Abstract B068: Methionine aminopeptidase II (MetAP2) activated in situ self-assembly of small-molecule probes for imaging prostate cancer

Abstract

Abstract Prostate cancer is the most common noncutaneous malignancy among men in the United States and a leading cause of cancer death worldwide. The major clinical challenges in prostate cancer diagnosis include accurate staging, localizing tumors within the prostate, and developing imaging prognostic biomarkers. PET is routinely used in the clinical management of many cancers dues to its high sensitivity (10-15 M), spatial resolution (2-4 mm3), rapid whole-body scan times (<20 min), noninvasiveness, and its ability to provide both anatomic and molecular information when combined with computed tomography (PET/CT). Several PET tracers (e.g., 18F-FDG, 18F-NaF, 11C-choline, 11C-acetate, 18F-fluciclovine, etc.) have been studied for early stage prostate cancer, bone metastases, and recurrent disease; nevertheless, all of these tracers rely on cell uptake and their applications are often limited by the low metabolic activity and a low growth rate of prostate cancer. In this project, we aim to develop a novel enzymatic activity-based PET tracer for in vivo imaging of prostate cancer by targeting methionine aminopeptidase II (MetAP2), a cytosolic metalloprotease that catalyzes the cotranslational removal of the N-terminus initiator methionine residue from nascent proteins. We hypothesize that MetAP2 can serve as a novel diagnostic biomarker of prostate cancer. A MetAP2 activatable molecular imaging probe that self-aggregates in situ can be utilized to image and define this disease. To test our hypothesis, we first measured the expression level of MetAP2 in primary benign human prostate epithelial cells (BS403) and prostate tumor cell lines by Western blot. BS403 cells express significantly lower levels of MetAP2 than PC3 (by 4-fold), DU145 (3-fold), and 22Rv1 (3-fold). The expression of MetAP2 in DU145 tumor xenografts is 12-fold higher and for 22Rv1 14-fold higher, compared to BS403 cells. Immunohistologic analysis of tissues derived from DU145 and 22Rv1 xenografts confirms strong staining of MetAP2. We performed immunohistochemistry on a prostate cancer tissue microarray containing 225 independent patient samples represented in quadruplicate. Positive staining for MetAP2 was found in nearly all of the cancer samples. Encouraged by these data, we designed and synthesized a nonradioactive MetAP2 sensitive nano-aggregation probe called M-SNAP. Incubation of M-SNAP with recombinant MetAP2 enzyme confirmed the formation of the cyclized and aggregated product M-SNAP-cycl by HPLC, TEM (transmission electron microscopy), and DLS (dynamic light scattering). Treatment of PC3 and DU145 cells with or without M-SNAP and the MetAP2 specific inhibitor TNP470 demonstrated MetAP2 dependent intracellular probe aggregation/signal retention using post fluorescent labeling of the cyclized and aggregated products. In future work, we will prepare and study an MetAP2 activatable radioisotope-labeled probe in vitro for sensing and imaging and will evaluate the PET probe in different human prostate xenograft models. MetAP2 sensing probes could provide a highly sensitive and noninvasive PET imaging approach for prostate cancer detection that could be useful in prostate cancer detection, staging, and monitoring of therapeutic response. Citation Format: Jinghang Xie, Meghan Rice, Yunfeng Cheng, Guosheng Song, Christian Kunder, James D. Brooks, Tanya Stoyanova, Jianghong Rao. Methionine aminopeptidase II (MetAP2) activated in situ self-assembly of small-molecule probes for imaging prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr B068.