Prostate carcinoma is one of the most common malignant diseases, claiming more than 84,000 lives per year in the EU and the United States. In cooperation with the University of Constance, the Thurgau Biotechnology Institute (BITg) is working on ways to remove prostate carcinomas and other tumours that are difficult to treat by using tiny particles made of biologically degradable polyester. Prof. Dr. Marcus Groettrup and his team of researchers have now succeeded in using mouse models to obtain a reasonably effective immune response to the known antigen.
The microparticles that Prof. Dr. Marcus Groettrup and his team are focusing on are made up of lactic acid and glycolic acid and are just one micrometre in size. The researchers hope that the particles will be taken up by the dendritic cells, which are the only cells in the human body that remove dangerous tumour cells by stimulating T-killer cells that are not exposed to antigens. "The particles resemble a kind of pharmaceutical substance that makes the antigens in the body reach those parts of the body that generate an anti-tumour response," explains Prof. Marcus Groettrup. In the aqueous environment of the body, the particles are gradually broken down into their constituent parts, namely lactic acid and glycolic acid.
Immature dendritic cells are located below the skin or the mucosa where they actively take up the microparticles, which then release the antigens. The antigens are fragmented in the cells and transported to the surface by MHC class I and II molecules, a set of molecules displayed on cell surfaces that control the immune response through recognition of self and non-self. "The dendritic cells enter the draining lymph nodes where the passing T-cells are stimulated by the dendritic cells," explains the 45-year-old.
The immunologist from Constance sees distinct advantages in the microparticles . “An important aspect is that they can be easily and fully metabolised in the citrate cycle,” said Groettrup. In addition, he finds their depot function very effective, as this function means that the antigens are released over a period of 30 days. “We were able to show that mice immunised with microspheres are still able to stimulate T-cells that are injected 20 days after the administration of the microparticles. Another advantage is that the polyester the scientists use has already been approved for clinical application, for example in the production of biologically degradable surgical threads. Furthermore, Professor Groettrup and his team can encapsulate peptides, proteins and nucleic acids individually or in combination, making it possible to define the cocktail required for the effective treatment of a particular tumour.Groettrup and his team carry out the tests in a transgenic mouse model that has very similar characteristics to the human disease: the tumour grows in the organ, where it develops hyperplasia and carcinoma in situ and finally metastasises. “We have tested a new strategy that can also be transferred to tumours where there are no known antigens,” said Groettrup. The team of researchers lyses tumour cells with a known antigen and encapsulates the lysate into the microparticles together with immunostimulants (toll-like receptor ligands, a Drosophila receptor), such as CpG (oligonucleotides), which are analogues of bacterial DNA for which the dendritic cells have receptors. “When we immunise a mouse with this mixture, there is an excellent immune response to the known antigen,” said Prof. Marcus Groettrup. The scientists can therefore assume that other tumour antigens in an individual tumour will also stimulate the immune system.
One particular approach that the researchers might chose, takes into account the fact that each tumour has different antigens. Such an approach would consist of a custom-made, patient-specific therapy, since prostate carcinomas are removed surgically. “If metastases nevertheless developed, it would be possible to lyse the frozen tumour tissue, encapsulate it in microspheres and apply it to the patients," said the head of the Department of Immunology. The microsphere particles are exposed to ultrasound in order to prevent them from clumping together. They are then injected below the skin of the mice. With regard to the production of microspheres, the polyester is taken up in an organic phase. “We start with the preparation of an emulsion, which is then turned into tiny particles using a spray dryer. The organic solvents completely evaporate,” said the immunologist from Constance. Spray drying creates ideally sized particles that can be taken up efficiently by the dendritic cells.
In the near future, Prof. Groettrup and his team hope to find out how microspheres need to be designed in order for the carcinoma to be effectively removed, both for prostate carcinoma and other forms of carcinoma. “Vaccination with microspheres can be used for all types of tumours for which tumour-specific antigens are known,” emphasised Groettrup. As far as the development of antigens is concerned, the scientists are currently only making minor progress. The production of the four prostate carcinoma antigens as highly pure recombinant proteins in bacterial, yeast or mammalian cells has proven to be difficult. “We need large quantities of the proteins and we are still working on the optimisation of the process,” said Prof. Marcus Groettrup. He envisages an anti-prostate cancer vaccine consisting of two to three antigens (tumour-specific proteins), an attractant for dendritic cells (chemokines) and two different TLR ligands. Groettrup is optimistic that in around two to three years’ time they will have optimised the production of antigens to such a degree that “sufficient material can be easily produced”.Groettrup is pleased to be able to work with industrial partners in this research project. “Only recently we were contacted by a German company who had read our publications and wanted to work with us,” said a delighted Prof. Marcus Groettrup. The team of researchers is currently looking for a company to produce the microspheres under GMP conditions as well as a company to provide the financial support needed for phase I clinical testing.
Further information:Prof. Dr. Marcus GroettrupUniversity of ConstanceDepartment of ImmunologyUniversitätsstrasse 1078457 KonstanzTel.: +49 7531 882130E-mail: Marcus.Groettrup(at)uni-konstanz.de