>> Good morning, everyone.
I'm delighted to be able to introduce our speaker today, Dr. Michael dean, a good friend
and colleague of mine in Frederick.
Michael did his undergraduate work at Boston university and went on to do a Ph.D. there
in the biochemistry department.
he then came to Frederick and worked in the group of Dr. George (indiscernible), they
lured him to stay on and he eventually became the chief of the human genetics section in
the laboratory of genomic diversity.
and he's now recently moved to the cancer and inflammation program in Frederick.
mike's won a number of eye Wards and published nearly 300 articles.
and one thing that I think is particularly remarkable about mike is the work that he's done
for the scientific community in general and the lay community in teaching and
participating on editorial boards and really a lot of work that's self-less.
mike was involved in the identification of the cystic fibrosis gene.
and since that time he became very interested in ATP binding cassette transporter family
and he's done major work in that regard and started to look at more complex diseases
including adult macular degeneration.
so we're looking forward to your talk, mike and thanks very much.
>> I was thinking about having a friend to pay him too much to say nice things.
it's a pleasure to be here.
it's never a pleasure to commute here but I made it.
so what I'm going to talk to you about today is what -- at least in my mind has been a
revolution of understanding of cancer and how it's caused and why it has been so difficult
to treat and providing a pathway for moving forward.
and much of what I'm going to talk about maybe are things that were obvious to you or
some of you have known for decades but at least to me the recent data on the role of
inflammation in cancer and the role of stem cells in cancer has crystallized into a view
where I think we now for the first time understand cancer as a disease and how it arises
and why it is so difficult to treat.
the pathway to going forward in curing it is another story.
so what I'm going to talk about is essentially to what me at least has been a revolution
many thinking about this.
and we have revolutions every once in a while in science.
Einstein completely changed the way we think of time and space.
Darwin and Wallace changed how we think about species and their origin.
but the revolution I think that's the most compelling that's occurred in science has been in
astronomy and in the heavens.
we had a view of the universe created by Aristotle and (indiscernible) that survived 1500
years which consists of essentially what we see, that the sun comes up and sets every day
and the moon and stars and the planets revolve around us overhead.
and we can use observation in science and mathematics to predict the path of all those
celestial bodies and was very, very much hard science.
the problem became that people like THOLEMY and BRAHI started tracking the planets
and more -- in more detail and finding this view that they moved around in circles really
wasn't the case.
of course, it wasn't until COPERNICUS thought about the problem in a new light and put
the center at the universe and put the planets revolving in an or bit that the beauty of this
came back into focus.
and people like GALILEO recognized this.
he probably kicked himself this he didn't think of it first but what he did do was take the
new invention, the telescope and observed this is a page from a scientific notebook which
is about as neat as any of mine are.
and this shows for the first time the planets revolving around -- moons revolving around
the planet Jupiter.
this was the first observational evidence that celestial bodies didn't all revolve around the
and it goes to show you it's important not to only have the right ideas but the right piece
so what does this have to do with cancer?
Well, I think many of us -- most cancer biology has gone under the notion a tumor is a
relatively homogenous collection of cells that all pretty much have the potential to go on
themselves and form a tumor.
and so many of us have done this, have taken tumor cell lines and you can clone out
clones and you get back a cell line that looks pretty much identical to the one you started
you can do this hundreds of times.
We do know there's heterogeneity in a tumor.
tumors can evolve properties like resistance, but the model is okay, some cell in there
happened to get a mutation and becomes drug resistant and when you select the presence
of drug you select it for that cell.
so this is the model that we're essentially throwing out the window.
but almost all cancer biology and molecular biology has been using this property that we
take hold tumors and look at the growth of the cells, with grind them up and look at their
RNA and DNA and protein again with the notion that studying all of the cells in the
tumor is the right thing to study.
and this gets then completely thrown out the window if we think of a tumor more as like
a normal tissue containing within it cells with a property of self-renewal that are called
cancer stem cells, tumor stem cells but the vast majority of the cells in the tumor actually
have a limited life span and cannot repopulate the tumor.
and if thee tumor stem cells have many of the properties of normal stem cells, that is their
resistant to drugs and radiation, they may be QUIESCENT and less susceptible by drugs,
less propensity to go into apoptosis.
