Hematopoietic growth factors: Current knowledge, future prospects

PEGylated G-CSF (BBT-015), GM-CSF (BBT-007), and IL-11 (BBT-059) analogs enhance survival and hematopoietic cell recovery in a mouse model of the hematopoietic syndrome of the acute radiation syndrome

Hematopoietic growth factors (HGF) are recommended therapy for high dose radiation exposure, but unfavorable administration schedules requiring early and repeat dosing limit the logistical ease with which they can be used. In this report, using a previously described murine model of H-ARS, survival efficacy and effect on hematopoietic recovery of unique PEGylated HGF were investigated. The PEGylated-HGFs possess longer half-lives and more potent hematopoietic properties than corresponding non-PEGylated-HGFs. C57BL/6 mice underwent single dose lethal irradiation (7.76-8.72 Gy, Cs, 0.62-1.02 Gy min) and were treated with various dosing regimens of 0.1, 0.3, and 1.0 mg kg of analogs of human PEG-G-CSF, murine PEG-GM-CSF, or human PEG-IL-11. Mice were administered one of the HGF analogs at 24-28 h post irradiation, and in some studies, additional doses given every other day (beginning with the 24-28 h dose) for a total of three or nine doses. Thirty-day (30 d) survival was significantly increased with only one dose of 0.3 mg kg of PEG-G-CSF and PEG-IL-11 or three doses of 0.3 mg kg of PEG-GM-CSF (p ≤ 0.006). Enhanced survival correlated with consistently and significantly enhanced WBC, NE, RBC, and PLT recovery for PEG-G- and PEG-GM-CSF, and enhanced RBC and PLT recovery for PEG-IL-11 (p ≤ 0.05). Longer administration schedules or higher doses did not provide a significant additional survival benefit over the shorter, lower dose, schedules. These data demonstrate the efficacy of BBT's PEG-HGF to provide significantly increased survival with fewer injections and lower drug doses, which may have significant economic and logistical value in the aftermath of a radiation event.

Survival efficacy of the PEGylated G-CSFs Maxy-G34 and neulasta in a mouse model of lethal H-ARS, and residual bone marrow damage in treated survivors

In an effort to expand the worldwide pool of available medical countermeasures (MCM) against radiation, the PEGylated G-CSF (PEG-G-CSF) molecules Neulasta and Maxy-G34, a novel PEG-G-CSF designed for increased half-life and enhanced activity compared to Neulasta, were examined in a murine model of the Hematopoietic Syndrome of the Acute Radiation Syndrome (H-ARS), along with the lead MCM for licensure and stockpiling, G-CSF. Both PEG-G-CSFs were shown to retain significant survival efficacy when administered as a single dose 24 h post-exposure, compared to the 16 daily doses of G-CSF required for survival efficacy. Furthermore, 0.1 mg kg of either PEG-G-CSF affected survival of lethally-irradiated mice that was similar to a 10-fold higher dose. The one dose/low dose administration schedules are attractive attributes of radiation MCM given the logistical challenges of medical care in a mass casualty event. Maxy-G34-treated mice that survived H-ARS were examined for residual bone marrow damage (RBMD) up to 9 mo post-exposure. Despite differences in Sca-1 expression and cell cycle position in some hematopoietic progenitor phenotypes, Maxy-G34-treated mice exhibited the same degree of hematopoietic stem cell (HSC) insufficiency as vehicle-treated H-ARS survivors in competitive transplantation assays of 150 purified Sca-1+cKit+lin-CD150+cells. These data suggest that Maxy-G34, at the dose, schedule, and time frame examined, did not mitigate RBMD but significantly increased survival from H-ARS at one-tenth the dose previously tested, providing strong support for advanced development of Maxy-G34, as well as Neulasta, as MCM against radiation.

Serum levels of endogenous thrombopoietin and granulocyte-colony stimulating factor in patients with acute or lymphoma type adult T-cell leukemia during multicycle chemotherapy

Recent multidrug chemotherapy for adult T-cell leukemia (ATL) showed improved findings, however, these protocols often induced persistent myelosuppression. Among 67 patients with acute and lymphoma type ATL treated between January 1996 and December 1998, 42 patients died during this period and showed chemotherapy-induced myelosuppression. To characterize the relation between the severity of myelosuppression and the endogenous thrombopoietin (TPO) or granulocyte-colony stimulating factor (G-CSF) levels in ATL patients, we measured these hematopoietic factors using ELISA method. Nineteen patients with acute or lymphoma type ATL and 16 healthy individuals were examined. During thrombocytopenia, the serum TPO levels were significantly higher than that of controls (P < 0.0001) and were inversely correlated with the platelet counts (r = -0.687 P < 0.001). Later in the chemotherapy cycle, severe persistent thrombocytopenia occurred and TPO levels elevated and remained at a high level approximating the TPO levels of exogenous TPO administration (0.3 microg/kg body weight). On the other hand, the serum G-CSF levels with absolute neutrophil counts (ANC) below 0.5 x 10(9)/L were significantly higher than controls (P = 0.009) and inversely correlated with ANC (r = -0.382 P = 0.0034). However, G-CSF levels in six samples obtained after 6 h of G-CSF (100-150 microg per body) administration was approximately 50-fold higher than that in the neutropenic states. These findings suggested that G-CSF can effectively reduce the severity and duration of intensified chemotherapy-induced neutropenia and higher dose exogenous TPO (higher than 0.6 microg/kg per day) therapy may be required to enhance platelet recovery after intensive chemotherapy in ATL patients.

