Pharmacology 9/1/00 2:00 pm Scribe: Fathy/Robb
Professor: Syapin
IMMUNOPHARMACOLOGY
Dr. Syapin graciously followed his notes to make our lives easier. If he reworded something in class, I put his wording here. After class I asked whether we should follow his thorough notes or his more simplified lecture. His answer: “You must be able to answer the objective questions”. Finally, he told me that his slides will be available online, although they were not available as of this writing.
1. A brief review of the immune response.
A. Immune response: two major components
1. Cell-mediated immunity
2. humoral (antibody) immunity
B. Quote: The key word is “cytokines”. Cytokines are proteins that have a vital role in initiation and regulation of immune responses.
1. He listed off IL-1, 2, 4, 5, 6 as “all very important in different aspects of immunity”.
2. CD4 T helper cells cause proliferation of CD8 T-cell via IL-2.
C. Two categories of immunopharmacologicals: immunosuppressors and immunostimulators.
1. We are much better at immunosuppressin than stimulation.
D. Guiding principles of immunosuppression
1. Primary immune responses are more easily suppressed than secondary (memory cells-mediated) responses
2. Immunosuppressive agents have different effects on different immune reactions (seriously, go use his notes).
3. Chances of success are better if treatment begins before exposure to the immunogen, especially with allergens.
E. This section is in his notes but not in lecture.
2. Four classes of immunosuppressive agents: (1) helper T-cell blockers, (2) glucocorticoids (“as I’m fond of calling them”), (3) cytotoxic drugs, and (4) antibodies used to modulate and suppress.
A. Helper T-cell Blockers: Cyclosporine (Pharmcard #59) and Tacrolimus. Cyclosporin was a revolutionary advancement in medicine…making organ transplants a reality. Tacrolimus is its competitor.
1. Both inhibit helper T-cell release of IL-2 by “effecting the gene for IL-2” (discussed below).
2. Other more minor actions of Cyclosporin
a. Inhibit Mast cell degranulation
b. Promotes expression of TGF-β (anti-IL-2) by unknown mechanisms
3. Tacrolimus previously known as FK506.
4. Active site of both is a “multi-ring type of a structure” (is this helping?).
5. “The important thing for you to remember is how they work”
a. The mechanism of action of cyclosporine is to bind to the intracellular protein cyclophilin and inhibit the enzyme calcineurin phosphatase, thus blocking activation (dephosphorylation) of the nuclear factor of activated T-cells (NF-AT) transcription factor. Activated NF-AT forms a dimmer and stimulates IL-2 gene transcription (see his slides for a cartoon).
b. It acts via a mechanism similar to cyclosporine to inhibit helper T cell activation, but binds to a different intracellular target protein (FK506 binding protein; FKBP) to inhibit calcineurin phosphatase. FKBP is related to the cyclophilin family.
6. These drugs are taken orally but their bioavailability is not great, often only up to 50%. A new microemulsion formulation of cyclosporin gives more consistent absorption.
7. Cyclosporin is metabolized in the Liver by liver cytochrome P4503A enzymes.
a. Drugs known to induce the hepatic P450 microsomal enzyme system have caused graft rejection due to accelerating cyclosporine metabolism to below therapeutic levels.
b. Other drugs inhibit P4503A and can cause toxic levels of cyclosporin to exist.
8. Both drugs are used for all types of transplants, but usually in combination with other drugs.
a. It is most commonly used in combination with prednisone (a glucocortisoid) to prevent allograft rejections in renal, hepatic and cardiac transplants
b. Tacrolimus is only approved for Liver transplants by the FDA but surgeons probably don’t follow that rule.
c. Treatment is begun well before surgery begins (please go read your notes).
9. Toxicity is a problem the patient must live with because non-toxic levels don’t work.
a. Nephrotoxicity: more prevalent with cyclosporin. DO NOT use NSAIDS with patients on either of these drugs because of risk of kidney damage.
b. Neurotoxicity is more common with Tacrolimus (but occurs with both).
c. Both “cause” equal incidence of GI problems.
d. Hypertension caused mainly by cyclosporin
e. Hyperkalemia
f. Hyperglycemia
g. There is increased incidence of infections, but generally less than occurs with other types of immunosuppressant drugs
h. When used in combination with immunosuppressants like prednisone and azathioprine, cyclosporine can cause malignant lymphomas with a high incidence of brain metastases! Yikes!
B. Synthetic glucocorticosteroids (glucocorticoids): the most extensively used immunosuppressants.
1. Prednisone and prednisolone (both on Pharmcard #157) are most often used.
a. They are orally active and used at high to moderate doses.
1. They are used “with other drugs” to prevent transplant rejection.
b. They glucocorticoids are also used during GVHD
c. During acute organ rejection, methylprednisolone is given i.v. for several days at doses up to 1.5 grams per day
d. Also used prior to use of anti-suppressant antibodies.
2. Major side effects are common because of the high glucocorticoid doses needed for immunosuppression
a. These include cushingoid reactions, glucose intolerance, infections, bone dissolution, muscle wasting and “other toxic effects”.
3. Glucocorticoids reduce the number of immune cells and interfere with immune processes. These processes result in:
a. Lymphopenia
b. Monocytopenia
c. Neutrophils actually increase because glucocorticoids block transmigration of neutrophils out of the blood.
