New accurate and powerful in vitro diagnostics could hasten future drug development. Pacific Biomarkers’ Timothy Carlson and Amar Sethi explain how.
Evidence is accumulating that several novel biomarkers will become powerful clinical tools in detection of treatment-induced acute kidney injury (AKI) and in the diagnosis of impaired kidney function in future.1 The US Food and Drug Administration’s Critical Path Initiative (CPI),2 launched in 2004, has inspired a biomarker programme3 with the aim of identifying biomarkers useful for the assessment of drug-induced toxicity for drugs that are in development.
The biomarkers qualified in this programme would, following detailed analytical validations, be used in clinical trials with the ultimate goal of being accurate and powerful in vitro diagnostics (IVDs) that could replace or augment less sensitive existing tests. Current costs associated with drug development from discovery to final approval have been estimated to be US$1bn (€720m) or more.4
Drug-induced organ toxicity accounts for 30% of all drugs that fail prior to reaching the market;5 the sooner this toxicity is discovered, the sooner further development costs can be curtailed, enabling drug developers to focus on other, safer drugs.
Early diagnosis of drug-induced organ toxicity during drug development would not only reduce the cost associated with development, but also avert injury to future and current patients involved in clinical trials. Thus, the appropriate acute organ injury biomarker panel has the potential to detect organ-specific toxic drug effects that are currently being missed in clinical trials.
This kind of timely detection of early organ injury in clinical trials could potentially reduce the time needed for drug development by a number of years. Accomplishing this might also reduce overall healthcare costs if drug-induced organ injury can be diagnosed early enough to avoid severe and costly complications in patients taking the drug after its approval.
A key strategic goal of this kind of programme is to provide pharma and biotech companies with services for testing robust novel biomarkers that have undergone thorough analytical validation and clinical qualification to diagnose early organ injury. As stated above, this kind of work is now underway in response to recommendations made by the US FDA for improving drug development outcomes as outlined in the CPI.2 Thus, efforts toward these ends are currently in progress under the direction of the Predictive Safety Testing Consortium (PSTC) and the Health and Environment Sciences Institute (HESI).
The aim of the CPI is to characterise not only the analytical performance of these novel biomarkers, but also their clinical performance through collaboration among the pharma companies that are members of the various consortia. The anticipated qualification of organ injury biomarkers will ultimately demand the development of stringent standardisation procedures, which currently do not exist. As mentioned, the analytical performance of some AKI biomarkers has already been characterised while the validation of others is in progress.
The best approach to accomplishing the goals of the CPI programme is to validate each biomarker using rigorous protocols for singlicate assays that generate the most robust data possible. During this process, it may be necessary to modify the assay methods or validate new ones. Excellent analytical performance is necessary to ensure that data generated from the studies evaluating the utility of the novel biomarkers provides the best possible basis for choosing the appropriate biomarkers for further development. Once a panel of five to seven biomarkers with strong clinical performance has been identified, investigations on multiplex procedures for these biomarkers can also be initiated.
Unfortunately, for many biomarkers, analytical performance deteriorates significantly during multiplexing. Therefore, high priority will be given to establishing excellent performance for the individual biomarkers before attempts can be made to perform them on a multiplex platform. The preliminary work will provide assay performance targets to be used for subsequent multiplex assay evaluation. Hence, because the initial evaluation of biomarker clinical utility requires the best possible analytical performance, it is vital initially to find methods and platforms with superior analytical and diagnostic performance.
markers and their uses
Approximately 30 biomarkers for AKI have been identified by different consortia and key-opinion leaders.6 The biomarkers with the greatest current level of analytical and clinical evidence are being targeted and investigated in the present programme. They fall into three categories as summarised here.
The first group includes biomarkers of specific renal tissue injury, such as Kidney Injury Molecule 1 (KIM-1), a type 1 transmembrane protein that is not detectable in normal kidney tissue, but is expressed at high levels in human and rodent kidneys with dedifferentiated proximal tubule epithelial cells after ischemic or toxic injury.7 Neutrophil gelatinase-associated lipocalin (NGAL), another biomarker of specific renal injury, is a ubiquitous 25kDa protein generally expressed in low concentrations but which increases greatly in the presence of epithelial injury and inflammation.8 Also, a biomarker specific for proximal tubular damage is n-acetyl glucosaminadase (NAG).9 Increased interleukin 18 (IL-18), another marker in this group, has been associated with a variety of causes of renal injury from endotoxemia to cisplatin toxicity,10 while yet another, Clusterin, is thought to reflect renal ischemia-reperfusion injury. At present, all of these biomarkers are available for use in clinical trials.
A second group of biomarkers, which includes Cystatin C11, albumin,12 total protein levels,13 and β2-microglobulin,14 are good global kidney markers assessing glomerular function. Most of these markers have been known for some time, and thus a great amount of clinical evidence has accumulated to establish their clinical utility. A drawback of these biomarkers, however, is their lack of specificity to localised regions of the kidney. All four of these markers are available for the support of clinical trials.
