Mushrooming Secret Army

 

We have in these pages talked quite a bit about our ‘secret army’ — the bugs that share our body to the extent that bacteria outnumber us on a cell-to-cell basis by at least three to one. As we noted in Secret Army: More Manoeuvres Revealed, bacteria are just one part of what is collectively called the microbiota’ but with over 2000 different species and a total gene pool hundreds of times bigger than our own 20,000 or so, they are by far the biggest. And it’s gradually become clear that they are not with us just because our bodies are warm, damp and comfortable but they help us get the most out of our food and they’re important in the working of our immune system.

Bacteria and cancer

Most critically, in the present context, we now know that shifts in proportions of species in the microbiome can influence cancer development and perhaps even the spread of tumour cells around the body.

Small fry

Important though they are, bacteria aren’t the only members of the microbiome — which includes fungi, viruses and various single-celled parasites (protozoa). Today’s story is about fungi, a group of microorganisms familiar to gardeners world-wide, that includes yeasts and molds, as well as the more familiar mushrooms. There’s estimated to be several million species of fungi, although only about 120,000 have been described. Some we can eat, some can kill us and, of course, there’s magic mushrooms.

With all this diversity you might wonder whether any fungi have elbowed their way into us to share the delights of the human body alongside bacterial microbes. Of course they have: most people will have heard of candidiasis — a fungal infection caused by Candida yeasts that belong to the genus Candida. Candida normally finds its niche in places like the mouth (giving the condition called thrush), gut, vagina and on the skin and usually doesn’t give us any trouble. But, truth to tell, we’ve known very little about fungi in us until recently when the power of DNA sequencing has started to be applied to the topic. This has confirmed that we do carry lots of fungi around with us, albeit that they are only a tiny fraction of the microbial community (somewhat less than 0.1%).

New actor in the cancer cast

This fungal force of microbes is known as the mycobiome (as distinct from the microbiome) and, in contrast to bacteria, there is no evidence that it has a role in cancer. Until, that is, the recent publication from New York University School of Medicine by Berk Aykut, George Miller and friends showing that fungi travel from the gut to the pancreas where a particular species can actually give cancer a helping hand. The cancer in question is pancreatic ductal adenocarcinoma (PDA) that has a particularly dismal prognosis.How a fungus can drive cancer. The scheme represents a tumour in the pancreas changing the make up of the adjacent fungal community and how a protein in the blood called mannose binding lectin (MBL) can attach to the outer surface of a fungal cell. When this happens MBL changes shape so it can then stick to another protein (C3) which in turn activates a relay of proteins called the complement cascade. One upshot of this can be to promote tumour growth. From Dambuza and Brown 2019.

How did they do it?

Aykut et al. first used DNA sequencing to look for fungus-specific sequences in the pancreas of humans with PDA and in mouse models of PDA, They’d previously shown that the bacterial load goes up by about 1000-fold in tumours compared with healthy tissue and, lo and behold, they found a similar increase in fungi. Next they tagged strains of fungus with a fluorescent label and showed that the cells could migrate from the gut to the pancreas of mice in under 30 minutes.

They then tracked down a protein called mannose binding lectin (MBL) expression of which is associated with poor survival in human PDA patients. MBL is a ‘serum protein’, meaning that it floats around in blood. This led to the discovery that MBL can bind to the surface of fungal cells and when it does so changes shape to permit activation of a relay of signal proteins called the complement system. This ‘complement cascade’ is part of our immune system, enhancing the capacity of antibodies and phagocytic cells to clear microbes from the circulation.

Jules Bordet was the chap who first showed that something in normal blood plasma could help to kill off bacteria back at the end of the 19th century and, as such, deserves to be better remembered as a famous Belgian.

The complement system is pretty amazing because, whilst it can trigger an immune response against invading pathogens, it can also switch on inflammatory pathways that help cells grow and move around — in other words, give a helping hand to tumours.

Fungible?

I met this word for the first time a few days ago, courtesy of the journalist and author Ann Treneman. You’d think that no piece on fungi would be complete without it but it turns out to have nothing to do with mushrooms: it just means interchangeable or switchable. But hang on! We can squeeze it in by asking a very relevant question: are pancreatic fungi fungible in terms of their capacity to promote cancer? Aykut et al. did just that and the answer was ‘no they’re not.’ One species seems to be particularly abundant in PDA: the genus Malassezia. This was true for both mouse and human tumours and perhaps that shouldn’t surprise us as Malassezia is the most abundant fungal species in mammalian skin, accounting for more than 80% of our skin mycobiome. So it’s Malassezia not other species (e.g., Candida) that has the power to drive cancer.

Spores of the yeast Malassezia

Fungal footnote

In a final exciting experiment Aykut et al. showed that antifungal drugs halted PDA progression in mice and improved the ability of chemotherapy to shrink the tumour. This obviously raises the notion that if we can find ways of shifting the balance of fungal communities or interfering with the link to the complement cascade we might have a completely new line on desperately needed therapies for this disease.

References

Aykut, B. et al., (2019). The fungal mycobiome promotes pancreatic oncogenesis via activation of MBL. Nature 574, 264–267.

Dambuza, I.M. and Brown, G.D. (2019). Fungi accelerate pancreatic cancer. Nature 574, 184-185.

