Browsing by Author "Wotherspoon, ATL"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    ANSTO Nuclear Foresnics Research Facility: method development and applications
    (Australian Nuclear Science and Technology Organisation, 2012-10-16) Wotherspoon, ATL; Hill, DM; Keegan, EA; Evans, T; Blagojevic, N; Loi, E; Toole, K; Griffiths, GJ; Smith, KL; Reinhard, MI
    The IAEA defines nuclear forensic science, commonly shortened to “nuclear forensics” as ‘the scientific analysis of nuclear or other radioactive material, or of other evidence that is contaminated with radioactive material, in the context of legal proceedings, including administrative, civil, criminal or international law’1. In broad terms, the job of the nuclear forensic scientist is to support investigations that involve a nuclear security event. Nuclear forensic examinations will provide information to key questions posed by the investigative authority: What is it? How much is there? Is there any more out there? Is it ours? As an investigation proceeds other questions that may arise are; How old is it? What contaminants are present? Does it pose a threat? Who is responsible for the loss? Where did the material come from? Many of the techniques required to answer these questions are based on environmental radiochemistry. The Nuclear Forensic Research Facility (NFRF) at ANSTO is developing expertise in analysing nuclear and other radioactive material material based upon the precepts of the ‘model action plan’ of the International Technical Working Group for Nuclear Forensics (ITWG) and other best practices. We are also investigating the validity of traditional forensic techniques (like fingerprints and DNA) on evidence contaminated with radioactive material alongside more novel parameters, e.g. the isotopic composition at the ‘bulk’ material and the micro scale using advanced micro-analytical techniques. We are moving towards the integration of a range of radio analytical techniques such as mass spectrometry, electron microscopy and the simulation/modelling of material production signatures, to provide a range of different information streams to assist attribution. With each advance in our technical competencies we enhance our means to ensure the security of nuclear or other radioactive material.
  • Thumbnail Image
    Item
    Fluorine-18 radiolabelling and in vitro / in vivo metabolism of [18F]D4-PBR111
    (John Wiley & Sons, Inc, 2019-05-26) Wyatt, NA; Safavi-Naeini, M; Wotherspoon, ATL; Arthur, A; Nguyen, AP; Parmar, A; Hamze, H; Day, CM; Zahra, D; Matesic, L; Davis, E; Rahardjo, GL; Yepuri, NR; Shepherd, R; Murphy, RB; Pham, TQ; Nguyen, VH; Callaghan, PD; Holden, PJ; Grégoire, MC; Darwish, TA; Fraser, BH
    Objectives The purinergic receptor P2X ligand-gated ion channel type 7 (P2X7R) is an adenosine triphosphate (ATP)-gated ion-channel, and P2X7R is a key player in inflammation. P2X7R is an emerging therapeutic target in central nervous system (CNS) diseases including Alzheimer's disease (AD) and Parkinson's disease (PD), because P2X7R also plays a pivotal role in neuroinflammation. P2X7R represents a potential molecular imaging target for neuroinflammation via biomedical imaging technique positron emission tomography (PET), and several radioligands targeting P2X7R have been developed and evaluated in animals. In our previous work, we have developed and characterized [11C]GSK1482160 as a P2X7R radioligand for neuroinflammation,2 clinical evaluation of [11C]GSK1482160 in healthy controls and patients is currently underway, and the estimation of radiation dosimetry for [11C]GSK1482160 in normal human subjects has been reported.3 Since the half-life (t1/2) of radionuclide carbon-11 is only 20.4 min, it is attractive for us to develop derivatives of [11C]GSK1482160, which can be labeled with the radionuclide fluorine-18 (t1/2, 109.7 min), and a fluorine-18 ligand would be ideal for widespread use.4 To this end, a series of [18F]fluoroalkyl including [18F]fluoromethyl (FM), [18F]fluoroethyl (FE), and [18F]fluoropropyl (FP) derivatives of GSK1482160 have been prepared and examined as new potential P2X7R radioligands. © 2019 The Authors
  • Thumbnail Image
    Item
    A rapid MS/MS method to assess the deuterium kinetic isotope effect and associated improvement in the metabolic stability of deuterated biological and pharmacological molecules as applied to an imaging agent
