Breaking down cancer’s defense mechanisms

A possible new method for treating pancreatic cancer which enables the body’s immune system to attack and kill cancer cells has been developed by researchers.

The method uses a drug which breaks down the protective barrier surrounding pancreatic cancer tumours, enabling cancer-attacking T cells to get through. The drug is used in combination with an antibody that blocks a second target, which improves the activity of these T cells.

Initial tests of the combined treatment, carried out by researchers at the University’s Cancer Research UK Cambridge Institute, resulted in almost complete elimination of cancer cells in one week. The findings, reported in the journal PNAS, mark the first time this has been achieved in any pancreatic cancer model. In addition to pancreatic cancer, the approach could potentially be used in other types of solid tumour cancers.

Pancreatic cancer is the fifth most common cause of cancer-related death in the UK and the eighth most common worldwide. It affects men and women equally, and is more common in people over the age of 60. As it has very few symptoms in its early stages, pancreatic cancer is usually only diagnosed once it is relatively advanced, and prognosis is poor: for all stages combined, the one and five-year survival rates are 25% and 26% respectively. Tumour removal is the most effective treatment, but it is suitable for just one in five patients.

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Left: pancreatic cancer cells (in green) Right: after six days of combined tumour immunotherapy, the cancerous cells had been killed. Credit: Douglas Fearon

Immunotherapy – stimulating the immune system to attack cancer cells – is a promising therapy for several types of solid tumours, but patients with pancreatic cancer have not responded to this approach, perhaps because the human form of the cancer, as in animal models, also creates a protective barrier around itself.

The research, led by Professor Douglas Fearon, determined that this barrier is created by a chemokine protein, CXCL12, which is produced by a specialised kind of connective tissue cell, called a carcinoma-associated fibroblast, or CAF. The CXCL12 protein then coats the cancer cells where it acts as a biological shield that keeps T cells away. The effect of the shield was overcome by using a drug that specifically prevents the T cells from interacting with CXCL12.

“We observed that T cells were absent from the part of the tumour containing the cancer cells that were coated with chemokine, and the principal source of the chemokine was the CAFs,” said Professor Fearon. “Interestingly, depleting the CAFs from the pancreatic cancer had a similar effect of allowing immune control of the tumour growth.”

The drug used by the researchers was AMD3100, also known as Plerixafor, which blocks CXCR4, the receptor on the T cells for CXCL12, enabling T cells to reach and kill the cancer cells in pancreatic cancer models. When used in combination with anti-PD-L1, an immunotherapeutic antibody which enhances the activation of the T cells, the number of cancer cells and the volume of the tumour were greatly diminished. Following combined treatment for one week, the residual tumour was composed only of premalignant cells and inflammatory cells.

“By enabling the body to use its own defences to attack cancer, this approach has the potential to greatly improve treatment of solid tumours,” said Professor Fearon.

Feig et al., (2013).Targeting CXCL12 from FAP-expressing carcinoma-associated fibroblasts synergizes with anti–PD-L1 immunotherapy in pancreatic cancer. PNAS110, 20212-20217 [pdf]

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New immunotherapy for malignant brain tumors

It is relatively easy to treat cancer in the early stages. However, it is far more difficult to successfully treat advanced cancer. Treatment of brain tumors is particularly challenging because regulatory T-cells accumulate in brain tumors and suppress an immune attack.

In several steps using a new strategy and a novel drug, Burkhard Becher’s team from the Institute of Experimental Immunology at the University of Zurich has now succeeded in doing exactly this in the case of glioblastoma, one of the most dangerous brain tumors. First step, they stimulated the body’s own immune system in such a way that it recognised and then killed the brain tumor cells even in advanced stages of the disease.

The initial objective of their new study was to break through the tumor’s protective shield. “We wanted to establish whether we can actually elicit an immune response to a tumor growing within the brain”, explains Burkhard Becher. To this end, the team used the immune messenger substance, Interleukin-12. When Interleukin-12 is produced in the tumor, immune cells are stimulated locally in such a manner that the tumor is attacked and rejected. Once this procedure had worked well in the early stages of the tumor, the researchers waited in the next stage until the tumor was very large and the life expectancy of the untreated test animals was less than three weeks. “We only began treatment when it was, in fact, already too late”, says the first author of the study Johannes vom Berg. The success rate was low, Berg adds. “We then injected biopharmaceutical Interleukin-12 into the large brain tumor. This did induce an immune response but only led to tumor rejection in one-quarter of the animals.”

