Description

A combined system for diagnosis and therapeutics will have other components. The term diagnosis will broadly include screening for identification of risk factors, whereas therapeutics also includes the monitoring of therapy. Prevention is added to this system because detection of predisposing factors can enable disease prevention by correction of risk factors or preemptive treatment. A key factor that will drive the integration of diagnostics and therapeutics is the availability of improved and more precise diagnostic methods that are easy to perform and are not expensive. As discovery of genes for diseases progresses, the genes may form the link between diagnosis and gene-based medicines.

Screening. It would be ideal to detect predisposition and risk factors before the development of a disease. The classical risk factors for major diseases are known but screening for genetic risk factors would be helpful in detecting specific risk factors for certain diseases. This would form the basis of preventive strategies.

The search for disease targets is revealing a variety of molecular biomarkers that can be used for molecular diagnosis, staging, and stratification of patient. Molecular diagnostics can be used for detection of disease predisposition. With increasing emphasis on preventive medicine in the future, there will be an increasing emphasis on automated genotyping and individual risk profiling. Proactive identification of risk would enable prevention and management in a logical manner.

Biomarkers. Research activity in biomarkers will facilitate the integration of diagnostics with therapeutics. Any specific molecular alteration of a cell either on DNA, RNA, or protein level can be referred to as a molecular biomarker. A biomarker is a characteristic that can be objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacological responses to a therapeutic intervention. Biomarkers may be revealed by brain imaging. Biomarkers can serve as the basis for diagnostic tests as well as therapeutic agents (13).

Prevention. This could imply early detection and prevention of progression of a degenerative disease. Correction of risk factors may either prevent the development of a disease or its complications. Preemptive treatment may be based on a correctable gene abnormality.

Combination of diagnosis and therapy. This combination is applicable to early, acute, or chronic stages of a disease. The patient may be treated by a medication determined to be safe and effective as determined by molecular diagnostics. Not only would the cause of the illness be better defined by the molecular diagnosis, the most effective specific medication for a disease in a patient can be selected.

Monitoring of therapy. Appropriate diagnostic tests can facilitate the frequent monitoring of the effects of therapy to verify the success by objective measurements, as well as to detect the failure of therapy as early as possible so that appropriate changes in treatment can be instituted. Biomarkers, particularly those that can be determined by examination of body fluids, are more convenient and suitable for monitoring the course of a disease being treated. However, imaging biomarkers have certain advantages.

Response to therapy in patients with neurologic disorders can be assessed during treatment by functional brain imaging studies. PET is the most sensitive and specific technique for imaging molecular pathways in humans. Molecular imaging provides in vivo information in contrast to the in vitro diagnostics. Moreover, it provides a direct method for the study of the effect of a drug in the human body.

Therapeutic drug monitoring combines the quantification of drug concentrations in blood, pharmacological interpretation, and treatment guidance. It involves measurements of levels of drugs in blood as a guide to therapy and to maintain optimal drug levels during the therapeutic window. This is particularly important in the case of antiepileptic drugs. Guidelines for application of therapeutic drug monitoring for neuropsychiatric agents can help clinicians enhance safety and efficacy of treatment (24).

Nanobiotechnology for combination of diagnostics and therapeutics. Nanoparticles have improved the diagnosis and can also be used as therapeutic agents, and both the functions can be combined in 1 nanoparticle complex (14). An example is experimental treatment of malignant brain tumors by polymer nanoparticles containing iron oxide nanoparticles for imaging and a photosensitizing agent for applying photodynamic therapy after localizing the tumor. Future nanoparticle-based systems aim to employ simultaneous delivery of drugs that are targeted to specific biomarkers on brain tumor surface and imaging of their delivery, but several technical and safety issues need to be resolved (20).

Combination of nanomaterials with stem cell therapy is another example of integration of diagnostics with therapeutics in treatment of various neurologic diseases such as ischemic stroke, spinal cord injury, multiple sclerosis, Parkinson disease, and Alzheimer disease. Nanoparticles not only play a role in stem cell imaging and tracking but also promote stem cell proliferation as well as differentiation in vitro or in vivo (28).

Neuromodulation. In the concept of closed loop stimulation, diagnosis is linked to therapy. Implanted devices can incorporate diagnostics to trigger or adjust treatment. Use of mobile devices for diagnosis as well as therapy in 1 closed system is also being explored. Continuous high frequency deep brain stimulation therapy for several neurologic disorders can further improve management by providing adaptive, on-demand therapy. Closed-loop deep brain stimulation based on local field potentials requires simultaneous recording and stimulating, which is problematic due to persistent stimulation artefacts that distort underlying local field potential biomarkers. A method has been proposed to provide continuous and artefact-free recording of local field potentials close to the stimulation target, and thereby facilitate the implementation of more advanced closed-loop deep brain stimulation using local field potentials as feedback (04).

