The story of a man, some rats, a virus, and a cancer

     In August of 2005, in the city of Poznań, Poland, 38-year-old Aleksy Kowalski suddenly felt an intense throbbing headache. As days followed, the bout of severe headaches continued to strike, accompanied by nausea. Thinking they would go away soon, just like any other headache, he didn’t take them seriously during the initial weeks. But when these symptoms did not stop for months, he finally decided to seek medical help. During his initial visit, the doctor did not notice any visible abnormalities in his head. However, a brain scan the following month brought his life to a standstill. His brain’s black and white image showed a significant tumor growth of approximately the size of a grape on the right side of his brain.

     At the beginning of 2006, Kowalski underwent surgery. The entire tumor lesion was removed, and pathologists’ analysis of the tumor sections confirmed an advanced stage glioblastoma. Glioblastoma is one of the most aggressive types of cancer affecting the brain. The average survival time for patients since the initial symptom is 12-18 months. However, 13 months after Kowalski’s surgery, no brain tumor recurrence was found during a follow-up scan. It looked like he had defeated the tumor. Or so he thought until February 2009, when the brain tumor reappeared. His fight with glioblastoma was not over just yet.

   While the Polish man battled for his life, something intriguing was happening in a lab 800 km away at the University of Heidelberg, Germany. Dr. Jean Rommelaere and his team were engrossed in a particular experiment. They inoculated a few cancerous cells into the brain of 12 rats. In a few days, as intended, the rats developed brain tumors. Some of these rats were then injected multiple times with a peculiar virus. Three days after the injection of the virus, surprisingly, in eight of the twelve rats, the size of the tumor got smaller. In four of the eight rats, the cancer was gone entirely, and these animals survived for more than one year without any remaining or recurrent tumors. A closer analysis of the brain sections showed that the tumor tissue had been destroyed without the virus causing any damage to the surrounding healthy tissues. This virus, called H-1PV, actively infected and killed only tumor cells inside the rat brains.

     H-1PV, also known as parvovirus H-1, was discovered serendipitously in 1959. While working with human tumors, Dr. Helene Wallace Toolan and her colleagues at the Sloan-Kettering Institute for Cancer Research in New York noticed something quite strange. The solution obtained after grinding and filtering these tumors when injected into hamsters induced deformity. The causative agent for such deformation was soon identified as a virus and was named H-1. Since the virus had been initially discovered in human tumor cells, it was speculated that it could be causing the tumor. However, the virus displayed a natural preference to infect human cancer cells and eventually was found to kill them. They soon realized that the infection was not causative of the tumor but rather opportunistic. Later in the 1960s, Toolan and her colleagues showed that H-1PV suppressed tumors and reduced spontaneous tumor growth in animal models. This formed the basis for many future studies following H-1PV and its ability to kill cancer cells.

     Rommelaere,  currently a professor emeritus, came across these tiny parvoviruses by accident in the 1970s. Being a molecular biologist by training, Rommelaere was introduced to parvoviruses by Nobel prize laureate Dr. David Baltimore during his post-doctoral research at the Massachusetts Institute of Technology, USA. Rommelaere was interested in studying the effects of radiation on DNA replication, and these single-stranded DNA viruses were a perfect fit for his research. While reading previous academic literature for his work, he came across the oncolytic (cancer-killing) properties of these viruses, which instantly drew his interest. In the late 1980s, Rommelaere and his team were the first to show that healthy cells resistant to infection by H1-PV became susceptible when the cells were made cancerous. Further, the cancerous cells supported the virus to replicate productively, resulting in more virus particles and efficient killing of tumor cells. These initial studies motivated his team to actively test H1-PV as a potential cancer-killing agent against various cancer cells.

    Viruses that preferably infect and damage cancerous tissues without causing harm to normal tissues are called oncolytic viruses. For a virus to be used in oncolytic therapy, it must selectively infect only cancerous cells and, upon infection, kill them. It must also be safe enough to be used on human patients. Rommelaere and his team observed that altered intracellular components in cancer cells made them susceptible to H1-PV infection compared to their healthy counterparts. The virus also produces a protein called NS1, which is toxic to cancer cells once infected. Finally, the natural host of H1-PV is rats; hence this virus doesn’t cause any diseases in humans. All these factors make this virus a promising oncolytic virus for clinical use.

     H1-PV is a naturally occurring oncolytic virus. However, oncolytic viruses can also be engineered by modifying natural viruses in the lab. For example, T-VEC (Imlygic®) is a modified herpes simplex virus and the only oncolytic virus approved by the FDA to treat cancer. Other viruses like measles virus, coxsackievirus, polioviruses, reoviruses, poxviruses, and Newcastle disease viruses are under preclinical and clinical development as therapeutics against different cancers. However, H1-PV poses an advantage over many other viruses for brain tumor treatment. Our brain is surrounded by a protective layer called the blood-brain barrier. It is like a border control unit that prevents toxic and harmful compounds from entering the brain. Hence, many conventional cancer drugs and many viruses cannot be used to treat brain tumors as they fail to cross this barrier. Interestingly, researchers in Heidelberg noticed that when the H1-PV virus was given to the rats intravenously, the virus could cross the blood-brain barrier and infect tumor cells in the brain. Hence, H1-PV could be given to patients through intravenous injection, preventing the need to perform invasive procedures.

