ImmunosuppressantsProf. Alhaider, 1431 H

I. DefinitionII. Clinical Uses (Organ transplants &

Autoimmune diseases)III. Pre-requisite to understand immunosuppressive

drugs (Basic immunology).IV. Review of immune system (see Table 56-1)

I. Cell mediated vs humoral immunityII. Importance of cytokinesIII. ImmunophilinsIV. Calcineurin

Classification of Immunosuppressant (Based on

Mechanism of Action) • A) Antiprolifirative Agents

1) Drugs Acting on Immunophilins: a) Selective Inhibitors of Cytokine production ) (Calcineurin Inhibitors) (e.g: Cyclosporine; Tacrolimus) b) Inhibitor of cytokine function (e.g. Sirolimus).

3) Antimetabolites (Azathioprine; Mycophenolate Mofetil)

4) Alkylating Agents (Cyclophosphamide)

B) Lymphocyte Depletion Agents 1) Corticosteroids 2. Immunosuppressive Antibodies

a) Polyclonal Antibodies (Antilymphocyte Globulin)

b) Monoclonal Antibodies (Selective inhibitors of IL2 (Basiliximab; Daclizumab)

Immunosuppressant Classes

Non-selective• Corticosteroids Prednisone (PO) &

Methylprednisolone (IV)• Antimetabolite (DNA

synthesis inhibitors) Azathioprine &

Myclophenolate mofetil Immunoglobulins Anti-lymphocyte antibodies

Selective• Calcineurin Inhibitors Cyclosporine Tacrolimus (Rapamycin)• Selective IL-2 Receptor

antagonists Basiliximab, Daclizumab &

Infliximab Mamalian target of

Rapamycin (mTOR) inhibitors

Sirolimus

Selective Inhibitors of Cytokine Production (Drugs Acting on Immunophilins)

• 1) Cyclosporine (Cyclic peptide from Soil Fungus (1971)– MOA: (See Figure 40.4)

• CsA binds to cyclophillin forming a comlex Bind to Calcineurin dephosphorylation NFATc Synthesis of IL 2 proliferation of T cells

• Thus, decreases the level of IL-2, the primary chemical stimulus for increasing the number of T lymphocytes

• Note: Suppress only cell immunity with no effect on humoral immunity.

– PK• CsA available as oral (capsule) or parental (i.v)• Oral bioavailability (20-50%), it undergoes

extensive hepatic metabolism by CytP450 (CYP3A4) (Affected by some drugs EXAMPLES) and mainly excreted in the bile.

– Clinical Uses of Cyclosporine:• 1) Drug of choice for preventing organ transplant rejection in combination

with steroids and other immunosuppressants.• 2) Severe active rheumatoid arthritis, as alternative for methotrexate

• 3) Lower doses (7.5 mg/kg/d) for autoimmune diseases (Uveitis; RA; early Rx of DM 1)

• 3) Psoriasis and asthma ?.

– Side Effects (remember most immunosuppressant are very toxic)• Dose-dependent nephrotoxicity ( Risk of Rejection); enhanced of given

with other nephrotoxic drugs (Aminoglycosides; NSADs)• Hepatotoxicity• Neurotoxicity as tremor and hallucination• Infection How?• Lymphoma and cancer How?• Hypertension; hyperlipedemia; Hyperkalemia; D.M; Osteoporosis

Hirsutism and gum hyperplacia (So What)

• 2. Tacrolimus (FK 506):– More potent than Cyclosporine

– MOA: Similar to Cyclosporine (Calcineurin Antagonist) but it bind to different immunophilin (FKBP) Figure 40.6.

– PK: Almost Similar to Cyclosporine

– Side Effects: differ from Cyclosporine, that it ((Tac) has no hirsutism or gum hyperplasia but may show more hyperglycemia than cyclosporine.

– Note: It is like cyclosporine, could lead to nephrotoxicity and hyperglycemia (more hyperglycemia than cyclosporine) , and hyperlipedemia.

• Clinical uses of Tacrolimus:

Preferred over CsA because: of more potency (50-100 times more potent than cyclosporine).lower rejection episodes, and lower doses of glucocorticoids are used with lower side

effectsBetter first choice for woman?

