Moving to Nature Networks

Dear everybody.

From now on this blog is moving to Nature Networks. Find it following this link.

See you there!

Mini workshop in Oxford

Today Marcus Tindall has organised a mini symposium (for lack of a better name) for me and the guys here working on mathematical models of cancer to get to know each other. I have given a very small presentation [PDF] (<30m) that covers stuff I presented before.

From the CMB I got to know the work of:

• Philip Murray, who has created a CA model to study the role of the cell cycle in tumours and that is now trying to obtain a continuous model that displays the same behaviour.
• Alex Fletcher who studies hypoxia in tumour development at the sub-cellular scale.
• Matt Johnston who works with W. Bodmer (whose game theory models have inspired my own work) to study the dynamics of cell populations in a colon crypt in colorectal cancer. His model shows how a homeostatic population could explode by slightly altering some of the paramers.
• Natasha Li who collaborates with Gatenby to study, using Cellular Automaton and continuous models, the role of glycolysis in tumour invasion and the influence of the stromal environment. This is specially relevant to me since it is one of my two main lines of work at the moment. She mention in her talk that glycolytic cells are especially sensitive to glucose deprivation.
  
• Rebecca Carter works on multiscale models of fluid and drug transportation in tumours.
• Marcus Tindall gave a brief introduction to his multiscale model of interaction between the cell cycle and cell density.

The presentations were all quite short but I hope to hear more from these people in the coming days.

Queerer than we can suppose

I found this video from a Richard Dawkins's talk in which he talks about the strangeness of science.

He talks that science is about truth but that our brain is evolved to cope with every day's reality, within the scope of the reality we have to live with. He cites the example that matter is mostly composed of space but we do not perceive it like that since it is more useful for us to perceive it as solid and opaque. He argues that a living being of the size of a neutrino and capable of vision would see matter as mostly empty space only by the nature of the space it inhabits. Similarly, things that look entirely unlikely to us (the existence of life) become inevitable when considering the vast amounts of time and space the universe has been going on compared to the space and time of our human lifetimes.

More shockingly to me he claims that humans are more akin to automata than to agents seeking what they consider positive things and avoiding negative things. The reason being that evolutionarily we rather model fellow humans as people with a purpose than as systems made of components whose design and integration we ignore.

In any case this is an important issue for scientists and philosophers of science: our brains have evolved for certain purposes and with certain biases and that should impose some limitations and constraints in what things we can understand and how we chose to interpret natural phenomena.

Oxford

I will be staying one month at the Centre for Mathematical Biology directed by Philip Maini at the University of Oxford. With a little of luck I will be able to meet people interested in mathematical discrete models of cancer evolution and angiogenesis.

In the Centre they have some interesting (and relevant) research lines like "individual and collective behaviour in ecology" and of course "cancer modelling". The Centre is pioneering (with Arizona's Gatenby and Oxford's Comlab Gavaghan) the idea that glycolytic acidity promotes invasion. Maybe this could be an opportunity to test my hypothesis that this invasion comes in waves.

Talk in Girona

I have been invited by Josep Vehi to give a talk about my research at the institute he directs at the University of Girona.

In this talk I have introduced for the first time the game theory model in which I have worked with people in Dresden (Andreas Deutsch, Haralambos Hatzikirou) and Bonn (Matthias Simon) in which I study Gatenby's hypothesis of acid mediated tumour invasion. I have also talked about the Cellular Automata model I have developed with Benjamin Ribba (Lyon) to study the microenvironmental influence in cancer evolution which I have previously presented in Lyon, Dundee and Dresden.

The presentation can be found here in PDF format.

cancer and the cell cycle

Last Friday I came to the Max Planck Instute for Cell Biology, at the other side of Dresden, to attend a series of seminars including one from a colleague and friend of mine, Babis Hatzikirou, about the cell cycle.

The classical view on the cell cycle can be seen in this picture that I took from Babis's presentation (and which I suspect he took from somewhere else :)):
This is quite interesting although not precisely research news. Most of the cell cycle is of course devoted to interphase and only a minority of the time (assuming that the cell is not in arrest mode) is devoted to create a copy of itself (through mitosis and cytokinesis). The cell cycle is controlled by a finely tuned balance of proteins cdc2-cdc13 and a number of checkpoints make sure that before changing the phase of the cell cycle everything is in order. These checkpoints and their associated proteins (such as the famous TP53) are quite critical to prevent tumour formation as they impede the growth of cells that need DNA repair.

What science is not

From an extract of the book The invisible sex: Uncovering the true roles of Woman in Prehistory (review in Nature 3rd of May issue).