Advantages of combined approach. Main advantages of the combined approach are as follows:

Limitations of integration of diagnosis and therapy. The interest of the biopharmaceutical industry is in packaging diagnostic and therapeutic materials to facilitate marketing. However, some limitations are as follows:

Clinical applications

Systems combining diagnostics and therapeutics are commercially available for the management of virus infections, such as the human immunodeficiency and hepatitis C viruses. The combination of diagnostics and therapeutics for neurologic disorders is still in development; the potential applications that indicate their components are shown in Table 1. There is an urgent need for biomarkers to diagnose neurodegenerative disorders early in their course when therapy is likely to be most effective and to monitor responses of patients to new therapies. Many components are still missing, but this outline is a starting point for clinical neurologists interested in developing an integrated system of management for these neurologic disorders. Initially, such systems will be developed in larger neurologic centers, but it is anticipated that neurologists in practice in smaller centers would be able to use these in the future.

Table 1. Potential Applications of Combination of Diagnosis and Therapy

Alzheimer disease. Alzheimer disease is a polygenic disorder. Several genes and polymorphisms are being identified, and their role as a risk factor and relation to certain forms of the disease is under investigation. Available information that may be used for screening and designing systems for combined use of diagnostics and therapeutics in this disease are as follows:

Apolipoprotein E genotype tests. These are useful for predicting response to certain drugs for Alzheimer disease. ApoE genotyping can be used for identification of responders to choline esterase inhibitors. At least 15% of the Caucasian population does not respond to choline esterase inhibitors or other noncholinergic compounds or can develop adverse reactions when receiving these drugs. ApoE genotype tests may be used as diagnostic biomarkers in clinical trials. Although genotype-specific responses of Alzheimer disease patients to a drug or combination of drugs has been demonstrated, several studies examining the role of ApoE produced conflicting results.

Apolipoprotein E as a risk factor for Alzheimer disease. Persons with 1 copy of the apolipoprotein E4 variant develop Alzheimer disease 5 to 10 years earlier than those with apolipoprotein E2 or apolipoprotein E3 variants. People with 2 copies of apolipoprotein E4 develop Alzheimer disease 10 to 20 years earlier.

Biomarkers. Biomarkers of different pathogenic steps that contribute to Alzheimer disease will also be important in assessing efficacy of new therapies. For example, F2-Isoprostanes, in vivo biomarkers of lipid peroxidation, are increased in the CSF of patients with advanced Alzheimer disease and, a decrease in their level may serve as a measure of efficacy of experimental antioxidant therapeutics. A panel of serum protein biomarkers, including alpha-2-macroglobulin, complement C1 inhibitor, complement factor H, and apolipoprotein E expression, has shown correlation with therapeutic efficacy of rosiglitazone in clinical trials as represented by a change in the Alzheimer Disease Assessment Scale-Cognitive score (01). Noninvasive neuroimaging of MRI biomarkers for Alzheimer disease may enable earlier clinical diagnosis and the monitoring of therapeutic effectiveness. Amyloid imaging by PET could be useful as an early diagnostic biomarker of Alzheimer disease for selecting patients for anti-amyloid-beta therapy.

Simufilam (PTI-125), an oral small molecule drug candidate that binds and reverses an altered conformation of the scaffolding protein filamin A found in Alzheimer disease brain is in development as a treatment for Alzheimer disease. Altered filamin A links to the α7-nicotinic acetylcholine receptor to allow Abeta42's toxic signaling through this receptor to hyperphosphorylate tau. CSF P-tau, neurofilament light chain, neurogranin, total tau, and Abeta42 are being used as biomarkers to assess the efficacy of simufilam for Alzheimer disease in a phase 2 clinical trial (27).

Several miRNAs have been identified as biomarkers of Alzheimer disease. For example, miRNA-9, miRNA-34a, miRNA-125b, miRNA-146a, and miRNA-155 are upregulated in postmortem brain tissue–derived extracellular fluid from Alzheimer disease patients. Use of serum, instead of CSF, provides satisfactory results as the data on miRNA correlate with cognitive functions and with changes in cortical integrity (19). miRNAs are also potential therapeutic targets in Alzheimer disease as some neuroprotective antiinflammatory drugs act by modulating expression of miRNAs. Current evidence suggests that miRNAs may serve as both biomarkers and therapeutic agents in Alzheimer disease (02).

Parkinson disease. Current therapeutic strategies comprise symptomatic and restorative treatment. Neuroprotective treatments are in development and would be useful in preclinical or early Parkinson disease patients. Radiotracer imaging of the dopaminergic system is a biomarker of Parkinson disease and can facilitate drug discovery for the disease. Among other tests, dopaminergic imaging may be helpful in identifying the preclinical stage of Parkinson disease to start neuroprotective approaches.

