112 research outputs found
Development and Evaluation of Selective Matrix Metalloproteinase-13 PET Radiotracers for Imaging Atherosclerosis
No full textAtherosclerosis is a chronic inflammatory disease characterized by the buildup of lipid-rich plaques within the coronary arteries and a leading cause of death worldwide. Given that plaque rupture occurs due to molecular changes in plaque composition and is considered the primary cause of heart attack and stroke, molecular imaging by positron emission tomography (PET) provides the opportunity to assess disease severity and may assist in the prevention of severe cardiovascular events and associated fatal outcomes.
Matrix metalloproteinases (MMPs) represent a class of zinc-chelating enzymes with diverse functions in extracellular matrix (ECM) remodeling during normal physiological processes and inflammatory diseases. As MMPs possess distinct substrate specificity and differential roles in disease progression, selective targeting of individual MMPs should be prioritized for diagnosis and therapy. Upregulated MMP-13 activity has been extensively implicated with atherosclerotic plaque destabilization due to uncontrolled ECM degradation and formation of thin-capped and collagen-poor plaques that are most susceptible to rupture. As such, MMP-13 represents a compelling molecular biomarker of unstable atherosclerosis for selective PET radiotracer development. This thesis outlines the synthesis, optimization, and evaluation of MMP-13 selective PET radiotracers for imaging atherosclerosis. Chapter I introduces atherosclerosis, provides an overview of MMPs as therapeutics and diagnostics, and describes available strategies for MMP-13 selective radiotracer development.
Chapter II outlines a head-to-head comparison of MMP-13 selective and broad-spectrum MMP imaging with existing fluorine-18 labeled PET radiotracers. In this study, the first in vivo evaluation of [18F]FMBP and [18F]BR-351, as MMP-13 selective and non-selective MMP-targeted radiotracers based on the pyrimidine-dicarboxamide and non-peptidic aryl sulfonamide inhibitor classes, was performed in a mouse model of atherosclerosis. Determination of radiotracer pharmacokinetics, target specificity, and sensitivity to atherosclerotic tissue validated the feasibility of using an MMP-13 selective PET radiotracer to detect ECM remodeling in atherosclerotic plaques and demonstrated several advantages to this strategic imaging approach.
Chapter III describes the development and evaluation of novel MMP-13 selective PET radiotracers based on the most potent and selective quinazoline-2-carboxamide inhibitor class for imaging atherosclerosis. Structure-activity relationship (SAR) studies were performed with a particular focus on modifications that would facilitate late-stage radiolabeling with carbon-11 or fluorine-18 and pharmacokinetic characterization in atherosclerotic mice. The first biological evaluation of three candidate radiotracers [11C]5b, [11C]5f, and [18F]5j was conducted and elucidated the structural determinants required to obtain in vivo functional activity, MMP-13 specificity/selectivity, and desirable pharmacokinetics for vascular imaging. This study further highlighted the superiority of the quinazoline-2-carboxamide scaffold for selective MMP-13 PET radiotracer development and identified [18F]5j as a promising lead for ex vivo atherosclerotic plaque imaging.
Chapter IV focuses on the synthesis and design of highly functionalized second-generation MMP-13 selective PET radiotracers based on the quinazoline-2-carboxamide scaffold with greater contrast for non-invasive atherosclerotic plaque imaging. Structural modifications focused on restoring critical binding interactions, incorporating a new site for fluorine-18 or carbon-11 radiolabeling, and reducing lipophilicity. SAR uncovered the optimized inhibitor 29f as a promising lead radiotracer candidate with remarkably enhanced MMP-13 potency and off-target selectivity. In vivo evaluations of [11C]29f in atherosclerotic mice demonstrated its favorable pharmacokinetic properties and assessed its potential utility for atherosclerosis
Preliminary Evaluation of Matrix Metalloproteinase-13 Selective Radiotracers for Imaging Atherosclerosis
No full textIntroduction: Rupture of atherosclerotic plaques is associated with strokes, myocardial infarctions and cardiovascular complications. Collagen, known to be the most abundant protein in atherosclerotic plaques, stabilizes the cap and prevents the lesion from rupture. One of the enzymes responsible for cleaving collagen in plaques is MMP-13. Therefore, we hypothesized that imaging MMP-13 in atherosclerotic plaques using PET radiotracers can be a good indicator in monitoring plaque development and stability.
