Potential drug lessens neurodegeneration in Parkinson’s disease model

 


andy westAndy WestThe first test in a mammalian model of a potential new class of drugs to treat Parkinson’s disease shows abatement of neurodegeneration in the brains of test rats and no significant toxicities, University of Alabama at Birmingham and Pfizer Inc. researchers report online in The Journal of Biological Chemistry.

At present, there are no therapies to slow or block the progression of Parkinson’s disease, a common neurodegenerative disorder that affects 7 million to 10 million people worldwide.

The rat model overexpresses the protein α-synuclein in one side of the brain. This leads to degeneration of the dopamine-generating neurons of the substantia nigra region of the brain.

“Because our observations were limited to a four-week period, we are not sure whether neurodegeneration associated with α-synuclein is truly prevented or just delayed,” senior author Andrew West, Ph.D., and colleagues wrote. “Either way, any interruption of neurodegeneration associated with Parkinson’s disease might represent a significant therapeutic advance.”

“For a patient with disease onset in the mid-60s, Parkinson’s disease runs its course over 10 to 15 years,” explained West, co-director of the Center for Neurodegeneration and Experimental Therapeutics, and the John A. and Ruth R. Jurenko Professor of Neurology at UAB. “So, if we can slow down the disease by even 50 percent, that may be effectively as good as a cure, given the available symptomatic treatments.”

The rat model used mimics two cardinal features of Parkinson’s disease: degeneration of dopamine neurons in the brain, and the accumulation of alpha-synuclein in surviving neurons. Patients with Parkinson’s have significant degeneration of dopaminergic neurons in the substantia nigra, up to 70 percent losses at even mid-stages of their disease, and abnormal accumulation of α-synuclein in many of the surviving neurons that occurs years earlier. Details of how Parkinson’s begins and how it progresses are still unclear.

“For a patient with disease onset in the mid-60s, Parkinson’s disease runs its course over 10 to 15 years. So, if we can slow down the disease by even 50 percent, that may be effectively as good as a cure, given the available symptomatic treatments.”
The potential new class of drugs is kinase inhibitors that are active against the enzyme “leucine-rich repeat kinase 2” (LRRK2, pronounced “lark two”). Two clues point to LRRK2 as a possible target for therapy in Parkinson’s. First, about 2 percent of Parkinson’s disease patients have a specific mutation in LRRK2 called G2019S that increases the kinase activity of LRRK2; this suggests that increased activity plays a role in progression of the disease. Second, the West lab last year reported that gene “knockout” rats with no LRRK2 are completely protected from neurodegeneration in the α-synuclein-overexpression model, suggesting pharmacological inhibition may be a viable approach.

The model uses rats that express a cloned human G2019S-LRRK2 gene. Then these rats are injected in the brain (specifically a part of the brain called the substantia nigra) with a virus that expresses human α-synuclein. Test rats were fed the test inhibitor for four weeks, beginning at the time of infection. The small-molecule inhibitor easily passes through the blood-brain barrier to reach the brain from the bloodstream. Besides protecting against neurodegeneration, the inhibitor also lessened an inflammatory response by microglial cells seen in the brain in association with G2019S-LRRK2 expression.

West and colleagues also tested the inhibitor in outbred, wild-type rats, animals that are distinct from the strain that has the human G2019S-LRRK2. With the placebo, these rats showed about a 20 percent loss of neurons after four weeks of α-synuclein overexpression; but treatment with the inhibitor completely abated that loss. This result suggests that the inhibitor also has efficacy in the absence of the human G2019S-LRRK2.

“That is important because only 2 percent of Parkinson’s disease patients have the G2019S mutation,” West said. “These wild-type rats really excited us because it suggests the therapeutic action of the drug may extend to the majority of Parkinson’s disease patients. This has invigorated our collaborative efforts with Pfizer Inc. and the Michael J. Fox Foundation for Parkinson’s Research to invest more effort in LRRK2 inhibitors.”

