Turning Ourselves On

 

It may seem a bit tasteless but we have to admit that cancer’s a very ‘trendy’ field. That is, there’s always a current fad — something for which either the media or cancer scientists themselves have the hots. Inevitable I suppose, given the importance of cancer to pretty well everyone and the fact that something’s always happening.

If you had to pick the front-running trends of late I guess most of us might go for ‘personalized medicine’ and ‘immunotherapy.’ The first means tailoring treatment to the individual patient, the second is boosting the innate power of the immune system to fight cancer.

Few things are trendier than this blog so it goes without saying that we’ve done endless pieces on these topics (e.g. Fantastic Stuff, Outsourcing the Immune Response, Self-Help – Part 2, bla, bla, bla).

How considerate then of Krijn Dijkstra, Hans Clevers, Emile Voest and colleagues from the Netherlands Cancer Institute to have neatly combined the two in their recent paper.

Simple really

What they did was did was easy — in principle. They grew fresh tumour tissue from patients in dishes in the laboratory. Although it doesn’t work every time, most of the main types of cancer have been grown in this way to give 3D cultures called tumour organoids — tumours-in-a-dish. That’s the ‘personalized’ bit.

Then they took blood from the patient and grew the lymphocytes therein in a dish to expand the T cells that were specific for the patient’s tumour. That’s the ‘‘immuno’ bit.

Growing tumour tissue (from non-small-cell lung cancer (NSCLC) and colorectal cancers [CRC] in culture as tumour organoids. This permits the expansion of T cells from peripheral blood to give an enlarged population of cells that will kill those tumours. From Dijkstra et al. 2018.

And the results?

They were able to show that enriched populations of tumour-reactive T cells could kill tumour organoids and, importantly, that organoids formed from healthy tissue were not attacked by these T cells.

Stained organoids (left) and original tissue (right) from two colorectal cancers (CRC-2 & CRC-5) showing how the organoids grow to have an architecture similar to the original tumour. From Dijkstra et al. 2018.

Their method worked for both bowel tumours and non-small-cell lung cancer but there’s no reason to suppose it can’t be extended to other types of cancer.

Some of their videos showing tumour organoids being chomped up by enriched killer T cells are quite dramatic. Cells labelled green that can be seen in this video are dying.

So there you have it: DIY tumour therapy!

Reference

Dijkstra, K.K. et al. (2018). Generation of Tumor-Reactive T Cells
by Co-culture of Peripheral Blood Lymphocytes and Tumor Organoids. Cell 174, 1–13.

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Self Help – Part 2

In the second type of cancer immunotherapy a sample of a patient’s T lymphocytes is grown in the lab. This permits either expansion of the number of cells that recognize the tumour or genetic engineering to modify the cells so they express receptors on their surface that target them to the tumour cell surface. Infusion of these manipulated cells into the patient enhances tumour cell killing. We’re now in the realms of ‘personalized medicine’.

A little more of a good thing

The first of these methods picks up a weakness in the patient’s immune system whereby it makes lymphocytes that kill tumour cells but can’t make enough – their protective effect is overwhelmed by the growing cancer. By taking small pieces of surgically removed tumours and growing them in the lab, it’s possible to select those T cells that have killing capacity. These are expanded over a few weeks to make enough cells to keep on growing when they’re infused back into the patient. The upshot is a hefty boost for the natural anti-tumour defence system. The pioneer of this method, called adoptive cell therapy, is Steven Rosenberg (National Cancer Institute, Bethesda) and it has been particularly effective for melanomas. Responses are substantially improved by treatment with drugs that reduce the white cell count before samples are taken for T cell selection – probably because the system responds by making growth factors to restore the balance and these drive the expansion of the infused cells.

A wonderful benefit of this method is its efficacy against metastases – i.e. tumour growths that have spread from the primary site – perhaps not surprising as it’s what Rosenberg calls a “living” treatment, in other words it just gives a helping hand to what nature is already trying to do.

93. Fig. 1Selecting naturally occurring T cells with anti-tumour activity

Tumour fragments are grown in the laboratory: lymphocytes that kill tumour cells are selected and expanded in culture.  About 6 weeks growth yields enough cells to infuse into the patient.

Gene therapy

A more sophisticated approach to boosting innate immunity is to introduce new genes into the genetic material (the genome) of T cells to target them to tumour cells with greater efficiency. An ordinary blood sample suffices as a starting point from which T cells are isolated. One way of getting them to take up novel genes uses viruses – essentially just genetic material wrapped in an envelope. The virus is ‘disabled’ so that it has none of its original disease-causing capacity but retains infectivity – it sticks to cells. ‘Disabling’ means taking just enough of the original genome to make the virus – a viral skeleton – and then inserting your favourite gene, so the engineered form is just a handy vehicle for carrying genes. No need to panic, therefore, if you see a press headline of the “HIV cures cancer” variety: it just means that the human immunodeficiency virus – well and truly disabled – has been used as the gene carrier.

