Several types of chemotherapy drugs are employed to treat cancer. They function by inhibiting cell division.
Chemotherapy drugs may be be classified as follows-
- Alkylating agents (or) DNA- damaging agents
Alkylating agents act by chemically altering the cellular DNA.They add alkyl groups to the electronegative groups. Some examples include: Cisplatin, Oxaliplatin, Carboplatin, Chlorambucil, Cyclophosphamide, Mechloethamine and Melphalan.
The anti- metabolic drugs function as the building blocks of DNA by imitating the role of purine or pyrimidine.These anti-metabolites stop cell division and are widely employed for their efficacy. Some of the important drugs include methotrexate, fludarabine, and cytarabine.
- Plant alkaloids and terpenoids
These plant-based chemicals block cell division by inhibiting microtubule function.The spindle fibres, made of microtubules, help to separate the chromatids during cell division.
Examples are vinca alkaloids (derived from Catharanthus roseus) and taxanes.
The vinca alkaloids include: Vincristine,Vinorelbine,Vinblastine and Vindesine.
These plant-derived compounds are primarily extracted from Podophyllum peltatum (American mayapple). They prevent the cells from entering the G1 phase and also affects DNA synthesis. Two cytostatic drugs derived from podophyllotoxin are etoposide and teniposide.
Taxanes are plant- based compounds that increase the stability of microtubules thereby preventing the separation of chromatids during mitotic anaphase.
- Topoisomerase inhibitor
Topoisomerases are enzymes that are essential to maintain the topology of the DNA. Interfering with these enzymes prevents the normal functions of the DNA, such as transcription, replication and repair.
Type I topoisomerase inhibitors include irinotecan and topotecan.
Type II inhibitors include amasacrine, etoposide phosphate and etoposide.
- Antitumour antibiotics
Dactinomycin, daunorubicin, doxorubicin, idarubicin, and mitoxantrone are important drugs under this category.
Prednisone and dexamethasone are examples of hormones which, in high doses, can damage lymphoma or lymphocytic leukemia cells.
- Monoclonal antibodies
Monoclonal antibodies attach themselves to tumour- specific antigens, thereby increasing immune response to tumour cell.Examples are- rituximab, cetuximab, trastuzumab. Some monoclonal antibodies, like imatinib mesylate, a tyrosine kinase inhibitor, targets an abnormality in certain cancer cells. Imatinib targets the philadelphia chromosome common to Chronic Myeloid Leukemia(CML). It is also used to treat gastrointestinal stromal tumors.