American Journal of Transplantation 2008; 8: 267–270Blackwell Munksgaard

C© 2008 The AuthorsJournal compilation C© 2008 The American Society of

Transplantation and the American Society of Transplant Surgeons

doi: 10.1111/j.1600-6143.2007.02063.xPersonal Viewpoint

Qualification of Biomarkers for Drug Developmentin Organ Transplantation

Gilbert J. Burckarta,∗, Shashi Amurb,

Federico M. Goodsaidb, Lawrence J. Leskob,

Felix W. Fruehb, Shiew-Mei Huangb

and Marc W. Cavaille-Collc

aSchool of Pharmacy, University of Southern California,Los Angeles, CAbOffice of Clinical Pharmacology, Office of TranslationalScience and cDivision of Special Pathogen and TransplantProducts, Office of New Drugs, Center for DrugEvaluation and Research, FDA, Silver Springs, MD∗Corresponding author: Gilbert J. Burckart,burckart@usc.edu

The drug development process is dependent upon hav-ing established end points for measuring drug efficacyand adverse effects. New drug development in organtransplantation suffers from having end points whichare either outdated or which do not serve the purposeof addressing the current critical drug therapy prob-lems. Numerous biomarkers have been examined inorgan transplantation, but almost all would be clas-sified as exploratory for drug development purposes.Some of the possible pathways out of this dilemmainclude investigator- or consortium-initiated researchthat would qualify the biomarkers as either probableor known valid biomarkers, help in identification ofnew end points in transplantation and their associatedbiomarkers, co-development of a new biomarker anddrug for transplantation and the use of new clinical trialdesign methods which facilitate enriched or stratifiedtransplant patient populations. With new biomarkersand new study design methodologies for drug devel-opment, improvement in the drug development pro-cess for transplantation is a real possibility that thetransplant clinical and research community can helpto bring about.

Key words: Biomarker, drug development, drugs,end points, surrogate end points

Received 27 July 2007, revised 03 October 2007 andaccepted for publication 19 October 2007

Drug development for organ transplantation has become amore difficult and costly process over time. One methodof expediting drug development in transplantation is toidentify and qualify biomarkers that can be utilized in clin-ical transplant studies. Biomarkers are characteristics that

are objectively measured and evaluated as an indicatorof normal biological processes, pathogenic processes orpharmacologic responses to a therapeutic intervention (1).Biomarkers in transplant patients may represent biopsyfindings, functional studies, biochemical analysis of serumor urine, flow cytometric analysis of blood cells, genomicanalyses of DNA or mRNA or any test that is reflective ofthe biological or pathological process taking place in thepatient. The statistical considerations for using biomarkersin clinical trials in transplantation have been reviewed pre-viously (2).

Surrogate end points are a subclass of biomarkers wherethe biomarker is intended to substitute for a clinical endpoint. For the purpose of drug development in transplan-tation, the recognition of the biomarker that is being mea-sured as a qualified surrogate end point by the Food andDrug Administration (FDA) is an essential part of the drugdevelopment process. In the following viewpoint, valida-tion will refer to the assay method while qualification isthe evidentiary process that connects the biomarker, thebiological process and the clinical end point (3). The objec-tive of this viewpoint is to point out the biomarkers thathave been used previously for immunosuppressive drugapprovals, and to review the process of biomarker quali-fication within the FDA that can lead to advances in drugdevelopment for organ transplant patients.

Biomarkers in Transplantation

The established biomarkers for drug approval in transplan-tation have come from previous drug approvals. The im-munosuppressive drugs and end points that have beenused since 1980 are listed in Table 1. Biopsy-proven acuterejection is the primary biomarker that has been used toassess drug efficacy.

Acute rejection does have significant consequences in themanagement of transplant patients, so it acts as an impor-tant intermediate end point (4) rather than as a biomarkerof long-term graft survival (5). The sponsors of clinical tri-als and data and safety monitoring committees still useacute rejection, death and graft loss to make decisionsabout stopping studies or continuation of the develop-ment of a new drug or regimen. More recently, protocolbiopsies allow the detection of subclinical acute rejection,where rates of occurrence within the first 6 months after

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Table 1: End points used for the approval of the currently marketed immunosuppressive agents since 1980

Agent Year Comparator Basis End point

Cyclosporine 1983 (kidney) Azathioprine/steroids Superiority Patient/graft survivalTacrolimus 1994 (liver) Cyclosporine Noninferiority Patient/graft survival at 12 months” 1997 (kidney) ” ”” 2006 (heart) ” ” ”Mycophenolate 1995 (kidney) Azathioprine Superiority Treatment failure1 (6 months) and Mofetil (MMF)

” ” Noninferiority Patient/graft survival (12 months)” 1998 (heart) Azathioprine Noninferiority Patient death/retransplant (12 months)” 2000 (liver) Azathioprine Superiority Acute rejection (6 months) and

