Neutralizing RGMa with Elezanumab Promotes Cerebroprotection and Recovery in Rabbit Middle Cerebral Artery Occlusion.

Repulsive guidance molecule A (RGMa) is an inhibitor of neuronal growth and survival which is upregulated in the damaged central nervous system following acute spinal cord injury (SCI), traumatic brain injury, acute ischemic stroke (AIS), and other neuropathological conditions. Neutralization of RGMa is neuroprotective and promotes neuroplasticity in several preclinical models of neurodegeneration and injury including multiple sclerosis, AIS, and SCI. Given the limitations of current treatments for AIS due to narrow time windows to intervention (TTI), and restrictive patient selection criteria, there is significant unmet need for therapeutic agents that enable tissue survival and repair following acute ischemic damage for a broader population of stroke patients. In this preclinical study, we evaluated whether elezanumab, a human anti-RGMa monoclonal antibody, could improve neuromotor function and modulate neuroinflammatory cell activation following AIS with delayed intervention times up to 24 h using a rabbit embolic permanent middle cerebral artery occlusion model (pMCAO). In two replicate 28-day pMCAO studies, weekly intravenous infusions of elezanumab, over a range of doses and TTIs of 6 and 24 h after stroke, significantly improved neuromotor function in both pMCAO studies when first administered 6 h after stroke. All elezanumab treatment groups, including the 24 h TTI group, had significantly less neuroinflammation as assessed by microglial and astrocyte activation. The novel mechanism of action and potential for expanding TTI in human AIS make elezanumab distinct from current acute reperfusion therapies, and support evaluation in clinical trials of acute CNS damage to determine optimal dose and TTI in humans. A: Ramified/resting astrocytes and microglia in a normal, uninjured rabbit brain. B: Rabbit pMCAO brain illustrating lesion on right side of brain (red), surrounded by penumbra (pink) during acute phase post stroke, with minimal injury to left brain hemisphere. Penumbra characterized by activated astrocytes and microglia (region in crosshair within circle), with upregulation of free and bound RGMa. C: Elezanumab binds to both free and bound RGMa, preventing full activation of astrocytes and microglia. D: Elezanumab is efficacious in rabbit pMCAO with a 4 × larger TTI window vs. tPA (6 vs. 1.5 h, respectively). In human AIS, tPA is approved for a TTI of 3-4.5 h. Elezanumab is currently being evaluated in a clinical Ph2 study of AIS to determine the optimal dose and TTI (NCT04309474).

A Phase 1 and Biodistribution Study of ABT-806i, an 111In-Radiolabeled Conjugate of the Tumor-Specific Anti-EGFR Antibody ABT-806.

ABT-806 is a tumor-specific antibody targeting the epidermal growth factor receptor (EGFR). This study assessed safety, biodistribution, and pharmacokinetics of 111In-radiolabeled ABT-806 (ABT-806i) and effects of repeated doses of ABT-806 on receptor occupancy. Methods: Eligible patients had advanced tumors likely to express EGFR/EGFRvIII; adequate performance status and organ function; and measurable disease by RECIST 1.1. In cohort 1, 6 patients received a bolus administration of ABT-806i and underwent SPECT followed by whole-body planar scans. In cohort 2, 12 patients were imaged similarly as in 1 initially; thereafter, they received 3 doses of unlabeled ABT-806, before another dose of ABT-806i with associated SPECT and whole-body planar scans. At the end of both cohorts, patients who had stable or responding disease were able to enroll into an extension study (M12-326) in which they received unlabeled ABT-806 every 2 wk until disease progression, withdrawal of consent, or intolerable toxicity. Results: No toxicity related to ABT-806i infusion was observed. ABT-806i showed minimal uptake in normal tissues and cleared gradually from blood with a half-life of 6.0 ± 1.5 d. The mean effective dose of ABT-806i was 0.137 mSv/MBq for males and 0.183 mSv/MBq for females. ABT-806i tumor uptake varied and did not correlate with archived tumor EGFR expression. No change in ABT-806i uptake was observed after interval ABT-806 treatment, indicating stable EGFR expression in tumor. The patient with highest tumor uptake of ABT-806i had advanced head and neck cancer and experienced a partial response. Conclusion: ABT-806i allows for real-time imaging of EGFR conformational expression in tumors, has an acceptable radiation dosimetry, and provides important additional information about antigen expression compared with standard approaches using archival tissue. Its role to assist in patient selection for EGFR-based therapeutics and investigate treatment resistance should be further investigated.

