Protein APG101
Q: How relevant is the recombinant protein APG101 to therapy?
A: APG101 is a protein that simulates the cell-death receptor CD95 and binds with a stable antibody fragment. By doing so, it blocks the signaling pathway between CD95 ligand and receptor. The interaction between the CD95 ligand and the CD95 receptor activates an intracellular signaling pathway, which in turn stimulates the invasive growth and migration of tumor cells.
APG101 blocks the CD95 ligand and thereby prevents the activation of the CD95 signaling pathway, which leads to a reduction in the invasive cell growth and migration.
Apoptosis, programmed cell death, is a system we have used throughout our evolution to kill off the cell components we no longer need. During tumor development, this system is perverted, so to speak. Here, the stimulation of this system does not actually lead to cell death but rather to cell movement (i.e., to cell mobility). And in principle, APG101 blocks this mobility.
To date, I only know of three studies in which the medication has been used for tumors. One study was published 8 years ago. We demonstrated that we can achieve a relatively good effect with APG101 in connection with repeat irradiation, compared with repeat irradiation alone. We consider this effect to most likely be due to this influence on cell mobility.
There is a study on primary therapy: a four-arm study by the Neuro-Oncological Working Group. The results are still not available, however. In addition, a study on primary therapy with APG101 is currently being conducted in China. It is investigating whether the mechanism of action influences mobility. Whether it will be pushed through as therapy remains to be seen.
Vaccinations and antigens
Q: Vaccinations are of course a part of immunotherapy. What is their status?
A: We are looking at the IDH1 protein, which is present in mutated form in a group of brain tumors, as a very good target for a vaccine. The reason is that the protein is present in its mutated form in every cell of the tumor but not in healthy cells. That is a prerequisite for immunotherapy.
We started a study with peptides a few years ago. These peptides are injected under the skin on the stomach and leg. They cause an immune response systemically and in the brain tumor. This immune response may cause an inflammatory reaction (we can demonstrate this inflammatory reaction). And in this noncontrolled study, the approach was successful, at least compared to historical controls. There is no randomized study with treatment-naive control patients.
However, we are cautious because we know that peptide, unlike CAR T cells or RNA-based vaccines, for example, only triggers a relatively small immune response in many patients. The scale of the immune response is important, rather than the specificity. The scale is probably not large enough in most patients for a long-term effect to be expected.
But there are exceptions. Patients we vaccinated many years ago still have a very remarkable immune status. But we also have patients in whom an immune status cannot even be seen anymore, after just a short period of time.
Therefore, our aim is to perform the immune strategy with more effective, stronger measures – not more specific, but stronger. Unfortunately, it is often the case with glioblastomas that there is not a single antigen that can be vaccinated against. Instead, a relatively large cocktail is needed, which unfortunately also often varies from patient to patient. The conditions are difficult.
Q: You mentioned that glioblastomas can be classified into subgroups. Does this improve the prognosis?
A: Yes, in certain subgroups the prognosis improves. That is the case with those usually very small groups that are molecularly well defined. I believe that by better understanding the individual groups, we have succeeded in making major progress in those groups. But where there is light, there is also shadow. We know that there are many groups with which we have not achieved a great deal.
Fundamental research leads to a better understanding, and the next step in this is to be able to adapt the therapy. Instead of it being one therapy for everyone, it will become a part of various differing therapies for these quite different groups. We are making a lot of progress with individual groups. But unfortunately, we have not come quite as far as we want with many patients.
This article was translated from the Medscape German edition. A version of this article first appeared on Medscape.com.