Drug Induced Immunosuppression

Front 1

Drug‐induced Neutropenia

Back 1

Entails the study of drugs that induce
neutropenia (↓Neutrophils) as side
(undesirable) effects
• May occur via either:
– ↓Granulocyte production or
– ↑Destruction

Front 2

Two Basic Mechanisms

Back 2

-Immune‐mediated, drug‐induced neutropenia
-Direct or Indirect toxicity to bone marrow granulocyte precursors

Front 3

Mechanisms of D-I Neutropenia

Back 3

1. Both mechanisms are mediated by formation of reactive metabolites by NADPH oxidase/
Myeloperoxidase enzyme system
2. The drug or its reactive metabolites bind to neutrophil membrane irreversibly causing
production of either (a) antibodies, or (b) anti‐neutrophil auto‐antibodies against membrane
3. Example 1: Propylthiouracil (PTU) →→→→ Propyl‐thioester/sulfinic acid/sulfonic acid →→
→→ Bind covalently to neutrophil membrane →→→→ Antibody/Auto‐antibody production
4. Example 2: Amodiaquine →→→→→ Mono‐desmethyl amodiaquine (reactive metabolite)

Front 4

D-I Neutropenia, Clinical Presentation

Back 4

Clinical presentation: Days to Weeks ‐ following immune‐mediated destruction versus
months ‐ following direct/indirect toxicity

Front 5

D-I Neutropenia Treatment

Back 5

Treatment: Withdraw offending drug agent; resolution take 1‐3 weeks after drug cessation

Front 6

Clozapine

Dapsone

Back 6

Drugs that cause direct damage to
myeloid precursors also do so via
reactive metabolites
Clozapine is chlorinated to form “Nitrenium ion”
which bind covalently & irreversibly → Toxicity to
bone marrow precursors
– Dapsone also is oxidized to form “Reactive
hydroxylamine” which causes toxicity via covalent &
irreversible binding to bone marrow precursors
• Presentation of direct/indirect toxicity takes months

Front 7

Immuno‐suppressive Therapies

Drugs, biologics, & irradiation ‐

Back 7

used primarily for immuno‐suppression as
therapeutic goal

Conditions prompting their use:
• Treatment of malignant disease
• Maintenance of tissue/organ transplant
• Prevention of graft‐versus‐host disease
• Treatment of some auto‐immune/connective tissue disease

Front 8

Immuno‐suppressive Therapies

Two categories of Immuno‐suppressive drugs:

Back 8

– Broad‐spectrum immuno‐suppression
• Glucocorticoids
• Cytotoxic chemotherapeutics
• Radiation therapy
– Selective targeting of cells & pathways of the immune system → Specific
therapeutic effects
• Monoclonal antibodies

Front 9

Glucocorticoids

Steroids hormones; bind to:

Back 9

– Cytosolic receptors → G-R complex;
translocate to the nucleus → bind to GREs
(glucocorticoid response elements (in promoter region of specific genes) → ↑ or ↓Regulation of
specific genes

Front 10

Glucocorticoids

Broad anti-inflammatory effects

Back 10

– Induces lipocortins → ↓PLA2→ ↓AA
(Arachidonic acid) release → ↓Formation and
Release of eicosanoids, e.g., PGI2 - blood vessels
– Down-regulates expression of cytokines (IL-1,
IL-4 and TNF-α)

PGI2 is a vasodilator

Front 11

Glucocorticoids

Adverse effect:

Back 11

• Long-term use → diabetes mellitus;
↓Resistance to infections, osteoporosis,
hypertension, ↑Appetite → Weight gain
• Avoid abrupt stoppage; taper dosage
slowly

Front 12

Calcineurin-inhibiting Drugs
I. Cyclosporine (Cs) and Tacrolimus (FK506)

In Normal T-cells

Back 12

T-cell activation → ↑[Ca2+]; Ca2+/Calmodulin → activates Calcineurin-mediated dephosphorylation of
NFATc (cytosolic Nuclear Factor of Activated T-cells)
– Activated NFAT translocates to nucleus → IL-2 gene
transcription

Front 13

Calcineurin-inhibiting Drugs
I. Cyclosporine (Cs) and Tacrolimus (FK506)

Actions of Cs & FK506 (see A of diagram):

Back 13

– Cs and FK506 cross into cytoplasm; bind to cyclophilin
(CyP) and FK-binding protein (FKBP), respectively
– Cs-CyP complex or FK-FKBP complexes bind to
Calcineurin → ↓Calcineurin phosphatase activity by
Ca2+/Calmodulin
– Tacrolimus → ↓IL-3; IL-4, IFN-γ; 50-100x > potent vs Cs
– Tacrolimus – immunosuppressant for transplantation; use
of Cs: limited by adverse effects – hepato-, nephro-,
& neuro—toxicity; hypertension, hyperlipidemia

Front 14

Sirolimus

Back 14

Activation of IL-2 receptors → mTOR
(molecular target of rapamycin ) Phosphorylation
– mTOR – a kinase that phosphorylates & regulates
activity of PHAS-1 and p70 S6 kinase
• Sirolimus (S) binds to FKBP → S-FKBP complex
→ ↓mTOR → ↓Protein synthesis (Translation) &
Arrest of T-cell division in G1 phase

Front 15

Sirolimus

Clinical Use/ Adverse Effects

Back 15

• Clinical use:
– Sirolimus-eluting stents - Approved for coronary artery
disease
• Adverse effects:
– Hyperlipidemia
– Leukopenia
– Thrombocytopenia

Front 16

Cytotoxic Agents – Antimetabolites
(Uses: Immunosuppression & Antineoplastic chemotherapy)
Examples

Back 16

Azathioprine,
Methotrexate, Mycophenolate

Front 17

Azathioprine (AZA)

