About that Hold


Geron has revealed the reason for the FDA hold on its Spinal Cord Injury Investigational New Drug application. In an August 27th press release, Geron scientists revealed that the implanted GRNOPC1 cells caused cysts in a small proportion of the animals injected with them. These cysts were not cancerous. The report calls them “non-proliferative,” which simply means that they are not growing. Additionally. the cysts are very small – microscopic in size. Finally, the cysts were confined to the region of the injury and did not adversely affect the laboratory animals.

Why the hub-hub? A recent animal study reported a greater frequency of cysts. Once again, they are non-proliferative (non-growing), restricted in location to the site of injury and do not affect the animals.

What’s going on? Cyst formation is common in spinal cord injury. Once the spinal cord is injured, inflammation ensues and this involves the invasion of the spinal cord by immune cells that mop up the dead cells and debris from the injury. Unfortunately, immune cells are sloppy eaters and they do a great deal of damage to the spinal cord. The damage they cause also tends to summon more immune cells, which come to the scene of the injury and damage the spinal cord even more. the whole thing is a positive feedback mess.

To put an end to it the spinal cord makes a plug called a glial scar. The glial scar comes from the stem cell population in the spinal cord. These stem cells form support cells called “glial cells” and these cells plug the hole in the spine and shut out the immune response, thus saving the spinal cord. The formation of this glial scar, however has a severe downside for spinal cord regeneration: the glial scar is loaded with chemicals that repel growing neurons. Therefore, those neurons that were severed by the injury could not regrow their extensions if they wanted to. The glial scar acts like a bunch of burly security guards that prevent the neuronal extensions from getting to the other side.

These cysts are probably the result of the GRNOPC1 cells forming tiny glial scars to help the injured spinal cord heal. Now they do not seem to affect the laboratory animals, but they are inhibitors of neuronal healing. Therefore, while they may not affect the laboratory animals, they may represent a fix that sentences the spinal cord to never being fixed by anything else again.

GERON’S IND FOR SPINAL CORD INJURY PLACED ON HOLD


Geron Corporation has made a cell line called GRNOPC1 from embryonic stem cells. GRNOPC1 is an “oligodendrocyte precursor cell” or OPC line. Before you blow a gasket at the sight of such a long-winded description, just remember that nerves are like wires and wires need insulation.  OPCs are the cells that make the insulation.  During spinal cord injury, the insulation dies off and it causes nerves to malfunction.

In collaboration with Hans Keirstead at UC Irvine, Geron developed a protocol for the administration of GRNOPC1 cells to animals with acute spinal cord injuries. His protocol showed that the OPCs were safe (no tumors were seen, even after one year) and somewhat effective. Some scientists were skeptical, since the mice had somewhat less severe spinal cord injuries.  Nevertheless, Geron was granted an Investigational New Drug Application from the FDA to conduct a Phase I trial with their OPC cell line.

They apparently, however, have bit a bit of a snag. Here is a press release from Geron Corporation.

Geron Corporation today announced that its IND (Investigational New Drug application) for GRNOPC1, a cell therapy for neurologically complete, subacute spinal cord injury, has been placed on clinical hold by the FDA pending the agency’s review of new nonclinical animal study data submitted by the company. A clinical hold is an order that the FDA issues to a sponsor to delay a proposed trial or to suspend an ongoing trial.

Since filing the IND, Geron has been undertaking studies to enable dose escalation of its spinal cord injury product, and has been investigating application of the product to other neurodegenerative diseases. The company has also been performing additional product characterization and conducting further animal studies. Data from this work has been submitted to the FDA. Geron will work closely with the FDA to facilitate their review of the new data and to release the clinical hold. No patients have yet been treated in this study.

From the sound of it, this hold is merely an administrative procedure that the FDA routinely undergoes when presented with new data.  However, if the new data is completely consonant with previous findings, why would there be a hold? We simply do not know at this time.  It is entirely possible that nothing is amiss, and this is merely FDA policy.  However, it is also possible that Geron’s new product does not behave exactly as they thought.

The development of the first cholesterol-lowering drug (lovastatin) experienced a slow-down when a related product being developed in Japan caused cancer in dogs. Roy Vagelos, president of Merck at the time, contacted the FDA and suspended all clinical trials. Further testing by Merck showed that this was an anomaly, and extensive clinical use has vindicated this finding. Maybe this is a similar situation for Geron’s OPC line?  Only time will tell.

Huntington Disease therapy fails


Huntington Disease in a fatal, inherited disease that causes degeneration of the central nervous system. It clinically manifests itself as severe movement and cognitive problems, and the patient gradually loses control of their body in a slow, painful slide to death that is difficult to watch.

A treatment for Huntington Disease that generated a far amount of hope in the 1990s was to transplant healthy neural tissue from fetuses. In particular, the striatum — the brain region most severely affected in Huntington disease was replaced by fetal neural tissue. Unfortunately, this tissue came from babies who were killed by selective abortion. Unfortunately, clinical follow-up of this approach has shown that technique does not work (Cicchetti, F. et al. Proc. Natl Acad. Sci. USA advance online publication doi:10.1073/pnas.0904239106 (2009).

Source: http://www.glaucoma.org/uploads/eye-anatomy-2012_650.gif
Source: http://www.glaucoma.org/uploads/eye-anatomy-2012_650.gif

University of South Florida neurosurgeon Thomas Freeman and his colleagues have conducted a post-mortem analysis of the brains of three people with Huntington’s disease who received fetal striatal-tissue transplants a decade before they died. The results were rather clear – instead of slowing or stopping the progression of the disease, the grafts degenerated even more severely than the patients’ own tissue.

Early results for this procedure generated some hope.  Animal experiment in rats (Kendall, A. L. et al. Nature Med. 4, 727-729 (1998) and non-human primates (Isacson, O. et al. Nature Med. 1, 1189-1194 (1995) showed that transplanted tissue could replace lost striatal neurons and improve behavioural symptoms.  Also, early clinical results tended to support the efficacy of this technique.  Patients who had received these striatial grafts showed modest improvements and autopsies showed that the grafts of fetal neural tissue had survived and integrated into the brain (see Hauser, R. A. et al. Neurology 58, 687-695 (2002), and Bachoud-Lévi, A.-C. et al. Lancet Neurol. 5, 303-309).

Unfortunately, this more recent examination shows that the animal models were deceptive.  The animals were treated with chemicals that destroyed the striatum but left the rest of the brain intact.  In the case of human patients, the entire brain is diseased, and dying neurons release extensive amounts of neurotransmitters that kill neurons by overdosing them on these neurotransmitters.  The transplanted tissue is killed by neurotransmitter overdose.

This has implications for stem cell treatments of Huntington Disease.  Transplanted stem cells or neural progenitor cells will be subjected to this same cocktail of death.  Therefore another strategy is needed.

Fortunately, some cells can surround transplanted cells and protect them from death by neurotransmitter overdose.  For example, co-transplantation of testicular Sertoli cells with neural grafts not only produce an area of localized immuno-suppression (due to local secretion of GDNF by the Sertoli cells) but they can push stem cells into dopaminergic neurons, which are killed in Parkinson Disease (see Halberstadt C, Emerich DF, Gores P. Expert Opin Biol Ther. 4, (2004): 813-25).  Therefore, some new thinking on this front might provide a new treatment scheme.