Severe refractory atopic dermatitis, local application of an ointmentAn ointment for psoriasis.

• 3. Sirolimus (Rapamycin Maclolides)– MOA:

• 1) Binds to the same immunophilin as Tacrolimus, but does not form a complex with calcineurin, instead, it binds to mTOR (Mammalian Target of Rapamycin) which is essential for many cellular functions (See Figure 40.6)

• 2) Potent inhibitor of B-cell proliferation and immunoglobulin production (humor immunity)

• 3. Sirolimus (Rapamycin Maclolides)– MOA:

• 1) Binds to the same immunophilin as Tacrolimus, but does not form a complex with calcineurin, instead, it binds to mTOR (Mammalian Target of Rapamycin) which is essential for many cellular functions (See Figure 40.6)

• 2) Sirolimus does not affect IL-2 production, unlike CsA & TAc, rather inhibits T-cell response to it (Blocks cytokine-stimulated cell proliferation)

• 3) Potent inhibitor of B-cell proliferation and immunoglobulin production (humor immunity)

• Uses of Sirolimus:– 1) can be used together with cyclosporine (to

increases the activity of cyclosporine for organ transplanted patients.

– 2) As replacement of cyclosporine if transplanted patient developed cancer of skin or lips.

– 3) used in cardiac catheter stint to prevent stenosis??

– 4) as an ointment for atopic dermatitis and psoriasis

• Side Effects:– 1) Pneumonitis – 2) hyperlipedemia (more then calcineurin-

antagonist)

• Antiproliferatives (Continue…)• 2. Antimetabolites (Cytotoxic Drugs)

– 1) Azathioprine: is a prodrug of mercaptopurine.• Cytotoxic, rarely used as chemotherapeutic drug, but

commonly used for immunosuppression.• It is a pro-drug converted in the body to the active

metabolite, 6-mercaptopurine and thioinosinic acid.

• MOA: (see Figure) – Simply, it inhibits purine synthesis (antimetabolite), thus

interfering with nucleic acid metabolism and lead to inhibition of the proliferation of leukocytes and lymphocytes.

– Why it is considered as cytotoxic agent?– Because the purine analog of Azathioprine can destroy

lymphoids cells.

– Why it is very important to know the structure of azathioprine?.

Metabolic pathway for azathioprine

6-thiouracil (-)

Xanthine Alloburinol

Oxidase

Nonenzymatic HPRT

AZA 6-MP thioiosinic acid 6-thioguanine

(TIMP) ( 6-TG)

TPMT TPMT

6-MMP 6-MMP

ribonucleides

• Cliniclal Uses of Azathioprine (ImuranR)– 1) maintenance of renal allograft and other transplantations

together with steroids and cyclosporine.– 2) Can be used for glomerulonephtitis and SLE; RA;

Crohn’s disease and multiple sclerosis.

• Side Effects– 1) it is like cyclosporine, not teratogenic (Unlike TAC or

Siro) but carcinogenic if given together with alkylating agents. (here higher doses are used as compared to autoimmune diseases.

– 2) strong bone marrow suppression (Leucopenia; anemia; thrombocytopenia How?

– 3) Hepatic dysfunction as increase AP and mild jaundice.– 4) Hypersensitivity reactions (as rashes, fever, diarrhea)

Why?.

Adverse Effects: bone marrow suppression (leukopenia, thrombocytopenia, anemia), hepatotoxicity,

Combination with ACEIs or cotrimoxazole can cause severe leukopenia in renal transplants

It can be given both orally and by IV

• 2) Mycophenolate Mofetil (CellceptR)– The most important discovery among the

immunosuppressant agents.

– MOA: (See Figure)• Mycophenolic acid acts as non-competitive, selective 7

reversible inhibitor of inosine monophosphate dehydrogenase • Decreases GMP, which is a key enzyme in the de novo pathway

of purine synthesis. This leads to suppression of both B and T lymphocyte activation.

• PK: Good oral absorption;

– Side Effects• Less than azathioprine, Bone marrow suppresion (leukopenia

and anemia); NV and diarrhea (decresed by Enteric-coated form).

• Unlike azathiorine it is teratogenic.

