Altering the gut microbiome may reduce the tumor-promoting effects of cigarette smoking, based on a preclinical study.
Mice treated with microbiome-depleting antibiotics or genetically modified to lack an adaptive immune response did not show increased rates of cancer growth when exposed to cigarette smoke, reported lead author Prateek Sharma, MBBS, of the University of Miami, and colleagues.
Although previous research has shown that the gut microbiome plays a role in the progression of cancer and that smoking alters the gut microbiome, the collective effects of these changes have not been studied, the investigators wrote in an abstract released as part of the annual Digestive Disease Week, which was canceled because of COVID-19.
“There is information that smoking changes the gut microbiome ... but the impact of this change is not known,” Dr. Sharma said in a virtual press conference.
To learn more, the investigators first performed an experiment using wild-type mice. All mice were injected with a cancer cell line from the pancreas, colon, or bladder. Mice were then sorted into four groups, in which they were given microbiome-depleting antibiotics and exposed to smoke, given antibiotics alone, exposed to smoke alone, or left untreated and unexposed to serve as controls. Tumor size was then measured over the course of 2 months.
The experiment revealed that mice exposed to smoke but not treated with antibiotics had increased rates of tumor growth regardless of cancer type. But in mice treated with antibiotics, the tumor-promoting effects of smoke exposure were completely lost; the mice had rates of tumor growth even lower than controls.
This experiment was repeated with mice genetically engineered to lack an adaptive immune response. Regardless of smoke or antibiotic exposure, all mice had comparable rates of tumor growth.
Dr. Sharma offered a summary of the findings and their possible implications for human medicine.
“Cigarette smoking changes the gut microbiome, and this changed gut microbiome interacts with the immune system to affect cancer progression,” he said. “If we can target this changed microbiome with modulation strategies like antibiotics, probiotics, or administration of good bacteria, we can alter this process. And if the same results are found in human studies, it could go a long way to affect cancer outcomes in smokers.”
In addition to human studies, Dr. Sharma said that future research should aim to uncover the underlying mechanisms involved in this process, including the types of bacteria that play a role.
When asked if the study might lessen concerns about the negative impacts of smoking among cancer patients, Dr. Sharma suggested that, even if the findings do translate to humans, smoking would still carry significant health risks.
“Even if gut microbiome modulation strategies do work in these patients, it may help a little, but it’s not going to bring it down to the level of nonsmokers, so it’s no way an excuse to not fear or continue [smoking],” he said.
The study was funded by the Florida Department of Health. The investigators reported no conflicts of interest.