Use of broad-spectrum antibiotics in mice with malignant melanoma, an aggressive form of skin cancer, accelerated the growth of their metastatic bones, likely because the drugs depleted the mice's gut flora and weakened their immune response, according to a new study by scientists from Emory University in Atlanta, Medical Xpress writes. The findings underscore the importance of the gut microbiome to overall health and suggest that doctors should carefully weigh the gastrointestinal consequences when they use antibiotic therapy to treat cancer or other diseases, said one of the study's authors, Subhashis Pal, PhD, a postdoctoral fellow in endocrinology at Emory University School of Medicine.In the study, the scientists found that the gut microbiome inhibits the progression of bone melanoma lesions in mice by promoting an increase in intestinal natural killer (NK) and T-helper (Th1) cells and enhancing their migration to the tumor site. The use of oral antibiotics depleted the gut microbiome and reduced the population of intestinal NK and Th1 cells. This made the mice more vulnerable to tumor growth. They had a greater melanoma tumor burden than control mice whose gut microbiome was intact.Osteolytic bone metastasis is a complication of malignant melanoma. The researchers hypothesized that using antibiotics to deplete the gut microbiome of the mice would affect their gut immune cells and thus alter their immune response, leading to accelerated bone metastasis. They injected B16-F10 melanoma cells into the heart and bones of mice treated with broad-spectrum antibiotics. As expected, the antibiotic injections accelerated the growth of bone metastases in these mice compared to control mice that did not receive the injections.This study strongly suggests that microbiome changes induced by antibiotics can have negative clinical consequences not only in melanoma but also in other diseases, the researchers noted.
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