The Power of Flower

 

We know we don’t ‘understand cancer’ — for if we did we would at least be well on the way to preventing the ten million annual deaths from these diseases and perhaps even stymieing their appearance in the first place. But at least, after many years of toil by thousands of curious souls, we might feel brave enough to describe the key steps by which it comes about.

Here goes!

Our genetic material, DNA, carries a code of four different units (bases) that enables cells to make twenty-thousand or so different types of proteins. Collectively these make cells — and hence us — ‘work’. An indicator of protein power is that we grow from single, fertilized cells to adults with 50 trillion cells. That phenomenal expansion involves, of course, cells growing and dividing to make more of themselves — and, along the way, a bit of cell death too. The fact that there are nearly eight billion people on planet earth testifies to the staggering precision with which these proteins act.

Nobody’s perfect

As sports fans will know, the most successful captain in the history of Australian rugby, John Eales, was nicknamed ‘Nobody’ because ‘Nobody’s perfect’. Well, you might care to debate the infallibility of your sporting heroes but when it comes to their molecular machinery, wondrous though it is, perfect it is not.

Evidence: from the teeming eight billion there emerges every year 18 million new cancer cases (that’s about one in every 444). And cancers are, of course, abnormal cell growth: cells growing faster than they should or growing at the wrong time or in the wrong place — any of which means that some of the masterful proteins have suffered a bit of a malfunction, as the computer geeks might say.

How can that happen?

Abnormal protein activity arises from changes in DNA (mutations) that corrupt the normal code to produce proteins of greater or lesser activity or even completely novel proteins.

These mutations may be great or small: changes in just one base or seismic fragmentation of entire chromosomes. But the key upshot is that the cell grows abnormally because regulatory proteins within the cell have altered activity. Mutations can also affect how the cell ‘talks’ to the outside world, that is, the chemical signals it releases to, for example, block immune system killing of cancer cells.

Clear so far?

Mutations can change how cells proliferate, setting them free of normal controls and launching their career as tumour cells and, in addition, they can influence the cell’s environment in favour of unrestricted growth.

The latter tells us that cancer cells cooperate with other types of cell to advance their cause but now comes a remarkable discovery of a hitherto unsuspected type of cellular collaboration. It’s from Esha Madan, Eduardo Moreno and colleagues from Lisbon, Arkansas, St. Louis, Indianapolis, Omaha, Dartmouth College, Zurich and Sapporo who followed up a long-known effect in fruit flies (Drosophila) whereby the cells can self-select for fitness to survive.

Notwithstanding the fact that flies do it, the idea of a kind of ‘cell fitness test’ is novel as far as human cells go — but it shouldn’t really surprise us, not least because our immune system (the adaptive immune system) features much cooperation between different types of cell to bring about the detection and removal of foreign or damaged cells.

Blooming science

So it’s been known for over forty years that Drosophila carries out cell selection based on a ‘fitness fingerprint’ that enables it to prevent developmental errors and to replace old tissues with new. However, it took until 2009 before the critical protein was discovered and, because mutant forms of this protein gave rise to abnormally shaped nerve cells that looked like bunches of flowers, Chi-Kuang Yao and colleagues called the gene flower‘.

Cells can make different versions of flower proteins (by alternative splicing of the gene) the critical ones being termed ‘winner’ and ‘loser’ because when cells carrying winner come into contact with cells bearing loser the latter die and the winners, well, they win by dividing and filling up the space created by the death of losers.

The effect is so dramatic that Madan and colleagues were able to make some stunning movies of the switch in cell populations that occured when they grew human breast cancer cells engineered to express different version of flower tagged with red or green fluorescent labels.

Shift in cell populations caused by two types of flower proteins. 

Above are images at time zero and 24 h later of co-cultures of cells expressing  green and red proteins (losers and winners). From Madan et al. 2019.

Click here to see the movie on the Nature website.

Winner takes almost all

The video shows high-resolution live cell imaging over a 24 hour period compressed into a few seconds. Cells expressing the green protein (hFwe1 (GFP)) were co-cultured with red cells (hFwe2 (RFP)). Greens are losers, reds winners. As the movie progresses you can see the cell population shifting from mainly green to almost entirely red, as the first and last frames (above) show.

How does flower power work?

Flower proteins form channels across the outer membrane of the cell that permit calcium flow, and it was abnormal calcium signalling that caused flowers to bloom in Drosophila nerves. It would be reasonable to assume that changes in calcium levels are behind the effects of flower on cancer cells. Reasonable but wrong, for Madan & Co were able to rule out this explanation. At the moment we’re left with the rather vague idea that flower proteins mediate competitive interactions between cells and these determine whether cells thrive and proliferate or wither and die.

Does this really happen in human cancers?

Madan and colleagues looked at malignant and benign human tumours and found that there was more ‘winner’ flower protein in the former than the latter and that ‘loser’ levels were higher in normal cells next to a tumour than further away. Both consistent with the notion that tumour cells express winner and this induces loser in nearby normal cells leading to their death. What’s more they reproduced this effect in mice by transplanting human breast cancer cells expressing winner.

So there we are! After all this time a variant on how cancer cells can manipulate their surroundings to promote the development of tumours. Remarkable though this finding is, in a way that is familiar it’s just the beginning of this story. We don’t know how flower proteins work in giving cancers a helping hand and we don’t know how effective they are. Until we answer those questions it would be premature to try to come up with therapies to block their effect.

