16 November 2010

Cancer drugs: each case is unique

On mice and humansAnastasia Kazantseva, STRF.RU
"Neither I nor anyone else in the world has a drug that would work for cancer in general," says biologist Vladimir Katanaev.

– Apparently, such a medicine is impossible in principle, because each case of cancer is a separate disease." It is impossible to create a cure for cancer, because there is no such disease. Moreover, the diseases "lung cancer" or "leukemia" do not exist either. The diseases "small cell lung cancer" or "acute myeloblastic leukemia" still exist, but they are also divided into dozens of varieties for effective treatment, depending on which molecules work incorrectly.

Katanaev Vladimir Leonidovich, Candidate of Biological Sciences, Professor of Pharmacology at the University of Lausanne (Switzerland), head of the research group at the University of Constance (Germany) and Head of the Development Genetics Group at the Protein Institute of the Russian Academy of Sciences. On Thursday, November 11, Katanaev gave a public lecture "Modern approaches to the development of drugs against cancer" at the Polytechnic Museum.

"We can develop a remedy that will work against certain groups of cancer cases," explains Katanaev. The drugs that are being developed today are based on a detailed study of the mechanisms of cell damage, and to create them it takes to sort through a million substances, attract a hundred specialists, a thousand experimental animals, find a dozen years, a billion dollars. That is why modern cancer drugs are very expensive. But they work effectively – as a rule.

The inner enemyThe existence of cancer is an inevitable consequence of the structure of our body.

Cells must retain the ability to divide, errors cannot occur during division, some of them lead to malignant cell degeneration. Normal cells divide when they receive such an order from the body. After division, they differentiate and perform their functions. Malignant cells divide uncontrollably, and they refuse to specialize and work at all.

In order for the cell to "listen", there are systems for receiving and processing signals in it. There are not so many of them: there are 17 main types, and they all work on similar principles. A signaling molecule (for example, a hormone) binds to a receptor protein on the cell membrane. After that, the intracellular part of the receptor changes and triggers a chain of chemical transformations – a signaling cascade. In many cases, this chain of reactions leads to the activation (or, conversely, blocking) of some transcription factor - a protein capable of binding to DNA and influencing the work of genes. And a change in the activity of genes can already lead to any given goal – growth, division, specialization, programmed death, movement, an increase in the synthesis of some substance.

Slide from the lecture presentation

After the signaling molecule binds to a receptor protein on the cell membrane, it triggers a signaling cascade: a change in one protein activates a change in another, then a third, and so on. In many cases, the last member of this chain works in the cell nucleus, activating or suppressing the synthesis of a gene or group of genes. "This picture, however, is greatly simplified, because in reality we are dealing with a very complex network of protein activations and inhibitions," Katanaev notes. 

Five types of signaling cascades are of the greatest importance for the occurrence of cancer. They are named after the names of signaling molecules or receptors: Wnt, TGFbeta (receptor serine/threonine kinase), hedgehog, receptor tyrosine kinase and Notch/Delta pathway. These five cascades are well known to any biofac student: they are analyzed in detail in the course of developmental biology, because their main role is participation in embryogenesis, stimulation of active cell division at a given time in the right place. In an adult, these signaling pathways are normally almost never turned on. If, as a result of any mutations, the embryonic signaling pathway begins to work in adult cells, these cells will begin to grow as actively as they would in the embryo's body. An adult does not need such active cell growth at all. If complex multi-stage control systems worked in the embryo's body, allowing to stop division in a timely manner and begin cell differentiation, then in an adult the regulation systems of these signaling cascades do not work. Therefore, the inclusion of the embryonic signaling cascade at an unintended time for it is one of the main causes of the development of tumors.

Accordingly, one of the most promising approaches to the development of cancer drugs is the study of embryonic signaling cascades and the search for substances capable of suppressing their work in an adult. Vladimir Katanaev's laboratory and hundreds of other laboratories and dozens of pharmaceutical companies around the world are working in this direction.

Find, improve and testTo develop a modern medicine, you first need to choose a target.

It can be a broken protein, an overactive gene, or a whole signaling cascade with all its proteins and genes. After scientists have collected enough information to claim that excessive activation of this process is associated with the development of cancer (or another disease under study), the search for ways to suppress it begins.

To do this, using genetic engineering methods, cells are created in which the signal cascade under study is actively working and at the same time manifests itself in some easily noticeable way (for example, such cells glow). And after that, high-performance screening begins: cells are exposed to various substances and see which of them can suppress the work of the signaling cascade.

You should imagine the scale of the work. "You have, say, fifty thousand, a hundred thousand, a million different chemicals – this is a library of compounds. And you assume that among these substances there are one or two that are able to perform the function you need, namely, to inhibit your target protein," explains Katanaev. The amount of substances depends on how large a library of compounds the research laboratory can buy from the manufacturer. The more substances you can test, the more likely it is that some of them will fit.

