Personalized medicine is a field of health care offering better precision and effectiveness than traditional medicines. Each person has a unique genetic make-up and hence, traditional medicines are not always most effective in every patient. The use of an individual’s genetic information, combined with other clinical information, “to stratify them into sub-populations that differ in susceptibility to a particular disease or response to a specific treatment” is the basis of personalized medicine.
Every patient does not respond to a drug identically according to observation of clinicians. A large number of patients show variable response to the drugs given to them in treatment of cancer, cardiovascular conditions, respiratory diseases, other metabolic disorders etc. To improve efficacy and reduce the side effects of drugs by properly using unique biology of patients is the major objective of personalized medicine. This allows for customization of therapeutics to maximize their benefits and minimize toxicity. Personalized medicine can be regarded as the right drug to the right patient in right doses.
‘‘Targeted therapies’’ or ‘‘targeted dosing’’ are the part of personalized medicine to select or optimize patient's prophylactic and therapeutic care. Personalized medicine involves the proper selection of drugs and doses according to an individual’s genetic make-up to make them safer and optimally effective. This also translates into lower disease management cost and possibilities of earlier and successful intervention.
Blockbuster personalized medicine
Since personalized medicine has started becoming the order of the day. In future, marketing the prescription drugs will depend largely on the way that drug is going to be fit individual patient's biology.
Many blockbuster drugs are well marketed but only 30 per cent drugs are able to achieve and surpass their multi-billion dollar R&D cost. Due to this realization, top pharmaceutical companies have re-structured their drug discovery and delivery approaches to achieve desired success rate in inventing blockbuster drugs. There are various steps involved in the implementation of personalized medicine like division of patients into biological subgroups and keeping them in mind while attempting drug discovery and delivery. The improved diagnostics have fuelled the growth of personalized medicine. In coming few years, we will find prescriptions of more and more drugs based on the results of genomic findings.
Pharmacogenomics and personalized medicine
Information obtained from gene variation analysis is used with the objective to guide drug’s Pharmacogenomics and Pharmacogenetics. Pharmacogenomics deals with the drug response variability due to the contribution of multiple genes (or entire genome), whereas pharmacogenetics selectively focuses on the association between drug response and candidate gene variability. Pharmacogenomics and pharmacogenetics taken into account together aid in shaping the concept of personalized medicine into reality.
Pharmacokinetics (processing of drug by the body) and pharmacodynamics (how drugs interact with receptors to cause drug response) are the two functional components involved in pharmacogenetics that link pharmacology to genetics. Pharmacokinetics is strongly connected to the metabolism of drug mainly by the liver and their subsequent elimination by kidney.
Pharmacodynamics deals with the understanding of drug-receptors interaction and their subsequent response. However, gene polymorphisms (Drug metabolizing enzymes polymorphisms, drug transporters, etc.) that modify the concentration of a drug and its metabolites at the site of action are a part of pharmacokinetics.
Pharmacodynamic genes: Serotonin transporter or dopamine receptors (these gene tests are not yet ready for clinical use)
Pharmacokinetic genes: CYP2D6 and CYP 2C9 are entered in clinical practice.
Understanding of pharmacodynamic and pharmacokinetic gene variability will address the lacunae of current disease management strategies.
Personalized medicine in cancer
Personalized treatment has taken significant strides in cancer therapeutics. Pharmaceutical and biotech companies working in oncology sector are today well aware of the development of personalized medicine for treatment of cancer. The well demonstrated case is that of discovery of estrogen receptor in 1960s and subsequent introduction of the anti-estrogen tamoxifen in the 1970s. The high proportion of patients responded to treatment of tamoxifen with estrogen receptor-positive breast cancer demonstrated by clinical studies. The entry of tamoxifen leads to more individualized treatment approach to cancer.
For precise diagnosis and better treatment option for the patients, new molecular testing methods like testing of global gene, protein and protein pathway activation expressions profiles and somatic mutation in cancer cells are likely to be helpful.