But it is a moment to sit back and reflect on the astonishing complexity of living organisms and their continuing capacity to surprise.

Reference

Madan, E. et al. (2019). Flower isoforms promote competitive growth in cancer. Nature 572, 260-264.

Yao, C-K., et al., (2009). A synaptic vesicle-associated Ca2+ channel promotes endocytosis and couples exocytosis to endocytosis. Cell 138, 947–960.

Secret Army: More Manoeuvres Revealed

 

I don’t know about you but I find it difficult to grasp the idea that there are more bugs in my body than there are ‘me’ cells. That is, microorganisms (mostly bacteria) outnumber the aggregate of liver, skin and what-have-you cells. They’re attracted, of course, to the warm, damp surfaces of the cavities in our bodies that are covered by a sticky, mucous membrane, e.g., the mouth, nose and especially the intestines (the gastrointestinal tract).

The story so far

Over the last few years it’s become clear that these co-residents — collectively called the microbiota — are not just free-loaders. They’re critical to our well-being in helping to fight infection by other microrganisms (as we noted in Our Inner Self), they influence our immune system and in the gut they extract the last scraps of nutrients from our diet. So maybe it makes them easier to live with if we keep in mind that we need them every bit as much as they depend on us.

We now know that there are about 2000 different species of bacteria in the human gut (yes, that really is 2,000 different types of bug) and, with all that diversity, it’s not surprising that the total number of genes they carry far exceeds our own complement (by several million to about 20,000). In it’s a small world we noted that obesity causes a switch in the proportions of two major sub-families of bacteria, resulting in a decrease in the number of bug genes. The flip side is that a more diverse bug population (microbiome) is associated with a healthy status. What’s more, shifts of this sort in the microbiota balance can influence cancer development. Even more remarkably, we saw in Hitchhiker Or Driver? That the microbiome may also play a role in the spread of tumours to secondary sites (metastasis).

Time for a deep breath

If all this is going on in the intestines you might well ask “What about the lungs?” — because, and if you didn’t know you might guess, their job of extracting oxygen from the air we inhale means that they are covered with the largest surface area of mucosal tissue in the body. They are literally an open invitation to passing microorganisms — as we all know from the ease with which we pick up infections.

In view of what we know about gut bugs a rather obvious question is “Could the bug community play a role in lung cancer?” It’s a particularly pressing question because not only is lung cancer the major global cause of cancer death but 70% lung cancer patients have bacterial infections and these markedly influence tumour development and patient survival. Tyler Jacks, Chengcheng Jin and colleagues at the Massachusetts Institute of Technology approached this using a mouse model for lung cancer (in which two mutated genes, Kras and P53 drive tumour formation).

In short they found that germ-free mice (or mice treated with antibiotics) were significantly protected from lung cancer in this model system.

How bacteria can drive lung cancer in mice. Left: scheme of a lung with low levels of bacteria and normal levels of immune system cells. Right: increased levels of bacteria accelerate tumour growth by stimulating the release of chemicals from blood cells that in turn activate cells of the immune system to release other effector molecules that promote tumour growth. The mice were genetically altered to promote lung tumour growth (by mutation of the Kras and P53 genes). In more detail the steps are that the bacteria cause macrophages to release interleukins (IL-1 & IL-23) that stick to a sub-set of T cells (γδ T cells): these in turn release factors that drive tumour cell proliferation, including IL-22. From Jin et al. 2019.

As lung tumours grow in this mouse model the total bacterial load increases. This abnormal regulation of the local bug community stimulates white blood cells (T cells present in the lung) to make and release small proteins (cytokines, in particular interleukin 17) that signal to neutrophils and tumour cells to promote growth.

This new finding reveals that cross-talk between the local microbiota and the immune system can drive lung tumour development. The extent of lung tumour growth correlated with the levels of bacteria in the airway but not with those in the intestinal tract — so this is an effect specific to the lung bugs.

Indeed, rather than the players prominent in the intestines (Bs & Fs) that we met in Hitchhiker Or Driver?, the most common members of the lung microbiome are Staphylococcus, Streptococcus and Lactobacillus.

In a final twist Jin & Co. took bacteria from late-stage tumours and inoculated them into the lungs of mice with early tumours that then grew faster.

These experiments have revealed a hitherto unknown role for bacteria in cancer and, of course, the molecular signals identified join the ever-expanding list of potential targets for drug intervention.

References

Jin, C. et al. (2019). Commensal Microbiota Promote Lung Cancer Development via γδ T Cells. Cell 176, 998-1013.e16.

Fantastic Stuff

 

It certainly is for Judy Perkins, a lady from Florida, who is the subject of a research paper published last week in the journal Nature Medicine by Nikolaos Zacharakis, Steven Rosenberg and their colleagues at the National Cancer Institute in Bethesda, Maryland. Having reached a point where she was enduring pain and facing death from metastatic breast cancer, the paper notes that she has undergone “complete durable regression … now ongoing for over 22 months.”  Wow! Hard to even begin to imagine how she must feel — or, for that matter, the team that engineered this outcome.

How was it done?

Well, it’s a very good example of what I do tend to go on about in these pages — namely that science is almost never about ‘ground-breaking breakthroughs’ or ‘Eureka’ moments. It creeps along in tiny steps, sideways, backwards and sometimes even forwards.

