ImmunosuppressantsProf. Alhaider, 1432 H

Definition Clinical Uses (Organ transplants & Autoimmune

diseases) Pre-requisite to understand immunosuppressive

drugs (Basic immunology). Review of immune system (read Table 56-1,

next slide) Cell mediated vs humoral immunity Importance of cytokines Immunophilins Calcineurin

MOA: next slide

Classification of Immunosuppressant (Based on Classification of Immunosuppressant (Based on

Mechanism of Action)Mechanism of Action) A) Antiprolifirative Agents

I) Drugs Acting on Immunophilins: (most importanat )

a) Selective Inhibitors of Cytokine production (Calcineurin Inhibitors) e.g: Cyclosporine; Tacrolimus

b) Inhibitor of cytokine function (e.g. Sirolimus).

II) Antimetabolites (Azathioprine; Mycophenolate Mofetil)

III ) Alkylating Agents (Cyclophosphamide)

B) Lymphocyte Depleting Agents:1. Corticosteroids (Prednisone (orall) & Methylprednisolone (IV) )2. Immunosuppressive Antibodies

a) Polyclonal Antibodies (Antilymphocytic Globulins)

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

Immunosuppressant ClassesImmunosuppressant Classes

Non-selectiveCorticosteroids Prednisone (PO) &

Methylprednisolone (IV)

Antimetabolite (DNA synthesis inhibitors)

Azathioprine & Myclophenolate mofetil

Immunoglobulins Anti-lymphocyte

antibodies

SelectiveCalcineurin Inhibitors Cyclosporine Tacrolimus (Rapamycin)Selective IL-2

Receptor antagonists Basiliximab, Daclizumab

& Infliximab Mamalian target of

Rapamycin (mTOR) inhibitors

Sirolimus

Selective Inhibitors of Cytokine Production Selective Inhibitors of Cytokine Production (Drugs Acting on Immunophilins)(Drugs Acting on Immunophilins)

1) Cyclosporine (CsA) (Cyclic peptide from Soil Fungus (1971)◦MOA: (See slide 5)

CsA binds to cyclophillin forming a comlex Bind to Calcineurin dephosphorylation NFATc * Synthesis of IL-2 cell-mediated immune response (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-mediated immunity with no effect on B lymphocytes/humoral immunity.

*NFATc = cytosolic nuclear factor of activated T cells

◦ PK1. CsA available as oral (capsule) or

parentral (i.v)2. Oral bioavailability (20-50%), 3. It undergoes extensive hepatic

metabolism by Cyt P450 (CYP3A4) (Affected by drugs affecting the microenzymes cimetidine, rifampin, cefaporazone)

4. 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 an 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 ? Not used anymore

◦ Side Effects (remember: most immunosuppressant are very toxic) Dose-dependent nephrotoxicity ( Risk of Rejection);

enhanced when given with other nephrotoxic drugs (Aminoglycosides; NSIADs, amphotericin B)

Hepatotoxicity Neurotoxicity as tremor and hallucination Infection, opportunistic Lymphoma and cancer How? immunity Hypertension; hyperlipidemia; Hyperkalemia; DM;

osteoporosis, hirsutism, and gum hyperplasia (So What? don’t prescribe it to female patints)

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

◦ MOA: Similar to Cyclosporine (Calcineurin Antagonist) but it bind to a different immunophilin (FKBP) slide 14

◦ PK: Almost Similar to Cyclosporine

◦ Side Effects: differ from Cyclosporine, that it 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 hyperlipidemia.

Clinical uses of Tacrolimus:Preferred over CsA for:

Its greater potency (50-100 times more potent than cyclosporine)

lower rejection episodeslower doses of glucocorticoids are used

with lower side effectsBetter first choice for women, can you

tell why? Less hirsutism and gum hyperplasia

Severe refractory atopic dermatitis, local application of an ointment

An ointment for psoriasis.