"science is not truth; it is, instead, a method for diminishing ignorance"

A 3D model of human breast cancer

This has been covered in a few places like the BBC and ScienceDaily. It seems that some researchers at Queen Mary College in London have recently come with a non animal 3D human breast cancer model.

This is interesting at more than one level. Their research was funded by a research charity (Dr Hadwen Trust) that supports the development of methods that avoid animal experiments. Working with rats is not that satisfactory for ethical reasons and also because there are many cases in which the results of rat experiments cannot be extrapolated to humans (seems we are not so similar in some respects after all). It is also much more realistic than just taking some human cancer cells and studying them on a petri dish.

Being capable of performing experiments using realistic 3D models quickly and efficiently is one of the holy grails of theoreticians since it would make experimental validation of our models much easier (confusingly enough what theoreticians call model, eg, equations or computer rules, is not what experimentalists understand as a model, eg. rat, arabidopsis or drosophila). This validation is quite complicated as I have already mentioned in another post. Making this validation easier and more convenient will go a long way in terms of making our work more reliable and quantitative.

Somatic and non somatic evolution

Many ecologists study evolution of the non somatic kind. That is, evolution that happens as a consequence of mutations in the germ line of multicellular organisms during reproduction. The evolution of cancer is of the somatic kind. This means that it affects cells of the soma, the ones that are not transmitted to the offspring.

Some time ago I got this paper from Crespi and Summers (nicely enough, publicly available). I will probably talk about this paper, entitled Evolutionary biology of cancer (and presented to a readership of ecologists) some other time but I liked a table in which they compare somatic and non somatic evolution.

Phenotypic variation. In most ecosystems of multicellular organisms variation is attained through genetic recombination (sexual reproduction) and mutation. In a tumour we also have to consider also genomic instability (a hypothesis by which some individuals have a higher probability of mutation) and epigenetic alteration (the environment also affects the behaviour of cells in ways that could make tumour progression to cancer more or less likely).
Selection. In most ecosystems it means dealing better with competitors, avoiding predators, parasites and producing many fit successors. In a tumour means being good at competing for resources with other cells (tumour or otherwise), avoiding the immune system and coping with environmental signals designed to maintain homeostasis.
Drift. That is similar in both types of evolution.
Inheritance. In many cases that involves the transmission of genes from parents to offspring through sexual recombination. In tumours there is no sexual reproduction.
Result. In most ecosystems the result is adaptation across generations. In a tumour the end results is in many cases the death of the individual and thus of all the cells in the body, including the cancer cells.

I think that this is a quite interesting and useful comparison of evolution although I am not sure I agree with all the differences suggested. In my view the evolution in a tumour does not differ much from other types of evolution. For instance, epigenetic changes do play a role in other ecosystems asides from cancer. Genetic instability is not a source of variation, genetic mutations are (genetic instability just makes genetic mutations more likely). Also the fact that tumour cells reproduce asexually is not a big difference with more conventional ecosystems. At the end of the day most of the biomass of the planet is made of bacteria that reproduces asexually. What it is true is that as far as we know, the end result of cancer evolution is either the end of the cancer itself or the end of the individual that hosts the cancer and thus the end of the cancer cells. Thus the only way tumour cells have to be successful is to evolve in such a way that the life of the host is not threatened (you can call that tumour sustainable growth).

Autophagy and cancer

This is a new cellular mechanism I did not know about: autophagy. Nature's issue of April 12th (I am bit behind I know) has an interesting article in the section Q&A on autophagy and its role in cancer.

Autophagy is the process by which cells degrade faulty or redundant components. It is used by cells when they need to reuse molecules for other uses and also it plays an important role in complementing apoptosis. Both apoptosis and autophagy are connected to cell death but in the case of autophagy cell death is not always the outcome although it can be a substitute when the apoptotic mechanism is crippled. In that case the cell literally eats itself to death.

The image bellow comes from the article. Autophagy has the potential of being useful for cancer supression but also for cancer promotion. The balance is important, too little and you get cell death when the cell cannot produce things it needs by reusing parts of itself. Too much of it and you also get cell death since the cell can eat itself. Altering this balance in a tumour cell could be the source of a new therapy although as usual it is important to remember that cells might evolve mechanisms to avoid the trouble of autophagy, maybe by inactivating the atophagy mechanism all together. Even in that case the tumour cell would be less capable of surviving in situations of stress since it would not be able to recycle material.

Autophagy seems to be a mechanism whose precise role in cancer has not been fully studied yet but could be a promising extra target for a multi target therapy that could hinder cancer evolution and growth.