Anti cancer therapy


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Anti cancer therapy

  2. 2. Conventional Anti-Cancer Therapy <ul><li>Chemotherapy: Imperfect </li></ul><ul><ul><li>Systematic nature of cytoxicity </li></ul></ul><ul><ul><li>Agents lack intrinsic anti-tumor selectivity </li></ul></ul><ul><ul><li>Anti-proliferative mechanism on cells in cycle, rather than specific toxicity directed towards particular cancer cell </li></ul></ul><ul><ul><li>Host toxicity: treatment discontinued at dose levels well below dose required to kill all viable tumor cells </li></ul></ul>
  3. 3. HISTORY <ul><li>Emil von Behring in 1890 </li></ul><ul><ul><li>Discovered antibodies </li></ul></ul><ul><li>Paul Ehrlich (16 years later) </li></ul><ul><ul><li>Coined phrase, “magic bullets and poisoned arrows”: use of antibodies to specifically target toxic substances in pathogenic substances </li></ul></ul><ul><li>Kohler and Milstein in 1975 </li></ul><ul><ul><li>Discovery of monoclonal antibodies (mAb) directed against well-characterized antigens </li></ul></ul><ul><ul><li>Use of DNA bio-engineered technologies within last 25 years </li></ul></ul>
  4. 4. Rationale <ul><li>mAb as efficient carriers for delivery of anti-tumor agents </li></ul><ul><ul><li>Enhanced vascular permeability of circulating macromolecules for tumor tissue and subsequent accumulation in solid tumors </li></ul></ul><ul><ul><ul><ul><li>Normal tissue: blood vessels have intact endothelial layer that permits passage of small molecules but not entry of macromolecules (like mAb) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Tumor tissue: blood vessels leaky, so small and large molecules have access to malignant tissue </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>-tumor tissue generally do not have a lymphatic drainage system; therefore, macromolecules are retained and can accumulate in solid tumors </li></ul></ul></ul></ul></ul>
  5. 5. Patho-physiology of Tumor Tissue <ul><li>Angiogenesis </li></ul><ul><li>Hypervasculature </li></ul><ul><li>Impaired lymphatic drainage </li></ul><ul><li>***Due to these characteristics, tumors can be exploited for tumor-selective drug delivery**** </li></ul>
  6. 6. Genetic Engineering <ul><li>Remove or modify effector functions of mAb: used to avoid unwanted side effects </li></ul><ul><li>Use mAb in their natural, fragmented, chemically modified, or recombinant forms </li></ul><ul><li>Use of phage display antibody libraries or transgenic animals </li></ul><ul><ul><li>Identify animals that make desired antibodies </li></ul></ul><ul><ul><li>Animals must be immunized using the cellular antigens and immunization procedures used to generate conventional antibodies </li></ul></ul><ul><ul><li>Perform cell fusions to generate clones and isolate stable clones, making mAb </li></ul></ul><ul><ul><li>Most mAb used in the clinical setting were generated </li></ul></ul><ul><ul><li>in mice </li></ul></ul>
  7. 7. Structure of Antibody <ul><li>Presently, all intact therapeutic antibodies are murine immunoglobulins of the IgG class </li></ul><ul><ul><li>Murine immunoglobulin = glycoprotein that has a Y-shaped structure: 2 identical polypeptide heavy chains and 2 identical light chains linked by an S-S bond </li></ul></ul><ul><ul><li>Chimeric antibody = genetically engineered construct containing a mouse Fab portion and a human Fc portion </li></ul></ul><ul><li>3 main components </li></ul><ul><ul><li>Two identical Fabs (fragment-antigen binding site): the arms of the Y </li></ul></ul><ul><ul><li>An Fc (for fragment crystallizable), the stem of the Y </li></ul></ul><ul><ul><ul><ul><li>Constant region responsible for triggering effector functions that eliminate the antigen-associated cells </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Constant region must be tailored to match requirements of the antibody (depending on which antigen you want it to bind to) </li></ul></ul></ul></ul>
