Biomarkers in Psychotropic Drug Development

678 Am J Geriatr Psychiatry 10:6, November-December 2002

Biomarkers in PsychotropicDrug Development

Saeeduddin Ahmed, M.D.P. David Mozley, M.D.

William Z. Potter, M.D., Ph.D.

The authors review the use of biomarkers in the development of novel psychotropicagents. They briefly review clinical drug development, emphasizing the importanceof incorporating biomarkers. For the development of psychotropic agents, biomarkersare particularly useful for assessing central nervous system exposure and effects andfor serving as surrogate measures for safety and efficacy. Collectively, biomarkers al-low for more accurate estimation of doses for clinical trials as drug developmentprogresses. For drugs that target the pathophysiology of Alzheimer disease, severalpromising biomarkers are becoming available that may allow improved signal detec-tion in clinical trials. Procedures for developing new drugs are evolving rapidly. Tech-nical advances in the field are making it possible to shift from empirically-basedmethods to mechanistically-driven schemes. Biomarkers enhance the quality andsafety of clinical drug development and reduce its cost and duration. (Am J GeriatrPsychiatry 2002; 10:678–686)

Received January 11, 2002; revised April 15, 2002; accepted April 17, 2002. From Lilly Research Laboratories, Indianapolis, Indiana. Addresscorrespondence to Dr. Ahmed, Lilly Corporate Center, Indianapolis, IN 46285. e-mail: [email protected].

Copyright � 2002 American Association for Geriatric Psychiatry

Until recently, pharmaceutical companies have gen-erally invested in new chemical entities (NCEs)

with mechanisms of actions similar to drugs that havebeen previously marketed. This is changing somewhat,as efforts expand to explore novel targets and mecha-nisms. Advances in genomics, proteomics, combinato-rial chemistry, and high-throughput screening have ledto a tremendous rise in the number of NCEs availablefor drug development.

Human studies during drug development are con-ducted in phases. Testing usually begins with small stud-ies in healthy young volunteers, but it is becoming morecommon to include elderly patients early in the devel-opment of NCEs that target degenerative or dementingconditions. Doses for initial human studies are deter-

mined by animal pharmacodynamic (PD) data, oftenwith the aid of allometric scaling to account for differ-ences in pharmacokinetic (PK) parameters among spe-cies.1 PK and PD of a drug refer to its time-dependentbiodistribution and effects, respectively.

An important advance has been the incorporationof biomarkers. Appropriate use of biomarkers enhancesthe probability of successful development of effectiveNCEs and allows for early termination of problematicones. A biomarker has been defined as “a characteristicthat is objectively measured and evaluated as an indi-cator of normal biological processes, pathogenic pro-cesses, or pharmacological responses to a therapeuticintervention.”2 There are many applications of bio-markers in drug development, three of which have par-

Ahmed et al.

Am J Geriatr Psychiatry 10:6, November-December 2002 679

ticular relevance to the development of psychotropicagents: 1) demonstrating central nervous system (CNS)penetration; 2) providing evidence of CNS effects; and3) for efficacy and safety, serving as surrogates.

CNS PENETRATION

Traditionally, initial human studies during drug de-velopment have not specifically assessed the extent ofCNS penetration. This can be problematic, because theblood–brain barrier may prevent sufficient exposure ofa drug at the site of action even if high plasma levelsare achieved. For many drugs, peripheral and centralconcentrations do not coincide.3 Symptoms and signssuch as dizziness, nausea, tremors, or impaired psycho-motor functioning may indicate direct brain effects, butthey may also be due to peripheral causes. Peripheralsymptoms, predetermined ceilings based on animal tox-icology data, or formulation limits may cap maximumdoses that may be administered to humans. In thesesituations, biomarkers can help establish whether dosesadministered in earlier human studies yield reasonableexposure at CNS target sites.

Cerebrospinal fluid (CSF). To obtain evidence of CNSpenetration, one can measure drug levels in the CSF.Levels in CSF are not identical to levels in neuronal syn-apses or inside cells, but the ependymal barrier thatseparates brain tissue from the CSF is much more per-meable than the blood–brain barrier,4 such that drugconcentrations in the CSF are generally more indicativeof “true” therapeutic levels than are plasma concentra-tions. Efficacious dose ranges may be estimated byachieving drug concentrations in the CSF that approx-imate binding constants for target receptors.5 It is nowpossible to do continuous CSF sampling for 12 hours ormore, which offers considerable advantages over singletime-point measurements.6

Drug detection using neuroimaging. Drug develop-ers may utilize non-invasive methods, such as magneticresonance spectroscopy (MRS) and tracer techniques,to obtain evidence of CNS penetration. MRS can pre-cisely measure concentrations of a drug and its metab-olites if the drug of interest contains an atom that is notnormally present in appreciable amounts in the brain.NCEs with one or more fluorine atoms are often wellsuited for direct measurements with fluorine–19MRS.7–10 In addition to being noninvasive, MRS does not

require exposure to ionizing radiation. Therefore, thereis no theoretical limit to the number of measurementsthat can be made in a single subject. However, severalpharmacological and technical factors limit the useful-ness of this method. The number of naturally fluori-nated NCEs is relatively small, and sensitivity is not ashigh as with other methods. Labeling drugs with non-radioactive carbon–13 is another option. However, car-bon–13 MRS is not as sensitive as fluorine–19 MRS, andboth methods require the administration of pharmaco-logical doses of a drug to detect its concentrations.