     The most commonly used treatment for glioblastoma is the surgical removal of the tumor mass followed by radiation therapy or chemotherapy. In radiation therapy, ionizing radiation is shot into the tumor mass to kill the cells. The most significant disadvantage of radiation therapy is the damage it causes to nearby healthy cells along with tumor cells. Meanwhile, chemotherapy which uses very strong chemicals to kill fast-growing cells in our body is limited by its severe side effects. In addition, chemotherapy or radiation alone fail to stop tumor growth or recurrence in case of glioblastoma.  

     Back in Poznan, in the spring of 2009, Kowalski underwent another surgery, and the entire reappeared tumor mass was again removed from his brain. Doctors advised him about the challenging nature of this tumor and recommended chemotherapy. But owing to the side effects, he decided instead to continue with radiotherapy. After a few months following the radiation therapy, no new tumor was observed. However, at the beginning of 2010, a new tumor was found growing in the previously irradiated region. The cancer was putting on a mighty fight that was becoming impossible to defeat.

     Meanwhile, the scientists in Heidelberg decided to further test the efficacy of H-1PV in human brain cells. They wanted to test if a combination of radiation therapy and H-1PV infection would be a better strategy for destroying aggressive brain tumor cells. They first grew some human brain tumor cells called gliomas, irradiated them, and then infected them with the H1-PV virus. They observed that this initial irradiation step before virus infection resulted in increased virus infection of the gliomas and led to the killing of leftover tumor cells initially resistant to radiation treatment. These promising results observed over the years formed the basis for taking the next step towards initiating a clinical trial for testing the safety and efficacy of H1-PV as a potential therapy in human patients suffering from Glioblastoma.     

     Given the aggressive nature of Glioblastoma, only as few as 5% of the patients survive more than five years with the tumor. It was 2010, and Kowalski had survived almost five years since his initial symptoms in 2005. He was one of the few patients who had survived tumor remission twice. This time, his doctors said that it was impossible to surgically remove the tumor again the third time due to the damage that such surgery would cause to the brain. Hence, he underwent radiation therapy again without surgery, but unlike the previous two times, radiation was not enough, and the tumor continued to grow. In November of 2010, after putting on a fight for five years, Kowalski breathed his last as the tumor finally engulfed a large enough part of his brain resulting in multiple organ failure.

     The process of the discovery of a novel therapy and its clinical application is long and tedious, including many experiments, improvements, and trials. Unfortunately, it is often too late for many patients like Kowalski, but it provides hope for those in the future. Almost a year after Kowalski ‘s death, 18 patients with recurrent glioblastoma were enrolled in Germany as part of the first parvovirus clinical trial, which was called ParvOryx01 and aimed to study the safety and efficacy of the H-1PV virus. Some of the patients were injected with H1-PV directly into their brain tumor, and others through intravenous injection. The trial, which ended in 2015, showed that H-1PV, also called ParvOryx, was safe for use and well tolerated by human patients. In patients who were given the treatment through intravenous infusion, the virus could cross the blood-brain barrier as previously seen in rats. Further, virus infection activated the patient’s immune system, which is beneficial for patients fighting cancer. There was increased glioblastoma progression-free survival for most of the patients enrolled in this study, and the overall survival was approximately two times higher compared to previously observed glioblastoma cases.

     Cancer is a very diverse disease. The same type of cancer can be very different in different patients. This is one of the reasons why treating cancer is very challenging, as one type of therapy could be beneficial to some and ineffective for others. During the six month follow-up after H1-PV administration, five of the 18 patients from the clinical trial died due to glioblastoma-related complications. In the rest of the patients, the tumor reappeared during or after the follow-up. When a drug is under clinical trial and yet to be approved for commercial use, it can still be given to patients under life-threatening conditions known as compassionate use. Based on this, in six trial patients, who developed second or third recurrence, H-1 PV was readministered in combination with a drug called bevacizumab. Strikingly long remissions and further extension of mean survival were observed, which could not be achieved when bevacizumab alone was given to patients. 

     Based on the promising evidence from the clinical trial and the compassionate use cases, a third clinical trial for H1-PV use in glioblastoma has been approved by the EMA and the FDA. Meanwhile, Rommelaere’s team continues to work towards improving the therapeutic potential of H1-PV. Previously they have shown that besides killing the tumor cells (oncolysis), this virus is also able to activate the immune system of the patients against virus-infected tumor cells. Hence, Rommelaere’s team is working towards engineering H1-PV derivatives that are better at triggering immune system-mediated anticancer effects than naturally occurring H1-PV. 

     The magic bullet against aggressive brain tumors has not been discovered yet. However, emerging therapies such as oncolytic virotherapy prolong patients’ life and improve their quality of life without having the side effects of conventional treatments. Almost sixty years after discovering the virus, Parvoryx is under clinical development. Maybe one day, hopefully not too far away in the future, we will have an effective treatment for Glioblastoma. Until then, we can only hope for strength and courage for people like Kowalski to keep fighting the mighty tumor.