Results: Our results indicate that developing potent selective MMP-13 inhibitors is possible and radiolabeling these compounds, although challenging, can be a useful tool for imaging MMP-13 in atherosclerotic plaques. Autoradiography and staining techniques show colocalization of our tracer with lipids, an essential indicator of the presence of atherosclerotic lesions. In addition, it was shown that the tracer had similar uptake in both groups of mice, confirmed by PET and biodistribution data. However, more selective MMP-13 tracers need to go though this process. Furthermore, more exclusive atherosclerotic markers should be stained for to confirm that the tracer is most selective for MMP-13.
Conclusion: In conclusion, this study was useful in identifying MMP-13 inhibitors with radiolabeling potential to image MMP-13 in atherosclerotic plaques
Preparation of ¹¹C-Carbonyl Compounds and Radiotracer Validation for Cardiac PET Imaging
No full textMolecular imaging techniques serve an integral role in clinical practice for the diagnosis and prognosis of various morbidities. Positron emission tomography (PET) is an imaging modality employing radiolabelled probes to visualize biochemical processes. Radiochemical synthesis is used to incorporate radioactive isotopes into small molecules or peptides targeting a protein of interest. Access to radiotracers is therefore dependent on the availability of radiochemical methods for the addition of radionuclides. This thesis describes the key steps in the process of developing a new radiotracer, from designing methodologies for their synthesis, to the production and evaluation of a novel probe, and finally the analysis of tracer kinetics in PET imaging. Beginning with Chapter 1, PET and radiochemistry will be introduced.
Chapter 2 is focused on a general methodology to access ¹¹C-amides, using transition metal-catalyzed additions of organozinc iodides to ¹¹C-isocyanates. In the chapter’s central article, [¹¹C]CO₂ produced directly from the cyclotron was captured and converted to reactive ¹¹C-isocyanate electrophiles before being derivatized by aryl and alkyl organozinc iodides. Additional work on the development of alternative ¹¹C-carbonyl compounds is also described.
Chapter 3 presents the radiolabelling of one such ¹¹C-carbonyl, describing the development of a radiotracer based on the selective Rev-erb inhibitor SR9009. Given recently elucidated potential for therapeutic applications of Rev-erb inhibitors like SR9009 in the management of cardiovascular disease, (R)- and (S)-[¹¹C]SR9009 were synthesized for cardiac investigation of circadian biology.
Chapter 4 explores a novel approach to prepare ¹¹C-amino acids with [¹¹C]CO₂ via carbon isotope exchange. In this chapter, α-amino acids are condensed to Schiff bases using aldehydes; this intermediate can then undergo a carboxylation/decarboxylation cycle in which isotopically-labelled carbon (¹¹C, ¹³C, ¹⁴C) is incorporated. The key paper details the optimization of carbon-11 labelling to prepare enantiopure L- and D-¹¹C-amino acids for imaging.
Chapter 5 discusses the pharmacokinetic and metabolic evaluation of [¹⁸F]flubrobenguane (FBBG) in clinical imaging populations to determine radiotracer kinetics. Patients underwent FBBG PET scans to evaluate cardiac denervation. Blood samples were collected and processed to derive vital parameters for image analysis and interpretation. Patient cohorts were statistically compared to evaluate disease-specific differences in the pharmacokinetics of FBBG
Jealous Men but Evil Women: The Double Standard in Cases of Domestic Homicide
No full textIn 1989, Sarah Thornton killed her abusive husband with a knife, after years of abuse and threats to her daughter. She was convicted of murder and sentenced to life imprisonment. Also in 1989, Kiranjit Ahluwalia soaked her husband’s bedclothes with petrol and set them alight. He died from burns 10 days later, and she was subsequently convicted of murder and sentenced to life in prison.
In 1991, Joseph McGrail kicked his alcoholic common-law wife to death whilst she lay unconscious. He walked free from court, the judge telling him that “this lady would have tried the patience of a saint”. In 1992, Les Humes told a court that he “saw a red mist” after his wife admitted loving someone else. He fatally stabbed her whilst their teenage children struggled with him. He was convicted of manslaughter due to provocation and was imprisoned for 7 years.
