You might be wondering, what does a time bomb have to do
with all the above conditions. The
answer is a substance in the human body called PAK1. PAK1 appears to have no useful bodily function,
after birth, but it appears to be behind very many dysfunctions in the
body. One scientist suggested that it is
there to ensure that we do not live forever.
PAK1 is at the centre of a very expensive effort to
develop effective cancer drugs; since the majority of cancers, for males or
females, involve PAK1. If you can block
or inhibit PAK1, you can stop tumour growth in many types of cancer. It turns out that PAK1 is also involved in
Alzheimer’s, Huntington's Disease, Neurofibromatosis, Autism, Schizophrenia, Fragile X and Shank
3.
Cancer drugs are big business and budgets seem to be
almost limitless. The good thing is that
as long as the PAK1 inhibitor can cross the blood brain barrier (BBB), what
works for cancer, is likely to have an effect in all the mentioned brain
conditions, including autism.
What is odd, is that in the rare condition of Neurofibromatosis Type 1, which in mild cases
might be considered autism with spots, families with the condition are widely
aware of PAK1 and are not waiting for drugs to be commercialized. They are using naturally available PAK
inhibitors, like a particular kind of Propolis from New Zealand. It seems that NF-1, along with PANDAS and
PANS, is thought of as a disease to be treated, whereas the much more common,
autism, still is not. Odd isn’t it?
Many
of the researchers looking at PAK are Japanese and this in itself is
interesting. Japanese medicine, like
Russian medicine, is a world of its own; indeed Russian researchers are also
heavily involved in PAK research. So
many clever minds are engaged in this effort.
There
are as yet no commercially available PAK1 drugs, but there are many experimental
ones.
One
problem I have observed is that there are three very similar types of PAK - PAK1,
PAK2 and PAK3. The new drugs seem to
inhibit all the three, to greater or lesser extents. The problem I have seen is that PAK2 is
actually good for you. Blocking PAK1 and
PAK2 in mice might work wonders, but in humans this might not be true. It appears we need PAK1-specific drugs, that
do not affect PAK2.
PAK Research in Detail
Since even
Wikipedia does not cover the science of PAK in any depth, neither will I. I have found an excellent collection of research
from 2013 that will tell the scientists among you, everything there is to
know. It is available as book or
electronically, if you look on google for a minute or two you may find a
free ebook version.
It is very
readable and if you are interested in cancer or Alzheimer’s it should also be
of interest.
In my post I
will just look at the treatment possibilities and research that shows it should
be effective.
I will look
at a wide range of conditions related to autism, namely:-
- Schizophrenia (adult-onset autism)
- Neurofibromatosis Type 1 (autism with spots)
- Fragile
X (autism with low muscle tone and MR)
- Shank
3
- Mental
Retardation (MR)
Mast cells
will also make another guest appearance.
I have
already suggested in early posts that following rare genetic conditions may not
lead us anywhere in our search for effective autism therapies; however, when you have three of them, plus
schizophrenia, then we have to take note.
As a bonus we have another Nobel Laureate, this time Susumu Tonegawa from MIT.
He works at MIT’s Picower Center for Learning and Memory, along with Mike
Bear, who we have previously covered in relation to both Arbaclofen and
mGluR5. Tonegawa suffered his own
tragedy when his teenage son committed suicide in his dorm room at MIT.
p21 activated kinases (PAKs) and PAK inhibitors
PAKs are not somethings you are likely to heard of, even
the ever up to date Wikipedia has virtually nothing to say on the subject; I
guess we must be at the cutting edge.
PAKs are a family of enzymes in the body. They are implicated in many biological
processes, one of which is cancer. The
chemicals that reduce the activity of these enzymes are called PAK inhibitors
We are interested in Group 1 PAKs that is to say PAK1,
PAK2 and PAK3; in particular we want to find PAK1 inhibitors.
