Inositol pentakisphosphate inhibits Ser phosphorylation of PI3-K
soowhat...@hotmail.com
Wed Sep 14, 2005 7:04 PM ET
LONDON (Reuters) - Eating a diet rich in beans, nuts and cereals could
help to prevent cancer because the foods contain a natural compound
that inhibits the growth of tumors.
Scientists at University College London (UCL) said on Thursday that the
substance called inositol pentakisphosphate, which is also found in
lentils and peas, could also help researchers develop new therapies
against the disease.
"Our study suggests the importance of a diet enriched in foods such as
beans, nuts and cereals which could help prevent cancer," said Dr Marco
Falasca, of UCL's Sackler Institute, who reported the finding in the
journal Cancer Research.
He and his team discovered that the compound inhibits an enzyme called
phosphoinositde 3-kinase which promotes tumour growth.
Scientists have been trying to develop drugs to inhibit the
cancer-promoting enzyme but have had difficulty so far.
When the researchers tested inositol pentakisphosphate in mice and
cancer cells in the laboratory, it killed the animal tumors and
enhanced the effect of drugs used against ovarian and lung cancer
cells.
"Our work will now focus on establishing whether the phosphate
inhibitor can be developed into an anti-cancer agent for human
therapy," Falasca said in a statement.
The researchers believe the compound, which was non-toxic even at high
concentrations, could also be used to increase the effectiveness of
chemotherapy drugs.
Here is an abstract of Falasca M et al on the issue from 2004:
Oncogene. 2004 Mar 4;23(9):1754-65. Related Articles, Links
Inositol pentakisphosphate promotes apoptosis through the PI 3-K/Akt
pathway.
Piccolo E, Vignati S, Maffucci T, Innominato PF, Riley AM, Potter BV,
Pandolfi PP, Broggini M, Iacobelli S, Innocenti P, Falasca M.
Department of Medicine, The Sackler Institute, University College
London, 5, University Street, London WC1E 6JJ, UK.
Phosphoinositide 3-kinase (PI 3-K) is implicated in a wide array of
biological and pathophysiological responses, including tumorigenesis,
invasion and metastasis, therefore specific inhibitors of the kinase
may prove useful in cancer therapy. We propose that specific inositol
polyphosphates have the potential to antagonize the activation of PI
3-K pathways by competing with the binding of PtdIns(3,4,5)P3 to
pleckstrin homology (PH) domains. Here we show that Ins(1,3,4,5,6)P5
inhibits the serine phosphorylation and the kinase activity of Akt/PKB.
As a consequence of this inhibition, Ins(1,3,4,5,6)P5 induces apoptosis
in ovarian, lung and breast cancer cells. Overexpression of
constitutively active Akt protects SKBR-3 cells from
Ins(1,3,4,5,6)P5-induced apoptosis. Furthermore, Ins(1,3,4,5,6)P5
enhances the proapoptotic effect of cisplatin and etoposide in ovarian
and lung cancer cells, respectively. These results support a role for
Ins(1,3,4,5,6)P5 as a specific inhibitor of the PI 3-K/Akt signalling
pathway, that may sensitize cancer cells to the action of commonly used
anticancer drugs.
PMID: 14755253 [PubMed - indexed for MEDLINE]
soowhat...@hotmail.com
timo...@my-deja.com
I posted some abstracts a while back that InsP(6) inhibited PI3-K.
Since it fit with the hypothesis that reduced insulin signaling
promotes longevity. I was rather perplexed about all this because
nothing fit together right. If you look at the effects of wortmannin, a
PI3K inhibitor its definitely not something you would want to ingest.
However, inhibiting PI3-K since it is a cellular pro-survival pathway
would kill cancer cells. EGCG has similar effects id est, protects
normal cells and kills cancerous ones.
Kofi
timo...@my-deja.com wrote:
What's the cost here? Doesn't this approach get to the heart of what's
wrong with low IGF-I in adults? You may get "longevity," yes, in a
petri dish or under ideal conditions but real organisms suffer cartilage
degradation from low IGF-I and their neurons are less able to survive
toxic insult because they can't detoxify. IGF-I also supplies a vital
signal to recruit stem cells to damaged areas. PI3K is vital for Nrf2
induction of HO-1, thioredoxin and peroxiredoxin-I [PMID 12832036].