  8. 8. IgG structure
  9. 9. 3 MECHANISMS RESULTING IN APOPTOSIS <ul><li>Antigen cross-linking </li></ul><ul><li>Activation of death receptors </li></ul><ul><li>Blockade of ligand-receptor growth or survival pathways </li></ul>
  10. 10. 1. Antigen Cross-Linking <ul><li>Target growth factor receptor </li></ul><ul><ul><li>Antagonize ligand-receptor signaling </li></ul></ul><ul><ul><li>Growth-factor signaling mediated by the receptor tyrosine kinase is inhibited </li></ul></ul><ul><ul><ul><ul><li>EGFR (epidermal growth factor receptor) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>IGF-1R (insulin-like growth factor-1 receptor) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>FGFR (fibroblast growth factor receptor) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>PDGFR (platelet-derived growth factor receptor) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>VEGFR (vascular endothelial growth factor) </li></ul></ul></ul></ul><ul><ul><li>Results in arrest of tumor cell growth </li></ul></ul>
  11. 11. 2. Activation of death receptors <ul><li>Cross-link targeted surface antigens on tumor cells and antibody agonists that mimic ligand-mediated activation of specific receptors </li></ul><ul><ul><li>Response: intracellular Ca II ions increase </li></ul></ul><ul><ul><li>Activate caspase-3 and caspase-9 (involved in cell apoptosis) </li></ul></ul>
  13. 13. 3. Delivery of Cytotoxic Agents <ul><li>Physically link antibodies to toxic substances for delivery </li></ul><ul><ul><li>Radio-immunoconjugates (aim of delivering radiation directly to the tumor) </li></ul></ul><ul><ul><li>Toxin-immunoconjugates (deliver toxins intracellularly) </li></ul></ul><ul><ul><li>Antibody-directed enzyme pro-drug therapy (ADEPT): localize enzymes to tumor cell surfaces </li></ul></ul>
  14. 14. General Drug Delivery System <ul><li>Drug molecules bound to macromolecule through spacer molecule </li></ul><ul><ul><li>Drug released from macromolecule after cellular uptake of the conjugate </li></ul></ul><ul><ul><li>Targeting moiety = monoclonal antibody </li></ul></ul>
  15. 15. TOXIN IMMUNOCONJUGATES <ul><li>Cell surface antigen must internalize upon mAb binding </li></ul><ul><li>When drug is released, it interferes with protein synthesis to induce apoptosis </li></ul><ul><li>3 methods to attach cytotoxic drug to variable regions of mAb </li></ul><ul><ul><li>a. Couple drug to lysine moieties in the mAb </li></ul></ul><ul><ul><li>b. Generation of aldehyde groups by oxidizing the carbohydrate region and subsequent reaction with amino-containing drugs or drug derivatives </li></ul></ul><ul><ul><li>c. Couple drugs to sulfhydryl groups by selectively reducing the interchain disulfides near the Fc region of the mAb </li></ul></ul>
  16. 16. Direct attachment of mAb to drug by S-S bonding
  17. 17. Immunoconjugate <ul><li>BR96-doxorubicin conjugate (BR96-DOX) </li></ul><ul><ul><li>Promising toxin-immunoconjugate </li></ul></ul><ul><ul><li>mouse/human chimeric mAb </li></ul></ul><ul><ul><li>Targets antigen over-expressed on surface of human carcinoma cells of breast, colon, lung, and ovary </li></ul></ul><ul><ul><li>Disulfide reduction attaches mAb to drug, BR96 </li></ul></ul><ul><ul><li>Dose that can be safely administered every 3 weeks is insufficient </li></ul></ul>
  18. 18. Other examples of toxin-immunoconjugates <ul><li>KS1/4-MTX </li></ul><ul><ul><li>Conjugate of methotrexate (MTX) </li></ul></ul><ul><ul><li>Coupling of MTX to the lysine moieties of the mAb </li></ul></ul><ul><ul><li>No significant clinical response </li></ul></ul><ul><li>KS1/4-DAVLB </li></ul><ul><ul><li>Conjugate of vinca alkaloid derivatives </li></ul></ul><ul><ul><li>Vinca alkaloid derivatives attached to amino groups of lysine residues on KS1/4 mAb </li></ul></ul><ul><ul><li>No significant clinical response </li></ul></ul>
