Testing a new model for brain tumor therapy

Gary Boas

Twenty-three percent of all brain tumors are malignant tumors occurring in children younger than age 15. Unfortunately, relatively few drugs and drug delivery systems have been developed for brain tumor therapy — in part because of a lack of appropriate models for studying the delivery systems in vitro.

Such models should take into account the interactions between brain tumors and host tissue that are most likely to affect therapy, such as tumor invasion of the host tissue. Researchers with the University of Nottingham and with Queen’s Medical Centre, both in Nottingham, UK, described a coculture model based on organotypic neonatal brain slices and 3-D spherical cell aggregates and used it to assess the behavior of nanoparticles developed for drug delivery.

Researchers have reported a tumor invasion model developed to test nanoparticles for drug delivery in brain tumor therapy. The model uses tissue slices and medulloblastoma-derived brain tumor aggregates and thus is more likely to be representative of what happens in vivo. They first validated the models with transmission electron micrography, observing patterns of behavior similar to those reported for previously described in vivo studies: the brain tumor aggregates (Ag) attaching to tissue slices (S) as a unit, with cells on the periphery detaching and gradually replacing normal brain cells. Images reprinted with permission of Experimental Biology and Medicine.

The study was the result of a collaboration among various groups with converging objectives. Martin C. Garnett, with the University of Nottingham School of Pharmacy, had long been interested in using nanoparticles in drug delivery systems, and Terry L. Parker, with the School of Biomedical Science, had worked extensively with a range of 3-D cell culture models. “We felt it would be useful to combine my drug delivery expertise and his knowledge of cell culture models to investigate the behavior of the nanoparticles in realistic models,” Garnett said. Ultimately, the research will benefit ongoing children’s brain tumor studies at the university.

Other groups have reported 3-D in vitro models of tumor invasion, but these typically used normal and tumor cell cultures that had been grown artificially with aggregates. The Nottingham researchers used tissue slices and medulloblastoma-derived brain tumor aggregates, both with normal compositions of the cell types. “Putting these two together will likely lead to a model that’s much more representative of how it behaves in vivo,” Garnett explained.

The model requires higher skill levels and additional setup time because of its complexity, and, because it involves fresh tissue slices, Garnett said, there are additional ethical issues to consider. Implementing the model is generally more difficult than it is for models described previously, but he feels that the payoff is worth the additional effort.

The investigators first validated the model by imaging fluorescently labeled brain tumor aggregates with a transmission electron microscope made by Jeol UK Ltd. of Welwyn and a confocal microscope made by Leica Microsystems of Milton Keynes, UK, with 488- and 543-nm filters and an ultraviolet laser. The experiments revealed that the brain tumor aggregates attached to the slices and invaded them as a unit, and that single cells on the periphery of the aggregates detached from the unit and slowly replaced normal brain cells. These patterns are similar to patterns observed in vivo and reported elsewhere, thus suggesting that the model can be used to explore the potential of the nanoparticles for brain tumor therapy.

Fluorescence microscopy revealed the behavior of the nanoparticles. Specifically, it showed higher rates of uptake in tumor cells than in normal host cells. In this image, cells with green and blue fluorescence represent brain tumor aggregates; normal brain cells exhibited only blue fluorescence. The labeled nanoparticles are represented by red fluorescence.

They then explored uptake of nanoparticles with the confocal microscope. These experiments showed that tumor cells exhibited higher rates of uptake than normal host cells, a finding supported by results reported elsewhere. Combined, these results recommended the model for assessment of the selectivity of drug delivery systems in brain tumor therapies.

The researchers plan to hone the model further, “so other scientists can feel good using it,” Garnett said. Thus far, they have completed only a basic characterization. They also have begun to explore its use for testing drug delivery systems.

Experimental Biology and Medicine, September 2007, pp. 1100-1108.