Types of Chemotherapy

Chemotherapy is a drug or chemical used to kill tumor cells. It also kills the healthy cells, which causes side effects. Wide varieties of anti cancer drugs are available into the market. These drugs differ in the manner how they attack cancer cells. These are taken orally, injected in the muscles or under skin or into the vein. He drugs are absorbed into the blood and circulated through out the body. For the chemotherapy treatment one or combination of drugs is used. However, there are various types of cancer those need different type of drugs that kill cancer cells in various ways at various phases in the cell cycle. The drugs selected for the treatment of chemotherapy are tested in clinical trials to prove to be most effective to destroy particular stages, types and grades of cancer. The other factors like age and tolerance of side effect are also important to select the chemotherapy drug. Chemotherapy is the process in which the combination of chemical and pharmaceutical are used to kill the cancer cells. The drugs like adriamycin, taxol, cisplatin, 5FU and others are used commonly. Chemotherapy treatment depends on the type and stage of the cancer.

Following are some types of chemotherapy:

Plant Alkaloids:
These are made up from certain type of plants found in nature. The bark of Pacific Yew Tree is used to make taxanes while for making vinca alkaloids, the periwinkle plant is used. Taxanes and vinca alkaloids are also known as antimicrotubule agents. The podophyllotoxins are obtained from the May apple plants. Camptothecan analogs are obtained from the Asian Happy tree. Plant alkaloids attack the cells during various phases of division because they are cells cycle specific. There are some plant alkloids such as docetaxel, taxens and paclitaxel and some vinca alkaloids that include vinblastine, vincristine and virorelbine.

Alkylating Agents:
In the resting phase of the cell the alkylting agents are most active. These cells directly damage DNA and prevent reproduction of cancer cell. It is very important to treat the various kinds of cancer. Following are some alkylating agents used in chemotherapy treatment.

• Alkylsulfonates: Busulfan
• Metal salts: Cispaltin, Carboplatin and Oxaliplatin.
• Ethylenimies: Hexamethylelmelamine and Thiotepa.
• Hydrazines and Triazines: Procarbazine, Altretamine, Dacarbazine and Temozolomide.
• Mustard gas derivatives: Mechlorethamine, Chlorambucil, Cyclophosphamide, Ifosfamide and Melphalan.
• Nitrosureas: Lomustine, Carustine, Streptozocin and Nitrosureas are unique and may cross blood brain barrier. These can also used to treat the brain tumors.

Anti-tumor Antibiotics:
These are the natural products produced by soil fungus streptomyces. These cells are considered as cell cycle specific and act during multiple phase of cell cycle. Following are few types of anti-tumor antibiotics.

• Chromomycins: Plicamycin and Dactinomycin.
• Anthracyclines: Mitoxantrone, Epirubicin, Doxorubicin, Idarubicin and Daunorubicin.
• Miscellaneous: Bleomycin and Mitomycin.

Anthracyclines:
Anthracyclines interfere with enzymes that are necessary for replication of DNA. Anthracyclines are cell cycle non specific and anti tumor antibiotic used to treat different kinds of cancer. The drugs like bleomycin, doxorubicin and mitomycin are examples of anthracyclines.

Topoisomerase Inhibitors:
These are various chemotherapy drugs that interfere with the action of toposiomerase enzymes. Topoisomerase enzymes also plays very important role in controlling the manipulation of DNA structure that is necessary for replication during chemotherapy treatment. There are few toposiomerase enzymes such as ironotecan, topotecan are included in topoisomerase I inhibitors and several enzymes like etoposide phosphate, amsacrine, etoposide and teniposide are included in topoisomerase II inhibitors.

Antimetabolities:
Antimetabolities are similar to normal substances present in the cell. Antimetabolities are the drugs that interfere with growth of DNA and RNA. These are cell cycle specific and kill cancer cells in a specific phase of cell division. Antimetabolities are unable to divide when cells incorporate normal substances into the cellular metabolism. The antimetabolitities are classified according to substances with which they interfere.

• Purine antagonist: 6-thioguanine and 6- Mercaptopurine
• Folic acid antagonist: Methotrexate.
• Pyrimidine antagonist: Foxuridine, Capecitabine, 5-fluorouracil, Cytarabine, and Gemcitabine.
• Adenosine deaminase inhibitor: Nelarbine, Fludarabine, Cladribine, and Pentostain.
  Mitotic Inhibitor

The cell division of cancerous cell is inhibited by mitotic inhibitor. These inhibitors work during the mitosis phase of cycle. These cells also interfere with the production of enzymes and it is necessary for cell reproduction.

Miscellaneous Antineoplastics:

• Enzymes: Pegaspargase and Asparaginase.
• Ribonucleotide reductase inhibitor: Hydroxyurea.
• Adrenocortical steroid inhibitor: Mitotane
• Retinoids : Baxarotene, Isotretinoin, tretinoin (ATRA)
• Antimicrotubule agent: Estramustine.