Targeting Cancer's Sweet Tooth

Biotech has made great strides in recent years towards developing new, targeted cancer therapies. Monoclonal antibody therapies such as Herceptin and Rituxin demonstrate drugmakers’ ability to effectively target specific types of cancer while minimizing the side effects associated with chemotherapy. The trade-off that comes with this specificity, however, is the need to develop new drugs for each type of cancer, and in some cases different drugs for different stages of the same cancer.

An ideal cancer therapy would be specific in targeting cancer cells over normal tissues, yet not be exclusive to one type or stage of cancer. This is the basic idea behind many of the traditional chemotherapies that target the cancer-cell characteristic of rapid cell division. The problem there is that many normal tissue types, such as the cells of the gastrointestinal tract, hair follicles, skin, and bone marrow, are also rapidly diving and thus negatively affected by these therapies.

In recent years, many oncology researchers have been turning their attention to a different aspect of cancer cell biology – the cells’ extremely high use of glucose. Cancer cells are referred to as “highly glycolytic” in that they consume glucose at a rate as much as 200 times higher than that of normal cells. This metabolic abnormality can be exploited as a therapeutic target.
In the January 1 2012 issue of Cancer Research, investigators from the Kyushu University Medical School and the University of California, San Diego published a report demonstrating promising results in animal models of cancer by treating the animals with a glucose analogue that helps to activate cells death. The glucose analogue, known as 2-deoxyglucose or 2-DG, is readily taken up by cancer cells but cannot be converted to energy. Instead, 2-DG primes the cells for death, by breaking up a three-protein complex, exposing a critical protein switch for programmed cell death or apoptosis. After this priming step, the animals received a second drug, ABT-263, that flips the exposed switch, turning on apoptosis. Brain cells are also highly glycolytic, but the second drug, ABT-263, cannot cross the blood-brain barrier, thus protecting brain cells and making cancerous cells the primary target for this potential new drug combination. The treatment has shown positive results in a variety of animal models of different cancers, including leukemia, liver, lung, breast and cervical cancers, as well as a chemo-resistant, metastasized version of prostate cancer.

The next step, of course, is human clinical trials. Both 2-DG and ABT-263 are already in Phase 2 trials for other indications, indicating that there is already significant safety data on each. If the drug combination proves to be safe and effective in human cancer patients, it may open the door to a new type of targeted treatments for a whole range of cancers.

Thwarting HIV: New Hopes for Vaccination

Developing a vaccine to thwart human immunodeficiency virus (HIV), the virus that causes AIDS, has been a major goal of researchers since the virus was first identified in 1983. There have been many false starts and a few signs of hope, but no real success stories. The latest development in this arena takes an entirely new approach to the problem.

Traditional vaccines rely on injecting a weakened or inactivated version of a virus, or some portion of a virus, into the patient, in hopes of training the patient’s immune system to recognize the virus and be prepared to defend against it in the event of an actual infection. One of the key ways in which the immune system can defend against a virus is by producing proteins called antibodies that recognize portions of the virus particle, bind those recognized portions, and prevent the virus from entering its target cell – rendering the virus harmless, or “neutralizing” it. This approach has not been successful as an HIV immunization strategy, in part because of the high rate of mutation that the virus exhibits – in effect, the immune system is trained to recognize Version One of the virus, and the patient becomes infected with Version Two.

In recent years, various investigators have identified what are referred to as “broadly neutralizing antibodies” – antibodies that are capable of neutralizing a broad range of different HIV strains. These antibodies arise by chance in a minority of HIV-infected individuals, and are thought to be able to recognize multiple strains of the virus because they target regions of the virus that mutate at a much lower frequency than other regions of the virus.

Although these antibodies are highly effective against the virus, they only arise in small number of patients – and only after the infection has already taken root. What if scientists could isolate the genes that provide the instructions for making these antibodies, and deliver them directly to patients – affording the chance to produce their own powerful antibodies capable of defending against multiple strains of HIV, prior to infection?

David Baltimore’s lab at the California Institute of Technology has taken the first steps towards doing just that. Using gene therapy technology, the team introduced the genes that code for these broadly-neutralizing antibodies into muscle cells of mice that have been genetically altered to contain a human immune system – and thus susceptible to HIV. These mice muscle cells then proceeded to make large quantities of the powerful antibodies – rendering the mice resistant to HIV infection. The lab refers to this technique as “vectored immunoprohylaxis (VIP)” – and in the words of Dr. Baltimore, “The advantage of VIP is simply that it works.” After almost thirty years of trying, this is indeed quite an accomplishment. Human clinical trials are expected to begin in 2012.

Baltimore’s work was published in the December 1st 2011 issue of Nature.

Fountain of Youth?

Fountain of Youth?

Forget the eye cream and aerobics classes – new research out of Dr. Darren Baker’s lab at the Mayo Clinic suggests that a better understanding of the molecular mechanisms of aging may one day result in treatments that intervene in the root causes of age-related degeneration, rather than simply treat the symptoms.