Structure-activity relationships of novel hematoregulatory peptides

Hematopoiesis is a lifelong cell renewal process regulated by a family of lineage specific hematopoietic growth factors. Several hematopoietic growth factors such as G-CSF, GM-CSF, and M-CSF have been clinically evaluated for enhancement of host defense in normal and immunocompromised patients and for the treatment of infectious diseases. This paper reports the structure-activity relationships of low molecular weight hematoregulatory peptides based on a nonapeptide (1, SK&F 107647). Like the macromolecular growth factors, these peptides modulate host defense. A molecular target for this class of compounds has not yet been identified. However, the structure-activity relationships established by this study implicate a very specific molecular recognition event that is pivotal for the biological activities of 1 and its analogues.

Biology and therapeutic uses of myeloid hematopoietic growth factors and interferons

Recent advances in basic science and clinical trials have demonstrated that IFNs and myeloid hematopoietins play crucial roles in host defense against pathogens and immune surveillance. Here we have reviewed the biologic functions of GM-CSF, G-CSF, IFN-alpha and IFN-gamma. For patients with neutropenia resulting from cytotoxic chemotherapy, bone marrow transplantation, congenital agranulocytosis and cyclic neutropenia, therapeutic uses of GM-CSF and G-CSF were reviewed. Application of these growth factors to patient management represents a major contribution of biotechnology to a difficult area of therapeutics in febrile, neutropenic patients. Because IFN-alpha plays crucial roles in antiviral responses, its clinical applications in hepatitis B and C, human papilloma virus, HIV infection and malignancy were discussed. The use of IFN-gamma in bacterial prophylaxis in patients with chronic granulomatous disease was also presented. Advances in clinical applications of IFNs and hematopoietic growth factors serve as a paradigm for further development to investigate the use of other important cytokines in modern therapeutics.

Hematopoietic stem cell cytokine response

The process of hematopoiesis can be modelled on the concept of a pluripotential stem cell able to differentiate and proliferate in multiple lineages. This process proceeds under the permissive or directive influence of "early" and "late" acting hematopoietic cytokines probably acting in synergistic combinations within the context of the marrow stromal microenvironment. Further characterization of the biochemical events that transduce cytokine signalling into cellular events and the ultimate description of the earliest progenitor cell populations and the cytokines which influence them will provide key insights into embryogenesis and tissue maintenance as well as suggest new therapeutic approaches for hematologic and malignant diseases.

Hematopoietic growth factors. Defining the appropriate clinical role in multimodality cancer therapy

Laboratory investigations have begun to elucidate the regulatory molecules that control the processes of blood cell growth and differentiation. Recombinant human colony-stimulating factors are examples of biotechnology-produced molecules that have epitomized the translation of such basic scientific investigation into therapeutic advances. Small cell lung cancer, a malignancy that is overall highly sensitive to aggressive myelosuppressive chemotherapy at initial presentation, has been used as a clinical model in which the activity of human colony-stimulating factors has been tested. In this article, the clinical applications of hematopoietic growth factors are reviewed in brief. The appropriate clinical use of these agents may allow novel therapeutic strategies to be developed in a research setting. Similarly, these agents have the potential to improve supportive care and improve certain clinical outcomes in the non-research clinical care of patients. Issues of cost of treatment are raised by these agents, but the true clinical value of hematopoietic growth factors needs to be studied more rigorously, with emphasis on quality of life and redistribution of care costs outside of hospitals before definitive statements can be made.

Changes in Tc-99m radionuclide bone scan images and peripheralization of marrow hematopoietic activity associated with the administration of granulocyte colony stimulating factor as an adjunct to dose-intensified chemotherapy for breast cancer. A case report

Granulocyte colony stimulating factor (G-CSF) is used clinically for chemotherapy-associated neutropenia. Very little is known about the manner in which pharmacologic dosing of G-CSF may affect radiologic studies in vivo. Dramatic changes on bone scan associated with the administration of G-CSF used to support dose-intensified combination chemotherapy in a patient with metastatic breast carcinoma are described. The scintigraphic findings were correlated histologically with increased hematopoietic activity in the bone marrow located in peripheral bones.

Impact of hematopoietic growth factors on the management of small-cell lung cancer

Hematopoietic growth factors regulate the production and differentiation of immature progenitor cells and activate mature effector cells. With recombinant DNA technology, these human proteins have been biosynthesized, and their clinical applications hold promise for beneficial therapeutic effects. The hematopoietic growth factors are generally classified in 2 groups, the colony-stimulating factors (CSFs) and the interleukins. In oncology, it has been shown that the administration of CSFs will attenuate chemotherapy-induced myelosuppression and permit administration of the planned chemotherapy doses, especially in chemosensitive tumors like small-cell lung cancer. Widespread clinical administration of the CSFs at this time without regard to the predicted risk of a given therapeutic regimen would seem to be inappropriate both therapeutically and economically. Continuing investigations should focus on important clinical end points. Until then, our ability to use the CSFs optimally, rationally, and in a cost-effective manner will remain limited.