Radioactive forms of several atoms make it possibleto synthesize radioactive versions of NCEs. For exam-ple, if the NCE can be radiolabeled with carbon–11 orfluorine–18, then highly sensitive positron emission to-mography (PET) scans to monitor the biodistribution ofdrugs in close to real-time can be serially con-ducted.11–13 Radiolabeling NCEs early in developmentand administering them to subjects in tracer doses canprotect against needless exposure at pharmacologicaldoses if the NCE does not penetrate the CNS in suffi-cient quantities. One limitation of this strategy is thatradiolabeled metabolites of the NCE may confoundquantification of the signal from the parent drug. An-other problem is that the PK profile of a drug adminis-tered in tracer doses may not be linearly related to itskinetic behavior at pharmacological doses. Administer-ing fixed amounts of a tracer dose of a labeled drugbefore and after administering pharmacological dosesof the same unlabeled drug can estimate nonlinearity.The main limitation of methods that demonstrate ex-posure of a drug in the CNS is that they do not providedirect evidence of an effect or response. To address thisneed, different tools are necessary.

MEASURING DRUGEFFECTS ON THE CNS

To ensure that functionally efficacious concentrationshave been achieved, we must conduct PD assessments.CNS PD biomarkers may be divided into those that arespecific to the scientific hypothesis on which the de-velopment of a drug is based, and nonspecific ones thatmay not be directly connected to a particular mecha-nism of action. Nonspecific PD biomarkers include elec-trophysiological techniques, functional neuroimaging,performance scores on cognitive tests, physiological pa-

Biomarkers in Psychotropic Drug Development


rameters, and biochemical measures. Biomarkers thatspecifically test mechanisms of action are preferred, butare far fewer in number. Occupancy studies of targetsin the CNS are the best example of specific methods.Dose–response curves for multiple PD biomarkers inconjunction with peripheral and CNS PK data allow formore accurate estimation of efficacious doses in laterclinical trials.

Electroencephalography (EEG)

EEG has been used as a nonspecific PD biomarkersince the 1930s, with the pioneering work of Hans Ber-ger. EEG recordings may be performed under variousconditions; electrode number and placement may bealtered; and data may be analyzed with different algo-rithms. EEG patterns have been claimed to provide “sig-natures” for individual drugs and drug classes, as mark-ers for illnesses, and as prognostic indicators.14–18 Themost convincing application of EEG has been for drugsthat suppress neuronal firing, and sleep EEG has beenfully incorporated into drug development for sedativeand hypnotic agents.19

In the 1970s, computerized algorithms for analyz-ing EEG data became available and led to the develop-ment of quantitative EEG (qEEG). Digital data acquisi-tion in qEEG allows temporal, spatial, and spectralanalysis of data that is not possible with traditional pa-per recordings. In the last two decades, several guide-lines have been published for the standardization ofEEG data collection and analysis.20–24 Unfortunately, de-spite these efforts, the application of this technologyhas not been consistent across investigational centers,and reproducibility of results is often an issue. Further-more, there are technical limitations relating to manysources of artifacts, false positives, and absence of “nor-mative” data. Nevertheless, EEG continues to be ex-plored in drug development because it is non-invasive,indefinitely replicable within subjects, relatively inex-pensive, and easy to implement. Newer methods, suchas magnetoencephalography,25,26 and improvements inacquisition methods and analytic algorithms27–29 mayimprove the applicability of EEG to drug development.

Functional Neuroimaging

Neuroimaging techniques, which may be dividedinto functional and structural methods, provide a num-ber of potentially useful PD biomarkers. Functional

techniques are more useful for drug development; someprovide nonspecific measures, whereas others can beused to quantify effects on specific molecular targets.PET can measure a variety of physiologic functions, in-cluding regional cerebral blood flow, oxygen extraction,glucose metabolism, enzyme activity, protein synthesis,DNA replication, and cell growth.30 Single photon emis-sion computed tomography (SPECT) can be a cost-ef-fective alternative to PET, but its applications are morelimited.

A more recent technique is functional magnetic res-onance imaging (fMRI). The magnetic properties of he-moglobin vary according to whether or not it is oxy-genated.31 The most common method of fMRI takesadvantage of this difference in magnetic properties toobtain a blood oxygenation level-dependent (BOLD)signal,32 which obviates the need for a radiolabeledtracer or a special contrast agent. Applications of fMRIare expanding, and include human PD studies.33–39 Co-registration of simultaneously acquired structural MRIdata enhances spatial resolution. Compared with thetechniques that rely on radiolabeled tracers, fMRI mea-surements may be acquired much more frequentlywithin subjects; however, fMRI has yet to be exten-sively validated for assessing drug effects.

Neuroimaging Occupancy Studies

In addition to being cornerstones of functional neu-roimaging methods, PET and SPECT scanning provide ameans to measure dose versus target occupancy curvesof drug-binding to receptors, transporters, and othercellular targets.40 The capacity to visualize drug/targetinteractions has been most clearly demonstrated forantipsychotics. There is a clear relationship between do-pamine receptor affinity and the clinical dose of anti-psychotics.41 In the 1980s, radioligands were first usedto calculate dose versus receptor occupancy in hu-mans,42 which allowed bridging of receptor occupancyto clinical response. It is now accepted that for mostantipsychotics, approximately 60%–70% dopamine2

(D2) receptor occupancy is optimal for clinical re-sponse, whereas more than 80% binding may lead tosignificant extrapyramidal side effects.43,44 The rela-tively low binding affinity of clozapine for D2 receptorsled to other receptor hypotheses, such as that of antag-onist activity at the serotonin-2A (5-HT2A) and dopa-mine-1 (D1) receptors. At doses that cause optimal D2

receptor occupancy, atypical antipsychotics generally

Ahmed et al.


show even greater binding to 5-HT2A receptors.44 Thesefindings have influenced the clinical development ofnewer antipsychotics45–50 and provided theoreticalbases for dosing older ones.51–55

