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.

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.

Evolution and medicine

Catriona MacCallum, an editor at PLoS Biology has posted the following essay (being PLoS, it is available to everybody) about medicine and evolution.

According to the article, physicians do not get much of a training in evolution as a method to study the origin of diseases. That is because most of the training of physicists is not to make them good scientists but to make them good at treating patients. Quoting the article: “does a mechanic need to understand the origins, history and technological advances that have gone into the modern motor vehicle in order to fix it?”.

This approach is not entirely wrong and once can treat things that are the result of an evolutionary process without having to spend too much time studying evolution. A different thing is when the disease is not a result of evolution but they are evolution itself. They never mention cancer in the article but cancer and infectious diseases are clear cases of diseases in which evolution should be dealt with if the disease is to be cured or even contained. Without an understanding of evolution a physician will be unable to understand how the bacteria or cancer cells will react and evolve when a treatment is used or what phenotypical traits are more likely to be evolved and thus cause problems to or be exploited by the medical community.

Cell article on science blogs

Blogs as a way to communicate science. This is quite an unusual topic for Cell that, as opposed to Science and Nature journals, devotes less space to the non-technical side of science. For those of you that are subscribed, the article is here.

According to the article there are approximately 20000 blogs with the label ‘science’. That is quite an impressive number since most of my colleagues seem to be doing lots of things but not blogging. It seems that most of these science blogs are actually about pseudo science which would be the number of more conventional science blogs to around 1200 (always according to sources cited in the article). These are generally blogs like mine (of course in many cases better written and updated more often) which deal with fairly specific issues in a specific field of science.

These science blogs can be just about anything. Many do like I do and comment (what we personally find) interesting stuff in our own field of research that we find reading, mostly, papers and journals. Some do also include bits about their own lifes and produce some sort of hybrid between the conventional blog (understood as a personal diary) and the scientific blog. Some take the idea of science blog a step further and every day record their latest results online (although in some fields, like biology, this behaviour seems to be quite rare due to the extreme levels of competition between experimental biologists).

Why would any one start a science blog? On top of the conventional reasons why people start a blog (and weighted down by the fact that most of us do not carry sizable audiences) is the thought that when you write something with the expectation (as unlikely as it might be) that someone will read it that surely helps to clarify that something in your mind.