Trojan-horse stem cells might offer an important new cancer therapy

There is a constant stream of news stories on new possible approaches to curing cancers.  Cancer research institutions love to see these.  They help to impress the funding sources.  But most of these press releases describe incremental progress on existing therapeutic approaches.  It is rare to see a news story on a basically new and promising way to control  or cure cancers.  I think such a news story may have appeared today.  (See ref and ref). 

The therapeutic concept is simple and based on two observations.  The first observation is that for some reason mesenchymal stem cells (MSCs which are normally found in bone marrow) circulating in the body seek out cancer cells.  I conjecture that this is because cancers excrete signaling molecules that cause the circulating MSCs to home in on them, a strategy cancers use to achieve rapid growth(ref). The second observation is that it is possible to attach a payload molecule to mesenchymal stem cells which cause them to kill cancer cells but not normal cells, a molecule called TRAIL (A TNF-related apoptosis-inducing ligand in case you wanted to know).  “TRAIL induces apoptosis via death receptors (DR4 and DR5) in a wide variety of tumor cells but not in normal cells(ref).”  

The new research involves genetically engineering mesenchymal stem cells to be “Trojan horses” carrying TRAIL.  The stem cells seek out cancer cells and the TRAIL kills them.  The approach is reported to work in-vitro for a number of different cancers and in-vivo in a mouse model of breast cancer.  “In culture, the stem cells caused lung, squamous, breast and cervical cancer cells to die (all p< 0.01), even at low stem cell/tumor cell ratios (1:16). In mice, the researchers showed that the stem cells could reduce the growth of subcutaneous breast tumors by approximately 80 percent (p< .0001). The stem cells could also be injected intravenously as therapy for mice with lung metastases and could eliminate lung metastases in 38 percent of mice compared to control mice, all of which still had metastases (p=0.03)(ref).”  

It will probably take a few years before this cancer therapy approach is tried out in humans but it sounds promising to me.  Unlike blunderbus chemotherapy approaches the approach would be highly targeted, first in that the treated stem cells specifically seek out cancer cells, and second in that the payload kills only cancer cells not normal ones. Result should be minimal collateral damage. Most likely a patient’s own mesenchymal stem cells would be used to avoid any problem of immune system rejection so the therapy would be minimally problematic or toxic for the patient.