Journal Articles
Journal Articles
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Emergent Fluorous Molecules and Their Uses in Molecular Imaging (Acc Chem Res 2021)

Summary

Role of CFT Used CFT to visualize NE biodistribution
CFT Advantage
3D imaging of NE, registration of WL and FL signal, high sensitivity compared to other fluorescence imaging modalities
Preclinical Application
Gene Therapy, Oncology, Neurology, Immunology, Drug Discovery
Probes Used In Xerra™
Cy5
λEx/Em: 673/707
Imaging Modalities Shown
CFT, 19F and 1H MRI, Bimodal PET/MRI, PET, CT, CFT, IVIS
Animal Model Used
Acute Inflammation Murine Model

Abstract

Conspectus: This Account summarizes recent advances in the chemistry of fluorocarbon nanoemulsion (FC NE) functionalization. We describe new families of fluorous molecules, such as chelators, fluorophores, and peptides, that are soluble in FC oils. These materials have helped transform the field of in vivo molecular imaging by enabling sensitive and cell-specific imaging using magnetic resonance imaging (MRI), positron emission tomography (PET), and fluorescence detection. FC emulsions, historically considered for artificial blood substitutes, are routinely used for ultrasound imaging in clinic and have a proven safety profile and a well-characterized biodistribution and pharmacokinetics. The inertness of fluorocarbons contributes to their low toxicity but makes functionalization difficult. The high electronegativity of fluorine imparts very low cohesive energy density and Lewis basicity to heavily fluorinated compounds, making dissolution of metal ions and organic molecules challenging. Functionalization is further complicated by colloidal instability toward heat and pH, as well as limited availability of biocompatible surfactants.We have devised new fluorous chelators that overcome solubility barriers and are able to bind a range of metal ions with high thermodynamic stability and biocompatibility. NE harboring chelators in the fluorous phase are a powerful platform for the development of multimodal imaging agents. These compositions rapidly capture metal ions added to the aqueous phase, thereby functionalizing NEs in useful ways. For example, Fe3+ encapsulation imparts a strong paramagnetic relaxation effect on 19F T1 that dramatically accelerates 19F MRI data acquisition times and hence sensitivity in cell tracking applications. Alternatively, 89Zr encapsulation creates a sensitive and versatile PET probe for inflammatory macrophage detection. Adding lanthanides, such as Eu3+, renders NE luminescent. Beyond chelators, this Account further covers our progress in formulating NEs with fluorophores, such as cyanine or BODIPY dyes, with their utility demonstrated in fluorescence imaging, biosensing, flow cytometry and histology. Fluorous dyes soluble in FC oils are also key enablers for nascent whole-body imaging technologies such as Cryo-Fluorescence Tomography (CFT). Additionally, fluorous cell-penetrating peptides inserted on the NE surface increase the uptake of NE by ∼8-fold in weakly phagocytic stem cells and lymphocytes used in immunotherapy, resulting in significant leaps in detection sensitivity in vivo.
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Brain Pharmacology of Intrathecal Antisense Oligonucleotides Revealed Through Multimodal Imaging (JCI Insight 2019)

Summary

Role of CFT Used CFT to define 2D and 3D spatiotemporal PK of ASO penetration in CNS structures and demonstrate their interaction with multiple molecular movement paths.
CFT Advantage
2D/3D imaging of ASO brain penetration, registration of WL and FL signal, and collection brain sections on glass slides for fluorescence microscopy and IHC.
Preclinical Application
Neurology, Drug Discovery
Probes Used In Xerra™
Cy7
λEx/Em: 756/779
Imaging Modalities Shown
CFT, SPECT/CT, 18F PET, Microscopy
Animal Model Used
Sprague Dawley Rats

Abstract

Intrathecal (IT) delivery and pharmacology of antisense oligonucleotides (ASOs) for the CNS have been successfully developed to treat spinal muscular atrophy. However, ASO pharmacokinetic (PK) and pharmacodynamic (PD) properties remain poorly understood in the IT compartment. We applied multimodal imaging techniques to elucidate the IT PK and PD of unlabeled, radioactively labeled, or fluorescently labeled ASOs targeting ubiquitously expressed or neuron-specific RNAs. Following lumbar IT bolus injection in rats, all ASOs spread rostrally along the neuraxis, adhered to meninges, and were partially cleared to peripheral lymph nodes and kidneys. Rapid association with the pia and arterial walls preceded passage of ASOs across the glia limitans, along arterial intramural basement membranes, and along white-matter axonal bundles. Several neuronal and glial cell types accumulated ASOs over time, with evidence of probable glial accumulation preceding neuronal uptake. IT doses of anti-GluR1 and anti-Gabra1 ASOs markedly reduced the mRNA and protein levels of their respective neurotransmitter receptor protein targets by 2 weeks and anti-Gabra1 ASOs also reduced binding of the GABAA receptor PET ligand 18F-flumazenil in the brain over 4 weeks. Our multimodal imaging approaches elucidate multiple transport routes underlying the CNS distribution, clearance, and efficacy of IT-dosed ASOs.
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Dynamic Dual-Isotope Molecular Imaging Elucidates Principles for Optimizing Intrathecal Drug Delivery (JCI Insight 2016)

Summary

Role of CFT Used CFT to determine the effects of the neuraxial exposure of drug surrogate molecules following an IT lumbar bolus in the rat.
CFT Advantage
CFT was used to follow the IT distribution of EBD, a small molecule (MW 961 Da), which binds tightly to albumin and can move from the CSF into the ISF of CNS tissue. Analysis software was used to create fly-through animations and 3D models of the rat spinal column and to estimate CSF volume by application of blue color detectors.
Preclinical Application
Neurology, Drug Discovery
Probes Used In Xerra™
Cy5
λEx/Em: 673/707
Imaging Modalities Shown
MRI, SPECT/CT, Autoradiography, Microscopy
Animal Model Used
Sprague Dawley Rats

Abstract

The intrathecal (IT) dosing route offers a seemingly obvious solution for delivering drugs directly to the central nervous system. However, gaps in understanding drug molecule behavior within the anatomically and kinetically unique environment of the mammalian IT space have impeded the establishment of pharmacokinetic principles for optimizing regional drug exposure along the neuraxis. Here, we have utilized high-resolution single-photon emission tomography with X-ray computed tomography to study the behavior of multiple molecular imaging tracers following an IT bolus injection, with supporting histology, autoradiography, block-face tomography, and MRI. Using simultaneous dual-isotope imaging, we demonstrate that the regional CNS tissue exposure of molecules with varying chemical properties is affected by IT space anatomy, cerebrospinal fluid (CSF) dynamics, CSF clearance routes, and the location and volume of the injected bolus. These imaging approaches can be used across species to optimize the safety and efficacy of IT drug therapy for neurological disorders.

The Next Generation of Imaging. Xerra.