Immunosuppressive Agents

Question 1

What is the receptor which glucocorticoids bind and what is complexed to it?

Answer 1

Steroid receptor in the cytosol, which is complexed to hsp90 and other stabilizing proteins

Question 2

What does the steroid receptor bind to? What does this do?

Answer 2

Glucocorticoid response elements - which bind in the promotor or enhancer regions of appropriate response genes and modulates transcription

Question 3

What are two primary transcription factors that GRE modifies? What is the net result?

Answer 3

Two inflammatory factors:

1. AP1
2. NF-kappaB

Net result is anti-growth, anti-inflammation, and immunosuppression

Question 4

What is the most commonly prescribed glucocorticoid and its active form?

Answer 4

Prednisone is most prescribed. It is a pro-drug which is easily activated in the liver to active form prednisolone (unless liver disease)

Question 5

When and how much of steroids are typically used?

Answer 5

Primarily used in the “induction” stage of solid organ or hematopoietic stem cell transplants at HIGH doses

Used in low doses in another regimen during the “maintenance” stage

Question 6

What is a common ocular side effect of glucocorticoids?

Answer 6

Cataracts

Question 7

What is a common vascular side effect of glucocorticoids?

Answer 7

Atherosclerosis (due to hyperlipidemia / hyperglycemia)

Question 8

What is a common musculoskeletal side effect of glucocorticoids?

Answer 8

Osteoporosis from inhibition of osteoblast function

Question 9

What is a common neurological side effect of glucocorticoids?

Answer 9

Insomnia -> euphoria -> depression

Question 10

What is the generalized effect of immunophilin binding? What drug classes are included in this?

Answer 10

Inhibitory effects on T-cell activation by selective block of IL-2 and other cytokines in T-helper cells

Includes:
Calcineurin inhibitors
Rapamycin

Question 11

What are the calcineurin inhibitors and how do they work in general?

Answer 11

1. Tacrolimus
2. Cyclosporin A

They work by having their protein - drug complex bind and inhibit calcineurin, a phosphatase which is required to activate NF-AT. NF-AT is responsible for increasing translation of IL-2 and other cytokines for T-cell proliferation.

Question 12

What are the drug targets of tacrolimus and cyclosporin A?

Answer 12

Tacrolimus - FK-binding proteins

Cyclosporin A - cyclophilins

Question 13

How is the distribution of the calcineurin inhibitors and how are they metabolized?

Answer 13

Very lipid-soluble so they get everywhere, with a relatively long halflife

Metabolized via Cytochrome P450 CYP3A4 -> remember this because Tacrolimus is a macrolide

Question 14

What drugs increase and decrease cyclosporine / tacrolimus levels?

Answer 14

Increase: CYP substrates i.e. azole antifungals, macrolides, grapefruit juice

Decrease: CYP inducers i.e. phenytoin, rifampin, carbamezepine

Question 15

What is the most significant and common side effect of calcineurin inhibitors and how does this relate to drugs which can / can’t be taken with them?

Answer 15

Nephrotoxicity -> manifests as azotemia (high BUN) and hyperkalemia

Drugs cannot take: NSAIDs, aminoglycosides, ACE-inhibitors, amphotericin B, acyclovir (other nephrotoxic drugs)

Question 16

What is an early side effect of calcineurin inhibitors and what should be used to treat it?

Answer 16

Hypertension -> due to sodium retention and vasoconstriction

Use calcium channel blockers because ace-inhibitors are nephrotoxic and diuretics can precipitate gout

Question 17

What cancer does calcineurin inhibitor pre-dispose you to?

Answer 17

non-Hodgkin’s lymphoma

Question 18

What is the non-calcineurin-inhibiting immunophilin and how does it work?

Answer 18

Sirolimus (rapamycin) - binds FKBP12 (similar to tacrolimus) but rather inhibits mTOR (mammalian target of rapamycin), a protein responsible for downstream signalling of IL-2. This will keep the cell arrested at G1 phase.

Question 19

Can sirolimus be used with tacrolimus?

Answer 19

Yes, even though they both bind FKBPs, they are present in such large amounts that they do not become a rate-limiting step

Question 20

How is sirolimus metabolized and why might it be preferable to tacrolimus / cyclosporin?

Answer 20

Metabolized via CYP3A4 (it is a macrolide after all)

Might be preferable because it is not nephrotoxic on its own

Question 21

What is azathioprine?

Answer 21

The nitroimidazole derivative of 6-mercaptopurine (6-MP) with good bioavailability

Question 22

What is the mechanism of action of azathioprine?

Answer 22

Suppression of intracellular inosine synthesis, thereby decreasing RNA production via inhibition of purines

This lowers the B and T lymphocyte numbers

Question 23

What is the drug interaction of note with azathioprine and why?

Answer 23

Since it is metabolized by xanthine oxidase, the gout drug allopurinol which inhibits xanthine oxidase can cause bone marrow aplasia (due to 6-MP buildup)

Question 24

What is the methotrexate mechanism of action and what is its worst drug interaction?

Answer 24

Irreversible inhibition of dihydrofolate reductase, decreasing pyrimidine production.

Major interaction with other folate-depleting drugs: TMP/SMX or probenecid

Question 25

What is methotrexate indicated for?

Answer 25

Rheumatoid arthritis and psoriasis + graft-versus host disease. Used for lots of chemotherapy.

Question 26

What drug is used in episodes of renal or other solid organ transplant rejection and how does it work?

Answer 26

Mycophenolate mofentil

Inhibits inosine monophosphate dehydrogenase, part of the de novo purine production pathway which makes guanine, needed for lymphocyte proliferation

Question 27

Why is mycophenolate really juicy?

Answer 27

It is easily hydrolyzed / glucuronated so it is not very toxic (just GI distress), and only decreases GTP pools in lymphocytes / monocytes but not neutrophils (bacterial infection less likely)

Question 28

What is the pro-drug inhibitor of pyrmidine synthesis?

Answer 28

Leflunomide

Question 29

Why is the mechanism of action of cyclophosphamide and when is it used?

Answer 29

It’s an alkylating agent which interferes with nucleic acids / enzyme macromolecules

Used for severe, life-threatening autoimmune diseases and induction phase of immunosuppression

Question 30

Why can we not used cyclophosphamide with tricyclic antidepressants?

Answer 30

TCA’s will decrease bladder emptying, leading to prolonged bladder exposure to “acrolein”, the toxic metabolite of cyclophosphamide

Question 31

In what way is drug metabolism of cyclophosphamide opposite of tacrolimus/sirolimus/cyclosporine?

Answer 31

Microsomal inducers will actually increase the action -> the drug is activated in the liver.

Microsomal blockers will decrease the action -> accumulation of unactivated drug

Question 32

Cyclophosphamide reduces plasma pseudocholinesterase activity. What drug should it NEVER be used with?

Answer 32

Succinylcholine

Question 33

Define the following endings for antibodies:

• imab
• umab
• omab
• zumab
• ximab

Answer 33

• imab or -ximab - chimeric antibodies
• omab - mouse monoclonal antibody
• zumab - humanized monoclonal antibody
• umab - human monoclonal antibody

Question 34

What is the polyclonal antibody used to “induce” immunosuppression?

Answer 34

anti-thymocyte globulin “ATG” -> polyclonal antibodies against thymus cells

Question 35

What is adalimumab?

Answer 35

Humira - recombinant monoclonal antibody to TNF