Towards HCP-Style macaque connectomes: 24-Channel 3T multi-array coil, MRI sequences and preprocessing

© 2020 The Author(s) Macaque monkeys are an important animal model where invasive investigations can lead to a better understanding of the cortical organization of primates including humans. However, the tools and methods for noninvasive image acquisition (e.g. MRI RF coils and pulse sequence protocols) and image data preprocessing have lagged behind those developed for humans. To resolve the structural and functional characteristics of the smaller macaque brain, high spatial, temporal, and angular resolutions combined with high signal-to-noise ratio are required to ensure good image quality. To address these challenges, we developed a macaque 24-channel receive coil for 3-T MRI with parallel imaging capabilities. This coil enables adaptation of the Human Connectome Project (HCP) image acquisition protocols to the in-vivo macaque brain. In addition, we adapted HCP preprocessing methods to the macaque brain, including spatial minimal preprocessing of structural, functional MRI (fMRI), and diffusion MRI (dMRI). The coil provides the necessary high signal-to-noise ratio and high efficiency in data acquisition, allowing four- and five-fold accelerations for dMRI and fMRI. Automated FreeSurfer segmentation of cortex, reconstruction of cortical surface, removal of artefacts and nuisance signals in fMRI, and distortion correction of dMRI all performed well, and the overall quality of basic neurobiological measures was comparable with those for the HCP. Analyses of functional connectivity in fMRI revealed high sensitivity as compared with those from publicly shared datasets. Tractography-based connectivity estimates correlated with tracer connectivity similarly to that achieved using ex-vivo dMRI. The resulting HCP-style in vivo macaque MRI data show considerable promise for analyzing cortical architecture and functional and structural connectivity using advanced methods that have previously only been available in studies of the human brain

Radiofluorinated probe for PET imaging of fatty acid binding protein 4 in cancer.

【Introduction】Cancer-associated adipocytes metabolically interact with adjacent cancer cells to promote tumor proliferation and metastasis. Fatty acid binding protein 4 (FABP4) participates in this interaction, and is gathering attention as a therapeutic and diagnostic target. Positron emission tomography (PET) is a useful diagnostic method that enables noninvasive in vivo quantitative imaging of biofunctional molecules with probes labeled with positron-emitting radioisotopes. Here a novel 18F labeled probe for PET FABP4 imaging developed through dedicated drug design from a radioiodinated probe we recently reported is evaluated in vitro and in vivo.【Methods】We designed the [18F]-labeled FTAP1 and FTAP3 probe, composed of a single or triple oxyethylene linker and a triazolopyrimidine scaffold derived from an FABP4 inhibitor. FABP4 binding affinities for chemically synthesized FTAP1 and FTAP3 were measured using FABP4 and 8-anilino-1-naphthalene sulfonic acid. Cell membrane permeability was measured using a commercially available plate assay system. After radiosynthesis, [18F]FTAP1 affinity and selectivity were evaluated using immobilized FABP3, FABP4, and FABP5. Cell uptake was investigated using differentiated adipocytes expressing FABP4 with inhibitor treatment. Following biodistribution studies in C6 glioblastoma-bearing mice, ex vivo autoradiography and immunohistochemistry were performed using thin sliced tumor sections. PET/CT imaging was then performed on C6 tumor bearing mice.【[Results】FTAP1 showed high FABP4 affinity (Ki = 68 ± 8.9 nM) and adequate cell permeability. [18F]FTAP1 with ≥ 98% radiochemical purity was shown to selectively bind to FABP4 (16.3- and 9.3-fold higher than for FABP3 and FABP5, respectively). [18F]FTAP1 was taken up by FABP4 expressing cells, and this uptake could be blocked by an inhibitor, indicating very low non-specific cell binding. [18F]FTAP1 showed high tumor accumulation, which demonstrates its potential use for in vivo tumor PET imaging, and the intratumoral radioactivity distribution corresponded to the FABP4 expression profile.【Conclusion】][18F]FTAP1 is a promising PET probe to target FABP4

Development of a Radioiodinated Triazolopyrimidine Probe for Nuclear Medical Imaging of Fatty Acid Binding Protein 4