The Pfizer inhibitor is one of a number of LRRK2 inhibitors under development by drug companies, and also at UAB in collaboration with the Southern Research Institute. West says there will be room for several different inhibitors if this class of drugs shows promise in initial clinical trials, which hopefully will occur within the next year.

The next steps for the Pfizer inhibitor will be testing a variety of doses and testing what happens if treatment begins after the α-synuclein expression has already started. West notes that any possible therapy for Parkinson’s disease will need to be incredibly safe because treatment would last for years.

“We have to be very careful with what our models can tell us,” West cautioned about extrapolating from the rat model. “We need to think critically about what type of benefit we can expect to see in humans because there are recent examples where improper clinical trial design have hindered the development of a new class of drugs for years and sometimes decades.”

For example, it is not clear where and how the inhibitor acts in the rat model, especially since inflammatory microglia cells in the brain also express LRRK2. Knowing such information might be critical to the success of these drugs in the clinic. In a separate trail of evidence, researchers, who include David Standaert, M.D.,Ph.D., have found that gene knockout of several neuroinflammatory processes can block α-synuclein neurodegeneration. Thus, the inhibitor may have an effect on just neurons or just microglia, or it may be a two-hit process affecting both neurons and microglia. Standaert is the John N. Whitaker Professor and chair of the Department of Neurology at UAB.

Co-authors of the paper, “LRRK2 Pharmacological Inhibition Abates α-Synuclein Induced Neurodegenerationα-Synuclein Induced Neurodegeneration,” are João Daher, Hisham Abdelmotilib, Xianzhen Hu, Laura Volpicelli-Daley, Ph.D., Mark Moehle and Kyle Fraser, all from the Center for Neurodegeneration and Experimental Therapeutics, Department of Neurology, UAB School of Medicine; Elie Needle, Yi Chen and Warren Hirst, of the Pfizer Neuroscience Research Unit; Stefanus Steyn, Pfizer Pharmacokinetics, Dynamics and Metabolism, Cambridge; and Paul Galatsis, Pfizer Worldwide Medicinal Chemistry, Cambridge, Massachusetts.

This study was supported by the Michael J. Fox Foundation for Parkinson’s Disease Research, the National Institute of Neurological Disorders and Stroke, and the American Parkinson’s Disease Association.



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UAB study says race influences warfarin dose – an advance for personalized medicine


        

nita limdi labNita Limdi, Ph.D., Pharm.D., UAB professor of neurology

A new report from researchers at the University of Alabama at Birmingham demonstrates that clinical and genetic factors affecting dose requirements for warfarin vary by race. The study, published online today in Blood, the Journal of the American Society of Hematology, proposes race-specific equations to help clinicians better calculate warfarin dosage.  

Warfarin is the most widely used blood thinning medication, or anticoagulant, prescribed to prevent stroke and to treat blood clots. Determining the optimal warfarin dose to prevent clots while avoiding dangerous bleeding is difficult. To ensure that a safe balance is achieved, patients taking warfarin must regularly visit their doctor for blood tests.

Investigators have identified several factors that affect how the body breaks down warfarin and that consequently influence dose requirements. These include clinical factors such as height and weight and the presence of genes that help the body break down warfarin (CYP2C9) and help to activate clotting (VKORC1).

While researchers agree that these clinical and genetic factors affect individual patients’ dose requirements, whether this translates to achieving and maintaining a safe level of anticoagulation was explored in two recent clinical trials with conflicting results.

In 2013, the EU-PACT trial reported that calculating a patient’s warfarin dose based on the presence of genetic factors (known as genotype-guided dosing) improved anticoagulation control. Meanwhile, the Clarification of Optimal Anticoagulation through Genetics trial reported that a similar genotype-guided dosing strategy did not appear to make a difference among patients enrolled. Of note, the COAG trial included more African-Americans than did EU-PACT (27 percent of the study population vs. 0.9 percent), and the African-Americans enrolled actually fared worse after receiving genotype-guided therapy.