From 25 to 80 percent: combined treatment leads to success

The researchers were successful when they drew on a new development in skin cancer treatment. They combined intra-tumoral Interleukin-12 treatment with the intravenous administration of a novel immunostimulating drug that suppresses the regulatory T-cells. The rejection of the tumor then worked in 80 percent of the test animals. “I have rarely seen such convincing data in preclinical glioma treatment”, says Michael Weller, neurooncologist and Director of the Clinic for Neurology at the University Hospital Zurich. He added, “That’s why this development should be tested as soon as possible in clinical trials.”

In a joint trial, the team then tested the treatment in a further tumor model which mimics the clinical situation of the brain tumor patient even better. And once again they were successful.

The next step: a clinical trial as soon as possible

The findings of the current research work have been published in the Journal of Experimental Medicine. Their promising results do not mean that the treatment can already be as effective in brain tumor patients. This has to be examined in the next phase for which the team now actively seek commercial partners. Burkhard Becher puts it like this, “We are cautiously optimistic but it’s time that we adopted completely new strategies to really get to grips with this fatal tumor”

vom Berget et al.,(2013). Intratumoral IL-12 combined with CTLA-4 blockade elicits T cell mediated glioma rejection. J. Exp. Med., EPub Ahead of Print, doi: 10.1084/jem.20130678 [Abstract]

Microencapsulation produces uniform drug release vehicle

Consistently uniform, easily manufactured microcapsules containing a brain cancer drug may simplify treatment and provide more tightly controlled therapy, according to Penn State researchers.

“Brain tumors are one of the world’s deadliest diseases,” said Mohammad Reza Abidian, assistant professor of bioengineering, chemical engineering and materials science and engineering. “Typically doctors resect the tumors, do radiation therapy and then chemotherapy.”

The majority of chemotherapy is done intravenously, but, because the drugs are very toxic and are not targeted, they have a lot of side effects. Another problem with intravenous drugs is that they go everywhere in the bloodstream and do not easily cross the blood brain barrier so little gets to the target tumors. To counteract this, high doses are necessary.

Perfect microspheres were produced using 4 percent by weight of the polymer.
Click here for more information.

Current treatment already includes leaving wafers infused with the anti-tumor agent BCNU in the brain after surgery, but when the drugs in these wafers run out, repeating invasive placement is not generally recommended.“We are trying to develop a new method of drug delivery,” said Abidian. “Not intravenous delivery, but localized directly into the tumor site.”

“BCNU has a half life in the body of 15 minutes,” said Abidian. “The drug needs protection because of the short half life. Encapsulation inside biodegradable polymers can solve that problem.”

Encapsulation of BCNU in microspheres has been tried before, but the resulting product did not have uniform size and drug distribution or high drug-encapsulation efficiency. With uniform spheres, manufacturers can design the microcapsules to precisely control the time of drug release by altering polymer composition. The tiny spheres are also injectable through the skull, obviating the need for more surgery.

Microfibers were produced using 10 percent by weight solutions of the polymer.
Click here for more information.

Abidian, working with Pouria Fattahi, graduate student in bioengineering and chemical engineering, and Ali Borhan, professor of chemical engineering, looked at using an electrojetting technique to encapsulate BCNU in poly(lactic-co-glycolic) acid, an FDA-approved biodegradable polymer. In electrojetting, a solution containing the polymer, drug and a solvent are rapidly ejected through a tiny nozzle with the system under a voltage as high as 20 kilovolts but with only microamperage. The solvent in the liquid quickly evaporates leaving behind anything from a perfect sphere to a fiber.

“Electrojetting is a low cost, versatile approach,” said Abidian. “We can produce drug-loaded micro/nano-spheres and fibers with same size, high drug-loading capacity and high drug-encapsulation efficiency.”

