Exam 4 Flashcards
Major clinical uses for immunosuppressiveagents
- Transplantation induction and maintenance
- autoimmune disorders
- hypersensitivity- pathological antigen antibody reaction
- they dampen the immune response
Which immune responses are more effectively suppressed?
Primary, more than secondary
Limitations of immunosuppressive therapy:
- increased risk of infections of all types
- increased risk of lymphomas and related malignancies
Induction therapy: Depleting agents
- used to get rid of T cells
1. Lymphocyte immune globulin (ALG and ATG)
2. Anti-CD3 antibodies
Induction therapy: Modulators
- do not deplete T cells
- blocks IL2 mediated T cell activation, takes advantage of the fact that resting T cells don’t have IL2R
ALG
anti-lymphocyte globulin
ATG
anti-thymocyte globulin
Major classes of immunosuppressive therapy
- Calcineurin inhibitors (cyclosporine, tacrolimus)
- anti-proliferative/antimetabolic drugs (sirolimus, myco. mofetil)
- antibodies (ATG, ALG, Anti-CD3: muromonab, teplizumab. Anti-IL2R modulators: Daclizumab, Basiliximab)
- glucocorticoids: Anti-inflammatory steroids (predisone, dexamethasone, etc)
Calcineurin inhibitors: cyclosporine
-binds to a cytoplasmic receptor protein called cyclophilin, resulting in the inhibition of calcineurin activity
- this blocks dephosphorylation events required for cytokine gene expression/T cell activation
How is cyclosporine metabolized?
- in the liver, can lead to numerous Drug-drug interactions
Major adverse effects of cyclosporine
- renal toxicity/nephrotoxicity
- may appear as a similar reaction for graft rejection
Calcineurin inhibitors: Tacrolimus (FK506)
- binds to a cytoplasmic receptor protein (FKBP) resulting in the inhibition of calcineurin activity which blocks dephosphorylation critical for cytokine gene expression and T cell activation
Major adverse effects of Tacrolimus
- 100x more potent than cyclosporine
- nephrotoxicity/renal tox
- drug drug interactions
- glucose intolerance
- diabetes
Antiproliferative/antimetabolic drugs
- prevent the clonal expansion of both B and T lymphocytes
- Sirolimus
- mycophenolate mofetil
- other (azathioprine, methotrexate, cyclophosphamide)
Sirolimus
- Rapamycin
- Mech: binds to FKBP to inhibit key enzyme in cell cycle progression (mTOR), blocking progression from G1 to S phase in IL2 driven T cell proliferation
Sirolimus toxicity
- dose dependent increase in cholesterol and triglycerides
- nephrotoxicity
- increased risk of lymphomas and infections
- drug drug interactions with CYP3A4
Mycophenolate mofetil (MMF)
- organ transplantation drug
- Mech: a metabolite of MMF is an inhibitor of inosine monophosphate dehydrogenase (IMPDH), important for guanine nucleotide synthesis required for B and T cells
Toxicity of mycophenolate mofetil (MMF)
- hematologic (leukopenia)
- gastrointestinal (diarrhea, vomiting)
Antibodies for immunosuppressive therapy
- Depleting agents eliminate lymphocytes
- anti-thymocyte globulin
- anti-CD3 antibodies
- Muromonab-CD3 mAb
- Teplizumab-CD3 mAb
Antibody modulators that affect cell function
- anti-IL2R mAb including:
- daclizumab
- basiliximab
Anti-thymocyte globulin
- purified Igs prepared commercially from hyperimmune serum of animals following immunization with human thymocytes
- Igs bind to thymocytes in circulation, resulting in lymphopenia and impaired T cell immune responses
Toxicity of Anti-thymocyte globulin
- Ig being recognized as foreign resulting in serum sickness and nephritis
- anaphylaxis (rare)
Anti-CD3
- Muromonab Cd3
- a mouse monoclonal antibody that binds to the alpha chain of the Cd3 glycoprotein that is part of the T cell receptor complex on T cells –> T cell receptor complex is internalized and it prevents antigen recognition
Cytokine release syndrome
- Mild flu-like illness to life threatening shock
- occurs with Anti-CD3 as an initial interaction of Muromonab-CD3 with T cells combined with the Fc mediated crosslinking
- Frequent, negative side effect
Administration of what before anti-Cd3 can reduce the risk of cytokine release syndrome?