To date a lot of money has been spent looking for drugs
that are effective PAK inhibitors, but also safe for humans
The Role of PAK1
in Brain Dysfunction
PAK1 appears to play a central role in lost brain cell
function in Schizophrenia, Fragile X, Shank 3
and Neurofibromatosis Type 1 (NF-1). Different scientists are involved in these
different areas and their explanation of what is going on does vary. But in effect they all found (in their mouse
models) that by inhibiting PAK, they could restore lost brain function.
There is now
a research drug called FRAX486 that looks particularly effective and this is
the drug used in the trials I will detail later.
The problem
is that research drugs take decades to become approved human drugs and I do not
want to wait decades. So the choice is
either to use the research drug or find another PAK-inhibitor. I opt for the latter.
Note on Mast
Cells
Regular readers will have noticed how I believe mast
cells play a surprisingly important role in autism. Here is a link and a summary from a paper
showing how PAK2 plays a role in stabilizing mast cells, whereas PAK1 plays an
opposing role in making them degranulate.
When this happens histamines, IL-6 and other inflammatory agents are
released. So PAK2 does some good.
The Research
Studies
Susumu Tonegawa at MIT is one of the
clever scientists pursuing PAK inhibitors;
he is looking at Fragile-X and now, it appears autism. I think he is the clear expert in this field.
Having established its role in many
cancers, next came its role NF-1,
Shank-3, Fragile-X and most recently schizophrenia. Since schizophrenia is very common and
clearly overlaps mainstream autism, we will start there.
"A new study shows that one of a class of compounds known
as PAK inhibitors, appears to have reversed behaviors associated with
schizophrenia and restored some lost brain cell function in adolescent mice
with a rodent version of the mental illness. The researchers at Johns
Hopkins found that the compound FRAX486 appears to halt an out-of-control
biological “pruning” process in the schizophrenic brain during which important
neural connections are unnecessarily destroyed."
Moreover, this PAK
inhibitor—which we call FRAX486—also rescues seizures and behavioral
abnormalities such as hyperactivity and repetitive movements, thereby
supporting the hypothesis that a drug treatment that reverses the spine
abnormalities can also treat neurological and behavioral symptoms. Finally, a single administration
of FRAX486 is sufficient to rescue all of these phenotypes in adult Fmr1 KO mice, demonstrating the
potential for rapid, postdiagnostic therapy in adults with FXS.
Significance
Drug discovery in psychiatry has been limited to chemical
modifications of compounds originally discovered serendipitously. Therefore,
more mechanism-oriented strategies of drug discovery for mental disorders are
awaited. Schizophrenia is a devastating mental disorder with synaptic
disconnectivity involved in its pathophysiology. In this study, we studied a
biological pathway underlying synaptic disturbance and examined whether
p21-activated kinase inhibitors ameliorate the pathology in vitro and in vivo. The beneficial effects of
these inhibitors reported here may provide us with an opportunity for drug
discovery in major mental illnesses with synaptic disturbance.
Abstract
Drug discovery
in psychiatry has been limited to chemical modifications of compounds
originally discovered serendipitously. Therefore, more mechanism-oriented
strategies of drug discovery for mental disorders are awaited. Schizophrenia is
a devastating mental disorder with synaptic disconnectivity involved in its
pathophysiology. Reduction in the dendritic spine density is a major alteration
that has been reproducibly reported in the cerebral cortex of patients with
schizophrenia. Disrupted-in-Schizophrenia-1 (DISC1), a factor that influences
endophenotypes underlying schizophrenia and several other neuropsychiatric
disorders, has a regulatory role in the postsynaptic density in association
with the NMDA-type glutamate receptor, Kalirin-7, and Rac1. Prolonged knockdown
of DISC1 leads to synaptic deterioration, reminiscent of the synaptic pathology
of schizophrenia. Thus, we tested the effects of novel inhibitors to
p21-activated kinases (PAKs), major targets of Rac1, on synaptic deterioration
elicited by knockdown expression of DISC1. These compounds not only significantly ameliorated the
synaptic deterioration triggered by DISC1 knockdown but also partially reversed
the size of deteriorated synapses in culture. One of these PAK inhibitors
prevented progressive synaptic deterioration in adolescence as shown by in vivo
two-photon imaging and ameliorated a behavioral deficit in prepulse inhibition
in adulthood in a DISC1 knockdown mouse model. The efficacy of PAK inhibitors
may have implications in drug discovery for schizophrenia and related
neuropsychiatric disorders in general.