The result being that most of our cytotoxic therapy leave behind the population of cells
that were innately resistant to the therapies.
so as so often happens when a tumor grows back, it's these cells that are repopulating the
so of course then we need to understand these cells and figure out how to kill them if
we're going to completely cure the tumor.
but what's more important also I think is to think of a tumor more as an extension of a
This is not some grossly abnormal group of cells, these are cells that come from our
human body and are behaving mostly like normal cells, although slightly aberrantly.
and the concept arose that tumors arise by chronic inflammation or chronic damage of the
tissue leading to disruption of the architecture of these cells, creating an environment
where some of those cells become eradiated, their DNA becomes damaged, that starts
you down this process of generating a tumor.
so it's important to have a little bit of background.
there's a lot of discussion on what do we call these cells in a tumor?
Do we call them tumor initiating cells and not confuse this with the nomenclature of stem
But the important property is the property of self-renewal, asymmetric division.
one unique property of stem cells when it divides it gives rise to a cell identical to itself.
it may give rise to another cell committed to differentiate and the daughter cells may
continue to differentiate.
only a number of cell doublings you generate the point where you have a minor
population of stem cells and a large population of cells committed to divide and
sometimes a cell can divide and give rise to two stem cells or zero stem cells and that
process is rather complex.
now, these ideas are not new.
you can go back in the cancer literature and find people talking about inflammation
causing cancer or cancer deriving from stem cells or embryonic cells back a hundred
and we had some intriguing experiments independently done by Ralph and beatrice mints
in 1975 taking tear toe carcinoma cells and put into a mouse in a normal mouse develop
so that shows clearly in some cancers there are embryonic stem cells that are not only
have stem cell properties but are completely TOTO potent.
in the 1980s, hamburger, Salmon and others showed that some fraction of cells out of a
tumor or cell line can grow in soft OGER like stem cells and developed a stem cell assay
and the real hard evidence came with John Dick and colleagues work showening AML
there's a compartment of cells that have a stem cell component.
but the experiments that really I think galvanized the field have been in solid tumors
coming from originally mike Clark and max wishes lab showing in this case in breast
cancers you can isolate a fraction of cells, it's about 1% of the tumor that is high hi
tumorgenic, whereas the other 99% of cells are not tumorgenic.
so this immediately generated a a problem, what we want to know about is this 1% of
cell, what are their properties, what genes do they express, what proteins do they express,
how might we target them and eliminate them?
And you're not going to get that information if you grind up the whole tumor and look at
all the cells tame.
-- at the same time.
so one of the -- and this is important relevance I think to the two major problems with
and that is drug resistance that we have many therapies for many cancers that lead to
regression of the tumor but we have very few that don't eventually lead to resistance of
the tumor to drugs.
the second major problem is metastasis which kills virtually all tumors.
I'm going to talk about both topics.
but important property of normal stem cells is they have mechanisms to protect them
They express a number of drug transporters, E flux transporters and resistant to radiation
in a number of mechanisms so cancer stem cells are likely to retain the properties.
what is fascinating about the paradigm is a couple of areas we have worked on for many
years turn out to be very relevant.
so I'm going to talk to you about two of those.
One is an important drug transporter and another is a tumor suppressor involved in
we're now developing therapies targeting both of these proteins.
so one of these proteins is ADCG-2, a transporter that Susan baits and our group cloned
ten years ago and it was shown this is one of the three major E flux transporters in cancer
cells that like a protein MRP-1 and ABCG-2 account for the vast majority E flux of drugs
out of tumor cells.
and so this now again sort of creates a new paradigm of how we might think of drug
the old model of how this works as i described before, somewhere in the tumor you have
a cell that just happens to acquire the ability of drug resistance.
if you put the tumor in drug you select for the cells.
The stem cell model says those cells already exist.
Those are cancer stem cells, they're already innately resistant to the therapy so they
then if they grow back, the tumor grows back, essentially identical to what it was.
of course it's certainly possible that those cancer stem cells can have a mutation making
them even more resistant.
