Hematopoietic recovery following autologous bone marrow transplantation in a nonhuman primate: effect of variation in treatment schedule with PEG-rHuMGDF

Nonhuman primates as models for the discovery and development of radiation countermeasures

INTRODUCTION

Despite significant scientific advances over the past six decades toward the development of safe and effective radiation countermeasures for humans using animal models, only two pharmaceutical agents have been approved by United States Food and Drug Administration (US FDA) for hematopoietic acute radiation syndrome (H-ARS). Additional research efforts are needed to further develop large animal models for improving the prediction of clinical safety and effectiveness of radiation countermeasures for ARS and delayed effects of acute radiation exposure (DEARE) in humans. Area covered: The authors review the suitability of animal models for the development of radiation countermeasures for ARS following the FDA Animal Rule with a special focus on nonhuman primate (NHP) models of ARS. There are seven centers in the United States currently conducting studies with irradiated NHPs, with the majority of studies being conducted with rhesus monkeys. Expert opinion: The NHP model is considered the gold standard animal model for drug development and approval by the FDA. The lack of suitable substitutes for NHP models for predicting response in humans serves as a bottleneck for the development of radiation countermeasures. Additional large animal models need to be characterized to support the development and FDA-approval of new radiation countermeasures.

Identification of a potent small molecule capable of regulating polyploidization, megakaryocyte maturation, and platelet production

Background

Megakaryocytic cell maturation involves polyploidization, and megakaryocyte (MK) ploidy correlates with their maturation and platelet production. Retardation of MK maturation is closely associated with poor MK engraftment after cord blood transplantation and neonatal thrombocytopenia. Despite the high prevalence of thrombocytopenia in a range of setting that affect infants to adults, there are still very limited modalities of treatment.

Methods

Human CD34⁺ cells were isolated from cord blood or bone marrow samples acquired from consenting patients. Cells were cultured and induced using 616452 and compared to current drugs on the market such as rominplostim or TPO. Ploidy analysis was completed using propidium iodide staining and flow cytometry analysis. Animal studies consisted of transplanting human CD34⁺ cells into NOD.Cg-Prkdc^scidIl2rg^tm1Wjl/SzJ mice followed by daily injections of 15 mg/kg of 616452.

Results

Within one week of culture, the chemical was able to induce polyploidization, the process required for megakaryocyte maturation with the accumulation of DNA content, to 64 N or greater to achieve a relative adult size. We observed fold increases as high as 200-fold in cells of 16 N or greater compared to un-induced cells with a dose-dependent manner. In addition, MK differentiated in the presence of 616452 demonstrated a more robust capacity of MK differentiation than that of MKs cultured with rominplostim used for adult idiopathic thrombocytopenic purpura (ITP) patients. In mice transplanted with human cord blood, 616452 strikingly enhanced MK reconstitution in the marrow and human peripheral platelet production. The molecular therapeutic actions for this chemical may be through TPO-independent pathways.

Conclusion

Our studies may have an important impact on our fundamental understanding of fetal MK biology, the clinical management of thrombocytopenic neonates and leukemic differentiation therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0358-y) contains supplementary material, which is available to authorized users.

Molecular and cellular profiling of acute responses to total body radiation exposure in ovariectomized female cynomolgus macaques

PURPOSE

The threat of radiation exposure requires a mechanistic understanding of radiation-induced immune injury and recovery. The study objective was to evaluate responses to ionizing radiation in ovariectomized (surgically post-menopausal) female cynomolgus macaques.

MATERIALS AND METHODS

Animals received a single total-body irradiation (TBI) exposure at doses of 0, 2 or 5 Gy with scheduled necropsies at 5 days, 8 weeks and 24 weeks post-exposure. Blood and lymphoid tissues were evaluated for morphologic, cellular, and molecular responses.

RESULTS

Irradiated animals developed symptoms of acute hematopoietic syndrome, and reductions in thymus weight, thymopoiesis, and bone marrow cellularity. Acute, transient increases in plasma monocyte chemoattractant protein 1 (MCP-1) were observed in 5 Gy animals along with dose-dependent alterations in messenger ribonucleic acid (mRNA) signatures in thymus, spleen, and lymph node. Expression of T cell markers was lower in thymus and spleen, while expression of macrophage marker CD68 (cluster of differentiation 68) was relatively elevated in lymphoid tissues from irradiated animals.

CONCLUSIONS

Ovariectomized female macaques exposed to moderate doses of radiation experienced increased morbidity, including acute, dose-dependent alterations in systemic and tissue-specific biomarkers, and increased macrophage/T cell ratios. The effects on mortality exceeded expectations based on previous studies in males, warranting further investigation.