PI3K also lies on an important nerve growth pathway [PMIDs 12911630,
15207235]. EGCG stimulates PI3K making it cytoprotective and
antiapoptotic [PMID 15288510].
Poisoning yourself is a great idea if you've got cancer (e.g., taking
methotrexate to deplete your folate) but it doesn't necessarily seem
like such a hot idea for avoiding cancer in the first place or living
longer under realistic conditions of environmental stress. That's what
stood with to me when I heard researchers talking about eating more
beans to avoid cancer because they blocked PI3K. For one thing, the
phytates in beans can block the absorption of zinc which is bad (and
given that zinc inhibits GSK-3b, I'm assuming that it also stimulates
PI3K in which case how do the researchers know what PI3K inhibition is
due to InsP(6) in the beans or low zinc uptake)?
http://news.bbc.co.uk/1/hi/health/4247984.stm
Last Updated: Thursday, 15 September 2005, 16:09 GMT 17:09 UK
E-mail this to a friend Printable version
'Eat more beans' to stop cancer
Beans contain a potent anti-cancer compound
A diet rich in beans, nuts and cereals could be a way to prevent cancer,
believe UK researchers.
Scientists at University College London have discovered that these
everyday foods contain a potent anti-cancer compound.
This blocks a key enzyme involved in tumour growth, they told Cancer
Research journal.
The researchers say, in the future, it might be possible to mimic this
compound in an anti-cancer drug.
Our study suggests the importance of a diet enriched in foods such as
beans, nuts and cereals which could help prevent cancer
Researcher Dr Marco Falasca
Scientists have been exploring the enzyme phosphoinositide 3-kinase as a
target for cancer treatment for some time but inhibitors have been
difficult to develop because of problems with chemical stability and
toxicity.
Dr Marco Falasca and colleagues have discovered that a natural compound,
called inositol pentakisphosphate, which is found in most legumes as
well as in wheat bran and nuts, blocks the activity of the enzyme.
When they tested its action in mice with ovarian and lung cancer they
found it not only blocked tumour growth but also enhanced the effect of
other cancer-killing drugs.
In addition, it appeared to be non-toxic, unlike conventional
chemotherapy agents.
Dr Falasca said: "Our study suggests the importance of a diet enriched
in foods such as beans, nuts and cereals which could help prevent
cancer.
"Our work will now focus on establishing whether the phosphate inhibitor
can be developed into an anti-cancer agent for human therapy.
The next step is to look at whether inositol pentakisphosphate is able
to inhibit tumour growth in cancer patients
Henry Scowcroft of Cancer Research UK
"We believe that inositol pentakisphosphate is a promising anti-cancer
tool and we hope to bring it to clinical testing soon."
Henry Scowcroft of Cancer Research UK said: "It is always encouraging
when a newly discovered chemical is shown to have anti-cancer activity
in the laboratory, especially when it occurs naturally in foods like
beans and peas.
"Obviously, the next step is to look at whether inositol
pentakisphosphate is able to inhibit tumour growth in cancer patients,
in properly controlled clinical trials."
He said researchers were also looking at whether people who eat more
lentils, peas and beans are actually at lower risk of developing cancers
"What we do know already is that a diet that includes at least five
portions of fruit and vegetables a day can help to reduce the risk of
cancer."
soowhat...@hotmail.com
Here are the entire text of Introduction and the Discussion sections of
the full study which I believe may answer your questions.
