Disorientating dormant tumor cells

Left: Based on X-ray crystal structures the inhibitors were optimized and their binding affinity for Ena/VASP increased. Top right: Treated cancer cells loose their ability to migrate towards an attractant. Optimized inhibitors cause this effect with decreased concentration. Bottom right: Cancer cells (red) metastasize from the bloodstream (green) into the tail fin of zebrafish. Optimized inhibitors (Inh. 7) impair this process © Matthias Barone

Cancer is insidious. Even if the tumor appears to have been fully removed, numerous disseminated tumor cells often remain dormant in the bloodstream. Cytostatic drugs are intended to prevent a relapse, but dormant cancer cells are resistant to chemotherapy. This is because most cytostatics only kill cells that are rapidly dividing. Dormant tumor cells are inactive, and it is only a matter of time before such cells develop resistance to the therapy. Drawn to growth hormones, they then migrate from the lymphatic system or the bloodstream, and invade into organs. This route enables them to form growing metastases that are now resistant to the therapy.
Researchers at the FMP therefore seek to prevent invasive cancer cells from migrating. In doing so, they target the Ena/VASP protein family. These proteins are used by all cells that change shape, such as immune cells, nerve cells and platelets; they are significantly overexpressed in highly invasive cancer cells. In interaction with other proteins, Ena/VASP proteins remodel the cytoskeleton, enabling the cell to migrate in a specific direction; this protein family is therefore a critical factor in metastatic cancer progression. And this is precisely the researchers’ point of attack: “The idea is that dormant cancer cells become disoriented if we use inhibitors to stop the fatal machinery,” remarked Dr. Matthias Barone, biochemist in Ronald Kühne’s “Drug Design” group.

Successful modification of a set of molecules
As early as 2015, the team of researchers identified a molecule that binds to the protein family. However, it was not sufficiently effective in small quantities to have an impact in a living organism. This has now been achieved by making further chemical modifications to the molecule.
Cell experiments have demonstrated that cancer cells treated with the substances lose their ability to migrate towards attractants. The higher the concentration, the stronger the effect. “Our molecules bind specifically to the Ena/VASP protein family, preventing interaction with other proteins or displacing partner proteins,” stated Matthias Barone, explaining how the method works. “Although this method does not destroy the cancer cells, they become disoriented and can no longer find their way into the bloodstream or other organs.”
Experiments with breast cancer cells implanted in zebrafish embryos showed that this method also works in the living organism. Fish embryos that swam in these substances subsequently exhibited significantly fewer breast cancer cells metastasizing from the bloodstream into the tailfin.
An important factor regarding further development of the substances: the research team was able to demonstrate that the modified molecules bind specifically to the protein family and not to other related proteins, which could have far-reaching adverse consequences.

Blockade prevents metastasis
“In this study, we have shown, firstly, that this protein family is absolutely necessary for the process of cancer cell metastasis,” stated group leader Dr. Ronald Kühne, summarizing the results published in PNAS. “And secondly, we were the first group of researchers in the world to develop a set of molecules that can recognize the protein family and inhibit the process. This, of course, opens up the possibility of stopping, or at least slowing, metastasis in parallel with cytostatic therapies.”
In the next step, the Berlin-based drug designers will optimize the pharmacological properties of the molecule so that it can be tested in animal models. At the end of a long process of development, a drug that significantly improves cancer survival could be created in cooperation with the pharmaceutical industry. There is a long way to go before achieving this goal, but the key first stage has been reached.

Publication
Matthias Barone, Matthias Müller, Slim Chiha, Jiang Ren, Dominik Albat, Arne Soicke, Stephan Dohmen, Marco Klein, Judith Bruns, Maarten van Dinther, Robert Opitz, Peter Lindemann, Monika Beerbaum, Kathrin Motzny, Yvette Roske, Peter Schmieder, Rudolf Volkmer, Marc Nazaré, Udo Heinemann, Hartmut Oschkinat, Peter ten Dijke, Hans-Günther Schmalz, Ronald Kühne, Designed nanomolar small-molecule inhibitors of Ena/VASP EVH1 interaction impair invasion and extravasation of breast cancer cells, Proceedings of the National Academy of Sciences, Nov 2020, 117 (47) 29684-29690; DOI: 10.1073/pnas.2007213117

Contact
Dr. Ronald Kühne
Drug Design
Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP)
kuehne@fmp-berlin.de
Phone: +49 30 947 93 229
www.leibniz-fmp.de/kuehne