Molecular imaging in oncology drug development.

Tremendous breakthroughs are being made in cancer drug discovery and development. However, such breakthroughs come at a high financial cost. At a time when there is increasing pressure on drug pricing, in part because of increased life expectancy, it is more important than ever to drive new therapeutics towards patients as efficiently as possible. In this review we discuss the applications of molecular imaging in oncology drug development, with a focus on its ability to enable better early decision making, to increase efficiency and thereby to lower costs.

An integrated multi-study analysis of intra-subject variability in cerebrospinal fluid amyloid-ß concentrations collected by lumbar puncture and indwelling lumbar catheter.

INTRODUCTION: Amyloid-ß (Aß) has been investigated as a diagnostic biomarker and therapeutic drug target. Recent studies found that cerebrospinal fluid (CSF) Aß fluctuates over time, including as a diurnal pattern, and increases in absolute concentration with serial collection. It is currently unknown what effect differences in CSF collection methodology have on Aß variability. In this study, we sought to determine the effect of different collection methodologies on the stability of CSF Aß concentrations over time. METHODS: Grouped analysis of CSF Aß levels from multiple industry and academic groups collected by either lumbar puncture (n=83) or indwelling lumbar catheter (n=178). Participants were either placebo or untreated subjects from clinical drug trials or observational studies. Participants had CSF collected by lumbar puncture or lumbar catheter for quantitation of Aß concentration by enzyme linked immunosorbent assay. Data from all sponsors was converted to percent of the mean for Aß40 and Aß42 for comparison. Repeated measures analysis of variance was performed to assess for factors affecting the linear rise of Aß concentrations over time. RESULTS: Analysis of studies collecting CSF via lumbar catheter revealed tremendous inter-subject variability of Aß40 and Aß42 as well as an Aß diurnal pattern in all of the sponsors' studies. In contrast, Aß concentrations from CSF samples collected at two time points by lumbar puncture showed no significant differences. Repeated measures analysis of variance found that only time and draw frequency were significantly associated with the slope of linear rise in Aß40 and Aß42 concentrations during the first 6 hours of collection. CONCLUSIONS: Based on our findings, we recommend minimizing the frequency of CSF draws in studies measuring Aß levels and keeping the frequency standardized between experimental groups. The Aß diurnal pattern was noted in all sponsors' studies and was not an artifact of study design. Averaging Aß concentrations at each time point is recommended to minimize the effect of individual variability. Indwelling lumbar catheters are an invaluable research tool for following changes in CSF Aß over 24-48 hours, but factors affecting Aß concentration such as linear rise and diurnal variation need to be accounted for in planning study designs.

Monitoring tumor response to linifanib therapy with SPECT/CT using the integrin αvß3-targeted radiotracer 99mTc-3P-RGD2.

