A common antibiotic may improve mesothelioma patients’ response to radiation therapy.
The concept is based on new research from the Perelman School of Medicine at the University of Pennsylvania.
Doctors there gave the antibiotic vancomycin to genetically modified mice. The mice had been modified to develop cancer. Mice that got the antibiotic had a better response to radiation therapy than untreated mice.
The effect applied not only to the treated tumor but also to tumors outside the treatment area. A heightened response to radiation therapy could be good news for patients with metastatic mesothelioma.
Understanding Cancer Response to Radiation Therapy
Radiation therapy combats malignant mesothelioma by disrupting the DNA inside cancer cells. Mesothelioma tumors are irregularly-shaped which can make them hard to treat. Radiotherapy is not usually the first-line treatment for mesothelioma.
New targeted therapies have improved the response to radiation therapy for mesothelioma and other cancers. So has changing how it is delivered. When patients have larger doses of radiation spaced farther apart, it appears to trigger a response in distant tumors, too. This the abscopal effect.
Vancomycin may boost response to radiation therapy – including the abscopal effect – by boosting the immune system.
Gut Bacteria Linked to Immune Response
The microbiome is the mix of bacteria in a patient’s gut. A mesothelioma patient’s microbiome has a direct impact on their immune system.
When the University of Pennsylvania team gave vancomycin to sick mice, it changed their microbiome. This changed their immune system’s response to cancer, which enhanced their response to radiation therapy.
“Our study shows that vancomycin seems to boost the effect of the hypofractionated radiation itself on the targeted tumor site while also aiding the abscopal effect, helping the immune system fight tumors away from the treatment site,” write Mireia Uribe-Herranz and colleagues.
The vancomycin appears to improve the function of dendritic cells. Dendritic cells signal the immune system to attack mesothelioma tumors. The next step is to see if the treatment improves response to radiation therapy in human patients.
“Since vancomycin is a widely used clinical agent with a relatively safe profile, these findings raise the potential for utilizing this antibiotic to enhance the effects of RT in patients with cancer,” writes Dr. Uribe-Herranz.
Chemotherapy is still the most common first-line treatment for mesothelioma. Surgery is the next most common treatment in patients who are healthy enough.
Radiation is typically used to shrink a mesothelioma tumor to a more manageable size prior to surgery or to reduce mesothelioma symptoms. It can also help kill residual cells after surgery to prevent new mesothelioma tumors.
Uribe-Herranz, M, et al, “Gut microbiota modulate dendritic cell antigen presentation and radiotherapy-induced antitumor immune response”, December 9, 2019, The Journal of Clinical Investigation, https://www.jci.org/articles/view/124332