Preparation and bioevaluation of [99mTc]Tc-labeled A7R and DA7R for SPECT imaging of triple-negative breast cancer

Abstract

Novel strategies for diagnosing triple-negative breast cancer (TNBC) are essential for effective clinical treatment. Vascular endothelial growth factor receptor 2 (VEGFR2) and neuropilin-1 (NRP-1) are potential targets for tumor imaging agents. We designed and synthesized [^99mTc]Tc-labeled heptapeptide (A7R) and its D-type peptide (^DA7R) with high affinity and specificity for VEGFR2 and NRP-1 as novel single-photon emission computed tomography (SPECT) probes for TNBC imaging. The specificities of A7R and ^DA7R were first evaluated in vitro using flow cytometry and confocal microscopy and ex vivo using fluorescence imaging. Subsequently, A7R and ^DA7R were labeled with [^99mTc]Tc through 6-hydrazino nicotinamide (HYNIC), and their radiochemical purities (RCPs) and stability in vitro were assessed. The imaging performance and biodistribution of [^99mTc]Tc-HYNIC-A7R and [^99mTc]Tc-HYNIC-^DA7R were evaluated in TNBC mouse models. A7R and ^DA7R exhibited good TNBC cell-targeting abilities and were readily labeled with [^99mTc]Tc through HYNIC. Both [^99mTc]Tc-HYNIC-A7R and [^99mTc]Tc-HYNIC-^DA7R had high RCPs and stability in vitro, and their accumulation in tumor tissues in the TNBC models was evident, with fast blood clearance and favorable biodistribution. More importantly, [^99mTc]Tc-HYNIC-^DA7R showed better tumor-to-muscle ratios and lower renal uptake than [^99mTc]Tc-HYNIC-A7R. These results suggest that both [^99mTc]Tc-HYNIC-^DA7R and [^99mTc]Tc-HYNIC-A7R have substantial potential as probes for targeted SPECT imaging of TNBC, and the former may be considered for future clinical translation owing to its superior tumor imaging performance.