Dr. Baker’s research focuses on a protein known as p16INK4A. This is a protein that is produced when cells approach the upper limit of the number of times that they can divide – a number known as the Hayflick limit, thought to be an anti-cancer mechanism in cells but also associated with cell senescence – aging and death. The challenge has been to figure out a way around this Hayflick limit without inducing cancer.

The Baker lab may have found such a workaround. Studying a type of mouse born with progeria – a condition that causes the mice to age much more rapidly than normal – Dr. Baker’s group observed that not only do rapidly aging cells deteriorate, but that they also seem to have adverse affects on other, healthy cells nearby. This led them to hypothesize that if they could somehow selectively kill the most rapidly aging cells, the mice would get two benefits for the price of one.

Since the most rapidly aging cells are also the first cells to start producing p16INK4A, this protein could also serve as a targeting mechanism for the selective destruction of rapidly aging cells. Dr. Baker’s team genetically engineered a strain of progeriatric mice that would produce a second protein whenever the production of p16INK4A increased. This second protein is harmless, but is converted into a toxic form when the mice are administered an activating drug. This toxic form results in the death of the cells that contain it – but not the surrounding healthy cells.
The results of this experiment, published last month in Nature, were nothing short of astounding. The engineered mice exposed to the activating drug showed markedly fewer signs of aging – less muscle wasting, fewer cataracts, better performance on treadmill tests. These results offer the tantalizing possibility that there may in fact someday be a silver bullet to selectively destroy aging cells in humans, leaving behind stronger, healthy cells and tissues.

CHO Cells Explained

Many non-scientists who work in the biotech industry have heard of CHO cells, and know that they are a cell line commonly used to manufacture biologic drugs. But what are these ubiquitous CHO cells?

CHO stands for Chinese Hamster Ovary. This means that this cell line was derived from the cells of a Chinese hamster – a particular breed of hamster that originated in the deserts of Northern China and became a common animal model for the typing of pneumococci in the early 20th century. In the 1950s, scientists began deriving cell lines from these hamsters, and found that they grew well in tissue culture, demonstrating resiliency and relatively fast generation times. This made them an invaluable tool for a host of areas of basic science research ranging from genetics to cancer biology.

Twenty years later, when the biotechnology revolution began and scientists began to use cells to make therapeutic proteins in large quantities, the first cell type used was the bacterial cell E. coli, used to produce human insulin by Genentech scientists. Although E coli worked well for relatively simple proteins such as insulin, as researchers began to explore the possibility of producing other, more complex proteins as therapeutics, it became clear that another cell type was needed. Bacterial cells are simply not capable of producing complex human proteins in the correctly folded and post-translationally modified form required for a human therapeutic.

The obvious choice for human therapeutic protein production was some sort of mammalian cell. Why not a human cell line? It turns out that human cell lines are relatively difficult to keep alive in cell culture. They simply do not survive and multiply as well as rodent cell lines such as CHO cells. Decades of experience with CHO cells had taught scientists that these cells were not only easy to grow in culture, but could also be adapted to grow in liquid suspension cultures to high volumes – a very important trait when considering the production of biologics. CHO were also found to be capable of taking up foreign genetic material. Finally, these cells are safe for the production of human therapeutics – in fact, they are probably safer than an actual human cell line would be, because most human pathogenic viruses, including HIV, influenza, herpes, and measles, do not infect these cells. From a regulatory perspective, CHO cells have stood the test of time and have a special status – Generally Regarded As Safe (GRAS).

The first human therapeutic to be produced in CHO cells was Activase, a recombinant version of the human protein tissue plasminogen activator used in the treatment of acute myocardial infarction. Activase was approved in 1987. Since that time, CHO cells have been used to produce dozens of other life-saving biologics. For all of these reasons – ease in growing to large volumes, ability to manipulate genetically, and a proven track record in producing safe human therapeutics – we can expect CHO cells to remain a favorite workhorse of the biotech industry.

Regulation of Biosimilars

Biosimilar Regulations

In the last blog post, I discussed the differences between biosimilar drugs and small molecule drugs. In this post, I will discuss the guidelines that the World Health Organization and the European Medicines Association have laid down in terms of marketing approval for biosimilar drugs.

First, why are new regulatory guidelines required? As explained in the last blog post, it is currently not possible to conclusively demonstrate that one therapeutic protein is identical to another – even if both are produced by the same gene – if different cell lines or manufacturing processes are used. Because of these potential differences, regulatory agencies cannot simply approve a biosimilar drug based on the safety and efficacy data that was used for approval of the innovator drug. However, in many cases the two drugs will be similar enough that a complete data portfolio supporting the safety and efficacy of the biosimilar is unneccasary.