The objective of this study was to determine the utility of (99m)Tc-3P-Arg-Gly-Asp (RGD2) single photon emission computed tomography (SPECT)/computed tomography (CT) for noninvasive monitoring of integrin αvß3-expression response to antiangiogenic treatment with linifanib. Linifanib or vehicle therapy was carried out in female athymic nu/nu mice bearing U87MG glioma (high αvß3 expression) or PC-3 prostate (low αvß3 expression) tumors at 12.5 mg/kg twice daily. The average tumor volume was 180 ± 90 mm(3) the day prior to baseline SPECT/CT. Longitudinal (99m)Tc-3P-RGD2 SPECT/CT imaging was performed at baseline (-1 day) and days 1, 4, 11, and 18. Tumors were harvested at all imaging time points for histopathological analysis with H&E and immunohistochemistry. A significant difference in tumor volumes between vehicle- and linifanib-treated groups was observed after 4 days of linifanib therapy in the U87MG model. The percent injected dose (%ID) tumor uptake of (99m)Tc-3P-RGD2 peaked in the vehicle-treated group at day 11, while the %ID/cm(3) tumor uptake decreased slowly over the whole study period. During the first 2 days of linifanib treatment, a rapid decrease in both %ID/cm(3) tumor uptake and tumor/muscle ratios of (99m)Tc-3P-RGD2 was observed, followed by a slow decrease until day 18. No decrease in tumor uptake of (99m)Tc-3P-RGD2 or tumor volume was observed for either treatment group in the PC-3 model. Changes in tumor vasculature were confirmed by histopathological H&E analysis and immunohistochemistry. Longitudinal imaging using (99m)Tc-3P-RGD2 SPECT/CT may be a useful tool for monitoring the downstream biologic effects of linifanib therapy.

Pharmacological modulation of brain activity in a preclinical model of osteoarthritis.

The earliest stages of osteoarthritis are characterized by peripheral pathology; however, during disease progression chronic pain emerges-a major symptom of osteoarthritis linked to neuroplasticity. Recent clinical imaging studies involving chronic pain patients, including osteoarthritis patients, have demonstrated that functional properties of the brain are altered, and these functional changes are correlated with subjective behavioral pain measures. Currently, preclinical osteoarthritis studies have not assessed if functional properties of supraspinal pain circuitry are altered, and if these functional properties can be modulated by pharmacological therapy either by direct or indirect action on brain systems. In the current study, functional connectivity was first assessed in order to characterize the functional neuroplasticity occurring in the rodent medial meniscus tear (MMT) model of osteoarthritis-a surgical model of osteoarthritis possessing peripheral joint trauma and a hypersensitive pain state. In addition to knee joint trauma at week 3 post-MMT surgery, we observed that supraspinal networks have increased functional connectivity relative to sham animals. Importantly, we observed that early and sustained treatment with a novel, peripherally acting broad-spectrum matrix metalloproteinase (MMP) inhibitor (MMPi) significantly attenuates knee joint trauma (cartilage degradation) as well as supraspinal functional connectivity increases in MMT animals. At week 5 post-MMT surgery, the acute pharmacodynamic effects of celecoxib (selective cyclooxygenase-2 inhibitor) on brain function were evaluated using pharmacological magnetic resonance imaging (phMRI) and functional connectivity analysis. Celecoxib was chosen as a comparator, given its clinical efficacy for alleviating pain in osteoarthritis patients and its peripheral and central pharmacological action. Relative to the vehicle condition, acute celecoxib treatment in MMT animals yielded decreased phMRI infusion responses and decreased functional connectivity, the latter observation being similar to what was detected following chronic MMPi treatment. These findings demonstrate that an assessment of brain function may provide an objective means by which to further evaluate the pathology of an osteoarthritis state as well as measure the pharmacodynamic effects of therapies with peripheral or peripheral and central pharmacological action.

Pharmacological properties and procognitive effects of ABT-288, a potent and selective histamine H3 receptor antagonist.

