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MECHANISM OF ACTION
Many forms of anti cancer drugs are targeted at the process of cell division. The rationale being that cancer cells are more likely to be replicating than normal cells. Unfortunately as their action is not specific, they are associated with significant toxicity.
Let's see the mechanism of some of the anti cancer drugs:-
ALKYLATING AGENTS
Alkylating agents contains chemical groups that produce highly reactive carbanium ion intermediates that can form covalent bonds with the particular nucleophilic substance in the cell. These ions are highly reactive with the electron donor such as amine, hydroxy and sulfydryl group. The nitrogen at position 7 in guanine residues of DNA is strongly nucleophilic and is especially susceptible, other molecular sites such as N1 and N3 of Adenine and N3 of Cytosine may also be effected. most of the alkylating agents are bi-functional and react with two groups causing intra or inter chain cross linking. This can interfere with not only transcription but also with replication. Thus alkylation may result in cross linking, cross scission or abnormal base pairing thus killing the rapidly dividing cancerous cells.Alkylating agent mainly exert cytotoxic action.(Jordan et.al., 2002)[24]
ANTIMETABOLITES
Anti-metabolites are structurally related to normal component of DNA or of co-enzymes involved in nucleic acid synthesis. These generally interfere with the availability of purine or pyrimidine nucleotide precursors by inhibiting synthesis or by competing with them in DNA or RNA synthesis.(Jordan et.al.,2002),[24]
PLANT EXTRACTS
Vincristine, Vinblastine and vindesine are main vinca alkaloids used in cancer chemotherapy. These are obtained from plant Vinca rosea
These act by inhibitting mitosis. They bind to tubulin and inhibit its polymerization into micro-tubules and thus prevent spindle formation in mitoting cells and cause arrest of meta-phase. Hence, the are both cycle specific and phase specific.
Paclitaxel is another type of anticancer drug obtained from bark of western yew tree . The drug reversibly binds to tubulin and results in the stable non functioning micro-tubule by promoting polymerization and stabilization of the microtubules.Thus, it interferes with the mitosis causing death of cancerous cells.(Cragg and Newmam, 2000).[24]
ANTIBIOTICS
Actinomycin D is a very potent antineoplastic antibiotic obtained from the species of streptomyces. The drug intercalates in the minor groove of the double helix between guanine-cytosine base pairs of DNA and interfere with the movement of RNA polymerase along the gene and thus preventing transcription. It may also cause strand breaks and stabilize DNA topoisomerase II complex .[24]
According to scientist combination therapy is more effective than mono-therapy since combination therapy decreases the possibility of development of resistant to individual agents. Combination chemotherapy can be useful in achieving higher responsive rates due to both additive or potential cytotoxic effect or non-overlapping host toxicities.[24]
REFERENCES:-http://ki.se/en/onkpat/mechanisms-of-action-of-anti-cancer-drugs
Let's see the mechanism of some of the anti cancer drugs:-
ALKYLATING AGENTS
Alkylating agents contains chemical groups that produce highly reactive carbanium ion intermediates that can form covalent bonds with the particular nucleophilic substance in the cell. These ions are highly reactive with the electron donor such as amine, hydroxy and sulfydryl group. The nitrogen at position 7 in guanine residues of DNA is strongly nucleophilic and is especially susceptible, other molecular sites such as N1 and N3 of Adenine and N3 of Cytosine may also be effected. most of the alkylating agents are bi-functional and react with two groups causing intra or inter chain cross linking. This can interfere with not only transcription but also with replication. Thus alkylation may result in cross linking, cross scission or abnormal base pairing thus killing the rapidly dividing cancerous cells.Alkylating agent mainly exert cytotoxic action.(Jordan et.al., 2002)[24]
ANTIMETABOLITES
Anti-metabolites are structurally related to normal component of DNA or of co-enzymes involved in nucleic acid synthesis. These generally interfere with the availability of purine or pyrimidine nucleotide precursors by inhibiting synthesis or by competing with them in DNA or RNA synthesis.(Jordan et.al.,2002),[24]
PLANT EXTRACTS
Vincristine, Vinblastine and vindesine are main vinca alkaloids used in cancer chemotherapy. These are obtained from plant Vinca rosea
These act by inhibitting mitosis. They bind to tubulin and inhibit its polymerization into micro-tubules and thus prevent spindle formation in mitoting cells and cause arrest of meta-phase. Hence, the are both cycle specific and phase specific.
Paclitaxel is another type of anticancer drug obtained from bark of western yew tree . The drug reversibly binds to tubulin and results in the stable non functioning micro-tubule by promoting polymerization and stabilization of the microtubules.Thus, it interferes with the mitosis causing death of cancerous cells.(Cragg and Newmam, 2000).[24]
ANTIBIOTICS
Actinomycin D is a very potent antineoplastic antibiotic obtained from the species of streptomyces. The drug intercalates in the minor groove of the double helix between guanine-cytosine base pairs of DNA and interfere with the movement of RNA polymerase along the gene and thus preventing transcription. It may also cause strand breaks and stabilize DNA topoisomerase II complex .[24]
- Radioactive isotopes are used in the treatment of certain tumors by their property of producing ionization in the cells, thereby causing cell destruction.
- Monoclonal antibodies are also used in the cancer chemotherapy. They activate the host immune mechanism and kills the cancer cells. Examples: Rituximab, Trastuzsumab.
According to scientist combination therapy is more effective than mono-therapy since combination therapy decreases the possibility of development of resistant to individual agents. Combination chemotherapy can be useful in achieving higher responsive rates due to both additive or potential cytotoxic effect or non-overlapping host toxicities.[24]
REFERENCES:-http://ki.se/en/onkpat/mechanisms-of-action-of-anti-cancer-drugs