- glucocorticoids. It reduces the symptoms considerably
Newer Anti-CD3 antibodies:
- teplizumab CD3 mAb
- delays onset of Type 1 diabetes (autoimmune disease)
- does not bind Fc receptors, minimal mouse antibody structure (it is humainzed)
- very expensive
Daclizumab and Basiliximab
- Anti-CD25
- mouse antibody made to the IL2 receptor (CD25)
- Mech: binds IL2 receptor present on activated but not rested T cells to block IL2 mediated events
Daclizumab and Basiliximab, anti-CD25 toxicity
- no cytokine release syndrome
- lower incidence of lymphoproliferative disroders and infection
- However, anaphylactic reactions can occur
Steroids produced in the body
Corticosteroids (21C)
- mineralcorticosteroids (electrolyte balance)
- glucocorticoids (carb metabolism, anti-inflam)
Androgens (19C)
- body building steroids
Sodium retention
- ability of the steroid to reduce sodium excretion by the kidney in an adrenalectomized animal
Liver glycogen deposition
- ability of the steroid to cause hepatic deposition of glycogen in a fasted adrenal adrenalectomized animal
Why do we use anti-inflammatory steroid drug therapy?
- exogenous glucocorticoids will turn off the immune system. The endogenous ones are not doing enough
- we want to: minimized the drug action on mineralcorticosteroids and maximize drug action on the glucocorticoid receptor
Metabolism of the anti-inflammatory steroids
- administered orally, parenterally, or topically
- metabolized in the liver and excreted by kidneys
- inhaled glucocorticoids: enhanced uptake and prolonged tissue binding in the airway (also GI first pass inactivation)
Glucocorticoid effect on neutrophils
- more circulating neutrophils
- release from bone marrow is accelerated
- half time in circulation is increased
- blockage of neutrophil migration to inflammatory sites (decrease in adherence capabilities)
Glucocorticoid effect on lymphocytes
- profound transient lymphopenia
- cells are not lysed, but move to extravascular compartments like spleen, lymph nodes, thoracic duct, and bone marrow
Glucocorticoid effects on Monocytes and eosinophils
- decreased in peripheral blood
Systemic administration of anti-inflammatory therapy can cause:
- life-threatening effects (suppresses infection/inflammation reaction –> unknown causes result)
- host resistance to microbial and fungal infection is lowered
What can cause toxicity when using glucocorticoids?
- systemic administration
- continued use of large doses
- withdrawal or discontinuation of long term use
Continued use of large dose corticosteroids can cause:
- increased infection
- peptic ulceration
- behavioral disturbances
- cataracts
- osteoporosis and vertebral compression fractures
- inhibition of growth
withdrawal or discontinuation from long term corticosteroid use can cause:
- symptoms of acute adrenal insufficiency (fever, myalgia, arthralgia, malaise)
- death can occur with hypotension and shock
Immune checkpoint inhibitors attack what aspect of cancer hallmarks?
Avoiding immune destruction
Which protein-protein interactions (Co-stimulatory molecules) inhibit the activation of T cells?
- PD1 and PD1L
- CTLA4 and CD80/86
During tumor development, what types of cell receptors are selected for?
- decreased expression of MHC 1 (makes tumor cells less immunogenic)
2. increased expression of PD1L (to inhibit T cell activation)
Activating signals from the T cell receptor and co-receptors result in activation of what?
- AP-1
- NFAT
- NF-kB
- transcription factors
PD1 interaction with PDL1 or PDL2 does what?
- blunts the T cell receptor signal and serves as a checkpoint on T cell activation
Increased expression of PDL1/PDL2 on cancer calls can be the result of:
- oncogene activation
- IFN signaling from the T cell
Mechanisms of resistance for immune checkpoint therapies
- Increased expression of other immune checkpoint proteins (TIGIT, TIM3)
- Tumor infiltration of immune suppressive cells (Tregs, M2 macrophages)
- Increased cytokine signaling within the tumor microenvironment
Pembrolizumab
- Monoclonal antibody against human PD1
- checkpoint inhibitor
- Indicated in lung, breast, and melanoma cancers
- Acts by blocking the PD1, allowing cytotoxic T cells to kill tumor cells
- given via IV
- Side effects include: GI, colitis, dyspnea, and cough
Atezolizumab
- monoclonal antibody against human PDL1
- checkpoint inhibitor
- indicated in lung, breast, urothelial cancers
- Acts by blocking the PDL1, allowing cytotoxic T cells to kill tumor cells
- given via IV
- side effects include: GI, colitis, dyspnea, cough
Ipilimumab
- monoclonal antibody against human CTLA-4
- checkpoint inhibitor
- indicated in lung, breast, and urothelial cancers
- Acts by blocking the CTLA-4 interaction with CD80/86. allowing cytotoxic T cells to kill tumor cells
- given via IV
- side effects include: GI, colitis, fatigue, and anorexia
What hallmark of cancer is attacked by CDK4/6 inhibitors?