Blockade of the histamine H(3) receptor (H(3)R) enhances central neurotransmitter release, making it an attractive target for the treatment of cognitive disorders. Here, we present in vitro and in vivo pharmacological profiles for the H(3)R antagonist 2-[4'-((3aR,6aR)-5-methyl-hexahydro-pyrrolo[3,4-b]pyrrol-1-yl)-biphenyl-4-yl]-2H-pyridazin-3-one (ABT-288). ABT-288 is a competitive antagonist with high affinity and selectivity for human and rat H(3)Rs (K(i) = 1.9 and 8.2 nM, respectively) that enhances the release of acetylcholine and dopamine in rat prefrontal cortex. In rat behavioral tests, ABT-288 improved acquisition of a five-trial inhibitory avoidance test in rat pups (0.001-0.03 mg/kg), social recognition memory in adult rats (0.03-0.1 mg/kg), and spatial learning and reference memory in a rat water maze test (0.1-1.0 mg/kg). ABT-288 attenuated methamphetamine-induced hyperactivity in mice. In vivo rat brain H(3)R occupancy of ABT-288 was assessed in relation to rodent doses and exposure levels in behavioral tests. ABT-288 demonstrated a number of other favorable attributes, including good pharmacokinetics and oral bioavailability of 37 to 66%, with a wide central nervous system and cardiovascular safety margin. Thus, ABT-288 is a selective H(3)R antagonist with broad procognitive efficacy in rodents and excellent drug-like properties that support its advancement to the clinical area.

FDG-PET as a pharmacodynamic biomarker for early assessment of treatment response to linifanib (ABT-869) in a non-small cell lung cancer xenograft model.

Linifanib (ABT-869) is a multitargeted receptor tyrosine kinase inhibitor. This work aims to evaluate F-fluorodeoxyglucose-positron emission tomography (FDG-PET) as a pharmacodynamic (PD) biomarker for linifanib treatment utilizing the Calu-6 model of human non-small cell lung (NSCLC) cancer in SCID-beige mice. Animals received either vehicle or 12.5 mg/kg linifanib orally twice a day for the duration of the study. Imaging was performed at -1, 1, 3, and 7 days after beginning treatment (n = 12-14 per group). Linifanib inhibited tumor growth and suppressed tumor metabolic activity. Changes in tumor FDG uptake were observed as early as 1 day after beginning linifanib treatment and were sustained for the duration of the study. This study confirms that linifanib is efficacious in this xenograft model of human NSCLC and confirms FDG-PET is a potential PD biomarker strategy for linifanib therapy.

Xanomeline modulation of the blood oxygenation level-dependent signal in awake rats: development of pharmacological magnetic resonance imaging as a translatable pharmacodynamic biomarker for central activity and dose selection.

In vivo translational imaging techniques, such as positron emission tomography and single-photon emission-computed tomography, are the only ways to adequately determine that a drug engages its target. Unfortunately, there are far more experimental mechanisms being tested in the clinic than there are radioligands, impeding the use of this risk-mitigating approach in modern drug discovery and development. Pharmacological magnetic resonance imaging (phMRI) offers an approach for developing new biomarkers with the potential to determine central activity and dose selection in animals and humans. Using phMRI, we characterized the effects of xanomeline on ketamine-induced activation on blood oxygen level-dependent (BOLD) signal. In the present studies, xanomeline alone dose-dependently increased the BOLD signal across several regions of interest, including association and motor and sensory cortical regions. It is noteworthy that xanomeline dose-dependently attenuated ketamine-induced brain activation patterns, effects that were antagonized by atropine. In conclusion, the muscarinic 1/4-preferring receptor agonist xanomeline suppressed the effects of the N-methyl-D-aspartate channel blocker ketamine in a number of brain regions, including the association cortex, motor cortex, and primary sensory cortices. The region-specific brain activation observed in this ketamine challenge phMRI study may provide a method of confirming central activity and dose selection for novel antipsychotic drugs in early clinical trials for schizophrenia, if the data obtained in animals can be recapitulated in humans.

Characterization of 7- and 19-month-old Tg2576 mice using multimodal in vivo imaging: limitations as a translatable model of Alzheimer's disease.