D1 antagonists were hotly pursued as antipsychoticagents in the 1990s. For example, SCH39166 showedgood results in preclinical models,56 and doses that oc-cupied greater than 70% of D1 receptors were deter-mined.57 However, efficacy in schizophrenia was notdemonstrated at these doses.57 This set of studies pro-vided a clear negative result of D1 antagonism becauseat doses that achieved high receptor binding, clinicalefficacy was not seen.58

Unambiguous negative results are important, be-cause inadequately tested hypotheses can persist formany years. An example of this is the use of serotonin-1A (5-HT1A) antagonists for adjunctive treatment of de-pressive disorders. Pindolol, a partial 5-HT1A antagonist,has yielded mixed results in depression clinical tri-als.59–64 Only recently did receptor occupancy datashow that doses used in most of these trials were notsufficient to produce adequate clinical responses.65,66

Laboratory-Based PD Measures

Many blood-, urine-, saliva-, and CSF-based analyteshave served as biomarkers in psychopharmacology. Forexample, drug-related changes in CSF concentrationsof 5-hydroxyindoleacetic acid (5-HIAA), 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), and homovanil-lic acid (HVA) have been studied for three decades. Earlywork involved measuring changes in these markers afteradministration of antidepressants67–70 and antipsychot-ics.71–73 These biochemical measures have not foundwide applications in clinical settings, but are often use-ful during drug development, particularly in bridginganimal and human studies.

SURROGATES

A surrogate is a type of biomarker that has been vali-dated as a substitute for a clinical outcome measure.Clinical outcome measures in psychiatry provide sev-eral challenges for drug developers. Often, they are con-structed from rating scales, which are based on psycho-metric, rather than pathophysiologic, principles.Placebo response rates are high for many indications(particularly mood and anxiety disorders). Durations of

several weeks or longer are usually necessary to detectresponses. To overcome these hurdles, surrogate mea-sures can be applied. Uniform criteria for validation ofsurrogates have not been agreed upon, but includegood test characteristics (sensitivity, specificity, and pre-dictive values) and an unambiguous relationship to clini-cal outcomes.74 Demonstration of causal connectionsbetween surrogate markers and clinical outcome mea-sures is an even higher standard that has been pro-posed.75

Well-known surrogate biomarkers such as highblood pressure and elevated cholesterol (for coronaryartery disease), cell counts (for HIV-related illness), andblood glucose (for diabetes mellitus) have an acceptedrelationship to clinical outcomes. For psychiatric indi-cations, such validated surrogates do not exist yet. How-ever, to facilitate internal decision-making, pharmaceu-tical companies use surrogates for a variety ofconditions. Monoamine metabolites have been investi-gated as markers for diagnosis and prognosis of mood,anxiety, and psychotic disorders. The relationship be-tween D2 receptor occupancy and clinical efficacy iswell established. Similarities between the expression ofcertain neurotransmitter receptors on neurons and onplatelets have allowed the use of platelets as peripheralmodels of central neurotransmission, particularly forthe serotonergic and noradrenergic systems.76 More re-cently, platelet markers of beta-amyloid processing haveattracted attention.77,78 Measures of the hypothalamic–pituitary–adrenal and hypothalamic–thyroid axes havebeen extensively explored in a variety of psychiatricconditions, particularly mood disorders.79,80

A special type of efficacy surrogate is sometimesreferred to as a “challenge paradigm.” Challenge para-digms consist of clinical trials that include interventionsthat mimic illnesses. Challenge paradigms now exist forthe major classes of psychiatric disorders. Some exam-ples are panic provocation by carbon dioxide or lac-tate,81,82 serotonin and catecholamine depletion for thestudy of mood disorders,83,84 ketamine and phencycli-dine induction of psychosis,85,86 and the pharmacolog-ical induction of cognitive deficits.87,88 However, thepredictive value of these models is unclear, and ethicalconsiderations limit their widespread use, particularlywhen they involve patients, rather than healthy sub-jects.89,90 Drug developers need to carefully considerthe rationale for specific challenge studies in their in-vestigational plans. When these studies are conducted,



subjects must be fully informed and their safety main-tained throughout the investigation.

Safety

Biomarkers have a long tradition as surrogates ofsafety and are routinely applied in all clinical develop-ment programs. In this context, the most common bio-markers are physiologic parameters (such as heart rate,blood pressure, respiration, and temperature), electro-cardiograms, and laboratory-based measures (such aschemistry panels and blood counts). For developmentof compounds that influence the dopaminergic system,prolactin is an important safety surrogate because ele-vations in prolactin have been linked to problems withmenstruation, sexual function, breast engorgement, lossof bone mineral density, and behavior.91 EEG abnormal-ities are used as surrogates for epileptic potential, par-ticularly for NCEs that have caused seizures in animalsduring preclinical testing. Although measures of cogni-tion are used as clinical or surrogate endpoints for effi-cacy, for many medications these serve as importantendpoints to assess tolerability. Related measures rele-vant to daily functioning, such as driving simulators andspecialized cognitive instruments, may be used in thetesting of drugs that are associated with cognitive im-pairment or sedation.

Surrogate markers are essential to drug develop-ment and will continue to have an expanding role. Reg-ulatory-authority acceptance of surrogate efficacy mark-ers is highest for approval of generic versions ofpreviously approved drugs and for accelerated approv-als of NCEs in indications of greatest medical need.74,92

BIOMARKERS FORALZHEIMER DISEASE (AD)

Biomarkers can be used as aids to confirm the clinicaldiagnosis of AD and as measures of disease activity. Pres-ence of the apolipoprotein-E �4 allele and mutations ofthe presenilin-1, presenilin-2, and amyloid precursorprotein genes have been shown to predict the devel-opment of AD.93 For NCEs that are being evaluated fordisease-modifying properties, enrollment of patientswith susceptible genotypes can increase signal-detec-tion in clinical trials.