93. Fig. 2

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.

 This method of re-directing T cells to a desired target was pioneered by Gideon Gross and colleagues at The Weizmann Institute of Science in Israel in the late 1980s and it has led to sensational recent results in treating chronic lymphocytic leukemia (CLL), albeit in just a few patients so far. To the fore have been Renier Brentjens and his group from the Memorial Sloan-Kettering Cancer Center, New York. The genetic modification they used made the patient’s T cells express an artificial receptor on their surface (called a chimeric antigen receptor). This T cell receptor was designed to stick specifically to a protein known to be displayed on the surface of CLL cells. The result was that the T cells, originally unable to ‘see’ the leukemic cells, now homed in on them with high efficiency. Astonishingly, and wonderfully, the modified cells divide in the patient so that, in effect, their immune system has been permanently super-charged.

A critical part of the strategy is that CLL cells carry a known molecular target but the absence of such defined markers for most cancers is currently a severe limitation. On the bright side, however, this type of gene therapy has now been attempted in at least three different centres and, despite inevitable minor differences in method, it clearly works.

One of the leading figures in gene therapy is Carl June of the University of Pennsylvania. Some of his colleagues have made a brilliant video explaining how it works whilst June himself has described in wonderfully humble fashion what it means to work in this field.

References

Rosenberg, S.A. and Restifo, N.P. (2015). Adoptive cell transfer as personalized immunotherapy for human cancer. Science 348, 62-68.

Gross, G., et al. (1989). Expression of immunoglobulin-T-cell receptor chimeric molecules as functional receptorswith antibody-type specificity. Proc. Natl. Acad. Sci. U.S.A. 86, 10024–10028.

Brentjens, R.J., et al. (2013). CD19-Targeted T Cells Rapidly Induce Molecular Remissions in Adults with Chemotherapy-Refractory Acute Lymphoblastic Leukemia. Sci Transl Med., 5, 177ra38. DOI:10.1126/scitranslmed.3005930.

Kalos, M., et al. (2011). T cells with chimeric antigen receptors have potent antitumor effects and can establish memory in patients with advanced leukemia. Sci. Transl. Med. 3, 95ra73.

Kochenderfer, J.N., et al. (2012). B-cell depletion and remissions of malignancy along with cytokine-associated toxicity in a clinical trial of anti-CD19 chimeric-antigen-receptor–transduced T cells. Blood 119, 2709–2720.

 

Mission Impossible?

We make great play in these pages of the wonders of the genetic revolution. So we should. The technology is simply breathtaking, and the amount of data we can gather is so incomprehensibly vast the latest generation of computers is straining at the seams to record it all and, of course, it unveils the vision of a new world. No field has felt the impact more than cancer biology which now holds the promise that, shortly after being found, tumors will be sequenced: on the basis of identified ‘driver’ mutations appropriate drug cocktails will be devised to prevent remission after the initial treatment and these can even be tested in mouse ‘avatars’ to confirm their effectiveness against the patient’s own tumor cells. Finally, even if recurrence sets in at a later date, the same procedure can be repeated and a new drug combo used to target any evolution undergone by the cancer. The era of ‘personalized medicine’ has arrived.

Every Silver Lining …

But there are a few murky clouds drifting across this sky blue portrait of triumph.

  1. The first is that, as we’ve seen in Family Tree of Breast Cancer and Molecular Mosaics, cancers are an incredible mixture – that is, the mutation signature varies depending on the region sampled in primary tumors and is different for individual metastases. This means that a ‘signature’ at best represents a dominant hand of mutations and, worse still, it’s continuously evolving.
  2. The second problem is that, although there are several hundred ‘anti-cancer’ drugs that have been approved for use by the FDA against specific types or stages of cancer, fewer than half a dozen are ‘specific’ – meaning that they hit only tumor cells and leave normal tissue alone. The ‘few’ work because they knock out the activity of mutant proteins that are made only in tumor cells. Notable examples are vemurafinib/Zelboraf (hits the mutated form of BRAF that drives a high proportion of malignant melanomas) and imatinib/Gleevec (blocks the BCR-ABL protein that is formed in most chronic myelogenous leukemias) – and these ‘targetted therapies’ have produced spectacular remissions. Other agents that have attracted much media attention include Herceptin (trastuzumab), a monoclonal antibody that sticks to a protein present in large amounts on the surface of some types of breast cancer cell. This type of agent is highly specific for the protein it targets (i.e. it doesn’t interact with anything else) but it isn’t specific for cancer cells per se. They work because cells heavily loaded with the target get a relatively big hit – a kind of tall poppy syndrome.
  3. Virtually all other chemo agents work on the same principle: in essence they affect every cell they manage to reach and any anti-cancer effect is due to tumor cells being a bit more susceptible. Which is why, of course, the efficacy of any drug combo is to a considerable extent a matter of luck and side effects are such a common problem.
  4. Unquestionably more anti-cancer drugs will be developed, those that do come on line will be more specific and therefore less unpleasant to use, so it may well be that in 20 years time we will have a drug cabinet that is sufficiently well stocked to tackle the major cancers at key stages in their evolution. Which is all well and good but, regardless of how they work and what is meant by ‘specificity’, the biggest problem of all will remain. Resistance – the capacity of tumor cells to neutralize anything that is used with the idea of neutralizing them. They do this by two main routes (1) pumping out the drug and (2) adapting to reduce drug efficacy. The obvious counter is simply to throw more of the drug at them but, in the end, side-effects impose a limit. What this means is that even when drugs have initially startling effects, as do vemurafinib and imatinib, patients eventually become refractive and tumors recur.