There are many other neuropsychiatric disorders with
synaptic changes that might benefit from these compounds. The Tonegawa
laboratory previously published that PAK inhibition and knockout are protective
against synaptic deterioration in an animal model for Fragile X syndrome (38, 39). In addition, several lines of
evidence have suggested the involvement of PAKs in Alzheimer’s disease and mental
retardation (40⇓⇓–43). Studies that aim to identify rare variants associated
with neuropsychiatric disorders may further reveal PAK family genes as genetic
factors. Thus, consideration of these compounds in many other neuropsychiatric
disorders may also be an important subject in future studies.
As far as we are
aware, PAKs are regarded as therapeutic targets in cancer and immune/allergy-related
conditions. Although this
question requires careful consideration, we expect minimal adverse effects of PAK inhibitors when
we target neuropsychiatric disorders.
This is an
interesting patent that was granted on the basis of using PAK1 inhibitors to
treat social
learning disorders
Abstract
The use of Pak1 inhibitors to treat social or learning
disabilities is disclosed. In one embodiment patients exhibiting social or
learning disabilities as well as abnormally low NF1 activity are administered
PAK inhibitors to treat the social or learning disabilities. Reductions in PAK
activity have been found to ameliorate the effects of aberrant
neurofibromatosis type 1 activity.
Applicants
have demonstrated that defects in NF1 gene leads to deficiencies in learning
including for example, deficiencies in social learning. The NF1 gene encodes neurofibromin,
which negatively regulates Ras GTPase activation, and thereby reduces the
strength and duration of Ras signal transduction. P21-activated kinase (Pak1)
is a downstream effector regulated by the Rho family of GTPases that mediate diverse
cellular functions including cytoskeletal dynamics, vesicular transport, and
gene expression.
Applicants have discovered that the deficit in social learning associated
with Nf1+/− mice is rescued by deletion of the Pak1 gene. Accordingly, applicants anticipate that
patients having defective NF1 activity can be treated with PAK inhibitors
(e.g., a Pak1 inhibitor) to treat learning disabilities and other symptoms or
conditions resulting from deficient Nf1 activity. In accordance with one
embodiment a method for treating an NF1 deficiency (i.e., decreased NF1 gene
expression, decreased NF1 protein product, or decreases functionality of the
NF1 protein product relative to the native NF1 gene product) associated
learning disability is provided. In one embodiment the method comprises the
steps of identifying a patient with defective NF1 activity and administering to
said patient a pharmaceutical composition comprising an effective amount of a
PAK inhibitor
Neurofibromatosis
In case you
do not know, neurofibromatosis
(NF1) is one of the most common single gene disorders. It is associated with skin conditions of widely
varying magnitude, but surprisingly many autistic-like neurobehavioral developmental disorders are present. It seems that NF1 is highly comorbid with
autism and ADHD. A recent survey showed
half of parents reported autistic behaviours, far higher than the literature
had suggested. Since only 20% of cases
have physical complications, it would seem highly likely that many cases are
misdiagnosed as autism.
Neurofibromatosis
is considered a treatable medical condition, even in countries that do not
regard autism as treatable. In the
United Kingdom there are two clinical centres for the condition, and in Germany
it seems that Hamburg is the clinical centre of excellence.