Acetylcholinesterase activity in the CSF after admin-istration of cholinesterase inhibitors has been used as a

PD marker in clinical trials.94,95 There has also been in-terest in the assessment of tau- and beta-amyloid (par-ticularly the 42-unit form) proteins in the CSF.96 Thesemeasures are being incorporated in clinical trials as PDmeasures,97,98 and cross-sectional99–102 and longitudi-nal103–106 normative values are becoming available,which will encourage greater use of these biomarkers.

There is also a role for neuroimaging methods asbiomarkers in AD. Structural MRI can be used to aiddiagnosis and staging, and it has been suggested that ifthe primary outcome measure in clinical trials is definedusing this technique, fewer subjects may be required todetect drug effects than with conventional measures.107

However, the practical application of this suggestion re-quires further refinements in technique and standardi-zation. Functional neuroimaging with PET may helpidentify individuals who are susceptible to AD, espe-cially when evaluations are performed longitudinally orinclude cognitive activation tasks.108 Preliminary find-ings indicate that MRS and fMRI and may also be usedin a similar way.109,110 As more longitudinal data are col-lected, applications of these techniques as primary orsecondary endpoints in clinical trials are likely to grow.The recent direct visualization of beta-amyloid plaquesand neurofibrillary tangles in living patients by use oftracer techniques has considerable potential usefulnessfor drug trials because this technique may allow theeffect of interventions to be monitored in a very directway,111 complementing and perhaps supplanting clini-cal observations. Indeed, Colburn has asked the pro-vocative question “What makes clinical endpoints otherthan complete cure and/or prolongation of life clinicalendpoints without flaws?”92 For AD, this qualification isespecially relevant because there is some consensusnow that pathological processes begin years before sig-nificant clinical symptoms are evident. These processesmay not be evident using traditional clinical evaluations,but may be diagnosable using newer biomarker-basedtechniques.

CONCLUSION

Biomarkers have always been important to drug devel-opment. Recently, more attention has been paid to ex-panding their role in decision-making, dose selection,and for speeding up the development process. Table 1lists advantages and disadvantages of the various meth-

Ahmed et al.


TABLE 1. Advantages and limitations of selected biomarker technologies

Advantages Limitations

CSFa,b Measurement of drug PK in central compartmentSeveral surrogate markers availablePossible to combine PK and PD measures in one protocol

InvasiveSensitive assay required

EEGb Unequivocal positive results provide evidence of CNS effects ofintervention

Convenient for repeated measures within subjects

Observed effects generally not easily linked to specificmechanism of action

Prone to artifacts and not fully standardizedMRI

MRSa,b

fMRIb

sMRIb

Accurate measurement of pharmacological doses of certain drugsStructural and functional modalities can be combined to enhance

overall signal detection

Motion artifacts in agitated patientsMore validation necessary for surrogate marker useExpensive

PET/SPECTTracer

techniquesa

Functionalmethodsb

Occupancystudiesb

Highly sensitive detection of drugs that can be radiolabeledDirect evidence of effect of drug at site of action

Exposure to ionizing radiationTracers not available for every applicationExpensive

Note: PK�pharmacokinetic(s); PD�pharmacodynamic(s); CSF�cerebrospinal fluid; EEG�electroencephalography; CNS�central nervoussystem; MRI�magnetic resonance imaging; MRS�magnetic resonance spectroscopy; fMRI�functional MRI; sMRI�structural MRI;PET�positron emission tomography; SPECT�single photon emission computed tomography.

aModality can demonstrate central penetration of a drug.bMethod can show central PD effect of a drug and/or serve as a surrogate marker in selected situations.

ods. There are many more applications of biomarkersin drug development than have been covered in thisbrief review. When combining biomarkers in the devel-opment of a particular NCE, it is sometimes desirableto incorporate approaches that are not closely linked.This reduces the chances that consistent results fromtwo separate biomarker methods are unrelated to thedesired clinical effect. Another important reason for us-ing multiple biomarkers in clinical plans is that dose–response relationships often vary among biomarkers.Obtaining multiple dose–response curves makes it pos-sible to bracket doses and reduces the chances of beingcaught outside the clinically efficacious range.

Many newer techniques are becoming available.This field will progress rapidly because in many ways itis central to clinical psychopharmacology, and it rep-

resents the practical amalgamation of several related dis-ciplines that are themselves evolving rapidly, such asbrain-based pathophysiological underpinnings of men-tal disorders, molecular mechanisms of drug response,genomic and proteomic bases for individual differences,and bioinformatics. The payback for investments in bio-markers will not be restricted to academic institutionsand pharmaceutical companies. Ultimately, patients andhealthcare providers will benefit tremendously as betteragents become available sooner to treat the most dev-astating illnesses. Public safety will be enhanced as bio-markers make it possible to expose fewer research vol-unteers to new drugs, particularly during the earlystages of development.

We are grateful to Dr. David DeBrota and Ms. Mel-anie Wadman for their review of this manuscript.

