Chemotherapy: Mechanisms of Action
Topoisomerase Inh.
Alkylating agents
Purines and Pyrimidines
Antimetabolites
Asparaginase
Tubulin binders
Protein e.g., tubulin
An Example of DNA Crosslinking
Crosslinking: Joining two or more molecules by a covalent bond. This can
either occur in the same strand (intrastrand crosslink) or in the opposite strands
of the DNA (interstrand crosslink). Crosslinks also occur between DNA and
protein. DNA replication is blocked by crosslinks, which causes replication
arrest and cell death if the crosslink is not repaired.
Alkylating Agents (Covalent DNA binding drugs)
1. The first class of chemotherapy
agents.
2. Stop tumor growth by crosslinking
guanine nucleobases in
DNA double-helix strands -
directly attacking DNA.
3. This makes the strands unable to
uncoil and separate.
4. As this is necessary in DNA
replication, the cells can no longer
divide.
5. Cell-cycle nonspecific effect
6. Alkylating agents are also
mutagenic and carcinogenic
E.g., Mechlorethamine (Nitrogen Mustards)
Cyclophosphamide is an alkylating agent. It is a widely used as
a DNA crosslinking and cytotoxic chemotherapeutic agent.
•It is given orally as well as intravenously with efficacy.
•It is inactive in parent form, and must be activated to cytotoxic
form by liver CYT450 liver microsomaal system to 4-
Hydroxycyclophamide and Aldophosphamide.
•4-Hydroxycyclophamide and Aldophosphamide are delivered to
the dividing normal and tumor cells.
•Aldophosphamide is converted into acrolein and
phosphoramide mustard.
•They crosslink DNAs resulting in inhibition of DNA synthesis
Cyclophosphamide Metabolism
Clinical Applications:
2. Breast Cancer
3. Ovarian Cancer
4. Non-Hodgkin’s Lymphoma
5. Chronic Lymphocytic Leukemia (CLL)
6. Soft tissue sarcoma
7. Neuroblastoma
8. Wilms’ tumor
9. Rhabdomyosarcoma
Major Side effects
3. Nausea and vomiting
4. Decrease in PBL count
5. Depression of blood cell counts
6.Bleeding
7.Alopecia (hair loss)
8.Skin pigmentation
9.Pulmonary fibrosis
Ifosphamide
Mechanisms of Action
Similar to cyclophosphamide
Application
4.Germ cell cancer,
5.Cervical carcinoma,
6.Lung cancer
7.Hodgkins and non-Hodgkins lymphoma
8.Sarcomas
Major Side Effects
Similar to cyclophosphamide
1. Mechanism of Action
2. Clinical application
3. Route
4. Side effects