Introduction
Considerable evidence indicates that phosphoinositide 3-kinase (PI 3-K)
signalling plays a central role in the development of several features
of cancer (Chang et al., 1997; Khwaja et al., 1997; Vanhaesebroeck et
al., 1997; Fruman et al., 1998; Rameh and Cantley, 1999). It has been
shown that PIK3Ca, the gene encoding the p110a catalytic subunit of PI
3-K, is present in increased copy number in several ovarian cancer cell
lines (Shayesteh et al., 1999) and an elevated PI 3-K activity has been
found in lung cancer cell lines (Moore et al., 1998). In addition, it
is well established that the tumour suppressor protein, phosphatase and
tensin homolog (PTEN), whose gene is deleted or mutated in a wide
variety of human cancers, possesses a 3-phosphoinositide-phosphatase
activity (Maehama and Dixon, 1998). The lipid products of PI 3-K act
via specific interactions with some lipid-recognition/binding domains
of which the pleckstrin homology (PH) domain is now the largest
represented (Haslam et al., 1993; Corvera and Czech, 1998; Leevers et
al., 1999). This well-recognized, multifunctional structural domain
consists of some 100-120 amino acids that share a specific tertiary
structure (Shaw, 1996; Lemmon and Ferguson, 1998, 2000). The majority
of PH domain containing proteins appear to have a functional
requirement to be membrane-associated and several studies indicate that
PH domains function as membrane adapters or tethers, linking their host
proteins to the membrane surface where the proteins are required for
their function (Lemmon et al., 1997). Indeed, many PI 3-K downstream
effectors are activated through the binding of their PH domains to
lipid products of PI 3-K on the plasma membrane and their subsequent
translocation (Falasca et al., 1998; Maffucci and Falasca, 2001). Thus,
we propose that molecules able to bind specifically to the PH domains
of downstream effectors of PI 3-K have the potential to antagonize the
activation of these proteins by inhibiting their translocation to the
plasma membrane or to any specific membrane compartment (Berrie and
Falasca, 2000).
The serine/threonine protein kinase B (PKB), also known as Akt, is one
of the best-characterized PI 3-K downstream targets (Downward, 1998). A
crucial step in the activation of Akt is its translocation to the
plasma membrane via interaction of its PH domain with
30-phosphoinositides (Franke et al., 1997a; Frech et al., 1997; Klippel
et al., 1997). Once recruited to the plasma membrane, Akt can be
phosphorylated on Thr-308 by the phosphoinositide-dependent kinase-1
(PDK-1) (Alessi et al., 1996; Banfic et al., 1998) and on Ser-473 by a
still unknown kinase. PDK-1 itself is recruited to the plasma membrane
via the interaction of its PH domain with 30-phosphorylated
phosphoinositides (Stokoe et al., 1997). Several lines of evidence
indicate that activation of Akt is both necessary and sufficient for
survival since it regulates the downstream phosphorylation of further
signalling proteins which, in turn, leads to the choice of cellular
proliferation or apoptosis (Burgering and Coffer, 1995; Franke et al.,
1997b; Kennedy et al., 1997). In particular, it has been demonstrated
that Akt promotes survival through the inactivation of caspase-9 and
the activation of the transcription factor NF-kB (Baraud et al., 1999;
Kane et al., 1999). In addition it phosphorylates different components
of the apoptotic machinery, such as BAD and forkhead transcription
factor (FKHRL 1) (Cardone et al., 1998; Brunet et al., 1999). Our
attention is focused on the mechanisms of membrane targeting mediated
by the lipid products of PI 3-K. An approach to inhibition of PI 3-K is
through the disruption of the membrane localization of its targets by
the use of their headgroup target recognition pattern, the inositol
polyphosphates (Berrie and Falasca, 2000). Indeed, as different PH
domains possess different binding affinities towards different inositol
polyphosphates, this increases the possibility of specifically
inhibiting a particular membrane- targeted protein (Kavran et al.,
1998), without interfering with other PI 3-K-mediated pathways. In
combination with our recent work (Berrie and Falasca, 2000; Razzini et
al., 2000) we propose that inositol polyphosphates can act as specific
antagonists of these functions. The goal of this study is to
investigate inositol polyphosphates as potential inhibitors of PI 3-K,
as switch-off signal molecules, by competition with the localization of
PH domain-containing proteins to the plasma membrane. Our results
indicate that Ins(1,3,4,5,6)P5 is able to inhibit Akt phosphorylation
and kinase activity, leading to an induction of apoptosis in small cell
lung cancer (SCLC-H69), ovarian cancer (SKOV3) and breast cancer
(SKBR-3) cell lines. Overexpression of a constitutively active Akt
reversed the Ins(1,3,4,5,6)P5-mediated effects, confirming that Akt is
the target of Ins(1,3,4,5,6)P5 action. Moreover, Ins(1,3,4,5,6)P5
sensitizes breast, ovarian and lung cancer cell lines to anticancer
drugs.