Sustaining proliferative signaling
The G1/S phase checkpoint is controlled by the activity of:
cyclin dependent kinase 4 and 6 (CDK4/6), which become hyperactive in cancer and contribute to uncontrolled proliferation
In a healthy cell without mitogenic signaling, E2F gene transcription is inhibited by:
the retinoblastoma protein (Rb)
Pathway of mitogenic signaling
Mitogen signal –> increased cyclin D1 –> formation of CDK4/6 –> phosphorylation of Rb –> activating E2F –> gene expression –> cell cycle progresses to S phase
Cyclin dependent kinase inhibitors:
block the activity of CdK4/6 and arrest cells in G1 – tumor suppressors
E2F regulates the activity of:
Cyclin E –> activates CDK2 –> phosphorylates Rb –> increased progression through S phase
Breast cancer diverse changes in molecules/receptors and their effects:
- p16 - loss of CDKIs
- p21 - loss of p53
- ER/PR/AR - estrogen receptor signaling
- MAPK/PI3K/AKT - Her2, EGFR signaling
- Cyclin D1 - CDND1 gene amplification
How do CDK4/6 inhibitors work?
they keep Rb in its unphosphorylated state
- resistance occurs via loss of Rb protein and aberrant activity of p27
Ribociclib/palbociclib
- CDK4/6 inhibitor works by inhibiting CDK4/6 complexes (keep Rb unphosphorylated) preventing transition through the G1 checkpoint into S phase
- given orally
- Metabolized via CYP3A4
- side effects include: neutropenia, fatigue, increased risk of upper respiratory infections
Oxygen can be reduced to water through:
- four single electron transfers
- intermediates include superoxide, hydrogen peroxide, and hydroxyl radicals which are highly reactive
What are the 3 main sources of ROS?
- Coenzyme Q on the electron transport chain
- oxidases, peroxidases, and oxygenases
- ionizing radiation
Coenzyme Q reaction:
- accepts 2 electrons from NADH dehydrogenase, and transfers them to cytochrome b-c complex (cytochrome c reductase)
- semiquinone intermediate can leak single electrons to molecular O2, forming SUPEROXIDE
When is superoxide a signaling molecule?
During hypoxia/ low O2 levels
How does the cardiomyopathy occur from Doxorubicin?
- it can accept single electrons to form a semiquinone and undergo redox cycling like CoQ –> the oxidative damage to mitochondria causes the cardiomyopathy
Sulfamethoxazole gets metabolized by what?
- CYP2C9
- myeloperoxidase (MPO)
- cyclooxygenase (COX)
– forms sulfamethoxazole hydroxylamine –> reduces O2 to superoxide and bonds sulfhydryl groups on proteins to form adducts
CYP2E1 oxidizes what?
Ethanol –> acteylaldehyde in the MEOS reaction
Ethanol metabolism by CYP2E1 contributes to oxidative stress by:
- Generation of superoxide
- depletion of NADPH
Monoamine oxidase catalyzes the conversion of an amino group containing carbon –> aldehyde, this reaction produces what?
Hydrogen peroxide
What is the rate limiting step in converting purine nucleotides to uric acid?
- Xanthine oxidase
- this pathway produces ROS and plays a key role in reperfusion injury after tissue ischemia
Without oxygen, what accumulates?
Hypoxanthine and xanthine (O2 is a substrate for both of them to move along)
Low versus high concentrations of O2 and what gets produced by xanthine oxidase:
LOW: hydrogen peroxide
HIGH: superoxide
Where are VLCFAs oxidized?
- Peroxisomes, unlike regular FA beta-oxidation, which is in the mitochondria
- this forms hydrogen peroxide
Ionizing radiation splits water into:
- hydrogen atoms and a hydroxyl radical
Where does ionizing radiation come from?
