Arizona Republican Sen. John McCain has been diagnosed with an aggressive form of brain cancer called a glioblastoma, and his office said he's exploring treatment options.
For now, those are slim, but there are a few promising therapies in the works, according to Johns Hopkins Medicine researchers.
One of them is a veterinary drug mebendazole that had been used to deworm the mice used in the cancer lab. It prolonged the rodents' lives by months and the researchers now are exploring how to produce bigger effects, said Dr. Gregory Riggins, a Hopkins professor of neurosurgery and oncology who is preparing for the second phase of clinical trials.
He explains glioblastomas and his lab's work.
What is a glioblastoma and who is usually affected?
Glioblastoma is a type of brain cancer that is the most common and most deadly of the malignant brain tumors. It is responsible for about 12,000 deaths annually in the USA. It is a malignancy arising from a glial cell whose normal function is to help maintain and protect the neurons and the environment in the brain.
What treatments are available and why aren't they very effective?
Over the last decades treatment has steadily improved, despite this being the most aggressive of brain cancer malignancies. However, progress has been very slow and incremental. Improvements in surgery, radiation and the introduction of one type of chemotherapy have moved what used to be a 3 to 6 month survival to 15 to 20 months at the best centers, with the best trained surgeons, oncologists and radiation therapists. One of the main reasons that treatments have not improved more is the location of the cancer cells, intertwined with the most vital areas in the human body. Although the surgeon can remove the bulk and majority of the tumor in most cases, depending on the location within the brain, individual glioblastoma cells diffuse or migrate throughout the brain long before the tumor is diagnosed. These cells cannot be removed, and the chemotherapies we have so far don't reach the brain in sufficient concentrations to be effective, and/or are too toxic to be useful. So far there is just one oral drug that is proven to improve survival, temozolomide, but it is just months of improved survival benefit.
Are there new treatments on the horizon?
Absolutely. Investigators worldwide, including here at Johns Hopkins, have been putting more and more effort into brain cancers. Some of the latest approaches include immunotherapy, new small molecule drugs, therapies from live agents like engineered viruses and bacteria, better genomic classification of tumors, etc.
What is mebendazole and what did your lab discover about it?
Mebendazole is an antiparisitc drug developed in 1972 to treat infections from pinworms, hookworms, roundworms and the like. It has been a very safe and effective drug. We found accidentally that mebendazole has anticancer properties for brain cancers when it was used in our mouse colony to treat pinworm infection. We have since improved the drug to make it more efficiently absorbed and reach the concentrations in brain cancer that can kill some of the tumor cells, stop the growth of new tumor blood vessels, and in general slow the growth of glioblastoma — at least in experimental models in the lab. Johns Hopkins, under the direction of Dr. Gary Gallia, has run a phase 1 trial to test the safety of this drug in patients newly diagnosed with brain cancer — the situation that Sen. McCain now unfortunately finds himself. While the drug looks promising, not overly toxic and safe, we won't know for sure if it is really benefiting survival until a much larger (phase 2) trial is performed. Right now we are between trials for the adult patients, looking at the phase 1 results and raising funding for the phase 2. Since there is no drug company backing our trials we raise the money through donations and foundation funding, such as Accelerate Brain Cancer Cure, who funded the phase 1 in adults.
Can the low-cost veterinary version work in humans?
There has been problems with price gouging for this class of drugs, the antihelminthics approved for human use that include albendazole and mebendazole. With approval from the ethics committee for human subjects research and the FDA, we have an experimental version of the drug made that we believe is improved in its absorption, dosing and tested for safety. The veterinary version would not have the regulatory approval to use in humans at this point. Our experimental version was provided free to patients enrolled in the trial.
What are the barriers?
The first trial was to test safety and toxicity, and serum levels of the drug of successively higher doses of our improved mebendazole. There were multiple barriers, but perhaps the biggest was obtaining the drug for the trial. This and the other barriers of funding and regulatory approval were all overcome with time, but the clinical trial process is far from nimble and not set up to test drugs and drug combinations quickly.
What about children?
Children unfortunately get brain cancer, including pediatric glioblastoma. They also get a form of glioblastoma in the brain stem called a DIPG. Brain cancers as a group are now the most common cause of cancer deaths in children. Mebendazole is now being tested for certain pediatric brain cancers that resist standard treatment, including for pediatric glioblastoma.