References

1. Mahmood I: Allometric issues in drug development. J Pharm Sci1999; 88:1101–1106

2. Downing GJ: Introduction, in Biomarkers and Surrogate End-points: Clinical Research and Applications. Proceedings of theNIH–FDA Conference (April 15–16, 2000, Bethesda, MD). Ed-ited by Downing GJ. Amsterdam, Netherlands, Elsevier, 2000,pp 1–12

3. Hammarlund-Udenaes M: The use of microdialysis in CNS drugdelivery studies: pharmacokinetic perspectives and results withanalgesics and antiepileptics. Advances in Drug Delivery Review2000; 45:283–294

4. Davson H, Segal MB: Physiology of the Cerebrospinal Fluid andBlood–Brain Barriers. Boca Raton, FL, CRC Press, 1996

5. Kornhuber J, Quack G: Cerebrospinal fluid and serum concen-trations of the N-methyl-D-aspartate (NMDA) receptor-antagonistmemantine in man. Neurosci Lett 1995; 195:137–139

6. Cutler NR, Sramek JJ: Exploratory studies: implications for drugdevelopment in Alzheimer’s disease. Rev Neurol (Paris) 1998;154(suppl2):S131–S136

7. Strauss WL, Layton ME, Hayes CE, et al: 19F magnetic resonancespectroscopy investigation in vivo of acute and steady-state brainfluvoxamine levels in obsessive-compulsive disorder. Am J Psy-chiatry 1997; 154:516–522

8. Renshaw PF, Guimaraes AR, Fava M, et al: Accumulation of flu-oxetine and norfluoxetine in human brain during therapeuticadministration. Am J Psychiatry 1992; 149:1592–1594



9. Komoroski RA, Newton JEO, Cardwell D, et al: In vivo 19-F spinrelaxation and localized spectroscopy of fluoxetine in humanbrain. Magn Reson Med 1994; 31:204–211

10. Christensen JD, Yurgelun-Todd DA, Babb SM, et al: Measurementof human brain dexfenfluramine concentration by 19F magneticresonance spectroscopy. Brain Res 1999; 834:1–5

11. Christian BT, Livni E, Babich JW, et al: Evaluation of cerebral phar-macokinetics of the novel antidepressant drug BMS-181101, bypositron emission tomography. J Pharmacol Exp Ther 1996;279:325–331

12. Bergstrom M, Cass LM, Valind S, et al: Deposition and dispositionof [11C]zanamivir following administration as an intranasalspray: evaluation with positron emission tomography. Clin Phar-macokinet 1999; 36(suppl1):33–39

13. Salazar DE, Fischman AJ: Central nervous system pharmacoki-netics of psychiatric drugs. J Clin Pharmacol 1999; suppl:10S–12S

14. Saletu B, Grunberger J: Drug profiling by computed electroen-cephalography and brain maps, with special consideration of ser-traline and its psychometric effects. J Clin Psychiatry 1988;49(suppl):59–71

15. Itil TM, Menon GN, Itil KZ: Computer EEG drug database in psy-chopharmacology and in drug development. PsychopharmacolBull 1982; 18:165–172

16. Fink M: EEG and human psychopharmacology. Annu Rev Phar-macol Toxicol 1969; 9:241–258

17. Holschneider DP, Leuchter AF: Clinical neurophysiology usingelectroencephalography in geriatric psychiatry: neurobiologicimplications and clinical utility. J Geriatr Psychiatry Neurol 1999;12:150–164

18. Itil TM, Simeon J: Proceedings: Computerized EEG in the predic-tion of outcome of drug treatment in hyperactive childhood be-havior disorders (abstract). Psychopharmacol Bull 1974; 10:36

19. Dietrich B: Polysomnography in drug development. J Clin Phar-macol 1997; 37(suppl1):70S–78S

20. Dumermuth G, Ferber G, Herrmann WM, et al: InternationalPharmaco-EEG Group (IPEG): Committee on Standardization ofData Acquisition and Analysis in Pharmaco-EEG Investigations.Neuropsychobiology 1987; 17:213–218

21. Ferber G, Abt K, Fichte K, et al: IPEG Guideline on StatisticalDesign and Analysis for Pharmacodynamic Trials. InternationalPharmaco-EEG Group. Neuropsychobiology 1999; 39:92–100

22. Nuwer M: Assessment of Digital EEG, Quantitative EEG, and EEGBrain Mapping: Report of the American Academy of Neurologyand the American Clinical Neurophysiology Society. Neurology1997; 49:277–292

23. Stille G, Herrmann WM: Guidelines for pharmaco-EEG studies inman, in Electroencephalography in Drug Research. Edited byHerrmann WM. New York, Gustav Fischer, 1982, pp XII–XIX

24. Versavel M, Leonard JP, Herrmann WM: Standard operating pro-cedure for the registration and computer-supported evaluationof pharmaco-EEG data. “EEG in Phase I” of the Collegium Inter-nationale Psychiatriae Scalarum (CIPS). Neuropsychobiology1995; 32:166–170

25. Reite M, Teale P, Rojas DC: Magnetoencephalography: applica-tions in psychiatry. Biol Psychiatry 1999; 45:1553–1563

26. Hari R, Forss N: Magnetoencephalography in the study of humansomatosensory cortical processing. Philos Trans R Soc Lond BBiol Sci 1999; 354:1145–1154

27. Anderer P, Saletu B, Pascual-Marqui RD: Effect of the 5-HT1A par-tial agonist buspirone on regional brain electrical activity in man:a functional neuroimaging study using low-resolution electro-

magnetic tomography (LORETA). Psychiatry Res 2000; 100:81–96

28. Pascual-Marqui RD, Michel CM, Lehmann D: Low-resolution elec-tromagnetic tomography: a new method for localizing electricalactivity in the brain. Int J Psychophysiol 1994; 18:49–65

29. Leuchter AF, Cook IA, Mena I, et al: Assessment of cerebral per-fusion using quantitative EEG cordance. Psychiatry Res 1994;55:141–152

30. Cherry SR, Phelps ME: Imaging brain function with positronemission tomography, in Brain Mapping: The Methods. Edited byToga AW, Mazziota JC. San Diego, CA, Academic Press, 1996, pp191–221

31. Pauling L, Coryell CD: The magnetic properties and structure ofhemoglobin, oxyhemoglobin, and carbonmonoxyhemoglobin.Proc Natl Acad Sci U S A 1936; 22:210–216

32. Ogawa S, Lee TM, Kay AR, et al: Brain magnetic resonance im-aging with contrast dependent on blood oxygenation. Proc NatlAcad Sci U S A 1990; 87:9868–9872