With 90% of neuroscience clinical trials failing to see efficacy, there is a clear need for the development of disease biomarkers that can improve the ability to predict human Alzheimer's disease (AD) trial outcomes from animal studies. Several lines of evidence, including genetic susceptibility and disease studies, suggest the utility of fluorodeoxyglucose positron emission tomography (FDG-PET) as a potential biomarker with congruency between humans and animal models. For example, early in AD, patients present with decreased glucose metabolism in the entorhinal cortex and several regions of the brain associated with disease pathology and cognitive decline. While several of the commonly used AD mouse models fail to show all the hallmarks of the disease or the limbic to cortical trajectory, there has not been a systematic evaluation of imaging-derived biomarkers across animal models of AD, contrary to what has been achieved in recent years in the Alzheimer's Disease Neuroimaging Initiative (ADNI) (Miller, 2009). If animal AD models were found to mimic endpoints that correlate with the disease onset, progression, and relapse, then the identification of such markers in animal models could afford the field a translational tool to help bridge the preclinical-clinical gap. Using a combination of FDG-PET and functional magnetic resonance imaging (fMRI), we examined the Tg2576 mouse for global and regional measures of brain glucose metabolism at 7 and 19 months of age. In experiment 1 we observed that at younger ages, when some plaque burden and cognitive deficits have been reported, Tg2576 mice showed hypermetabolism as assessed with FDG-PET. This hypermetabolism decreased with age to levels similar to wild type (WT) counterparts such that the 19-month-old transgenic (Tg) mice did not differ from age matched WTs. In experiment 2, using cerebral blood volume (CBV) fMRI, we demonstrated that the hypermetabolism observed in Tg mice at 7 months could not be explained by changes in hemodynamic parameters as no differences were observed when compared with WTs. Taken together, these data identify brain hypermetabolism in Tg2576 mice which cannot be accounted for by changes in vascular compliance. Instead, the hypermetabolism may reflect a neuronal compensatory mechanism. Our data are discussed in the context of disease biomarker identification and target validation, suggesting little or no utility for translational based studies using Tg2576 mice.

Pharmacodynamic evaluation of irinotecan therapy by FDG and FLT PET/CT imaging in a colorectal cancer xenograft model.

PURPOSE: Longitudinal changes of 3'-[(18) F]fluoro-3'-deoxythymidine (FLT) and 2-deoxy-2-[(18) F]fluoro-D-glucose (FDG) in response to irinotecan therapy in an animal model of colorectal cancer were compared. PROCEDURES: SCID/CB-17 mice with HCT116 tumors were treated with 50 mg/kg irinotecan by intraperitoneal injection weekly for 3 weeks. FLT and FDG-positron emission tomography (PET) were performed at baseline, the day after each treatment, and 5 days after the first treatment. Proliferation and apoptosis were evaluated by immunohistochemistry (IHC) after day 15 of imaging. RESULTS: Irinotecan treatment resulted in a suppression of tumor growth. Tumor FLT uptake was decreased the day after each treatment but to a lesser extent 5 days after the first treatment. FDG uptake increased the day after each treatment with a continuous increase throughout the experiment. IHC analysis of phospho-H3 and Ki67 confirmed FLT-PET results, indicating a decrease in proliferation the day after the final irinotecan treatment. Increased apoptosis monitored by caspase-3 was observed after day 15 with irinotecan treatment. CONCLUSIONS: FLT-PET may be a better method than FDG-PET for assessing treatment response to irinotecan. Changes in imaging occur before changes in tumor volume.

A novel multi-targeted tyrosine kinase inhibitor, linifanib (ABT-869), produces functional and structural changes in tumor vasculature in an orthotopic rat glioma model.

