Advanced brain tumors are typically treated by surgical removal. However, it is difficult in the extreme to extirpate an entire tumor and therefore, tumor relapse is a perennial problem. A special group of small proteins known as ‘cytotoxic proteins” can target and destroy remaining cancer cells, but these proteins have short half-lives in the body and recent clinical trial called the PRECISE trial was not able to demonstrate that administered cytotoxic proteins had any efficacy against glioblastoma multiforme (GBM) brain tumors.
A new study, however, published online from the journal Stem Cells, a research group led by Khakid Shah from the Harvard Stem Cells Institute, have devised a new strategy designed around these engineered cytotoxic proteins has shown that neural stem cells (NSCs) can be genetically engineered to express these proteins and help treat GBM tumors.
So how did Shah and his colleagues design this novel strategy? They engineered NSCs to not only express specific cancer cell-killing toxins, but also have resistance to these toxins. Secondly, they designed cytotoxins that have the ability to enter cancer cells and target proteins known to be over-expressed by GBM tumors. Then these neural stem cells were encapsulated, they were transplanted into the space left after the bulk of the tumor was surgically removed.
In a mouse model of GMB, the implanted engineered stem cells survived and mediated an increase in long-term survival. This therapy was also effective against multiple patient-derived GBM cancer cell lines, which demonstrated their potential clinical relevance and applicability.
Shah and his coworkers want to bring these results to human trials within the next five years. They hope that this strategy can be successfully deployed in combination with surgical removal of the tumor mass. Shah also hopes that this approach can be adapted to treat other tumor types by using tissue-specific stem cells that express tumor-specific cytotoxins.
See Stuckey DW, Hingtgen SD, Karakas N, et al. Engineering toxin-resistant therapeutic stem cells to treat brain tumors. Stem Cells 2014.