Then you end up with a tumor where you have resistant stem cells giving rise to resistant
progeny and have what we observe in many tumors that the therapy is now completely
useless and none of the cells respond to the therapy.
so how do we force -- how might we sensitize these cells so that we can kill them off in
the very beginning?
How can we target the cancer stem cells?
One way might be to target these drug transporters which we in fact are no important -- a
number of groups have shown ABCG-2 and glycoprotein are expressed early in stem
the population method for isolating stem cells from bone marrow is based on expression
of the ABCG-2 transporter.
so we set about with the molecular targets development program in Frederick to identify
new inhibitors of ABCG-26789 we started with a cell line Susan Bates provided that's
overexpressing ABCG-2 and a substrate field 4 bite A. and they adapted this to a 384
well high through put assay to identify compounds that will inhibit A BCG-2, therefore
the cells would retain the substrate and flouresce.
so this is the data you get out of that with a fluorescent signal from a number of
We screened about 200,000 compounds, about 100,000 known pure compounds and
about 100,000 natural product extracts from the collection out in Frederick, identified
over 100 compounds confirmed hits.
and then have gone on to study those in more detail.
(indiscernible) lab has done this work looking at inhibiting binding, looking at whether
these compounds inhibit the ATPASE of the purified protein.
one group of compounds that's come out of this has been very interesting, a group of
natural products that have come out of Marine sponge which are being called
out of these screen came a number of derivatives.
There were many active derivatives similar to each other so that's allowed us to begin to
explore structure function relationships and figuring out which of these residues are
critical for the resistance and which are not.
and unlike most natural products this is a relatively simple compound, so it would be
conceivable to start making a large number of synthetic derivatives of this and perhaps
identify a lead compound which could go on to further study.
now, this is relevance not only for cancer therapy but really for all pharmacology.
it's becoming increasingly clear that these ABC transporters play a major role in barrier
organs in the body.
for instance, in the blood/brain barrier, NRP-1 and ABCG-2 are known to control what
molecules get in and out the blood brain barrier.
similar for other barriers in the body, the placenta, the intestine, and many other organs
it's becoming clear that these transporters play a critical role.
this is very important obviously in many different pharmacological therapies.
For instance, in epilepsy it's been shown that during epilepsy P glycoprotein is
the reason that 40% of epileptics don't respond to many drugs is because they're getting
pumped out and don't have access to the -- across the blood brain barrier.
so if we can be ain't to modulate either the expression of these transporters or have
inhibitors to be able to regulate their function, we might be able to better use the drugs
that we have available to access certain tissues.
there's a problem of course if we inhibit drug transporters in stem cells and give a
cytotoxic therapy if we sensitize the cancer cells to cytotoxic therapy we're sensitizing the
patients themselves to the same therapies.
You hope that's a therapeutic index where you kill the tumor stem cells without killing all
the patient's normal stem cells but that is obviously going to be problematic.
is there another approach?
Can we look at other pathways, critical to the formation of stem cells and target them?
And so here we have to go to a little bit of genetics.
in 1960 the late Robert gorrell described basal cell carcinoma syndrome, a dominantly
inherited genetic syndrome, patients get jaw cysts, they get hundred of thousands of basal
cell carcinomas and are at high risk for blastomas.
Most features aren't fatal, you can assemble large pedigrees, this is one assembled here at
many, many years ago it was one of the pedigrees used to map the gene.
our lab was involved in international collaboration in eventually positionally cloning the
it's interesting to show this table because this represents about 100 graduate an post-doc
years work to assemble the clones and make a map of the genome.
anybody here with your -- even your black before you could click on -- go online and get
the entire sequence of this region.
but back at that time this was heroic piece of effort.
we identified in the middle of that region a gene called patched which was a very famous
gene to developmental biologists.
This is a gene discovered in the 1980s as being critical in part of a critical pathway
involved in the development of drosophila and in the development of all U carotic
so what is this gene patched?
It's a cell surface protein which is the receptor for a group of signaling molecule,
It inhibits another membrane called smoothen, the front of a cell signaling pathway
leading to the expression of glee family of transcription factors.
