A mainstay of prostate cancer treatment is to deprive it of androgens, the hormones that make it grow. The testes are the main source of these hormones, so treatment can either be surgical removal of these organs or the use of drugs to block their hormone production.
Over time, some prostate cancers become resistant to these treatments and begin to spread again. As with many cancers that exhibit these behaviors, figuring out exactly what makes them resistant can be difficult.
Bacteria that live in the intestines can be a culprit. Researchers found that some of these gut bacteria in castrated mice and in people on androgen deprivation therapy begin to produce androgens that can be easily absorbed into the bloodstream. According to this new finding, published in the journal Science, the androgens appear to aid prostate cancer growth and resistance to treatment.
This study is the first to show that bacteria can produce testosterone, although researchers aren’t yet sure what makes them start doing it. Treatment for androgen deprivation can also result in more of these hormone-producing microbes being present in the gut, the results suggest. Fecal bacteria from people with treatment-resistant prostate cancer have also been shown to be associated with lower life expectancy.
Stool transplants from mice with treatment-resistant prostate cancer could induce resistance in animals with a disease susceptible to these hormones. When these mice received stool transplants from people with resistant cancer, the effect was the same: a shift towards treatment resistance.
But the opposite was also the case: stool transplants from mice or people with hormone-sensitive cancers helped to limit tumor growth.
The results could point to new therapeutic targets: the microbes that live in the gut. In studies with mice, the researchers found that if they eradicate these bacteria, the cancer progresses to treatment resistance much more slowly. The authors of a commentary on the study say there are other places to look for bacteria that could produce these hormones, including the urinary tract or even inside the tumor itself.
Science: “Commensal bacteria promote endocrine resistance in prostate cancer through androgen biosynthesis”, “Intestinal bacteria enable prostate cancer to grow.”