Alpha-tocopherol succinate- and AMD3100-mobilized progenitors mitigate radiation combined injury in mice

The purpose of this study was to elucidate the role of alpha-tocopherol succinate (TS)- and AMD3100-mobilized progenitors in mitigating combined injury associated with acute radiation exposure in combination with secondary physical wounding. CD2F1 mice were exposed to high doses of cobalt-60 gamma-radiation and then transfused intravenously with 5 million peripheral blood mononuclear cells (PBMCs) from TS- and AMD3100-injected mice after irradiation. Within 1 h after irradiation, mice were exposed to secondary wounding. Mice were observed for 30 d after irradiation and cytokine analysis was conducted by multiplex Luminex assay at various time-points after irradiation and wounding. Our results initially demonstrated that transfusion of TS-mobilized progenitors from normal mice enhanced survival of acutely irradiated mice exposed 24 h prior to transfusion to supralethal doses (11.5-12.5 Gy) of (60)Co gamma-radiation. Subsequently, comparable transfusions of TS-mobilized progenitors were shown to significantly mitigate severe combined injuries in acutely irradiated mice. TS administered 24 h before irradiation was able to protect mice against combined injury as well. Cytokine results demonstrated that wounding modulates irradiation-induced cytokines. This study further supports the conclusion that the infusion of TS-mobilized progenitor-containing PBMCs acts as a bridging therapy in radiation-combined-injury mice. We suggest that this novel bridging therapeutic approach involving the infusion of TS-mobilized hematopoietic progenitors following acute radiation exposure or combined injury might be applicable to humans.

Characterization of the radiation-damaged precursor cells in bone marrow based on modeling of the peripheral blood granulocytes response

Bone marrow failure is the major cause of radiation lethality in mammals. Since bone marrow is distributed heterogeneously within trabecular spongiosa encased in a cortex of cortical bone, it is very difficult to measure the extent of the radiation damage directly. However, indirect consequences of damage to marrow, such as reductions in peripheral blood cell counts, are easily measured. In this paper, the authors investgate a mathematical model of the granulopoiesis system that provides quantitative relationships between reductions in peripheral blood cells and the bone marrow precursor cells following radiation exposure. A coarse-grained architecture of cellular replication and production as well as a mechanism for implicit regulation used in this model are discussed. The model is based on previous investigations of rodents. The authors test how well the model matches, in the principal dynamic regime of hematopoiesis, experimental data on large animals as well as empirical data on humans following radiation exposure. Due to its ability to infer, albeit indirectly, radiation damage to bone marrow, this model will provide a useful computational tool in radiation accident management, military operations involving nuclear warfare, radiation therapy, and space radiation risk assessment.

A randomized, double-blind, placebo-controlled, dose ranging study to assess the efficacy and safety of eltrombopag in patients receiving carboplatin/paclitaxel for advanced solid tumors

OBJECTIVES

Eltrombopag, an oral, nonpeptide thrombopoietin receptor agonist, has been shown to increase platelet counts in adults with chronic immune thrombocytopenia and chronic hepatitis C. This multicenter phase 2 study assessed the efficacy and safety of eltrombopag in patients receiving first-line carboplatin/paclitaxel for the treatment of advanced solid tumors.

RESEARCH DESIGN AND METHODS

Patients (N = 183) were randomized to placebo or eltrombopag 50 mg, 75 mg, or 100 mg given orally following chemotherapy on days 2 through 11 of each 21-day cycle, for at least two cycles. The primary endpoint was the difference in platelet count from day 1 in cycle 2 to the platelet nadir in cycle 2.

CLINICAL TRIAL REGISTRY NUMBER

NCT00102726.

RESULTS

Although the primary endpoint was not met, postnadir platelet counts increased during cycles 1 and 2 in all eltrombopag treatment groups compared with placebo. The most commonly reported adverse events across all study arms (including placebo) were nausea and alopecia and eltrombopag was generally well tolerated.

CONCLUSIONS

This study provides preliminary information that eltrombopag does increase platelets in patients receiving chemotherapy for advanced solid tumors. Further investigation is needed to identify the optimal dose(s) and schedule of eltrombopag in patients receiving myelosuppressive chemotherapy.

Reconstitution of the myeloid and lymphoid compartments after the transplantation of autologous and genetically modified CD34+ bone marrow cells, following gamma irradiation in cynomolgus macaques

Background

Prolonged, altered hematopoietic reconstitution is commonly observed in patients undergoing myeloablative conditioning and bone marrow and/or mobilized peripheral blood-derived stem cell transplantation. We studied the reconstitution of myeloid and lymphoid compartments after the transplantation of autologous CD34⁺ bone marrow cells following gamma irradiation in cynomolgus macaques.

