7 - Hematopoietic Growth Factors Flashcards
What is hematopoiesis?
Process of production and maturation of blood cells
How does the stem cell pool maintain itself?
- By asymmetrical cell division w/o extensive depletion
- When a stem cell divides, one daughter cell remains in the stem cell pool and the other becomes a committed colony-forming unit (CFU)
- CFUs proliferate at a greater rate than the other stem cells and are more limited in self-renewal than pluripotent hematopoietic stem cells
- Stem cell splits into 2 cells, then one cell will continue to divide but the other won’t
- When a multipotential hematopoietic stem cell is stimulated by colony stimulating factor (CSF), it splits into either common myeloid progenitor or common lymphoid progenitor
Cells committed to myeloid pathway can develop into ___
RBCs (erythrocytes), platelets (thrombocytes), monocytes and macrophage, granulocytes (neutrophils, eosinophils and basophils), or tissue mast cells
Cells committed to lymphoid pathway give rise to ____
B- or T-lymphocytes (natural killer cells) or plasma cells
What is the difference between white cell factors, red cell factors, and platelet factors?
- White cell factors = granulocyte colony-stimulating factor (G-CSF) and granulocyte macrophage colony stimulating factor (Gm-CSF)
- Red cell factors = erythropoietins (EPO) and darbepoetin alfa
- Platelet factor = thrombopoietin (TPO) / megakaryocyte growth and development factor (MGDF) and interleukin-11 (IL-11)
What is an early acting HGF?
Stem cell factor
Pharmacology and physiology of HGFs
- HGFs bind to their specific cellular membrane receptors => cascade of intracellular signaling and altered gene expression
- May induce another gene expression that produces a different HGF or cytokine, which in turn to stimulate another target cell
- Therefore, it is difficult to delineate the pharmacologic activity of individual HGF
Cytokine receptor families
- Growth hormone family = cytokines that signal through a single chain (EPO, G-CSF)
- gp130 family = cytokines that signal through gp130 or a gp130-related subunit
- gp140 family = cytokines that signal through the gp140-subunit and a ligand-binding-subunit (GM-CSF)
- Interleukin-2 receptor family = cytokines that signal through a common gamma-chain and alpha and/or beta ligand-binding subunits
- Interferon family = cytokines that signal through 2 or more subunits
Signaling pathway of cytokines
- Ligand binding to cytokine receptors induces their dimerization, which then phosphorylates JAKs
- Phosphorylated JAKs subsequently phosphorylate STATs
- Activated STATs dimerize, translocate to the nucleus whereby they activate or repress target gene promoters
- In addition to JAKs and STATs, cytokine receptors also activate additional signaling pathways involving proteins such as Akt and extracellular responsive kinase (ERK)
In vitro activity of HGFs
- Determined by evaluating the effect of adding HGF to cell culture containing immature progenitor cells from the bone marrow
- Lineage specific growth factor (G-CSF, EPO) predominantly affect one cell lineage
- Multilineage growth factor (GM-CSF) affect more than one cell lineage
- This phenomenon is concentration dependent (ex: GM-CSF regulate monocytes and granulocytes at 5-20 pg/mL while they regulate eosinophils and platelets at 20-2000 pg/mL)
In vivo activity of HGFs
- Can be evaluated by measuring endogenous concentrations under different conditions or by administering growth factors to animals or humans
- Results are often consistent w/ those predicted by in vitro studies
- Differences between the in vivo and in vitro activities of HGFs could be due to interspecies variability, difference in clearance, PK, and glycosylation
Cellular source of G-CSF
Monocytes, fibroblasts, endothelial cells, bone marrow stroma
Cellular source of GM-CSF
T-cells, monocytes, fibroblasts, endothelial cells
Cellular source of EPO
Kidney, liver
Cellular source of SCF
Fibroblasts, bone marrow stroma
Cellular source of TPO
Kidney, liver
Stimuli for release of G-CSF
Lipopolysaccharide induction, TNF-alpha, IL-1, cytokine activation
Stimuli for release of GM-CSF
Antigens, lectins, IL-1, lipopolysaccharide induction, TNF-alpha
Stimuli for release of EPO
Hypoxia
Stimuli for release of SCF
Constitutively expressed
Stimuli for release of TPO
Constitutively expressed
Physiological role of G-CSF and GM-CSF. Compare and contrast functions of each.