4. Inhibit release of IL-2 and T-cell activation.
5. Have direct effects on CTLs.
C. Cytotoxic agents
1. Antineoplastic agents that prevent clonal expansion of T and B cells are used for immunosuppression. They prevent T-cell and B-cell expansion.
a. 3-Azathioprine (Pharmcard #30) is a prodrug for 6-mercaptopurine, a nucleotide antimetabolite that disrupts DNA and RNA synthesis. Used to prevent organ transplant rejection.
b. Mycophenolate Mofetil is hydrolyzed in blood to mycophenolic acid (MPA), the active agent, a potent inhibitor of inosine monophosphate dehydrogenase which is important for nucleic acid synthesis.
c. Cyclophosphamide (Pharmcard #17) is an alkylating agent and alkylates DNA. Used in bone marrow transplants.
d. Methotrexate (Pharmcard #123) is a potent inhibitor of the enzyme dihydrofolate reductase, resulting in the reduced biosynthesis of thymidylate and purines. Used prophylactically to guard against GVHD.
. Antibody preparations
1. Anti-thymocyte antibodies have been used as immunosuppressants. Lymphocyte immune globulin, anti-CD3 monoclonal antibody, and anti-Tac
a. At present all are derived from non-human sources and hence run the risk of inducing anti-idiotype antibodies, even in an immunosuppressed host.
b. Lymphocyte immune globulin is a preparation from horses and can destroy human thymus-derived lymphocytes and inhibit the normal responses of T-cells.
c. The anti-CD3 monoclonal antibody is prepared from mouse hybridoma cells. OKT3 binds to a component of the CD3 complex on CD3+ lymphocytes and quickly eliminates these cells, thus inhibiting their actions.
d. Anti-Tac is also a murine monoclonal antibody and binds the IL-2 receptor expressed by already activated T cells and inactivates them.
2. Rh(D) immune globulin is an IgG class antibody at high titer. It blocks the sensitization of Rh-negative mothers to the D antigen of an Rh(D)-positive offspring that can occur during miscarriage, ectopic pregnancies, and parturition.
a. When the immune globulin is administered to the mother within 72 hours of exposure to Rh(D)-positive blood, no hemolytic disease of the newborn has been observed in subsequent pregnancy.
3. For treatment to be successful the mother must be Rh(D)-negative must not have been previously immunized to the Rh(D) factor.
3. Specific Immunostimulants: Bacteria-derived agents, synthetic agents, intravenous immune globulin, and cytokines. It is believed that if you can stimulate the immune system, it helps people with immunodeficiencies (are you still reading this?).
A. Bacteria-derived agents (natural adjuvants).
1. Bacille Calmette-Guérin (BCG) is an attenuated live strain of Mycobacterium bovis. Promotes release of TNF-α from macrophages. It has been approved for a very specific type of bladder cancer.
a. Adverse effects include hypersensitivity and shock, chills, fever, malaise and immune complex disease.
B. Synthetic agents
1. Levamisole-HCl is approved for use as an immunostimulant to potentiate the stimulation of lymphocytes, granulocytes and macrophages by antigens, mitogens, lymphokines and chemotactic factors.
a. It has been licensed for use with 5-fluorouracil in resected patients with Dukes C colon cancer.
2. Intravenous immune globulin formulations are prepared from pooled plasma from up to 50,000 donors.
a. The products contain no IgM, varying amounts of IgA, and normal relative amounts of IgG subclasses.
b. IVIG formulations act by replacement therapy in primary immune deficiency diseases such as X-linked agammaglobulinemia. This is a form of passive immunity.
c. All six licensed IVIG preparations are approved for primary immune deficiency
A. Gammar-IV® and Iveegam® are not approved for idiopathic thrombocytopenic purpura
B. Iveengam® is the only IVIG approved for Kawasaki disease
C. Gammagard® is the only IVIG approved for treating B-cell chronic lymphocytic leukemia
D. All IVIG, except Gammagard®, are contraindicated in patients with IgA deficiency
3. Cytokines
a. Interferons inhibit viral replication and modulate immune responses and exist in three types: alpha, beta and gamma.
A. Interferons bind to specific cell surface receptors to initiate their effects
B. High doses inhibit B-cell and T-cell proliferation and immune responses
C. Lower doses, and particularly interferon- γ , are immunostimulatory, activating natural killer (NK) cells, macrophages, and cytotoxic T-cells.
D. Interferon-γ is approved for the prevention of infections in persons with chronic granulomatous disease.
E. IFN-α is used to treat leukemias, sarcomas and Hepatitis C infections.
F. Interferon-β -1b is expected to receive approval soon for use in treating relapsing-remitting multiple sclerosis.
G. Adverse effects of interferons include fever, fatigue, headaches, myalgias, and GI and cardiovascular disturbances.
b. Interleukin-2 (IL-2) acts by binding to the IL-2 receptor and inducing proliferation and differentiation of T helper cells and T cytotoxic cells, leading to increases in other cytokine levels.
A. Human recombinant IL-2 (rIL-2) was recently approved for treatment of metastatic renal cancer
B. rIL-2 toxicity is high, including the capillary leak syndrome associated with edema, reduced organ perfusion and hypotension, cardiac arrhythmias, and myocardial infarction.
c. Two colony stimulating factors have been approved for clinical use
A. Granulocyte colony-stimulating factor (G-CSF) induces the maturation of bone marrow stem cells into neutrophils
A. It is used after cancer chemotherapy to decrease the incidence of infection in patients with non-myeloid malignancies
B. The primary adverse effect of short-term G-CSF treatment is bone pain. Splenomegaly and abnormal uric acid levels may also occur
d. Granulocyte-macrophage colony-stimulating factor (GM-CSF) induces development of neutrophils, eosinophils and macrophages
A. It is used for acceleration of myeloid recovery after autologous bone marrow transplantation in non-Hodgkin's lymphoma, Hodgkin's disease, and acute lymphoblastic leukemia