What has become interesting, not only is patched the tumor suppressor but all these genes
in red are oncogenes.
so here we have a pathway critical to embryonic development to pattern formation and to
the regulation of growth of stem cells in which most of the genes in here are also
involved in cancer, either as tumor suppressor genes or when overexpressed are
so this provided a really exciting molecular connection between embryonic development
and cancer and going back hundreds of years if there's a connection between the genes
involved and regulation of growth of stem cells and embryonic development and in
so in those patients where the patched gene is mutated or inactivated the smoothen
protein is active and this protein is constituently on leading to abnormal growth of those
we and others show the patched gene was mutated in virtually all sporadic basal cell
It's mutated in subset of blastomas.
what it has found more recently and this progress has accelerated, is the pathway is
abnormally regulated in a very large number of different cancer types.
so what is happening there is that hedge hog molecules are overexpressed.
and the mechanism by which this happens is not entirely clear but if hedge hog is
overexpressed it sequesters and inhibits patched and the pathway is constituently on just
as if the patch was mutated or inactivated.
Smoothen is a critical target, the regulator of this pathway downstream of these two
genes so if you had an inhibitor this protein would that, in fact, be useful for cancer
This was validated by Phil beech's lab where they show the pathway is overexpressed in a
number of prostate cancer cell lines.
If you give a small molecule antagonist of smoothen called cyclopamine you inhibit the
growth of those cells in vitro.
if you inject that compound into mice with human scene graphs those two cell lines
a number of drug companies tried to develop analogs of cyclopamine.
most of which have failed but there are a number of other analogs targeting this same
now, the role of this pathway in cancer stem cells is also been clarified here, pancreatic
stem cells which express a very large amount of so Nick hedge hog as compared to the
bulk of the tumor or normal pancreas. in the brain stem cells if you stimulate them with
sonic hedge hog you can make them grow. if you inhibit the pathway by
CYCLOPAMINE you can make the brain tumor stem cells regress or not grow.
we have taken the approach with Nadia TERASOVA up in Frederick of not going for
small molecule drugs but of synthesizing peptides that correspond to intracellular
smoothen is evolutionarily a member of the G protein coupled retentor family of
transporters or signaling molecules.
It actually does not bind G proteins and the mechanism by which it signals is not entirely
clear but it had been known from other groups peptides against G coupled receptors,
these intracellular loops were inhibitory.
but smoothen is unique in that there is only one smoothen gene in the genome of all
vertebrate organisms and it's extremely heavily conserved, especially these loop regions,
virtually identical across all vertebrate organisms.
suggesting that these loop regions play a very important role but also suggesting that if an
inhibitor targeted those loop regions it would be very, very specific to the smoothen
protein and would not cross-react with other G protein coupled retentors which have
many other important functions in the body.
so we synthesize these peptides with acid on the endodome to allow them to bind and bet
into cells and then tested their function.
and found that peptides to the loops both the second and third loops were very specific
and sensitive inhibitors working down in the low micromolar level.
And when we even made so-called retro and versa peptides using D amino acids and
reversing the positions of the side chains we get molecules that work down in the
nanomolar and subnanomolar ring of activity.
in the curse of D amino acids they're not subject by degradation by proteases in the cell.
so we don't know exactly how these peptides maybe working.
one model is that smoothen signals through some unknown protein which we have not
identified which binds to these intracellular loops.
Of course then the peptides to these might disrupt that interaction like so.
as I said, the peptides have a POLMINIC acid residue to put them into membrane into the
It could be they all simply assemble into the native protein and disrupt its structure
and that we haven't -- we haven't figured out yet one of the next experiments we would
like to do would be to label these peptides and cross link them and see what they're
are they binding to smoothen itself or are they binding the some other protein which
might give us a handle on a downstream signaling pathway.
we have evidence this these peptides are specific because they specifically down regulate
the target genes in this pathway.
so they down regulate the GLY family transcription factors.
