Chemotherapy and radiotherapy are by their very nature highly toxic processes. Whilst often helpful, and sometimes curative, they are also capable of causing much ‗collateral damage‘ in other, healthy tissues. Natural medicines can be used to mitigate the side effects of these treatments, and to enhance their activity, potentially reducing the dosage or duration of treatment required.

Some natural medicines have the capacity to interfere with or reduce the effectiveness of these treatments, and for this reason should be used cautiously or avoided during active treatment periods. Generally these natural medicines can be safely used before and after the treatment periods.

Radiation therapy works by damaging cell DNA. The damage is caused by a photon, electron or proton beam directly or indirectly ionising the atoms which make up the DNA chain. Indirect ionisation happens as a result of the ionisation of water, forming free radicals, notably hydroxyl radicals, which then damage the DNA. In the most common forms of radiation therapy, most of the radiation effect is through free radicals. Because cells have mechanisms for repairing DNA breakage, it is when both strands of the DNA are broken that is most significant in modifying cell characteristics. Because cancer cells generally are undifferentiated and stem cell-like, they reproduce more, and have a diminished ability to repair sub-lethal damage compared to most healthy differentiated cells. The DNA damage is inherited through cell division, accumulating damage to the cancer cells, causing them to die or reproduce more slowly. Proton radiotherapy works by sending protons with varying kinetic energy to precisely stop at the tumour.

One of the major limitations of radiotherapy is that the cells of solid tumours become deficient in oxygen. This is because solid tumours usually outgrow their blood supply, causing a low-oxygen state known as hypoxia. The more hypoxic the tumours are the more resistant they are to the effects of radiation because oxygen "fixes" or makes permanent the radiation damage to DNA. Much research has been devoted to overcoming this problem including the use of high pressure oxygen tanks, blood substitutes that carry increased oxygen, hypoxic cell radiosensitisers such as misonidazole and metronidazole, and hypoxic cytotoxins, such as tirapazamine. Interestingly, recent data has indicated that patients ingesting excess amounts of antioxidant vitamins (such as C or E) may actually diminish the effectiveness of the radiation treatment.

Broadly, most chemotherapeutic drugs work by impairing mitosis (cell division), effectively targeting fast-dividing cells. As these drugs cause damage to cells they are termed cytotoxic. Some drugs cause cells to undergo apoptosis.

As chemotherapy affects cell division, tumours with high growth fractions (such as acute myelogenous leukaemia and the lymphomas, including Hodgkin's disease) are more sensitive to chemotherapy, as a larger proportion of the targeted cells are undergoing cell division at any time.

Chemotherapeutic drugs affect "younger" tumours (i.e., less differentiated) more effectively, because at a higher grade of differentiation, the propensity to growth usually decreases. Near the centre of some solid tumours, cell division has effectively ceased, making them insensitive to chemotherapy. Another problem with solid tumours is the fact that the chemotherapeutic agent often does not reach the core of the tumour. Solutions to this problem include radiation therapy (both brachytherapy and teletherapy) and surgery.

Version 5 Page 7 of 8 Jul 09

Other uses of cytostatic chemotherapy agents are the treatment of autoimmune diseases such as multiple sclerosis and rheumatoid arthritis, the treatment of some chronic viral infections such as hepatitis, and the suppression of transplant rejection.