Tyrosine kinase inhibitors represent a class of targeted therapy that has proven to be successful for cancer treatment. Linifanib is a novel, orally active multi-targeted receptor tyrosine kinase (RTK) inhibitor that exhibits potent antitumor and antiangiogenic activities against a broad spectrum of experimental tumors and malignancies in patients. The compound is currently being evaluated in phase 2 and 3 clinical trials. To investigate the effectiveness of linifinib against gliomas and the mechanism of drug action, we characterized treatment-induced antitumor and antiangiogenic responses to linifanib in an orthotopic rat glioma model. The effect of linifanib treatment on tumor growth was determined by tumor volume assessment using anatomical magnetic resonance imaging (MRI). Changes in tumor microvessel function were evaluated with dynamic contrast-enhanced MRI (DCE-MRI). Immunohistochemistry (IHC) was applied to excised tumor samples to examine underlying changes in vascular structures and target receptor expression. Linifanib (10 mg/kg) given twice daily inhibited tumor growth following treatment for 7 days with tumor volumes being 149 ± 30 and 66 ± 7 mm(3) for vehicle-and linifanib-treated groups, respectively. A significant reduction of 37 ± 13% in tumor perfusion and microvessel permeability (measured by K (trans)) was observed as early as 2 h after administration compared with vehicle treatment. Continuous linifanib administration further reduced K (trans) at later time points until the end of the study (7 days post-treatment). At day 7, K (trans) was reduced by 75 ± 32% for linifanib treatment compared with vehicle treatment. Significant reduction in total blood vessel density and improved vessel wall integrity were observed, and staining for target receptor expression confirmed inhibition of phospho VEGFR-2 and PDGFR-ß by linifanib treatment. These results demonstrate significant antitumor and antiangiogenic activity against gliomas by linifanib, a property that may result from the inhibition of VEGFR-2 and PDGFR-ß-mediated vascular changes. DCE-MRI measured K (trans) changes at early treatment stages may be a useful pharmacodynamic marker for linifanib activity in clinical trials, and basal K (trans) may provide predictive value for tumor progression.

PET imaging for receptor occupancy: meditations on calculation and simplification.

This invited mini-review briefly summarizes procedures and challenges of measuring receptor occupancy with positron emission tomography. Instead of describing the detailed analytic procedures of in vivo ligand-receptor imaging, the authors provide a pragmatic approach, along with personal perspectives, for conducting positron emission tomography imaging for receptor occupancy, and systematically elucidate the mathematics of receptor occupancy calculations in practical ways that can be understood with elementary algebra. The authors also share insights regarding positron emission tomography imaging for receptor occupancy to facilitate applications for the development of drugs targeting receptors in the central nervous system.

Default-mode-like network activation in awake rodents.

During wakefulness and in absence of performing tasks or sensory processing, the default-mode network (DMN), an intrinsic central nervous system (CNS) network, is in an active state. Non-human primate and human CNS imaging studies have identified the DMN in these two species. Clinical imaging studies have shown that the pattern of activity within the DMN is often modulated in various disease states (e.g., Alzheimer's, schizophrenia or chronic pain). However, whether the DMN exists in awake rodents has not been characterized. The current data provides evidence that awake rodents also possess 'DMN-like' functional connectivity, but only subsequent to habituation to what is initially a novel magnetic resonance imaging (MRI) environment as well as physical restraint. Specifically, the habituation process spanned across four separate scanning sessions (Day 2, 4, 6 and 8). At Day 8, significant (p<0.05) functional connectivity was observed amongst structures such as the anterior cingulate (seed region), retrosplenial, parietal, and hippocampal cortices. Prior to habituation (Day 2), functional connectivity was only detected (p<0.05) amongst CNS structures known to mediate anxiety (i.e., anterior cingulate (seed region), posterior hypothalamic area, amygdala and parabracial nucleus). In relating functional connectivity between cingulate-default-mode and cingulate-anxiety structures across Days 2-8, a significant inverse relationship (r = -0.65, p = 0.0004) was observed between these two functional interactions such that increased cingulate-DMN connectivity corresponded to decreased cingulate anxiety network connectivity. This investigation demonstrates that the cingulate is an important component of both the rodent DMN-like and anxiety networks.

Potentiation of analgesic efficacy but not side effects: co-administration of an α4ß2 neuronal nicotinic acetylcholine receptor agonist and its positive allosteric modulator in experimental models of pain in rats.