According to a research group led by Nita Limdi, Ph.D., Pharm.D., professor in the UAB Department of Neurology and interim director of the Hugh Kaul Personalized Medicine Institute, the studies’ disparate findings may be attributed to differences in racial diversity among participants.

Warfarin is the most widely used blood thinning medication, or anticoagulant, prescribed to prevent stroke and to treat blood clots. Determining the optimal warfarin dose to prevent clots while avoiding dangerous bleeding is difficult. To ensure that a safe balance is achieved, patients taking warfarin must regularly visit their doctor for blood tests.

“As the outcomes of disease can vary by race, so can response to medications,” Limdi said. “Therefore, warfarin dosing equations that combine race groups for analysis (race-adjusted analysis) assume that the effect of variables — such as age and genetics — are the same across race groups, which may compromise dose prediction among patients of both races.”

In order to better understand how genetics and clinical factors influence warfarin dose across race groups, investigators analyzed 1,357 patients (595 African-American; 762 European-American) treated with warfarin, calculating and comparing their recommended dose according to both race-adjusted dosing models (e.g., COAG) and race-specific dosing models. As 43 percent of the study population was African-American, the research team was able to conduct a robust assessement of the impact of clinical and genetic factors on warfarin dose by race.

After calculating and comparing recommended warfarin dose for study participants according to race-combined dosing models and race-specific dosing models, researchers made several significant observations. While genetic factors accounted for a larger proportion of the dose variability for European-American patients, clinical factors accounted for a larger dose variability in African-Americans. They noted that gene variants may have a different effect on dose across race groups. For example, European-Americans with a variant of CYP2C9 (CYP2C9*2) required less of the drug according to race-specific dosing models, yet African-Americans did not. While all participants, regardless of race, who carried VKORC1 required lower dose, according to race-specific dosing models, the proportional dose reduction was greater among European-Americans.

Researchers conclude that the influence of genetic and clinical factors on warfarin dose differs by race, and therefore recommend that race-specific equations, rather than race-adjusted equations, be used to guide warfarin dosing.

“Our findings highlight the need for adequate racial representation in warfarin dosing studies to improve our understanding of how the factors that influence warfarin dose differ according to race,” said Limdi. “This is the first step to developing race-specific algorithms to personalize therapy.”


By Bob Shepard
UAB Media Relations

UAB study identifies pathway that may cause seizures and shorten survival for patients with severe brain tumors