MAPK

Cell signalling: cells receive many signals from messengers that attach to receptor proteins spanning the outer membrane. Activated receptors turn on relays of proteins (RAS, A, B, C, D) that talk to the nucleus, switching on genes that drive proliferation. RAS proteins are a focus for many incoming signals and they also set off several relay chains that converge on the nucleus. They work at the cell membrane to which they are escorted from where they’re made by a protein called PDEdelta. A new drug, deltarasin, blocks the escort’s action so that RAS cannot find its way to work and cell growth is arrested.

A Different Line of Attack

In view of that rather gloomy assessment should we try an alternative approach? The personalized scenario involves drug combos tailored to the individual cancer at a given stage of development. But if that seems unlikely to provide a solution remotely near to the ideal, is there another way of selecting targets? Time to try ‘impersonalized medicine’ perhaps?

This notion comes from the thought that what we’re trying to do is block signals that release the brakes on cell proliferation. Many distinct signal pathways impact on the machinery that drives this process, themselves driven by different types of external signal, but it would seem obvious that somewhere along the line these must converge on one or two key regulators – master controllers if you like of cell multiplication. Indeed they do and one of these foci is a protein called RAS (there are three close relatives in the RAS family). RAS is a major junction in cell signalling: many messages from the outside world eventually converge on RAS and lots of pathways radiate from it. When a cell launches itself into the division cycle it does so as an integrated response to these signals.

RAS is mutated to a hyperactive form in about 20% of human cancers (turning on cell growth) so obviously it would be good to have a drug that can hit RAS and an enormous amount of effort has gone into coming up with one. Unfortunately a variety of clever strategies aimed directly at RAS proteins simply haven’t worked. Enter Gunther Zimmermann and his team.

Inhibiting RAS Signalling

RAS proteins do their signaling attached to the inside of the outer membrane of the cell – but they’re made in the interior and to get to their place of work they are escorted to the membrane by a protein called PDEδ (a phosphodiesterase). To upset this cosy arrangement, the Dortmund group developed small molecule, deltarasin, that sticks tightly to the escort which, in response, changes shape just enough to prevent it being able to hold hands  with RAS. The result is that the key signaller (KRAS in fact) is no longer distributed to the membrane. This prevents it working and impairs the growth of KRAS-mutant pancreatic tumour cells.

The great attraction of this approach is that it’s indirect – so the hope is that cells won’t realize that RAS is wandering aimlessly around doing nothing and therefore not simply overwhelm the drug by making more mutant RAS. It remains to be seen how many off-target effects this drug has but for the moment an exciting new idea holds the promise of hitting cancers where it hurts them most – in a key node essential for unregulated cell growth.

References

Baker, N.M. and Der, C.J. (2013). Cancer: Drug for an ‘undruggable’ protein. Nature 497, 577–578.

Zimmermann, G., Papke, B., Ismail, S., Vartak, N., Chandra, A., Hoffmann, M., Hahn, S.A., Triola, G., Wittinghofer, A., Bastiaens, P.I.H. and Waldmann, H. (2013). Small molecule inhibition of the KRAS–PDEδ interaction impairs oncogenic KRAS signaling. Nature 497, 638–642.

Don’t Read This!!

Now here’s something I bet you’ve never thought about. Well I certainly hadn’t when I stepped outside the boundary of ‘science’ and into the world of ‘pop sci’ – aka Betrayed by Nature.

