L6: Molecular Targeted Therapies (II) Flashcards
Current approaches of targeted therapies
- Small molecules
- Therapeutic antibodies (Works by neutralizing, immune modulating, ADCC, immunoradiotherapy)
- T-cells immunotherapy
- Nanotechnology (Using liposomes, nanocarbons etc)
Advantages of small molecules
1) Low cost and high chemical stability as compared to biologics
2) Drug discovery is facilitated through high throughput screening (HTS) techniques
3) Often cell permeable and can be used for intracellular targets as compared to Ab (extracellular due to its size)
Advantages of therapeutic Ab
1) High potential affinity/specificity (made by mammalian system)
2) High stability (very long half life as compared to small molecules; 2 weeks vs 24h)
3) Amenable to engineering
MOA of therapeutic Ab
1) Neutralizing Ab (Eg. blocking GF from binding to growth factor receptor eg. VEGF)
2) Effector cell-mediated cytotoxicity (injecting Ab to activate body’s immune system to kill cancer cells; using Ab for how they were designed)
3) Ab drug conjugate (Ab not designed to kill the cancer cells but to deliver small molecules to the cancer cells; Ab bind to cancer cells -> small molecules internalize -> kill cancer cells)
Adv of neutralizing Ab/When to use
- Ideal for cell surface receptors and extracellular ligands
- Highly expressed in cancer cells and mediate essential tumour-promoting pathways
Adv of effector-mediated cytotoxicity/what are the mechanisms associated with this
- Takes advantage of endogenous function of Ab (can enter cell endogenously)
- Mechanism 1: Antibody dependent cell-mediated cytotoxicity (Ab bind to antigens on target cell via Fab portion -> Effector cells with the FcR portion for the Fc portion on Ab are recruited and activated by receptor cross-linking -> Effector triggers apoptosis in target cells via cytotoxic molecules and receptor signalling)
- Mechanism 2: Complement-dependent cytotoxicity (activation of C1 complex on effector cells)
- Detailed CDC mechanism: C1q binds to antibodies -> Triggers the complement cascade -> resulting in the formation of a membrane attack complex (MAC) (C5b to C9) on the surface of target cells -> further resulting in a classical pathway of complement activation
- Ideal for cancer but less ideal for other indications
- May be modulated by engineering or by post-translational modifications
- Eg. lgG1 strongly activates ADCC but lgG4 weakly activated ADCC (if we want a drug to target ADCC, change Fc portion to lgG1)
Structure of Ab drug conjugate (ADC)
1) Antibody: High tumour specificity, high antigen expression, high avidity (overall strength of binding between Ab and antigen), internalized upon binding (criticial for ADC; if able to internalize, it is a good target)
2) Linker, link between drug and Ab: Stable during storage, stable in circulation (cannot be cleared by serum proteases or factors in blood, should be cleared by lysozyme in cell), cleaved inside target cell)
3) Drug: highly potent (toxic), linkable, water soluble, usually poor TI as free drug (a lot of toxicity as a small mol but distribution changed when using ADCC)
Advantage of ADC
- Conferring specificity to cytotoxic drugs (higher tumour selectivity for drugs that are too toxic to be used on their own)
- Conferring cell killing power to mAb that are tumour-specific but not sufficiently cytotoxic
- Ideal ADC: Remains non-toxic in circulation in vivo until it reaches its target
Examples of ADC
1) Kadcyla (mAb: trastuzumab, drug: maytansine (DM1) - antimitotic, prevents tubulin polymerization)
2) Adcetris (mAb: brentuximab, drug: monomethyl auristatin E (MMAE) - antimitotic, prevents tubulin polymerization)
MOA of Adcetris/Brentuximab vedotin
- For T cell lymphoma
- ADC binds to CD30 and initiates internalization of ADC-CD30 complex by forming endosomes -> proteasomes/enzymes cleave linker -> release MMAE/auristatin -> MMAE binds to tubulin and disrupts microtubule network -> cell cycle arrested -> apoptosis of cell
MOA of immunoradiotherapy/molecular targeted radiotherapy
- similar to ADC (categorised under ADC) but MOA slightly different
- Similar to external beam therapy: cancer cell destruction achieved by means of radiation induced DNA damage
- Similar to chemotherapy: systemic treatment that uses a molecule, but in this case carrying a radiolabel to deliver cytotoxic substance to disease sites
- Has a “bystander” or crossfire effect: potential destruction of adjacent cells; important since tumour are heterogenous
- Can be used for primary and metastatic tumours: including malignant cell populations undetectable by diagnostic imaging (compared to normal radiotherapy where we need to know the location to apply therapy)
- Less SE for molecular targeted radiotherapy, less radioactive isotopes hitting normal cells (eg. skin)
Types of T-cell immunotherapy
1) [Old/Previously]: Adoptive cell transfer
- Patient T-cells have not develop the target/antigen, hence do not kill the cancer cells
- Engineering patient’s own immune cells to target and kill cancer cells
- Isolating cells from blood -> express as dendritic cells -> implant dendritic cells into body and hope it recognises cancer cell as foreign and kill them
2) [New/creating superkiller T-cells]: Chimeric antigen receptor (CAR) T-cells
- T cells are engineered to overexpress CARs that recognises cancer cells
- Promising clinical trials, particularly in acute lymphoblastic leukemia (ALL), targeting CD19+ malignant B cells (killing all cells with CD19+ target)
- CD19 is expressed in both normal and malignant B cells, but better to be immunocompromised than killed by cancer (do not need B/T cells to live)
- FYI: CD19 expression is maintained in B-lineage cells that have undergone neoplastic transformation, and therefore CD19 is useful in diagnosis of leukemias and lymphomas using monoclonal antibodies (mAbs) and flow cytometry
Structure of CAR
[Refer to slides]
- Targeting element (Single chain variable fragments scFvs, similar to GF receptor): Recognizes tumour-specific antigen
- Spacer: to link targeting element to transmembrane domain
-Transmembrane domain
- Costimulatory domain (CD28/4-1BB): Secondary signal to promote survival and replicative capacity
- CD3z (zeta) (Essential signalling domain): Required to induce T-cell proliferation
-> Costimulatory + CD3z: To proliferate and survive longer than normal T-cell -> becoming super T cells
How is CAR-T immunotherapy performed?
1) Extracting T cells from patient
2) Reprogramming T cells by inserting viral vector containing CAR T gene into T cells
3) Manufacturing CAR T cells - CAR T cells are proliferated in vitro to a specific clinically relevant quantity and quality (“Expanded” in the bioreactor with the help of magnetic beads coated with two Ab, Anti-CD3 and Anti-CD28 (cytokines) to signal T cells to proliferate. After ~10 days of proliferation, the magnetic beads are washed out)
4) Patient pre-conditioning - Patients are treated with chemotherapy to lower WBC count to readily accept T cells (Body will reject if there is too many cells)
5) Treatment with CAR-T cells (Multiple myeloma, 100% response for CAR T therapy, targeting plasma cells)
Advantages of cancer nanomedicine
- Wide range of nanomaterials with their pros and cons
- Functionalize with a wide range of therapeutics and targeting mechanisms
- Capable of making multi-functional complexes
- Improve tumour-specific drug delivery and impair general systemic distribution
[Look at next slide for overview of different nanomaterials for therapy]
