Tuesday, April 24, 2012
Genomics Is And Will Be A Transformational Megatrend In Medical Care But The Path to Targeted Drugs Will Be Rocky At Best
Tuesday, April 17, 2012
Early and rapid diagnosis
Prediction of diseases to develop later in life
Genomics is proving to be very valuable in disease classification, especially with cancer. A pathologist’s evaluation looking at a microscopic slide has been the basis for most cancer classification - separating out breast cancer from lung cancer but then sub classifying each such as small cell and non-small cell lung cancer or the various subcategories of lymphomas. To this was added some years ago histochemical analysis to learn if a breast cancer was high in estrogen or progesterone receptors and then molecular diagnosis to find, for example, if the tumor had a high complement of the receptor Her2neu – each being important markers for the approach to treatment. Now genomics is adding an ability to delve much more deeply and find what the DNA mutations are in the individual tumor and how they are similar or different from others. This in turn is leading to searches for new drugs, as discussed last time.
This same work allows for early prognostication. Consider 100 women with breast cancer that appear by all the usual criteria to be the same type and of the same early stage. We know that most of them will respond well to current therapy of surgery, radiation locally and, in certain circumstances, systemic chemotherapy or hormonal therapy. But a small percentage will have a relapse. The problem is that there has been no way to determine in advance who is at risk of relapse. Genomics has begun to answer this problem. Analyzing the genomics of the tumor at the time of diagnosis, it is possible to separate these women into a good prognosis group and a poor prognosis group. The former rarely relapse and one might even consider if they need the same level of aggressive therapy as they are now getting. And the latter group is at high risk of recurrence; they are obvious candidates for clinical trials of alternate approaches to determine if relapses can be reduced. One such genomic prognostic test has been approved by the FDA and others are in the works for multiple cancers.
Genomics can be used for early diagnosis, especially in the field of infectious diseases. Remember the gentleman who flew to Italy on his honeymoon but who had tuberculosis? It led to an international concern that he might have infected others and that his TB might be of the drug resistant variety. One of the problems was that it takes about six weeks to grow the TB bacteria in the laboratory and then, if present, another six weeks to test for antibiotic susceptibility. But genomic tests can speed that process up to just hours. The TB bacteria (Mycobacterium tuberculosis) has a characteristic genomic profile so, if present in a sample from the patient, it can be detected within hours. And since antibiotic susceptibly is driven by the bacteria’s genes, they can be analyzed at the same time. A huge improvement in time to diagnosis and getting the right drug started from the beginning.
We might want to know if we are predisposed to develop a certain disease later in life. It is possible that genomics can be of real assistance here; indeed this has been a major “promise.” It turns out that most of the common, important diseases such as diabetes and coronary artery disease have not one but vast numbers of genes that have some impact on their development. So we will not find a simple answer for many of these. But as more is learned it is very possible that each of us will be able to learn our relative risk to some important and common illnesses. If you knew, for example, that you were at increased risk of heart disease, it might be a stimulus to you to be more diligent in eating a Mediterranean style diet, exercising more often and looking for ways to control stress- and it would be an added inducement to stop smoking. Similarly, if you were at risk for early onset colon cancer, you might be more careful to eat a diet high in fiber and low in fat and begin having colonoscopies at an earlier age.
These are just some of the advances coming from genomics; expect to see many more because genomics represents a true revolution in medicine and we have only seen the beginning.
Here is a video on medical megatrends
Tuesday, April 10, 2012
Little more than a decade ago, most people had never heard of the word “genomics;” today it is used frequently. It is indeed a revolutionary science that is and will transform medical research and medical care. To better understand how this new science will markedly change medicine, it is convenient to consider it through a few categories:
Early and rapid diagnosis
Prediction of diseases to develop later in life
Pharmacogenomics, the topic of this posting, can itself be subdivided into
Drug creation and development
Drug prescribing to achieve greater efficacy and fewer side effects
The concept of drug development using genomics is to “target” a specific function in the cell, usually an enzyme that is the proximate culprit in a disease process. Here is an example using chronic myelocytic leukemia.
