Used with specific types of chemotherapy, chemoprotective agents are drugs that protect the body from chemotherapy or minimize its side effects. Commonly used chemoprotective agents include mesna, amifostine, and dexrazoxane.
Mesna received FDA approval in 1988. It is used to reduce bladder irritation (hemorrhagic cystitis) that can occur due to specific high-dose chemotherapy protocols.
Amifostine received FDA approval in 1995. It helps reduce the extent of renal injury in certain patients who receive chemotherapy. Research on this drug was carried out during World War II, with a view to protect soldiers during chemical warfare.
Dexrazoxane received FDA approval in 1995. Its use has significantly reduced cardiac related complications in cancer patients receiving chemotherapy treatments.
These drugs do not eliminate side effects; they protect the body against some potentially severe side effects. Since these chemoprotective agents have their own side effects, they are used only with certain specialized chemotherapies or when it is clear that benefits are more than the associated risks.
Chemotherapy resistance refers a situation where cancers that were earlier responding to a specific chemotherapy start to regenerate. In such a scenario, doctors need to change the drug or drug combinations being used.
Factors that can result in chemotherapy resistance include
- Cancer cells that survive the chemotherapy can mutate and develop resistance to the drug. When these cells multiply, a higher fraction of resistant cells are left than before chemotherapy treatment.
- Gene amplification: Cancerous cells can produce hundreds of copies of a specific type of gene. The gene stimulates an increased production of protein that negates the effects of the anticancer drug.
- By using a molecule known as p-glycoprotein, cancer cells can eliminate the drug as fast as the drug enters.
- If the protein that carries the drug across the cell walls stops functioning, the drug may not reach the cancer cells.
- Cancer cells may develop the ability to repair the damage in DNA strands, as may have been caused by specific types of anti-cancer drugs. The cells can develop certain mechanisms to inactivate the drug.
Research is currently underway to study newer methods of minimizing or preventing chemotherapy resistance.
The risk of drug resistance is a primary reason for the use of drug combinations. Often, when a cancer stops responding to a specific drug or drug combination, there is a possibility that the cancer may have become resistant to other drugs as well. This makes it necessary to choose the most effective treatment protocol FIRST. It implies that one should utilize the best weapon available in the treatment of cancer whenever there is this slightest chance of chemotherapy resistance.