Personalized medicine in metabolic disorders and other disorders
There are enough evidences to vouch for the advantages of personalized medicine.
Higher anesthetic requirement of desflurane (Suprane®) as well as topical and subcutaneous administration of lidocaine is required in individual with melanocortin-1 receptor gene (MC1R) mutations than individuals with a normal genotype.
Among the enzymes involved in metabolism, cytochrome P450 (CYP) plays a major role in drug metabolism. CYP enzyme activity depends on several factors such as age, gender, diet, and genetic changes. It has been reported that in some metabolic reactions, the activity of the CYP enzymes vary up to 50-fold between individuals.
Variability in response to drug therapy has been observed with many drugs such as ß –blockers, proton-pump inhibitors, anti-epileptics and antidepressants those are metabolized through the CYP2D6 and CYP2C19 enzymes.
HIV drug maraviroc (Selzentry, Pfizer, NY, USA), a CCR5 co receptor antagonist is one of the latest examples where diagnostic testing has given a better therapeutic choice.
Recently, FDA approved important drug-related diagnostic test known as Nanosphere’s Verigene Warfarin Metabolism Nucleic Acid Test (Nanosphere, IL, USA). Anticoagulant Warfarin metabolism related genes CYP2C9 and VKORC1 are detected by this test. Warfarin shows higher risk of bleeding as well as metabolizes differently than expected in some patients. This test help the physician to assess whether patient is sensitive to warfarin or dose adjustment is warranted.
An economy of scale
For the first time, genome sequencing cost was around $ 3 billion . In 2007, sequencing cost was around a million dollars. Few months later sequencing cost was around $ 60,000. With the advent of newer technologies, we can expect sequencing cost in the range of $1000-5000 soon.
“Where we see this headed from our perspective is scale” said by Cliff Read CEO of Complete Genomics. Firstly, reducing cost is more important because mass sequencing will be affordable for researchers to sequence thousands of peoples with disease. Secondly, it requires computing data from thousands of genomes and existing biotech and pharma companies are not yet prepared for processing that much data.
Creating awareness
The public is burdened with broad misunderstanding about genomic medicine. To create awareness and to fill this gap considerable work is necessary.
Public willingness to accept personalized medicine is interfered with various factors such as certain level of mistrust of the government, researchers and physicians as well as public lack of information about emerging genetic information and technology. Proper collection and review of genetic information is necessary because personalized medicine will only be effective when utilized properly.
Future perspectives
Better way of treatment is the way to personalized medicine. In coming few years, most of the genes for multigene disorders will be identified.
For future decision-making in pharmacogenetics, numerous opportunities are there that utilize the basic principles of clinical pharmacology and to provide a biological, mechanistic, quantitative, and model-based frame work. In the coming years, high-throughput technologies, rapid and cheap sequencing will also become available such as the new generation of 454 life science sequencers, which can sequence 20 million bases per day. Risk of relapse, detecting oncogenic events and changes involved in drug resistance analysis will be done by bioinformatics. A clinical pharmacology framework for progress in pharmacogenetics is already in place and currently used for regulatory decision making as exemplified by the Sheiner learn-confirm paradigm used for making predictions and decisions in the drug development process. But establishing the functional significance of genetic polymorphisms involved in various conditions is not enough; additional, rigorous, well-designed, large-scale prospective clinical trials with consistent efforts and follow-up are also necessary, so that such genotypical features may lead to the identification of new therapeutic populations and the widespread use of the results. Personalized medicine will become a reality when medicine no longer needs to be described as personalized medicines. This signifies that prescriptions will be routinely written for patients based on the specific genetic patterns of polymorphisms in their genome – then it will be only called as medicines.
‘‘Knowing is not enough; we must apply. Willing is not enough; we must do it’’.
Johann Wolfgang von Goethe
Author is Dean, Faculty of Technology & Engineering, The Maharaja Sayajirao University of Baroda, Vadodara