R. M. Vigneulle

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 μg/kg, or daily at 50 μg/kg, or i.v. daily or every‐other‐day schedules at 200 μg/kg dose. Other cohorts received G‐CSF (Neupogen® [Filgrastim]) in an every‐other‐day schedule at 100 μg/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.

Structural and functional alterations of the gastrointestinal tract following radiation-induced injury in the rhesus monkey

A severe and debilitating diarrhea is a dose-limiting toxic result for patients receiving abdominal radiation or chemotherapy. To correlate changes in intestinal structure and function, nonhuman primates were exposed to 9.5 Gy total abdominal x-irradiation. Diarrhea and weight loss were correlated with intestinal crypt and villus histology, in vivo assessed intestinal permeability, and ex vivo functional studies performed in Ussing chamber assays before and at 7, 14, and 35 days after irradiation. Peak gut structural damage occurred early and paralleled functional changes of the intestinal mucosa, including increased epithelial permeability (both in vivo and ex vivo), activation of secretory pathways, decreased nutrient absorption, diarrhea, and weight loss. Recovery of gut integrity and epithelial resistance began thereafter, in spite of incomplete histological recovery. Our integrated approach allowed a comprehensive study of the relationship between postirradiation tissue injury and changes in function over time in the gastrointestinal tract of the nonhuman primate.

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 μg/kg on day 1, while two other groups (both n = 4) received peg‐leridistim at 200 μg/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.

The Relative Biological Effectiveness of Mixed Fission-Neutron-γ Radiation on the Hematopoietic Syndrome in the Canine: Effect of Therapy on Survival@@@The Relative Biological Effectiveness of Mixed Fission-Neutron-g Radiation on the Hematopoietic Syndrome in the Canine: Effect of Therapy on Survival

Acute lethality syndromes produced by the accidental exposure of humans to mixed neutron and gamma radiation from external sources can be related to acute lethality from photon irradiation using the relative biological effectiveness (RBE) for common end points. We used the canine as a model to study injury following exposure to mixed neutron and gamma radiation from the AFRRI TRIGA reactor. Exposures from the reactor were steady-state mode (40 cGy/min, bilateral) with an average neutron energy of 0.85 MeV; tissue-air ratio = 0.59 at midline abdominal. Healthy male and female canines were irradiated free-in-air behind a 6-in. lead wall; the neutron-gamma ratio was 5.4:1 at the entrance skin surface; exposures are reported as midline tissue doses. Bilateral exposure resulted in an LD50/30 of 153 cGy without therapeutic clinical support. Addition of clinical support consisting of fluids, antibiotics, and fresh irradiated platelets/whole blood increased the bilateral LD50/30 to 185 cGy, a dose modifying factor (DMF) of 1.21. This corresponds to respective LD50/30 values for bilateral 60Co gamma exposures of 260 and 338 cGy for nonsupported and clinically supported animals, and a DMF of 1.30. The RBE based on the values determined at midline tissue is approximately 1.69. Clinical support after bilateral irradiation produced a similar DMF to those of mixed fission neutrons and gamma rays and 60Co gamma rays alone. The RBE of 1.69 for midline tissue bilateral exposures is higher than 1, an RBE often cited for large animals. Therapeutic support administered to lethally irradiated canines significantly improved survival and increased the LD50/30 independent of radiation quality.

Survival of Erythroid Burst-Forming Units and Erythroid Colony-Forming Units in Canine Bone Marrow Cells Exposed in Vitro to 1 MeV Neutron Radiation or X Rays

Conditioned media (CM) from allogeneic stimulated cultures of light density cells (less than 1.08 g/cm3) from the peripheral blood of normal dogs were used to stimulate the growth of erythroid burst-forming units (BFU-E) in bone marrow from normal dogs. Maximum numbers of BFU-E were obtained when 5% (vol/vol) 3 X CM and 2 U/ml erythropoietin were added to plasma clot cultures of bone marrow cells. In addition, the radiation sensitivity (D0 value) was determined for CFU-E and for BFU-E in bone marrow cells exposed in vitro to 1 MeV fission neutron radiation or 250 kVp X rays. BFU-E were more sensitive than CFU-E to the lethal effects of both types of radiation. For bone marrow cells exposed to 1 MeV neutron radiation, the D0 for CFU-E was 0.27 +/- 0.01 Gy, and the D0 for BFU-E was 0.16 +/- 0.03 Gy. D0 values for CFU-E and BFU-E were, respectively, 0.61 +/- 0.05 Gy and 0.26 +/- 0.09 Gy for cells exposed to X rays. The neutron RBE values for the culture conditions described were 2.3 +/- 0.01 for CFU-E and 1.6 +/- 0.40 for BFU-E.

Nonuniform irradiation of the canine intestine. I. Effects.

To investigate the effects of nonuniform irradiation on the small intestine, we prepared 24 dogs for continent isoperistaltic ileostomies under aseptic surgical conditions and general anesthesia. After a 3-week recovery period, the ileum was catheterized with a fiberoptic endoscope to observe the intestinal mucosa and to harvest mucosal biopsies. The baseline macroscopic and microscopic appearance of the intestinal mucosa was determined. Two weeks later, the ileum was catheterized with a 100-cm soft tube containing 40 groups of three thermoluminescent dosimeters placed at equally spaced intervals, and a dose of either 4.5, 8, 10, 11, or 15 Gy 60Co gamma rays was delivered to the right abdomen (nonuniform exposure). This method allowed a direct and precise assessment of the dose received at 40 sites located in the 100-cm intestinal segment. The intestinal mucosa was again evaluated 1, 4, and 6 days after irradiation. All animals exposed to 4.5 and 8 Gy survived, whereas none survived after 11 and 15 Gy. After exposure to 10 Gy, 60% of the animals died within 4-6 days and 40% survived with symptoms associated with both the intestinal and the hematopoietic syndromes. Crypt cell necrosis, blunting of villi, and reduction of the mucosal lining increased between 1 and 4 days after irradiation, and mucosal damage was correlated with intraintestinal dosimetry at Day 6. The granulocyte counts at Day 4 were significantly lower than baseline level in animals that died within 4-6 days but not in survivors. The present model appears to be realistic and clinically relevant, allowing the concurrent study of the intestinal and hematopoietic effects of high-dose nonuniform irradiation similar to that received by patients during radiation therapy as well as by radiation accident victims.