Hybrid 18F-Fluoroethyltyrosine PET and MRI with Perfusion to Distinguish Disease Progression from Treatment-Related Change in Malignant Brain Tumors: The Quest to Beat the Toughest Cases

Conventional MRI has important limitations when assessing for progression of disease (POD) versus treatment-related changes (TRC) in patients with malignant brain tumors. We describe the observed impact and pitfalls of implementing 18F-fluoroethyltyrosine (18F-FET) perfusion PET/MRI into routine clinical practice. Methods: Through expanded-access investigational new drug use of 18F-FET, hybrid 18F-FET perfusion PET/MRI was performed during clinical management of 80 patients with World Health Organization central nervous system grade 3 or 4 gliomas or brain metastases of 6 tissue origins for which the prior brain MRI results were ambiguous. The diagnostic performance with 18F-FET PET/MRI was dually evaluated within routine clinical service and for retrospective parametric evaluation. Various 18F-FET perfusion PET/MRI parameters were assessed, and patients were monitored for at least 6 mo to confirm the diagnosis using pathology, imaging, and clinical progress. Results: Hybrid 18F-FET perfusion PET/MRI had high overall accuracy (86%), sensitivity (86%), and specificity (87%) for difficult diagnostic cases for which conventional MRI accuracy was poor (66%). 18F-FET tumor-to-brain ratio static metrics were highly reliable for distinguishing POD from TRC (area under the curve, 0.90). Dynamic tumor-to-brain intercept was more accurate (85%) than SUV slope (73%) or time to peak (73%). Concordant PET/MRI findings were 89% accurate. When PET and MRI conflicted, 18F-FET PET was correct in 12 of 15 cases (80%), whereas MRI was correct in 3 of 15 cases (20%). Clinical management changed after 88% (36/41) of POD diagnoses, whereas management was maintained after 87% (34/39) of TRC diagnoses. Conclusion: Hybrid 18F-FET PET/MRI positively impacted the routine clinical care of challenging malignant brain tumor cases at a U.S. institution. The results add to a growing body of literature that 18F-FET PET complements MRI, even rescuing MRI when it fails.

Skeletal muscle metabolic responses to physical activity are muscle type specific in a rat model of chronic kidney disease

Chronic kidney disease (CKD) leads to musculoskeletal impairments that are impacted by muscle metabolism. We tested the hypothesis that 10-weeks of voluntary wheel running can improve skeletal muscle mitochondria activity and function in a rat model of CKD. Groups included (n = 12-14/group): (1) normal littermates (NL); (2) CKD, and; (3) CKD-10 weeks of voluntary wheel running (CKD-W). At 35-weeks old the following assays were performed in the soleus and extensor digitorum longus (EDL): targeted metabolomics, mitochondrial respiration, and protein expression. Amino acid-related compounds were reduced in CKD muscle and not restored by physical activity. Mitochondrial respiration in the CKD soleus was increased compared to NL, but not impacted by physical activity. The EDL respiration was not different between NL and CKD, but increased in CKD-wheel rats compared to CKD and NL groups. Our results demonstrate that the soleus may be more susceptible to CKD-induced changes of mitochondrial complex content and respiration, while in the EDL, these alterations were in response the physiological load induced by mild physical activity. Future studies should focus on therapies to improve mitochondrial function in both types of muscle to determine if such treatments can improve the ability to adapt to physical activity in CKD.

Beta Cell Imaging-From Pre-Clinical Validation to First in Man Testing

There are presently no reliable ways to quantify human pancreatic beta cell mass (BCM) in vivo, which prevents an accurate understanding of the progressive beta cell loss in diabetes or following islet transplantation. Furthermore, the lack of beta cell imaging hampers the evaluation of the impact of new drugs aiming to prevent beta cell loss or to restore BCM in diabetes. We presently discuss the potential value of BCM determination as a cornerstone for individualized therapies in diabetes, describe the presently available probes for human BCM evaluation, and discuss our approach for the discovery of novel beta cell biomarkers, based on the determination of specific splice variants present in human beta cells. This has already led to the identification of DPP6 and FXYD2ga as two promising targets for human BCM imaging, and is followed by a discussion of potential safety issues, the role for radiochemistry in the improvement of BCM imaging, and concludes with an overview of the different steps from pre-clinical validation to a first-in-man trial for novel tracers.