You may recall that in Self Help – Part 2, talking about ‘personalized medicine’, we described how in one version of cancer immunotherapy a sample of a patient’s white blood cells (T lymphocytes) is grown in the lab. This is a way of either getting more immune cells that can target the patient’s tumour or of being able to modify the cells by genetic engineering. One approach is to engineer cells to make receptors on their surface that target them to the tumour cell surface. Put these cells back into the patient and, with luck, you get better tumour cell killing.

An extra step (Gosh! Wonderful GOSH) enabled novel genes to be engineered into the white cells.

The Shape of Things to Come? took a further small step when DNA sequencing was used to identify mutations that gave rise to new proteins in tumour cells (called tumour-associated antigens or ‘neoantigens’ — molecular flags on the cell surface that can provoke an immune response – i.e., the host makes antibody proteins that react with (stick to) the antigens). Charlie Swanton and his colleagues from University College London and Cancer Research UK used this method for two samples of lung cancer, growing them in the lab to expand the population and testing how good these tumour-infiltrating cells were at recognizing the abnormal proteins (neo-antigens) on cancer cells.

Now Zacharakis & Friends followed this lead: they sequenced DNA from the tumour tissue to pinpoint the main mutations and screened the immune cells they’d grown in the lab to find which sub-populations were best at attacking the tumour cells. Expand those cells, infuse into the patient and keep your fingers crossed.

Adoptive cell transfer. This is the scheme from Self Help – Part 2 with the extra step (A) of sequencing the breast tumour. Four mutant proteins were found and tumour-infiltrating lymphocytes reactive against these mutant versions were identified, expanded in culture and infused into the patient.

 

What’s next?

The last step with the fingers was important because there’s almost always an element of luck in these things. For example, a patient may not make enough T lymphocytes to obtain an effective inoculum. But, regardless of the limitations, it’s what scientists call ‘proof-of-principle’. If it works once it’ll work again. It’s just a matter of slogging away at the fine details.

For Judy Perkins, of course, it’s about getting on with a life she’d prepared to leave — and perhaps, once in while, glancing in awe at a Nature Medicine paper that does not mention her by name but secures her own little niche in the history of cancer therapy.

References

McGranahan et al. (2016). Clonal neoantigens elicit T cell immunoreactivity and sensitivity to immune checkpoint blockade. Science 10.1126/science.aaf490 (2016).

Zacharakis, N. et al. (2018). Immune recognition of somatic mutations leading to complete durable regression in metastatic breast cancer. Nature Medicine 04 June 2018.

The Shocking Effect of Boiled Bugs

There’s never a dull moment in science – well, not many – and at the moment no field is fizzing more than immunotherapy. Just the other day in Outsourcing the Immune Response we talked about the astonishing finding that cells from healthy people could be used to boost the immune response – a variant on the idea of taking from patients cells that attack cancers, growing them in the lab and using genetic engineering to increase potency (generally called adoptive cell therapy).

A general prod

Just when you thought that was as smart as it could get, along comes Angus Dalgleish and chums from various centres in the UK and Spain with yet another way to give the immune system a shock. They used microorganisms (i.e. bugs) as a tweaker. The idea is that bacteria (that have been heat-killed) are injected, they interact with the host’s immune system and, by altering the proteins expressed on immune cells (macrophages, natural killer cells and T cells) can boost the immune response. That in turn can act to kill tumour cells. It’s a general ‘immunomodulatory’ effect. Dalgleish describes it as “rather like depth-charging the immune system which has been sent to sleep”. Well, giving it a prod at least.

bugs-pic

Inactivating bugs (bacteria) and waking up the immune system.

And a promising effect

The Anglo-Spanish effort used IMM-101 (a heat-killed suspension of a bacterium called Mycobacterium obuense) injected under the skin, which has no significant side-effects. The trial was carried out in patients with advanced pancreatic cancer, a disease with dismal prognosis, and IMM-101 immunotherapy was combined with the standard chemotherapy drug (gemcitabine). IMM-101increased survival from a median of 4.4 months to 7 months with some patients living for more than a year and one for nearly three years.

Although the trial numbers are small as yet, this is a very exciting advance because it looks as though immunotherapy may be able to control one of the most serious of cancers in which its incidence nearly matches its mortality.

References

Dalgleish, A. et al. (2016). Randomised, open-label, phase II study of gemcitabine with and without IMM-101 for advanced pancreatic cancer. British Journal of Cancer doi: 10.1038/bjc.2016.271.

 

Outsourcing the Immune Response

We’re very trendy in these pages, for no other reason than that the idea is to keep up to date with exciting events in cancer biology. Accordingly, we have recently talked quite a lot about the emerging field of cancer immunotherapy – the notion that our in-built immune system will try to kill cancer cells as they emerge, because it ‘sees’ them as being to some extent ‘foreign’, but that when tumours make their presence known it has not been able to do the job completely. The idea of immunotherapy is to give our in-house system a helping hand and we’ve seen some of the approaches in Self Help – Part 2 and Gosh! Wonderful GOSH.

The immune see-saw

Our immune system walks a tight-rope: on the one hand it should attack and eliminate any ‘foreign’ cells it sees (so that we aren’t killed by infections) but, on the other, if it’s too efficient it will start destroying out own cells (which is what happens in auto-immune diseases such as Graves disease (overactive thyroid gland) and rheumatoid arthritis.