There's negative feedback regulation where inhibition of the pathway inhibits the express
of smoothen and patched and we see that.
what is also exciting about this pathway is very recent evidence of the signaling
mechanism of how patched inhibits smoothen.
and it's now been demonstrated that patched is actually a transporter for very famous
molecule vitamin D-3.
So that the natural Ligand of patched appears to be vitamin D-3 which is transported and
which has a binding site and inhibitor binding site on the smoothen protein.
now, for any of you with an epidemiology or cancer prevention interest, vitamin D is one
of the most important molecules of interest in cancer prevention.
throughout the world people that have higher sun exposure or have higher levels of
vitamin D in their diet have lower incidents of many, many types of cancer, the
mechanism that we don't exactly understand.
We know vitamin D has receptors inside the cell like steroid receptors and much of the
action of vitamin D-3 is through those receptors.
but it's very intriguing to think of the cancer preventive action of vitamin D-3 through the
smoothen protein and inhibition of this pathway activated in a lot of tumors an critical to
tumor stem cells so it proposes a very interesting question of should we be providing or
recommending much higher levels of vitamin D in people's diet?
Should we encourage people to go out and get more sun exposure?
Obviously not too much because we don't want them to get melanoma but it's an
intriguing question as to the role I think vitamin D-3 and this mechanism of action.
of course, also question is can we develop other analogs, there are a number of analogs of
vitamin D-3 that have been envisioned for cancer therapy and should we now sort of
resurrect or place more emphasis on that idea?
so I want to end with a little bit of talking more about the big picture of how does this fit
into the bigger picture of the cause of cancer and the role of inflammation?
So the emerging picture of cancer then is that we have normal tissues in which all normal
tissues have normal stem cells which are sitting there surrounded by other normal stem
cells in a structure called the niche and are quiescent or remain in that quiescent state
until tissue damage comes along or natural renewal of the tissue.
if you have tissue damage you release the stem cells from their QUIESCENT state.
they start dividing and differentiating cells and repair the damage and you're back to
where you started from.
the problem backs when you have chronic tissue damage you have this process occurring
continuously and then you have these stem cells that are continuously dividing and
having to repair this damage.
now you have a population of dividing cells that can be the target for mutations which
could lead them to lose control of growth, lose their inhibition by cells in the niche, and
then create a pre-malignant lesion which then potentially could suffer more mutation an
lead you into a full-blown tumor.
so when I talk to people like Ron Mckay, what he'll tell me is that those guys wineberg
and all those guys are wrong.
mutations don't cause cancer, what causes cancer is tissue damage, the chronic disruption
of the normal architecture of the tissue which is the key event in starting a cancer.
I happen to think that both groups are essentially right and that the complete picture is
that you need that chronic damage to generate a population of cells which is then subject
to mute generals in our environment to make pre-malignant leagues occur and tumors to
develop and progress.
it's interesting then to think of all the common cancers and what we know about what
You can place all these agents into those that cause tissue damage or chronic
inflammation or stem cell activation and those that inactivate tumor suppressor genes and
so we know that tobacco smoke is associated with lung cancer, tobacco smoke over long,
long periods of time causes chronic tissue damage and inflammation of the lung,
disrupting the tissue and the architecture of the lung as we as contains mutaGENS which
mutagenize those cells giving you lung cancer.
colon cancer we know disorders leading to inflammation like crone's disease,
inflammatory bowl disease causing chronic inflammation are huge risk factors for colon
liver cancer we have hepatitis B about C virus causing chronic damage and cirrhosis of
if you ingest enough APLO toxin the two together synergize to increase your risk for
some can cause chronic inflammation as well as mutaGENIZED cells in the skin giving
gastric cancer, you can go down the line in virtually every cancer identify an agent
causing disruption of the tissue as well as agents in the environment, many of which we
don't know perhaps enough about yet that together lead to the formation of pre-malignant
leagues and eventually to malignant lesions.
There's two types of Karens that don't fit into this paradigm very well.
and this confused me for a while until I read a review that (indiscernible) wrote ten years
ago which he explained the whole situation.
he's a genius.
that's how that works.
And he described -- separated cancer into three different types.
