HC31: Targeted therapy and hematological malignancies

Monoclonal antibodies

Tumor specific monoclonal antibodies:

CD20 is an IgG isotype expressed antigen on normal and malignant B-cells. It is used for treatment of many B-cell lymphomas → by targeting CD20 antigens, both malignant and normal B-cells are depleted.

Rituximab:

Chemotherapy combined with CHOP monoclonal antibodies leads to a significant increase of survival rates. Rituximab, a monoclonal antibody against CD20, leads to:

• Complement system activation
  • A MAC is formed
• NK-cell recruitment
  • Receptors bind to the humanized tail of rituximab
• Apoptosis
  • Macrophages are attracted

Mechanisms of action:

Monoclonal antibodies can have different mechanisms of action:

• Complement dependent cytotoxicity (CDC)
  1. The complement system is activated
  2. Hollow pipes are made in the cell surface
  3. Water enters the cell
  4. The cell explodes
• Antibody dependent cellular cytotoxicity (ADCC)
  1. A B-lymphocyte plasma cell secretes antibodies which bind to an antigen on the pathogen
  2. The pathogen is phagocytosed by macrophages, destroyed by NK-cells or lysed via the complement system
• Radio immunotherapy
  1. A radioactive particle such as yttrium is coupled to an IgG monoclonal antibody such as CD20 → can get close to the tumor cells
     • A form of local treatment
  2. Yttrium gives a small dose of β- or γ-radiation
  3. The tumor is directly targeted
• Antibody drug conjugate
  1. A drug is bound to a monoclonal antibody such as CD30 → an ADC-CD30 complex is created
     • CD30 is expressed in Hodgkin lymphomas and anaplastic large cell lymphomas
  2. The ADC-CD30 complex travels to the lysosome
  3. MMAE is released in the cell → disrupts the microtubule network
     • Physical cell division is prevented by binding on a microtubule during cell division
  4. The G2-/M-phase is arrested → the cell cycle stops → apoptosis

Bispecific antibodies

Bispecific antibodies are a combination of 2 different antibodies to target B-cells with CD8 T-cells. A bispecific T-cell engager (BiTE) causes proliferation of T-cells via the following mechanism:

1. 2 antibodies are coupled to create a bispecific monoclonal antibody with binatunumab → an antibody against CD3 antibody is coupled with an antibody against CD19
   • Anti-CD3 antibodies target T-cells
   • Anti-CD19 antibodies target B-cells
2. The T-cell becomes activated and starts its immune function → cytokines are made
   • A T-cell can kill more cells than 1 B-cell
3. The T-cell attacks malignant B-cells → perforins enter the B-cells and kill them

CAR T-cells

A T-cell has a T-cell receptor, which can recognize a peptide presented in an HLA molecule. To activate a T-cell receptor, additional costimulatory signals such as CD28 are necessary as well. If a T-cell receptor is activated, the T-cell proliferates and kills the target cell. A Chimeric antigen receptor (CAR) T-cell uses the intracellular part of a TCR and the extracellular part of a monoclonal antibody:

1. T-cells are extracted through a leukapheresis procedure
2. T-cells are expanded if necessary
   • Usually there already are enough T-cells
3. CARs are reprogrammed into the T-cell
   • Using a viral vector, T-cells with a new gene part are transfused with costimulatory signals and the extracellular part is transfused with part of a monoclonal antibody
     • The CD3 zeta-chain of the TCR is used
     • An anti-CD19 antibody is used as monoclonal antibody
4. Re-infusion of the CAR T-cells
   • Chemotherapy is used for lymphocyte depletion to make the CAR T-cells more effective
5. The target cell is killed

(Dis)advantages:

CAR T-cells have several risks, but also benefits:

• Risks
  • Normal B-cells are also destroyed
  • T-cells are activated and cytokines are excreted → cytokine release syndrome can occur
    • For this reason, CAR T-cells are only used in hospitals with good IC-departments
• Benefits
  • Upon activation, CAR T-cells go into a memory state → a reaction is induced in case of tumor relapse
    • However, CAR T-cell survival is not as good as normal T-cell survival

Side effects

Side effects of monoclonal antibodies, BiTEs and CAR T-cells are:

• Allergic reactions at the beginning of the infusion
  • Caused by monoclonal antibodies
• Cytokine release syndrome
  • Symptoms
    • Hypotension
    • Fever
    • Tachycardia
    • Dyspnea
  • Released cytokines
    • TNF-α
    • IFN-γ
    • Interleukin-6
    • Interleukin-2
  • Caused by blina and CAR T-cells
    • People have died due to treatment with CAR T-cells
• Tumor lysis syndrome
  • Lysis causes renal failure due to formation and release of uric acid crystals
    • Prevention with rasburicase or allopurinol → no release of uric acids
  • LDH release
• Polyneuropathy
  • Monomethyl auristatin E (MMAE) conjugates to anti-CD30

Small molecules

Small molecules are also a form of targeted therapy. Small molecules can be used to treat chronic myeloid leukemia, where due to a translocation of chromosome 9 and 22 a fusion protein is made. This causes constitutive activation and increased proliferation. Targeted therapy consists of a drug that can take up the place of an ATP molecule, inhibiting phosphorylation of substrates → the effector mechanism doesn’t take place anymore. Imatinib is an example of target therapy.

In short, there are many signal transduction pathways, and many drugs which can inhibit particular molecules. In some tumors, the B-cell receptor is continuously active, which can be stopped by a small molecule.

Midostaurin:

Midostaurin is a new drug. It is an inhibitor of mutated Flt3, a surface cytokine receptor which is present on malignant acute myeloid leukemia cells. Inhibition of Flt3 results in increased cell death. Sometimes, midostaurin is used as maintenance treatment.