Like much of our biology, then, it’s a tug-of-war: to kill or to ignore? And, like the cell cycle that determines whether a cell should grow and divide to make two cells, it’s controlled by the balance between ‘accelerators’ and ‘brakes’. The main targets for anti-tumour immune activity are mutated proteins that appear on the surface of cancer cells – called neo-antigens (see The Shape of Things to Come?)

The aim of immunotherapy then is to boost tumour responses by disabling the ‘brakes’. And it’s had some startling successes with patients going into long-term remission. So the basic idea works but there’s a problem: generally immunotherapy doesn’t work and, so far, in only about one in ten of patients have there been significant effects.

Sub-contracting to soup-up detection

Until now it’s seemed that only a very small fraction of expressed neo-antigens (less than 1%) can turn on an immune response in cancer patients. In an exciting new take on this problem, a team of researchers from the universities of Oslo and Copenhagen have asked: “if someone’s immune cells aren’t up to recognizing and fighting their tumours (i.e. ‘seeing’ neo-antigens), could someone else’s help?” It turns out that many more than 1 in 100 neo-antigens are able to cause an immune response. Even more exciting (and surprising), immune cells (T cells) from healthy donors can react to these neo-antigens and, in vitro at least (i.e. in cells grown in the laboratory), can kill tumour cells.

118. pic

Genetic modification of blood lymphocytes

T cells are isolated from a blood sample and novel genes inserted into their DNA. The engineered T cells are expanded and then infused into the patient. In the latest development T cells from healthy donors are screened for reactivity against neo-antigens expressed in a patient’s melanoma. T cell receptors that  recognise neo-antigens are sequenced and then transferred to the patient’s T cells.

How does that work?

T cells (lymphocytes) circulating in the blood act, in effect, as scouts, scanning the surface of all cells, including cancer cells, for the presence of any protein fragments on their surface that should not be there. The first contact with such foreign protein fragments switches on a process called priming that ultimately enables T cells to kill the aberrant cells (see Invisible Army Rouses Home Guard).

What the Scandinavian group did was to screen healthy individuals for tissue compatibility with a group of cancer patients. They then identified a set of 57 neo-antigens from three melanoma patients and showed that 11 of the 57 could stimulate responses in T cells from the healthy donors (T cells from the patients only reacted to two neo-antigens). Indeed the neo-antigen-specific T cells from healthy donors could kill melanoma cells carrying the corresponding mutated protein.

What can possibly go wrong?

The obvious question is, of course, how come cells from healthy folk have a broader reactivity to neo-antigens than do the cells of melanoma patients? The answer isn’t clear but presumably either cancers can make T cell priming inefficient or T cells become tolerant to tumours (i.e. they see them as ‘self’ rather than ‘non-self’).

And the future?

The more critical question is whether the problem can be short-circuited and Erlend Strønen and friends set about this by showing that T cell receptors in donor cells that recognize neo-antigens can be sequenced and expressed in the T cells of patients. This offers the possibility of a further type of adoptive cell transfer immunotherapy to the one we described in Gosh! Wonderful GOSH.

https://cancerforall.wordpress.com/2015/11/19/gosh-wonderful-gosh/

As one of the authors, Ton Schumacher, put it “Our findings show that the immune response in cancer patients can be strengthened; there is more on the cancer cells that makes them foreign that we can exploit. One way we consider doing this is finding the right donor T cells to match these neo-antigens. The receptor that is used by these donor T-cells can then be used to genetically modify the patient’s own T cells so these will be able to detect the cancer cells.”

And Johanna Olweus commented that “Our study shows that the principle of outsourcing cancer immunity to a donor is sound. However, more work needs to be done before patients can benefit from this discovery. Thus, we need to find ways to enhance the throughput. We are currently exploring high-throughput methods to identify the neo-antigens that the T cells can “see” on the cancer and isolate the responding cells. But the results showing that we can obtain cancer-specific immunity from the blood of healthy individuals are already very promising.”

References

Strønen, M. Toebes, S. Kelderman, M. M. van Buuren, W. Yang, N. van Rooij, M. Donia, M.-L. Boschen, F. Lund-Johansen, J. Olweus, T. N. Schumacher. Targeting of cancer neoantigens with donor-derived T cell receptor repertoires. Science, 2016.

“Fighting cancer with the help of someone else’s immune cells.” ScienceDaily. ScienceDaily, 19 May 2016.

The Shape of Things to Come?

One of the problems of trying to keep up with cancer – and indeed helping others to do so – is that you (i.e. ‘I’) get really irritated with the gentlemen and ladies of the press for going over the top in their efforts to cover science. I have therefore been forced to have a few rants about this in the past – actually, when I came to take stock, even I was a bit shocked at how many. Heading the field were Not Another Great Cancer Breakthough, Put A Cap On It and Gentlemen… For Goodness Sake. And not all of these were provoked by The Daily Telegraph!

If any of the responsible reporters read this blog they probably write me off as auditioning for the Grumpy Old Men tv series. But at least one authoritative voice says I’m really very sane and balanced (OK, it’s mine). Evidence? The other day I spotted the dreaded G word (groundbreaking) closely juxtaposed to poor old Achilles’ heel – and yes, it was in the Telegraph – but, when I got round to reading the paper, I had to admit that the work referred to was pretty stunning. Although, let’s be clear, such verbiage should still be banned.