Those that derived from embryonic tissue.
and so in that case what I would say is in retinoblast developing in early fetal
development or early childhood development you have an activated stem cell.
You don't need that, you don't need that inflammation or that activation status because
these stems -- stem cells are rapidly divides.
so if they have an inactivated RB-1 gene that's all they need to go the rest of the way to
a similar case for other embryonic tumors is during embryonic development you have a
rapidly dividing population of stem cells if you genetically inherit a altered tumor
suppressor gene or this happens by chance, that maybe all you need to go on to form a
the other is what he called conditional growth tissues.
Tissues dependent on hormonal stimulation for growth.
so the best example is the breast where we have during puberty a massive proliferation of
stem cells in the breast which go from a dormant state into an active highly dividing state.
of course you have active cell division through each menstrual cycle as well.
Here you don't need an exogenous agent.
you don't need a virus or asbestos or chemical to cause this activation because this
naturally occurs during development.
then you have a population of activated stem cells which can undergrow inact vision of
other genes -- inactivation of other genes leading to progression on to cancer.
the other interesting thing about this model is it brings back the whole field of cancer cell
biology where people painting chemical agents on to the skin of mice identify that there
were initiators and promotors.
we now know initiators are mutaGENS, compounds that bind to DNA and cause
mutations of DNA.
promotors are not mutaGENIc it's been a mystery to me how these agents might
contribute to cancer.
These are things like mineral oil, physical wounding.
and we can now understand these agents as those agents causing inflammation and tissue
so you need an agent from this class as well as a mutaGEN so just as I described here you
can call these promotors and these initiators.
let me finish up talking about metastasis because this is the critical thing weapon to solve.
virtually all cancer patients die from their metastatic lesions not from the primary lesions.
so if we had a way to figure out how to inhibit metastasis from happening, we could
make major advances in cancer therapy.
again, in the old view of cancer, at least I was always brought up to think the metastasis
was some extremely abnormal program that somehow cancer cells turned on.
that somehow they went off into some completely abnormal state of being in order to
develop the ability to metastasize.
normal stem cells are programmed to migrate throughout the body.
the cells in the neurocrest of a developing embryo migrate all down through the embryo
down into the GONADS.
so what if metastasis is a normal activity of cancer stem cells?
That is what they're programmed to do, that's what they think they're supposed to do and
they're following those innate instructions.
now, this all seemed like a very interesting idea but it was not clear to me how one would
demonstrate until I went to cancer stem cell meeting we had about a year or so ago and
Mary Hendrix showed this absolutely mind-blowing experiment where she was able to
take highly metastatic melanoma cell, human melanoma cells and implant them into the
neural crest of a developing zebra fish or in this case a chicken an low and behold the
cells don't sit there, they migrate down the neural crest just like the normal stem cells do
and essentially behave in that environment normally.
she could ablate the stem cells out of the chicken and human cancer cells would migrate
down through those same pathways responding to those same signals.
so this provides I think a beautiful validation of that idea.
that metastatic cells in tumors maybe responding to the exact same normal signals that
embryonic stem cells would.
if we could understand that process and find ways to inhibit it, maybe we can inhibit
migration of those cells so I envision down the road hopefully not in too distant a future
combined therapeutic approach where we will have our old favorite cytotoxic drugs an
radiation and surgery to get rid of the bulk of the cells in the tumor.
we may have agents which will inhibit the expression or inhibit the activity of E-flux
transporters and allow us to sensitize the cancer stem cells in a tumor to the same
And we'll have an array of molecularly targeted agents that are targeting the normal
pathways in the cancer stem cell.
and by combining these together maybe we'll be able to eliminate not only the essentially
all of the cells in the tumor including the stem cell.
and as I said, even if we don't get rid of the primary tumor, if we can inhibit the those
stem cells that leave the primary tumor and migrate through the bloodstream, if we can
inhibit those from either growing or from setting up in other organs, and inhibit
metastasis, that would have a huge impact on therapy.
and so again, from my discussions from my friend Ron Mckay, he would like to suggest
that really cancer therapy then becomes the flip side of the whole field of regenerative
medicine which of course there's a huge amount of interest now in taking normal stem
cells, figuring how to grow them, figuring out how to differentiate them, and control their
growth and development so we can use those in regenerative medicine.
