23 - Hematopoietic Growth Factors Flashcards
Lecture Overview: Simplified Diagram of the Hematopoietic Hierarchy
- Multipotent hematopoietic stem cells (HSC) give rise to
all of the final differentiated blood cells. - The subsequent survival of cells at each differentiation
stage is determined by the presence of specific
hematopoietic growth factors.
* The life span of differentiated hematopoietic cells can range from years in the case of T and B cells involved in immunological memory, to 3 months in the case of red blood cells, to days, in the case of granulocytes.
* Therefore, HSCs are constantly called upon to supply a steady stream of hematopoietic progenitors that can generate new hematopoietic cells.
- Given the massive rate of hematopoietic cell turnover
(e.g., in humans is estimated to be 1012 cells), a stable
pool of functional HSCs must be continuously
maintained.
Lecture Overview: Growth factors
- The subsequent survival of cells at each differentiation stage is determined by the presence of specific hematopoietic growth factors.
- Hematopoietic growth factors are glycoproteins that stimulate the proliferation and development of clonogenic precursor cell populations.
- If the stage - or lineage-specific hematopoietic growth factor is absent, the cells undergo apoptosis.
- Hematopoietic growth factors can be generally grouped into:
1. Stem Cell Growth Factors: Osteopontin, Angiopentin-like 2/3, etc.
2. Early Acting Hematopoietic factors: IL-3, IL-6, Granulocyte Macrophage Colony Stimulating Factor (GM-CSF), stem cell factor (SCF) and thrombopoietin** (TPO).
3. Lineage-specific hematopoietic factors: erythropoietin (EPO), G-CSF, macrophage colony-stimulating factor [M-CSF**], and TPO
Outline: Hematopoietic Growth Factors
Erythroid Growth Factors
Erythropoietin (EPO):
* Most important regulator of the proliferation of committed erythrocyte progenitors (EP) cells.
* It is a 34-39 kDa Glycoprotein, synthesized in the kidneys, that was originally isolated from patients with anemia
* EPO receptors (EPOR) is a tyrosine kinase receptor that signals mainly through JAK/STAT2 pathway.
* EPO synthesis increases 100-fold with anemia or hypoxemia (next slide)
* EPO production altered in patients with kidney disease, marrow damage, iron deficiency.
* Proinflammatory cytokines suppress EPO production
Erythroid Growth Factors - Erythropoiesis Stimulating Agents (ESA) - Overview
(Pharmacological substance that stimulates RBC production)
* Preparations: Epo-alpha, -Beta, -Omega, -Zeta, etc
- Recombinant human erythropoietin or rHUEPO (Epo alpha)
* IV half-life 4-13 hours, subcutaneous 16-67 hours
* Given 3 times per week – once weekly
* Effects on marrow last significantly longer
* Peak hemoglobin effect 2-6 weeks - Darbepoetin alfa (highly glycosylated)
* IV half-life: 21-46 hours, subcutaneous 46-74 hours
* Given once weekly – every 3 weeks
* Therapeutic use: treatment of symptomatic anemia associated with HIV (zidovudine therapy), chemotherapy, chronic kidney disease (CKD), myelodysplastic syndrome (off label) - Epoetin Beta and Methoxy polyethylene glycol-epoetin beta
* continuous erythropoietin receptor activator and is used monthly
* (half-life approx.130 hrs in patients with anemia associated with CKD
Erythroid Growth Factors - Erythropoiesis Stimulating Agents (ESA) - Benefits
- Benefits
- Reduces need for RBC transfusion
- Symptom relief not consistently shown in clinical trials
- Patients with endogenous erythropoietin < 100 IU/L most likely to respond, 100-500 IU/L may respond
- Note: Banned by athletic organizations
- Dosage adjustments to achieve hemoglobin (Hgb) goals
- Hgb increases in 2-6 weeks (reticulocytes in 10 days)
- Decrease dose if Hgb increases > 1 g/dL in 2 weeks
- Increase dose if Hgb doesn’t increase by >1 g/dL in 4 weeks
- Goal Hgb in CKD: 10 - 12 g/dL
- Most also need iron supplementation
- Cancer: use conservatively when Hgb < 10 g/dL and only when myelosuppressive therapy anticipated for > 2 months
Erythroid Growth Factors - Erythropoiesis Stimulating Agents (ESA) - ADE
Outline: Hematopoietic Growth Factors
Hematopoietic Growth Factors - HIF inhibitors — Hypoxia-inducible factor prolyl hydroxylase inhibitors (HIF PHIs)
- EPO synthesis increases 100-fold with anemia or hypoxemia.
* The body’s adaptation to low oxygen levels (hypoxia) is largely influenced by signaling from hypoxia-inducible factors (HIFs). - The HIFs that primarily control this response are HIF-1 and HIF-2, with HIF-3 playing a less defined role.
- cDNA microarrays have identified at least 70 hypoxia-responsive genes have been identified which are under HIF control.
- There are two types of HIF-1, ⍺ and β, which are codified by different genes on chromosome 14 and 1, respectively.