Combined blockade of EGFR and glutamine metabolism in preclinical models of colorectal cancer

Improving response to epidermal growth factor receptor (EGFR)-targeted therapies in patients with advanced wild-type (WT) RAS colorectal cancer (CRC) remains an unmet need. In this preclinical work, we evaluated a new therapeutic combination aimed at enhancing efficacy by targeting cancer cell metabolism in concert with EGFR. We hypothesized that combined blockade of glutamine metabolism and EGFR represents a promising treatment approach by targeting both the "fuel" and "signaling" components that these tumors need to survive. To explore this hypothesis, we combined CB-839, an inhibitor of glutaminase 1 (GLS1), the mitochondrial enzyme responsible for catalyzing conversion of glutamine to glutamate, with cetuximab, an EGFR-targeted monoclonal antibody in preclinical models of CRC. 2D and 3D in vitro assays were executed following treatment with either single agent or combination therapy. The combination of cetuximab with CB-839 resulted in reduced cell viability and demonstrated synergism in several cell lines. In vivo efficacy experiments were performed in cell-line xenograft models propagated in athymic nude mice. Tumor volumes were measured followed by immunohistochemical (IHC) analysis of proliferation (Ki67), mechanistic target of rapamycin (mTOR) signaling (pS6), and multiple mechanisms of cell death to annotate molecular determinants of response. In vivo, a significant reduction in tumor growth and reduced Ki67 and pS6 IHC staining were observed with combination therapy, which was accompanied by increased apoptosis and/or necrosis. The combination showed efficacy in cetuximab-sensitive as well as resistant models. In conclusion, this therapeutic combination represents a promising new precision medicine approach for patients with refractory metastatic WT RAS CRC.

Further exploration of an N-aryl phenoxyethoxy pyridinone-based series of mGlu3 NAMs: Challenging SAR, enantiospecific activity and in vivo efficacy

This letter describes the further optimization of a series of mGlu₃ NAMs based on an N-aryl phenoxyethoxy pyridinone core. A multidimensional optimization campaign, with focused matrix libraries, quickly established challenging SAR, enantiospecific activity, differences in assay read-outs (Ca²⁺ flux via a promiscuous G protein (G_α15) versus native coupling to GIRK channels), identified both full and partial mGlu₃ NAMs and a new in vivo tool compound, VU6017587. This mGlu₃ NAM showed efficacy in tail suspension, elevated zero maze and marble burying, suggesting selective inhibition of mGlu₃ affords anxiolytic-like and antidepressant-like phenotypes in mice.

Automated radiosynthesis of 5-[11C]l-glutamine, an important tracer for glutamine utilization

INTRODUCTION

The natural amino acid l-Glutamine (Gln) is essential for both cell growth and proliferation. In addition to glucose, cancer cells utilize Gln as a carbon source for ATP production, biosynthesis, and as a defense against reactive oxygen species. The utilization of [¹¹C]Gln has been previously reported as a biomarker for tissues with an elevated demand for Gln, however, the previous reports for the preparation of [¹¹C]Gln were found to be lacking several crucial aspects necessary for transition to human production. Namely, the presence of unreacted precursor and the use of non-commercialized, custom built, reaction platforms. Herein, we report the development and utilization of methodology for the automated production of [¹¹C]Gln that meets institutional criteria for human use.

METHODS

The preparation of [¹¹C]Gln was carried out on the GE FX₂N platform. Briefly, after trapping of [¹¹C]HCN with a solution of CsHCO₃ in DMF, the [¹¹C]CsCN was reacted with a commercially available precursor. This intermediate was then purified by HPLC and deprotected/hydrolyzed under acidic conditions. Following pH adjustment, the product was filtered to give the desired [¹¹C]Gln as a sterile injectable. The resulting product was then analyzed for quality assurance.

RESULTS

Automated production by this method reliably provides over 3.7 GBq (100 mCi) of [¹¹C]Gln. The resulting final drug product was found to have a >99% radiochemical purity, <5% of D-Gln present, no detectable impurities, and the total preparation time was roughly 45 min from the end-of-bombardment.

CONCLUSIONS

A fast, reliable and efficient automated radiosynthesis was developed using a commercially available module. Purifications used throughout allow for both a radiochemically and chemically pure final product solution of [¹¹C]Gln.