we can use the same ideas and the same techniques and the same findings to go in the
opposite way in cancer therapy where we want to inhibit the growth of stem cells or want
to force them to differentiate and, therefore, become inactive.
so I think if the two fields increasingly talk to each other and learn from each other, that
both fields may move forward more rapidly into the future.
so in conclusion then, many solid tumors have a population of cells that we're calling
cancer stem cell, tumor initiating cells innately resistant to many of the therapies that we
already throw at these tumors.
and isolating and studying these cells may give us important new insights into cancer and
how it arises and how to treat it.
one of the critical pathways in these tumors is the hedge hog patch pathway which is
activated in a vast majority of cancers.
and are in development therapies targeting this pathway which may be effective drugs
into treating these tumors.
and I would like to thank the people in my lab, hung LU and (indiscernible) who worked
on this, collaborated with Nadia (indiscernible) and the molecular target development
program, develop the ABCG-2 agents along with Susan Bates, (indiscernible) are all long
time collaborators in drug resistance.
and I'll thank you and stop there.
>> Joe all has a question.
>> I come up with a dozen.
but the question I wonder about is the interaction between vitamin D-3 and the hedge hog
Ligands for this receptor.
one, do they compete with each other?
And two, do they lead to internalization and turn over of the receptor or disappearance?
And how can this be regulated and manipulated at this level?
>> I think it's clear the binding sites for hedge hog and the binding sites for vitamin D are
different parts of the molecule.
but it's not very well studied.
that sort of internalization and down regulation as of yet.
so there's a lot left to do on that.
really at this point there's only one publication out there that I have seen.
>> Yeah, I don't know and I don't think the hedge hogs -- well, it's been hard to establish
for hedge hogs because they have a molecule of cholesterol and another fatty acid
molecule on to them.
so the hedge hog proteins themselves essentially designed to be localized in terms of
but I don't really know whether they're chemotactic.
I don't think they are.
smoothness is not your typical G protein coupled receptor because we don't know how it
We know it doesn't signal through G proteins as far as we can tell.
so it's evolutionnarily part of that family but functionally quite distinct.
>> Michael, I always enjoy listening to you talk about stem cells.
you didn't say much about the model in your model.
this process might work if the mutations or the translocations or whatever the events
occurred somewhere down the line the terms of the cell, progenitor cells, the potential for
the -- I guess a reprogramming of the cells to give it stem cell like.
would you comment on that?
it shouldn't be implied the cancer stem cell idea that it has to arise from a stem cell.
it's obviously one model that a normal stem cell in the tissue could have enough genes
damage that it could lose control and turn into another cancer stem cell.
the other possibility is cells committed further down the pathway can revert back in terms
of developing this sort of self-renewal property.
that's really all -- the only property this cell has to have, the ability of self-renewal, the
ability to divide and give rise to a cell identical to itself.
we know we can take NIH fibroblasts and if you mutate enough oncogenes you can turn
those cells into tumorgenic cells obviously with self-renewal property so we know if we
damage enough genes on a committed cell, we can get it to develop that self-renewal
capacity and turn intok a, quote, stem cell that's why I think people don't like that
terminology because there is this alternative route.
and there is evidence that both activities are happening, that both pathways are possible.
of course, there's a whole gradient between TOPOPOTIC cells and multi-potent cells and
so down the line so the target could be cells anywhere down that pathway.
>> Michael, have any of your smoothen peptides been tested in animals in vivo?
>> That's about to happen very soon.
that was presented before the molecular targets committee and that project approved.
We had discussions with pat Steve today on how to move that forward.
so that's in the works.
>> Thank you for many provocative comments in your talk, Michael.
I think it's -- will stimulate a lot of discussion.