- HIF-1α is a ubiquitously expressed protein containing an oxygen-dependent degradation domain that under normal conditions regulates its constant degradation. HIF-1β is a stable constitutively expressed protein that localizes to the nucleus.
* HIF-1⍺ isoforms serve as the oxygen-regulated subunit that controls HIF transcriptional activity in response to hypoxia, while HIF-1β is a constitutive binding partner needed to form an active HIF complex.
HYPOXIA-INDUCIBLE FACTOR (HIF) PATHWAY.
- HIF-1α is constitutively produced and rapidly degraded under normoxic conditions.
- Degradation of HIF-1α is mediated by prolyl hydroxylasedomain (PHD) 1, PHD2, and PHD3 enzymes, which hydroxylate specific proline residues within HIF-α.
- Hydroxylated HIF-α is ubiquitylated by the von Hippel–Lindau (VHL)–E3 ubiquitin ligase complex, leading to its proteasomal degradation.
- PHDs utilize O2 and 2-oxoglutarate as substrates in an iron-dependent reaction, resulting in the formation of hydroxylated HIF-α, succinate, and CO2.
-
Hypoxia or HIF–PHD inhibitors (PHIs such as Daprodustat) reduce PHD catalytic activity, which leads to cellular accumulation of HIF-α, its nuclear translocation,
heterodimerization with HIF-1β - This leads to increased transcription of HIF-regulated genes, which are involved in multiple biological processes.
Blood Doping?
Myeloid Growth Factors
Growth factors that stimulate proliferation and differentiation of one or more myeloid cell lines
Myeloid Growth Factors: Recombinant Human G-CSF
- Filgrastim (recombinant human G-CSF), pegfilgrastim (pegylated recombinant human G-CSF)
- Primary effects
- Stimulates proliferation & differentiation of progenitor cells committed neutrophil lineage
- Activates phagocytic activity of mature neutrophils & prolongs survival
- Mobilizes hematopoietic stem cells increasing concentrations in peripheral blood when blood is being collected for leukapheresis
- Therapeutic uses
- Treatment of neutropenia after stem cell transplant or
chemotherapy - Severe congenital neutropenia, cyclic neutropenia
- Peripheral blood stem cell collection (promotes release of CD34+ progenitor cells)
- Anemia along with erythropoietin (off label)
Myeloid Growth Factors: Recombinant Human G-CSF - PK and ADE
* Pharmacokinetics
* Filgrastim half-life: 3.5 hours
* Pegfilgrastim half-life: 42 hours
* Response in 7-21 days
* Usually started within 24-72 hours after completing chemotherapy
* Filgrastim (IV, sc) dosed daily for up to 14 days
* Pegfilgrastim (sc) one dose per chemo cycle
* Benefits
* Reduced duration of febrile neutropenia
* Reduced morbidity secondary to bacterial, fungal infections
* Reduced length of hospital stay, interruptions in chemotherapy
* No benefit on long-term survival
* Adverse Effects
Innocuous: **Bone pain **(mild/moderate) and local skin reactions following, rarely necrotizing vasculitis
Serious but rare: Allergic reactions (produced in E. Coli); mild splenomegaly with chronic use - rarely splenic rupture
Myeloid Growth Factors: Stem Cells Mobilizer and Recombinant GM-CSF
Myeloid Growth Factors - Stem Cell Mobilizers
Stem Cell Mobilizers
* Plerixafor, Mozobil, Ancestim, Stemgen
Plerixafor
* Originally developed as HIV drug due inhibition of CXC chemokine receptor 4 (CXCR4), a co-receptor for HIV entry into CD4+ T cells
* MOA
* Prevents chemokine stromal cell-derived-factor-1α (SDF-1α ) from binding to CXCR4 and directing CD34 cells to go to the bone marrow -> Increases CD34 cells in peripheral blood
- Therapeutic use
- In combination with G-CSF in multiple myeloma or NHL patients who don’t respond to G-CSF alone, mobilization of hematopoietic stem cells
- Given subcutaneously
- Optimal mobilization is critical since the yield of hematopoietic progenitors directly affects engraftment success and recovery following autologous hematopoietic cell transplantation.