Pharmacological blockade of ASCT2-dependent glutamine transport leads to antitumor efficacy in preclinical models

The unique metabolic demands of cancer cells underscore potentially fruitful opportunities for drug discovery in the era of precision medicine. However, therapeutic targeting of cancer metabolism has led to surprisingly few new drugs to date. The neutral amino acid glutamine serves as a key intermediate in numerous metabolic processes leveraged by cancer cells, including biosynthesis, cell signaling, and oxidative protection. Herein we report the preclinical development of V-9302, a competitive small molecule antagonist of transmembrane glutamine flux that selectively and potently targets the amino acid transporter ASCT2. Pharmacological blockade of ASCT2 with V-9302 resulted in attenuated cancer cell growth and proliferation, increased cell death, and increased oxidative stress, which collectively contributed to antitumor responses in vitro and in vivo. This is the first study, to our knowledge, to demonstrate the utility of a pharmacological inhibitor of glutamine transport in oncology, representing a new class of targeted therapy and laying a framework for paradigm-shifting therapies targeting cancer cell metabolism.

Optimized Translocator Protein Ligand for Optical Molecular Imaging and Screening

Translocator protein (TSPO) is a validated target for molecular imaging of a variety of human diseases and disorders. Given its involvement in cholesterol metabolism, TSPO expression is commonly elevated in solid tumors, including glioma, colorectal cancer, and breast cancer. TSPO ligands capable of detection by optical imaging are useful molecular tracers for a variety of purposes that range from quantitative biology to drug discovery. Leveraging our prior optimization of the pyrazolopyrimidine TSPO ligand scaffold for cancer imaging, we report herein a new generation of TSPO tracers with superior binding affinity and suitability for optical imaging and screening. In total, seven candidate TSPO tracers were synthesized and vetted in this study; the most promising tracer identified (29, K_d = 0.19 nM) was the result of conjugating a high-affinity TSPO ligand to a fluorophore used routinely in biological sciences (FITC) via a functional carbon linker of optimal length. Computational modeling suggested that an n-alkyl linker of eight carbons in length allows for positioning of the bulky fluorophore distal to the ligand binding domain and toward the solvent interface, minimizing potential ligand-protein interference. Probe 29 was found to be highly suitable for in vitro imaging of live TSPO-expressing cells and could be deployed as a ligand screening and discovery tool. Competitive inhibition of probe 29 quantified by fluorescence and ³H-PK11195 quantified by traditional radiometric detection resulted in equivalent affinity data for two previously reported TSPO ligands. This study introduces the utility of TSPO ligand 29 for in vitro imaging and screening and provides a structural basis for the development of future TSPO imaging ligands bearing bulky signaling moieties.

New structure-activity relationships of N-acetamide substituted pyrazolopyrimidines as pharmacological ligands of TSPO

Translocator protein (TSPO) represents an attractive target for molecular imaging and therapy due to its prevalence and critical roles played in oncology and other pathologies. Based upon our previously optimized pyrazolopyrimidine scaffold, we elucidated new structure activity relationships related to N,N-disubstitutions of the terminal acetamide on pyrazolopyrimidines and further explored the impacts of these substituents on lipophilicity and plasma protein binding. Several novel chemical probes reported here exhibited significantly increased binding affinity, suitable lipophilicity and protein binding compared with contemporary TSPO ligands. We illustrate that N,N-acetamide disubstitution affords opportunities to introduce diverse chemical moieties distal to the central pyrazolopyrimidine core, without sacrificing TSPO affinity. We anticipate that further exploration of N-acetamide substitutions may yield additional TSPO ligands capable of furthering the field of precision medicine.

2-Amino-4-bis(aryloxybenzyl)aminobutanoic acids: A novel scaffold for inhibition of ASCT2-mediated glutamine transport

Herein, we report the discovery of 2-amino-4-bis(aryloxybenzyl)aminobutanoic acids as novel inhibitors of ASCT2(SLC1A5)-mediated glutamine accumulation in mammalian cells. Focused library development led to two novel ASCT2 inhibitors that exhibit significantly improved potency compared with prior art in C6 (rat) and HEK293 (human) cells. The potency of leads reported here represents a 40-fold improvement over our most potent, previously reported inhibitor and represents, to our knowledge, the most potent pharmacological inhibitors of ASCT2-mediated glutamine accumulation in live cells. These and other compounds in this novel series exhibit tractable chemical properties for further development as potential therapeutic leads.

Substituted indoles as selective protease activated receptor 4 (PAR-4) antagonists: Discovery and SAR of ML354

Herein we report the discovery and SAR of an indole-based protease activated receptor-4 (PAR-4) antagonist scaffold derived from a similarity search of the Vanderbilt HTS collection, leading to MLPCN probe ML354 (VU0099704). Using a novel PAC-1 fluorescent αIIbβ3 activation assay this probe molecule antagonist was found to have an IC50 of 140nM for PAR-4 with 71-fold selectivity versus PAR-1 (PAR-1IC50=10μM).

