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Immunotherapy is a promising option for cancer treatment. This is a relative newcomer to cancer treatment, especially compared to traditional therapies like chemotherapy and radiation. Immunotherapy uses the body’s immune system to kill cancer cells or slow the spread of tumors.
The use of immunotoxins is one immunotherapy strategy currently being tested in clinical trials for patients with mesothelioma and other cancers. Several ongoing trials are determining if these immune-mediated drugs can kill cancer cells selectively, halting progression of the disease. Some reported results are promising and involve using immunotoxins with other types of treatment.
What is an Immunotoxin?
Immunotoxins are therapeutic compounds that use the patient’s immune system to attack and kill cancer cells. An immunotoxin is a combination of an antibody and a toxin. The antibody is designed to find and attach to proteins called an antigen on the surface of cancer cells. The cell then uses the toxin to consume the cell.
Immunotoxin treatment harnesses the natural power of the immune system, using it to specifically target cancer cells. While toxins have long been used to treat cancer through chemotherapy, this treatment is generally not specific. Chemotherapy drugs circulate the entire body, killing cancer cells and healthy cells. The immunotoxin strategy specifically targets and kills cancer cells.
Clinical Trials Using SS1P Immunotoxin
Researchers have been studying immunotoxins for a number of cancer types for years. Some are using these therapies to target mesothelioma cancer cells. A clinical trial that began in 2011 showed promise for patients with mesothelioma. Supported by the National Cancer Institute, this phase I trial used an immunotoxin known as SS1P.
In this trial, patients received SS1P along with standard chemotherapy drugs, cisplatin and pemetrexed. In the first part of this trial, only 2 out of 13 patients experienced disease progression. Ten patients had a measured partial response, meaning their tumors were reduced by at least 30 percent. Results were better than patients who received chemotherapy alone, proving immonotoxins are a promising treatment for mesothelioma.
In another trial with SS1P, 60 percent of patients showed a partial response when the drug was combined with other drugs. One patient had a stunning response, seeing 74 percent reduction in tumor size. In this trial, the drugs combined with SS1P were immune suppressants.
Results were even more positive than those seen with the chemotherapy drugs. In previous trials, patient immune systems began developing antibodies that reacted to the immunotoxins used to target the cancer cells. In other words, the immune system began to work against the drug. With immune suppressant drugs, this activity was limited and the immunotoxin worked more effectively.
Immunotoxin Trial Recruitment Halted
While there have been great results with immunotoxin drugs for mesothelioma, there have also been some unexpected results. A phase I trial tested the combination of immunotoxin LMB-100 with an immune suppressant, SEL-110. Both pleural and peritoneal mesothelioma patients participated in the trial.
Although this combined therapy has great promise for treating mesothelioma, the recruitment was halted due to adverse reactions. Several patients developed a severe type of pneumonitis, an inflammation of the tissue around the lungs. Pneumonitis can cause difficulty breathing, coughing, fatigue, and loss of appetite. Some drugs were known to cause pneumonitis. While recruitment for this trial was stopped, no results for effectiveness in original participants has been reported.
Clinical Trial Currently Recruiting
One trial using the LMB-100 immunotoxin is currently recruiting pleural and peritoneal mesothelioma patients. LMB-100 targets mesothelin, a protein heavily expressed by mesothelioma cells. The study is using LMB-100 along with pembrolizumab, a different kind of immunotherapy drug.
Pembrolizumab works by interfering with an interaction between cancer cells and immune system cells that protects the cancer cells. This drug allows immune system T-cells to recognize cancer cells as harmful, boosting the immune system’s effectiveness.
Qualified patients must have peritoneal or pleural mesothelioma that cannot be treated by surgery. Patients must also meet several health and medical markers to be accepted. There are also many health factors that can exclude a patient. Your oncologist or medical team can help you determine if you qualify for this trial.
Potential Adverse Events
Immunotoxin therapy is still very new. Therefore, all potential side effects are not yet known. However, one potential risk is hepatotoxicity, or liver damage. Liver function may decline in patients receiving immunotoxin therapy.
Other recorded side effects include vascular leak syndrome (which causes swelling and edema), pleuritic syndrome (an inflammation of the pleural tissue), and hemolytic uremic syndrome (which can cause anemia and kidney damage).
Immunotoxin therapy is an emerging approach to cancer treatment that is being tested for a wide variety of cancers. There is great hope for patients with difficult-to-treat cancers like mesothelioma. These clinical trials may show combinations of immunotoxins with other drugs could extend patient lives. If you are interested in trying these therapies, talk to your medical team about finding and enrolling in an appropriate immunotoxin clinical trial.
Page Edited by Patient Advocate Dave Foster
Dave has been a mesothelioma Patient Advocate for over 10 years. He consistently attends all major national and international mesothelioma meetings. In doing so, he is able to stay on top of the latest treatments, clinical trials, and research results. He also personally meets with mesothelioma patients and their families and connects them with the best medical specialists and legal representatives available.