33. Vaidya CJ, Austin G, Kirkorian G, et al: Selective effects of meth-ylphenidate in attention-deficit hyperactivity disorder: a func-tional magnetic resonance study. Proc Natl Acad Sci U S A 1998;95:14494–14499

34. Streeter CC, Ciraulo DA, Harris GJ, et al: Functional magneticresonance imaging of alprazolam-induced changes in humanswith familial alcoholism. Psychiatry Res 1998; 82:69–82

35. Stein EA, Pankiewicz J, Harsch HH, et al: Nicotine-induced limbiccortical activation in the human brain: a functional MRI study.Am J Psychiatry 1998; 155:1009–1015

36. Risch SC, McGurk S, Horner MD, et al: A double-blind, placebo-controlled case study of the use of donepezil to improve cogni-tion in a schizoaffective disorder patient: functional MRI corre-lates. Neurocase 2001; 7:105–110

37. Kalin NH, Davidson RJ, Irwin W, et al: Functional magnetic res-onance imaging studies of emotional processing in normal anddepressed patients: effects of venlafaxine. J Clin Psychiatry 1997;58(suppl16):32–39

38. Honey GD, Bullmore ET, Soni W, et al: Differences in frontal cor-tical activation by a working memory task after substitution ofrisperidone for typical antipsychotic drugs in patients withschizophrenia. Proc Natl Acad Sci U S A 1999; 96:13432–13437

39. Bloom AS, Hoffmann RG, Fuller SA, et al: Determination of drug-induced changes in functional MRI signal using a pharmacoki-netic model. Hum Brain Mapp 1999; 8:235–244

40. Halldin C, Gulyas B, Langer O, et al: Brain radioligands: state ofthe art and new trends. Q J Nucl Med 2001; 45:139–152

41. Seeman P, Lee T, Chau-Wong M, et al: Antipsychotic drug dosesand neuroleptic/dopamine receptors. Nature 1976; 261:717–719

42. Farde L, Wiesel FA, Halldin C, et al: Central D2-dopamine receptoroccupancy in schizophrenic patients treated with antipsychoticdrugs. Arch Gen Psychiatry 1988; 45:71–76

43. Farde L, Nordstrom AL, Wiesel FA, et al: Positron emission to-mographic analysis of central D1 and D2 dopamine receptor oc-cupancy in patients treated with classical neuroleptics and clo-zapine: relation to extrapyramidal side effects. Arch GenPsychiatry 1992; 49:538–544

44. Kapur S, Zipursky RB, Remington G: Clinical and theoretical im-plications of 5-HT2 and D2 receptor occupancy of clozapine, ris-peridone, and olanzapine in schizophrenia. Am J Psychiatry1999; 156:286–293

45. Offord SJ, Wong DF, Nyberg S: The role of positron emissiontomography in the drug development of M100907, a putativeantipsychotic with a novel mechanism of action. J Clin Pharma-col 1999; suppl:17S–24S

Ahmed et al.


46. Bench CJ, Lammertsma AA, Dolan RJ, et al: Dose-dependent oc-cupancy of central dopamine D2 receptors by the novel neuro-leptic CP-88,059-01: a study using positron emission tomographyand 11C-raclopride. Psychopharmacology (Berlin, Germany)1993; 112:308–314

47. Fischman AJ, Bonab AA, Babich JW, et al: Positron emission to-mographic analysis of central 5-hydroxytryptamine2 receptor oc-cupancy in healthy volunteers treated with the novel antipsy-chotic agent ziprasidone. J Pharmacol Exp Ther 1996; 279:939–947

48. Jones HM, Travis MJ, Mulligan R, et al: In-vivo 5-HT2A receptorblockade by quetiapine: an R91150 single photon emission to-mography study. Psychopharmacology (Berlin, Germany) 2001;157:60–66

49. Kufferle B, Tauscher J, Asenbaum S, et al: IBZM SPECT imagingof striatal dopamine2 receptors in psychotic patients treated withthe novel antipsychotic substance quetiapine in comparison toclozapine and haloperidol. Psychopharmacology (Berlin, Ger-many) 1997; 133:323–328

50. Gefvert O, Lundberg T, Wieselgren IM, et al: D2 and 5HT2A re-ceptor occupancy of different doses of quetiapine in schizophre-nia: a PET study. Eur Neuropsychopharmacol 2001; 11:105–110

51. Remington G, Kapur S, Zipursky R: The relationship betweenrisperidone plasma levels and dopamine D2 occupancy: a posi-tron emission tomographic study. J Clin Psychopharmacol 1998;18:82–83

52. Kapur S, Zipursky RB, Remington G, et al: 5-HT2 and D2 receptoroccupancy of olanzapine in schizophrenia: a PET investigation.Am J Psychiatry 1998; 155:921–928

53. Nyberg S, Eriksson B, Oxenstierna G, et al: Suggested minimaleffective dose of risperidone based on PET-measured D2 and 5-HT2A receptor occupancy in schizophrenic patients. Am J Psy-chiatry 1999; 156:869–875

54. Meisenzahl EM, Dresel S, Frodl T, et al: D2 receptor occupancyunder recommended and high doses of olanzapine: an iodine-123-iodobenzamide SPECT study. J Psychopharmacol 2000;14:364–370

55. de Haan L, Lavalaye J, Linszen D, et al: Subjective experience andstriatal dopamine D2 receptor occupancy in patients with schizo-phrenia stabilized by olanzapine or risperidone. Am J Psychiatry2000; 157:1019–1020

56. Chipkin RE, Iorio LC, Coffin VL, et al: Pharmacological profile ofSCH39166: a dopamine D1 selective benzonaphthazepine withpotential antipsychotic activity. J Pharmacol Exp Ther 1988;247:1093–1102

