[This is the first of three stories on CIRM’s Cancer Fight that we will post this week. Tomorrow’s will discuss two projects that attack cancer stem cells directly and Thursday’s will describe three projects that help our immune system wipe out the traitorous cells.]
It’s back—two words we would like to remove from the cancer caregivers’ vocabulary. Many researchers blame cancer stem cells for this too common occurrence, saying cancer stem cells have ways of avoiding most traditional therapies and trigger the tumor’s return. Others prefer the term “tumor initiating cells.” But whatever you call them they need to be dealt with if we are going to make major improvements in cancer patient survival.
CIRM is investing $56 million in five clinical trials targeting cancer stem cells (CSCs), the most advanced projects in our over $200 million commitment so far, to fighting cancer. Two of these trials use agents that target the cancer stem cells directly and three use agents that enable a person’s immune system to do a better job of getting rid of the CSCs.
Trials that target cancer stem cells directly
One of the clinical trials directly targeting CSCs uses a type of protein called an antibody to seek out the renegade stem cells and initiate their demise. Antibodies home to specific proteins on the surface of cells called antigens. Researchers have been able to identify a few antigens that seem to be almost exclusively on the surface of CSCs and they have become targets for therapy.
A team at the University of California, San Diego uses an antibody named after our agency Cirmtuzumab to fight chronic lymphocytic leukemia. It targets the protein ROR1 that is abundant on CSC in the leukemia but not on normal blood-forming stem cells. Once bound on the cells Cirmtuzumab seems to prevent them from proliferating and migrating to other parts of the body and promotes them to go through a form of cell death called apoptosis.
The second trial directly attacking CSCs, at the University of California, Los Angeles, targets various solid tumors. They use a drug that affects the CSCs ability to replicate. It binds to and inhibits a protein, called a kinase, that the CSCs use when they divide.
Trials that activate the immune system
A third clinical trial, at Stanford, also uses an antibody, but in this case it blocks a protein the CSCs use to fend off the cells in our immune system that routinely destroy emergent cancers in all of us. Immuno-oncology, the process of juicing up our immune response to cancer, is one of the hottest areas in cancer research and on Wall Street right now. But most of those efforts target a part of the immune system called the T cell. The Stanford team mobilizes a different immune cell, the macrophage, which routinely gobbles up dying, damaged or cancerous cells.
One beautiful thing about all three of these therapies is they could reverse a decade-long trend of new cancer therapies being targeted to increasingly narrow populations of cancer patients, resulting in extremely high costs per patient. Because the proteins targeted by these therapies seem to be shared across a great many types of tumors, they could be broad-spectrum cancer strategies that could be delivered at a lower cost.
CIRM currently funds five clinical trials targeting cancer stem cells.
- Leukemia at UCSD
- Various solid tumors at UCLA
- Various solid tumors at Stanford
- Melanoma at Caladrius Biosciences
- Glioblastoma at ImmunoCellular Therapeutics
An additional five cancer clinical trials have been undertaken based on early research funded by CIRM.
The fourth CIRM-funded clinical trial also seeks to increase our natural immune response, in this case in notoriously hard to treat metastatic melanoma. Like the Stanford team, this project by researchers at the firm Caladrius Biosciences targets a type of cell different from most immuno-oncology. In this case they derive cells called dendritic cells from the patients’ blood and establish a cell line from their tumor. In the lab they mix the cell types together and the dendritic cells gobble up the tumor cells including the cancer’s antigens, those surface proteins that act as identification tags. When re-infused into the patient the dendritic cells do what they are really good at: presenting antigens to the immune cells responsible for getting rid of tumors. Dendritic cells display the antigens like road maps to the immune cells that can then seek out and kill the cancer stem cells.
The fifth CIRM-funded trial uses a similar concept activating a patient’s dendritic cells with antigens from their brain cancers, known as glioblastomas. That trial is being conducted by ImmunoCellular Therapeutics
The first three trials are all early phase studies looking to test safety and determine what is the best dose to use going forward. The last two trials are more advanced, so-called Phase 3 studies of a dose already having shown signs of benefit in earlier trials.