- 2 myeloid growth factors have complementary role
- G-CSF helps maintain neutrophil production during steady-state conditions and increase production during infection
- GM-CSF is a locally active growth factor that remains at the site of infection to localize and activate neutrophils
- rhG-CSF reduces neutrophil maturation time from 5 days to 1 day, leading to rapid release of mature neutrophils from the bone marrow into circulation, while rhGM-CSF doesn’t reduce the mean maturation time
- Neutrophils treated w/ rhG-CSF show normal intravascular t1/2 while neutrophils treated w/ rhGM-CSF have increased serum t1/2 of 48 h
- Neutrophils treated w/ rhG-CSG have enhanced superoxide production in response to chemoattractant; rhGM-CSF also enhances superoxide production but requires a long incubation
Physiological role of EPO
- Increases RBC count by causing committed erythroid progenitor cells to proliferate and differentiate into normoblasts (a nucleated precursor cell in the erythropoietic lineage)
- Shifts reticulocytes (mature RBCs) from the bone marrow into peripheral circulation
- Unlike other HGFs, EPO release isn’t mediated by inflammatory stimuli
- Tissue hypoxia resulting from anemia induces kidney to increase EPO production
Physiological role of SCF (stem cell factor)
- SCF = early acting HGF that stimulates proliferation of primitive hematopoietic and non-hematopoietic cells
- Produced by bone marrow stroma and has important role in steady-state hematopoiesis
- Circulates in relatively high concentrations in normal human plasma
- In vitro, SCF alone has minimal colony stimulating activity on hematopoietic progenitor cells, however, it synergistically increases colony-forming or stimulatory activity of other HGFs
Target cells of G-CSF
Granulocyte progenitors, mature neutrophils
Target cells of GM-CSF
Granulocyte, macrophage progenitors, eosinophil progenitors
Target cells of EPO
Erythroid progenitors
Target cells of SCF
Granulocyte-erythroid progenitors, lymphoid progenitors, NK cells
Target cells of TPO
Stem cells, megakaryocytes, erythroid progenitors
Target cells of IL-11
Early hematopoietic progenitors, megakaryocytes
Actions of G-CSF
Increase neutrophil counts
Actions of GM-CSF
Increase neutrophil, eosinophil, and monocyte counts
Actions of EPO
Increase RBC counts
Actions of SCF
Increase pluripotent stem cells and progenitor cells for all other cell types
Actions of TPO
Increase platelet counts
Actions of IL-11
Increase platelet counts
Pharmaceutical issues w/ HGFs
- Pharmaceutical formulation **know that filgrastim can’t be diluted w/ saline (will form precipitate) and must use 5% dextrose
- Storage and stability
- All recombinant HGF preparations should be kept from freezing and shouldn’t be shaken as shaking can denature the proteins
- All preparations should be visually inspected for participate matter before administration
- rhG-CSF = filgrastim, lenograstim, and pegfilgrastim (end in “grastim”)
- rhGM-CSF = molgramostim and sargramostim (end in “gramostim”)
Clinical use of HGFs
- Ability to augment hematopoietic cell cycling using hematopoietic growth factors has led to 2 interrelated areas of clinical investigation
- Application of hematopoietic growth factors to facilitate more dose-intense tx (in an attempt to improve upon primary therapeutic outcomes)
- Application for supportive care management (in an attempt to decrease tx-related complications)
- Established uses –> cancer tx (chemotherapy-induced neutropenia, bone marrow or stem cell transplantation, anemia), peripheral blood progenitor cell mobilization for harvesting and transplantation, severe chronic neutropenia, thrombocytopenia
Describe the use of HGFs for prophylaxis in the context of chemotherapy
- Prophylactic use: administration of a growth factor to prevent febrile neutropenia
- Primary prophylaxis: use of CSFs following the first cycle of multicourse chemotherapy prior to any occurrence of febrile neutropenia
- Secondary prophylaxis: use of CSFs to prevent a subsequent episode of febrile neutropenia in a pt who has already experienced infectious complications in a previous chemotherapy cycle
Describe the therapeutic use of HGFs in the context of chemotherapy
- Therapeutic use: administration of a growth factor at the time when neutropenia or neutropenic fever is documented in a pt who had not been previously receiving CSFs (colony stimulating factors)
- CSF use can permit chemotherapy dose maintenance or allow modest increases in dose intensity in clinical scenarios where the main toxicity is neutropenia
- Ex: delivery of dose-dense chemotherapy q2weeks w/ G-CSF support has improved survival compared w/ standard q3week dosing in women w/ breast cancer receiving adjuvant cyclophosphamide and doxorubicin, followed by paclitaxel
What is a reason NOT to prescribe CSF support?
