Scripps researchers find new way to target cancerous cells

To target and attack cancerous B cells, Scripps scientists attach a specialized ligand to a doxorubicin-loaded liposome, turning nanoparticles into a kind of Trojan horse

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LA JOLLA, Calif.—Scientists with the Scripps Research Institute have discovered a new way to target and destroy a type of cancerous cell, and the findings could lead to the development of novel drug therapies to treat leukemia, lymphomas and related cancers. At the heart of it all are glycoproteins, and while these molecules have traditionally proven challenging to understand, limiting their pharmaceutical applications, the Scripps team has pioneered new techniques to study and manipulate them.

"We have been working on lymphoma-targeted liposomal nanoparticles for about two years," notes James Paulson, a Scripps Research professor who led the research, adding that in his research program at Scripps Research, he also has studied glycoproteins, which are proteins decorated with sugars, for many years. In the new research, Paulson and his colleagues applied some of the lab's insights in combining a certain specialized sugar with a nanoparticle loaded with a chemotherapy drug, in hopes of finding a new way to target and destroy cancer cells.

"By targeting B lymphomas with chemtherapeutic loaded nanoparticles, it effectively enhances the effective dose of chemotherapeutic delivered to the lymphoma cells while simultaneously protecting normal tissues," Paulson notes. "It also delivers the drug with a novel mechanism, that is expected to be synergistic with other biologicals like Rituxan and perhaps be active in Rituxan-resistant patients."

The study, which appeared in the June 10 edition of the journal Blood, showed in animal models the new technique was successful in drastically reducing B cell lymphoma, a cancer of immune molecules called B cells. According to Paulson, the method "worked immediately."

"We are very interested in moving this technology forward to see if it would be applicable to treatment of humans and to investigate other applications for this kind of targeting," Paulson says. Each yearapproximately 70,000 people are diagnosed with B cell lymphomas in theUnited States alone, according to the American Cancer Society. While the drug rituximab is often effective at treating the disease, each year22,000 patients still die from B cell malignancies.

Normally, B cells provide an important immune function circulating throughout the bloodstream to help in the attack of infectious agents. But when B cells become cancerous, the question becomes how to pick them out of the crowd of other molecules in the body to target them for destruction, ideally without affecting surrounding tissues.

Paulson points out that researchers had a simple reason for tackling B cell Lymphoma.

"The motivation came out of the ability to selectively target the CD22 receptor on B cells," he says. "Targeting lymphoma was an obvious application."

Because of his previous research, Paulson knew that B cells had a unique receptor protein on their surfaces that recognized certain sugars found on glycoproteins. Could the team create a viable potential therapeutic that carried these same sugars to identify and target these cells?

Paulson says he and his colleagues decided to utilize a different approach to the problem.  

The research team combined two different types of molecules into one, using both new and tried-and-true technology.

"One part of the potential therapeutic was composed of a specialized sugar (ligand) recognized by the B cell receptor, called CD22, expressed on the surface of B cells," Paulson explains. "This was attached to the surface of the other portion of the potential therapeutic, a nanoparticle called a 'liposome,' loaded with a potent dose of a proven chemotherapy drug."

According to Paulson, the  advantage is that scientists already know a lot about how liposomes act in the body because they are approved drugs.

"They have a long circulatory half-life," he said. "They are formulated so they are not taken up by the macrophages in the liver. So we just used the same formulation, attached these ligands, and went right into in vivo studies."

The chemotherapy drug chosen was doxorubicin, which is used in the treatment of a wide range of cancers. The team used a nanoparticle formulation of doxorubicin called Doxil, in which the drug is encapsulated inside the liposomal nanoparticle, which Paulson explains protects normal cells from the drug until it reaches the cancer.  

Normally Doxil is passively delivered to tumors by exiting leaky tumor vasculature, and the drug slowly leaks out to kill the tumor. But by decorating the nanoparticles with the CD22 ligand, the team made the nanoparticles into a type of Trojan horse that is actively targeted to and taken up by human lymphoma B cells, carrying the drug inside the cell.

In the current research, the team administered their new compound to immune-compromised mice that had been infected with B cell lymphoma cells (Daudi Burkitt type). The team used two different formulations of the molecule, one decorated with two percent ligands, the other with five percent. The mice received only one dose.

Paulson said the results were intriguing. No mouse in the control group lived to the end of the 100-day trial, but five of the eight mice receiving the higher ligand dose of the compound survived.

The scientists then looked to see if they could detect any residual tumor cells in the survivors, knowing that in a mouse that is paralyzed by the disease 95 percent of the cells in the bone marrow are tumor cells.

"When we looked at the bone marrow of those that had survived to 100 days, we couldn't detect any [tumor cells]," Paulson said. "Our detection limit was down to 0.3 percent. It was pretty impressive."

To extend the results, the scientists examined their compound's activity in blood samples from human patients with three types of B cell lymphomas—hairy cell leukemia, marginal zone lymphoma, and chronic lymphocytic leukemia. The scientists found that the compound also effectively bound to and destroyed these diseased B cells.

Encouraged by the results, the team is now working to further improve the drug platform, looking for ways to increase the specificity of B cell targeting as well as exploring the technology's use with other chemotherapy agents.

"We intend to further improve the selectivity of the therapeutic for B lymphoma cells, and investigate delivery of other more effective chemotherapeutic drugs in place of doxorubicin studied in this report," Paulson said. "We view this as a prudent time effective step before moving to human clinical trials."

The first author of the paper, "In vivo targeting of B-cell lymphoma with glycan ligands of CD22," was Weihsu Chen of Scripps Research. In addition to Paulson, additional authors were Gladys Completo of Scripps Research, Darren Sigal, and Alan Saven of Scripps Clinic Medical Group, and Paul Crocker of the University of Dundee (UK).

The research was funded by grants from the National Institute of Allergy and Infectious Diseases (NIAID) and the National Institute of General Medical Sciences (NIGMS) of the National Institutes of Health (NIH).

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