Double standards in judicial processes are notorious. Chivalric justice is the case in which women are given lighter sentences for similar offences to men. This does not apply in the case of domestic homicide, where women are seen as evil and calculating when killing a spouse, men are seen as provoked beyond reason. Women who kill husbands do so with weapons that they need to acquire, men do it with their hands or weapons that are immediately available. So it is seems the defence of crime passionnel is reserved for men; women, it is implied, premeditate the murder of abusive husbands, and are justifiably punished. This paper explores the double standard in uxoricide vs. mariticide, and why it appears that killing a wife is justified and killing a husband is evi
Unprotected Aziridine Aldehydes in Isocyanide-based Multicomponent Reactions
No full textWhile unprotected amino aldehydes are typically not isolable due to imine formation and consequent polymerization, stable unprotected aziridine aldehydes are useful and available reagents. Moreover, reversible hemiacetal and hemiaminal formation enable these compounds to reveal both their electrophilic and nucleophilic functional groups. This exceptional arrangement allows for aziridine aldehyde dimers to participate in and disrupt the mechanisms of an array of well-known organic reactions, including isocyanide-based multicomponent reactions. The scope and selectivity patterns of aziridine aldehyde induced amino acid or peptide macrocyclization have been investigated. A small library of constrained tri-, tetra-, and penta-peptide macrocycles – representing the most difficult cyclic peptides to synthesize – has been prepared. The scope of aziridine aldehyde participation in multicomponent reactions was also expanded to Ugi and Passerini reactions that do not employ tethered amine and acid functional groups. In order to facilitate cellular imaging of peptide macrocycles a fluorescent isocyanide reagent was prepared and applied to prepare mitochondrial targeting macrocycles. Thioester isocyanide reagents were synthesized to enable rapid assembly of cycle-tail peptides through ligation technology.Ph
Unprotected Aziridine Aldehydes in Isocyanide-based Multicomponent Reactions
No full textWhile unprotected amino aldehydes are typically not isolable due to imine formation and consequent polymerization, stable unprotected aziridine aldehydes are useful and available reagents. Moreover, reversible hemiacetal and hemiaminal formation enable these compounds to reveal both their electrophilic and nucleophilic functional groups. This exceptional arrangement allows for aziridine aldehyde dimers to participate in and disrupt the mechanisms of an array of well-known organic reactions, including isocyanide-based multicomponent reactions. The scope and selectivity patterns of aziridine aldehyde induced amino acid or peptide macrocyclization have been investigated. A small library of constrained tri-, tetra-, and penta-peptide macrocycles – representing the most difficult cyclic peptides to synthesize – has been prepared. The scope of aziridine aldehyde participation in multicomponent reactions was also expanded to Ugi and Passerini reactions that do not employ tethered amine and acid functional groups. In order to facilitate cellular imaging of peptide macrocycles a fluorescent isocyanide reagent was prepared and applied to prepare mitochondrial targeting macrocycles. Thioester isocyanide reagents were synthesized to enable rapid assembly of cycle-tail peptides through ligation technology.Ph
ChemInform Abstract: Aziridine‐2‐carboxaldehyde Dimers Undergo Homo‐Ugi 4‐Component‐5‐center Reactions.