Chromosomes occasionally break apart but the cellular repair mechanisms put them back together. Chromosomes are basically long sections of DNA with collections of multiple genes. One chromosome, #22, carries a normal gene known as BCR. We all have it, it is normal. Another chromosome, #9, carries a gene called ABL (and usually pronounced as “abel”.) As with BCR, we all have it and it is an important normal gene called a tyrosine kinase.
Imagine that some of Chromosome #22 breaks off such that a portion of the BCR gene comes with it. At the same time, Chromosome #9 breaks leaving ABL exposed at the end. Now, instead of the repair mechanisms putting the two pieces back where they came from, instead, the two pieces are “translocated” so that now the piece of the BCR gene is attached to Chromosome #9 next to ABL. This effectively creates a new fusion gene which we will call BCR-ABL. This additional material on the ABL gene is enough to change its active site such that it launches a cascade of additional proteins that cause continuous cell division thereby creating chronic myelocytic leukemia. This single leukemic cell divides without control until eventually the disease is manifested.
The concept of “targeted therapy” is to find a compound that blocks the action of this new abnormal protein without affecting other normal tyrosine kinases. As it turned out, Novartis had a compound on the shelf, created for other purposes, which fit the need. It binds to the BCR-ABL protein’s active site and effectively stops it from working. The cell now dies a normal death and the leukemia is rapidly brought under control with very limited side effects, especially as compared to the major side effects of cancer chemotherapy. Gleevec (imatinib,) the first of a number of now available targeted BCR-ABL tyrosine kinase inhibitors, has been very successful and has dramatically changed the approach to this otherwise fatal disease.
This is an example of knowing the gene that is abnormal, then finding its abnormal protein product and then finding or creating a compound that blocks its action, targeted to just that abnormal enzyme. Other examples to date have mostly been in the cancer field such as Herceptin (trastuzumab) for breast cancer. In the coming years there will be a wellspring of new compounds developed as the underlying genomic basis for many diseases are unraveled.
Genomics can be used not just to develop new drugs but to make the prescribing of drugs more effective and safe. Albuterol is a drug used for acute episodes of asthma. It works for most people but there are a few where it works less well and some where it has no effect at all. The problem is that the prescribing physician has no idea whether an individual patient will respond or not. Too bad for the non-responsive patient who does not discover this until during an attack in the middle of the night. The reason for non response is straight forward. Albuterol is inhaled and binds to a specific site, called a beta adrenergic receptor, on the cells that line the small airways. When this binding occurs, it leads to relaxation of the smooth muscles around the airways, relieving the asthma attack. This receptor is, in turn, created by a gene. In some people there is a “one letter” difference at codon #27 on the gene that codes for this enzyme. This seemingly minimal difference is enough to cause the substitution of the amino acid glycine for the usual arginine in the long chain of amino acids that make up in the beta adrenergic receptor protein. And this is enough that the Albuterol will no longer bind. Since we have two sets of chromosomes, one from Mom and one from Dad, then if one of our parents had this difference, we would still make some of the beta adrenergic receptor but not the full amount. And if both our parents had this different gene, then we would not make any of the typical receptor. So the former people respond somewhat but not fully to albuterol and the latter do not respond at all.
At some point there will be a simple test done in the doctor’s office to check for this occasional difference thus allowing the physician to prescribe a different drug up front.
Just as the doctor does not know if a drug will work or not in an individual patient, he or she does not know if a specific person will or will not have a side effect to a given drug. But if this could be known in advance, adjustments could be made and the side effect avoided. Here is an example with a cancer drug. 6-mercaptopurine (6-MP) is used for children with acute leukemia. The doctor calculates the correct dose based on the child’s height and weight and it is given orally. Normally, it is converted (metabolized) by an enzyme called cytochrome P-450 in the liver. But some people have a much reduced level of this enzyme because of a slightly different gene. When they take a normal dose of 6-MP the drug remains in the blood stream for much longer than usual leading to serious side effects. Now there is a simple test which prevents the child from receiving what could have been a fatal dose of 6-MP.