– Clinical Uses • 1) As a replacement for the more cytotoxic drug, azathioprine

in renal allograft patients as well as liver, heart et act. Why?• As replacement of azathioprine or cyclophosphamide for

autoimmune diseases (RA, SLE (especialy before lupus nephritis); Glomerulonephritis

• Has good oral bioavailability

• Note: in renal or liver transplant, patients may take the followings:

• Corticosteriods as prednisolone (Low dose) + cyclosporine or Tac + Mycophenolate Mofetil

– 3. Lefunomide:- A Pro-drug of an inhibitor ofn PYRIMIDINE synthesis rather than

purine like azathioprine and mycophenolate.– Orally active used only for RA– Side effects: Alopecia; increase LFT, nephrotoxicity, teratogenicity.

• 3. Alkylating Agents (e.g. Cyclophosphamide)– The most potent immunosuppressant – Destroys proliferating lymphoid cells (cytotoxic agent) also alkylate

some resting cells (Thus, it is very toxic) – Clinical Uses:

• Before the discovery of Mycophenolate, cyclophosphamide was the drug of choice for treatment of many autoimmune diseases like SLE; autoimmune hemolytic diseases and RA.

– Side Effects• Pancytopenia• Hemorrhagic cystitis• Infertility• Teratogenic

B) Lymphocyte Depletion Agents

• 1. Corticosteroids• The most commonly used immunosuppressant• MOA:

– At biochemical level: act on gene expression, which lead to decrease synthesis of PGs; LKTs; cytokines and other signaling molecules that participate in immune response.

– At the cellular level: they inhibit the proliferation of T lymphocytes (cell mediated) and slightly dampen humoral immunity (by increasing the catabolism of immunoglobulins).

– At immunosuppressive doses, Corticosteroids are cytotoxic and continuous uses lowers IgG.

• Uses:– In combination with other

immunossppressants for transplanted patients (To prepare the patients as well as maintenance).

– To Rx acute rejection episodes (high doses)– To Rx undesirable immunoreactions (to drugs

or asthma).– To autoimmune diseases (ITP; IBD; RA; SLE;

GN)

– Side Effects:

Adverse effects: (revise endocrine system)

Increased blood pressure How? hyperglycemia due to increased gluconeogenesis, insulin resistance, and

impaired glucose tolerance ("steroid diabetes"); Osteoporosis Visceral and truncal fat deposition (central obesity) and appetite stimulation Weight gain (water & salt retention) How? Muscle breakdown (proteolysis), weakness; reduced muscle mass and

repair Increased skin fragility, easy bruising Cataracts Adrenal cortex suppression (NO ABRUPT WITHDRAWAL) Increase tendency to infections How?

–

2. Immunosuppressive Antibodies

a) Polyclonal Antibodies (Antilymphocyte Globulins)Definition: Thymocytes are considered as T-cell precursors.What are the differences between polyclonal and monoclonal antibodies?

1) Antithymocyte (Antilymphocyte) Globulins (ALG): this antisera can be obtained by immunization of large animals (e.g.rabbits) with human lymphoid cells.

MOA: Antibodies bind to the surface of circulating T lymphocytes forming a comlex. This complex will be phagocytosed in liver or spleen and leading to destruction or inactivation of T cells. ALG mainly affects the cellular immunity with no effect on humoral, resulting in antibodies against these foreign proteins. PK: Administered by IM or slow IV infusion with long half-life of 3-9 days

Side Effects:1) Mainly result from the introduction of foreign proteins obtained from

heterogeneous serum (Anaphylactic and serum sickness reactions; Local pain and erythema at site of injection).

2) Chills & fever and Leukopenia & thrombocytopenia3) Viral infections and skin rashes

4) Lymphoma and cancer

Polyclonal Antibodies (continue…)

Clinical Uses of ALG :1) Rx of hyperacute phase of allograft rejection2) To prepare the bone marrow transplanted patient

(Large doses of ALG for 7 days)

2) Immune globulin Intravenous (IGIV):

- Prepared from a pool of thousands of healthy donors.

Uses: 1) Refractory ITP

Advantages: Has no antigenicity

B) Monoclonal Antibodies (Muromonab; Basiliximab; Abciximab; Daclizumab.

