University of Groningen
Development of PET tracers for investigation of arginase-related pathways
dos Santos Clemente, Gonçalo
DOI:
10.33612/diss.143845684
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date: 2020
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
dos Santos Clemente, G. (2020). Development of PET tracers for investigation of arginase-related pathways. University of Groningen. https://doi.org/10.33612/diss.143845684
Copyright
Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
Take-down policy
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum.
Chapter 1
Background and aim
Molecular imaging is a discipline in clinical healthcare and research that comprises a succession of procedures with the ultimate purpose of detecting, preferably at the earliest possible stage, molecular changes that can be associated with the genesis or progression of diseases (Figure 1). Specific pathological mechanisms can be unraveled and understood by targeting the appropriate biomarkers with an imaging agent, which enables to monitor the dynamics, localization, and expression of the target, and may enhance the development of more effective therapies.
Figure 1. Key steps involved in the development of a molecular imaging study.
In addition to being decisive for the staging of several diseases, these minimally invasive molecular imaging techniques have also shown great potential to aid in drug development by assessing the pharmacokinetics and pharmacodynamics within living subjects in real-time, and are considered a key strategy towards personalized medicine [1]. Therefore, the quest for new biomarkers by which a particular pathological process can be identified, being indicators of disease progression and prognosis, is a continuously active field in medicinal chemistry [2]. Arginase, a vital enzyme of the urea cycle that catalyzes the hydrolysis of ʟ-arginine to ʟ-ornithine and urea, has been regarded as a potential biomarker of disease progression. With two isoforms widespread throughout the body, the action of arginase goes far beyond the boundaries of hepatic ureogenic function. The production of ʟ-ornithine, while competing with nitric oxide synthase (NOS) for the same physiological substrate (ʟ-arginine), can influence the endogenous levels of polyamines, proline, and NO•. Several pathophysiological processes may
deregulate the subtle arginase/NOS balance, disturbing essential signaling pathways that maintain the homeostasis and functionality of the organism. Thus, an upregulated expression of arginase can be associated with several pathological processes that range from cardiovascular, immune-mediated, inflammatory, and tumorigenic conditions to neurodegenerative disorders [3].
Although it has long been known that arginase might be involved in pathological or counter-regulatory mechanisms of several diseases, it was only recently that this enzyme emerged as a potential therapeutic target, stimulating the development of highly potent arginase inhibitors [4]. As arginase is a potential biomarker of disease and a novel therapeutic target, it was hypothesized that these arginase inhibitors might have a second life outside pharmacological applications by being used as reference scaffolds to develop molecular imaging probes. These probes might aid in the early clinical detection of changes in arginase expression that are intrinsically related to poor prognosis and severity. Additionally, it was also proposed that the challenge of a real-time assessment, within living subjects, of the pharmacokinetic suitability and therapeutic efficacy of the arginase inhibitors can be facilitated by the use of molecular imaging.
Another phenomenon that has attracted research interest, and whose mechanisms are still subject of discussion, is the potential therapeutic implication of statin-induced arginase/NOS signaling pathways, particularly the possibility of statins to influence the levels of polyamines or NO• [5]. These implications brought
the perspective of the therapeutic use of statins in some of the most prevalent pathologies, such as cardiovascular disease [6], cancer [7], and especially
Chapter 1: General introduction
asthma [8]. Therefore, the development of a specific "toolbox" of molecular imaging probes that can be used to map arginase expression, and to assess statin-related mechanisms of action, might provide a basis to support the design of further research aiming to identify the spectrum of pleiotropic and off-target effects of statins, including possible interactions with ʟ-arginine metabolic pathways.
Outline of the thesis
Driven by the potential of arginase as a biomarker of disease progression, chapter 2 reviews the pathophysiological role of this enzyme and brings a new perspective regarding the use of arginase inhibitors as scaffolds for the development of molecular imaging probes. Among molecular imaging modalities, positron emission tomography (PET) has an ideal combination of essential features, such as high detection and quantification sensitivity, penetration depth, and spatiotemporal resolution, being especially suitable for mapping subcellular processes in vivo [9]. The production of small molecules labeled with β+-emitting radionuclides to be
used as PET imaging agents requires the establishment of reliable procedures, therefore recently developed and published late-stage labeling methods should be customized. Thus, chapter 3 describes a copper-mediated 18F-fluorodeboronation
strategy suitable for the radiolabeling of non-activated (hetero)arenes [10]. This radiolabeling strategy was implemented for the first time in the radiochemistry laboratory of the Nuclear Medicine and Molecular Imaging (NGMB) department of the University Medical Center of Groningen (UMCG) by using, as a preliminary proof-of-concept test, several biorelevant arylboronic acid pinacol ester precursors synthesized via convergent multicomponent reactions (MCR). This optimized
18F-fluorodeboronation strategy was then used to synthesize and evaluate the first
radiolabeled arginase inhibitors reported in the literature. The results of these experiments, including the successful PET mapping of the arginase expression in preclinical models of allergic asthma and carcinoma, are described in chapter 4.
