Imaging PARP with [18F]rucaparib in pancreatic cancer models

Supplementary Information is available online at: https://link.springer.com/article/10.1007/s00259-022-05835-4#Sec18 .Purpose: Rucaparib, an FDA-approved PARP inhibitor, is used as a single agent in maintenance therapy to provide promising treatment efficacy with an acceptable safety profile in various types of BRCA-mutated cancers. However, not all patients receive the same benefit from rucaparib-maintenance therapy. A predictive biomarker to help with patient selection for rucaparib treatment and predict clinical benefit is therefore warranted. With this aim, we developed [18F]rucaparib, an 18F-labelled isotopologue of rucaparib, and employed it as a PARP-targeting agent for cancer imaging with PET. Here, we report the in vitro and in vivo evaluation of [18F]rucaparib in human pancreatic cancer models. Method: We incorporated the positron-emitting 18F isotope into rucaparib, enabling its use as a PET imaging agent. [18F]rucaparib binds to the DNA damage repair enzyme, PARP, allowing direct visualisation and measurement of PARP in cancerous models before and after PARP inhibition or other genotoxic cancer therapies, providing critical information for cancer diagnosis and therapy. Proof-of-concept evaluations were determined in pancreatic cancer models. Results: Uptake of [18F]rucaparib was found to be mainly dependent on PARP1 expression. Induction of DNA damage increased PARP expression, thereby increasing uptake of [18F]rucaparib. In vivo studies revealed relatively fast blood clearance of [18F]rucaparib in PSN1 tumour-bearing mice, with a tumour uptake of 5.5 ± 0.5%ID/g (1 h after i.v. administration). In vitro and in vivo studies showed significant reduction of [18F]rucaparib uptake by addition of different PARP inhibitors, indicating PARP-selective binding. Conclusion: Taken together, we demonstrate the potential of [18F]rucaparib as a non-invasive PARP-targeting imaging agent for pancreatic cancers.This research was supported by Cancer Research UK through the Oxford Institute for Radiation Oncology, Medical Research Council (MRC) (MR/R01695X/1, G.D. and F.G., and H3R00580, C.Y.C) and Pancreatic Cancer UK (PCUK H3R00510, C.Y.C)

[123I]CC1: A PARP-Targeting, Auger Electron–Emitting Radiopharmaceutical for Radionuclide Therapy of Cancer

Poly(adenosine diphosphate ribose) polymerase (PARP) has emerged as an effective therapeutic strategy against cancer that targets the DNA damage repair enzyme. PARP-targeting compounds radiolabeled with an Auger electron–emitting radionuclide can be trapped close to damaged DNA in tumor tissue, where high ionizing potential and short range lead Auger electrons to kill cancer cells through the creation of complex DNA damage, with minimal damage to surrounding normal tissue. Here, we report on [123I]CC1, an 123I-labeled PARP inhibitor for radioligand therapy of cancer. Methods: Copper-mediated 123I iododeboronation of a boronic pinacol ester precursor afforded [123I]CC1. The level and specificity of cell uptake and the therapeutic efficacy of [123I]CC1 were determined in human breast carcinoma, pancreatic adenocarcinoma, and glioblastoma cells. Tumor uptake and tumor growth inhibition of [123I]CC1 were assessed in mice bearing human cancer xenografts (MDA-MB-231, PSN1, and U87MG). Results: In vitro and in vivo studies showed selective uptake of [123I]CC1 in all models. Significantly reduced clonogenicity, a proxy for tumor growth inhibition by ionizing radiation in vivo, was observed in vitro after treatment with as little as 10 Bq [123I]CC1. Biodistribution at 1 h after intravenous administration showed PSN1 tumor xenograft uptake of 0.9 ± 0.06 percentage injected dose per gram of tissue. Intravenous administration of a relatively low amount of [123I]CC1 (3 MBq) was able to significantly inhibit PSN1 xenograft tumor growth but was less effective in xenografts that expressed less PARP. [123I]CC1 did not cause significant toxicity to normal tissues. Conclusion: Taken together, these results show the potential of [123I]CC1 as a radioligand therapy for PARP-expressing cancers

