Solid phase radiosynthesis of an olaparib derivative using 4-[18F] fluorobenzoic acid and in vivo evaluation in breast and prostate cancer xenograft models for PARP-1 expression

Nucl Med Biol. 2022 Nov-Dec:114-115:65-70. doi: 10.1016/j.nucmedbio.2022.09.002. Epub 2022 Sep 26.

Abstract

Introduction: Solid-phase synthesis and conjugation reactions of acids and amines using coupling reagents are common in organic synthesis, but rare in 18F radiochemistry. 4-[18F]Fluorobenzoic acid (FBA) is a useful building block, but is seldom used directly with coupling reagents for the preparation of 18F radiopharmaceuticals. To overcome the inconveniences associated with using [18F]FBA in conjugation reactions, we have developed a non-covalent solid-phase synthesis (SPS) strategy for the radiosynthesis of [18F]PARPi, a derivative of olaparib as a Poly (ADP-ribose) polymerase-1 (PARP-1) radioligand.

Methods: Fluoro-, bromo- and iodo-benzoic derivatives of olaparib were synthesized, and their PARP-1 affinities were measured using a recently developed cell culture-based competitive assay. To produce [18F]PARPi, [18F]FBA was radiosynthesized and purified using a cation-exchange cartridge, and then trapped by an anion-exchange resin cartridge, on which the solid-phase radiosynthesis was carried out to produce the desired product. [18F]PARPi was evaluated in vivo in breast and prostate xenograft tumor models by microPET imaging, biodistribution and autoradiography.

Results: The best derivatives of olaparib were identified as compound 4, 7 and 8. [18F]4 ([18F]PARPi) was radiosynthesized in high radiochemical yield, high molar activity and high radiochemical purity using this SPS strategy. The in vivo evaluation of [18F]PARPi demonstrates the PARP-1 specific uptake of [18F]PARPi in the animal models.

Conclusions: This method is simple and efficient, having great potential for the synthesis of radiopharmaceuticals starting from [18F]FBA or other radiolabeled aromatic acids. Using [18F]PARPi prepared by this method, we demonstrated the promise of [18F]PARPi in the nuclear imaging of PARP-1 expression.

Keywords: 4-[(18)F]fluorobenzoic acid; Olaparib; PARP-1; PET imaging; Solid phase radiosynthesis.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Heterografts
  • Humans
  • Male
  • Poly (ADP-Ribose) Polymerase-1 / metabolism
  • Poly(ADP-ribose) Polymerase Inhibitors*
  • Positron-Emission Tomography / methods
  • Prostatic Neoplasms* / diagnostic imaging
  • Radiopharmaceuticals / chemistry
  • Tissue Distribution

Substances

  • olaparib
  • Poly (ADP-Ribose) Polymerase-1
  • Poly(ADP-ribose) Polymerase Inhibitors
  • Radiopharmaceuticals