Abstract 2058: Molecular imaging of glutaminolysis as a tool for evaluating therapeutic response in preclinical models of colorectal cancer

The metabolic repertoire of cancer cells diverge significantly from that of normal cells. Energy production in cancer cells tends to depend on aerobic glycolysis, a feature that is routinely monitored by positron emission tomography (PET) imaging using 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG). In addition to predilection for glycolysis, cancer cells may possess other unique metabolic characteristics, such as increased consumption of glutamine. As with glucose, glutamine also serves as a key carbon source for ATP production and biosynthesis. Given this, quantitative measures of glutaminolysis may reflect critical processes in oncology. Accordingly, PET agents targeting glutamine uptake, such as 4-[18F]fluoro-glutamine ([18F]4F-GLN), have been reported and used in preclinical models of cancer.

The goal of this study was to elucidate the feasibility of using [18F]4F-GLN PET to predict response to targeted therapy within the context of colorectal cancer (CRC). Initially we validated expression of SLC1A5, the primary plasma membrane transporter of glutamine, in tumor and normal colon specimens for 58 patients with primary and advanced CRC. We found that SLC1A5 expression was elevated in over 80%of primary tumor specimens but did not correlate with grade or gender. Furthermore, elevated SLC1A5 expression correlated strongly with elevated Ki67, a molecular marker of proliferation.

Given this, we evaluated [18F]4F-GLN PET in preclinical models of V600EBRAF-expressing CRC as a means of detecting anti-proliferation responses to targeted therapeutics. Simulating a clinical study within the context of the Vanderbilt GI SPORE, the regimen included an inhibitor of mutant BRAF, a PI3K/mTOR inhibitor, and a combination there of. Strikingly, [18F]4F-GLN PET was found to correlate more closely to markers of anti-proliferative responses in vivo than analogously performed [18F]FDG PET imaging studies. We believe that these findings not only provide a greater understanding of the role that glutaminolysis plays in CRC but also illuminate the potential impact that glutaminolysis derived PET could have towards guiding drug development clinical trials as an imaging metric of early therapeutic response detection.

Citation Format: Matthew R. Hight, Michael L. Schulte, Samir Saleh, Gregory D. Ayers, Frank L. Revetta, M. Kay Washington, Robert J. Coffey, H. Charles Manning. Molecular imaging of glutaminolysis as a tool for evaluating therapeutic response in preclinical models of colorectal cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2058. doi:10.1158/1538-7445.AM2014-2058

Microwave-assisted, one-pot reaction of 7-azaindoles and aldehydes: a facile route to novel di-7-azaindolylmethanes

A novel and highly efficient synthetic method leveraging microwave-assisted organic synthesis (MAOS) to yield di-7-azaindolylmethanes (DAIMs) is reported. Under MAOS conditions, reaction of 7-azaindole with aldehydes resulted predominantly in DAIMs, as opposed to the expected 7-azaindole addition products that form at ambient temperature. Based upon studies of different indoles and azaindoles with various aromatic and aliphatic aldehydes, we herein propose a mechanism where rapid and efficient microwave heating promotes nucleophilicity of 7-azaindoles towards the corresponding alkylidene-azaindolene intermediate to form the DAIM. This sequence provides a versatile approach to efficiently synthesize novel DAIMs that may be useful pharmaceuticals.

Total synthesis of stemaphylline N-oxide and related C9a-epimeric analogues

Winning the relay: The first total synthesis of stemaphylline N-oxide has been completed utilizing a bistandem relay ring-closing-metathesis (RRCM) strategy, necessitated by the conformation of the requisite tetraene. This effort also gave unnatural 9a-epi-stemaphylline and 9a-epi-stemaphylline N-oxide.

Synthesis of indole derived protease-activated receptor 4 antagonists and characterization in human platelets

Protease activated receptor-4 (PAR4) is one of the thrombin receptors on human platelets and is a potential target for the management of thrombotic disorders. We sought to develop potent, selective, and novel PAR4 antagonists to test the role of PAR4 in thrombosis and hemostasis. Development of an expedient three-step synthetic route to access a novel series of indole-based PAR4 antagonists also necessitated the development of a platelet based high-throughput screening assay. Screening and subsequent structure activity relationship analysis yielded several selective PAR4 antagonists as well as possible new scaffolds for future antagonist development.