Correlation between molar activity, injection mass and uptake of the PARP targeting radiotracer [18F]olaparib in mouse models of glioma

Supplementary information is available online at: https://ejnmmires.springeropen.com/articles/10.1186/s13550-022-00940-9#Sec15 .Purpose: Radiopharmaceuticals targeting poly(ADP-ribose) polymerase (PARP) have emerged as promising agents for cancer diagnosis and therapy. PARP enzymes are expressed in both cancerous and normal tissue. Hence, the injected mass, molar activity and potential pharmacological effects are important considerations for the use of radiolabelled PARP inhibitors for diagnostic and radionuclide therapeutic applications. Here, we performed a systematic evaluation by varying the molar activity of [18F]olaparib and the injected mass of [TotalF]olaparib to investigate the effects on tumour and normal tissue uptake in two subcutaneous human glioblastoma xenograft models. Methods: [18F]Olaparib uptake was evaluated in the human glioblastoma models: in vitro on U251MG and U87MG cell lines, and in vivo on tumour xenograft-bearing mice, after administration of [TotalF]olaparib (varying injected mass: 0.04–8.0 µg, and molar activity: 1–320 GBq/μmol). Results: Selective uptake of [18F]olaparib was demonstrated in both models. Tumour uptake was found to be dependent on the injected mass of [TotalF]olaparib (µg) but not the molar activity. An injected mass of 1 μg resulted in the highest tumour uptake (up to 6.9 ± 1.3%ID/g), independent of the molar activity. In comparison, both the lower and higher injected masses of [TotalF]olaparib resulted in lower relative tumour uptake (%ID/g; P 18F]olaparib intratumoural uptake correlated with PARP1 expression. Substantial upregulation of PARP1-3 expression was observed after administration of [TotalF]olaparib (> 0.5 µg). Conclusion: Our findings show that the injected mass of [TotalF]olaparib has significant effects on tumour uptake. Moderate injected masses of PARP inhibitor-derived radiopharmaceuticals may lead to improved relative tumour uptake and tumour-to-background ratio for cancer diagnosis and radionuclide therapy.Pancreatic Cancer U.K.; the Pancreatic Cancer Research Fund; CRUK through the Oxford Institute for Radiation Oncology, the CRUK Oxford Centre, and the CRUK/EPSRC Imaging Centre in Oxford; the EPSRC (EP/L025604/1, NS/A000024/1); and CRUK C5255/A16466

Copper-mediated radiosynthesis of [18F]rucaparib

The poly(ADP-ribose) polymerase (PARP) inhibitor rucaparib is used in the clinic to treat&nbsp;BRCA-mutated cancers. Herein, we report two strategies to access the&nbsp;18F-isotopologue of rucaparib by applying a copper-mediated nucleophilic&nbsp;18F-fluorodeboronation. The most successful approach features an aldehydic boronic ester precursor that is subjected to reductive amination post-18F-labeling and affords [18F]rucaparib with an activity yield of 11% &plusmn; 3% (n&nbsp;= 3) and a molar activity (Am) up to 30 GBq/&mu;mol. Preliminary&nbsp;in vitro&nbsp;studies are presented.</p

Radiosynthesis of [18F]ArylSCF2H using aryl boronic acids, S-(chlorofluoromethyl)benzenesulfonothioate and [18F]fluoride

Herein, we report a mild and practical protocol for the copper-catalyzed chlorofluoromethylthiolation of (hetero)aryl boronic acids with the novel reagent PhSO2SCFClH. The resulting products are amenable to halogen exchange 18F-fluorination with cyclotron-produced [18F]fluoride affording [18F]ArSCF2H. This process highlights the combined value of reagent development and (hetero)aryl boron precursors for radiochemistry by adding the [18F]SCF2H group to the list of 18F-motifs within reach for positron emission tomography studies

[18F]AZD2461, an insight on difference in PARP binding profiles for DNA damage response PET imaging