Back 17

– Pro-drug for 6-Mercaptopurine
-Slow-release from AZA; reacts
non-enzymically with sulfhydryl
compounds, e.g., glutathione
– < Efficacious than
Mycophenolate for long-term
survival of kidney allografts

– Immunosuppressants in patients
with inflammatory bowel disease

Front 18

Methotrexate (MTX)/Uses

Back 18

– Immune-mediated diseases, e.g., RA
– Prevention of graft versus host
disease
• Folate-independent anti-inflammatory
effect (unknown mechanism
– Perhaps via increasing adenosine (A) levels
– A→ Neutrophil adhesion/Phargocytosis,
& ROS generation (→ anti-inflammatory
effect)
– Cytotoxic action → Apoptosis of activated CD4 and CD8 T cells
• MTX has anti-neutrophil; anti-T cell, &
anti-humoral effects

Front 19

MPA = inosine monophosphate
dehydrogenase (IMPDH) inhibitor

Back 19

Front 20

MPA or MMF

Back 20

Mycophenolic Acid & Mycophenolate Mofetil
MPA or MMF → ↓IMPDH

Front 21

Leflunomide

Mech

Back 21

Leflunomide inhibits dihydroorotate dehydrogenase →
inhibition of pyrimidine synthesis
– Lymphocytes depend on de novo pyrimidine synthesis for cell replication &
clonal expansion after immune cell activation
– Depletion of pyrimidine pool → ↓Lymphocyte expansion

Front 22

Leflunomide

Adverse effects:

Back 22

Diarrhea

Front 23

Leflunomide

Clinical uses:

Back 23

– Currently approved for rheumatoid arthritis
– Efficacious for other immune disease, e.g., myasthenia gravis,
lupus erythematosus

Front 24

Cyclophosphamide, CyP

Effect

Back 24

Orally administered, highly toxic drug; alkylates DNA
• CyP→ Hydroxylated intermediates by hepatic CYP
• → Phosphoramide mustard (PhM; active product) + Acrolein
• PhM + DNA → Cytotoxic effects; Acrolein → Risk of cancer
• Major effect on B-cell proliferation; can ↑T-cell responses
• Particularly used for disorders of humoral immunity, e.g., systemic lupus
erythematosus

Front 25

Cyclophosphamide, CyP

Adverse Effects

Back 25

Severe and widespread
• Leukopenia, cardiotoxicity, & ↑Risk of cancer, especially bladder cancer [due to
high Acrolein (carcinogenic) concentration in urine]

Front 26

Cyclophosphamide (CyP)

Resistance to CyP may be caused by

Back 26

↑DNA repair; ↓Drug permeability, and/or reaction of drug with glutathione or
other thiol-containing molecules

Front 27

TNF (tumor necrosis factor):

Back 27

TNF-α Inhibitors: Etanercept, Infliximab, Adalimumab
– Secreted by activated macrophages →
multiple pro-inflammatory effects
– TNF → activation of ECs & ↑ expression of
surface adhesion molecules → Leukocyte
adhesion & diapedesis
– Positive feedback on monocytes & macrophages
→ ↑Cytokine (e.g., IL-1) secretion

Front 28

TNF-α Inhibitors: Etanercept, Infliximab, Adalimumab

Adverse effects:

Back 28

↑Risk of reactivating latent tuberculosis – screen
patients for TB; ↑Risk of demyelinating disease

Front 29

TNF-α Inhibitors: Etanercept, Infliximab, Adalimumab

Uses

Back 29

– Etanercept – non-specific (binds TNF-α and TNF-β) –
approved for rheumatoid arthritis
– Infliximab and Adalimumab – TNF-α-specific -
approved for rheumatoid arthritis, Crohn’s disease,
ulcerative colitis

Front 30

II. Interleukin-1 (IL-1) inhibitors

Back 30

IL-1 – generated by activated mononuclear cells & stimulates IL-6
production → ↑Expression of adhesion molecules → ↑Cell
proliferation
– IL-1 Receptor antagonist → ↓IL-1 activity

Anakinra

Front 31

Anakinra

Effect and adverse reactions

Back 31

• A recombinant form of IL-1 receptor antagonist (IL-1ra)
• Blocks IL-1-induced metalloproteinase release from synovial fluid
• Adverse effects:
• Neutropenia
• ↑Susceptibility to infection

Front 32

Antibodies - Polyclonal
• Anti-thymocyte globulin (ATG)

Back 32

– Derived from animal sera, e.g., rabbits following
injection with human thymocytes
• ATG targets all T cells → Broad
immuno-suppression
– Inhibit T lymphocytes & cause their lysis →
Inhibition of cell-mediated immune reactions
(e.g., graft rejection; delayed hypersensitivity)
• Polyclonal Ab affect all lymphocytes &
cause general immunosuppression
– Can predispose to infection
• Acute reaction (characterized by fever, or
even anaphylaxis) to treatment is common
due to high immunogenicity of polyclonal
Abs

Front 33

Muromonab

Back 33

Muromonab-CD3, anti-CD3
• Mouse monoclonal antibody against human
CD3 (a cell-surface signaling molecule for
activation of T-cell receptor)
• Body produces antibody against Mouse antibody (a
foreign protein

Front 34

Rituximab

Back 34

– a partially humanized anti-
CD20 antibody (approved for rheumatoid arthritis)
• CD20 – expressed on surface of all mature
B cells; Rituximab → depletion of
circulating B cells

Front 35

Daclizumab and Basiliximab

Back 35

– Induction therapy for renal transplantation
– Antibodies against CD25 – the high affinity IL-2
receptor (CD25 – expressed only on activated T-cells)
• Anti-CD25 antibody = specific activated T-cells targets