I, like you, thinkal KANOTSEN is a genius and actually he's one of my favorite
so when you showed his hypothesis about certain tumors where there's a stem cell like
retinol blastoma, one thing that I find difficult to explain with our current constructs,
that's really what they are, there's precious little data for any of this, is in fact probably
most pediatric tumors are much more related to an UMBRINAL phenotype, we know
that by looking under the microscope.
so I think that model of retinol blastoma is probably true, yet we're much more successful
in treating pediatric tumors and BRINAL tumors with standard cytotoxic therapy, we
cure the vast majority of pediatric tumors in 2007.
so what that suggests is that stem cell or not, we can cure those tumors.
in fact, when we get into -- not arguments, we get into discussions not infrequently about
why are pediatric tumors more curable than adult carcinomas?
Inevitably it's, well there are different tumor types.
They're stem cell like so that sort of turns the whole thing on its side.
and says maybe stem cells are not the problem in terms of curing with our currently
so I don't have an answer, just it creates a lot more questions I think.
and I don't -- I guess I don't have a great answer either.
obviously the fact that we can cure some tumors means that our therapies do work in
and you can't think of a stem cell by itself, the stem cell is sitting inside a niche so it may
well be that in some tumors if you kill all of the cells all of the non-stem cells in the
tumor, that there's nothing left to support the stem cells and they will regress and die too.
and of course, on top of this is the immune system which we know the immune system is
keeping in check many cancers, the more and more we study, immune suppressed and
transplant patients the clearer that become.
-- that we come.
so we can't leave that out either, that maybe in pediatric cases we have a much different
immune system than you have in the adult.
and obviously in adult -- an adult tumor, lung cancer had to arise over 30 years an maybe
during that time there was enough adaptation to the immune system that now it's not
recognizing the same way.
so I agree.
there are all kinds of questions that this brings up.
but at least when you have a model or a construct to put everything in you can ask
specific questions and probe that and figure out what parts might be true and what might
>> So the stem cell concept for cancer you described has many attractive features.
But I was thinking of the situation that many of us deal with as mouse tumor model
experimentalists face, which is that we can take certain mouse tumor lines that we can
grow in tissue culture and can sub clone those and get clones that derive from a single
grow those up, put those into a mouse, and grow up a tumor, and in some cases for
example with the 4 T 1 breast carcinoma, you can plant it and it will metastasize and so
when we sub clone those an grow those up we assume we're growing a population of
identical cells from that cloning process.
are we cloning out stem cells or how do you fit that kind of experiment in with this
there are two issues there.
one, we know that cells you have grown in plastic on CAF serum for decades maybe
very, very different from the cells out of a primary tumor.
obviously in a cell line has to be some self-renewing population of cells, otherwise you
wouldn't get a cell line and you wouldn't be able to clone the cells and do all the things
we can do.
so obviously those cells have the property of self-renewal.
there's been a lot of interest in looking in cell lines, it would be great if we can take
HELA cells and purify the tumor stem cells out of a culture and study them but it's not
clear, it's not clear that we can do that, that that works in the same -- in the same fashion.
But I think the paradigm would be is that -- I mean, you know if you take a thousand
tumor cells and plate them out and say each into one well, you don't get a thousand cell
lines growing up.
you may get one or ten or 5 or depending how clonable that cell line is.
and same, you can't inject a single cell, you can't implant a single cell orthotopically in a
mouse and expect to get a tumor.
you're injecting hundreds of thousands and sometimes millions of cells to get a tumor.
so I think you still consistent with the idea that after you grow up a population of cells
that those cells are not -- do not all have the same capacity to reform a tumor.
>> That's a very artificial system with these transplantable tumors but nevertheless, it
maybe when you clone them and grow out cell you are in fact cloning out stem cells and
you might have that -- they might have some of the properties you're looking for.
but certainly the initial cell that started that cell line has to have the self-renewal property.
but after a number of divisions it doesn't mean all of the cells all of the daughter cells do
so it may be after you grow up a million cells only 1% of the cells have a cell property
and the rest don't.
so this makes it all a great challenge to study and figure this out.
we don't have great assays.
Admittedly the assays that Clark and wishes started are artificial, taking human cells and
implanting them and using the assay do they grow a tumor in a mouse?
And a lot of people argued that that's -- that's an artificial system where we're seeing what
maybe not necessarily an artifact but a property that's dependent on a system which is