Cancer therapy: mini capsules with "sesame-open" function

New method for tumor control presented

Microcapsules in a cell before (a) and after (b) laser exposure, the arrow indicates the focus of the laser. The laser beam opens the capsules so that they emit their fluorescent content. © MPI for Colloids and Interfaces
Read out

Medicines help best if they get directly into the diseased organs or cells - for example, in cancer cells. German scientists have now come a step closer to this goal: they have packed a substance into tiny capsules, introduced it into cancer cells and unpacked it there with a laser pulse. The laser light has cracked the polymer shells by heating them up and breaking their molecules, according to the researchers in the journal Angewandte Chemie.

{1l}

The treatment of a malignant tumor is a difficult matter: On the one hand, doctors must destroy even the last remnant of the tumor, on the other hand, they want to spare healthy tissue. Although chemotherapy kills the diseased cells, it also does a lot of damage to the body. So researchers are looking for ways to destroy only the proliferating cells. They could achieve this, for example, by transporting the substances with microcapsules into the tumor cells and releasing them there.

The researchers led by André Skirtach and Gleb Sukhorukov from the Max Planck Institute for Colloids and Interfaces in Potsdam and Wolfgang Parak from the Ludwig Maximilian University Munich have now used a laser beam to selectively open microcapsules that had previously invaded a tumor cell. The capsules have their contents, a fluorescent test substance, then released into the cell. As the luminous substance distributed in the cell, the scientists have followed in a light microscope.

Polymer capsule as a vehicle

The researchers used a polymer capsule with a diameter of a few micrometers as the vehicle. The walls of the capsules were built up of several layers of charged polymers - always alternately one layer of positively charged molecules and one layer of negatively charged ones. At least in the laboratory, this is now a common method for producing microscopic transport containers for medicines, cosmetics or nutrients that can also migrate through cell membranes. display

Skirtach and his colleagues have now equipped the capsules with a kind of sesame-open-yourself. However, they do not need magic to do that, but nanoparticles made of gold or silver atoms. They mix charged metal particles under the molecules that make up the walls of the bubbles. Once the tumor cells have picked up the microcapsules, they irradiate the transport containers with an infrared laser. Since the metal ions absorb the heat of the light particularly well and pass it on to their environment, the walls heat up. They become so hot that the bonds between the polymers of the shell break and the capsules finally break up.

Method tested on isolated tumor cells

For the time being, scientists have only tested the method on isolated tumor cells. "In principle, it is also possible to release active substances in the body, " says Helmuth M hwald, Director at the Max Planck Institute for Colloids and Interfacial Research and one of the scientists involved. This is also because the light of the infrared laser penetrates at least one centimeter deep into the tissue. Since it is hardly absorbed there, the cells of the body hardly heat up. Only the metal particles in the microcapsules absorb the heat. But only if the microcapsules are in a cell. Because only on it affects the laser.

In addition to the thermal ffner, the Potsdam and Munich scientists have also found a way to make the capsules more stable. Simply by slightly heating the freshly formed microcapsules, shrinking the diameter of the hollow spheres. At the same time, the molecules store closer in their hulls, so that the walls of the capsules become thicker and more secure in their contents.

However, scientists still have to solve a major problem before they can selectively channel drugs with microcapsules into tumor cells. The control for the microcapsules is still missing: "For this one would attach on the capsules characteristics, which recognize only the target cells, " says M hwald. Only these cells then allowed the microcapsules to slip through their membrane.

(idw - MPG, 24.07.2006 - DLO)