Development of novel compounds for the molecular imaging of hypoxia: 18F-labeled nitroimidazoles and hypoxia inducible factor 1 alpha (HIF-1a)-targeting compounds

• Author / Creator

  Woodfield, Jenilee D

• Imaging of hypoxia has been previously achieved using positron emission tomography (PET) with radiotracers such as [18F]fluoroazomycin arabinoside ([18F]FAZA) [1] or [18F]fluoromisonidazole ([18F]FMISO) [2]. These typical nitroimidazole containing compounds are reductively trapped in hypoxic areas. Herein, we propose two novel ways to imaging hypoxia, one with a novel 2-nitroimidazole of N-(4-[18F]fluorobenzyl)-2-(2-nitro-1H-imidazol-1-yl)-acetamide ([18F]FBNA). Secondly, we propose to directly image the master regulator of hypoxia of hypoxia inducible factor 1 alpha (HIF-1a). We will comparatively assess the imaging of HIF-1a versus traditional imaging agents of [18F]FMISO, [18F]FAZA and the novel 2-nitroimidazole imaging agent of [18F]FBNA.
  We have developed two lead structures that bind to HIF-1a, and have radiolabelled them using [18F]fluorine prosthetic group chemistry. [18F]SFB-link-c-(Ppg)LLFVY was prepared using the prosthetic group of [18F]SFB and the primary amine containing peptide link-c-(Ppg)LLFVY. [18F]SFB-link-c-(Ppg)LLFVY was prepared in 66.2 ± 5.4% decay corrected recovered radiochemical yield from [18F]fluoride (n=8) with a purity >99%. [18F]FPeP4 was prepared using Pd-mediated SONOGASHIRA cross-coupling reaction between [18F]FPA and N-(4-iodophenyl)-4-((4-(pyridine-3-ylmethyl)piperazin-1-yl)methyl)benzamide. [18F]FPeP4 was prepared in 5 ± 2% decay corrected recovered radiochemical yield from [18F]fluoride (n=5) with a purity >99%. Novel nitroimidazole [18F]FBNA was synthesized starting from the prosthetic group of [18F]FBAmine. [18F]FBNA was prepared in 47.4 ± 5.4% decay corrected recovered radiochemical yield from [18F]FBAmine (n=8) with a purity >99%.
  Radiopharmacological profile of [18F]FPeP4, [18F]SFB-link-c-(Ppg)LLFVY and [18F]FBNA were evaluated in comparison to [18F]FAZA and [18F]FMISO using triple negative breast cancer cell line MDA-MB-231. In HIF-1a overexpressing MDA-MB-231 cells, cellular uptake of [18F]SFB-link-c-(Ppg)LLFVY reached an internalized maximum of 30% applied radioactivity/mg protein at 120 min and [18F]FPeP4 reached an internalized maximum of 400% applied radioactivity/mg protein at 120 min. In non-transfected hypoxic MDA-MB-231 cells, [18F]FBNA reached an internalized maximum of 9% applied radioactivity/mg protein at 120 min in hypoxic conditions.
  Radiopharmacological evaluation of all compounds included small animal PET imaging. Small animal PET studies of both HIF-1a targetting radiotracers demonstrated poor tumor uptake compared to [18F]FAZA, [18F]FMISO and [18F]FBNA. This was due to the poor pharmacokinetics of these radiotracers in vivo, with both radiotracers exhibiting large amounts of first pass liver trapping. [18F]FPeP4 demonstrated a SUVmax of 0.3 in MCF7 tumor bearing NIH-III mice compared to [18F]FBNA which had a SUVmax of 0.75. Tumor to muscle ratio of [18F]FBNA in MFC-7 tumor model was 3 which was equal to [18F]FPeP4 at 3. Yet, [18F]FBNA was found to be metabolically unstable, whereas [18F]FPeP4 was metabolically stable.
  [18F]SFB-link-c-(Ppg)LLFVY and [18F]FPeP4 are the first novel radiotracers to be designed that bind to HIF-1a. Their in vitro uptake showed increased uptake in HIF-1a overexpressing cells, yet their biodistribution in vivo is currently poor. Improvements to the delivery of these radiotracers in vivo could improve their future usage as radiotracers targeting HIF-1a.

• Subjects / Keywords

  • PET
  • Radiochemistry
  • HIF-1a
  • Hypoxia
  • Breast Cancer

• Graduation date

  Spring 2023

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-2cqe-hx59

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.