Another example of usefulness of diagnostics as an aid to management is differentiation of idiopathic Parkinson disease from drug-induced parkinsonism due to the anti-arrhythmic drug amiodarone, which is sometimes clinically difficult. Dopamine transport system imaging by FP-CIT is used, and a normal scan suggests drug-induced parkinsonism, which requires reduction or discontinuation of amiodarone, whereas an abnormal scan indicates idiopathic Parkinson disease that requires treatment (09).

Epilepsy. Several forms of epilepsy, particularly those with genetic component, would be ideal for an integrated diagnostic and therapeutic approach. Apart from screening and diagnosis, selection of antiepileptic therapy can be guided by genotyping to select the most appropriate drug for the patient with the least adverse reactions. Genotyping for polymorphisms of the cytochrome P450 enzyme CYP2C9 is useful prior to the start of the antiepileptic drug phenytoin because the gene for this enzyme is associated with markedly impaired metabolic capacity this drug. This information may be helpful for dosage adjustment based on CYP2C9 genotype to lower the risk of drug toxicity associated with raised serum concentrations of the drug in carriers. Genetic factors may be associated with resistance to antiepileptic drugs.

Use of diffusion tensor MRI to study microstructural brain matter changes makes it possible to assess the course of epilepsy and predict the outcomes of pharmacotherapy (06). Further refinements in the methods of monitoring the effects of antiepileptic drugs would facilitate their integration into the system for guiding and evaluating the therapy. The term integration is used currently in connection with surgical treatment of epilepsy. Data derived from different test modalities (ie, electroencephalography, magnetic resonance imaging, and positron emission tomography) are integrated in delineating the seizure focus in epilepsy surgery candidates. An example of combination of diagnosis and therapy is the use of preoperative noninvasive functional brain mapping for image-guided resection of brain lesions. This is supplemented by intraoperatively identified functional locations mapped by cortical stimulation.

Several closed loop systems are in development for the management of epilepsy. These link diagnostic devices, such as EEG and ECG monitors for predicting onset of a seizure, to management response, such as abortive pharmacotherapy or neurostimulation (23).

Infections of the central nervous system. This is an area where integration of all components of diagnosis and therapy can be achieved particularly for infections that are treatable. Molecular diagnostic methods are a useful adjunct to brain imaging and other routine laboratory tests. Ability to detect infections in preclinical and asymptomatic phase provides the opportunity for prophylactic measures. Treatment can be monitored for efficacy and to determine eradication of the infection if feasible.

Rapid detection of infectious agents and drug resistance by molecular diagnostics is important for proper management of infections of the nervous system as long waiting periods for reports on culture of microorganisms are not practical in making prompt decisions.

Serum uric acid levels are reduced in patients with acute CNS viral infections. Although similar findings occur in multiple sclerosis, this finding is a useful guide in management of the patients where the viral infection has been diagnosed with another test. Effective therapy of CNS viral infection significantly increases serum uric acid levels and can be used for predicting treatment outcome and prognosis (17).

Ischemic stroke due to thromboembolism. The value of screening for risk factors, as well as strategies for prevention based on these, is well recognized. Monitoring of some treatment results is also available. It is feasible to develop integrated treatments in the setting of stroke centers that can be made available to neurologists in practice. Use of a combination of plasma biomarkers may improve the diagnosis of cardioembolic stroke in the acute phase, accelerating the start of optimal secondary prevention.

Use of quantitative diagnostic methods such as EEG and brain imaging techniques as adjuncts to traditional clinical measures enable sensitivity in quantifying the abnormal muscle activity associated with post-stroke spasticity and its management (26).

Personalized therapeutic strategies based on specific diagnostic data are important for the management of stroke. Routinely used MRI or CT angiography show the obstruction of blood flow within the arterial lumen rather than the thrombus itself. Direct thrombus imaging can be used to make decision for tissue plasminogen activator-mediated thrombolysis and/or endovascular clot retrieval. Thrombus imaging can guide personalized acute stroke therapy by enabling assessment of the size and nature of the thrombus more precisely, serially monitor the therapeutic effects of thrombolysis, and detect post-treatment recurrence (16).

Brain imaging can identify viable tissue in stroke; thus, it can help in the selection of patients most likely to benefit from reperfusion (10). Imaging can show penumbra zone with reduced blood flow but preserved metabolism indicating potential of benefit by hyperbaric oxygen. Response to hyperbaric oxygen by activation of penumbra zone demonstrated by brain imaging and clinical improvement is an indication for continuation of hyperbaric oxygen therapy in stroke patients (15).