After screening, scientists select several substances that best suppress the work of the signaling cascade. These substances need to be thoroughly investigated: to understand which molecules they bind to, whether these molecules are involved in any vital processes in all cells, whether they break down into their component parts in the blood. After that, it is possible to optimize the found substance – its chemical modification in order to preserve its positive properties and get rid of negative ones. Then you can start testing on animals.

At this stage, it is necessary to find out how toxic the new drug is (if the mouse dies from it faster than from cancer, then the tests can not be continued), evaluate the dosage and effectiveness. For these studies, naked mice are most often used, nude mice is a laboratory line in which, as a result of mutation, not only the hair disappears, but the thymus practically does not work and, accordingly, T–lymphocytes are not produced. Such animals do not reject human cancer cells transplanted into their body, and therefore serve as a standard object for the study of cancer control methods. However, it is more difficult to work with these mice than with ordinary ones: they require a sterile vivarium, because their immune system practically does not function, and they can die from any infection.

If the drug effectively suppressed tumors in mice and did not cause them severe side effects, phase I clinical trials begin. They usually involve no more than 50 people. These can be healthy volunteers or people with terminal cancer (that is, their disease has gone so far that existing medicine cannot help them with anything other than anesthesia). Katanaev explains: "At this stage – maybe it will even sound a little cynical – the goal is not to save a person, but to make sure that the substance will not kill him."

The second phase of clinical trials involves several hundred patients. Here the effectiveness of the substance is analyzed, the optimal dose is evaluated, and side reactions are studied. Thousands of patients take part in the third phase trials, which allows us to study in detail the effects of the drug, its side effects and compatibility with other drugs.

After that, all the data obtained on the production of the drug and the experience of its use are provided to the state institution that is engaged in the registration of medicines. In the USA it is the FDA, in Russia it is Roszdravnadzor. With a positive assessment of the totality of data on the drug, its entry into the market is allowed.

After entering the market, the company conducts clinical trials of the fourth phase: monitoring of possible negative effects of the new drug and collecting information aimed at further improving the use of the new drug.

It is clear that only a very large corporation can carry the substance through all these stages. For example, talking about a drug created by Novartis, Katanaev compared its turnover with Gazprom: "It is interesting to mention here in general what is the sales volume of this pharmaceutical giant Novartis. In 2009, it amounted to 28.5 billion US dollars. And since there is now active talk in our country that it is necessary to develop big pharma, it is interesting just to compare the scale. What is a real big pharma? For example, on the Gazprom website for 2008, I found data that sales amounted to 82 billion US dollars. Novartis' drug sales are comparable in volume. Accordingly, in order to create a big pharma in Russia, it is necessary to create a company that will be comparable in scale to Gazprom."

There are already medicationsVladimir Katanaev spoke about two medications based on the suppression of the work of embryonic signaling cascades.

The first of them, Gleveec, has already entered the market. This drug inhibits tyrosine kinase involved in one of the five types of embryonic signaling pathways, the tyrosine kinase cascade. Activation of the tyrosine kinase cascade in an adult occurs as a result of a mutation in which fragments of the ninth and twenty-second chromosomes are reversed. After such a mutation, a new type of tyrosine kinase, the BCR-ABL protein, begins to be produced. It begins to work continuously, activates the proliferation of cells in the bone marrow and leads to the development of chronic myeloblastic leukemia.

The other drug is called GDC-0449. He does not have a market "name" yet, because it has not yet been registered, and phase two clinical trials are currently underway. This substance suppresses the hedgehog-dependent cascade. Translated from English, hedgehog is a hedgehog. The signaling molecule underlying the cascade was so named because when this cascade is disrupted, the fruit fly larva becomes covered with prickly bristles and becomes like a hedgehog. When similar signaling proteins were discovered in mammals, one of them was named Sonic the Hedgehog in honor of the hedgehog from the video game. Now many researchers are proposing to rename the protein, because they believe that it is not funny for patients to find out that Sonic the hedgehog is to blame for their disease. Activation of the hedgehog-dependent cascade can lead to the development of basal cell carcinoma (a type of skin cancer) or medulloblastoma (a type of brain cancer, usually develops in the cerebellum). In clinical trials of the first phase (in the treatment of terminal patients), the drug proved effective for both types of cancer, nevertheless, it will be brought to the market only for basal cell carcinoma: the fact is that medulloblastoma usually develops in children and adolescents, and experiments on mice have shown that disabling the hedgehog-dependent cascade at a young age leads to to severe developmental disorders and is permissible only for adult animals and humans.

Katanaev concludes his lecture by explaining once again that it is impossible to do without large pharmaceutical companies in modern drug development. "I showed you the process of drug development. Actually, this process takes about 10 years on average and costs about a billion US dollars, and it is clear that bigpharma is able to carry out this process from beginning to end. However, other players may be included in it at different stages. For example, academic laboratories. I said that each next stage is more and more expensive, and academic laboratories, and small companies, startups – they cannot afford to conduct clinical trials because of their extreme high cost. However, they can conduct the substance up to pre-clinical tests on animal models, and if everything goes well, then these substances are then sold to large pharmaceutical companies that already have enough funds to carry the substance through all the following stages."