Discussion
In the present study, we show that Ins(1,3,4,5,6)P5 inhibits Akt kinase
activity and phosphorylation and induces SKOV3, SCLC and SKBR-3 cell
apoptosis. Among the different inositol polyphosphates tested,
Ins(1,3,4,5,6)P5 is the most active compound. Interestingly,
Ins(1,3,4,5,6)P5 sensitizes breast, ovarian and lung cancer cell lines
to anticancer drugs. These results support an inhibitory activity of
Ins(1,3,4,5,6)P5 on cell proliferation and a proapoptotic action, and
the target of this activity seems to be the PI 3-K/Akt signalling
pathway. In our previous work (Razzini et al., 2000) we demonstrated
that Ins(1,4,5,6)P4 inhibited cell growth as potently as
Ins(1,3,4,5,6)P5 and this could be in contrast with the weak or lack of
effect found on apoptosis. This apparent controversy is explained by
the fact that in the present work we have used pure synthetic inositol
polyphosphates whereas in our previous observation we used commercial
compounds since synthetic inositol polyphosphates were not available.
In fact, when tested on apoptosis commercial Ins(1,4,5,6)P4 possesses
an activity comparable to that of Ins(1,3,4,5,6)P5 (data not shown).
The reason for this discrepancy is still unclear. However, we
definitively rely more on purity of our synthetic compounds that
satisfy the criteria proposed on the use of inositol polyphosphates as
discussed below (Shears, 2001). The effect of Ins(1,3,4,5,6)P5 on
apoptosis is of particular interest in SKOV3 cells since, in general,
ovarian cancer cells present a poor propensity to undergo apoptosis
(Vikhanskaya and Broggini, 2002). Recently, wortmannin and InsP6 have
been found to possess antitumour activity in vitro and in vivo through
PI 3-K inhibition, although the general toxicity of wortmannin and the
very high concentrations (1-5mM) of InsP6 for activity should be
taken into account (Shamsuddin, 1999; Ng et al., 2001; Stein, 2001). In
addition, the lack of selectivity of these compounds, together with the
instability of wortmannin and the insolubility of LY294002, means that
neither has very promising pharmaceutical potential. One major concern
in the use of inositol polyphosphates provided exogenously is the
presence of multiple negatively charged phosphate groups and, as a
consequence, they are generally considered not to be membrane permeant.
Despite the large number of reports indicating that InsP6 possesses
antitumour activity, none of these works provides clear evidence that
this compound may enter cells. By contrast, we have already shown that
the inositol polyphosphate Ins(1,3,4,5)P4 may enter SCLC-H69 cells when
applied extracellularly (Razzini et al., 2000). This is very
surprising; although several commonly used drugs possess negatively
charged groups and are able to enter cells, none of these are
polyphosphates. The mechanism by which cell entry occurs is at present
unknown. An intriguing hypothesis is that only certain cell types may
be permeant to inositol polyphosphates and this may involve specificity
in the mechanism of action of inositol polyphosphates. Specific and
nonspecific uptake of water-soluble drugs can occur across the plasma
membrane through known transporters or by the process of endocytosis or
by pinocytosis (Gottesman, 2002). Recent data show that InsP6 ionically
bound to lipophilic ammonium or polyammonium cations can be delivered
across the plasma membrane of erythrocytes indicating that, by
complexing the negative charges of the phosphate groups, inositol
polyphosphates may be rendered membrane permeant (Vincent et al.,
2002). Another aspect regarding the use of higher inositol
polyphosphates is that their activity could reflect some unspecific
effect on cell functions due to their peculiar chemical properties
(Shears, 2001). Therefore, a set of criteria, designed to avoid
experimental artifacts, has been proposed (Shears, 2001) and we have
employed these in our evaluation of Ins(1,3,4,5,6)P5 activity. In
particular, the fact that we have used pure Ins(1,3,4,5,6)P5, and that
other inositol polyphosphates are inactive may rule out any unspecific
or toxic effect. It is known that tumour cell survival reflects a fine
balance between hyperproliferative, proapoptotic, and antiapoptotic
events. Since tumour cells are more sensitive to proapoptotic factors
than normal cells, combination of proapoptotic factors with other
anticancer agents may be more effective in the treatment of cancer. In
fact, inhibitors of PI 3-K have been shown to increase the ability of
conventional anticancer drugs to induce apoptosis (Stein, 2001).
