03.02.5.1 Cytotoxic Anti-Cancer Drugs

One of the characteristics, of cancers cells, is that they are very rapidly dividing, compared to most normal cells. In the G1 phase of the cell cycle cells grow, and then in the S phase there is replication of the DNA (Figure 3.27). After replication of the DNA, cells go through the G2 phase were they are preparing to divide. The division is called mitosis (M), and you end up with 2 cells. Any drug that interferes with this cell cycle will reduce the generation of new cells, including cancer cells.

Figure 3.27 The cell cycle (Copyright QUT, Sheila Doggrell)

Probably one of the best known cytotoxic drugs is cyclophosphamide. Cyclophosphamide inhibits the cell cycle by preventing the production of RNA for the new cell. Cyclophosphamide is used in a variety of cancers, including leukemia and lymphoma. As a cytotoxic drug, cyclophosphamide causes lots of adverse effects. Severe bone marrow suppression can occur 1-2 weeks after treatment. Cyclophosphamide can also cause anaemia and thrombocytopenia, and haemorrhagic cystitis. Indeed the adverse effects with cyclophosphamide and other cytotoxic drugs are endless. Cyclophosphamide can also cause nephrotoxicity, nausea and vomiting, gastrointestinal dysfunction, hair loss, impaired wound healing, darkening of skin, gonadal suppression (missed menstrual periods), cardiotoxicity etc.

Thus, it is obvious that cytotoxic drugs are not the ideal anti-cancer drugs, and that it would be better to have drugs that killed the cancer cells but not the normal drugs. This led to the idea of targeted anti-cancer drugs.