No full textFluorine-18-Labeled Fluorescent Dyes for Dual-Mode Molecular Imaging
No full textRecent progress realized in the development of optical imaging (OPI) probes and devices has made this technique more and more affordable for imaging studies and fluorescence-guided surgery procedures. However, this imaging modality still suffers from a low depth of penetration, thus limiting its use to shallow tissues or endoscopy-based procedures. In contrast, positron emission tomography (PET) presents a high depth of penetration and the resulting signal is less attenuated, allowing for imaging in-depth tissues. Thus, association of these imaging techniques has the potential to push back the limits of each single modality. Recently, several research groups have been involved in the development of radiolabeled fluorophores with the aim of affording dual-mode PET/OPI probes used in preclinical imaging studies of diverse pathological conditions such as cancer, Alzheimer’s disease, or cardiovascular diseases. Among all the available PET-active radionuclides, 18F stands out as the most widely used for clinical imaging thanks to its advantageous characteristics (t1/2 = 109.77 min; 97% β+ emitter). This review focuses on the recent efforts in the synthesis and radiofluorination of fluorescent scaffolds such as 4,4-difluoro-4-bora-diazaindacenes (BODIPYs), cyanines, and xanthene derivatives and their use in preclinical imaging studies using both PET and OPI technologies
Neural mechanisms and functional signficance of peri-saccadic response modulation
No full textActive vision involves fast eye movements (saccades) with brief inter-saccadic fixations. This presents two interesting problems. (1) During each saccade the moving eye creates motion signals on the retina, and yet we are unaware of this sweeping visual input. (2) Upon each brief fixation the visual system is input with a new scene, and tasked to quickly encode many stimulus features. Regarding the first problem, a decrease in contrast sensitivity during saccades (saccadic suppression) is thought to contribute to our lack of intra-saccadic perception. Chapters 2 & 3 of this thesis seek to further understand the neural mechanisms of saccadic suppression. Regarding the second problem, a post-saccadic change in neural activity is thought to specialize processing of newly fixated stimuli. Chapter 4 investigates the changes in visual response properties that occur after a saccade. Chapter 2 used a signal-detection model that describes the psychophysical phenomenon of saccadic suppression in computational terms. The model is built up of visual detectors in which gain, noise, and spatial uncertainty can be varied. Thus saccadic suppression is recast in terms that provide testable predictions of neural activities. We found that saccadic suppression is the result of reduced detector gain. Chapter 3 studied neural responses from permanently implanted multi-electrode arrays in V1 of macaques. Based on our Chapter 2 results, we looked specifically at how contrast responses change during saccades. We found saccadic gain reduction that begins before saccade onset, suggesting that V1 is a neural site of suppression, and that saccadic gain reduction is the result of a corollary discharge signal. Chapter 4 studied the effect of post-saccadic modulation on contrast response properties. Using model fitting and signal detection measures, we showed that post-saccadic modulations in V1 lead to an increased range of discriminable contrasts. We argue that this increased operating range gives a functional benefit when encountering newly fixated stimuli. Chapter 5 concludes by relating the saccadic gain reduction shown in Chapters 2 & 3 to the post-saccadic response changes shown in Chapter 4 – arguing that saccadic suppression can be viewed as part of a more general process to improve post-saccadic vision.Ph.D.Includes bibliographical referencesby Jonathan Simon Gue
Investigating the emergence of problem-solving behaviors in Physarum polycephalum from self-organized physical and biochemical interactions within a single cell
No full textDecision-making refers to the process by which living organisms, ranging from animals to plants, bacteria, and single-celled entities, evaluate and choose among different options or courses of action to enhance their chances of survival, growth, and reproduction. While animals with centralized nervous systems often exhibit specialized decision-making, many other organisms lacking such systems rely on intricate self-organized cellular processes to navigate their environments and make choices that optimize their chances of success. This dissertation probes decision-making dynamics in non-neuronal organisms, focusing on the unicellular slime mold Physarum polycephalum as a model system.
In this dissertation, I examine the role of cytoskeletal forces, chemical signaling, mechanical properties, and fluid dynamics in shaping problem-solving behaviors in Physarum. I begin by exploring the relationship between cytoskeletal mechanisms and decision-making. Through experimentation, I established a correlation between the slime mold's preference for nutrient sources and actin filament distribution. Disruption of actin validates its influence on cell movement, proposing a mechanism involving Ca2+-sensitive actin-severing proteins and calcium gradients.
Moving forward, I develop a computational model that integrates biochemical and biophysical components to decipher resource allocation in Physarum. This model captures the organism's oscillatory behaviors, resource allocation dynamics, and information flow patterns, offering insights into the complex decision-making processes involved. Expanding our investigation, I employed a two-dimensional phase-field method to better understand network formation and decision-making in the organism and decision-making in the organism. Through simulations, I uncover how migration decisions could stem from a combination of mechanical properties and intracellular signaling, enabling the organism to navigate the Exploration versus Exploitation tradeoff effectively.
This study provides a mechanistic exploration of decision-making processes in non-neuronal organisms, using Physarum polycephalum as a model system. By investigating the interplay of cytoskeletal forces, chemical signaling, mechanical properties, and fluid dynamics, I uncover the roles of cellular mechanisms underlying problem-solving behaviors. These findings contribute to a deeper understanding of how decentralized control mechanisms drive decision-making without a centralized nervous system. This work not only enhances our comprehension of the adaptive strategies employed by basal eukaryotes but also offers insights into the evolution of problem-solving systems across diverse biological contexts.Ph.D.Includes bibliographical reference
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