I am involved in stem cell research and I’m involved in a complex programme involving IFOM and other institutions.

What makes stem cells unique?

Stem cells are the only cells that can regenerate an organ so essentially when we look at an organ the only possibility of regenerating real tissue comes from stem cells.

So the majority of the cells in the organ are differentiated cells which originate from the stem cell.

As a matter of fact, in normal tissues really what happens over time is that stem cells decrease in number and this is one of the leading causes of ageing in the mind of several people because basically the stamina, the capability of regenerating, gets exhausted.

Now, not surprisingly, in cancer a very similar situation occurs.

Cancers basically in several ways they can be compared to organs which are just being formed with an aberrant plan so they are also fuelled by stem cells.

So stem cells are the only subpopulation of cells through which cancer growth can be achieved and cancer can expand and regenerate.

There are important differences between normal and cancer stem cells; they are not completely clear, of course, that’s the major focus of investigation now in the field.

From the phenotypical point of view, really perhaps the major characteristic of cancer stem cells is that for a stem cell to become a cancer stem cell or for a more differentiated cell to revert to the state of a cancer stem cell, what needs to happen is what is called epithelial to mesenchymal transition.

Now in epithelial to mesenchymal transition the cell acquires essentially migratory capability in addition to several phenotypes.

This is one of the reasons why one of the leading hypotheses in the field is that stem cells are really the cells responsible for metastasis.

So they become… the importance in cancer becomes twofold: they not only regenerate the cancer but they also cause what is the most dramatic occurrence in cancer which is metastasization.

There is another characteristic which is important in cancer that we should bear in mind, it is that stem cells spend most of their time in a quiescence state which means that they do not replicate.

As many of the weapons, of the drugs that we have at our disposal in cancer, interfere with proliferation one way or the other, not all of them but a good number of them, there is the legitimate suspicion that stem cells will evade therapy simply as a function of their state of quiescence.

So in a nut shell these are the major phenotypical differences, at least if you look at the thing from the cancer point of view.

Can you tell us more about your research?

It started a few years back.

We were involved in a collaboration group that led to two major avenues of investigation.

On the one hand we developed technologies to purify stem cells to near homogeneity.

We used a very simple method, we used a vital dye that gets diluted when the cell divides and does not get diluted if the cell is quiescent. In this way the stem cell retains the dye and can be FACS sorted.

This applied to the old mammosphere assay which has been a basic tool in the field to identify cells which were capable of proliferation in vivo and maybe in colonies in vitro, led us to the possibility of purifying the stem cells in a number sufficient to do more regular genetics and to do protein analysis and these kinds of studies.

What you have to bear in mind is that, say in a normal mammary gland in the normal condition, there will be one stem cell out of 40-50,000 cells maybe, or maybe even less.

Basically you cannot cultivate stem cells because as soon as you start cultivating them they will differentiate into progenitors and so you will lose the stem cell.

So essentially the work here is repurifying every time that you have to do an experiment and the yield is everything that counts.

So with this methodology we managed to get enough cells for experimental needs system but mostly from patients, normal counterpart and tumour tissue.

By applying this technology we found out a number of things.

We found out, for instance, that a critical determinant is p53.

The presence of p53 in the stem cell is really what determines the quiescent phenotype of the stem cell.

The mechanism is very interesting because when the stem cell first divides and gives rise to two different cells, one that retains the stem cell fate and one that becomes a progenitor, and I’m now talking about the normal condition, the activity of p53 is only retained in the stem cell.

So this is the way through which the stem cells, in our opinion, withdraw into quiescence.

Now, the question is why this happens.

Here comes our historical expertise.

Over the years we have been very interested in the field of membrane trafficking which is basically all the infrastructure that in the cell organises logistics, so endocytosis, transport, all the vesicles and biomembrane that regulates cell transport.

We discovered a protein, well actually we re-discovered a protein many years ago, which is called NAM which is involved in these pathways which has been known for a very long time to be a cell fate determinant.

These are studies that date now perhaps 20-30 years in which by using model systems like Drosophila they found proteins that did exactly the thing that I was telling you about before which is the partition in one cell and not in the other when the stem cell divides originally.

So the idea that we have there is if a protein like NAM does this in a model system perhaps it does this also in humans and perhaps this is important for cancer. Indeed we found that in mammary stem cells NAM partitions asymmetrically between the stem cell and the progenitor, the daughter cell that does not retain the stem cell fate.