Noninferiority Patient death/retransplant (12 months)Sirolimus 1999 (kidney) Azathioprine/Placebo Superiority Efficacy failure2

Mycophenolate sodium 2004 (kidney) MMF Noninferiority BPAR, graft loss, death at 6 and 12 monthsDaclizumab 1997 (kidney) Placebo Superiority BPAR (6 months)Basiliximab 1998 (kidney) Placebo Superiority BPAR, graft loss, death at 6 and 12 months1Treatment failure was defined as biopsy-proven rejection on treatment, death, graft loss or early termination from the study withoutprior biopsy-proven rejection.2Efficacy failure was defined as first occurrence of a biopsy-proven acute rejection episode, graft loss or death.BPAR, biopsy-proven acute rejection.

kidney transplantation vary from 19% to 43% dependingon the drug regimen (6). A recent 1-day symposium onprotocol biopsies concluded that, ‘A critical need is for in-terventional studies to qualify the biopsy as a surrogatemarker’. (7).

With the present high rates of patient and graft survivalafter kidney transplantation, clinical outcomes at 6 and 12months after transplantation are not viable end points todistinguish immunosuppressive drug regimens that will im-prove the long-term transplant outcome. A decrease in theacute rejection rate over time to the present rate of approx-imately 15% or less in deceased donor renal transplantpatients in the first year posttransplantation has createdproblems with even this intermediate biomarker. To provesuperiority on the basis of biopsy-proven acute rejectionnow takes large number of patients and a prolonged phaseIII clinical portion of the drug development process. There-fore, the end points listed in Table 1, which have been pre-viously used for immunosuppressive drug approvals, arestill useful for the noninferiority studies in the first yearposttransplantation, but may be of little use in ultimatelypredicting the long-term graft and patient survival.

Transplant researchers have continued to identify biomark-ers related to acute rejection and adverse drug effects,but have carried out this work without regard to qualifyingthese biomarkers for drug development. Therefore, noneof these biomarkers are able to contribute to the develop-ment of new drugs for transplant patients since none are“known valid” or “probable valid,” as defined in the FDA’sguidance documents (8).

Biomarker Qualification Process in the FDA

The FDA’s Pharmacogenomics Guidance (8) classifiesbiomarkers as exploratory, probable valid or known valid,but does not describe a process by which an exploratory

biomarker can be qualified as a valid biomarker. A processmap can be drawn showing how these two classificationsmay be bridged (9), reflecting qualification needs for pre-clinical biomarkers. This process map reflects the expecta-tion for a continued interaction between the sponsors andthe FDA in the critical steps in this process, including ini-tial evaluation, qualification protocol draft and data review.This process map may also be tested in a pilot process forregulatory qualification.

The FDA has established a pilot process for biomarker qual-ification (10). This qualification process requires a definitionof the context of use for exploratory biomarkers leadingto a scientific consensus within the agency, and the datasupporting qualification in this context. This process doesnot preclude independent qualification in contexts differentfrom those proposed to the FDA. This qualification processis also closely aligned with the review of the drug submis-sions at the FDA. The FDA and its sponsors have collab-orated on the design of an efficient qualification process,and the FDA has established a review structure to reflectthis process. Currently over 30 Voluntary Genomic DataSubmissions (VGDS) have been received by the FDA, withtwo-thirds of these focusing on the clinical study designissues (11).

One example of a VGDS submission to the FDA was basedon a phase II study in which a gene expression signaturewas proposed as a marker for a favorable outcome (10).The question of whether that gene expression signaturecould be used for patient stratification in a phase III trial isa complex one, but it was agreed that predictive modelscould be developed for the phase III trials. The success ofthe VGDS program has led to the inclusion of a broaderset of biomarkers under a voluntary ‘exploratory’ data sub-mission or a Voluntary Exploration Data Submission (VXDS)process.

268 American Journal of Transplantation 2008; 8: 267–270

Qualification of Biomarkers for Drug Development

Figure 1: A graphic illustration of the development of a new biomarker and a drug for the treatment of chronic allograft

dysfunction. The central gold arrow depicts the normal drug development process. Above the arrow is the process of developing andtesting new biomarkers for chronic allograft dysfunction, and the Biomarker Qualification Pilot Process of the FDA. Below the gold arrow,the green, blue and yellow boxes depict the stages of developing a biomarker concurrently with the new drug development and approval.The purple box indicates methods of streamlining clinical trials for transplant patients. Abbreviations: NIH-CTOT, Clinical Trials in OrganTransplantation study sponsored by the National Institutes of Health; CRADAs, cooperative research and development agreements.