1) Muromonab-CD3 (IL-2-antagonist):

From its name, it is murine monoclonal antibody that prepared by hypridoma technology and directed against the glycoprotien CD3 antigen of human T cells. Used mainly for cases of acute allograft rejections of kidney, heart and liver.

it is also used to deplete T cells from donor bone marrow before transplantation.

Advantage over ALG: More specific and T lymphocytes return to normal within 24 hr.

Side Effects:

1) Cytokine release syndrome (Anaphylactoid reactions) Why; and seizure (contraindication)

Therefore it is not used.

Side Effect of Muromonab

• Its use has been declined much because of multiple side effects and the emergence of newer and more selective antibodies therapyAnaphylaxis may occurCytokine release syndrome, flu-like to dangerous

shock-like reactions can occur, & high feverCNS: Seizures, encephalopathy, cerebral edema

& headacheInfection like CMVContraindicated with pregnancy, breast feeding,

history of seizures, uncompensated heart failure

• 2) Modified Types of monoclonal antibodies (e.g: Selective Inhibitors of IL2):

• Note: Monoclonal Antibodies are not limited for immunosuppression but could be utilized for other purposes (See Table 56-3)

• By using the genetic engineering, most murine amino acids of Muromonab have been replaced by human ones; producing monoclonal antibody designated humanized (e.g. Daclizumab; Transtuzumab). While the chimeric (Mixed) antibodies contain XI in their name (e.g. Abciximab; Infliximab; Rutuximab).

• Clinical Uses: See Table 56-3• Advantages over polyclonal antibodies

B- Selective IL-2 Receptor Antagonists Basiliximab & Daclizumab

• Basiliximab is a chimeric antibody composed of 25% murine & 75% human protein. Block IL

• Daclizumab is humanized antibody composed of 90% human protein

• Therapeutic Use: Prophylaxis against acute rejection of

kidney transplantationUsed in combination with steroids or CsA

Selective IL-2 Receptor Antagonists Basiliximab & Daclizumab (Continue…)

• Mechanism of action:They are anti-CD25 antibodiesThey bind to the -chain of the IL-2R (CD25

or TAC subunit) on the activated T-cellsThen, IL-2 binding to IL-2R is prohibited &

T-cell activation and proliferation are suppressed

VI- Selective IL-2 Receptor Antagonists Basiliximab & Daclizumab (Continue...)

• Pharmacokinetics: Given by IV routeDaclizumab has serum half-life of 20 days

& receptor blockade for 120 days Administered in 5 doses; the first 24 hours

before transplantation and next 4 doses at 14-days intervals

Basiliximab has serum half-life of 7 days Administered in two doses; the first at 2-

hours before transplantation & the second at 4 days after surgery

Selective IL-2 Receptor Antagonists Contiue..)) Basiliximab & Daclizumab

• Adverse Effects:Both are well-toleratedGastrointestinal toxicity is the major oneNO antibodies, of clinical relevance, to the

drugs are producedInfection & malignancy are not reported

• Alemtuzumab:

• Humanized monoclonal antibody directed against CD-52, and produce profound depletion of T cells.

• Used for refractory B- cell chronic lymphocytic leukemia. However, it is currently in use for organ transplant.

3 -RhoD Immunoglobulin• Rho(D) Immune Globulin (Rhogam)Rhogam is an immunoglobulin that recognizes the

Rho(D) antigenPrepared from pooled sera from Rho-negative

volunteers immunized with D+ erythrocytesIt prevents erythroblastosis fetalis or hemolytic

disease of the newbornWhen a Rho(D)-negative mother carries a Rho(D)-

positive fetus, mother becomes sensitizedSubsequent pregnancies can strengthen response

increasing chance of Ab transfer to fetus

RhoD Immunoglobulin

• It is usually given to the mother within 72 hours after the birth of Rh-positive baby

• This would prevent hemolytic anemia that may occur in subsequent pregnancies

• Adverse Effects:ChillsFeverAnaphylaxis (rare)

•Rho(D) Immune Globulin:– Used to prevent Rh hemolytic disease in

newborn.– Thus, Rho(D) Immune Globulin antibodies are

given to the mother within 72 Hrs after birth of Rh positive baby.

– Uses:• Erythroblastosis Faetalis• Miscarriages