<div><p>Fatty acid binding protein 4 (FABP4) is the most well-characterized FABP isoform. FABP4 regulates inflammatory pathways in adipocytes and macrophages and is involved in both inflammatory diseases and tumor formation. FABP4 expression was recently reported for glioblastoma, where it may participate in disease malignancy. While FABP4 is a potential molecular imaging target, with the exception of a tritium labeled probe there are no reports of other nuclear imaging probes that target this protein. Here we designed and synthesized a nuclear imaging probe, [¹²³I]TAP1, and evaluated its potential as a FABP4 targeting probe in <i>in vitro</i> and <i>in vivo</i> assays. We focused on the unique structure of a triazolopyrimidine scaffold that lacks a carboxylic acid to design the TAP1 probe that can undergo facilitated delivery across cell membranes. The affinity of synthesized TAP1 was measured using FABP4 and 8-anilino-1-naphthalene sulfonic acid. [¹²⁵I]TAP1 was synthesized by iododestannylation of a precursor, followed by affinity and selectivity measurements using immobilized FABPs. Biodistributions in normal and C6 glioblastoma-bearing mice were evaluated, and excised tumors were subjected to autoradiography and immunohistochemistry. TAP1 and [¹²⁵I]TAP1 showed high affinity for FABP4 (<i>K</i>_i = 44.5±9.8 nM, <i>K</i>_d = 69.1±12.3 nM). The FABP4 binding affinity of [¹²⁵I]TAP1 was 11.5- and 35.5-fold higher than for FABP3 and FABP5, respectively. In an <i>in vivo</i> study [¹²⁵I]TAP1 displayed high stability against deiodination and degradation, and moderate radioactivity accumulation in C6 tumors (1.37±0.24% dose/g 3 hr after injection). The radioactivity distribution profile in tumors partially corresponded to the FABP4 positive area and was also affected by perfusion. The results indicate that [¹²⁵I]TAP1 could detect FABP4 <i>in vitro</i> and partly <i>in vivo</i>. As such, [¹²⁵I]TAP1 is a promising lead compound for further refinement for use in <i>in vivo</i> FABP4 imaging.</p></div

Western blotting analyses of FABP4 and β-actin expression in mouse adipose tissue, excised tumor, C6 cultured cells and rat adipose tissue.

<p>Western blotting analyses of FABP4 and β-actin expression in mouse adipose tissue, excised tumor, C6 cultured cells and rat adipose tissue.</p

Biodistribution of radioactivity after intravenous administration of [¹²⁵I]TAP1 in normal mice.

<p>Data are presented as % injected dose per gram. Each value represents the mean±S.D. for 3 animals at each interval.</p>a<p>Presented as % injected dose per organ.</p

Regional distribution of radioactivity after [¹²⁵I]TAP1 injection and FABP4 expression in tumor sections.

<p>Autoradiogram (A) and immunohistochemical staining (B, C, E) of tumor sections. The frames in (B) show the location of the areas captured at higher magnification in C (solid line) and E (dashed line). (D) Oil Red staining of the same area as C. Bar = 1 mm (B, E) and 200 µm (C, D)</p

Reagents and conditions.

<p>(a) 3-iodophenol, K₂CO₃, DMF. (b) 3-bromophenol, K₂CO₃, DMF. (c) (Bu₃Sn)₂, (Ph₃P)₄Pd, Et₃N, DMF. (d) [¹²⁵I]NaI, NCS, MeOH (1% acetic acid).</p

Uptake of [¹²⁵I]TAP1 into differentiated THP-1 cells and inhibition by TAP1 or BMS309403.

<p><i>P</i><0.05 vs. 0 µM group, ^§<i>P</i><0.05 vs. 0.01 µM.</p

Binding saturation assay of [¹²⁵I]TAP1.

<p>(A) Saturation curve of [¹²⁵I]TAP1 for FABP4. (B) Scatchard plots of [¹²⁵I]TAP1 binding to FABP4.</p

Binding of [¹²⁵I]TAP1 to FABP3, 4, and 5.

<p>^*<i>P</i><0.05 vs. FABP4 group.</p