Professional evisceration

To get sciency stuff published you have to endure the dread process of ‘peer review’. Your paper is sent to experts who apply their giant brains, formidable grasp of the subject and sadistic natures to a completely impartial assessment of whether it is of sufficient merit to appear in whichever journal you have favoured with your attentions. Or, put another way, it gets put through a mincer that takes fiendish delight in dissecting every syllable, making ‘suggestions’ that amount to a total re-write and demanding a further series of experiments (to ‘solidify’ the data) that would see you past retirement, if not into the beckoning abyss beyond. If, by combining grovelling submission, bartering, and deviousness you finally get the thing into print, what happens next? Nothing. Not a squeak. The vast majority of papers disappear as surely as if dropped into the Mariana Trench in a lead-lined box. Just occasionally, if a few of the co-authors have Nobel Prizes, you might find your opus clambering up one or another citation index, meaning that some other bunch of numpties have mentioned it in their own feeble scribblings – doesn’t mean they actually read it, of course. And that’s it.

Pop in public

But out in the real world ‘pop’ stuff comes out – and then gets reviewed – so it’s like writing chick-lit (I’ve no idea what that is but I quite fancy having a go). And the critics turn up from all over the place. Their views get emailed to you by well-intentioned friends, someone in the coffee queue regales you (“just seen ….”) or you stumble over one when your surfing fingers inadvertently hit ‘sci reviews’ instead of ‘sex reviews.’

So Monty Python was wrong – you do expect The Spanish Inquisition – that any minute you’ll be dragged naked through the streets of Cambridge – well, emotionally at least. So, after all that, a lady friend has told me to be a man (very naughty to have peeked) and to bravely blog reviews received.

You have been warned!

Reviews of BETRAYED BY NATURE The War on Cancer by Robin Hesketh Palgrave Macmillan 272 pp. £16.99 (2012)

1.  William Hanson, MD, author of The Edge of Medicine: Dr. Hesketh brings an expert’s easy familiarity and depth to this comprehensive, at times almost affectionate, look at a deadly adversary. He tells us what cancer is, what causes it, what we can do to prevent it and how we are systematically battling the disease on many fronts.

2.  Kirkus Reviews (The World’s Toughest Book Critics) 1 March 2012:  Informative, optimistic tour of the science of cancer: Hesketh (Biochemistry/Cambridge Univ.), familiar to lay audiences from BBC radio and TV, opens Part 1 with a capsule history of cancer, ranging from papyrus records of ancient Egypt to the scientific breakthroughs of the 21st century. He follows with a look at the distribution of different types of cancers around the world and what the data suggests about cancer’s causes. Matters get technical in Part 2, but the author assumes little previous knowledge on the part of readers; he takes time to explain DNA, RNA, genes, chromosomes and how some genes mutate into cancer genes. In Part 3 he tackles cancer cells and the behavior of tumors. Throughout Parts 2 and 3, relatively simple diagrams and some black-and-white photographs help to clarify the technical discussions. For most readers, the final section – “Where Are We? Where Are We Going?” – will be of greatest interest. Here Hesketh explains how genome sequencing has begun to change how cancers are diagnosed and classified, and the promise this holds for therapy. We are at the beginning, he writes, of the era of personalized medicine, which holds the promise that we will someday be able to detect the threat of cancer long before it manifests itself by sequencing an individual’s genome and using that information to design an individualized therapeutic strategy. The back matter includes a helpful glossary and two delightful odes to cancer, one written in 1964 by the noted geneticist (and cancer patient) J.B.S. Haldane and the other a modern version by Hesketh.

Despite the author’s occasionally breezy style – “cancer is jolly complicated” – this is not a book to breeze through, but rather a solid account of how cancer works, how it has been combated and what the future holds for its treatment.

https://www.kirkusreviews.com/search/?q=hesketh&x=16&y=13

3.  Nature 485, 579 (31 May 2012): It afflicts one in three people globally and kills more than 7 million a year. Yet cancer is, at base, simply an abnormal growth of cells. In this admirably clear overview, biochemist Robin Hesketh gives us the history, basic science and characteristics of cancer cells, charting how tumours spread and detailing genetics, detection, therapies and drugs. There is much to fascinate — from eighteenth-century physician Percivall Pott’s deduction that there was a link between soot and scrotal cancer in chimney sweeps, to the challenges of treating the biological “hodgepodge” that is a tumour.

http://libsta28.lib.cam.ac.uk:2157/nature/journal/v485/n7400/full/485579a.html

4.  John P. Moore, Professor of Microbiology and Immunology, Weill Cornell: In Betrayed by Nature, Robin Hesketh melds medicine, science and history to create a clear and highly readable explanation of the complexities of cancer.

5.  Interview on The Leonard Lopate Show: lopate050812apod.mp3

6.  For Amazon reviews see their web site.