Current Understanding and Treatment Options
for Niemann-Pick Disease Type C
April, 2007
The Hide & Seek Foundation for Lysosomal Disease Research
4123 Lankershim Boulevard
N. Hollywood CA 91602-2828
Tel: 818-762-8621• Fax: 818-762-2502
Info@hideandseek.org
www.hideandseek.org
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What we currently know about Niemann-Pick C disease

Niemann-Pick type C disease (NPC) is a neurovisceral lipid storage disorder originally
grouped with Niemann-Pick types A and B (NPA and NPB) in 1958 on the basis of
clinical symptoms and biochemical features. In 1966, Niemann-Pick types A and B
were identified as inherited deficiencies of lysosomal acid sphingomyelinase. The
biochemical and molecular bases of NPC disease remained uncertain for many years
since variable impairment of acid sphingomyelinase was found in different tissues.

The discovery of defects in esterification of cholesterol in fibroblasts from NPC
patients by Pentchev and colleagues in the early 1980’s and the power of this
observation as a diagnostic tool led to the view that NPC disease was primarily a
cholesterol storage disease, further differentiating NPC from NPA and B in which
sphingomyelin was the primary storage material.

In addition to storage of unesterified cholesterol, NPC was also documented to exhibit
massive storage of another class of compounds known as glycosphingolipids (GSLs),
including gangliosides.

Neurons in NPC are known to accumulate cholesterol and GSLs over long periods of
time with some cell types appearing more vulnerable than others. Cerebellar Purkinje
cells are particularly sensitive to the disease and die early in most cases of NPC disease
leading to motor system abnormalities. Other brain lesions include microglial
activation and related inflammatory events, ectopic dendritogenesis, axonal spheroid
formation, and neurofibrillary tangle formation. The latter feature is also a hallmark of
Alzheimer’s disease, and why this occurs in NPC and other secondary tauopathies is
unknown.

In 1997 the defective gene and protein responsible for the majority (~95%) of cases of
NPC disease was identified. Named NPC1, the protein consists of 1278 amino acids
and exhibits 13-16 membrane spanning domains. NPC1 shows high homology with
Patched, a critical element in sonic hedgehog signaling pathway, as well as with
proteins involved in cholesterol homeostasis, including 3-hydroxy-3-methylglutaryl
coenzyme A (HMG-CoA) reductase and with SCAP, the sterol regulatory elementbinding protein (SREBP)-cleavage-activating protein (SCAP). NPC1 was believed
localized to membranes of vesicles known as late endosomes.

It was subsequently discovered that defects in another protein (NPC2) are responsible
for the remaining 5% of cases of NPC disease. NPC2 is a 151 amino acid soluble
protein of late endosomes and lysosomes that has been shown to bind unesterified
cholesterol. Deficiencies of NPC1 and NPC2 proteins appear to cause essentially
identical diseases in both humans and in mouse models of NPC disease.

Both NPC1 and NPC2 genes are highly conserved in evolution and are found, for
example, in the simplest of eukaryotic organisms, yeast. For NPC1, a homologous gene
may also exist in prokaryotic organisms (bacteria), further emphasizing its role in a
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critically important “housekeeping” function in the cell. Numerous experimental
models of NPC1 deficiency exist or are being developed, including in yeast, nematodes,
fruit flies, mice and cats. The larger mammalian models are particularly advantageous
in terms of more accurately replicating the human disease and offering a means to test
therapeutic efficacy.
The state of current research

The major sources of funding for NPC research are the National Institutes of Health
(NIH) and the Ara Parseghian Medical Research Foundation (APMRF). The National
Niemann-Pick Disease Foundation (NNPDF) and a few family-based foundations also
make smaller grants for NPC research. In 2006, total direct cost of funding provided by
the NIH, APMRF and others was between $3,500,000 and $4,000,000.

Basic science research today is focusing on:
o Molecular modeling and function of the NPC1 and NPC2 proteins;
o Mechanisms by which NPC1 and NPC2 proteins may interact;
o Specific impact of NPC1/NPC2 deficiencies on neuron viability;
o The relationship between the two major storage products in NPC disease –
cholesterol and glycosphingolipids relative to the function of NPC1 and NPC2
proteins;
o Developing additional models of NP-C in simple organisms (yeast, fly, flat
worm) and in mice where detailed knowledge of the defect can be gained
through genetic modulation.