57. Karlsson P, Sedvall G, Halldin C, et al: Evaluation of SCH 39166as PET ligand for central D1 dopamine receptor binding and oc-cupancy in man. Psychopharmacology (Berlin, Germany) 1995;121:300–308

58. Farde L: The advantage of using positron emission tomographyin drug research. Trends Neurosci 1996; 19:211–214

59. Perez V, Soler J, Puigdemont D, et al: A double-blind, randomized,placebo-controlled trial of pindolol augmentation in depressivepatients resistant to serotonin reuptake inhibitors. Arch Gen Psy-chiatry 1999; 56:375–379

60. Zanardi R, Franchini L, Gasperini M, et al: Faster onset of actionof fluvoxamine in combination with pindolol in the treatment ofdelusional depression: a controlled study. J Clin Psychopharma-col 1998; 18:441–446

61. Tome MB, Isaac MT, Harte R, et al: Paroxetine and pindolol: arandomized trial of serotonergic autoreceptor blockade in thereduction of antidepressant latency. Int Clin Psychopharmacol1997; 12:81–89

62. Perez V, Gilaberte I, Faries D, et al: Randomised, double-blind,placebo-controlled trial of pindolol in combination with fluoxe-tine antidepressant treatment. Lancet 1997; 349:1594–1597

63. Moreno FA, Gelenberg AJ, Bachar K, et al: Pindolol augmentationof treatment-resistant depressed patients. J Clin Psychiatry 1997;58:437–439

64. Berman RM, Anand A, Cappiello A, et al: The use of pindololwith fluoxetine in the treatment of major depression: final resultsfrom a double-blind, placebo-controlled trial. Biol Psychiatry1999; 45:1170–1177

65. Martinez D, Broft A, Laruelle M: Pindolol augmentation of anti-depressant treatment: recent contributions from brain imagingstudies. Biol Psychiatry 2000; 48:844–853

66. Rabiner EA, Bhagwagar Z, Gunn RN, et al: Pindolol augmentationof selective serotonin reuptake inhibitors: PET evidence that thedose used in clinical trials is too low. Am J Psychiatry 2001;158:2080–2082

67. Asberg M, Bertilsson L, Tuck D, et al: Indoleamine metabolites inthe cerebrospinal fluid of depressed patients before and duringtreatment with nortriptyline. Clin Pharmacol Ther 1973; 14:277–286

68. Muscettola G, Goodwin FK, Potter WZ, et al: Imipramine anddesipramine in plasma and spinal fluid: relationship to clinicalresponse and serotonin metabolism. Arch Gen Psychiatry 1978;35:621–625

69. Martensson B, Nyberg S, Toresson G, et al: Fluoxetine treatmentof depression: clinical effects, drug concentrations, and mono-amine metabolites and N-terminally extended substance P in ce-rebrospinal fluid. Acta Psychiatr Scand 1989; 79:586–596

70. Potter WZ, Scheinin M, Golden RN, et al: Selective antidepres-sants and cerebrospinal fluid. lack of specificity on norepineph-rine and serotonin metabolites. Arch Gen Psychiatry 1985;42:1171–1177

71. Harnryd C, Bjerkenstedt L, Gullberg B, et al: Time course foreffects of sulpiride and chlorpromazine on monoamine metabo-lite and prolactin levels in cerebrospinal fluid from schizophrenicpatients. Acta Psychiatr Scand (suppl) 1984; 311:75–92

72. Wode-Helgodt B, Fyro B, Gullberg B, et al: Effect of chlorprom-azine treatment on monoamine metabolite levels in cerebrospi-nal fluid of psychotic patients. Acta Psychiatr Scand 1977;56:129–142

73. Sedvall G, Fyro B, Nyback H, et al: Mass fragmentometric deter-mination of homovanillic acid in lumbar cerebrospinal fluid ofschizophrenic patients during treatment with antipsychoticdrugs. J Psychiatr Res 1974; 11:75–80

74. Lesko LJ, Atkinson AJ Jr: Use of biomarkers and surrogate end-points in drug development and regulatory decision-making: cri-teria, validation, strategies. Annu Rev Pharmacol Toxicol 2001;41:347–366

75. Fleming TR, DeMets DL: Surrogate endpoints in clinical trials:are we being misled? Ann Intern Med 1996; 125:605–613

76. Sneddon JM: Blood platelets as a model for monoamine-contain-ing neurones. Prog Neurobiol 1973; 1:151–198

77. Padovani A, Borroni B, Colciaghi F, et al: Platelet amyloid precur-sor protein forms in AD: a peripheral diagnostic tool and a phar-macological target. Mech Ageing Dev 2001; 122:1997–2004

78. Davies TA, Long HJ, Sgro K, et al: Activated Alzheimer diseaseplatelets retain more beta-amyloid precursor protein. NeurobiolAging 1997; 18:147–153

79. Holsboer F: The corticosteroid receptor hypothesis of depres-sion. Neuropsychopharmacology 2000; 23:477–501

80. Joffe RT, Sokolov ST: Thyroid hormones, the brain, and affectivedisorders. Crit Rev Neurobiol 1994; 8:45–63



81. Pitts FN Jr, McClure JN Jr: Lactate metabolism in anxiety neurosis.N Engl J Med 1967; 277:1329–1336

82. Griez E, Schruers K: Experimental pathophysiology of panic. JPsychosom Res 1998; 45:493–503

83. Miller HL, Delgado PL, Salomon RM, et al: Clinical and biochem-ical effects of catecholamine depletion on antidepressant-in-duced remission of depression. Arch Gen Psychiatry 1996; 53:117–128

84. Salomon RM, Miller HL, Delgado PL, et al: The use of tryptophandepletion to evaluate central serotonin function in depressionand other neuropsychiatric disorders. Int Clin Psychopharmacol1993; 8(suppl2):41–46

