As technological advan-ces in proteomics, genomics and pharmacogenomics accelerate in the wake of the mapping of the human genome, biomarkers are moving to the front line of drug development. Molecular biomarkers are individual components of the proteome, the total protein expression of the genome, and as such represent a new product development tool kit of vast proportions providing a basis for the selection of lead candidates for clinical trials, for contribution to the understanding of the pharmacology of candidates, and for characterisation of the subtypes of disease for which a therapeutic intervention is most appropriate. Furthermore, biomarker assays help improve and speed up the drug development process by providing information on drug safety and efficacy.
Today, biomarkers find application as preclinical and clinical endpoints in the evaluation of new drugs and medical devices, ultimately resulting in more accurate, timely and transparent regulatory decisions.
Measurements of biomarkers can help explain empirical results of clinical trials by relating the effects of interventions on molecular and cellular pathways to clinical responses. In doing so, biomarkers provide an avenue for researchers to gain a mechanistic understanding of the differences in clinical response that may be influenced by uncontrolled variables (for example, drug metabolism).
What are biomarkers?
In medicine, a biomarker is an indicator of a particular disease state or a particular state of an organism. Traditionally, biomarkers have been primarily anatomic (e.g. tumor formation in cancer) or physiological indicators (e.g. blood pressure or heart rate). More recently, however, the term biomarker is becoming synonymous with molecular biomarker which is an enzyme, protein, or hormone associated with organ function, damage or failure.
Some of the tests are specific for a particular organ while others are less selective and sensitive. The marker of choice is able to selectively detect the presence and severity of an acute condition as early as possible with a rapid turnaround time.
Different biomarkers have different kinetics as their levels rise, peak, and fall within the body, allowing them to be used not only to track the progress of the disease but also to estimate when it began and to monitor for recurrence.
Biomarkers of disease: covering measurement of endogenous substances or parameters indicative of a disease process and the use of pharmacodynamic and genetic markers in evidence-based laboratory medicine and treatment (markers of efficacy);
Biomarkers of exposure: covering detection and measurement of internal exposure to drugs and other chemicals;
Biomarkers of response: including measures of endogenous substances or parameters indicative of pathological or biochemical changes, both toxicodynamic and pharmacodynamic, resulting from exposure to drugs and other chemicals;
Biomarkers of susceptibility: including genetic factors which alter susceptibility to drugs and other chemicals.
Applications
There is a variety of ways that biomarker measurements can aid in the development and evaluation of novel therapies. Biomarkers have a great value in early-phase clinical trials to establish proof of concept. Biomarkers contribute knowledge about clinical pharmacology and provide a basis for the design of clinical trials that expeditiously and definitively evaluate safety and efficacy. Biomarkers provide information for guidance in dosing and minimise interindividual variation in response. For example, rapid clearance of 99mTc-sestamibi, a substrate for P-glycoprotein that is associated with multidrug resistance, has been shown to predict lack of tumor response to adjuvant chemotherapy in some forms of breast cancer. Biomarkers that represent highly sensitive and specific indicators of disease pathways have been used as substitutes for outcomes in clinical trials, so-called surrogate endpoints, when evidence indicates that they predict clinical risk or benefit.
Novel biomarker assays require careful method development and validation. Part of the development work must tackle the identification and characterisation of the biomarker and also the feasibility and suitability of the test
Further applications include the following:
*Use as a diagnostic tool for the identification of those patients with a disease or abnormal condition (e.g., elevated blood glucose concentration for the diagnosis of diabetes mellitus)
*Use as a tool for staging of disease (e.g., measurement of carcinoembryonic antigen-125 for various cancers) or classification of the extent of disease (e.g., prostate-specific antigen concentration in blood used to reflect extent of tumor growth and metastasis)
*Use as an indicator of disease prognosis (e.g., anatomic measurement of tumor shrinkage of certain cancers)
*Used for prediction and monitoring of clinical response to an intervention (e.g., blood cholesterol concentrations for determination of the risk of heart disease).
Areas of biomarker research
Biomarkers are becoming important assessment tools in various therapeutic areas such as:
*Cancer Prevention and Therapeutics
*Cardiovascular Diseases
*Neurosciences
*Immune Diseases, Transplantation, Joint Destruction and Repair
*Chronic Lung Diseases, Infections and Septic Shock, Pain Assessment, Osteoporosis
Assays and technologies
Current assays and technologies used for the determination of biomarkers include, mostly immunoassays, such as ELISA and RIA, but also capillary electrophoresis, HPLC/MS/MS, gel electrophoresis, western blots, and enzymatic assays using UV-VIS spectrophotometry or fluorometry (enzyme kinetics, FRET assays).
Assays are typically carried out in complex matrices such as plasma, blood, urine, tissue and body fluids. Sample preparation (extraction) is not always required. However, whether the matrix interferes with the assay must be always assessed. Typical extraction methods include solid and liquid phase extractions, ultrafiltration and precipitation. In most cases, the extraction methods must be suitable for a large sample throughput.
Novel biomarker assays require careful method development and validation. Part of the development work must tackle the identification and characterisation of the biomarker and also the feasibility and suitability of the test.
A full GLP-assay validation according to the FDA and CDER/CVM guidelines ("Guidance for Industry, Bioanalytical Method Validation") includes the determination of the following parameters: linearity, accuracy and precision, limit of detection, specificity and selectivity, recovery and extraction efficacy, effect of dilution, interference and matrix dilution.
Once a method is fully validated, partial validations must be performed when the test is carried out in a different matrix (cross-validation, e.g., determination of a biomarker in urine versus plasma) or when a validated method is newly implemented in a
different laboratory (transfer validation).
The author is head of biochemical analysis Business Unit Pharma, RCC Ltd)