  •                      glioma cells large Researchers at the University of Alabama at Birmingham have identified a chemical pathway that may be associated with seizures and shorter patient survival in some patients with malignant glioma, the most common and deadly form of brain tumor. In findings published May 27 in Science Translational Medicine, the researchers suggest that a transporter known as SXC is responsible for boosting levels of glutamate in the brains of some glioma patients.
    cell1System x­c-(SXC) expression in human glioma cells growing in vitro. The catalytic subunitof SXC, SLC7A11/xCT (green) is highly expressed in approximately half of gliomas. The cell structure (red) and nuclei (blue) show the morphology of these glioma cells. Confocal image by Stephanie Robert and Ian Kimbrough.Glutamate is a vital neurotransmitter in the brain; but increased expression of glutamate can kill healthy cells surrounding a malignant tumor, giving the tumor more room for growth. Glioma-produced glutamate may also be responsible for seizures that are present in about half of all glioma patients.
    “We hypothesized that the SXC glutamate transporter, and in particular a sub-unit called SLC7A11, was responsible for this increase in glutamate,” said Harald Sontheimer, Ph.D., professor in the Department of Neurobiology and senior author of the study. “In both animal models and in human glioma cells, we found that approximately 50 percent of patient tumors had elevated SLC7A11 expression, and those tumors grew faster, killed more healthy cells, induced seizures and shortened overall survival than did tumors lacking this transporter.”
    cell2Human astrocytes expressing glial fibrillary acidic protein (GFAP, blue) and their nuclei (orange) in the brain of a patient suffering from seizures. Confocal image by Stephanie Robert and Ian Kimbrough. Analysis of human glioma tissue showed that 54 percent of glioma patients had elevated tumor SLC7A11 expression, whereas the remaining 46 percent had lower expression, comparable to controls. Gliomas with elevated SLC7A11 corresponded well with the incidence of tumor-associated seizures reported in the glioma patient population. The findings also showed that lack of SLC7A11 expression conferred an improved clinical outcome for patients, who lived nine months longer on average.
    “These findings suggest that SXC is the major pathway for glutamate release from gliomas and that SLC7A11 expression predicts accelerated growth and seizures,” said Stephanie M. Robert, a graduate trainee in the M.D/Ph.D. program in Sontheimer’s laboratory and first author of the paper.
    The team had previously discovered that an FDA-approved drug for ulcerative colitis and inflammatory bowel disease called sulfasalazine can inhibit glutamate release via SLC7A11. The researchers then conducted a clinical pilot trial with nine glioma patients. Using magnetic resonance spectroscopy, glutamate levels were measured before and after patients took an oral dose of sulfasalazine.
    cell3Spectral image of human glioma cells expressing enhanced green fluorescent protein (EGFP, green) growing intracranially in a mouse. Confocal image by Ian Kimbrough.“In the nine glioma patients with biopsy-confirmed expression of SXC, we found that the presence of SXC positively correlates with glutamate release, which is acutely inhibited with oral sulfasalazine,” said Sontheimer, who is also the director of the UAB Center for Glial Biology in Medicine.
    While the study findings suggest that reducing glutamate levels in patients with elevated expression of SXC would be beneficial in controlling seizures and slowing tumor growth, sulfasalazine is an imperfect drug for that role.
    “Sulfasalazine is approved as an oral medication, and most of each dose is absorbed in the gut. Perhaps as little as 20 percent makes it to the brain,” Sontheimer said. “It also has a very short biological half-life and quickly loses its effectiveness. More specific SXC inhibitors with improved specificity and bioavailability are under development and may soon enter clinical trials.”
    Also of potential clinical relevance is the finding that magnetic resonance spectroscopy may serve as a tool to determine whether a patient has elevated tumor SLC7A11 expression.
    cell4Human glioma cells (green) expressing enhanced green fluorescent protein (EGFP) migrating away from the tumor mass (bottom left of image) along the vasculature of the brain.Image acquired in a live mouse using two-photon microscopy. In vivo two-photon image by Ian Kimbrough. “Future studies will be needed to examine whether SXC-mediated glutamate release measured by magnetic resonance spectroscopy may serve as a sensitive, noninvasive clinical marker to identify those patients who will experience more rapid disease progression and seizure complications,” Robert said. “This screening could also help identify patients who may benefit from therapies that target SXC inhibition.”
    The wide-ranging study benefited from diverse UAB expertise in several fields. UAB’s neuro-oncology program, led by co-author Louis B. Nabors, M.D., professor in the Department of Neurology, was instrumental in conducting the clinical studies. Co-author Adrienne C. Lahti, M.D., professor in the Department of Psychiatry and Behavioral Neurobiology, brought expertise in magnetic resonance imaging from studies she is doing examining the association of glutamate with anti-psychotic drugs.

Other co-authors are:

Susan C. Buckingham, Ph.D., Susan L. Campbell, Ph.D., Stefanie Robel, Ph.D., Kenneth T. Holt, Toyin Ogunrinu-Babarinde, UAB Center for Glial Biology in Medicine; Paula Province Warren, UAB Division of Neuro-oncology; David M. White, Meredith A. Reid, Ph.D., UAB Department of Psychiatry and Behavioral Neurobiology; and Jenny M. Eschbacher, M.D., and Michael E. Berens, Ph.D., Cancer and Cell Biology Division, the Translational Genomics Research Institute, Phoenix, Ariz.

By: Bob Shephard
UAB Media Relations