The treatment consists of a combination of pemetrexed (Alimta), the first chemotherapy drug approved specifically for the treatment of malignant pleural mesothelioma, and photodynamic therapy (PDT) that kills cancer cells with light.
To test the combination, doctors with Tokyo Medical University and the Nippon Medical School injected lab mice with four different human mesothelioma cell lines. Mice were given pemetrexed and a drug called NPe6 which makes the cells sensitive to light. While the combination helped to some degree in all cases, the order in which the two treatments were delivered appeared to have a major impact on their level of effectiveness.
When mice with mesothelioma were treated using a combination of pemetrexed and NPe6-PDT, the tumor volume decreased by 50%, but immediately began to regrow. Tumors were back to their pre-treatment size again within two weeks. The mice had ten percent more reduction in tumor size when they were treated with NPe6-PDT first and then given pemetrexed. But, because NPe6-PDT increased cellular expression of a chemical that makes them resistant to pemetrexed, the results did not last and tumors again started to regrow.
However, when pemetrexed was administered prior to NPe6-PDT, the results were dramatically better. “Pemetrexed pre‑treatment enhanced the lethal effect of NPe6‑PDT in the four malignant mesothelioma cell lines,” writes investigator Dr. Sachio Maehara, the lead author on the study. Mice treated on this scheduled experienced an 80% reduction in tumor size. Just as importantly, their tumors did not grow back quickly.
Writing in the International Journal of Oncology, the Japanese team recommends that the pemetrexed/NPe6-PDT treatment combination be further investigated as a possible way to prolong survival in people with malignant pleural mesothelioma.
Although mesothelioma is an exceptionally rare cancer in the U.S. with about 2,500 cases each year, it is also highly lethal. To date, there is no cure for mesothelioma and traditional cancer therapies are only marginally effective.
Maehara, S et al, “Combination effect of photodynamic therapy using NPe6 with pemetrexed for human malignant pleural mesothelioma cells”, November 10, 2014, International Journal of Oncology, Epub head of print