Imaging Therapeutic PARP Inhibition In Vivo through Bioorthogonally Developed Companion Imaging Agents

Abstract

A number of small-molecule poly (ADP-ribose) polymerase (PARP) inhibitors are currently undergoing advanced clinical trials. Determining the distribution and target inhibitory activity of these drugs in individual subjects, however, has proven problematic. Here, we used a PARP agent for positron emission tomography-computed tomography (PET-CT) imaging ((18)F-BO), which we developed based on the Olaparib scaffold using rapid bioorthogonal conjugation chemistries. We show that the bioorthogonal (18)F modification of the parent molecule is simple, highly efficient, and well tolerated, resulting in a half maximal inhibitory concentration (IC(50)) of 17.9 ± 1.1 nM. Intravital imaging showed ubiquitous distribution of the drug and uptake into cancer cells, with ultimate localization within the nucleus, all of which were inhibitable. Whole-body PET-CT imaging showed tumoral uptake of the drug, which decreased significantly, after a daily dose of Olaparib. Standard (18)F-fludeoxyglucose imaging, however, failed to detect such therapy-induced changes. This research represents a step toward developing a more generic approach for the rapid codevelopment of companion imaging agents based on small-molecule therapeutic inhibitors.

PET of Poly (ADP-Ribose) Polymerase Activity in Cancer: Preclinical Assessment and First In-Human Studies

“…The area under the receiver operating characteristic curve (AUC, in g/mL· min) for 18 F-FTT was assessed in normal mouse organs before and after treatment with olaparib (n = 14), a PARP inhibitor, or iniparib (n = 11), which has no PARP inhibitory activity. Murine biodistribution studies were performed to support human translational studies.…”

“…Murine biodistribution studies were performed to support human translational studies. Eight human subjects with cancer and eight healthy volunteers underwent imaging to verify the human radiation dosimetry of 18 F-FTT. The Wilcoxon signed rank test was used to assess for differences among treatment groups for the mouse studies.…”

Molecular Imaging of PARP

“…High-contrast imaging of PARP1-expressing nuclei in vitro and in vivo implies high cell permeability and rapid washout of unbound PARPi-FL (7,9,11,13,16), indicating that the dye conjugation and resulting increase in molecular weight (PARPi-FL, 640 g/mol; olaparib, 435 g/mol) do not strongly perturb the molecule's binding affinity and cell permeability. Uptake specificity was shown by correlation of PARP1 protein expression and PARPi-FL retention, as well as by the ability to block PARPi-FL uptake by saturating PARP with olaparib (13). One set of studies (7,8) presented PARPi-FL as a tool to measure drugtarget interaction in real time at subcellular resolution in vitro and in vivo using multiphoton fluorescence anisotropy microscopy.…”

“…MDA-MB-436 xenografts showed an SUV of 0.9, and specificity was shown by blocking with a 100 mg/kg dose of olaparib 12 h before 18 F-BO imaging, which reduced the SUV to 0.4. 18 F-BO uptake also correlated with PARP1 expression in ovarian (SKOV3, A2780) and pancreatic (MIAPaCa-2, PANC-1) tumor models (13). To evaluate the potential of 18 F-BO to monitor treatment response, A2780 xenograft-bearing mice were treated with therapeutic doses of olaparib and imaged with 18 F-BO and 18 F-FDG before and after treatment.…”

Advancing biomedical imaging

“…A growing list of fluorescent companion imaging drugs enables these advances (9, [75][76][77][78][79][80][81][82] and immobilization techniques allow orthotopic imaging (83)(84)(85) and methods to study drug/target binding (86). These advances allow detailed insight into when and why drugs fail.…”