No indications for CSF use to treat uncomplicated neutropenia w/o fever; thus, low neutrophil counts alone don’t represent a reason to prescribe CSF support
Recommendations for CSF use in the context of chemotherapy
- Effective way to use CSFs is 24-48 h after chemotherapy is completed; CSF therapy should be continued until neutrophil recovery is adequate
- Check blood counts before initiating the next cycle of chemotherapy
- Initiation of the next cycle of chemotherapy is not recommended for at least 24 h after the completion of CSF therapy b/c of potential concern that progenitor cells, which are rapidly dividing following CSF administration, may be sensitized to chemotherapy
- B/c of the same concern, concurrent administration of CSFs w/ chemotherapy or radiotherapy isn’t recommended outside clinical trials
Dose-intensity – hematopoietic cell transplantation
- Autologous stem-cell and/or BMT – high dose chemotherapy w/ autologous hematopoietic stem-cell support has been used in the tx of several malignancies
- Prolonged period of high-dose therapy shows myelosuppression w/ increased risk of infectious and bleeding complications
- Several randomized trials have documented that CSFs can effectively reduce duration of neutropenia, infectious complications, and hospitalization in px who are receiving high-dose chemotherapy w/ autologous BMT
- Allogenic BMT: similar beneficial effects of CSFs have been seen following allogeneic BMT, and the routine use of hematopoietic growth factors is appropriate in this setting
- There has been no evidence of any increase in graft vs. host disease, graft rejection, or relapse w/ the use of CSFs
HGF use for supportive care of anemia
- Anemia can be caused by chronic renal failure in predialysis or dialysis px, or zidovudine tx in HIV px, or chemotherapy in cancer px
- EPO can be used to treat anemia in the above conditions as well as px w/ anemia, who schedule for elective, non-cardiac, non-vascular surgery
- Anemia caused by chemotherapy is due mainly to drug effects on bone marrow precursor cells and is proportional to chemotherapy dose intensity
- In addition, w/ platinum agents, anemia may be related to renal effects of these drugs on the production of EPO
Concerns w/ HGFs
- Many HGFs, especially multipotential factors that act on early progenitor cells, are associated w/ constitutional sx -> bone pain, fever/ chills, rash, myalgia, injection-site reaction (pain), edema
- Potential for generating immunogenic reactions
- Short plasma t1/2 necessitating repeated parenteral administration
Types of immune responses to HGFs
- Activation of the classical immune system by foreign proteins, similar to the immune response against pathogens or vaccines
- Breach of B and T cell tolerance to autologous proteins – a complicated series of immunological events that isn’t fully understood
Epoetin-associated pure red cell aplasia
- PRCA is characterized by severe anemia, low reticulocyte count, erythroblasts absence, epoetin non-response, and neutralizing antibodies against EPO
- *When you give a pt a protein drug, must think that they can develop Abs (less severe) or it might cause breach of immune tolerance (more severe)
What are the 5 amino acid substitutions in darbepoetin?
- Ala30Asn
- His32Thr
- Pro87Val
- Trp88Asn
- Pro90Thr
Compare and contrast epoetin and darbepoetin
- Epoetin has the same AA sequence as erythropoietin while darbepoetin has 5 AA substitutions
- Epoetin has 3 N-linked glycosylation sites while darbepoietin has 5 N-linked glycosylation sites
- Epoetin has higher receptor binding; darbepoetin has longer serum t1/2 and biological activity
Physiological role of TPO (thrombopoietin)
- TPO/MGDF stimulates production of megakaryocyte precursors, megakaryocytes and platelets
- Endogenous TPO is produced by the liver and enters the peripheral circulation
- Eventually reaches bone marrow and stimulates bone marrow megakaryocytes to produce platelets
- IL-11 works synergistically w/ IL-3, TPO, MGDF or SCF to stimulate various stage of megakaryocytopoiesis and thrombopoiesis