The Future of Biomarkersin Transplant Drug Development

The transplant community is therefore faced with thehurdles of outdated end points and a drug developmentpipeline that has few candidates that will make a significantimpact on the long-term patient and graft survival. Whilethese hurdles are not easily overcome, there are pathwaysfor improving the current situation. Some of these path-ways include:

Investigator or consortium submission

to the Biomarker Qualification Pilot Process

The Biomarker Qualification Pilot Process is a significantchallenge for an individual researcher. Recently, consortiahave been formed that foster data sharing and make theprocess much more efficient (12). For example, an industryPredictive Safety Testing Consortium (PSTC) was initiatedby the FDA and the C-Path Institute for the qualificationof the new preclinical and clinical biomarkers for nephro-toxicity, hepatotoxicity, vascular injury and genotoxic andnongenotoxic carcinogenicity. The launch of the PSTC wasin March 2006, and the PSTC first presented 23 biomark-ers for nephrotoxicity to the FDA for qualification consid-eration in June 2007. Goodsaid and Frueh have previouslypresented nephrotoxicity biomarkers as a case study in thebiomarker qualification process at the FDA (13).

Federal agencies are also coordinating trials directed atthe development of biomarkers, such as the NCI CancerBiomarker Project and the Clinical Trails in Organ Transplan-tation (CTOT) program. In October of 2006, a public-private

partnership, which includes the FDA, was established asThe Biomarkers Consortium to search for and qualify newbiomarkers for drug development (14). The BiomarkersConsortium is expected to centralize the identification andtesting and qualification of biomarkers for the new and pre-viously approved drugs (15). The Biomarkers Consortiumaccepts Project Concept Submissions, and works to findfunding for those approved. The upper part of Figure 1 indi-cates that this qualification process can take place through-out the cycle of drug development.

Transplant researchers conducting these studies should beencouraged to participate in the Biomarker Qualification Pi-lot Process and to discuss the process of biomarker quali-fication with the FDA. The sources for funding the studiesthat are necessary to qualify a biomarker in transplant pa-tients are multiple, and include cooperative research anddevelopment agreements (CRADAs), federal agencies, de-vice manufacturers that can market the test and the phar-maceutical industry. Once a biomarker is qualified as aknown valid biomarker in the FDA process, the expecta-tion is that this biomarker would then be included in allfuture drug development processes in transplantation.

Identification of new end points for transplant drugs

and their associated biomarkers

Adverse drug effects have a major impact on long-termtransplant patient survival. Therefore, equivalent efficacywith less nephrotoxicity, lipid abnormalities or posttrans-plant diabetes mellitus are reasonable goals for drug de-velopment in transplantation.

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Codevelopment of a biomarker and a new drug

The concurrent development of a new biomarker and adrug has proven to be a very effective approach for thevalidation and qualification of a biomarker. The best recentexample of this process is the development of the HER2test along with trastuzumab (Herceptin, Genentech, SouthSan Francisco, CA). Using the development of a biomarkerfor chronic allograft dysfunction as a model, Figure 1 pro-vides an approximate timeline for the development of thebiomarker in the context of drug development. The clinicalphase of drug development would provide the evidence ofclinical utility for the test, and allow its qualification as ei-ther a probable valid or a known valid biomarker. The claimfor the test would be for use with the drug, and the drugwould be cross-labeled for use with the diagnostic test forthe biomarker. The use of the biomarker test would thenbe viewed as a requirement for the appropriate use of thedrug.

New clinical trial design methods

for transplant drug development

The FDA is now discussing new trial designs that couldstreamline clinical trials (12) and may work well in smallerpatient populations such as is found in transplantation. Forexample, sample enrichment strategies could exclude thepatients at a lower risk of rejection, use established risk fac-tors including genomic studies for enrollment criteria andperform separate trials for recipients of organs from liv-ing donors or deceased donors. Stratifying the transplantpatient population into subsets may allow for a more effi-cient clinical trial in a smaller number of patients. Adaptivetrial designs may also accommodate the smaller number ofpatients that are frequently encountered in transplant stud-ies; and a guidance on the use of these trials is expectedfrom the FDA in 2008. The impact of these new clinicaltrial design methods would primarily be during phases 2and 3 of drug development, as indicated in Figure 1. Whencoupled with regulations for accelerated approval of newdrugs for serious or life-threatening illnesses, there aremultiple ways forward for the transplant drug developmentprocess.

Conclusion

A large number of exploratory biomarkers exist in trans-plantation that has not been qualified. While areas exist forfurther development, such as with adverse drug effects,the transplant research and clinical community can focuson fully qualifying biomarkers as one method of advanc-ing the development of drug therapy for organ transplantpatients. The FDA’s Critical Path document and the experi-ences gained from initiatives such as the VGDS, CRADAsand Consortia allow the FDA to partner with the transplantcommunity to advance the drug development process intransplantation. With new biomarkers and new study de-

sign methodologies for drug development, improvement inthe drug development process for transplantation is a realpossibility that the transplant clinical and research commu-nity can help to bring about.

Acknowledgments

The views expressed in this article are those of the authors and not neces-sarily those of the U.S. Food and Drug Administration.

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