In the coming years we can expect to learn about new drugs developed using genomic approaches as with Gleevec and Herceptin; tests to advise the doctor as to what drugs will or will not work in a given patient and many new tests to prevent a patient from having an unwarranted side effect. Such is the power of genomics for the future; it will indeed be a revolution.
The next post will continue the discussion of what genomics is doing to change medical practice. There is more on this video
Friday, April 6, 2012
These are the megatrends in medical care that are coming whether there is any change in health policy or not. First, expect that medical care will become much more custom-tailored to your personal needs. Genomics will allow you physician to select the most appropriate medication for you not just the one that on average works for most people. And he or she [more and more she since 50% of medical school graduates are now women] will also be able to select a drug that is less likely to cause a side effect as a result of you body’s reaction to it – all from knowing your genomic information. The surgeon will use your image such as a CT scan to program the simulator and practice the correct approach for your personal surgery. A vaccine may be made up specifically for you – a designer vaccine – to treat your specific cancer.
Second, expect that medicine will finally begin to focus more and more on prevention. . For example, genomics will allow your doctor to tell you at a young age if you personally are at high-risk for, say, heart disease and then prescribe a regimen of life style changes and medications selected specifically for you to reduce the risk. New vaccines will ward off serous infections and even many chronic debilitating diseases like Alzheimer’s.
Third, there will be major advances in repairing, restoring and replacing damaged and diseased organs and tissues. New surgical techniques will allow for remarkable repairs in a much less invasive manner; medical devices will allow the heart to beat regularly and stop the tremor and rigidity associated with Parkinson’s disease. And stem cells will allow for new tissues when old ones no longer function. Xenotransplantation – using an organ from an animal rather than a human – will be come available so that a person needing a heart or kidney will get it immediately and not need to wait and “hope” for someone else to die.
Medial information will be readily available no matter where you are. This will increase safety, convenience and improve medical care quality immensely.
Finally, care will become much safer as genomics adds to our knowledge of what drugs to prescribe, technologies such as simulators teach and demand competency and digitized medical information is readily available
These are the megatrends coming in medical care. They will occur and are coming in not that many years. Hopefully health care policy can advance as well and as fast, but that is much less certain.
For a video of these megattrends go here http://bit.ly/HnD3gE
Praise for Dr Schimpff
The craft of science writing requires skills that are arguably the most underestimated and misunderstood in the media world. Dumbing down all too often gets mistaken for clarity. Showmanship frequently masks a poor presentation of scientific issues. Factoids are paraded in lieu of ideas. Answers are marketed at the expense of searching questions. By contrast, Steve Schimpff provides a fine combination of enlightenment and reading satisfaction. As a medical scientist he brings his readers encyclopedic knowledge of his subject. As a teacher and as a medical ambassador to other disciplines he's learned how to explain medical breakthroughs without unnecessary jargon. As an advisor to policymakers he's acquired the knack of cutting directly to the practical effects, showing how advances in medical science affect the big lifestyle and economic questions that concern us all. But Schimpff's greatest strength as a writer is that he's a physician through and through, caring above all for the person. His engaging conversational style, insights and fascinating treasury of cutting-edge information leave both lay readers and medical professionals turning his pages. In his hands the impact of new medical technologies and discoveries becomes an engrossing story about what lies ahead for us in the 21st century: as healthy people, as patients of all ages, as children, as parents, as taxpayers, as both consumers and providers of health services. There can be few greater stories than the adventure of what awaits our minds, bodies, budgets, lifespans and societies as new technologies change our world. Schimpff tells it with passion, vision, sweep, intelligence and an urgency that none of us can ignore.
-- N.J. Slabbert, science writer, co-author of Innovation, The Key to Prosperity: Technology & America's Role in the 21st Century Global Economy (with Aris Melissaratos, director of technology enterprise at the John Hopkins University).