  19. 19. Why are these toxin-immunoconjugates unsuccessful? <ul><li>Cause gastrointestinal toxicity </li></ul><ul><li>Inner regions of solid tumors poorly vascularized and have low blood flow (reduce amount of immunoconjugate reaching these parts of the tumor) </li></ul><ul><li>Antigen expression is heterogenous on tumor cells </li></ul><ul><ul><li>Restricts the amount of cells that can be effectively targeted by antibody conjugates </li></ul></ul>
  20. 20. ADEPT ENZYMES (Antibody-directed enzyme pro-drug therapy) <ul><li>Chemically link the mAb to the enzyme of interest; can also be a fusion protein produced recombinantly with the antibody variable region genes and the gene coding the enzyme </li></ul><ul><li>Convert subsequently administered anti-cancer pro-drugs into active anti-tumor agents </li></ul><ul><ul><li>Upon binding to targeted enzymes, it is converted into active drug </li></ul></ul>
  21. 22. Anti-growth factor mAb Therapy <ul><li>Angiogenesis </li></ul><ul><ul><li>Formation of nascent blood vessels </li></ul></ul><ul><li>VEGF </li></ul><ul><ul><li>One of the most upregulated antigens in cancer </li></ul></ul><ul><ul><li>Protect endothelial cells from apoptosis via activation of PKC pathways and upregulation of anti-apoptotic proteins such as Bcl-2 </li></ul></ul><ul><ul><li>Activity mediated by tyrosine kinase receptors, VEGFR 1 and VEGFR 2 </li></ul></ul><ul><ul><li>Functions indirectly as survival factor for tumor cells </li></ul></ul><ul><li>Inhibit VEGF signaling </li></ul><ul><ul><li>Block the receptor </li></ul></ul><ul><ul><li>Inhibits tumor growth and metastasis </li></ul></ul><ul><ul><li>Deprives tumors of nutrient-providing blood vessels </li></ul></ul>
  22. 23. RITUXIMAB (Rituxan) <ul><li>1 st therapeutic mAb approved by FDA in 1997 </li></ul><ul><ul><li>High-level expression of the gene encoding Rituximab was found </li></ul></ul><ul><ul><li>a mouse-chimeric mAb </li></ul></ul><ul><ul><li>Contains the human IgG1 and murine variable regions that target CD20 B-cell antigen </li></ul></ul><ul><ul><ul><li>CD20 antigen function: cell cycle progression </li></ul></ul></ul><ul><ul><ul><li>Binding Rituximab to CD-20 causes: autophosphorylation, activation of serine/tyrosine protein kinases, and induction of oncogene expression --- induces apoptosis </li></ul></ul></ul><ul><li>Response rates of 50% to 70% in follicular lymphomas </li></ul><ul><li>Response rates of 90% to 100% when used in combination with various chemotherpay procedures </li></ul><ul><li>Concluded that the dose of 4, once-weekly 375 mg/m squared IV infusions of Rituximab was safe and effective in patients with relapse or refractory B non-Hodgkin’s lymphoma </li></ul>
  23. 24. Toxic effects of Rituximab <ul><li>Short-lived mild reactions to infusion after first treatment: fever, chills, rigors, rash, and nausea </li></ul>
  24. 25. Factors affecting pharmacokinetic parameters <ul><li>Circulating target antigens (which can lead to rapid clearance) </li></ul><ul><li>Antigen-antibody internalization in cells (which affect serum clearance and half-life) </li></ul><ul><li>Antibody size and domains with the Fc region </li></ul><ul><ul><li>Fragments have shorter half-lives and more rapid clearance rates than their full-sized immunoglobulins </li></ul></ul>
  25. 26. FUTURE <ul><li>Researchers hope to define the optimal combinations of the use of mAb with conventional chemotherapeutic agents and with radiation therapy </li></ul><ul><li>Determine best therapy candidates and expand clinical trials to other tumor types </li></ul>