A Bivalent Inhibitor of Prostate Specific Membrane Antigen Radiolabeled with Copper‐64 with High Tumor Uptake and Retention

Prostate-specific membrane antigen (PSMA) is a biomarker expressed on the surface of prostate cancer (PCa). In an effort to improve the detection and treatment of PCa, small urea-based PSMA inhibitors have been studied extensively. In the present study, we aimed to develop 99mTc-tricabonyl labeled urea-based PSMA conjugates containing isonitrile (CN-R)-coordinating ligands ([99mTc]Tc-15 and [99mTc]Tc-16). Both the PSMA conjugates were obtained at high radiochemical efficiency (≥98.5%). High in vitro binding affinity was observed for [99mTc]Tc-15 and [99mTc]Tc-16 (Kd = 5.5 and 0.2 nM, respectively) in PSMA-expressing 22Rv1 cells. Tumor xenografts were conducted using 22Rv1 cells and rapid accumulation of [99mTc]Tc-16 (1.87 ± 0.11% ID/g) was observed at 1 h post-injection, which subsequently increased to (2.83 ± 0.26% ID/g) at 4 h post-injection. However, [99mTc]Tc-15 showed moderate tumor uptake (1.48 ± 0.18% ID/g), which decreased at 4 h post-injection (0.81 ± 0.09% ID/g). [99mTc]Tc-16 was excreted from non-targeted tissues with high tumor-to-blood (17:1) and tumor-to-muscle ratio (41:1) at 4 h post-injection at approximately 4 times higher levels than [99mTc]Tc-15. Uptakes of [99mTc]Tc-15 and [99mTc]Tc-16 to PSMA-expressing tumor and tissues were significantly blocked by co-injection of 2-(Phosphonomethyl)-pentandioic acid (2-PMPA), suggesting that their uptakes are mediated by PSMA specifically. Whole-body single photon emission computed tomography imaging of [99mTc]Tc-16 verified the ex vivo biodistribution results and demonstrated clear visualization of tumors and tissues expressing PSMA compared to [99mTc]Tc-15. In conclusion, using [99mTc]Tc-16 rather than [99mTc]Tc-15 may be the preferable because of its relatively high tumor uptake and retention.

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JHU-2545 Selectively Shields Salivary Glands and Kidneys during PSMA-Targeted Radiotherapy

10.1101/457085 ◽

2018 ◽

Cited By ~ 1

Author(s):

Michael T. Nedelcovych ◽

Ranjeet P. Dash ◽

Ying Wu ◽

Eun Yong Choi ◽

Rena S. Lapidus ◽

...

Keyword(s):

Salivary Glands ◽

Prostate Specific Membrane Antigen ◽

Tumor Uptake ◽

Castration Resistant Prostate Cancer ◽

Castration Resistant ◽

Psma Pet ◽

Promising Treatment ◽

Specific Membrane ◽

Psma Inhibitor ◽

Efficacy Profile

ABSTRACTPURPOSEProstate-specific membrane antigen (PSMA) radiotherapy is a promising treatment for metastatic castration-resistant prostate cancer (mCRPC) with several beta or alpha particle-emitting radionuclide-conjugated small molecules showing efficacy in late stage patients. However, PSMA is also expressed in kidneys and salivary glands where specific uptake causes dose-limiting xerostomia and potential for nephrotoxicity. The PSMA inhibitor 2- (phosphonomethyl)pentanedioic acid (2-PMPA) can prevent kidney uptake in mice, but also blocks tumor uptake, precluding its clinical utility. Selective delivery of 2-PMPA to non-malignant tissues could improve the therapeutic window of PSMA radiotherapy.EXPERIMENTAL DESIGNA tri-alkoxycarbonyloxy alkyl (TrisPOC) prodrug of 2-PMPA, JHU-2545, was synthesized to enhance 2-PMPA delivery to non-malignant tissues. Preclinical pharmacokinetic and imaging experiments were conducted prior to assessment in 3 mCRPC patients receiving PSMA PET and radiotherapy.RESULTSJHU-2545 resulted in 3- and 53-fold greater exposure of 2-PMPA in rodent salivary glands (18.0 ± 0.97 h*nmol/g) and kidneys (359 ± 4.16 h*nmol/g) versus prostate tumor xenograft (6.79 ± 0.19 h*nmol/g). JHU-2545 also blocked rodent kidneys and salivary glands uptake of the PSMA PET tracers 68Ga-PSMA-11 and 18F-DCFPyL by up to 85% without effect on tumor. In a mCRPC patient, JHU-2545 treatment prior to 68Ga-PSMA-617 administration reduced kidney SUVmax by 76% without effect on metastatic lesions. When administered prior to injection of the beta emitter 177Lu-PSMA-617, JHU-2545 shielded both the salivary glands (72% Gy reduction) and kidneys (45% Gy reduction) without effect on metastases’ dose.CONCLUSIONSJHU-2545 pre-treatment raises the cumulative dose limit and improves the safety and efficacy profile of PSMA radiotherapy.STATEMENT OF TRANSLATIONAL RELEVANCEProstate Specific Membrane Antigen (PSMA) molecular radiotherapy has emerged as a promising treatment for metastatic castration-resistant prostate cancer (mCRPC), but endogenous expression of PSMA in kidneys and salivary glands causes uptake into these organs resulting in dose-limiting toxicities. We describe the discovery of JHU-2545, a PSMA inhibitor prodrug that selectively blocks kidney and salivary gland uptake of PSMA theranostics without altering tumor uptake in both preclinical models and in mCRPC patients. Pretreatment of JHU-2545 thereby improves the safety and efficacy profile of the multiple PSMA radiotherapies in development.