Chapter 5 presents an overview of the potential impact of statins on ʟ-arginine
metabolic pathways. Thus, to develop a potential molecular imaging tool for assessing statin-related mechanisms of action, a radiofluorinated analog of atorvastatin, one of the highest-selling clinically prescribed drugs and a potent fluorine-containing statin, was synthesized for the first time using different labeling strategies.
In chapter 6, the radiofluorination of atorvastatin was attempted via the copper-mediated 18F-fluorodeboronation strategy previously optimized and
successfully applied to the radiolabeling of arginase inhibitors. However, the final yields achieved with this radiolabeling strategy were very modest and unreliable, not being compatible with further in vivo applications.
To improve the synthesis of [18F]atorvastatin, another recently developed
late-stage radiofluorination strategy was attempted: the Ru-intermediated
18F-deoxyfluorination of phenols. Due to its novelty and some practical drawbacks,
this radiolabeling strategy still lacks multicenter assessments and was established for the first time in the radiochemistry laboratory of the NGMB department of the UMCG. Although the previous reports [11] had some practical disadvantages, which hindered broader applications, a newly enhanced, optimized, and easily automated approach is described in chapter 7. The successful and facilitated synthesis of [18F]atorvastatin enabled further evaluations in an atherosclerotic ex vivo model,
and the pharmacokinetics of this radiotracer in healthy female and male rats is evaluated in chapter 8.
Finally, chapter 9 summarizes the studies performed and describes future perspectives with concluding remarks.
References
[1] M. L. James, S. S. Gambhir, Physiol Rev, 2012, 92, 897.
[2] L. Zhang, S. Wan, Y. Jiang, et al., J Am Chem Soc, 2017, 139, 2532.
[3] R. W. Caldwell, P. C. Rodriguez, H. A. Toque, et al., Physiol Rev, 2018, 98, 641. [4] M. Pudlo, C. Demougeot, C. Girard-Thernier, Med Res Rev, 2017, 37, 475. [5] A. M. Gorabi, N. Kiaie, S. Hajighasemi, et al., J Clin Med, 2019, 8, 2051.
[6] a) E. Kosenko, L. Tikhonova, A. Suslikov, et al., J Clin Pharmacol, 2012, 52, 102; b) L. A. Holowatz, W. L. Kenney, Am J Physiol Regul Integr Comp Physiol, 2011, 301, R763; c) L. A. Holowatz, L. Santhanam, A. Webb, et al., J Physiol, 2011, 589, 2093.
[7] a) H. Erbaş, O. Bal, E. Çakır, Balk Med J, 2015, 32, 89; b) S. Kotamraju, C. L. Willams, B. Kalyanaraman, Cancer Res, 2007, 67, 7386; c) A. Sassano, L. C. Platanias, Cancer Lett, 2008, 260, 11.
[8] a) A. L. Linderholm, J. M. Bratt, G. U. Schuster, et al., Immunol Allergy Clin North Am, 2014, 34, 809; b) A. A. Zeki, Curr Med Res Opin, 2014, 30, 1051; c) C. Yuan, L. Zhou, J. Cheng, et al., Respir Res, 2012, 13, 108; d) A. A. Zeki, J. M. Bratt, M. Rabowsky, et al., Transl Res, 2010, 156, 335; e) A. A. Zeki, M. Elbadawi-Sidhu, Expert Rev Respir Med, 2018, 12, 461.
[9] D. L. Bailey, D. W. Townsend, P. E. Valk, et al., Positron Emission Tomography: Basic Sciences, Springer London, 2005.
[10] M. Tredwell, S. M. Preshlock, N. J. Taylor, et al., Angew Chem Int Ed, 2014, 53, 7751.
[11] a) M. H. Beyzavi, D. Mandal, M. G. Strebl, et al., ACS Cent Sci, 2017, 3, 944; b) M. G. Strebl, A. J. Campbell, W.-N. Zhao, et al., ACS Cent Sci, 2017, 3, 1006; c) J. Rickmeier, T. Ritter, Angew Chem Int Ed, 2018, 57, 14207.
