To fight cancer, there are several therapeutic strategies among which there is radiotherapy: the therapy by radiation. Although this therapy has demonstrated a better management of patients, it generates side effects that can leave sequels. How could tea limit these side effects? Does it also limit the beneficial effects?
Ionizing radiation to destroy cancer cells.
Radiotherapy is based on the use of ionizing radiation (X-rays, radioactive sources, carbon ions, etc.). The radiation is directed directly against the tumor mass and will directly destroy the cancer cells. The destruction will be direct but also indirect: the radiation generates a chemical decomposition of the water surrounding the cells. Molecules called free radicals will be generated, they are very toxic for the cells. However, the emitted radiations also cross the healthy tissue. These phenomena are physically manifested by a large inflammatory zone, which sometimes extends much further than the irradiated area, and can cause tissue necrosis.
Antioxidants in tea: a cat and dog relationship with free radicals ?
Green tea contains molecules with a high antioxidant potential: catechins. These molecules are able to bind to free radicals, which prevents their action on the body's cells.
Xie et al. found that healthy intestinal cells irradiated and treated with a derivative of EGCG (catechin) suffered less damage (mortality, expression of inflammatory factors and responses to free radicals) than cells only irradiated. There would thus be a protective effect of this type of antioxidant on healthy cells. Moreover, the authors of this study observed that mice consuming this EGCG derivative during an irradiation protocol did not present destruction of the healthy intestinal tissue (unchanged cell population, no tissue necrosis, maintenance of the integrity of the intestinal tissue).
These results are rather interesting for the protection of healthy tissue during radiotherapy, yet one must ask whether this reduces the therapeutic effects on cancer cells. For example, Thomas et al. showed that irradiated prostate cancer cells died more than irradiated cells treated with EGCG. It seems that the increase in markers of free radical responses in cancer cells is due to EGCG and reduces the effects of radiation therapy. Conversely, a review of the literature by Yuan et al. reported that tea polyphenols did not affect the efficacy of radiotherapy while limiting the side effects on nasopharyngeal cancer cells.
It is very difficult to compare all the publications on radiotherapy because too many parameters can vary. First of all, the source of radiation and the way it is generated condition the effects that will occur. Second, the dose delivered, measured in Gy, will also condition the response of the cells. Some cells are able to withstand high doses delivered, such as certain brain tumors, while others will not. Thomas' study used a dose of 3.5 Gy (1.5 Gy higher than what is found in the clinic per day) while Xie used doses of 2 to 9 Gy.
When the idea reaches the clinic ...
Although the results in the literature may be mixed in in vitro and in vivo studies, the use of EGCG during radio-chemotherapy treatment is currently being studied in a clinical trial (currently in phase II) for the treatment of stage III (non-small cell) lung tumors. The results of the first phase of clinical development were published in 2014 and suggest that patients who received EGCG applied to the radiation-penetrated skin in addition to conventional treatment had a decrease in inflammation of the esophageal tissue induced by radio-chemotherapy and exhibited faster regeneration of damaged tissue. Moreover, the authors did not find a decrease in the efficacy of the treatment on these tumors compared to some in vitro studies.
Several questions arise: Is it the dose of polyphenol that is important? Is it the dose of polyphenol that is important? Is it the irradiation conditions? Is it the physiological context (single cells vs. whole organism)? Isolated polyphenol or tea infusion? We will have to wait a little longer before getting these answers!