Similarly, in the present study we observed that Ins(1,3,4,5,6)P5
potentiates the apoptotic effect of anticancer drugs in breast, ovarian
and lung cancer cell lines. Therefore, the use of Ins(1,3,4,5,6)P5 in
combination with commonly used anticancer drugs may allow us to
decrease the concentration of these drugs and their accompanying side
effects. Our attention is focused on the mechanisms of activation of
specific downstream effectors of PI 3-K through a PH domain-mediated
membrane targeting. We propose that the activation of such proteins may
be inhibited by blocking the interaction of PH domains with the lipid
product of PI 3-K that is responsible for the translocation and
activation of proteins. In particular, ligands of the PH domains have
the potential to antagonize the activation of specific proteins by
inhibiting their translocation to the plasma membrane (or to any
specific membrane compartment). Indeed, as different PH domains possess
different binding affinities towards different inositol polyphosphates,
this increases the possibility of specifically inhibiting a particular
membrane-targeted protein. Thus antagonism of PI 3-K signalling
pathways could give us the potential to block a very specific
downstream target without interfering with other PI 3-K-mediated
signals.
In combination with our recent work (Berrie and Falasca, 2000; Razzini
et al., 2000) we propose that some inositol polyphosphates, the
water-soluble headgroups of phosphoinositides, can provide specific
antagonists of these functions. The concentrations of extracellular
Ins(1,3,4,5,6)P5 (20-50 mM) used in this work are higher than the
concentrations normally found inside many mammalian cells (5-15 mM)
(Szwergold et al., 1987) and therefore compatible with a competitive
mechanism. Recently, the structure of the PH domain of Akt complexed to
Ins(1,3,4,5)P4 has been solved (Thomas et al., 2002), and this has
enabled the key interactions that allow Ins(1 ,3,4,5)P4 to bind the Akt
PH domain to be defined. It has been shown that the Akt PH domain binds
the lipid headgroup in a different mode from that observed in other
PtdIns(3,4,5)P3-binding PH domains such as those from Btk, Grp1 and
DAPP1 (Thomas et al., 2002). Notably, the 6-OH group of Ins(1,3,4,5)P4
is completely exposed to solvent, suggesting that the binding site
could accommodate the extra phosphate group present in
Ins(1,3,4,5,6)P5. In contrast, the 2-OH group is orientated towards the
binding pocket, which would explain the loss of activity when this
position is phosphorylated, as in InsP6 (Figure 9). In addition, the
loss of activity in Ins(3,4,5,6)P4 could be explained by the fact that
the 1-phosphate group seems to be very important for recognition
(Thomas et al., 2002). These observations may explain the specificity
of Ins(1,3,4,5,6)P5 binding to Akt PH (Takeuchi et al., 1997). In fact,
a comparison of relative Kd values for inositol phosphates binding by
PH domains shows that Ins(1,3,4,5,6)P5 binds to Akt PH with the highest
affinity when compared to other inositol polyphosphates whereas other
PtdIns(3,4,5)P3-binding PH domains such as those from Btk, Grp1 and
Gap1 bind Ins(1,3,4,5,6)P5 with much lower affinity (Kavran et al.,
1998). On the basis of these findings the use of Ins(1,3,4,5,6)P5
should give a more selective inhibition of the PI 3-K/Akt pathway than
the use of PI 3-K inhibitors such as wortmannin and LY294002, and this
may explain the differences observed in our data when Ins(1,3,4,5,6)P5
effect is compared to wortmannin and LY294002. Nevertheless, we cannot
exclude the possibility that Ins(1,3,4,5,6)P5 may possess other
intracellular targets. Our subsequent goal will be to develop more
selective and potent inhibitors of Akt PH domain binding to
phosphoinositides starting from the Ins(1,3,4,5,6)P5 structure. The
present study has been designed to provide new drugs that act by
mimicking known protein structure specificities at the level of their
membrane localization through protein--phosphoinositide
interactions. The PI 3-K signalling cascade may play a critical role in
tumorigenesis, invasion and metastasis. The identification of new
functional inhibitors of PI 3-K pathway would provide new tools for the
treatment of tumours whose progression is driven by PI 3-K activation
or PTEN gene alterations. Since the PTEN gene is deleted or mutated in
a wide variety of human cancers the results of this study may have wide
clinical implications.