Translational research oriented toward developing treatments for NPC is focusing on:
o Delineating mechanisms whereby single injections of allopregnanolone in early
life can double longevity in the NPC1 mouse;
o Determining means to stimulate cells to overcome their NPC1/NPC2 deficiency
by altered intracellular trafficking;
o Determining whether anti-inflammatory, anti-apoptotic, or anti-oxidative agents
can be significantly neuroprotective;
o Developing vectors for gene replacement therapy;
o High throughput screening of drugs that can alter the NPC disease cellular
phenotype;
o Determining the synergistic nature of combination therapies using mouse
models;
o Determining authentic biomarkers for disease progression in large animal
models and patients;

A longitudinal observational study was initiated at the National institutes of health in
2006. This clinical protocol is designed to evaluate clinical and biochemical markers of
of Niemann-Pick disease, type C. The goal of this protocol is to identify potential
outcome measures that could be used in a subsequent clinical trial. Serum, cerebral
spinal fluid, and urine specimens are being collected for analysis. Clinical evaluation
includes audiologic (including auditory brainstem responses), psychological, and
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neurological evaluation. Magnetic resonance spectroscopy and diffusion tensor
imaging are being preformed on a 3 Tesla instrument. Seventeen patients have been
enrolled into this observational study.
Current research efforts are directed at (1) understanding the biology of the NPC1 and NPC2
proteins, and (2) translating basic research into new therapies for NPC disease. While treatment
options at present are limited to substrate reduction therapy (i.e. miglustat), which reduces
glycosphingolipids (GSL) synthesis, a number of emerging therapies are being examined in
animal models of NPC disease.
Current treatment strategies
The current state of treatment options for NPC disease is presented below. Therapeutic
approaches are classified as Available (in clinical use), Emerging (less than three years from
clinical evaluation) or Developing (greater than three years from clinical evaluation).
Available treatment options:

Substrate Reduction Therapy (SRT). This treatment concept centers on the use of
inhibitors of GSL synthesis to slow the accumulation of materials in brain cells.
Similar to the use of so-called statin drugs to reduce high cholesterol, the rationale is
that reducing the synthesis of one of the major classes on storage compounds in brain
cells (in this case GSLs, or more specifically, gangliosides) might allow these cells to
function normally for a longer period of time (and thereby delay onset of clinical
disease). One such compound is miglustat, which is marketed by Actelion as Zavesca;
Genzyme is in Stage 2 development of a similar compound. Miglustat has been
approved for use in two other lysosomal storage diseases, Gaucher disease and Fabry
disease. It has shown modest benefits in some patients with advanced Niemann-Pick C
in a clinical trial now underway. Recent studies in NPC mice have also shown
significant synergy in terms of survival when miglustat was combined with early
treatment of allopregnanolone, a naturally-occurring brain steroid (described below).
Emerging treatment options:

Byproduct Replacement Therapy (BRT). This treatment approach emerged from
research over the past several years that has indicated (1) the brains of NPC mice are
deficient in the naturally-occurring brain steroid known as allopregnanolone, and (2)
injection of this compound in the early postnatal period has the ability to limit
lysosomal storage and thus prolong survival. It is not known if such neurosteroid
deficiencies are present in feline or human NPC. While the mechanism by which
allopregnanolone works is not fully understood, recent findings suggest a critical role
for its ability to act as a activator for the nuclear receptor known as the pregnane X
receptor (PXR) and thereby exert control over numerous genes, possibly including
those controlling cholesterol availability in cells. If these studies are borne out,
consideration should be given to testing existing drugs that cross into the CNS and have
been documented to activate nuclear receptors like PXR. Candidate compounds include
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ganaxolone (a synthetic variant of allopregnanolone available through Marinus
Pharmaceuticals), T0901317, DHEA, dexamethasone, hyperforin (an ingredient of St
John’s Wort), and a host of related compounds.

Anti-inflammatory Agents. The use of aspirin or NSAIDs (nonsteroidal antiinflammatory drugs), or other more potent anti-inflammatory drugs may be useful to
diminish inflammation in brain and other organs and thereby reduce early cell death,
including neuronal cell death. Such treatment would not be expected to stop the
underlying disease process, but might, as described above, be useful to ameliorate
disease progression in combination with other treatment approaches. This approach has
shown survival benefit in a mouse model of Sandhoff disease, another
neurodegenerative lysosomal disease.

Anti-oxidant Agents have been given by parents to a number of NPC patients. These
include Chinese herbs, CoQ10, DMSO and other supplements. DMSO was included
amongst agents in the first randomized clinical trial in NPC, and has no apparent effect
clinically or on cholesterol levels in the liver. An unpublished study of vitamin E in the
NPC mouse (Pentchev and Patterson) beginning in utero showed no benefit. It is not
known whether antioxidant therapy could slow the progression of NPC, but it has been
shown to provide some level of protection in the mouse model of Sandhoff disease.
Developing treatment options:

Rab Protein Therapy. Rab proteins (technically known as small GTPases) regulate
movement of cargo within cells. Increased levels of Rab proteins known as Rab 9 and
Rab 7 in NPC cells in culture have been shown to correct the cellular phenotype,
including clearance of accumulated cholesterol from the endosomal-lysosomal system.
Ongoing studies examining genetic means to increase the levels of Rab proteins in mice
have produced modestly promising but inconclusive results. The hope is that correcting
membrane traffic in NPC cells by modulating the levels of Rab proteins will make it
possible to bypass the deleterious effects of the defective NPC protein in humans. Two
researchers are investigating this approach, with at least one of them utilizing high
throughput screening to identify potential pharmacological compounds that could
influence Rab levels.

