Study identifies molecules that could help to prevent the development of brain tumors

Researchers from the University of Portsmouth’s Brain Tumour Research Centre of Excellence have identified molecules which are responsible for metastatic lung cancer cells binding to blood vessels in the brain.

In order for a cancer cell to enter the brain, it must first bind to the cells which line the structure separating the blood from the brain which is called the blood-brain barrier (BBB). Such information about the factors associated with this process may provide a way of preventing the cancer cells binding to the BBB and crossing over into the brain.

Twenty to 40 percent of patients with non-small cell lung cancer (NSCLC) develop brain metastasis.

The study, funded by the charity Brain Tumour Research and conducted by researchers at their UK Centre of Excellence at the University of Portsmouth, examined the factors present on the surface of NSCLC cells. These cells have different factors on their surfaces which determines how “sticky” the cells are and whether they are responsible for mediating the cancer cells binding to the blood vessel walls.

One of these factors is a molecule called CD15s. While it is present on a number of different types of cells in the body, it is expressed at higher levels on metastatic tumour cells, including those which have spread from the lung. It is only present at low levels in lung cancer cells which are not metastatic and remain within the lung.

The scientists examined what CD15s binds to on the blood vessel wall and identified another factor called CD62E. The researchers then used a specific tool to block the CD15s on the surface of the tumour cells, and this prevented the NSCLC cells from attaching to the blood vessels. They also used a model which simulated the cancer cells flowing through the blood vessels, and got the same result. So, blocking the adhesive properties of CD15s may provide a tool to prevent the establishment of secondary cancers.

Professor Geoff Pilkington, study co-author and Head of the Brain Tumour Research Centre, said: “Although this work is still at an early stage, we have demonstrated key elements that are associated with tumour cell binding to blood vessels and this may provide a target for future drug development to prevent the development of secondary tumours in the brain. Increasing our understanding of the adhesive properties of tumours may also help to develop new treatments to halt the development and spread of primary brain tumours.”

The adhesive properties of cancer cells play a key role in the formation and development of a tumour. While cells in a low-grade tumour bind very tightly together, the cells become less adhesive as the tumour becomes malignant. This is very important for the tumour cells which then spread into the surrounding nervous tissue.

Understanding more about the factors which mediate cell adhesion is key for the potential identification of new therapies.

Dr Kieran Breen, Director of Research at Brain Tumour Research, said: “Brain tumours kill more children and adults under the age of 40 than any other cancer, yet just 1 per cent of the national spend on cancer research has been allocated to this devastating disease. We are funding vital research in the UK to address this situation and are encouraged by Professor Pilkington’s findings.”

In addition to primary tumours which start in the brain, the secondary or ‘metastatic’ tumours which originate elsewhere and which migrate to the brain have been the focus of this new study. Secondary brain tumours are most likely to originate in the breast, lung or skin (melanoma). When they enter the brain, they generally form multiple tumours and can be extremely difficult to treat. Usually, treatment would require whole-brain radiation which is extremely toxic and the average survival time is just 3-6 months from diagnosis, with fewer than 20 per cent of patients surviving more than one year. If the people whose tumours are more likely to spread to the brain could be identified, researchers may be able to prevent this from happening.

Tumor immune fitness determines survival of lung cancer patients

In recent years, immunotherapy, a new form of cancer therapy that rouses the immune system to attack tumor cells, has captivated the public’s imagination. When it works, the results are breathtaking. But more often than not it doesn’t, and scientists still don’t know why.

Publishing in the June 19, 2017, issue of Nature Immunology, researchers at La Jolla Institute for Allergy and Immunology, identify a subpopulation of T cells in tumors known as tissue-resident memory T cells (TRM) as an important distinguishing factor between cancer patients whose immune system mounts an effective anti-tumor response and those who are unable to do so. Their finding emerged from the first large-scale effort to profile the gene expression patterns of cytotoxic T cells isolated directly from patients’ tumors.

“Systematically studying cancer patients’ immune cells reveals a lot of information,” says LJI Associate Professor and William K. Bowes Jr. Distinguished Professor Pandurangan Vijayanand, M.D., Ph.D., who co-directed the study with Professor Christian Ottensmeier at the University of Southampton, England. “It could be a baseline test to predict whether a patient will respond to immunotherapy and guide the choice of immunotherapy that is most likely to be effective. It is almost like judging tumor immune fitness,” adds Vijayanand. The systematic profiling of tumor-infiltrating T cells will also provide new insight into their basic biology revealing new potential immunotherapy drug targets.

Scientists initially found that when T cells were swarming a patient’s tumor that patient lived longer. Over time, however, they found that T-cells lose their fervor and cancer cells gain the upper hand. In the last decade they discovered why: Inhibitory molecular signals emitted from a tumor or its environment undercut the immune response, making tumor cells invisible to the immune system. One class of cancer immunotherapy drugs, known as checkpoint blockade inhibitors, disables either PD-1 or CTLA-4, two known molecules that allow cancer cells to live and multiply undetected by the immune system.

“The challenge with immunotherapy based on PD-1 and CTLA-4 is that if they work, they work miraculously, but they only work in about 30 percent of patients,” says the study’s first author, Anusha-Preethi Ganesan, M.D., Ph.D., a physician in the Division of Pediatric Hematology and Oncology at Rady’s Children’s Hospital, UC San Diego. “If we are doing all these immunotherapies based on activating T cells to kill tumor cells it is really important to know what the transcriptional profiles of these T cells are, what molecules do they make?”

To uncover the underlying reasons why some patients see little or no benefit and to identify those patients most likely to respond, Ganesan utilized advanced genomics tools to define the molecular features of a robust anti-tumor immune response using freshly resected tumors from patients with cancer. Comparing gene expression profiles of cytotoxic T cells (CTLs) isolated from 41 head and neck tumors and 36 untreated, early stage lung tumors with CTLs isolated from adjacent normal lung tissue, Ganesan identified a shared molecular fingerprint between different tumor types suggesting extensive reprogramming of CTLs infiltrating tumor tissue.

Beyond their shared molecular signature, tumor-infiltrating CTLs differed widely in their expression of molecules associated with T cell activation and known immune checkpoints. “There is a huge deal of heterogeneity, which has a lot of implications for immunotherapy,” says Ganesan. “We see the traditional immunotherapy targets but they are not expressed in every single patient, which means not every patient is a candidate for currently available immunotherapies targeted at PD-1 or CTL4-1. That’s why having the full transcriptional profile is so important to understand the entire complexity of the immune network and to identify novel targets.”

Interestingly, gene expression patterns that signal the presence of tissue resident memory T cells (TRM) corresponded with better anti-tumor activity. The only recently identified tissue resident memory T cells act as local first responders that provide rapid onsite immune protection. A large scale analysis in an independent cohort of 689 lung cancer patients confirmed that patients with a high density of TRM cells in tumor tissue survived significantly longer, demonstrating that these cells serve a critical role in protecting against tumor recurrence.

“Any time you remove a tumor, the patient is a ticking time bomb after that. In some people it will come back and it others it won’t,” says Vijayanand. “Our study suggests that the presence of these tissue resident memory cells is an important factor in determining whether somebody is having an effective immune response against cancer and whether they will live longer.”