for multilineage recovery in nonhuman primates after high-dose, radiation-induced myelosuppression.