Positive modulation of the neuronal nicotinic acetylcholine receptor (nAChR) α4ß2 subtype by selective positive allosteric modulator NS-9283 has shown to potentiate the nAChR agonist ABT-594-induced anti-allodynic activity in preclinical neuropathic pain. To determine whether this benefit can be extended beyond neuropathic pain, the present study examined the analgesic activity and adverse effect profile of co-administered NS-9283 and ABT-594 in a variety of preclinical models in rats. The effect of the combined therapy on drug-induced brain activities was also determined using pharmacological magnetic resonance imaging. In carrageenan-induced thermal hyperalgesia, co-administration of NS-9283 (3.5 µmol/kg, i.p.) induced a 6-fold leftward shift of the dose-response of ABT-594 (ED(50)=26 vs. 160 nmol/kg, i.p.). In the paw skin incision model of post-operative pain, co-administration of NS-9283 similarly induced a 6-fold leftward shift of ABT-594 (ED(50)=26 vs. 153 nmol/kg). In monoiodo-acetate induced knee joint pain, co-administration of NS-9283 enhanced the potency of ABT-594 by 5-fold (ED(50)=1.0 vs. 4.6 nmol/kg). In pharmacological MRI, co-administration of NS-9283 was shown to lead to a leftward shift of ABT-594 dose-response for cortical activation. ABT-594 induced CNS-related adverse effects were not exacerbated in presence of an efficacious dose of NS-9283 (3.5 µmol/kg). Acute challenge of NS-9283 produced no cross sensitization in nicotine-conditioned animals. These results demonstrate that selective positive allosteric modulation at the α4ß2 nAChR potentiates nAChR agonist-induced analgesic activity across neuropathic and nociceptive preclinical pain models without potentiating ABT-594-mediated adverse effects, suggesting that selective positive modulation of α4ß2 nAChR by PAM may represent a novel analgesic approach.

ABT-869, a multitargeted receptor tyrosine kinase inhibitor, reduces tumor microvascularity and improves vascular wall integrity in preclinical tumor models.

N-[4-(3-amino-1H-indazol-4-yl)phenyl]-N1-(2-fluoro-5-methyl phenyl)-urea (ABT-869) is a novel multitargeted receptor tyrosine kinase inhibitor that demonstrates single-agent activity in preclinical studies and has undergone phase I and II clinical trials. We characterized the mechanism of action of ABT-869 by examining vascular changes after treatment (25 mg/kg per day) in HT1080 fibrosarcoma and SW620 colon carcinoma cells, using immunohistochemistry, dynamic contrast enhanced-magnetic resonance imaging (DCE-MRI), and hypoxic protein detection. We observed the inhibition of vascular endothelial growth factor receptor 2 and platelet-derived growth factor receptor ß phosphorylation in both tumors and changes in tumor vasculature. Reductions in microvessel density and diameter were observed. Vascular-wall integrity was assessed by colocalization of pericytes and basement membrane. Although both microvessel density and total number of pericytes decreased with treatment, the percentage of pericyte coverage on remaining vessels significantly increased. These data suggest the selective ablation of microvessels lacking pericyte coverage. Functional vascular measures DCE-MRI and hypoxia formation were also tested. After 2 days of treatment on the HT1080 model, vascular permeability, K(trans), was reduced by >60% and hypoxic tumor fraction was significantly decreased, which was also seen in the SW620 tumors after 4 days of treatment. Taken together, decreases in vascular permeability and changes in vascular integrity observed in these studies define the mode of action of ABT-869 and may aid in optimizing the timing of therapeutic window for combination therapies.

Paradigm shift in translational neuroimaging of CNS disorders.

During the last two decades, functional neuroimaging technology, especially functional magnetic resonance imaging (fMRI), has improved tremendously, with new attention towards resting-state functional connectivity of the brain. This development has allowed scientists to study changes in brain structure and function, and probe these two properties under conditions of evoked stimulation, disease and drug administration. In the domain of functional imaging, the identification and characterization of central nervous system (CNS) functional networks have emerged as potential biomarkers for CNS disorders in humans. Recent attempts to translate clinical neuroimaging methodology to preclinical studies have also been carried out, which offer new opportunities in translational neuroscience research. In this paper, we review recent developments in structural and functional MRI and their use to probe functional connectivity in various CNS disorders such as schizophrenia, mood disorders, Alzheimer's disease (AD) and pain.