The researchers tested solutions of polymer from 1 percent by weight to 10 percent by weight and found that at 1 to 2 percent they obtained flattened microspheres, at 3 to 4 percent they had microspheres, at 4 to 6 percent they had microspheres and microfibers, at 7 to 8 percent they had beaded microfibers and above 8 percent they obtained only fibers. They report their results in the current issue of Advanced Materials.


This is a scanning electron micrograph of BCNU-loaded microspheres (black and white background) with 3D rendered images of brain cancers cells (yellow) and released BCNU (purple).
Click here for more information.

The researchers also investigated the sphericality of the spheres.“Depending on the desired applications, all the shapes are useful except for the beaded fibers,” said Abidian. “While fibers are not good for drug delivery, they are good for tissue engineering applications.”

“We looked at how spherical they were and found they were perfect,” said Abidian. They have a height versus width ratio of 1.05 and they have size uniformity. A perfect sphere would have a ratio of 1.

The researchers also looked into how BCNU releases from the microcapsules. Using mathematics, the researchers established a drug diffusion coefficient for the encapsulation system. This helps in designing how much drug to include in each microcapsule and how long the microcapsules will deliver the required dosage.

The researchers note that BCNU is not the only drug that can be encapsulated in polymer beads for drug delivery. Other drugs can be used but would have their own diffusion coefficients and half lifes.

Fattahi et al., (2013). Microencapsulation: Microencapsulation of chemotherapeutics into monodisperse and tunable biodegradable polymers via electrified liquid jets: Control of size, shape, and drug release.Adv. Mater., 25: 4529 [Abstract]

Technique filters cancer where chemo can’t reach

A cancer therapy that removes malignant cells from a patient’s cerebrospinal fluid may soon be available to prevent metastases and decrease complications of cancers involving the brain, according to Penn State medical researchers.

Many cancer types metastasize to the brain — including breast cancer, pancreatic cancer, prostate cancer and leukemia — but by filtering these malignant cells out of the cerebrospinal fluid (CSF), the researchers hope to decrease the chance of cancer spreading toward and away from the brain.

The brain and spinal cord are surrounded by cerebrospinal fluid, separated from the blood circulating throughout the rest of the body by a cellular lining known as the blood-brain barrier.

“Most chemotherapies have a difficult time crossing the blood-brain barrier, but cancer cells can if they have the right instructions,” said Joshua E. Allen, postdoctoral fellow at the Penn State Hershey Cancer Institute.

The researchers have devised a way to move CSF through a filter outside the body that catches the cancer cells and then allows the CSF to flow back into the patient, tumor cell-free.

“Currently nothing exists that can filter cerebrospinal fluid — which, in some patients, contains malignant active cancer cells,” said Akshal S. Patel, neurosurgery resident at the Penn State Milton S. Hershey Medical Center. “This therapy filters all cerebrospinal fluid.”

Many treatments, including chemotherapy, increase therapeutic resistance of cancer cells, Allen noted. However, filtering cells out does not offer the malignant cells an opportunity to develop therapeutic resistance.

Treatment providers can count the cells captured in the filter and use that to measure the severity of metastasis, another benefit to using this method.

Approximately 15 to 20 percent of metastatic breast cancer patients eventually develop brain metastases, according to the researchers.

“There is a high likelihood of breast cancer patients getting cancer cells in their cerebrospinal fluid,” said Patel.

The researchers monitored the number of tumor cells in nine breast cancer patients with confirmed metastatic spread to their central nervous system. They counted both the number of tumor cells in the bloodstream and in the CSF.

Approximately half of these patients had tumor cells that moved through the blood-brain barrier. Allen and Patel found that this movement of tumor cells is not necessarily restricted to later phases of breast cancer, as previously thought.

With this new knowledge in mind, the researchers’ proposed method can help treat breast cancer — and other metastasizing cancers — earlier and with potentially fewer drugs. This filtering of body fluid is similar to that used as standard care for leukemia, and offers potentially increased cure rates.

“The minimum this therapy would provide is straining the tumor cells out,” said Allen. “But we could also include other therapies when returning the CSF to the body.”

A provisional patent application for this method described by the inventors has been filed.