The last group includes ‘emerging’ or more exploratory AKI biomarkers. Thus, α-gluthathione s-transferase (α-GST) is believed to be specific of proximal tubule damage,15 as is Trefoil Factor 3 (TTF3)16 and Calbindin.17 Meanwhile, liver type fatty acid binding protein (L-FABP) is a promising biomarker of tubular injury,18 while γ-glutamyl transferase (γ-GT)19 and Π-glutathione s-transferase (Π-GST)20 may indicate tubular epithelium injury and distal tubular epithelium injury respectively.
Finally, Type IV Collagen levels could be useful as an indicator of glomerular injury.21 To date, only a-GST is ready for the support of new clinical research, but the rest of these biomarkers, and some others, such as Osteoactivin and Renal Binding Protein-4, must be considered emerging biomarkers, and may be available for clinical trials soon.
potential use as IVDs
Within the near future a handful of biomarkers that can be targeted as IVDs will be identified by the consortia and will be given FDA approval. This must be preceded by gathering additional clinical validation and strong analytical data suggesting that these bio-markers are fit for this purpose. All biomarkers highlighted above have potential utility as IVDs, but most likely, only a handful will pass the threshold put forward by the FDA’s biomarker validation process.
In addition to utility in identifying AKI during clinical trial, the panel of biomarkers encompassing the different categories of kidney injury will eventually have at least three other major roles: 1) general diagnostic utility for physicians for identification of patients with potential AKI; 2) diagnosis of AKI in patients in intensive care units with septic shock or following major surgeries, like coronary artery bypass graft surgery or kidney transplant; and 3) as tools to follow and evaluate kidney function in, among others, diabetic patients who are very prone to kidney disease.
Existing serum biomarkers that detect kidney toxicity include creatinine and blood urea nitrogen. Both are, however, associated with limitations as substantial injury is required before an increase is observed. Determination of the glomerular filtration rate is sometimes used to assess renal function, but it is tedious, can require injection of chemical, and in the end may still not be a reliable marker for the detection of early kidney injury. Thus, the currently available biomarkers of AKI all lack sensitivity and specificity for detecting impaired kidney function early enough.
The optimal new IVDs of AKI will have to satisfy multiple criteria: 1) identify kidney injury before levels of serum creatinine increase; 2) reflect degree of toxicity; 3) be specific to a localised site in the kidney; 4) track progression of injury and recovery; 5) predict outcome; 6) act as surrogate endpoints useful for clinical interventional studies; and 7) be readily detectable in available body fluids.6,22
A handful of biomarkers that can be targeted as IVDs will be identified by the consortia and will be given FDA approval
Currently, the US FDA’s In Vitro Diagnostics Database23 tabulates about 300 products involving the detection of creatinine levels approved by the FDA between 1976 and 2010. The number of products currently available for creatinine highlights the environment in which the new kidney biomarker studies are being conducted. A blend of various methods and platforms is currently available to healthcare professionals for measuring creatinine, the traditional kidney function marker.
It is likely that similar technologies will be applied to the measurement of new AKI bio-markers and will result in the same reliable and reproducible results. However, before getting to that point these novel biomarkers will have to go through the thorough clinical validation and qualification approval procedure as recommended by the FDA.24
clinical validation
Briefly, this begins with submission of biomarker data for review by the Interdisciplinary Pharmacogenomic Review Group (IRPG) at the FDA. The IPRG team, consisting of various experts from different FDA centres, will review the biomarker qualification data together with other biomarker data submitted through the voluntary data submission process. This evaluation will allow the FDA, together with the applicant, to design a biomarker qualification study that would produce the data that would justify either the acceptance or rejection of the suggested biomarker.
This process is obviously long and tedious, but each one of the novel organ safety biomarkers would need to go through it before consensus could be reached on which biomarkers are qualified for diagnostic use.
The diagnostic industry has already shown enormous interest in developing these novel biomarkers for diagnostic purposes. An interesting example of what the future of IVD treatment for AKI might be is measurement of urine neutrophil gelatinase-associated lipocalin (NGAL).
Bioporto Diagnostics is developing methods for the early diagnosis of AKI in critical illness, nephrotoxicity and kidney transplantation using NGAL. Thus, Bioporto has an established ELISA method for NGAL and is currently introducing an automated (research-use-only) assay that may be set up on an open channel on a variety of random-access chemistry analysers. The Bioporto assay would allow NGAL analyses in urine, plasma and serum samples.
Another major player that is developing a diagnostic NGAL assay is Abbott Laboratories, which has developed a unique urine NGAL test on the random access autoanalyser, the ARCHITECT. This test is currently being used in certain European countries after it received the Conformité Européene (CE) Mark of certification last year. Earlier this year, Abbott submitted the data it has generated with its NGAL assay to the US FDA for approval as the first novel diagnostic biomarker for detecting AKI in the US. Future biomarker-testing using devices featuring speed and accuracy comparable to that of the ARCHITECT, but which incorporate other specific biomarkers, are now being developed.
In conclusion, new and more accurate generation of IVD tests for kidney injury may result from the AKI biomarker initiative currently underway, and could join or supersede the products summarised above. However, such advances can come about only following thorough clinical evaluation of each specific biomarker.
references:
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