Using Drugs to Stimulate your Own Stem Cells to Treat Multiple Sclerosis

Paul Tesar from Case Western Reserve in Cleveland. Ohio and his colleagues have discovered that two different drugs, miconazole and clobetasol, can reverse the symptoms of multiple sclerosis in laboratory animals. Furthermore, these drugs do so by stimulating the animals’ own native stem cell population that insulates nerves.

Multiple sclerosis (MS) is a member of the “demyelinating disorders.” The cause of MS remains unknown, but all of our available evidence strongly suggests that MS is an autoimmune disease in which the body’s immune system attacks its own tissues. In MS the immune system attacks and destroys myelin — the fatty substance that coats and protects nerve fibers in the brain and spinal cord. We can compare myelin to the insulation that surrounds electrical wires. When myelin is damaged, the nerve impulses that travel along that nerve may be slowed or blocked.

The myelin sheath is made by cells known as “oligodendrocytes,” and oligodendrocytes are derived from a stem cell population known as OPCs, which stands for oligodendrocyte progenitor cells. If this stem cell population could be stimulated, then perhaps the damaged myelin sheath could be repaired and the symptoms of MS ameliorated.

In a paper that appeared in the journal Nature (522, 2015 216-220), Tesar and the members of his research team, and his collaborators used a pluripotent mouse stem cell line and differentiated them into OPCs. Thyroid hormone is a known inducer of OPC differentiation. Therefore, Tesar and others screened a battery of drugs to determine if any of these compounds could induce OPC differentiation as cell as thyroid hormone. From this screen using cultured OPCs, two drugs, the antifungal drug miconazole and clobetasol, a corticosteroid of the glucocorticoid class, proved to do a better job of inducing OPC differentiation than thyroid hormone.

Was this an experimental artifact? Tesar and others devised an ingenious assay to measure the effectiveness of these two drugs. They used brain slices from fetal mice that were taken from animals whose brains had yet to synthesize myelin and applied OPCs to these slices with and without the drugs. With OPCs, no myelin was made because the OPCs did not receive any signal to differentiate into mature oligodendrocytes and synthesize myelin. However in the presence of either miconazole or clobetasol, the OPCs differentiated and successfully myelinated the brain slices.

Experiments in tissue culture are a great start, but do they demonstrate a biological reality within a live animal? To answer this question, Tesar and his crew injected laboratory mice with purified myelin. The immune systems of these mice generated a robust immune response against myelin that eroded the myelin sheath from their nerves. This condition mimics human MS and is called experimental autoimmune encephalitis, and it is an excellent model system for studying MS. When mice with experimental autoimmune encephalitis (EAE) were treated with either miconazole or clobetasol, the EAE mice showed a remarkable reversal of symptoms and a solid attenuation of demyelination. Tissue samples established that these reversals were due to increased OPC activity.

When the mechanisms of these drugs were examined in detail, it became clear that the two drugs worked through distinct biochemical mechanisms. Miconazole, for example, activated the mitogen-activated protein kinase (MAPK) pathway, but clobetasol worked through the glucocorticoid receptor signaling pathway. Both of these signaling pathways converge, however, to increase OPC differentiation.

Both miconazole and clobetasol are only approved for topical administration. However, the fact that these drugs can cross the blood-brain barrier and effect changes in the brain is very exciting. Furthermore, this work establishes the template for screening new compounds that might be efficacious in human patients.

In the meantime, human patients might benefit from a clinical trial that determines if the symptoms and neural damage caused by MS can be reversed by the administration of these drugs or derivatives of these drugs.

Using Human Induced Pluripotent Stem Cells to Study Diamond Blackfan Anemia

Diamond-Blackfan Anemia or DBA results from mutations in a gene on chromosome 19 (in most cases). Mutations in the ribosomal protein S19 affects the ability of blood cells to make protein and causes low numbers of red blood cells. DBA patients are dependent on blood transfusions, but some are cured, to some extent at least, by bone marrow transplants. Unfortunately, some DBA patients have severe side effects from bone marrow transplants, which means that bone marrow transplants are not a panacea for all DBA patients.

Fortunately, Michell J. Weiss and his colleagues at the Children’s Hospital of the Philadelphia (CHOP) have used human induced pluripotent stem cells (iPSCs) to study DBA at the molecular level and even develop the beginnings of a cure for DBA patients. Weiss collaborated with Monica Bessler, Philip Mason, and Deborah French, all of whom work at CHOP.

Remember that red blood cells are made inside the bone marrow of the patient by hematopoietic stem cells (HSCs). HSCs divide to renew themselves, and to produce a daughter cell that will differentiate into one of several different types of blood cells. As a kind of gee-wiz number, a healthy adult person will produce approximately 10[11]–10[12] (100 billion to 1 trillion) new blood cells are produced daily in order to maintain steady state levels in the peripheral circulation.

In DBA patients, the bone marrow is empty of red blood cells. In order to get a better idea why, Weiss and his team isolated fibroblasts from the skin of DBA patients, and used genetic engineering techniques to convert them into iPSCs. When Weiss and his group tried to differentiate these iPSCs derived from DBA patients into red blood cells, they were not able to make normal red blood cells. However, Weiss and his colleagues used different genetic engineering techniques to fix the mutation in these iPSCs. After fixing the mutation, these cells could be differentiated into red blood cells. This experiment showed that it is possible to repair a patient’s defective cells.