Structural abnormalities revealed by magnetic resonance imaging in rats prenatally exposed to methylazoxymethanol acetate parallel cerebral pathology in schizophrenia.

Schizophrenia is a highly familial, neurodevelopmental disorder that is associated with several neuropsychiatric, psychological, and neuropathological features. Although pharmacological animal models of dopaminergic and glutamatergic dysfunction have helped advance our understanding of the disease biology, there is a clear need for translational models that capture the neuropathological and functional manifestations associated with the intermediate phenotype and the clinical illness. Neuroimaging of preclinical neurodevelopmental approaches such as methylazoxymethanol acetate (MAM) exposure may afford a powerful translational tool to establish endpoints with greater congruency across animals and humans. Using in vivo volumetric magnetic resonance imaging (MRI), manganese-enhanced MRI, and diffusion tensor imaging (DTI), we investigated morphological and cytoarchitectural changes of brain structures in MAM-exposed rats, a neurodevelopmental model of schizophrenia. Compared to saline-exposed controls, MAM-exposed rats showed significant enlargement of lateral and third ventricles as well as reduced hippocampal volumes, which is consistent with findings observed in schizophrenia. In addition, DTI revealed that diffusion fractional anisotropy retrieved from corpus callosum and cingulum were significantly decreased in MAM-exposed rats, suggesting that demyelination occurred in these white-matter fiber tracts. Imaging findings were confirmed by conducting histological analysis using hematoxylin and eosin and Luxol fast blue stainings. In summary, structural abnormalities resulting from a MAM environmental challenge parallel cerebral pathology observed in schizophrenia. The MAM model incorporating noninvasive imaging techniques may therefore serve as an improved translational research tool for assessing new treatments for schizophrenia.

Pharmacokinetic modeling and [¹²³]5-IA-85380 single photon emission computed tomography imaging in baboons: optimization of dosing regimen for ABT-089.

Neuronal acetylcholine nicotinic receptors (nAChRs) are targets for the development of novel treatments of brain diseases. However, adverse effects (for example, emesis or nausea) associated with high drug maximal exposures or C(max) at nAChRs often hinder the advancement of experimental compounds in clinical trials. Therefore, it is essential to explore the feasibility of maintaining exposures below a predetermined C(max) while sustaining targeted CNS effects. By use of a [¹²³I]5-IA [5-[¹²³I]iodo-3-[2(S)-azetidinylmethoxy]pyridine] displacement SPECT imaging paradigm in nonhuman primates, we compared brain nAChR binding activity elicited by either a bolus injection or by slow infusion of an identical dose of a novel neuronal nicotinic agonist, ABT-089 [2-methyl-3-(2-(S)-pyrrolidinylmethoxy)pyridine dihydrochloride], where the slow infusion scheme was derived from a two-compartment pharmacokinetic modeling designed to limit the C(max). We determined [¹²³I]5-IA displacement using doses of ABT-089 (0.04, 0.4, and 1.0 mg/kg i.v.) that encompassed efficacious drug exposures in nonhuman primates and examined the relationship between ABT-089 displacement ratios and plasma exposures. Our results indicated that calculated displacement ratios were quite similar between the two different dosing regimens despite substantial differences in C(max). In addition, displacement ratios correlated well with drug exposures calculated as the area-under-curve (AUC) of plasma concentration and varied in a dose-dependent manner, suggesting that displacement ratios are driven by the AUC of drug plasma exposure but not C(max). Our data demonstrate the feasibility of predicting plasma exposures using a two-compartment pharmacokinetic model and its potential for optimizing dosing regimens.