85. Lahti AC, Weiler MA, Michaelidis T, et al: Effects of ketamine innormal and schizophrenic volunteers. Neuropsychopharma-cology 2001; 25:455–467

86. Javitt DC, Zukin SR: Recent advances in the phencyclidine modelof schizophrenia. Am J Psychiatry 1991; 148:1301–1308

87. Hall ST, Puech A, Schaffler K, et al: Early clinical testing of cog-nition enhancers: prediction of efficacy. Pharmacopsychiatry1990; 23(suppl2):57–58

88. Riedel WJ, Jolles J: Cognition enhancers in age-related cognitivedecline. Drugs Aging 1996; 8:245–274

89. Vogel-Scibilia SE: The controversy over challenge and discontin-uation studies: perspective from a consumer-psychiatrist. BiolPsychiatry 1999; 46:1021–1024

90. D’Souza DC, Berman RM, Krystal JH, et al: Symptom provocationstudies in psychiatric disorders: scientific value, risks, and future.Biol Psychiatry 1999; 46:1060–1080

91. Dickson RA, Glazer WM: Neuroleptic-induced hyperprolactine-mia. Schizophr Res 1999; 35(suppl):S75–S86

92. Colburn WA: Optimizing the use of biomarkers, surrogate end-points, and clinical endpoints for more efficient drug develop-ment. J Clin Pharmacol 2000; 40:1419–1427

93. Holmes C: Genotype and phenotype in Alzheimer’s disease. Br JPsychiatry 2002; 180:131–134

94. Kennedy JS, Polinsky RJ, Johnson B, et al: Preferential cerebro-spinal fluid acetylcholinesterase inhibition by rivastigmine in hu-mans. J Clin Psychopharmacol 1999; 19:513–521

95. Cutler NR, Polinsky RJ, Sramek JJ, et al: Dose-dependent CSF ace-tylcholinesterase inhibition by SDZ ENA 713 in Alzheimer’s dis-ease. Acta Neurol Scand 1998; 97:244–250

96. Boss MA: Diagnostic approaches to Alzheimer’s disease. BiochimBiophys Acta 2000; 1502:188–200

97. Nitsch RM, Deng M, Tennis M, et al: The selective muscarinic M1

agonist AF102B decreases levels of total A-beta in cerebrospinalfluid of patients with Alzheimer’s disease. Ann Neurol 2000;48:913–918

98. Hock C, Maddalena A, Heuser I, et al: Treatment with the selec-

tive muscarinic agonist talsaclidine decreases cerebrospinal fluidlevels of total amyloid beta-peptide in patients with Alzheimer’sdisease. Ann N Y Acad Sci 2000; 920:285–291

99. Andreasen N, Minthon L, Clarberg A, et al: Sensitivity, specificity,and stability of CSF-tau in AD in a community-based patient sam-ple. Neurology 1999; 53:1488–1494

100. Galasko D, Chang L, Motter R, et al: High cerebrospinal fluid tauand low amyloid beta-42 levels in the clinical diagnosis of Alz-heimer disease and relation to apolipoprotein E genotype. ArchNeurol 1998; 55:937–945

101. Sjogren M, Vanderstichele H, Agren H, et al: Tau and A-beta-42in cerebrospinal fluid from healthy adults 21–93 years of age:establishment of reference values. Clin Chem 2001; 47:1776–1781

102. Shoji M, Matsubara E, Kanai M, et al: Combination assay of CSFtau, A-beta 1-40 and A-beta 1-42(43) as a biochemical marker ofAlzheimer’s disease. J Neurol Sci 1998; 158:134–140

103. Andreasen N, Hesse C, Davidsson P, et al: Cerebrospinal fluidbeta-amyloid (1-42) in Alzheimer disease: differences betweenearly- and late-onset Alzheimer disease and stability during thecourse of disease. Arch Neurol 1999; 56:673–680

104. Kanai M, Matsubara E, Isoe K, et al: Longitudinal study of cere-brospinal fluid levels of tau, A-beta, 1-40, and A-beta-1-42(43) inAlzheimer’s disease: a study in Japan. Ann Neurol 1998; 44:17– 26

105. Mecocci P, Cherubini A, Bregnocchi M, et al: Tau protein in ce-rebrospinal fluid: a new diagnostic and prognostic marker in Alz-heimer disease? Alzheimer Dis Assoc Disord 1998; 12:211–214

106. Sunderland T, Wolozin B, Galasko D, et al: Longitudinal stabilityof CSF tau levels in Alzheimer patients. Biol Psychiatry 1999;46:750–755

107. Fox NC, Cousens S, Scahill R, et al: Using serial registered brainmagnetic resonance imaging to measure disease progression inAlzheimer disease: power calculations and estimates of samplesize to detect treatment effects. Arch Neurol 2000; 57:339–344

108. Rapoport SI: Functional brain imaging to identify affected sub-jects genetically at risk for Alzheimer’s disease. Proc Natl AcadSci U S A 2000; 97:5696–5698

109. Pfefferbaum A, Adalsteinsson E, Spielman D, et al: In-vivo brainconcentrations of N-acetyl compounds, creatine, and choline inAlzheimer disease. Arch Gen Psychiatry 1999; 56:185–192

110. Bookheimer SY, Strojwas MH, Cohen MS, et al: Patterns of brainactivation in people at risk for Alzheimer’s disease. N Engl J Med2000; 343:450–456

111. Shoghi-Jadid K, Small GW, Agdeppa ED, et al: Localization of neu-rofibrillary tangles and beta-amyloid plaques in the brains of liv-ing patients with Alzheimer disease. Am J Geriatr Psychiatry2002; 10:24–35

Documents

Biomarkers in Psychotropic Drug Development