Purpose Poly(ADP-ribose) polymerase (PARP) inhibitors are extensively studied and used as anti-cancer drugs, as single agents or in combination with other therapies. Most radiotracers developed to date have been chosen on the basis of strong PARP1-3 affinity. Herein, we propose to study AZD2461, a PARP inhibitor with lower affinity towards PARP3 and to investigate its potential for PARP targeting in vivo . Procedures Using the Cu-mediated 18 F-fluorodeboronation of a carefully designed radiolabelling precursor, we accessed the 18 F-labeled isotopologue of the PARP inhibitor AZD2461. Cell uptake of [ 18 F]AZD2461 in vitro was assessed in a range of pancreatic cell lines (PSN-1, PANC-1, CFPAC-1 and AsPC-1) to assess PARP expression, and in vivo in xenograft-bearing mice. Blocking experiments were performed with both olaparib and AZD2461. Results [ 18 F]AZD2461 was efficiently radiolabelled via both manual and automated procedures (9% ± 3% and 3% ± 1% Activity yields non-decay corrected). [ 18 F]AZD2461 was taken up in vivo in PARP1-expressing tumours and the highest uptake was observed for PSN-1 cells (7.34 ± 1.16%ID/g). In vitro blocking experiments showed a lesser ability of olaparib to reduce [ 18 F]AZD2461 binding, indicating a difference in selectivity between olaparib and AZD2461. Conclusion Taken together, we show the importance of screening the PARP selectivity profile of radiolabelled PARP inhibitors for use as PET imaging agents

Manual and automated Cu-mediated radiosynthesis of the PARP inhibitor [18F]olaparib

Positron emission tomography (PET) is a diagnostic nuclear imaging modality that relies on automated protocols to prepare agents labeled with a positron-emitting radionuclide (e.g., 18F). In recent years, new reactions have appeared for the 18F-labeling of agents that are difficult to access by applying traditional radiochemistry, for example those requiring 18F incorporation into unactivated (hetero)arenes. However, automation of these new methods for translation to the clinic has progressed slowly because extensive modification of manual protocols is typically required when implementing novel 18F-labeling methodologies within automated modules. Here, we describe the workflow that led to the automated radiosynthesis of the poly(ADP-ribose) polymerase (PARP) inhibitor [18F]olaparib. First, we established a robust manual protocol to prepare [18F]olaparib from the protected N-[2-(trimethylsilyl)ethoxy]methyl (SEM) arylboronate ester precursor in a 17% ± 5% (n = 15; synthesis time, 135 min) non-decay-corrected (NDC) activity yield, with molar activity (Am) up to 34.6 GBq/µmol. Automation of the process, consisting of copper-mediated 18F-fluorodeboronation followed by deprotection, was achieved on an Eckert & Ziegler Modular-Lab radiosynthesis platform, affording [18F]olaparib in a 6% ± 5% (n = 3; synthesis time, 120 min) NDC activity yield with Am up to 319 GBq/µmol

F-18-Trifluoromethanesulfinate Enables Direct C-H F-18-Trifluoromethylation of Native Aromatic Residues in Peptides

18F-Labeling strategies for unmodified peptides with [18F]fluoride require 18F-prosthetics for bioconjugation more often with cysteine thiols or lysine amines. Here, we explore selective radical chemistry to target aromatic residues applying C–H 18F-trifluoromethylation. We report a one-step route to [18F]CF3SO2NH4 from [18F]fluoride, and its application to direct [18F]CF3-incorporation at tryptophan or tyrosine residues using unmodified peptides as complex as recombinant human insulin. The fully automated radiosynthesis of octreotide[Trp(2-CF218F)] enables in vivo PET imaging

18F-trifluoromethanesulfinate enables direct C–H 18F-trifluoromethylation of native aromatic residues in peptides

18F-Labeling strategies for unmodified peptides with [18F]fluoride require 18F-prosthetics for bioconjugation more often with cysteine thiols or lysine amines. Here, we explore selective radical chemistry to target aromatic residues applying C–H 18F-trifluoromethylation. We report a one-step route to [18F]CF3SO2NH4 from [18F]fluoride, and its application to direct [18F]CF3-incorporation at tryptophan or tyrosine residues using unmodified peptides as complex as recombinant human insulin. The fully automated radiosynthesis of octreotide[Trp(2-CF218F)] enables in vivo PET imaging