To put everything together in what was a real, I think, fundamental discovery we found out that NAM regulates p53. So now the circle is closed.

And actually NAM regulates p53 because it prevents its degredation.

So when there is NAM p53 stabilises; when there is no NAM p53 is lost.

Now, to make the story even more interesting, what we were finding out at the same time is that the expression of NAM is frequently lost in human mammary cancers.

So now the picture has started to become coherent, to make sense.

So when you lose NAM you would lose the stabilisation power over p53 so there would be no p53 and so now the stem cell can proliferate more or perhaps acquire even a new kind of destiny which would be compatible with that stem cell making the transition to a cancer stem cell.

So this is really what we are involved in right now, trying to understand how this mechanism can force the conversion from a normal stem cell to a cancer stem cell and how to interfere with this mechanism.

Because now the entire story is that you can take a NAM negative tumour, a tumour in which you can actually test that NAM is not present, and perhaps revert it to a normal state by interfering downstream with p53.

There has been a lot of interest, of course, in the p53 stabilising molecule so another field now can converge over these things and possibly we might stratify, at least at the experimental level right now, the patients that would be eligible for this kind of therapy or at least the cells that we would try in the lab to be eligible for this kind of therapy on the basis of the NAM status.

With regards to finding biomarkers and targets, what’s your progress so far?

Another interesting thing that we did, starting with our purification procedure is that we could purify stem cells from the tumour and from the normal counterpart from the very same patient.

So for the first time we could make expression profiles which would distinguish the cancer stem cells with respect to the normal stem cell in a completely isogenic pathway.

By doing that we identified a series of specific stem cell markers.

Now, these led to a number of discoveries, one which we published a few years back is that tumours, the aggressiveness of tumours, of breast tumours, is a direct function of their content in stem cells.

So tumours which have a lower number of stem cells are less aggressive and this patient has a better prognosis than patients that have a higher number of stem cells.

This is important and we could do it only because we finally got specific markers so we could actually stain in a stem cell specific way the tumour and actually count the cells in the tumour.

That led also to a distillate of this expression profile which was condensed in a signature which we are now validating and it is very promising in terms of patient stratification and eligibility for more or less aggressive chemotherapy in breast cancer.

In what ways have you stratified this?

Basically, based on the signature that we have developed we can assign a risk score based on an algorithm that takes into consideration the expression of every single gene and weighs them on the basis of their impact in the whole signature.

So every patient will be assigned a risk score which is a risk score of metastatic relapse and eventually an unfavourable outcome.

Has your work validated conventional methods in pathology?

The idea here is to use the signature in a way which is not different from the way in which other signature have been used.

We hope that ours will be better, of course, but that’s early to be said.

So the general idea is to go into groups which are already existent in terms of treatment, like taking luminal tumours that receive a certain kind of therapy and stratified within the luminal or within the luminal A and within the luminal B.

So to use the signature as an additional tool to dig deeper into somebody that cannot be resolved right now.

We know that in every subgroup of breast cancer there are patients which do not follow the typical course of that subgroup.

For example, in the luminal A which is normally a very good prognosis tumour there are patients that eventually will relapse with the disease and so these patients if they can be stratified in advance, of course, would be eligible, at least in principle, for a more aggressive therapy with respect to the bulk of the patients.

So essentially it’s the usage of a signature to achieve further stratification in addition to the usual tools which are being used.

What direction do you foresee stem cell research taking us in, in terms of personalised medicine?

The entire issue in the field right now is will we be able to develop stem cell specific drugs.

One possibility, of course, is that we will end up getting specific stem cell targets that are only expressed in the stem cells so they are a good therapeutic with respect to the stem cell and the progenitor or other cells.

The one I mentioned is this one relying on NAM and p53 which we think is going to be very, very important.

At the end of the day, clearly stem cell specific therapy might be very important.

It’s early to be said. In my opinion it will have to be coupled to conventional chemotherapy no matter what because there are several ways of making a stem cell.

A normal stem cell can be real and give rise to a cancer stem cell and perhaps that cell would be eligible for stem cell specific therapy but in cancer we know for a fact now that even more differential cells, like progenitor, can revert to a stem cell state and they can do it continuously.

So the simple idea of sterilising the tumour with stem cell specific therapy might not be enough, simply because the tumours find another way to keep on regenerating stem cells starting from a more downstream product.

So really the two things should go hand in hand - debulking the tumour with conventional chemotherapy and perhaps developing a more specific tool to sterilise the tumours by taking out all the stem cells present at the moment of therapy.