Animal Rights

Understanding Personalized Medicine

| by Dr Ray Greek

The following is from FAQs About the Use of Animals in Science: A handbook for the scientifically perplexed.

What is personalized medicine?

Personalized medicine involves the ability of physicians to treat patients based on their own unique genetic makeup. Pharmacogenomics is a part of this exciting new field of medicine. Researchers working in pharmacogenomics focus on the link between genomic variation and pharmacological properties.

How does personalized medicine differ from traditional medicine?

Historically, the practice of medicine has been based on statistics. Strange as it may seem, if you were sick, you would want to be treated as a statistic, rather than an individual, because you would be more likely to get well by being treated as a statistic. Say you were suffering from high blood pressure (HBP), and research showed that 98 percent of people with HBP responded well to medication A rather than medication B. It may turn out that you were among the very small minority of people who needed medication B to lower your HBP. More likely than not, however, you needed A. Since there was no way to determine beforehand if you were among the majority or minority, your best bet was to take medication A.

What’s the downside to the traditional method?

The downside is that millions of people are adversely affected by medications. Some have an allergic reaction, while others suffer from a side effect like bone marrow suppression, liver failure, stroke, heart attack, and so forth. Science has long been searching for a way not only to match the drug to the patient, but also to identify disease risk before the disease manifests.

What has happened to make personalized medicine possible?

Personalized medicine is a direct application of the knowledge gained from the Human Genome Project, which unraveled the human genetic code.

A 13-year international effort that began in 1990 and was completed in 2003, the Human Genome Project was a huge turning point for gene-based medicine. And it was a long time coming. In 1953, James Watson and Francis Crick discovered the double helix structure of the DNA molecule, and it was Watson who later urged the U.S. government to finance the Human Genome Project. In the end, what it accomplished has set the stage for a whole new era in modern medicine.

The successful completion of the process of mapping and sequencing the complete chemical instructions that control heredity has paved the way for scientists to focus on identifying the genetic differences that determine how individuals metabolize drugs.

Think of the entire human genome as an alphabet. Without an alphabet, it would be difficult to communicate with words. But an alphabet alone does nothing. Scientists are now finding what all the genes in the human body do, how they interact, what happens when they fail, and so forth. This is like using the alphabet to make words. Once we have a sufficient vocabulary, we can write sonnets and novels. And once scientists know enough about all our genes, they can cure diseases or even prevent them from happening in the first place.

But all this depends on first finding the structure of DNA, then decoding the genome, then mapping the genome, and so on.

How are medical scientists taking advantage of genome data?

We now know that people metabolize drugs differently—and thus have different pharmacological and toxicological responses to drugs—because of variations in their genes. A drug that is good for your mother may not be given to you because of your differences in genetic makeup. Today we even know that men differ from women in the way they respond to drugs and the diseases they suffer from. Even monozygotic twins do not always suffer from the same diseases. 

By isolating the particular gene involved in metabolizing a particular drug, scientists can now predict an individual patient’s ability to metabolize that drug based on a genetic profile.

How will personalized medicine improve health care delivery?

Personalized medicine will lead to genetic testing for common conditions and their treatments or cures. The cure may involve gene therapy, which will be the most efficient way to treat a disease. If you turn off the genes responsible for the disease, then it will never appear. The cure may even be applied in utero.

Personalized medicine will also eliminate the need for large-scale clinical trials, which take a long time to complete and drive up the costs of drug development—and ultimately the cost of drugs. Drugs will only need to be tested on individuals who have the appropriate genetic profile.

Another benefit to personalized medicine is that it has the potential to virtually eliminate the incidence of adverse reactions. Armed with precise data based on an individual’s genetic profile, doctors will be able to administer the exact dosage a patient needs to gain maximum therapeutic effect. And that means reduced hospitalizations and more successful outcomes.

Most intriguing of all is the possibility of bringing back drugs that were recalled due to severe adverse effects. For example, a drug that was recalled because it causes kidney failure in 30 percent of patients could now be given safely and effectively to the other 70 percent of people not at risk for kidney failure.

Would personalized medicine reduce the use of animals in the laboratory?

Scientists working in personalized medicine go straight to the source, using human DNA to sort out how cells react to certain chemicals. Tiny computer chips using very small samples of DNA are treated with a chemical to determine how individual genes are affected.

Pharmacogenomics uses human rather than animal DNA, which eliminates animals or animal-derived tissue from the process.

When will personalized medicine become a reality?

We are already seeing it, with breast cancer being a prime example. Breast cancer treatment is now determined in part based on a patient’s genetic makeup. About 25-30 percent of breast cancer patients overexpress the HER2 oncogene, which is a gene involved in the development of cancer. The overexpression results in an increase in the replication of the cancer cells. Physicians are now able to identify which breast cancer patients overexpress HER2 and give them Herceptin, a monoclonal antibody that inhibits HER2.

There is a dual benefit here. First, Herceptin has been designed to target only the cells that need to be killed, thus eliminating the need to administer large doses of toxic drugs that kill all cells. Additionally, being able to identify those patients who will benefit from the drug enables physicians to avoid administering the drug to patients who will not benefit from it, which also saves them from being exposed to any potential side effects.

Do you see this as the future of medicine?

Absolutely.

Finding cures and treatments for human disease takes a very long time, and the result society wants are at the very end of a long chain of events. Advances in our understanding of genes and gene expression have put us at the end of the chain for some diseases and nearing the end for others. It is this gene-based medicine that pharmaceutical companies and other industries are working to develop and utilize. Rather than a one-size-fits-all approach to medicine, we will be seeing in the not-so-distant future numerous drugs for a single disease, each designed for a specific genetic makeup. This is a far cry from basing treatment decisions on another species.

If these exciting technologies were supported with research funds that are currently earmarked for animals as predictive models-based research, the promise of people living longer, healthier lives could be fulfilled much sooner.