- Adverse effects (generally well tolerated)
- Injection site reactions, GI disturbances, dizziness, fatigue, headache
- Needs dose adjustment in renal dysfunction
Myeloid Growth Factors
Granulocyte-macrophage colony stimulating factor (GM-CSF) - Overview
Granulocyte-macrophage colony stimulating factor (GM-CSF)
* Sargramostim
* Primary effects
* Multipotential hematopoietic growth factor that stimulates proliferation and differentiation of early and
late granulocytic progenitor cells including neutrophils, eosinophils, monocytes, and macrophages
* Also stimulates erythroid & megakaryocyte progenitors
* Mobilizes peripheral stem cells (less efficacious, more toxic than G-CSF)
- Therapeutic uses
- Shorten duration of neutropenia following chemotherapy
- Mobilization of CD34+ progenitor cells for peripheral blood stem cell collection
- Congenital neutropenia, cyclic neutropenia, myelodysplasia and aplastic anemia
Myeloid Growth Factors
Granulocyte-macrophage colony stimulating factor (GM-CSF) - PK, ADE
Granulocyte-macrophage colony stimulating factor (GM-CSF)
- Pharmacokinetics
- Half-life 2-3 hours
- Given IV or sc
- Following administration
- Dose-dependent increase over 7-10 days
- Neutrophilic response with lower dose
- Monocytosis and eosinophilia at larger doses
- Adverse effects
- Bone pain, malaise, flu like symptoms, fever, diarrhea, dyspnea, rash, myalgas
- Capillary leak syndrome (peripheral edema, pleural or pericardial effusions) – some patients are extremely sensitive
- Allergic reactions (rare)
Hemapoietic Growth Factors: Megakaryocyte Growth Factors - Overview
Megakaryocyte Growth Factors - Recombinant IL-11 : Oprelvekin
Recombinant IL-11 : Oprelvekin
* MOA
* Stimulates multiple stages of megakaryocytopoiesis & thrombopoiesis -> proliferation of megakaryocyte
progenitors & maturation -> increased platelet production (modest effect in vivo)
* Also stimulates intestinal epithelial cell growth, osteoclasto-genesis, and inhibits adipogenesis
- Therapeutic use
- Patients with severe thrombocytopenia (< 20,000/ul) with previous cycle of chemotherapy for treatment of non-myeloid cancers
- Pharmacokinetics
- Half-life 7 hours (given sc)
- Thrombopoietic response in 5-9 days
- Adverse effects
- Fluid retention - major complication
- Heart failure, tachycardia, palpitations, edema, shortness of breath
- Concomitant diuretics often required
- Anaphylactic reactions (E. coli)
- Risks may outweigh benefits, therefore rarely used clinically
Megakaryocyte Growth Factors - Recombinant thrombopoietin
Recombinant thrombopoietin: cytokine that stimulates megakaryopoiesis
- Levels in body are inversely related to blood platelet count -> primary regulatory hormone for platelet production
- Original Agents
- rHuMGDF - recombinant human megakaryocyte growth and development factor
- rHuTPO - recombinant human thrombopoietin
- Associated with anti-recombinant thrombopoietin antibodies that interacted with native hormone ->
thrombocytopenia - Newer Agents and therapeutic use
- Romiplostim, eltrombopag - approved for use in immune thrombocytopenic purpura (ITP) who have failed to respond to more conventional treatments (corticosteroids, immune globulin, or splenectomy)
*Recombinant thrombopoietin: Eltrombopag (thrombopoietin nonpeptide agonist)
* Orally active thrombopoietin receptor agonist
* Also approved for Hepatitis C associated thrombocytopenia - to maintain interferon therapy
Megakaryocyte Growth Factors - Recombinant thrombopoietin: Romiplostim (thrombopoietin peptide mimetic)
- Recombinant thrombopoietin: Romiplostim (thrombopoietin peptide mimetic)
- “Peptibody” drug: Peptide bound to Fc fragments of human antibodies to extend peptide’s half life
- MOA
- Thrombopoietin peptide mimetic that binds to thrombopoietin (TPO) receptor, activates intracellular signal transduction pathways to increase proliferation and differentiation of marrow progenitor cells, stimulating platelet production
- Pharmacokinetics
- Half-life 3-4 days (inversely related to platelet count)
- Peak platelet count increase days 12-16
- Benefits in ITP
- ~80% of patients respond
- Dose to maintain platelet count > 50,000 cells/μL but thrombocytopenia worsens after discontinuation
- Adverse effects
- Mild Headache
- Not to be used in MDS- progression to AML in clinical trials
- Thromboembolism
Megakaryocyte Growth Factors - Recombinant thrombopoietin: Eltrombopag
- Recombinant thrombopoietin: Eltrombopag (thrombopoietin nonpeptide agonist)
- Orally active thrombopoietin receptor agonist
- Also approved for Hepatitis C associated thrombocytopenia - to maintain interferon therapy
- Used to be a restricted drug by FDA for concern for hepatotoxicity
- Restriction lifted in 2011
-
Black box warning : may increase risk of hepatic decompensation when used in combination with
interferon and ribavirin in patients with chronic hepatitis C
Hematopoietic Growth factors - summary
*Available hematopoietic growth factors include:
* EPO to increase red blood cell production
* G-CSF and GM-CSF to increase granulocyte production
* TPO mimetics to increase platelet numbers.
A. Erythroid growth factors: Epoetin alpha, Darbepoetin, Erythropoietin
B. Hypoxia-inducible factor prolyl hydroxylase inhibitors (HIF PHIs): Daprodustat
C. Myeloid growth factors: Filgrastim, Pegfilgrastim, Plerixafor, Sagramostim
D. Megakaryocyte growth factors: Interleukin 11, Oprelvekin, Romiplostim, Eltrombopag
*Clinical examples of HGFs use are:
* renal failure
* chemotherapy-induced cytopenia
* bone marrow failure syndromes
* thrombocytopenia of immune thrombocytopenic purpura (ITP).