Malignant brain tumors. Monitoring of response to chemotherapy of brain tumors is useful in reduction of toxicity associated with ineffective therapy. Brain imaging before and after chemotherapy include contrast-enhanced MRI, magnetic resonance spectroscopy and fluorodeoxyglucose PET. Early response or resistance to chemotherapy is detectable by Technetium-99m single photon emission computed tomography. Proton magnetic resonance spectroscopy, by detection of reduction in the tumor choline/water signal parallel to tumor volume change, may be useful for monitoring the therapeutic effect of temozolomide. Several molecular biomarkers have been identified in diffuse gliomas that carry diagnostic and prognostic information and can predict the response to various chemotherapeutic approaches. Advanced neuroimaging techniques are needed during treatment of malignant gliomas to distinguish recurrent disease from treatment-related changes such as radiation necrosis. Certain molecular biomarkers, particularly O(6)-methylguanine-DNA methyltransferase promoter hypermethylation, are associated with response to alkylating chemotherapy and longer survival in glioblastoma multiforme patients (07).

18F-fluoro-ethyl-tyrosine (18F-FET) PET imaging can be integrated into image-guided target selection for biopsy as well as resection of pediatric brain tumors (21). It enables visualization of metabolically active tumor tissue within diffuse tumors and its differentiation from therapy-associated changes.

The SynergySeq platform computes combinations of disease-specific gene expression signatures with the Library of Integrated Network-Based Cellular Signatures to identify preclinical combinations of approved drugs for glioblastoma, which can be tested in patients for synergistic effect (25).

Hyperkinetic disorder. Genotyping shows that polymorphisms of the dopamine D4 receptor and serotonin transporter genes are genetic risk factors for hyperkinetic disorder. Psychostimulant methylphenidate is effective in reducing in only 70% of the patients. Patients with dopamine D4 receptor and serotonin receptor polymorphisms are less responsive to this treatment. Treatment decision can, therefore, be based on the results of molecular diagnostics.

Multiple sclerosis. In vitro and ex vivo RNA expression profiles of multiple sclerosis patients under interferon-beta therapy have been determined by microarrays. Nonresponders and responders to interferon-beta as assessed by longitudinal gadolinium-enhanced MRI scans and clinical disease activity differ in their ex vivo gene expression profiles. These findings will help to optimize therapy of multiple sclerosis.

A statistically significant association has been detected between glatiramer acetate response and a single nucleotide polymorphism in a T cell receptor beta variant in patients with multiple sclerosis (08). Promising future approaches to multiple sclerosis should include the integration of clinical and imaging data with pharmacogenomic and pharmacogenetic databases to develop prognostic profiles of patients, which can be used to select therapy based on genetic biomarkers. Polymorphisms in genes for ATP-binding cassette transporters are linked to the therapeutic response to mitoxantrone in multiple sclerosis (03). The probability of patients with a genetic disposition to low transporter activity responding positively to mitoxantrone is 3.5 times higher than in the group with genetically caused higher transporter activity.

The soluble isoform of the interferon-beta receptor (sIFNAR2) is a diagnostic biomarker of multiple sclerosis (MS) as its serum levels are lower in untreated multiple sclerosis patients than in healthy controls. There is a significant increase in serum levels of IFNAR2 during the first year of therapy with IFN-beta in contrast to nonsignificant changes in patients treated with glatiramer and natalizumab (22). This diagnostic information can be used for making therapeutic decisions in multiple sclerosis.

Congenital myasthenic syndromes. These syndromes consist of several clinically as well as genetically heterogeneous disorders caused by defects in neuromuscular transmission, and an accurate diagnosis is important for management. A target gene capture/next generation sequencing approach has been shown to improve the mutation detection rate to almost 100% for expanding phenotypes and genotypes of congenital myasthenic syndromes as well as for guiding more precise therapies (18).

Sleep disorders. Sleep is a complex phenomenon in which several factors are involved. Therefore, a set protocol of pharmacotherapy is not a satisfactory approach to managing sleep disorders. Polysomnography is the gold standard of sleep investigation, but brain imaging, neuroendocrine testing, DNA sequencing, and other laboratory measures can be useful for obtaining a biomarker profile to select and guide therapies that are effective while minimizing adverse effects of drugs used to modulate sleep (05).

Neurologic manifestations of systemic disorders. Management of some systemic disorders such as insulin-dependent diabetes mellitus is possible with the integrated approach. Diagnosis and therapy are linked by controlled delivery systems for insulin guided by blood glucose levels. Integration of diagnosis and therapy may be considered in the management of neurologic complications of diabetes such as diabetic neuropathy. Screening and early detection is also applicable to diabetes mellitus.