A Tumour Tour de Force

The paper concerned was published in the leading journal Science by Nicholas McGranahan, Charles Swanton and colleagues from University College London and Cancer Research UK. It described a remarkable concentration of current molecular fire-power to dissect the fine detail of what’s going on in solid tumours. They focused on lung cancers and the key steps used to paint the picture were as follows:

1. DNA sequencing to identify mutations that produced new proteins in tumour cells (called tumour-associated antigens or ‘neoantigens’ – meaning molecular flags on the cell surface that can provoke an immune response – i.e. the host makes antibody proteins that react with (stick to) the antigens). Typically they found just over 300 of these ‘neoantigens’ per tumour – a reflection of the genetic mayhem that occurs in cancer.

2 tumoursVariation in neoantigen profile between two multi-region sequenced non-small cell lung tumours. There were approximately 400 (left) and 300 (right) neoantigens/tumour

  • Blue: proportion of clonal neoantigens found in every tumour region.
  • Yellow: subclonal neoantigens shared in multiple but not all tumour regions.
  • Red: subclonal (‘private’) neoantigens found in only one tumour region.
  • The left hand tumour (mostly blue, thus highly clonal) responded well to immunotherapy (from McGranahan et al. 2016).

2. Screening the set of genes that regulate the immune system – that is, make proteins that detect which cells belong to our body and which are ‘foreign.’ This is the human leukocyte antigen (HLA) system that is used to match donors for transplants – called HLA typing.

3. Isolating specialised immune cells (T lymphocytes) from samples of two patients with lung cancer, growing them in the lab to expand the population and testing how good these tumour-infiltrating cells were at recognizing the abnormal proteins (neo-antigens) on cancer cells.

4. Detecting proteins released by different types of infiltrating T cells that regulate the immune response. These include so-called immune checkpoint molecules that limit the extent of the immune response. This showed that T cell subsets that were very good at recognizing neo-antigens – and thus killing cancer cells (they’re CD8+ T cells or ‘killer’ T cells) also made high levels of proteins that restrain the immune response (e.g., PD-1).

5. Showing that immunotherapy (using the antibody pembrolizumab that reacts with PD-1) could significantly extend survival of patients with advanced non-small cell lung cancer. We’ve already met this approach in Self-help Part 1.

The critical finding was that the complexity of the tumour (called the clonal architecture) determines the outcome. Durable benefit from this immunotherapy requires a high level of mutation but a restricted range of neo-antigens. Put another way, tumours that are highly clonal respond best because they have common molecular flags present on every tumour cell.

6. Using the same methods on some skin cancers (melanomas) with similar results.

What did this astonishing assembly of results tell us?

It’s the most detailed picture yet of what’s going on in individual cancers. As one of the authors, Charles Swanton, remarked “This is exciting. This opens up a way to look at individual patients’ tumours and profile all the antigen variations to figure out the best ways for treatments to work. This takes personalised medicine to its absolute limit where each patient would have a unique, bespoke treatment.”

He might have added that it’s going to take a bit of time and a lot of money. But as a demonstration of 21st century medical science it’s an absolute cracker!

References

McGranahan et al. Clonal neoantigens elicit T cell immunoreactivity and sensitivity to immune checkpoint blockade. Science 10.1126/science.aaf490 (2016).

 

Mutating into Gold

It’s probably just as well that few us are aware that the bodies we live in are a battlefield – the cells and molecules that make us are in constant strife to ensure our survival. The lid is lifted from time to time – when we get a cold or pick up some other infection and our immune response sorts it out but not without giving us a headache or a runny nose, just to let us know it’s on the job. By and large though, we plough our furrow in glorious ignorance.

Saving our cells

Perhaps the most important of all the running battles is to save our DNA – that is, to repair the damage continuously suffered by our genetic material so we can carry on. It’s an uphill struggle. The DNA in one of our cells can take up to a million hits every day – and the bombardment comes from every direction: from radiation, air pollution and carcinogens in some of the food we eat. And, of course, we don’t need to mention cigarette smoke.

Damaged chromosomes (blue arrows)

Damaged chromosomes    (blue arrows)

On top of all that cells have to make a new DNA copy every time they reproduce – and we do a lot of that: recall that you set sail on the journey of life as one single, fertilized egg cell and now look at you: a clump of ten trillion (1013) cells that, just to stay as you are, has to make one million new cells every second. What’s more some of your cells deliberately break their own DNA in a process called ‘gene shuffling’ that goes to make the finished product of your aforementioned immune system. The biochemical machinery that does these jobs is mighty efficient but nobody’s perfect – except, of course, for John Eales, Australia’s most successful rugby union captain, nicknamed “Nobody” because “Nobody’s perfect”. When the three thousand million base-pairs of DNA are stuck together for a new cell there’s a mistake about once in every million units added – but a kind of quality control check (mismatch repair) then fixes most of these, so that the overall error is about one in a thousand million. That’s one example of the nifty ways evolution has come up with to fix the damage suffered by our genetic material from all this replicating, assaulting and constructing.

