Synthesis and Evaluation of New Bifunctional Chelators with Phosphonic Acid Arms for Gallium-68 Based PET Imaging in Melanoma

Abstract

Due to the increasing use of generator-produced radiometal Gallium-68 (Ga) in positron-emission tomography/computed tomography (PET/CT), reliable bifunctional chelators that can efficiently incorporate Ga into biomolecules are highly desirable. In this study, we synthesized two new bifunctional chelators bearing one or two phosphonic acid functional groups, named p-SCN-PhPr-NE2A1P and p-SCN-PhPr-NE2P1A, with the aim of enabling facile production of Ga-based radiopharmaceuticals. Both chelators were successfully conjugated to LLP2A-PEG, a very late antigen-4 (VLA-4) targeting peptidomimetic ligand, to evaluate their application in Ga-based PET imaging. NE2P1A-PEG-LLP2A exhibited the highest Ga binding ability with molar activity of 37 MBq/nmol under mild temperature and neutral pH. Excellent serum stability of Ga-NE2P1A-PEG-LLP2A was observed, which was consistent with the result obtained from density functional theory calculation. The in vitro cell study showed that Ga-NE2P1A-PEG-LLP2A had significantly longer retention in B16F10 cells comparing to the reported retention of Cu-NE3TA-PEG-LLP2A, although the uptake was relatively lower. In the biodistribution and micro-PET/CT imaging studies, high tumor uptake and low background were observed after Ga-NE2P1A-PEG-LLP2A was injected into mice bearing B16F10 tumor xenografts, making it a highly promising radiotracer for noninvasive imaging of VLA-4 receptors overexpressed in melanoma.

Targeted radiotherapy of pigmented melanoma with 131I-5-IPN

“…In clinical practice, TRNT has achieved great success against radiosensitive tumors, particularly neuroendocrine tumors [ 6 ] and lymphomas [ 7 , 8 ]. For melanoma, several different carrier molecules are currently being labeled with radionuclides for TRNT, such as 111 In labeled monoclonal antibody (mAb) KM871 targeting GD3 expressed on the surface of melanoma cells [ 9 ], 188 Re-labled mAb 6D2 targeting intracellular melanin antigen [ 10 ], and more and more peptides used for both radioimmunotherapy [ 11 – 13 ] and detection [ 14 ] of melanoma. During the past decade, many small benzamide molecules radiolabeled with 18 F [ 15 – 17 ], 11 C [ 18 ], or 131 I [ 19 – 21 ] have been developed for diagnosis or therapy of melanoma.…”

Novel Ligands Targeting α4β1 Integrin: Therapeutic Applications and Perspectives

“…For instance, the peptidomimetic LLP2A, displaying extraordinarily high affinity (IC 50 = 2 pM) to the α 4 β 1 integrin receptor (Peng et al, 2006), was conjugated with NIR tags through a PEG linker and applied to the detection of MOLT-4 tumor xenografts. Similar derivatives were linked to radioactive metal chelators for in vivo imaging (Denardo et al, 2009; Gai et al, 2018). More recently, 18 F-labeled LLP2A-trifluoroborate bioconjugates were successfully evaluated in α 4 β 1 integrin-overexpressing tumor models (Walker et al, 2016).…”

[18F]F-ET-OTSSP167 Targets Maternal Embryo Leucine Zipper Kinase for PET Imaging of Triple-Negative Breast Cancer

“…Log P. The partition coefficient was determined using the previously described method. 25 Briefly, [ 18 F]F-ET-OTSSP167 (3−6 kBq, 5 μL) was added to 1 mL of octanol and 1 mL of PBS (10 mM, pH 7.4). The mixture was vortexed for 10 min and then centrifuged for 10 min.…”