- Radon and cosmic
- nuclear power generation
- nuclear weapons
- materials testing equipment
- medical diagnostics/treatment
The Haber-Weiss reaction
Superoxide + hydrogen peroxide –> oxygen, water, hydroxyl radical
The Fenton reaction
H2O2 (hydrogen peroxide) + Fe2+ –> Hydroxyl radical + hydroxyl ion + Fe3+
Superoxide dismutase
superoxide –> hydrogen peroxide + O2
- has 3 isoforms (SOD1, 2, 3)
SOD1
- cytosolic
- uses copper and zinc
SOD2
- mitochondrial
- uses manganese
SOD3
- extracellular
- used copper and zinc
What does reactive oxygen and reactive nitrogen species damage?
- Cell membranes (lipids- targets unsaturated FAs)
- DNA
- proteins
Initiation and propagation of lipid cell membrane destruction via ROS
Initiation: hydroxyl radical takes electron from carbon on unsaturated fatty acid forming LIPID RADICAL
Propagation: lipid radical reacts with O2 to form LIPID PEROXYL RADICAL –> lipid peroxyl radical takes single electron from adjacent FA forming LIPID PEROXIDE and a new LIPID RADICAL
What is a breakdown product of lipid peroxides that can be measured?
Malondialdehyde, measured in the blood
What is a marker of oxidative stress in tissues?
8-hydroxyguanine (an oxidation mutation of guanine that base pairs with adenine resulting in G–>T mutations)
Oxidative damage to proteins:
- oxidized side chains form cross links with other side chains –> aggregates of misfolded proteins
- Iron sulfur cluster proteins in the ETC –> loses iron –> non-functional protein AND ROS generation
What does Nitric oxide synthase (NOS) do?
- catalyzes the cleavage of nitric oxide from the amino acid arginine
- 3 isoforms (iNOS, eNOS, nNOS)
nNOS
neuronal
eNOS
endothelial
iNOS
inducible NOS in immune cells (intentional)
Nitric oxide’s physiological function is to:
- bind iron in heme in soluble guanylyl cyclase, activating it. cGMP is produced, leading to activation of protein kinase G and promotion of VASODILATION
What happens when NO binds ferrous iron in heme in guanylyl cyclase and other enzymes?
- it changes the enzyme activity to depend on NO concentration (biphasic effect)
Derivatives of NO can:
Form adducts on amino acid side chains in proteins, interfering with protein function
When neutrophils encounter pathogens:
they undergo a respiratory burst, producing NADPH to power the generation of ROS and RNOS
Chronic granulomatous disease:
- inherited deficiency of NADPH oxidase causing deficient production of superoxide in the phagosome
- engulfs pathogens but cannot kill them
- characterized by recurrent infections
- mutations in transmembrane or cytoplasmic subunits can cause CGD
What are secreted into phagocytic vacuoles?
Myeloperoxidase (MPO) containing granules
- they convert hydrogen peroxide and chloride ion to hypochlorous acid (HOCl- bleach) which damages pathogen
Inducible nitric oxide synthase (iNOS)
- produces NO and combines with superoxide to form PEROXYNITRITE (ONOO-) which decays into nitrogen dioxide radical
- this destroys pathogen via oxygenation and peroxidation of lipids, DNA, and protein
In peroxisomes, hydrogen peroxide is neutralized by:
Catalase
Intracellularly, hydrogen peroxide is neutralized by:
- accepting electrons from reduced glutathione
- selenium dependent enzyme (selenocysteine acid in active site)
Which vitamins can accept single electron transfers to neutralize free radicals and limit oxidative damage?
- vitamin E (vegetable oil, liver, egg yolks)
- vitamin A (carrots- beta-carotene)
- vitamin C (citrus fruits)- scavenger, accepts 2 single electrons
What hallmark of cancer is attacked by CAR-T therapy?
avoiding immune destruction
Cancer cells evade the immune system by:
- downregulating MHC 1
- upregulated PDL1
Chimeric antigen receptors (CAR)
genetically engineered hybrid receptors that bind specific tumor antigen domains, has constructs with:
- an extracellular ligand binding domain with specificity for a tumor antigen (cloned from scFV fragment of a monoclonal antibody gene)
- Cytoplasmic domains that contain elements of TCR co-stimulatory domains (ex: from the zeta chain of the TCR— requires tyrosine kinase)
Tisaganlecleucal
- derives its extracellular domain form a monoclonal antibody that binds CD19
- CD19 marks the B cell lineage and is retained in B cell leukemia/lymphoma
Current CAR-T therapy utilizes:
- autologous transplant
- T cells isolated from patients –> transduced with CAR-T gene via lentiviral vector –> expanded in vitro –> lymphodepleting chemo –> infusion of T cells back into patient