Five year renal allograft survival in patients with cyclosporin or tacrolimus

3. Sirolimus (Rapamycin Macrolides)◦MOA: see next slide

1) Binds to the same immunophilin Tacrolimus binds to 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-cells response to IL-2 (Blocks cytokine-stimulated cell proliferation)

3) Potent inhibitor of B-cell proliferation and immunoglobulin production (decreases the humoral immunity)

Uses of Sirolimus:◦1) can be used together with cyclosporine to

increases the activity of cyclosporine for organ transplantion. Why not tacrolimus? Because it shares the same MOA.

◦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) Hyperlipidemia (even more than calcineurin-

antagonists)

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 prodrug, converted in the body to the active

metabolite, 6-mercaptopurine and thioinosinic acid.

MOA: (see next slide Figure) It inhibits purine synthesis (antimetabolite), thus interfering

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

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

lymphoids cells. Why is it very important to know the structure of

azathioprine?.

Metabolic pathway for azathioprineMetabolic pathway for azathioprine

6-thiouracil (-)

Xanthine Allopurinol

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 transplants together

with steroids and cyclosporine.◦ 2) Can be used for glomerulonephtitis and SLE; RA; Crohn’s

disease and multiple sclerosis (MS).

◦ PK:It can be given both orally and IV

Side Effects:◦ 1) Like cyclosporine, is not teratogenic (Unlike TAC and Siro)

but carcinogenic if given together with alkylating agents. Here, higher doses are used for immunosuppression as compared to its use in autoimmune diseases.

◦ 2) Strong bone marrow suppression (Leukopenia; anemia; thrombocytopenia How?

◦ 3) Hepatic dysfunction as increase ALP and mild jaundice.◦ 4) Hypersensitivity reactions (as rashes, fever, diarrhea) Why?.

Drug interactions:Combination with ACEIs or

cotrimoxazole can cause severe leukopenia in renal transplants

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

immunosuppressant agents.

◦ MOA: (See Figure in the coming 2nd slide) Mycophenolic acid acts as non-competitive, selective 7 reversible

inhibitor of inosine monophosphate dehydrogenase (IMD) 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, Reversible bone marrow suppresion

(leukopenia and anemia); N/V and diarrhea (decresed by Enteric-coated form).

Unlike azathioprine it is teratogenic.

◦ Clinical Uses 1) Drug of choice for preventing vasculopathy in cardiac

transplants 2)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 (especially 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 Prodrug of an inhibitor of PYRIMIDINE synthesis rather

than purine-like azathioprine and mycophenolate mofetil.◦ Orally active used only for RA◦ Side effects: Alopecia; raised LFT, nephrotoxicity,

teratogenicity.

33 . .Alkylating AgentsAlkylating Agents

e.g. Cyclophosphamide◦ The most potent immunosuppressant ◦ Destroys proliferating lymphoid cells (cytotoxic agent) also

alkylates some resting cellsvery 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 a unique Adverse effect Infertility Teratogenic

B) Lymphocyte Depleting Agents:

1. Corticosteroids: The most commonly used immunosuppressant MOA:

◦ At the biochemical level: act on gene expression, which leads to decrease synthesis of PGs; Leukotrienes, cytokines, and other signaling molecules which participate in the 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 causes lowering of IgGs.

Uses:◦In combination with other

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

◦To treat acute rejection episodes (high doses)

◦To treat undesirable immunoreactions (to drugs or asthma).

◦For autoimmune diseases (idiopathic thrompocytopenic purpura; inflammatory bowel diease; rheumatoid arthritis; systemic lupus erythematosus; and glomerulonephritis)

Adverse effects:

Increased blood pressure How? By their aldostrone-like moiety 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? Answered above! Muscle breakdown (proteolysis), weakness; reduced muscle

mass and repair Increased skin fragility, easy bruising Cataracts Adrenal cortex suppression (Avoid abrupt withdrawl) Increase tendency to infections

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 the liver or spleen 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 the site of injection).

2) Chills & fever and Leukopenia & thrombocytopenia

3) 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 patient undergoing bone marrow

translpant (Give large doses of ALG for 7 days)

2) Immune globulin Intravenous (IGIV):

- Prepared from a pool of thousands of healthy donors.