Tumors and peopleCancer is something that will happen to every person (if he lives), and therefore the audience, of course, asked Vladimir Katanaev a lot of questions, including completely stupid and very emotional ones ("the model," they say, "was not originally chosen very much!!!").

The lecturer shows fantastic, unthinkable respect for all listeners, answers every question very seriously, even if there is no question, but there is only a violent rejection of an emotionally unpleasant topic.

Although at the very beginning of the lecture Katanaev warned that he was a biologist, not a doctor, and questions on choosing a treatment strategy should be asked to medical professionals, he still touched on this topic, answering the question of whether the drugs he was talking about exist on the Russian market today. In addition, the participants were interested in the normal operation of embryonic cascades, computer modeling, and drug personalization. The dialogue between the lecturer and the audience stopped only when the staff of the Polytechnic Museum tried to find out whether it was possible to close it at night.

Some quotes from Katanaev's answers to listeners' questions:

"The situation is such that the most effective method of treating any form of cancer is surgical. If this cancer is diagnosed at an early stage and if we are not talking about different forms of blood cancer, where, in fact, there is nothing to surgically cut out. Accordingly, if a patient goes to the hospital with a form of cancer that is exposed to... which is available for surgical treatment, the oncologist has no choice: he will naturally go to the surgeon and they will cut out this tumor. There are also standard exposure packages – this is chemotherapy first of all. And the substances that are being put on the market now are, in a sense, still pioneering therapeutic agents, and I do not know how well oncologists from different countries, maybe in the Russian outback, will be aware of certain drugs, as well as how they can be available in this Russian outback.".

"This approach [computer modeling] has a right to exist and, moreover, is actively used. It has its limitations, because for such computer modeling it is required to know the specific three-dimensional structure of the target protein against which you want to find your medicine. That is why, by the way, large pharmaceutical companies have their own very large crystallization departments. And very often there is such a synergistic approach, when high-performance screening is combined with rational design at various stages. For example, the first stage, which I described, often occurs when the library is screened and the source hits are found. But the second stage, already their optimization, often involves computer modeling, which allows you to predict which groups can be planted on the starting substance in order to improve the initial properties and get rid of the initial bad properties. Computer modeling is actively used here. [...] Another limitation of computer modeling as an approach is that you limit yourself to one protein in advance. If we were talking about the hedgehog-dependent signaling cascade, using this computer simulation, you would say this: well, I think that the Gli protein, for example, the fourth main participant in this cascade, is the most important, and the development of substances that will bind to it is considered the key to finding effective drugs. You crystallized it, solved its three-dimensional structure, put molecular docking specialists behind supercomputers, they found the right substance for you, you synthesized such a substance, confirmed its activity. Then you give it to a cell culture or an organism, it turns out that it is not effective enough, less than you expected. And if you initially use not one protein as a target, but the entire signaling pathway, then your chances of finding an effective substance that you can bring to the medicine increase. [...] Very often, when you conduct screening using a whole signaling pathway as a target, you find very unexpected things, namely: you find a substance that very effectively suppresses this signaling cascade. Then you begin to explore what it actually acts on. And it turns out that it does not act on the first, not on the second, not on the third, not on the fourth of those substances that you expected, those proteins that you expected, but on a protein that was completely new and not known for its participation in this signaling cascade."

"These five signaling pathways are active to varying degrees in different parts of the adult body. For example, here is a Wnt-dependent signaling cascade – it is reactivated in pregnant women in the mammary gland. An increase in the number of milk-producing cells, which is necessary for the baby's nutrition, occurs when the Wnt-dependent signaling cascade is started again. Here the moment is very subtle, because, on the one hand, this cascade is necessary for the normal functioning, vital activity of a person, and on the other hand, if it is reactivated or activated not when a woman is pregnant, but when she seems to be normal ... I mean, pardon, not pregnant, then just you have a high risk of developing cancer, and 50 percent of all breast cancer cases are just associated with the activation of the Wnt/Frizzled-dependent signaling cascade."

"The idea of personalization of medicines is gaining more and more popularity, at least expressed in the fact that each patient needs to develop ... the selection of a certain dose. That is, if the same dose is given to the whole group of patients as standard, then the idea is that, before giving the medicine, certain studies and tests should be carried out, when this patient needs to be given twice as much dose as normal, and this, on the contrary, a dose of two is enough times less. This also applies to a combination of medications. This idea, I repeat, is gaining popularity, I can't say how widely it is used in everyday medical practice, I think it is not wide. But it will probably be used more and more."

Portal "Eternal youth" http://vechnayamolodost.ru16.11.2010

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