TY - JOUR T1 - Hybrid Tracers Based on Cyanine Backbones Targeting Prostate-Specific Membrane Antigen: Tuning Pharmacokinetic Properties and Exploring Dye–Protein Interaction JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 234 LP - 241 DO - 10.2967/jnumed.119.233064 VL - 61 IS - 2 AU - Albertus W. Hensbergen AU - Tessa Buckle AU - Danny M. van Willigen AU - Margret Schottelius AU - Mick M. Welling AU - Felicia A. van der Wijk AU - Tobias Maurer AU - Henk G. van der Poel AU - Gabri van der Pluijm AU - Wytske M. van Weerden AU - Hans-Jürgen Wester AU - Fijs W.B. van Leeuwen Y1 - 2020/02/01 UR - http://jnm.snmjournals.org/content/61/2/234.abstract N2 - Prostate cancer surgery is currently being revolutionized by the use of prostate-specific membrane antigen (PSMA)–targeted radiotracers, for example, 99mTc-labeled PSMA tracer analogs for radioguided surgery. The purpose of this study was to develop a second-generation 99mTc-labeled PSMA-targeted tracer incorporating a fluorescent dye. Methods: Several PSMA-targeted hybrid tracers were synthesized: glutamic acid-urea-lysine (EuK)-Cy5-mas3, EuK-(SO3)Cy5-mas3, EuK-Cy5(SO3)-mas3, EuK-(Ar)Cy5-mas3, and EuK-Cy5(Ar)-mas3; the Cy5 dye acts as a functional backbone between the EuK targeting vector and the 2-mercaptoacetyl-seryl-seryl-seryl (mas3) chelate to study the dye’s interaction with PSMA’s amphipathic entrance funnel. The compounds were evaluated for their photophysical and chemical properties and PSMA affinity. After radiolabeling with 99mTc, we performed in vivo SPECT imaging, biodistribution, and fluorescence imaging on BALB/c nude mice with orthotopically transplanted PC346C tumors. Results: The dye composition influenced the photophysical properties (brightness range 0.3–1.5 × 104 M−1 × cm−1), plasma protein interactions (range 85.0% ± 2.3%–90.7% ± 1.3% bound to serum, range 76% ± 0%–89% ± 6% stability in serum), PSMA affinity (half-maximal inhibitory concentration [IC50] range 19.2 ± 5.8–175.3 ± 61.1 nM) and in vivo characteristics (tumor-to-prostate and tumor-to-muscle ratios range 0.02 ± 0.00–154.73 ± 28.48 and 0.46 ± 0.28–5,157.50 ± 949.17, respectively; renal, splenic, and salivary retention). Even though all tracer analogs allowed tumor identification with SPECT and fluorescence imaging, 99mTc-EuK-(SO3)Cy5-mas3 had the most promising properties (e.g., half-maximal inhibitory concentration, 19.2 ± 5.8, tumor-to-muscle ratio, 5,157.50 ± 949.17). Conclusion: Our findings demonstrate the intrinsic integration of a fluorophore in the pharmacophore in PSMA-targeted small-molecule tracers. In this design, having 1 sulfonate on the indole moiety adjacent to EuK (99mTc-EuK-(SO3)Cy5-mas3) yielded the most promising tracer candidate for imaging of PSMA. ER -