Targeting IL-2 Flashcards
What is the role of IL-2?
- 15.5 kDa protein
- Important stimulator of cell-mediated immune system:
- Acts on IL-2 receptor - Recombinant IL-2 is used in the treatment of cancer
- Renal cell carcinoma
- Metastatic melanoma
How is IL-2 regulated in pharmacotherapy?
- Increase IL-2 levels
- Decrease IL-2 levels
- Block IL-2 receptors
- Block IL-2 signalling
Discuss cyclosporin (CSA)
- A cyclic undecapeptide - a fungal metabolite (Tolypocladium inflatum).
- Inhibits mixed lymphocyte reaction (MLR) but not cytotoxic.
- Inhibits antibody production against T-cell-dependent antigens (sheep erythrocytes) but not T-cell independent antigens (LPS).
Discuss FK506 (Tacrolimus).
- Macrolide antibiotic isolated from fungus (Streptomyces tsukubaensis)
- Inhibits MLR
- Structurally unrelated to cyclosporine
- Similar activity to cyclosporine but more potent (10-100x).
MOA of Cyclosporin and Tacrolimus.
- Inhibit gene transcription.
- IL-2, 3&4
- GM-CSF
- TNFa
- IFNg - Specific for pathways involving increase in intracellular Ca2+ (e.g., T-cell receptor)
Discuss Immunophilins and their relation to FK506 (Tacrolimus) and CSA.
- Both bind to a family of intracellular receptors known as immunophilins.
- Immunophilins are 0.1-0.4% of cell protein
- They’re prolyl-peptidyl cis-trans isomerases (rotamase)
- Involved in protein folding.
Discuss CSA binding protein.
- Binds to cyclophilin (CyP)
- Immunosuppression is mediated by CyPA&B.
- CyPC does not inhibit because it is localised to ER
Discuss FK506 binding protein.
- Binds to FK506-binding protein (FKBP).
- Inhibition mediated by FKBP12 but not FKBP13 (ER) or FKBP25 (nucleus).
- FK506 probably acts via FKBP12.6.
Discuss Calcineurin.
- Immunosuppressive activity is independent of rotamase activity.
- Drug immunophilin complexes bind to and inhibit calcineurin.
- Calcineurin is a serine-threonine phosphatase
What are transcription factors.
- Nuclear factor of activated T-cells (NF-AT) is a substrate for calcineurin
- NF-AT is a transcription factor that binds to the IL-2 promoter
Discuss Rapamycin (Sirolimus).
- Structural homolog of FK506.
- Existing antibiotic shown to have immunosuppressant activity.
- Isolated from Streptomyces hygroscopicus
- Similar profile to FK506
- Binds to FKBP
What are the targets of Rapamycin (TOR).
- Rapamycin-FKBP complex does not inhibit calcineurin or gene induction
- Rapamycin inhibits signal transduction by IL-2 receptor
- Rapamycin-FKBP binds to targets of rapamycin (mammalian* TOR- mTOR 1) a phosphatidylinositol 3-kinase
- Leads to reduced expression of adhesion molecules including sphingosine-1-phoosphate receptor
- Causes cell cycle arrest at G1
Discuss the clinical use of Rapamycin.
Immunosuppression:
- Used for prevention of allograft rejection and in autoimmune diseases
- Rapamycin can be used in conjunction with cyclosporine
- Increases levels of memory T-cells
- Increases longevity in mice by 10%
What are coated stents and what is there clinical use?
- Stents coated with drugs like Rapamycin to prevent atherosclerotic lesions.
- Uncoated stents results in intimal hyperplasia.
- Almost complete inhibition of stent induced hyperplasia
- Evidence of increased incidence of in-stent thrombosis
Clinical use of Rapamycin in cancer.
- mTOR implicated in cancer:
- Renal cell carcinoma (RCC)
- Melanoma
- Breast cancer - Everolimus & temsirolimus approved for RCC
Discuss the toxicity of Rapamycin.
- Less toxic than the cytotoxic immunosuppressants but nephrotoxicity is a problem.
- Cause of nephrotoxicity is probably due to endothelin release and inhibition of NOS.
- FK506 appears to activate NFkB in fibroblasts leading to increased IL-6 production in kidney.
- Rapamycin has less toxicity but causes dyslipidemia.
What are other IL-2 modulators.
- New rapamycin analogues under development
1. Zotarolimus
2. Biolimus
3. Deforolimus
Discuss anti IL-2 receptor antibodies.
- Daclizumab:
- Approved for MS but withdrawn from market due to encephalitis (Withdrawn!). - Basiliximab
- Approved for kidney transplants
Discuss Denileukin Diftitox.
- IL-2 and diphtheria toxin fusion protein
- Binds to cells expressing high affinity IL-2 receptor
- Inhibits protein synthesis resulting in cell death
- Used to treat certain leukemias
- Recurrent cutaneous T-cell lymphoma
- Withdrawn from market