The question, then, is in determining just what is required to assure the safety and efficacy of biosimilars without wasting the resources of drug companies and regulatory agencies alike. The standard that has been adopted by the European Medicines Association (EMA), and which the Food and Drug Administration (FDA) seems likely to adopt, is that of “comparability”. What this means is that if a biosimilar manufacturer is able to demonstrate, using state of the art analytics and lab-based functionality tests, that a the biosimilar product is in fact highly similar to an already licensed product, then the biosimilar product may be eligible for an abbreviated approval pathway in terms of preclinical and clinical testing.

The EMA approved its first biosimilar drug, Omnitrope, in 2006. Omnitrope is a biosimilar version of human growth hormone. Since that time, thirteen additional biosimilars have been approved in the EU – although all fourteen of the EU-approved biosimilars fall under just three different drug categories: human growth hormones, granulocyte-colony stimulating factors, and erythropoietins. These types of proteins are all relatively simple in terms of their structure – making it easier to demonstrate comparability. In May of 2011, the EMA released guidelines for the approval of biosimilar monoclonal antibodies, illustrating the need for a different approach to demonstrating comparability for these more complex molecules.

The FDA has not yet begun to approve biosimilars; however last month the FDA published a paper suggesting that their guidelines, promised to be released sometime this year, will be similar to the EMA guidelines , with demonstration of comparability as a minimum requirement for the reduction of preclinical and clinical trials data.

BioSimilars vs. Generic Drugs: What’s In a Word?

“Biosimilars” is a buzzword that isn’t going away anytime soon. Sometimes also referred to as “follow-on biologics”, biosimilar is the term used for a biologic drug that is produced using a different cell line, master cell bank, and/or different process than the one that originally produced the product.
How do biosimilars differ from so-called generic drugs? Generic drugs are essentially “copycat” versions of small molecule drugs – drugs that can be synthesized in the lab by following standardized, pre-defined procedures. Using well-established analytic techniques, the generic version of a small molecule drug can be demonstrated to be chemically and structurally identical to the innovator drug.

Biologic drugs, however, are much more complex than small molecule drugs. These drugs are proteins that must be produced by a living cell – they cannot be chemically synthesized in the lab by following a standard set of procedures. The cell makes these proteins by following a recipe provided by a short sequence of DNA – a gene – that is inserted into the cell. Here’s the catch: even if two different cells are provided the exact same recipe, the final product may be slightly different. This may happen even if the two cells are of the same type – very slight environmental differences can have a profound effect on how a given cell follows a particular recipe. This makes intuitive sense – we know that we can follow the same recipe that the gourmet chef at our favorite restaurant follows, but somehow, the dish doesn’t taste quite as good. Slight difference such as the exact temperature of the frying pan, the brand of the heavy cream, and even the humidity level and elevation of the kitchen will influence the final outcome. The restaurant industry depends on these “trade secrets” to keep us coming back for more.

Complicating matters further for biosimilar products is the fact that because biologic drugs are structurally much more complex than their small molecule counterparts, it is not currently possible to demonstrate conclusively that a biosimilar drug is in fact identical to the original biologic drug. Thus, since we know that there is a high likelihood that a biosimilar drug is not identical to the original biologic, and we have no way of precisely measuring whatever differences may exist, the term “biosimilar” is used rather than “generic”, which implies identity.

What implications does all of this have for regulation and marketing approval? Next week’s blog will discuss the similarities and differences in how various regions of the world have approached this issue.

Personalized Medicine: Seasonal Variation?

A class of liver enzymes known as cytochrome P450 (CYP450) enzymes are largely responsible for breaking down most prescription drugs. Researchers and physicians are already aware of specific genetic differences that make some individuals metabolize certain drugs more quickly or more slowly than other individuals, and a number of companies are developing diagnostic tests to identify which type of metabolizer a particular patient is: poor, normal, or ultra-metabolizer. Different drugs are metabolized by different sub-categories within this broad CYP450 family, so a patient may be a poor metabolizer for one type of drug, and a normal metabolizer for another type.

A recent publication in the journal Drug Metabolism and Disposition indicates that a person’s ability to metabolize certain drugs may also be influenced by how much sunlight they get. This is because one sub-category of the CYP450 enzymes, referred to as CYP3A4, is activated by higher levels of vitamin D, which in turn is produced by a person’s skin in response to sun exposure. A research team led by Erik Eliasson of the Karolinska Institute found that the levels of certain drugs known to be broken down by the CYP3A4 enzymes varied significantly, depending on the time of year and relative amounts of sunlight exposure, with higher drug levels corresponding to the winter months when the CYP3A4 enzymes were less active. This pattern was not seen in drug levels known to be metabolized by different CYP enzymes.

Of course, this seasonal variation will have the most profound impact in places where differences in sunlight exposure vary significantly throughout the year. It’s not a coincidence that the study’s authors live in Sweden, where the average number of daylight hours in December is six and one-half, and the average number in June is eighteen. In most regions of the world, the variation is not so extreme; still, it does exist, and it will be interesting to see if these less pronounced variations also influence drug metabolism. Physicians may indeed have yet another variable to take into account in order to determine the most accurate drug dosages.