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Preparation and Biological Evaluation of [99mTc]Tc-CNGU as a PSMA-Targeted Radiotracer for the Imaging of Prostate Cancer

Molecules ◽

10.3390/molecules25235548 ◽

2020 ◽

Vol 25 (23) ◽

pp. 5548

Author(s):

Di Xiao ◽

Xiaojiang Duan ◽

Qianqian Gan ◽

Xuran Zhang ◽

Junbo Zhang

Keyword(s):

Prostate Cancer ◽

Biological Evaluation ◽

Log P ◽

Tumor Uptake ◽

Biodistribution Studies ◽

Biological Target ◽

High Tumor Uptake ◽

Specific Membrane ◽

Psma Inhibitor

Prostate-specific membrane antigen (PSMA) is a well-established biological target that is overexpressed on the surface of prostate cancer lesions. Radionuclide-labeled small-molecule PSMA inhibitors have been shown to be promising PSMA-specific agents for the diagnosis and therapy of prostate cancer. In this study, a glutamate-urea-based PSMA-targeted ligand containing an isonitrile (CNGU) was synthesized and labeled with 99mTc to prepare [99mTc]Tc-CNGU with a high radiochemical purity (RCP). The CNGU ligand showed a high affinity toward PSMA (Ki value is 8.79 nM) in LNCaP cells. The [99mTc]Tc-CNGU exhibited a good stability in vitro and hydrophilicity (log P = −1.97 ± 0.03). In biodistribution studies, BALB/c nude mice bearing LNCaP xenografts showed that the complex had a high tumor uptake with 4.86 ± 1.19% ID/g, which decreased to 1.74 ± 0.90% ID/g after a pre-injection of the selective PSMA inhibitor ZJ-43, suggesting that it was a PSMA-specific agent. Micro-SPECT imaging demonstrated that the [99mTc]Tc-CNGU had a tumor uptake and that the uptake was reduced in the image after blocking with ZJ-43, further confirming its PSMA specificity. All of the results in this work indicated that [99mTc]Tc-CNGU is a promising PSMA-specific tracer for the imaging of prostate cancer.

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The Future of PSMA-Targeted Radionuclide Therapy: An Overview of Recent Preclinical Research

Pharmaceutics ◽

10.3390/pharmaceutics11110560 ◽

2019 ◽

Vol 11 (11) ◽

pp. 560 ◽

Cited By ~ 6

Author(s):

Eline A.M. Ruigrok ◽

Wytske M. van Weerden ◽

Julie Nonnekens ◽

Marion de Jong

Keyword(s):

Radionuclide Therapy ◽

Therapeutic Strategies ◽

Prostate Specific Membrane Antigen ◽

Targeted Radionuclide Therapy ◽

Tumor Uptake ◽

Research Projects ◽

Major Focus ◽

Preclinical Research ◽

Specific Membrane ◽

Focus Point

Prostate specific membrane antigen (PSMA) has become a major focus point in the research and development of prostate cancer (PCa) imaging and therapeutic strategies using radiolabeled tracers. PSMA has shown to be an excellent target for PCa theranostics because of its high expression on the membrane of PCa cells and the increase in expression during disease progression. Therefore, numerous PSMA-targeting tracers have been developed and (pre)clinically studied with promising results. However, many of these PSMA-targeting tracers show uptake in healthy organs such as the salivary glands, causing radiotoxicity. Furthermore, not all patients respond to PSMA-targeted radionuclide therapy (TRT). This created the necessity of additional preclinical research studies in which existing tracers are reevaluated and new tracers are developed in order to improve PSMA-TRT by protecting the (PSMA-expressing) healthy organs and improving tumor uptake. In this review we will give an overview of the recent preclinical research projects regarding PCa-TRT using PSMA-specific radiotracers, which will give an indication of where the PSMA-TRT research movement is going and what we can expect in future clinical trials.

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