This is a proof-of-principle experiment and there are many hurdles to overcome before this type of experiment can be done in the clinic to DBA patients. However, these iPSCs can play a vital role in deciphering some of the mysteries surrounding this disease. For example, two family members may have exactly the same mutation, but only one of them shows the disease whereas the other does not. Since iPSCs are specific to the patient from whom they were made, Weiss and his group hope to compare the molecular differences between them and understand the difference in expression of this disease.

Also, these cells offer a long-lasting model system for testing new drugs or gene modifications that may offer new treatments that are personalized to individual patients.

Weiss and his research group used this same technology to test drugs for the often aggressive childhood leukemia, JMML or Juvenile Myelomonocytic Leukemia. Once again, iPSCs were made from JMML patients and differentiated into myeloid cells, which divided uncontrollably just as the original myeloid cells from JMML patients.

Weiss and his colleagues used these cells to test two drugs, both of which are active against JMML. One of them is an inhibitor of the MEK kinase that was quite active against these cells. This illustrates how iPSCs can be used to test personalized treatment regimes for patients.

The stem cell core facility at CHOP is also in the process of making iPCS lines for several inherited diseases: dyskeratosis congenita, congenital dyserythropoietic anemia, thrombocytopenia absent radii, Glanzmann’s thrombasthenia, and Hermansku-Pudlak syndrome.

The even longer term goal is the use these lines to specifically study the behavior of such cells in culture and under certain conditions, test various drugs on them, and to develop treatment strategies on them as well.

The Use of Stem Cells in Drug Development

Why is it that one person can have surgery and wake up, eat a full lunch and show no ill effects while others are sick for several days after receiving general anesthesia?

The fact is that we all process drugs differently, and these differences are a function of the genetic diversity between all of us. These differences stem from 1) different targets; 2) different liver enzyme activities; and 3) different levels of absorption, excretion and distribution.

A few examples might be illustrative. It is fairly well established that a particular type of blood pressure medicines called “ACE inhibitors” do not work terribly well in African-Americans (see Park IU, Taylor AL. Ann Fam Med. 2007 Sep-Oct;5(5):444-52). The reason for this is that the target of ACE inhibitors, the enzyme angiotensin converting enzyme, which is mercifully abbreviated ACE, works on a substrate that already exists at low concentrations in most African-American patients. Thus a target difference causes differential responses to particular blood pressure medicines.

As a second example, two liver enzymes that degrade drugs, Cyp2C19 and Cyp2D6 are encoded by genes that are subject to genetic variation. In 3-10% of whites, the Cyp2D6 enzyme does not completely function and the drugs processed by this enzyme, a blood pressure medicine called debrisoquine and a heart medicine called sparteine, show impaired degradation. Thus these patients are in danger of overdosing on these drugs at normal dosages, since they are degraded and excreted at such low rates. Other people, however, have a version of Cyp2D6 that is hyperactive. This variant is most commonly found in Ethiopians and Saudi Arabians that consequently, drugs degraded by this enzyme, such as tricyclic antidepressants (e.g., nortriptyline) must be dosed at two the three times the normal concentration. Also, some drugs are given as prodrugs, which are inactive until the liver activates them. In individuals with the overactive Cyp2D6 enzyme variant, a prodrug, such as codeine is overactivated and at normal doses, causes severe side effects (stomach pains). Thus a distinct enzyme difference causes different clinical outcomes with the same drugs (see JK Hicks, et al., Clin Pharmacol Ther. 2013 May;93(5):402-8).

So then, how do we test for drug safety and efficacy given these variations in drug metabolism?

Stem cell technology has the ability to improve drug testing in a multitude of ways. Drug safety can be tested with stem cells as can drug efficacy without feeding them to human volunteers.

Now scientists from the University of Edinburgh have shown that stem cell-based drug tests are almost ready for the prime time. David Hay from the Medical Research Centre for Regenerative Medicine at the University at the University of Edinburgh and his colleagues have generated cell in the laboratory that reach the gold standard required by the pharmaceutical industry to test drug safety.

In this study, the Hay laboratory made liver cells from H9 human embryonic stem cells and from 33D6 human induced pluripotent stem cells. Since is the liver is the main organ that biochemically processes drugs in our bodies (a phenomenon known as biotransformation), testing drug safety in cultured liver cells makes good sense.

Next, Hay and his colleagues found that these pluripotent-derived liver cells were equally effective in drug safety tests as frozen human liver tissue extracted from cadavers. Such livers are in short supply and the results researchers derive from them varies wildly according to the genetic make-up of the donor. Thus frozen liver tissue is not optimal for such drug testing protocols.

However, these drug-testing protocols that use stem cell-based protocols can provide reproducible drug safety results and can also be adapted for individuals with particular genetic compositions who process drugs differently from other people.

David Hay explained it this way: “Differing genetic information plays a key role in how patients’ livers process drugs. We are now able to efficiently produce human liver cells in the laboratory from different people model the functional differences in human genetics.”

Hay and others hope to generate liver cells that contain distinct DNA sequences that will reflect the genetic variations in metabolism found in the population. These cultured liver cells from human pluripotent stem cells can be used to identify differences in drug biotransformation.

These laboratory-generation liver cells could also be used to screen certain drugs that need close monitoring in order to optimize the efficacy of patient treatment, and the safety of these treatment regimes.

Hay and his colleagues are working with Edinburgh BioQuarter in order to form a spin-off company that will commercialize this research and its clinical ramifications.