    (Elsevier B. V., 2019-08-08) Murphy, RB; Wyatt, AN; Fraser, BH; Yepuri, NR; Holden, PJ; Wotherspoon, ATL; Darwish, TA
    The deuterium kinetic isotope effect has been known for a period of 40 years, but it is only relatively recently that new drug entities (NDEs) incorporating deuterium demonstrating beneficial pharmacokinetics, pharmacodynamics, and toxicology have arrived to market. Determination of the precise location to deuterate and subsequently any evaluation for a kinetic isotope effect (KIE) is challenging. Typically, such an evaluation would be performed in an in vitro metabolic assay (e.g. liver microsomes) in separate reaction media for both the deuterated and non-deuterated analogues. Here, we have devised an approach whereby we incubate a 1:1 ratio of both the deuterated and protio-form of an imaging agent together in the same liver microsomal assay and determine the relative rate of consumption of both moieties, based upon specific MS-MS transitions unique to both molecules without the need for liquid chromatography-mass spectrometry (LC-MS) separation and quantification. Any deviation of the ratio of the MS transitions from the initial starting point indicated an observable KIE. A site specific deuteration of PBR111, a neuroinflammation imaging agent, was chosen for a proof-of-concept study. Based upon prior mechanistic knowledge of PBR111, two locations were selected for deuteration; an active and inactive site, to corroborate that there was no significant KIE for the inactive site and confirm the efficacy of the developed methodology. Crown Copyright © 2019 Published by Elsevier B.V.
  • Thumbnail Image
    Item
    To D or not to D – an in vitro/mass spectrometry screening method to confirm improved metabolic stability in deuterium-labelled radiotracers
    (Australian Nuclear Science and Technology Organisation, 2019-09-03) Murphy, RB; Wyatt, NA; Fraser, BH; Yepuri, NR; Holden, PJ; Wotherspoon, ATL; Darwish, TA
    Deuteration, where hydrogen within molecules is switched with the non-radioactive and naturally occurring isotope deuterium, can lead to enhanced material properties. For example, the deuterium kinetic isotope effect is well known to improve the metabolic stability of molecules such as drugs, as the C–D bond is stronger and more difficult for enzymes to break than the C–H bond. However, the specific molecular location to deuterate to gain a metabolically favourable outcome may not be clear, without undertaking separate assays of both the deuterated and non-deuterated molecules, followed by separate HPLC-UV/radiometric measurement. In the case of compounds which also contain a radiolabel (e.g. radiotracers for diagnostic medical imaging), specialist infrastructure and teams are required, and chemical synthesis and bioanalysis are time-critical. Our ongoing work with the radiotracer [18F]PBR111, a TSPO ligand showing potential for imaging neuroinflammation1,2,3, demonstrated that [18F]PBR111-d4 (where d4 is incorporated at a specific site) has slower metabolic breakdown4,5 and a decreased rate of formation of polar metabolites in vitro (rat and human liver microsomes) relative to non-deuterated 5,6. Our recently published MS/MS method4 demonstrates the relative difference in metabolic stability without radiolabelling, by analysing different time points from a liver microsome assay which has been administered a 50:50 mixture of deuterated/non-deuterated compound. Pharmacokinetic parameters can also be determined from the data. Deuteration adjacent to the fluoro-alkyl group in PBR111 showed ~50% improvement in the stability of the intact radiotracer relative to non-deuterated using a ratio determination of the analogous MS transitions unique to the deuterated/non-deuterated compounds4. As a control, a second deuterated analogue was also synthesised4 with deuterium purposely incorporated at a site significantly less metabolised than the first site5, which our newly developed method was also able to confirm. We expect this simple and rapid method could be applied to deuterated and non-deuterated analogues of other biologically important molecules to determine the suitability of the chosen site of deuteration. For radiotracers, there is no requirement to radiolabel until studies progress to in vivo PET imaging.