Uses: 1) Refractory Idipathic Thrombocutopenic

Purpura

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 prepared by hybridoma technology and directed against the glycoprotien CD3 antigen of human T cells. Used mainly for cases of acute allograft rejections of the 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 hours.Side Effects:1) Cytokine release syndrome (Anaphylactoid reactions); and seizure (contraindication)

Therefore, it is less used nowadays.

Side Effect of MuromonabSide 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 fever

CNS: Seizures, encephalopathy, cerebral edema & headache

Infection like CMVContraindicated with pregnancy,

breast feeding, history of seizures, uncompensated heart failure

2) Modified Types of monoclonal antibodies (e.g: Selective Inhibitors of IL-2):

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 a.a.; producing humanized designated monoclonal antibodies (e.g. Daclizumab; Transtuzumab). While the chimeric (Mixed) antibodies contain XI in their name (e.g. Abciximab; Infliximab; Rutuximab).

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

less immunoantigenic.

B- Selective IL-2 Receptor B- Selective IL-2 Receptor AntagonistsAntagonists BasiliximabBasiliximab && DaclizumabDaclizumab Basiliximab is a chimeric antibody

composed of 25% murine & 75% human protein. Blocks

IL-2 of activated lymphocytesDaclizumab is humanized antibody

composed of 90% human proteinTherapeutic Use: Prophylaxis against acute rejection of

kidney transplantationUsed in combination with steroids and

CsA

Selective IL-2 Receptor Selective IL-2 Receptor AntagonistsAntagonists BasiliximabBasiliximab && Daclizumab Daclizumab (Continue…)(Continue…)

Mechanism of action:They are anti-CD25 and IL-2

antibodiesThey bind to the -chain of the IL-2 R

(CD25 or TAC subunit) on the activated T-cells

Then, IL-2 binding to IL-2R is prohibited & T-cell activation and proliferation are suppressed

VI- Selective IL-2 Receptor VI- Selective IL-2 Receptor AntagonistsAntagonists BasiliximabBasiliximab && Daclizumab Daclizumab (Continue...)(Continue...) Pharmacokinetics: Given by IV route

Daclizumab 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 Selective IL-2 Receptor AntagonistsAntagonists Contiue..)Contiue..)) ) BasiliximabBasiliximab && DaclizumabDaclizumabAdverse Effects:Both are well-toleratedGastrointestinal toxicity is the

major oneNO antibodies, of clinical

relevance, to the antibodies are produced

Infection & malignancy were not reported

Alemtuzumab:Humanized monoclonal antibody

directed against CD-52, and produces profound depletion of T cells.

Used for refractory B-cell chronic lymphocytic leukemia. However, it is currently used in organ transplantation.

33 - -RhRhooDD Immunoglobulin ImmunoglobulinRho(D) Immune Globulin (Rhogam) Rhogam is an immunoglobulin that recognizes

the Rho(D) antigen Prepared from pooled sera from Rho-negative

volunteers immunized with D+ erythrocytes It prevents erythroblastosis fetalis (hemolytic

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

positive fetus, the mother becomes sensitized Subsequent pregnancies can strengthen

response increasing chance of Ab transfer to the fetus in the last trimester

How Does How Does RhRhoo(immunoglobulin work)(immunoglobulin work)The potion is a solution of IgG anti-D (anti-

RhD) antibodies that bind to, and lead to the destruction of, fetal Rh D positive red blood cells that have passed from the fetal circulation to the maternal circulation. Therefore, Rho in a Rhesus negative mother it can prevent sensitization of the maternal immune system to Rh D antigens, which can cause rhesus disease in the current or in subsequent pregnancies. Note: With the widespread use of Rho (D) Immune Globulin, Rh disease of the fetus and newborn has

almost disappeared.

RhRhooD ImmunoglobulinD ImmunoglobulinIt is usually given to the mother

within 72 hours after the birth of any of the Rh-positive babies she has.

This would prevent hemolytic anemia that may occur in subsequent pregnancies

Adverse Effects:ChillsFeverAnaphylaxis (rare)