Mental Retardation (MR)
I have
already mentioned in previous posts that some types of mental retardation may
indeed by treatable, this was based on my observation that certain drugs can
produce cognitive improvement in autism.
So it was a
nice surprise to find in the literature that PAK3 has been shown to be involved
in some types of MR. That would imply
PAK3 inhibitors might have some effect on MR.
Since MR is
highly comorbid with autism, perhaps PAK3 is also involved in autism.
Importance of the field
P21-activated kinases (PAKs) are involved in
multiple signal transduction pathways in mammalian cells. PAKs, and PAK1 in particular, play a role
in such disorders as cancer, mental retardation and allergy. Cell
motility, survival and proliferation, the organization and function of
cytoskeleton and extracellular matrix, transcription and translation are among
the processes affected by PAK1.
8. PAK1 in neurological
and mental disorders
PAK3 in clearly involved in some
neurodegenerative disorders and variants of mental retardation and plays a
special role in synapse formation and plasticity in hippocampus. However, the
involvement of PAK1 in these processes is less clear-cut. For example, both
PAK1 and PAK3 were reduced in the hippocampus affected by Alzheimer disease,
yet only PAK3 was affected in some other areas of the diseased brain. However,
this reported loss of the PAKs from the cytosol appears to be accompanied by
re-localization of PAKs to the membrano-cytoskeletal fractions, where they
appear to be active. Using staining for drebnin and reduction in dendrites as
indicators, Dr. Cole’s group has observed that a dominant-negative form of PAK1
sensitizes, while the wild type form protects from some effects of beta-amyloid
oligomers in cultured primary neurons. However, in both cases it is hard to
rule out that ectopically expressed PAK1 in some of these experiments acted as
a surrogate for the highly homologous PAK3.
Dominant-negative PAK1, which, potentially,
inhibits other PAK isoforms as well, upon expression in mouse forebrain
affected synapse morphology and consolidation of long-term memory, but rescued
some defects of a mouse model of Fragile X syndrome.
In case of Huntington’s disease, PAK1
specifically co-localizes with huntingtin inclusions in the affected brain146.
In tissue culture models, interference with PAK1 function modestly decrease the
formation of aggregates by mutant huntingtin, while the constitutively active
PAK1 enhances the aggregation. Accordingly, similar activity was reported for
PAK1 regulator α-PIX. The matter is complicated, however, by the observation
that kinase activity of PAK1 is dispensable for this phenomenon. Overall, it
appears that pathological changes in the brain could be associated both with
elevated and reduced function of PAKs and the specific role of PAK1 in these
processes may be variable as well.
Group I p21-activated kinases are a
family of key effectors of Rac1 and Cdc42 and they regulate many aspects of
cellular function, such as cytoskeleton dynamics, cell movement and cell
migration, cell proliferation and differentiation, and gene expression. The
three genes PAK1/2/3 are expressed in brain and recent evidence indicates their
crucial roles in neuronal cell fate, in axonal guidance and neuronal
polarisation, and in neuronal migration. Moreover they are implicated in
neurodegenerative diseases and play an important role in synaptic plasticity, with PAK3 being specifically
involved in mental retardation. The main goal of this review is to
describe the molecular mechanisms that govern the different functions of group
I PAK in neuronal signalling and to discuss the specific functions of each
isoform.
SHANK-3
The SHANK3 gene is a member of the Shank gene
family. Shank proteins are multidomain scaffold proteins of the postsynaptic
density that connect neurotransmitter receptors, ion channels, and other
membrane proteins to the actin cytoskeleton and G-protein-coupled signaling
pathways. Mutations of the SHANK3 gene
are known to be associated with autism.
