By Fatéma Dodat
Image Source : Pixabay
Over the past five years, the potential link between the intestinal microbiota and anti-cancer treatments has aroused great interest in the scientific community and hopes among patients. Studies are currently evaluating whether this microbiota could increase the effectiveness of oncology treatments. What is the intestinal microbiota and what is the basis for this hypothesis?
The human intestinal microbiota
The human intestinal microbiota includes the microorganisms (bacteria, fungi) that live in the intestines. Of all the microbiotes in the human body, this is the largest and amounts to almost 100,000 billion microorganisms - a weight of around 1.5 kilograms in an adult.
The intestinal microbiota is involved in many functions, the best known being digestion. Indeed, the bacteria of the microbiota can ferment food that is not digestible, produce vitamins or digest fibre. In addition, they actively participate in immunity by being crucial players in the barrier function of the intestine, which prevents pathogenic species from colonising this organ. The intestinal microbiota also participates in the maturation of the individual's immune system. Finally, imbalance of the intestinal microbiota is now associated with various diseases, such as inflammatory bowel diseases (Crohn's disease) or diabetes.
Role in the response to anti-cancer treatments
Ever since scientists highlighted the involvement of the Helicobacter pylori bacteria in the development of stomach cancer in the 1990s, the relationship between intestinal bacteria and cancer has continued to be explored.
In 2013, researchers proved that certain cancer treatments were based on the activation of the immune system by the intestinal microbiota. A study showed that cyclophosphamide, a drug used in chemotherapy, induces damage to the mucus layer that covers the intestinal wall, allowing intestinal bacteria to travel through the lymph nodes and the spleen, where they can activate immune cells. In mice bred without bacteria in their gut or had been given antibiotics, responsible of the alteration of gut flora, the molecule lost most of its anticancer activity.
Subsequently, intestinal bacteria also proved to be important for immunotherapy treatments. A study carried out in mice revealed that an immunotherapy treatment administered on an intact microbiota induces a reduction of tumour growth, process mediated by a factor involved in programmed cell death. Conversely, mice that have received a cocktail of antibiotics showed a decrease in this factor and the effectiveness of the treatment was reduced.
At the same time, a clinical researcher from the University of Chicago also demonstrated the role of Bifidobacteria in increasing the response to immunotherapy treatments in mice.
Finally, promising studies led by the team of Dr. Bertand Routy, a clinical researcher at the Centre Hospitalier Universitaire de Montréal research centre, show that patients who have taken antibiotics to treat infections unrelated to their cancer tend to respond poorly to immunotherapy.
All of these studies suggest an important role for the microbiota in the response to oncology treatments. However, the mechanisms underlying the role of these intestinal bacteria in the immune response are not yet fully understood and human trials are just beginning. In parallel, work is being carried out to identify the signature of a "healthy" intestinal microbiota and to evaluate the efficacy and safety of faecal transplants in order to boost the microbiota of patients who do not respond or respond poorly to treatments.