PT - JOURNAL ARTICLE AU - Lesniak, Wojciech AU - Ray, Sangeeta AU - Boinapally, Srikanth AU - Behnam Azad, Babak AU - Pomper, Martin TI - <strong>Evaluation of a PSMA-Targeted PAMAM Dendrimer in an Experimental Model of Prostate Cancer</strong> DP - 2019 May 01 TA - Journal of Nuclear Medicine PG - 548--548 VI - 60 IP - supplement 1 4099 - http://jnm.snmjournals.org/content/60/supplement_1/548.short 4100 - http://jnm.snmjournals.org/content/60/supplement_1/548.full SO - J Nucl Med2019 May 01; 60 AB - 548Background: Prostate specific membrane antigen (PSMA) is a useful biomarker for management of prostate cancer (PC). PSMA is also expressed in the neovasculature of solid tumors other than PC, including lung, kidney, colon, stomach, breast and brain. PSMA has also been leveraged for endoradiotherapy and targeted drug delivery by antibody-drug conjugates and polylactic acid-polyethylene glycol (PLA-PEG)-based nanoparticles, which have undergone clinical evaluation. Huang et al., demonstrated specific in vitro uptake and toxicity for a PSMA-targeted poly(amidoamine) (PAMAM) dendrimer/methotrexate conjugate. Those studies provided rationale for the development of PSMA-targeted drug nanocarriers based on dendrimers and low molecular weight (LMW) targeting agents. However, data regarding their in vivo specificity and pharmacokinetics for have not yet been reported. The advantage of small PAMAM nanoparticles (4 to 6 nm) compared to the aforementioned relatively large constructs (50 - 100 nm), is their low off-target tissue uptake and preferential active tumor accumulation mediated by the attached LMW targeting moieties. Here we report synthesis of control (G4-Ctrl) and PSMA-targeted (G4-PSMA) PAMAM dendrimers and their biological evaluation in vitro and in an experimental model of PC. Methods: A well-established LMW Lys-Glu-urea inhibitor with picomolar affinity to PSMA was utilized to prepare the targeting moiety. To construct PSMA-targeted nanoparticles, generation-4, amine-terminated PAMAM dendrimer was conjugated with two DOTA molecules for radiolabeling, three rhodamines for optical evaluation, and ten Lys-Glu-urea LMW PSMA-targeted ligands. The remaining terminal primary amines were reacted with glycidol to remove surface positive charge, thereby minimizing non-specific in vivo uptake and toxicity of the G4-PSMA nanoparticles. Non-targeted control dendrimers (G4-Ctrl) were prepared using the same surface modifications without conjugation of Lys-Glu-urea. Physicochemical properties of both nanoparticles were assessed using high performance liquid chromatography, matrix assisted laser desorption ionization mass spectrometry and dynamic light scattering. Targeting properties of G4-PSMA and G4-Ctrl nanoparticles were evaluated using isogenic human prostate cancer PSMA+ PC3 PIP and PSMA- PC3 flu cell lines in vitro and in vivo. Results: A facile, one-pot synthetic route gave nearly neutral nanoparticles with a narrow size distribution of ~5 nm in diameter and molecular weight of 27 kDa. G4-PSMA exhibited high in vitro target specificity with a dissociation constant (Kd) of 0.32 ± 0.23 µM. In vivo and ex vivo studies indicated that G4-PSMA and [64Cu]G4-PSMA showed preferential accumulation in PSMA+ tumors and predominant renal clearance in mice bearing PSMA+ PC3 PIP and PSMA- PC3 flu xenografts. Positron emission tomography and ex vivo biodistribution studies of [64Cu]G4-PSMA demonstrated highest PSMA+ PC3 PIP tumor accumulation at 24 h post-injection (45.83 ± 20.09 %ID/g) and a PSMA+ PC3 PIP/PSMA- PC3 flu ratio of 4.22 ± 3.74, 7.65 ± 3.35 and 3.94 ± 1.09 at 3 h, 24 h and 48 h post-injection, respectively. The specific accumulation of [64Cu]G4-PSMA in PSMA+ PC3 PIP tumors was inhibited by the known PSMA inhibitor, ZJ-43. On the contrary, [64Cu]G4-Ctrl accumulated to only ~1 %ID/g in either PSMA+ or PSMA- tumors as a further test of binding specificity. Conclusions: G4-PSMA may represent a suitable scaffold by which to target PSMA-expressing tissues with imaging and therapeutic agents. Funding: This work was funded by CA134675, CA184228, CA183031, EB024495, the Commonwealth Foundation.