Evaluation of a Radiolabeled Macrocyclic Peptide as Potential PET Imaging Probe for PD−L1

Abstract

The interaction between the immune checkpoint PD-1 and PDÀ L1 promotes T-cell deactivation and cancer proliferation. Therefore, immune checkpoint inhibition therapy, which relies on prior assessment of the target, has been widely used for many cancers. As a non-invasive molecular imaging tool, radiotracers bring novel information on the in vivo expression of biomarkers (e. g., PDÀ L1), enabling a personalized treatment of patients. Our work aimed at the development of a PDÀ L1specific, peptide-based PET radiotracer. We synthesized and evaluated a radiolabeled macrocyclic peptide adapted from a patent by Bristol Myers Squibb. Synthesis of [ 68 Ga]Ga-NJMP1 yielded a product with a radiochemical purity > 95 % that was evaluated in vitro. However, experiments on CHOÀ K1 hPDÀ L1 cells showed very low cell binding and internalization rates of [ 68 Ga]Ga-NJMP1 in comparison to a control radiopeptide (WL12). Non-radioactive cellular assays using time-resolved fluorescence energy transfer confirmed the low affinity of the reported parent peptide and the DOTA-derivatives towards PDÀ L1. The results of our studies indicate that the macrocyclic peptide scaffold reported in the patent literature is not suitable for radiotracer development due to insufficient affinity towards PDÀ L1 and that C-terminal modifications of the macrocyclic peptide interfere with important ligand/receptor interactions.

Development of Radiotracers for Imaging of the PD-1/PD-L1 Axis

“…[ 68 Ga]Ga-NJMP1 68 Ga PET 25.9 µM [63] Small Molecule [ 18 F]FLN 18 F PET 65.3 nM [64] [ 18 F]FLG-1 18 F 63.1 nM [65] HAC-PD1 DOTA-HAC 64 Cu PET ~110 pM [66] NOTA-HAC NOTA-HACA DOTA-HACA 1 Values for non-conjugated Atezolizumab. 2 Value for unsubstituted peptide; K D for substituted peptide was found to be in the same range.…”

“…Therefore, these results are promising for quantifying PD-L1 levels clinically for patient stratification and therapeutic monitoring. Inspired by the promising results of the cyclic peptides, Jouini et al developed a PD-L1-specific macrocyclic peptide NJMP1 based on a structure reported in a patent from Bristol Myers Squibb [63]. The 68 Ga-labeled peptide was studied on CHO-K1 hPD-L1 cells but showed very low cell binding and internalization rates in comparison to those of the control radiopeptide WL12.…”

“…Similarly, Sun et al also utilized the [ 18 F]AlF labeling method for a NOTA conjugate of the new PD-L1-targeting peptide IPB-PDL1P [62]. In vivo microPET studies in a mouse xenograft model showed a high uptake for [ 18 F]AlF-NOTA-IPB-PDL1P in the HCT116 and Inspired by the promising results of the cyclic peptides, Jouini et al developed a PD-L1-specific macrocyclic peptide NJMP1 based on a structure reported in a patent from Bristol Myers Squibb [63]. The 68 Ga-labeled peptide was studied on CHO-K1 hPD-L1 cells but showed very low cell binding and internalization rates in comparison to those of the control radiopeptide WL12.…”

68Ga-HBED-CC-WL-12 PET in Diagnosing and Differentiating Pancreatic Cancers in Murine Models

“…The potential of radiolabeled anti-PD-L1 antibodies, nanobodies, and small inhibitors to image PD-L1 expression have been demonstrated in different tumor models [ 11 , 12 , 13 , 14 , 15 ]. Atezolizumab [ 16 ], the first FDA-approved PD-L1 mAbs, has been utilized for PET imaging.…”

Noninvasive Imaging of Tumor PD-L1 Expression Using [99mTc]Tc-Labeled KN035 with SPECT/CT

“…Single photon emission computed tomography (SPECT) and positron emission tomography (PET) imaging can definitely resolve the practical issues encountered with IHC and provide a noninvasive method to detect PD-L1 expression with whole-body imaging dynamically and accurately. − Previous studies of immune-PET probes with antibodies to PD-L1 labeled with positron-emitting radionuclides (fluorine-18, copper-64, and zirconium-89, etc.) demonstrated that PET imaging could provide precise information on the PD-L1 status in all tumor lesions of cancer patients. − Despite its quantitative and radiochemical advantages, the availability of PET has remained rather limited due to the higher cost of the scanners, the cyclotron, and radiochemistry. , The popularization of immunotherapy requires the cheaper, more widely available, and routinely used clinical tool SPECT to detect PD-L1 expression, which is conducive to the widespread application at any standard hospital radiopharmacy.…”