It is complex, but it appears that the
reducing effect of Shank3 knockdown on NMDARs and F-actin is blocked by PAK1
inhibitors
Shank3, which encodes a scaffolding protein at
glutamatergic synapses, is a genetic risk factor for autism. In this study, we
examined the impact of Shank3 deficiency on the NMDA-type glutamate receptor, a
key player in cognition and mental illnesses. We found that knockdown of Shank3
with a small interfering RNA (siRNA) caused a significant reduction of
NMDAR-mediated ionic or synaptic current, as well as the surface expression of
NR1 subunits, in rat cortical cultures. The effect of Shank3 siRNA on NMDAR
currents was blocked by an actin stabilizer, and was occluded by an actin
destabilizer, suggesting the involvement of actin cytoskeleton. Since actin
dynamics is regulated by the GTPase Rac1 and downstream effector p21-activated
kinase (PAK), we further examined Shank3 regulation of NMDARs when Rac1 or PAK
was manipulated. We found that the reducing effect of Shank3 siRNA on NMDAR currents
was mimicked and occluded by specific inhibitors for Rac1 or PAK, and was
blocked by constitutively active Rac1 or PAK. Immuno cytochemical data showed a
strong reduction of F-actin clusters after Shank3 knockdown, which was occluded
by a PAK inhibitor. Inhibiting cofilin, the primary downstream target of PAK
and a major actin depolymerizing factor, prevented Shank3 siRNA from reducing
NMDAR currents and F-actin clusters. Together, these results suggest that Shank3 deficiency induces NMDAR hypofunction
by interfering with the Rac1/PAK/cofilin/actin signaling, leading to the loss
of NMDARmembrane delivery or stability. It provides a potential mechanism for
the role of Shank3 in cognitive deficit in autism.
PAK, p21-activated kinase, is the key downstream effector of
Rac1, which stimulates spine synapse formation and neurite outgrowth by
facilitating actin filament assembly. Different mutations in the PAK genes have
been identified in mental retardation cases. Mice expressing a
forebrain-specific dominantnegative form of PAK show fewer dendritic spines,
altered spine morphology, and changes in synaptic strength. Shank proteins have been shown to form a
complex with PAK and overexpression of Shank in cultured neurons promotes
synaptic accumulation of PAK. Consistently, we have found that Shank3 knockdown leads to reduced PAK1
activity. Moreover, inhibiting PAK1 decreases the basal NMDAR current, and the
reducing effect of Shank3 knockdown on NMDARs and F-actin is occluded by PAK1
inhibitors and blocked by constitutively active PAK1. These data suggest that
Rac1/PAK1- mediated actin dynamics is important for NMDAR membrane
delivery/maintenance and its regulation by Shank3.
Mast
Cells
Mast cells
are the cells that react will allergens and lead to the release of histamine
and many other inflammatory agents like the cytokine IL-6. It is shown that PAK1 plays a key role in
mast cell degranulation and could therefore play a key role in treating
allergies and asthma.
Abstract
Mast
cells coordinate allergy and allergic asthma and are crucial cellular targets
in therapeutic approaches to inflammatory disease. Allergens cross-link
immunoglobulin E bound at high-affinity receptors on the mast cell's surface,
causing release of preformed cytoplasmic granules containing inflammatory
molecules, including histamine, a principal effector of fatal septic
shock. Both p21 activated kinase 1 (Pak1) and protein phosphatase 2A (PP2A)
modulate mast cell degranulation, but the molecular mechanisms underpinning
these observations and their potential interactions in common or disparate
pathways are unknown. In this study, we use genetic and other approaches to
show that Pak1's kinase-dependent interaction with PP2A potentiates PP2A's
subunit assembly and activation. PP2A then dephosphorylates threonine 567 of
Ezrin/Radixin/Moesin (ERM) molecules that have been shown to couple F-actin to
the plasma membrane in other cell systems. In our study, the activity of this
Pak1-PP2A-ERM axis correlates with impaired systemic histamine release in
Pak1(-/-) mice and defective F-actin rearrangement and impaired degranulation
in Ezrin disrupted (Mx1Cre(+)Ezrin(flox/flox)) primary mast cells. This heretofore unknown
mechanism of mast cell degranulation provides novel therapeutic targets in
allergy and asthma and may inform studies of kinase regulation of
cytoskeletal dynamics in other cell lineages.
