Automated synthesis of [18F]DCFPyL via direct radiofluorination and validation in preclinical prostate cancer models

Abstract

BackgroundProstate-specific membrane antigen (PSMA) is frequently overexpressed and upregulated in prostate cancer. To date, various 18F- and 68Ga-labeled urea-based radiotracers for PET imaging of PSMA have been developed and entered clinical trials. Here, we describe an automated synthesis of [18F]DCFPyL via direct radiofluorination and validation in preclinical models of prostate cancer.Methods[18F]DCFPyL was synthesized via direct nucleophilic heteroaromatic substitution reaction in a single reactor TRACERlab FXFN automated synthesis unit. Radiopharmacological evaluation of [18F]DCFPyL involved internalization experiments, dynamic PET imaging in LNCaP (PSMA+) and PC3 (PSMA−) tumor-bearing BALB/c nude mice, biodistribution studies, and metabolic profiling. In addition, reversible two-tissue compartmental model analysis was used to quantify pharmacokinetics of [18F]DCFPyL in LNCaP and PC3 tumor models.ResultsAutomated radiosynthesis afforded radiotracer [18F]DCFPyL in decay-corrected radiochemical yields of 23 ± 5 % (n = 10) within 55 min, including HPLC purification. Dynamic PET analysis revealed rapid and high uptake of radioactivity (SUV5min 0.95) in LNCaP tumors which increased over time (SUV60min 1.1). Radioactivity uptake in LNCaP tumors was blocked in the presence of nonradioactive DCFPyL (SUV60min 0.22). The muscle as reference tissue showed rapid and continuous clearance over time (SUV60min 0.06). Fast blood clearance of radioactivity resulted in tumor-blood ratios of 1.0 after 10 min and 8.3 after 60 min. PC3 tumors also showed continuous clearance of radioactivity over time (SUV60min 0.11). Kinetic analysis of PET data revealed the two-tissue compartmental model as best fit with K1 = 0.12, k2 = 0.18, k3 = 0.08, and k4 = 0.004 min−1, confirming molecular trapping of [18F]DCFPyL in PSMA+ LNCaP cells.Conclusions[18F]DCFPyL can be prepared for clinical applications simply and in good radiochemical yields via a direct radiofluorination synthesis route in a single reactor automated synthesis unit. Radiopharmacological evaluation of [18F]DCFPyL confirmed high PSMA-mediated tumor uptake combined with superior clearance parameters. Compartmental model analysis points to a two-step molecular trapping mechanism based on PSMA binding and subsequent internalization leading to retention of radioactivity in PSMA+ LNCaP tumors.Electronic supplementary materialThe online version of this article (doi:10.1186/s13550-016-0195-6) contains supplementary material, which is available to authorized users.

An improved synthesis of the radiolabeled prostate-specific membrane antigen inhibitor, [18F]DCFPyL

“…Both of these platforms vastly improved the millicurie yield and specific activity compared with our original multistep synthesis of [ 18 F]DCFPyL that produced an average of 2.3 GBq (62 mCi) with an uncorrected specific activity at EOS of 193 GBq/μmol (5.2 Ci/μmol) in approximately 90 minutes. For comparison, a recent paper using the same precursor with somewhat different reaction and purification conditions produced an uncorrected yield of 16% (calculated from the reported decay‐corrected yield of 23%) of 3 GBq (81 mCi) of [ 18 F]DCFPyL with a specific activity of 81 to 100 GBq/μmol (2.2‐2.7 Ci/μmol) in 55 minutes.…”

“…While this paper was in preparation, another group published the simplified synthesis using similar conditions. 7 In this paper, a radiopharmacy production level synthesis is achieved, and full compliance with all US Pharmacopeia (USP) <823> acceptance criteria is confirmed and presented.…”

“…This paper describes an improved synthesis of [ 18 F]DCFPyL from a single precursor with an automated synthesis performed on both an in‐house custom‐build synthesis module and a commercial radiochemistry module involving a single reactor, 5 operational steps, and 65 to 87 minutes of synthesis time with an increased radiochemical yield. While this paper was in preparation, another group published the simplified synthesis using similar conditions . In this paper, a radiopharmacy production level synthesis is achieved, and full compliance with all US Pharmacopeia (USP) <823> acceptance criteria is confirmed and presented.…”

Discovery of 18F-JK-PSMA-7, a PET Probe for the Detection of Small PSMA-Positive Lesions

“…The manual synthesis and automated production of 18 F-JK-PSMA-7 on an FXNPro module (GE Healthcare) are shown in Supplemental Figure 2. 18 F-JK-PSMA-10 ( 18 F-7) was prepared applying the minimalist protocol to the procedure proposed for the preparation of 18 F-DCFPyL by Bouvet et al (15) and Ravert et al (16). 18 F-JK-PSMA-14 ( 18 F-11) was prepared as described elsewhere (17).…”

Minimalist approach meets green chemistry: Synthesis of 18F‐ labeled (hetero)aromatics in pure ethanol

“…[ 18 F]DCFPyL was recently described as a PET probe for the visualization of the prostate specific membrane antigen which is overexpressed in, e.g., prostate cancer . The radiolabeled intermediate [ 18 F] 4 was prepared in 47% RCY from the appropriate Me 3 N‐substituted precursor . Similarly, protected [ 18 F]JK‐PSMA‐7([ 18 F] 6 ) which contains an additional methoxy group in the pyridine ring was prepared in 89% RCY from the Me 3 N‐substituted precursor.…”