Cell-mediated Therapies. These approaches, which include stem cell and bone marrow
transplantation (BMT) therapy, have also been tested in multiple lysosomal disorders.
BMT has proven remarkably effective in ameliorating storage, even in the brain, in a
small number of lysosomal diseases (e.g., one known as alpha-mannosidosis). A critical
aspect of this therapy is known as cross-correction, whereby normal cells can
metabolically correct diseased cells by passing the missing protein to them. However,
NPC1, the defective protein in the most common form of NPC disease, is a nonsecreted transmembrane protein of late endosomes and it cannot be expected to be
transferred between cells. Nevertheless, while not protective by itself, it is possible that
BMT could indirectly be useful as part of a combination therapy with other approaches
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to therapy by acting to reduce inflammation. Reports of BMT and hepatic
transplantation in human NPC have shown no evidence of neurological benefit.

Anti-apoptotic Agents. Apoptosis (cell-death) takes place at a late stage of NPC and is
a very downstream disease event. There is research underway that is directed at
reversing apoptosis in NPC mice. However, there is concern that anti-apoptotic agents
might be harmful because normal programmed cell death, with which they would
conceivably interfere, is presumably important for general health. On the other hand, it
may be that an apoptotic drug, if safe, could be a useful add-on to other therapies.

Chemical Chaperone Therapy. This new treatment concept is based on the hypothesis
that many NPC mutations cause disease because the mutant protein is unable to mature
from the endoplasmic reticulum and is thus unable to be targeted to the late endosome.
Pharmacologically relevant chemical chaperones have shown great promise recently in
enhancing mutant protein maturation in other genetic diseases and thus partially
rescuing protein function. A few small molecule chaperones have already been
identified, which represents a critical step towards developing an actual drug that
literally chaperones proteins to their appropriate target, thereby potentially correcting
the NPC disease phenotype.

Gene Therapy. The possible use of gene therapy for treatment of lysosomal disorders is
under intensive investigation for some lysosomal disorders, although there are
significant central nervous system (CNS)-delivery and safety issues to be resolved.
Furthermore, the problem of NPC1 as a non-secreted transmembrane protein remains.
Thus, widespread cell transduction would be necessary because neurons and other cells
throughout the brain will need to receive the gene in order to be rescued, a difficult
outcome to achieve without innovative advances in gene delivery technology.

Cholesterol-Lowering Drugs. The discovery that cholesterol accumulated in NPC cells
was once believed to suggest that cholesterol-lowering agents might be therapeutic.
However, cholesterol in the brain is nearly all synthesized in the CNS, thus, lowering
cholesterol elsewhere in the body would probably have little effect on cholesterol in
neurons. More important, there is emerging evidence that points to cholesterol
accumulation in NPC-affected cells as a cause of deficiency of certain byproducts of
cholesterol metabolism, like allopregnanolone (see above). The first randomized
clinical trial in NPC examined the effects of cholesterol-lowering strategies in NPC.
Although unesterified cholesterol (i.e. cholesterol not attached to fatty acids) was
substantially reduced in the liver by combination therapy, subsequent follow up showed
no evidence of clinical benefit
There is widespread consensus in the lysosomal disease field that the next few years will see an
emphasis of combination therapies in the treatment of these disorders. For NPC disease, while
no single therapy on its own may be corrective, combining treatment approaches could be
beneficial. For example, treatment in the mouse model of NPC disease that combines
miglustat therapy with allopregnanolone, a naturally-occurring brain steroid (see BRT above),
extends life span by 2.5 times, the longest reported for this model to date.
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Some of the major questions about NPC disease that remain unanswered:
Basic science issues –
 What are the exact function(s) of NPC1 and NPC2 proteins?
 Do these two proteins function together as part of a single mechanism?
 What is the relationship between the function of these proteins and the accumulation of
unesterified cholesterol and GSLs?
 What are the key pathological steps set in motion by absence of NPC proteins?
 Why are some neurons highly vulnerable to NPC1/NPC2 deficiency, whereas others
are not?
 How does allopregnanolone extend lifespan of NPC mice? Is the action through PXR
or related nuclear receptors?
 Are allopregnanolone and other neurosteroids deficient in feline and human NPC, or is
this deficiency unique to NPC mice?
 Given the marked phenotypic variability seen amongst individuals in multiplex NPC
kindreds, what epigenetic factors or modifier genes interact with NPC1 and NPC2?
Translational science issues –
 What are the relative roles of overabundance of storage compounds or deficiency of
sequestered compounds and/or their byproducts in producing brain disease in NPC?
 What disease markers correlate with the clinical phenotype and could be used to follow
disease progression in clinical trials and permit accurate prognostication?
 How can NPC be identified early? The current diagnostic tests are cumbersome, and
can only be performed in a few laboratories.
 How do drugs like miglustat effect gene expression? Could a molecular genetic
analysis provide such information?
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