Where to find your PAK-inhibitor?
In the literature you will find that there are various
different PAK inhibitors
Not
surprising if you want to want to inhibit PAK1, PAK2 and PAK3, then FRAX486 is
a good choice.
But where do
you get FRAX486 from?
Susumu Tonegawa, Afraxis
and Roche
It looks
like in about 2007 Tonegawa has created a start-up company called Afraxis to
develop FRAX 486. Having done further
research and raised some venture capital they licensed their drug portfolio to
the drug major, Roche, in 2013.
I hope this works out better for
Tonegawa that Roche’s deal with his MIT colleague Mark Bear who also linked up
his start-up Seaside Therapeutics with Roche.
That one did not end so well.
Avalon Ventures’ Afraxis Licenses Entire Drug
Portfolio to Genentech
Roche’s Genentech has
licensed global rights to develop and commercialise Afraxis’ entire portfolio
of CNS compounds in a deal worth up to US$187.5 M. Afraxis’ lead programme
targets PAK (p21-activated kinase) and has initially been focused on
developing disease-modifying therapies for Fragile X syndrome, the most common
inherited cause of mental retardation. Although not a sale, the deal will still
provide an exit for Avalon Ventures, Afraxis’ sole shareholder, and follows the
acquisition of Avalon-backed Zacharon Pharmaceuticals by BioMarin
Pharmaceutical earlier in January 2013. For Roche, the deal supplements an
already robust neuroscience pipeline.
Any other alternatives?
Fortunately
another Japanese scientist, Hiroshi Maruta, has written a paper on all the possible PAK inhibitors
available today for humans.
If you read
his paper, he is pointing in the direction of the natural world and a special
kind of propolis rich in CAPE (caffeic acid phenethyl ester) produced by bees in New
Zealand. His fall back is an old drug
for humans and pets called ivermectin, which was found by chance to have a secondary affect as a
PAK-inhibitor.
It is a
substance, CAPE, specific to the New Zealand bees that makes their propolis act
as a PAK-inhibitor. Regular propolis
from your health food store is most likely made by the wrong type of bees.
So if you do
not fancy waiting 15 years for Roche to commercialize Susumu Tonegawa’s clever discoveries from MIT which may
or may not be effective in humans, you could stick with the clever Japanese and
follow Hiroshi Maruta’s
thinking and go down under to New Zealand.
During its long isolation, New Zealand developed a
distinctive biodiversity of animal, fungal and plant life; most notable are the
large number of unique bird species and by the sound of it some pretty special
bees.
Can a bee product really be an
effective drug? I definitely start as a sceptic, but the natural flavonoid
Quercetin really does work, so why not Propolis? Propolis has been used medicinally for more
than a thousand years, but only the New Zealand one and one Brazil variety contain
PAK inhibiting compounds.
There is
also an odd saying from Germany, that "bee keepers do not get cancer". Maybe
there is something in this?
The problem with many of the other natural PAK-inhibitors
is their bioavailability. They may work
in the test tube, but the human body does not absorb them enough for them to be
effective. Curcumin, Resveratrol, Honokiol (from Magnolia bark) all appear, but unless you can
absorb them and they can cross the blood brain barrier (BBB) they will not
work.
The NF-1 and NF-2 sufferers have zeroed in on
the BIO30 Propolis as the realistic alternative. I think they made the right choice.
Conclusion
The logical
conclusion is to buy some BIO30 Propolis and give it a
try. I hope Susumu Tonegawa and Roche eventually make a commercially available
drug, but new drugs seem to take 15
years to bring to the market. The
existing drug, Ivermectin, really should be given a clinical trial in NF-1 or Fragile-X.