[The issue of PETN is especially important and isn't covered well in
the Discussion section so here is something from the Results section on
the issue:]
1. Ins(1,3,4,5,6)P5 specifically inhibits PTEN -/- ES cell growth:
To study the specificity of inositol polyphosphates as PtdIns(3,4,5)P3
competitors, we performed a cell growth assay in PTEN-/- ES cells,
which are characterized by high levels of PtdIns(3,4,5)P3.
Ins(1,3,4,5,6)P5 inhibited cell growth and it was the most active of
the inositol polyphosphates tested, confirming our data obtained in
cancer cell lines (Figure 5a). Furthermore, we observed that
Ins(1,3,4,5,6)P5 specifically inhibited phosphorylation of Akt in
PTEN-/- ES cells (Figure 5b) whereas other inositol polyphosphates
tested such as Ins(3,4,5,6)P4 and InsP6 were inactive. These data
indicate that Ins(1,3,4,5,6)P5 is a specific PtdIns(3,4,5)P3 competitor
and is more active than other inositol polyphosphates.
timo...@my-deja.com
problem in both cancer and aging and perhaps cellular senescence (
could it be reversible via inositol supplementation? von Zglignicki
suggests a rise in caveolin levels which are under the control of PI3K
is responsible . also the disruption of IP3 that appears with cell
senescence). Insulin depletes both the plasma membrane IPs as well as
providing the signal to turn off insulin secretion. The result is a
dysfunctional system that elevates insulin and causes insulin
resistance ( Kenyon found such an effect in C. elegans) PI3k also
controls both pro and anti-apoptotic pathways. If you read all the
papers partcularly the one I recommended it's dysfunction of IP
signaling that causes cancer. I'll quote some sections of text.
"PI3K plays a central role in insulin-mediated metabolic functions.
Therefore, dysfunctional PI3K signaling would be expected to have
deleterious effects on glucose homeostasis. Extensive evidence supports
the role of dysfunctional PI3K recruitment in the development of
diabetes. Of particular note are the studies on targeted disruption of
the IRS-1 and IRS-2 adaptor proteins, which implicate impaired PI3K
signaling in the mild insulin resistance and overt diabetes that are
observed in the two studies, respectively. Impaired insulin-stimulated
PI3K activity has also been observed in type II diabetes patients and
in cultured fibroblasts of subjects with severe insulin resistance
suggesting the presence of intrinsic PI3K inracellular defects in
diabetes subjects."
In addition to deregulation of insulin signaling , alterations in fat
metabolism contribute tothe development of type II diabetes. PI3K
activity appears to be suppressed in sybjects with impaired fat
metabolism who display severe symptoms of hyperglycemia and insulin
resistance. A number of mouse models also support the role of PI3K in
obesity related diabetes."
IRS-1 and IRS-2 are under PI3K control. I think Michael P is probably
correct that it is just inositol that is responsible, as all the
various forms of inositol seem to have the same effects. You'll notice
that inositol not only increases insulin sensitivity and lowers insulin
and glucose levels it also prevents cancer and reduces tumor size. So
I'm suggesting that rather than lower insulin levels it's higher
inositol phosphate levels that are responsible for the longevity
effects of CR as insulin depletes inositol phosphate levels. Also
intracellular lipids (which may explain the effects of PPAR's on
longevity and insulin sensitivity) and ROS disrupt PI3K signaling. I
hope this makes it clear or read back through my postings.
Tim
Michael C Price
effect of CR is mediated by high inositol! Even if
it isn't I'd still take inositol for its anti-tumour effects.
Cheers,
Michael C Price
----------------------------------------
http://mcp.longevity-report.com
http://www.hedweb.com/manworld.htm
<timo...@my-deja.com> wrote in message
news:1127233718.9...@g43g2000cwa.googlegroups.com...
timo...@my-deja.com
Hopefully it works in non-diabetics and suggestions are that it is.
PI3K is actually an associated pathway with the insulin signaling
pathway which is seperate. By feedback inhibition of insulin secretion
inositol may decrease the insulin signaling pathway via tyrosine
kinase.
Tim