Synthesis and Evaluation of the First 68Ga-Labeled C-Terminal Hydroxamate-Derived Gastrin-Releasing Peptide Receptor-Targeted Tracers for Cancer Imaging with Positron Emission Tomography.

Gastrin-releasing peptide receptor (GRPR), overexpressed in many solid tumors, is a promising imaging marker and therapeutic target. Most reported GRPR-targeted radioligands contain a C-terminal amide. Based on the reported potent antagonist D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHOH, we synthesized C-terminal hydroxamate-derived [68Ga]Ga-LW02075 ([68Ga]Ga-DOTA-pABzA-DIG-D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHOH) and [68Ga]Ga-LW02050 ([68Ga]Ga-DOTA-Pip-D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHOH), and compared them with the closely related and clinically validated [68Ga]Ga-SB3 ([68Ga]Ga-DOTA-pABzA-DIG-D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHEt). Binding affinities (Ki) of Ga-SB3, Ga-LW02075, and Ga-LW02050 were 1.20 ± 0.31, 1.39 ± 0.54, and 8.53 ± 1.52 nM, respectively. Both Ga-LW02075 and Ga-LW02050 were confirmed to be GRPR antagonists by calcium release assay. Imaging studies showed that PC-3 prostate cancer tumor xenografts were clearly visualized at 1 h post injection by [68Ga]Ga-SB3 and [68Ga]Ga-LW02050 in PET images, but not by [68Ga]Ga-LW02075. Ex vivo biodistribution studies conducted at 1 h post injection showed that the tumor uptake of [68Ga]Ga-LW02050 was comparable to that of [68Ga]Ga-SB3 (5.38 ± 1.00 vs. 6.98 ± 1.36 %ID/g), followed by [68Ga]Ga-LW02075 (3.97 ± 1.71 %ID/g). [68Ga]Ga-SB3 had the highest pancreas uptake (37.3 ± 6.90 %ID/g) followed by [68Ga]Ga-LW02075 (17.8 ± 5.24 %ID/g), while the pancreas uptake of [68Ga]Ga-LW02050 was only 0.53 ± 0.11 %ID/g. Our data suggest that [68Ga]Ga-LW02050 is a promising PET tracer for detecting GRPR-expressing cancer lesions.

Multifunctional Compounds for Activation of the p53-Y220C Mutant in Cancer.

The p53 protein plays a major role in cancer prevention, and over 50 % of cancer diagnoses can be attributed to p53 malfunction. The common p53 mutation Y220C causes local protein unfolding, aggregation, and can result in a loss of Zn in the DNA-binding domain. Structural analysis has shown that this mutant creates a surface site that can be stabilized using small molecules, and herein a multifunctional approach to restore function to p53-Y220C is reported. A series of compounds has been designed that contain iodinated phenols aimed for interaction and stabilization of the p53-Y220C surface cavity, and Zn-binding fragments for metallochaperone activity. Their Zn-binding affinity was characterized using spectroscopic methods and demonstrate the ability of compounds L4 and L5 to increase intracellular levels of Zn2+ in a p53-Y220C-mutant cell line. The in vitro cytotoxicity of our compounds was initially screened by the National Cancer Institute (NCI-60), followed by testing in three stomach cancer cell lines with varying p53 status', including AGS (WTp53), MKN1 (V143A), and NUGC3 (Y220C). Our most promising ligand, L5, is nearly 3-fold more cytotoxic than cisplatin in a large number of cell lines. The impressive cytotoxicity of L5 is further maintained in a NUGC3 3D spheroid model. L5 also induces Y220C-specific apoptosis in a cleaved caspase-3 assay, reduces levels of unfolded mutant p53, and recovers p53 transcriptional function in the NUGC3 cell line. These results show that these multifunctional scaffolds have the potential to restore wild-type function in mutant p53-Y220C.