A General, Enantioselective Synthesis of 1-Azabicyclo[m.n.0]alkane Ring Systems

In this Letter, we describe a novel approach for the general and enantioselective synthesis of a diverse array of small to large 1-azabicyclo[m.n.0]alkyl ring systems with an embedded olefin handle for further functionalization. The stereochemistry is established via a highly diastereoselective indium-mediated allylation of an Ellman sulfinimine in greater than 9:1 dr., which is readily separable by column chromatography to afford a single diastereomer. This methodology allows for the rapid preparation of 1-azabicyclo[m.n.0]alkane ring systems that are not readily accessible through any other chemistry in excellent overall yields and, for many systems, the only enantioselective preparation reported to date.

The Discovery and Characterization of ML218: A Novel, Centrally Active T-Type Calcium Channel Inhibitor with Robust Effects in STN Neurons and in a Rodent Model of Parkinson's Disease

T-type Ca(2+) channel inhibitors hold tremendous therapeutic potential for the treatment of pain, epilepsy, sleep disorders, essential tremor and other neurological disorders; however, a lack of truly selective tools has hindered basic research, and selective tools from the pharmaceutical industry are potentially burdened with intellectual property (IP) constraints. Thus, an MLPCN high-throughput screen (HTS) was conducted to identify novel T-type Ca(2+) channel inhibitors free from IP constraints, and freely available through the MLPCN, for use by the biomedical community to study T-type Ca(2+) channels. While the HTS provided numerous hits, these compounds could not be optimized to the required level of potency to be appropriate tool compounds. Therefore, a scaffold hopping approach, guided by SurflexSim, ultimately afforded ML218 (CID 45115620) a selective T-Type Ca(2+) (Ca(v)3.1, Ca(v)3.2, Ca(v)3.3) inhibitor (Ca(v)3.2, IC(50) = 150 nM in Ca(2+) flux; Ca(v)3.2 IC(50) = 310 nM and Ca(v)3.3 IC(50) = 270 nM, respectively in patch clamp electrophysiology) with good DMPK properties, acceptable in vivo rat PK and excellent brain levels. Electrophysiology studies in subthalamic nucleus (STN) neurons demonstrated robust effects of ML218 on the inhibition of T-Type calcium current, inhibition of low threshold spike and rebound burst activity. Based on the basal ganglia circuitry in Parkinson's disease (PD), the effects of ML218 in STN neurons suggest a therapeutic role for T-type Ca(2+) channel inhibitors, and ML218 was found to be orally efficacious in haloperidol-induced catalepsy, a preclinical PD model, with comparable efficacy to an A(2A) antagonist, a clinically validated PD target. ML218 proves to be a powerful new probe to study T-Type Ca(2+) function in vitro and in vivo, and freely available.

Highly diastereoselective and general synthesis of primary β-fluoroamines

A short, high yielding protocol has been developed for the highly diastereoselective (dr >20:1) and general synthesis of primary β-fluoroamines by the enantioselective α-fluorination of aldehydes, conversion into the N-sulfinyl aldimine, nucleophilic addition of various organometallic species, and 1° amine liberation.

Cortical electrical stimulation alters erythrocyte perfusion pattern in the cerebral capillary network of the rat

The effect of direct cortical electrical stimulation on the pattern of erythrocyte perfusion in the capillary network of the rat cerebral cortex was studied by fluorescence intravital video-microscopy. The movement of fluorescently labeled red blood cells (FRBCs) in individual capillaries 50-70 microm subsurface in the dorsal somatosensory cortex was visualized using a closed cranial window. Cortical stimulation electrodes were placed on opposite sides of the window. FRBC velocity (mm/s) and supply rate (cells/s) were measured in 51 capillaries from six rats before and during electrical stimulation of increasing intensities (15-s trains of 3-Hz, 3-ms, 0.5-5.0-mA, square pulses). FRBC velocity, supply rate, and the instantaneous capillary erythrocyte content (lineal cell density, LCD, cells/mm) increased with the stimulation current and reached maxima of 110, 160 and 33% above control, respectively. Capillaries with low resting velocity showed a greater response than those with high resting velocity. The fraction of capillaries in which FRBC velocity increased was not constant, but increased with the stimulation current, as did the magnitude of the velocity change in these capillaries. A few capillaries showed a negative FRBC velocity response at stimulations <4 mA. These results suggest that a robust rise in the fraction of responding (engaged) capillaries and a smaller rise in the capillary LCD contribute to neuronal activation-induced cortical hyperemia. Thus, capillary engagement and erythrocyte recruitment appear to represent important components of the cortical functional hyperemic response. These results provide insight into some of the specific hemodynamic changes associated with functional hyperemia occurring at the capillary level.

