Swiss doctors have used a combination of photodynamic therapy and immunotherapy to dramatically shrink mesothelioma tumors in mice.
More than a third of mice treated with an immune checkpoint inhibitor and low-dose light therapy experienced complete regression of their cancer.
The new study explores how photodynamic therapy and immunotherapy can work together. The answers could have important implications for tens of thousands of people suffering from asbestos cancer.
Two Different Approaches to Mesothelioma
Mesothelioma is a rare but deadly cancer caused by asbestos exposure. Pleural mesothelioma occurs on the membrane around the lungs. It is the most common type of mesothelioma. Around 2,500 Americans receive a mesothelioma diagnosis each year. There is no cure.
Photodynamic therapy and immunotherapy both show promise for treating mesothelioma.
Immunotherapy uses the immune system to fight mesothelioma. But the results vary from patient to patient.
Photodynamic therapy uses light to influence cellular processes. In an earlier study, the Swiss researchers showed that it can impact the formation of blood vessels for mesothelioma tumors. They theorized that photodynamic therapy and immunotherapy could be even more powerful together.
Testing Photodynamic Therapy and Immunotherapy
Photodynamic therapy and immunotherapy is a multi-part therapy. The targeted cells first get a chemical to make them more sensitive to light. The chemical makes them react when light shines on them.
The Swiss researchers found that low-dose photodynamic therapy increased expression of E-selectin. E-selectin is a molecule that attracts cancer-fighting immune system cells. The researchers reasoned that the effect could boost the impact of an immunotherapy drug.
They treated mice with an immune checkpoint inhibitor. This kind of drug makes mesothelioma cells more visible to the immune system. Immune checkpoint inhibitors help control tumor growth.
Together, low-dose photodynamic therapy and immunotherapy had a remarkable effect on mesothelioma tumors.
“The combination of L-PDT with anti-CTLA4 caused complete MPM regression in 37.5% of animals,” the researchers report. Immune system cells increased with photodynamic therapy and immunotherapy made the cancer cells more susceptible to them.
The Swiss team concludes, “The combination of L-PDT with immune checkpoint inhibitor anti-CTLA4 allows best tumor control and regression.”
Clinical trials suggest that PDT can improve mesothelioma survival, especially when combined with surgery. The FDA granted orphan drug status to the main drug used in photodynamic therapy for mesothelioma.
Cavin, S, et al, “Low-dose photodynamic therapy promotes a cytotoxic immunological response in a murine model of pleural mesothelioma”, May 5, 2020, European Journal of Cardiothoracic Surgery, Epub ahead of print, https://academic.oup.com/ejcts/advance-article-abstract/doi/10.1093/ejcts/ezaa145/5830811?redirectedFrom=fulltext