I. Development of novel silicon precursors for rapid and efficient radiofluorination reactions: synthesis and biological evaluation of a 18f-labelled estrogen dendrimer conjugate II. Other studies on 18f-labelled estrogens

Carroll, Vincent

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Description

Title

I. Development of novel silicon precursors for rapid and efficient radiofluorination reactions: synthesis and biological evaluation of a 18f-labelled estrogen dendrimer conjugate II. Other studies on 18f-labelled estrogens

Author(s)

Carroll, Vincent

Issue Date

2012-09-04

Director of Research (if dissertation) or Advisor (if thesis)

Katzenellenbogen, John A.

Doctoral Committee Chair(s)

Katzenellenbogen, John A.

Committee Member(s)

• Katzenellenbogen, Benita S.
• Silverman, Scott K.
• Hergenrother, Paul J.

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• 2-fluoroestradiol
• estrogen dendrimer conjugate
• estrogen receptor
• fluorine-18

Abstract

Molecular imaging (MI) has revolutionized the visualization of complex biochemical processes in normal physiology and diseased states. Although still in its infancy, the data generated from MI studies aids in identifying sites of pathological involvement and provides key insight into the mechanisms that lead to the onset and progression of disease. Consequently, these techniques hold tremendous potential in the areas of diagnostics, therapy assessment, and drug development in the coming years. Amongst MI techniques, Positron Emission Tomography (PET) separates itself from the rest of the field with its exceptional sensitivity, near limitless depth of penetration and its ability to quantify metabolic processes in living patients. With the ability to visualize and quantify on an individualized basis, PET imaging has received considerable attention recently because of its potential for contributing to personalized medicine. Through better diagnosis, rational selection of targeted therapies, and individualization of therapy regimens for each patient, personalized medicine holds the promise of greatly improving patient outcomes as well as safeguarding against the use of unnecessary, harmful medical procedures. Given the current status of the PET field and the impact it has on many fields, significant effort is being made to expand the existing repertoire of imaging agents capable of further detailing pathophysiological processes beyond the most commonly used PET tracer, [18F]fluorodeoxyglucose, including the use of large, sensitive biomolecules such as peptides and antibodies, which may be of considerable clinical importance. However, the available methodology associated with PET isotope incorporation, specifically fluorine-18, involves rather harsh conditions that are incompatible with sensitive substrates, which restricts the availability of these agents and their subsequent clinical evaluation. Thus, there remains a tremendous need for rapid, mild and efficient methodology that can be used to label these previously inaccessible substrates in a direct, late-stage fashion. Chapter 1 presents a brief introduction into molecular imaging and the techniques available for use in the preclinical and clinical setting as well as in drug development. Additionally, the basics of PET principles and radiochemistry are introduced, with a significant focus on the synthetic difficulties involved in working with the most commonly used PET isotope, fluorine-18, and why there is a need for improved methodology for its incorporation into new radiopharmaceutical agents, especially sensitive ones. Chapter 2 details the development of methodology that targets the shortcomings of C-18F strategies through Si-18F bond formation approaches. We have developed a simple and straightforward strategy in radiofluorinating complex substrates at a late stage, at room temperature, or in an aqueous environment in high radiochemical yields and specific activities through a reactive silyl acetate moiety. The utility and versatility of the approach is showcased in three main areas of research: small adaptor molecules, small molecules, and peptides. We have applied this Si-18F labeling strategy (Chapter 3) to prepare a fluorine-18 labeled version of 17α-ethynylestradiol conjugated PAMAM dendrimer that can be used for in vivo distribution studies of this novel hormone-polymer conjugate. Through biodistribution studies, we have found that the EDC, a dendrimer-bound estrogen that provides selective cardiovascular protection without classical stimulation of uterus and mammary tissues, also shows selective, ER-mediated uptake and retention by the vascular target tissues, heart and aorta, but not the classical target, the uterus. These findings suggest that the selective cardiovascular protective effect of EDC is the result of two factors, one mechanistic (selective stimulation of the extra-nuclear pathway of ER action) and one pharmacokinetic (selective accumulation of EDC in vascular targets). This points to a new dimension for extending the selective, potentially beneficial actions of estrogens. Chapter 4 details the synthetic approaches towards the radiosynthesis a promising ER imaging agent, 2-[18F]fluoroestradiol, and illustrates the most well-known difficulty encountered in fluorine-18 chemistry, specifically the radiofluorination of electron-rich aromatic rings. Efforts have focused on the use of diaryliodonium salts which has afforded synthetically useful radiochemical yields of the desired compound and is currently being scaled up, in terms of radioactivity, for evaluation in animal studies.

Graduation Semester

2012-12

Type of Resource

text

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http://hdl.handle.net/2142/95662

Copyright and License Information

Copyright 2012 Vincent Carroll

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