Results

The bone marrow cells were first transduced ex vivo with a lentiviral vector encoding eGFP, with a mean efficiency of 72% ± 4%. The vector used was derived from the simian immunodeficiency lentivirus SIVmac251, VSV-g pseudotyped and encoded eGFP under the control of the phosphoglycerate kinase promoter. After myeloid differentiation, GFP was detected in colony-forming cells (37% ± 10%). A previous study showed that transduction rates did not differ significantly between colony-forming cells and immature cells capable of initiating long-term cultures, indicating that progenitor cells and highly immature hematopoietic cells were transduced with similar efficiency. Blood cells producingeGFP were detected as early as three days after transplantation, and eGFP-producing granulocyte and mononuclear cells persisted for more than one year in the periphery.

Conclusion

The transplantation of CD34⁺ bone marrow cells had beneficial effects for the ex vivo proliferation and differentiation of hematopoietic progenitors, favoring reconstitution of the T- and B-lymphocyte, thrombocyte and red blood cell compartments.

A multi-compartment cell repopulation model allowing for inter-compartmental migration following radiation exposure, applied to leukaemia

There is much uncertainty about cancer risks at the high radiation doses used in radiotherapy (RT). It has generally been assumed that cancer induction decreases rapidly at high doses due to cell killing. However, this is not seen in all RT groups, and a model recently developed by Sachs and Brenner [2005. Solid tumor risks after high doses of ionizing radiation. Proc. Natl Acad. Sci. USA 102, 13040-13045] proposed a mechanism for repopulation of cells after radiation exposure that explained why this might happen, at least for solid tumours. In this paper, this model is generalized to allow for heterogeneity in the dose received, and various alternate patterns of repopulation are also considered. The model is fitted to the Japanese atomic bomb survivor leukaemia incidence data, and data for various therapeutically irradiated groups. Two sets of parameters from these model fits are used to assess the sensitivity of model predictions. It is shown that in general allowing for heterogeneity in dose distribution and haematopoietic stem cell migration results in lower risks than the same average dose administered uniformly and without such migration, although this does not hold in the limiting case of complete stem cell repopulation between radiation dose fractions. We also investigate the difference made by assuming a compartmental repopulation signal, and a global repopulation signal. In general we show that in the absence of stochastic extinction, compartmental repopulation always predicts a larger number of mutated cells than global repopulation. However, in certain dose regimes stochastic extinction cannot be ignored, and in these cases the numbers of mutated cells predicted with global repopulation can exceed that for compartmental repopulation. In general, mutant cell numbers are highly overdispersed, with variance much greater than the mean.

Vascular Endothelial Cells Produce Soluble Factors That Mediate the Recovery of Human Hematopoietic Stem Cells after Radiation Injury

The risk of terrorism with nuclear or radiologic weapons is considered to be high over the coming decade. Ionizing radiation can cause a spectrum of hematologic toxicities, from mild myelosuppression to myeloablation and death. However, the potential regenerative capacity of human hematopoietic stem cells (HSCs) after radiation injury has not been well characterized. In this study, we sought to characterize the effects of ionizing radiation on human HSCs and to determine whether signals from vascular endothelial cells could promote the repair of irradiated HSCs. Exposure of human bone marrow CD34+ cells to 400 cGy caused a precipitous decline in hematopoietic progenitor cell content and primitive cells capable of repopulating nonobese diabetic/severe combined immunodeficient mice (SCID-repopulating cells), which was not retrievable via treatment with cytokines. Conversely, culture of 400 cGy-irradiated bone marrow CD34+ cells with endothelial cells under noncontact conditions supported the differential recovery of both viable progenitor cells and primitive SCID-repopulating cells. These data illustrate that vascular endothelial cells produce soluble factors that promote the repair and functional recovery of HSCs after radiation injury and suggest that novel factors with radiotherapeutic potential can be identified within this milieu.

Role of cytokines and growth factors in radioprotection

Cytokines and growth factors are growing groups of proteins that are responsible for the communication between cells of the immune system, hematopoietic cells, and other cell types. The cloning and large-scale production in a recombinant form of these agents in pharmacological quantities permitted investigations aimed at assessing the benefit they may provide in preserving and restoring functions of tissues compromised by irradiation. We have extensively examined past investigations which suggest that some cytokines and growth factors protect animals from radiation lethality when given prior to or after irradiation, and even in untreated animals, these cytokines serve in innate defenses against external stimuli. In contrast, some cytokines given before irradiation sensitize the animals to radiation lethality. Unfortunately, due to their adverse side effects, these cytokines were not found suitable as radioprotectors. Recent studies suggest that new approaches may bring cytokines and growth factors in clinic for radiation injury. The information and insight gained about therapeutic potential of cytokine manipulation will allow for more rational design of treatment protocols.