Toluidine blue O and methylene blue as endothelial redox probes in the intact lung

There is increasing evidence that the redox activities of the pulmonary endothelial surface may have important implications for the function of both lungs and blood. Because of the inherent complexity of intact organs, it can be difficult to study these activities in situ. Given the availability of appropriate indicator probes, the multiple-indicator dilution (MID) method is one approach for dealing with some aspects of this complexity. Therefore, the objectives of the present study were to 1) evaluate the potential utility of two thiazine redox indicators, methylene blue (MB) and toluidine blue O (TBO), as MID electron acceptor probes for in situ pulmonary endothelium and 2) develop a mathematical model of the pulmonary disposition of these indicators as a tool for quantifying their reduction on passage through the lungs. Experiments were carried out using isolated rabbit lungs perfused with physiological salt solution with or without plasma albumin over a range of flow rates. A large fraction of the injected TBO disappeared from the perfusate on passage through the lungs. The reduction of its oxidized, strongly polar, relatively hydrophilic blue form to its colorless, highly lipophilic reduced form was revealed by the presence of the reduced form in the venous effluent when plasma albumin was included in the perfusate. MB was also lost from the perfusate, but the fraction was considerably smaller than for TBO. A distributed-in-space-and-time model was developed to estimate the reduction rate parameter, which was approximately 29 and 1.0 ml/s for TBO and MB, respectively, and almost flow rate independent for both indicators. The results suggest the utility particularly of TBO as an electron acceptor probe for MID studies of in situ pulmonary endothelium and of the model for quantitative evaluation of the data.

Postnatal remodeling of the leptomeningeal vascular network as assessed by intravital fluorescence video-microscopy in the rat

An intriguing characteristic of the ontogenic development of the cerebral vasculature is the rapid differentiation of the neonatal leptomeningeal vascular plexus into the mature, adult network form. The physiological and cellular mechanisms of this cerebrovascular remodeling process are unclear. The objective of this work was to determine and correlate changes in vascular density, network pattern and flow velocity in leptomeningeal microvessels of the rat during postnatal development in vivo. To this end, microvascular diameter, segment length, and vascular density of reconstructed leptomeningeal networks were measured from video-recordings of the microcirculation visualized through a cranial window in 0-15-day-old Sprague-Dawley rats. The velocity of erythrocytes in the microvessels was measured by frame to frame tracking of fluorescently labeled red blood cells. We found that surface vascular density (total vessel length per area), node density and segment density (object per area) decreased significantly by the second week after birth. Anastomosing vascular polygons, characteristic to newborn networks, became less numerous and larger in diameter during the postnatal 2-week period, indicating progressive rarefaction of the networks. Vessel diameter and red cell velocity showed transient increases at 1.5 weeks. The velocity/diameter ratio (V/D), an index of wall shear rate, increased by the age of 1.5 weeks and remained unchanged afterwards. There was a negative correlation between V/D and diameter at 1 week; this relationship was reversed to a positive correlation at 2 weeks. We conclude that postnatal remodeling of the leptomeningeal vascular network is associated with rarefaction and an adaptation of vessel caliber to wall shear rate. These changes may contribute to arterio-venous differentiation and redistribution of blood flow from the superficial to the intracortical vasculature in the developing brain.

An angiographic method for in vivo study of arteries of the circle of Willis in small animals

An X-ray imaging technique designed to allow sequential diameter measurements of the cerebral vessels in intact, anesthetized small animals under relatively physiological conditions is described. The ferret and the rabbit were chosen as potentially useful animal models for studying the cerebrovascular system because of the advantageous anatomic characteristics of these relatively small species. A commercially available and relatively inexpensive X-ray imaging system with a small focal spot provides good spatial resolution. An external carotid perfusion loop allows for 1) the introduction of low-osmolality contrast medium without changing perfusion pressure or flow and 2) measurement of internal carotid and circle of Willis pressures at the same time that the vessel images are obtained. In the present study, detection of small changes in the diameters of the small vessels is facilitated by an algorithm utilizing the X-ray absorption by the entire vessel cross section. This avoids some of the problems of edge detection for small cylindrical vessels wherein the contrast is less than optimal and diminishes as the vessel perimeter is approached.