Keeping the show on the road

The overall upshot of the repair machinery is that less than one mutation per day becomes fixed in our genomes – and thus passed on to succeeding generations of cells. The range of things that can damage DNA – and hence the different forms that damage can take – tells you that there must be several different repair systems and indeed we now know that about 200 genes and their protein products have a hand in some repair process or another. There’s so much to know that DNA damage and repair has its own data-base called, inevitably, REPAIRtoire. Much of what we know is, to a considerable extent, thanks to the labours of Tomas Lindahl, Paul Modrich and Aziz Sancar who have just been jointly awarded this year’s Nobel Prize in Chemistry. Because damage to DNA – aka mutations – drives the development of cancers you might suppose that in these pages we will have met these gentlemen before – and indeed we have, if not by name.

Tomas Lindahl Paul Modrich Aziz Sancar

Tomas Lindahl                      Paul Modrich                       Aziz Sancar

Winners of the 2015 Nobel Prize in Chemistry

Forty odd years ago much of the above would have bewildered cell biologists. Thirty years before then, in 1944, Oswald Avery, Colin MacLeod and Maclyn McCarty had shown for the first time that genes are composed of DNA, a finding confirmed in 1952 by Alfred Hershey and Martha Chase in a classic experiment using a virus that infects and replicates within a bacterium. But with the acceptance that, however improbable, our genetic material was indeed made of DNA there came the assumption that it must be very stable. After all, if it carried our most valuable possession then surely it had to be made of molecular granite, absolutely resistant to any kind of chemical change or degradation. Had the bewildered boffins been told that in the twenty-first century we would be sequencing woolly mammoth DNA from samples that are millions of years old they would have been confirmed in their view.

It was Tomas Lindahl in the early 1970s who demonstrated that, although DNA is indeed more stable than its close rello RNA (the intermediate in making proteins) it nevertheless decays quite rapidly under normal conditions – it’s only when sealed in permafrost or blobs of amber that it becomes frozen in time. Lindahl realized that for life based on DNA to have evolved there had to be repair systems that could sustain our genetic material in a functional state and he went on to resolve how one of these did it. Aziz Sancar has worked particularly on the circadian clock (discovering that CRY is a clock protein) and how cells repair ultraviolet radiation damage to DNA: people born with defects in this system develop skin cancer if they are exposed to sunlight. Paul Modrich has contributed mainly to our knowledge of mismatch repair.

Lindahl, Modrich, Sancar and their colleagues over many years haven’t come up with the philosopher’s stone – the chemists still can’t transmute base metals into gold without the aid of a particle accelerator. But what they have done is much more useful for mankind. Revealing the detail of how genome maintenance works has already lead to new cancer treatments and from this beginning will come greater benefits as time goes by. They should enjoy the proceeds of turning molecular knowledge if not to gold then into Swedish kronor (8 million of them) – for the rest of the world it’s a bargain.

References

Lindahl, T. (1993). Instability and decay of the primary structure of DNA. Nature 362, 709-715.

Yang YG, Lindahl T, Barnes DE. (2007). Trex1 exonuclease degrades ssDNA to prevent chronic checkpoint activation and autoimmune disease. Cell 131, 873-886.

Shao, H, Baitinger, C, Soderblom, EJ, Burdett, V, and Modrich, P. (2014). Hydrolytic function of Exo1 in mammalian mismatch repair. Nucleic Acids Research 42, 7104-7112.

Tan C, Liu Z, Li J, Guo X, Wang L, Sancar A, Zhong D. (2015). The molecular origin of high DNA-repair efficiency by photolyase. Nat Commun. 6, 7302.

Blowing Up Cancer

To adapt the saying of the sometime British Prime Minister Harold Wilson, a month is a long time in cancer research. {I know, you’ve forgotten – as well you might. He was PM from 1964 to 1970 and again from 1974 to 1976. His actual words were “A week is a long time in politics”}. When I started to write the foregoing Self Helps (Parts 1 & 2) I had absolutely no intention of mentioning the subject of today’s sermon – viral immunotherapy. But how times change and a recent report has hit the headlines – so here goes.

The reason for my reticence is that this is not a new field – far from it. Folk have been trying to target tumour cells with active viruses for twenty years but efforts have foundered to the extent that the new report is the first time in the western world that a phase III trial (when a drug or treatment is first tested on large groups of people) of cancer “virotherapy” has definitively shown benefit for patients with cancer, although a virus (H101) made by the Shanghai Sunway Biotech Co. was licensed in China in 2005 for the treatment of a range of cancers.

Hard bit already done

I appreciate that getting the hang of immunotherapy in the two Self Helps wasn’t a total doddle – but it was worth it, wasn’t it, bearing in mind we’re dealing with life and death here. My friend and correspondent Rachel Bown had to resort to her GCSE biology notes (since she met me I think she keeps them on the coffee table) but is now up to speed.

Fortunately this bit is pretty easy to follow – it’s just an extension of the viral jiggery-pokery we met in Self Help Part 2. There we saw that using ‘disabled’ viruses is a neat way of getting new genetic material into cells. The viruses have key bits of their genome (genetic material) knocked out – so they don’t have any nasty effects and don’t replicate (make more of themselves) once inside cells. Inserting new bits of DNA carrying a therapeutic gene turns them into a molecular delivery service.

Going viral

In virotherapy there’s one extra wrinkle: the viruses, though ‘disabled’, still retain the capacity to replicate – and this has two effects. First, more and more virus particles (virions) are made in an infected cell until eventually it can hold no more and it bursts. The cell is done for – but a secondary effect is that the newly-made virions spill out and drift off to infect other cells. This amplifies the effect of the initial injection of virus and, in principle, will continue as long as there are cells to infect.

A new tool

The virus used is herpes simplex (HSV-1) of the relatively harmless type that causes cold sores and, increasingly frequently, genital herpes. The reason for this choice is that sometimes, not very often, science gets lucky and Mother Nature comes up with a helping hand. For HSV-1 it was the completely unexpected discovery that when you knock out one of its genes the virus becomes much more effective at replicating in tumour cells than in normal cells. That’s a megagalactic plus because, in effect, it means the virus targets tumour cells, thereby overcoming one of the great barriers to cancer therapy. In this study another viral gene was also deleted, which increases the immune response against infected tumour cells.

All this cutting and pasting (aka genetic engineering) is explained in entertaining detail in Betrayed by Nature but for now all that matters is that you end up with a virus that:

  1. Gets into tumour cells much more efficiently than into normal cells,
  2. Makes the protein encoded by the therapeutic gene, and
  3. Replicates in the cells that take it up until eventually they are so full of new viruses they go pop.

The finished product, if you can get your tongue round it, goes by the name of talimogene laherparepvec, mercifully shortened by the authors to T-VEC (made by Amgen). So T-VEC mounts a two-pronged attack – what the military would call a pincer movement. Infected tumour cells are killed (they’re ‘lysed’ by viral overload) and the inserted gene makes a protein that soups up the immune response – called GM-CSF (granulocyte macrophage colony-stimulating factor). The name doesn’t matter: what’s important is that it’s a human signaling molecule that stimulates the immune system, the overall result being production of tumour-specific T cells.

Fig. 1 Viral Therapy

Virotherapy. Model of a virus (top). The knobs represent proteins that enable the virus to stick to cells. Below: sequence of injecting viruses that are taken up by tumour cells that eventually burst to release new virions that diffuse to infect other tumour cells.

And the results?

The phase III trial, led by Robert Andtbacka, Howard Kaufman and colleagues from Rutgers Cancer Institute of New Jersey, involved 64 research centres worldwide and 436 patients with aggressive, inoperable malignant melanoma who received either an injection of T-VEC or a control immunotherapy. Just over 16% of the T-VEC group showed a durable response of more than six months, compared with 2% given the control treatment. About 10% of the patients treated had “complete remission”, with no detectable cancer remaining – considered a cure if the patient is still cancer-free five years after diagnosis.

Maybe this time?

We started with Harold Wilson and it was in between his two spells in Number 10 that President Nixon declared his celebrated ‘War on Cancer’, aimed at bringing the major forms of the disease under control within a decade or two. It didn’t happen, as we might have guessed. Back in 1957 in The Black Cloud the astrophysicist Sir Fred Hoyle has the line ‘I cannot understand what makes scientists tick. They are always wrong and they always go on.’ To be fair, it was a science fiction novel and the statement clearly is only partly true. But it’s not far off and in cancer there’s been rather few of the media’s beloved ‘breakthroughs’ and a great deal of random shuffling together with, overall, some progress in specific areas. Along the bumpy highway there have, of course, been moments of high excitement when some development or other has briefly looked like the answer to a maiden’s prayer. But with time all of these have fallen, if not by the wayside, at least into their due place as yet another small step for man. The nearest to a “giant leap for mankind” has probably been coming up with the means to sequence DNA on an industrial scale that is now having a massive impact on the cancer game.

When Liza Minnelli (as Sally Bowles in Cabaret) sings Maybe this time your heart goes out to the poor thing, though your head knows it’ll all end in tears. But this time, maybe, just maybe, the advent of cancer immunotherapy in its various forms will turn out to be a new era. Let us fervently hope so but, even if it does, the results of this Phase III trial show that a long struggle lies ahead before treatments arrive that have most patients responding.

We began Self Help – Part 1 with the wonderful William Coley and there’s no better way to pause in this story than with his words – reminding us of a bygone age when the scientist’s hand could brandish an artistic pen and space-saving editors hadn’t been invented:

“While the results have not been as satisfactory as one who is seeking perfection could wish, … when it comes to the consideration of a new method of treatment for malignant tumours, we must not wonder that a profession with memories overburdened with a thousand and one much-vaunted remedies that have been tried and failed takes little interest in any new method and shows less inclination to examine into its merits. Cold indifference is all it can expect, and rightly too, until it has something beside novelty to offer in its favour.”

References

Mohr, I. and Gluzman, Y. (1996). A herpesvirus genetic element which affects translation in the absence of the viral GADD34 function. The EMBO Journal 15, 4759–66.

Andtbacka, R.H.I. et al. (2015). Talimogene Laherparepvec Improves Durable Response Rate in Patients With Advanced Melanoma. 10.1200/JCO.2014.58.3377

A Refresher from the BBC

Regular readers will probably feel they know all this stuff but if you’re interested in a spirited and wide-ranging conversation about cancer with the wonderful Jeremy Vine on his BBC Radio 2 show yesterday you can find it at:

http://www.bbc.co.uk/programmes/b03yn0jd about 1 hour 10 min from the beginning.

BBC Radio 4As ever, any arising thoughts, questions or comments appreciated – apart, of course, from the below the belt: “Judging by the photo it’s a good job it was radio not t.v.”