TY - JOUR T1 - Preclinical Evaluation of <sup>203/212</sup>Pb-Labeled Low-Molecular-Weight Compounds for Targeted Radiopharmaceutical Therapy of Prostate Cancer JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 80 LP - 88 DO - 10.2967/jnumed.119.229393 VL - 61 IS - 1 AU - Sangeeta Ray Banerjee AU - Il Minn AU - Vivek Kumar AU - Anders Josefsson AU - Ala Lisok AU - Mary Brummet AU - Jian Chen AU - Ana P. Kiess AU - Kwamena Baidoo AU - Cory Brayton AU - Ronnie C. Mease AU - Martin Brechbiel AU - George Sgouros AU - Robert F. Hobbs AU - Martin G. Pomper Y1 - 2020/01/01 UR - http://jnm.snmjournals.org/content/61/1/80.abstract N2 - Targeted radiopharmaceutical therapy (TRT) using α-particle radiation is a promising approach for treating both large and micrometastatic lesions. We developed prostate-specific membrane antigen (PSMA)–targeted low-molecular-weight agents for 212Pb-based TRT of patients with prostate cancer (PC) by evaluating the matching γ-emitting surrogate, 203Pb. Methods: Five rationally designed low-molecular-weight ligands (L1-L5) were synthesized using the lysine-urea-glutamate scaffold, and PSMA inhibition constants were determined. Tissue biodistribution and SPECT/CT imaging of 203Pb-L1–203Pb-L5 were performed on mice bearing PSMA(+) PC3 PIP and PSMA(−) PC3 flu flank xenografts. The absorbed radiation dose of the corresponding 212Pb-labeled analogs was determined using the biodistribution data. Antitumor efficacy of 212Pb-L2 was evaluated in PSMA(+) PC3 PIP and PSMA(−) PC3 flu tumor models and in the PSMA(+) luciferase-expressing micrometastatic model. 212Pb-L2 was also evaluated for dose-escalated, long-term toxicity. Results: All new ligands were obtained in high yield and purity. PSMA inhibitory activities ranged from 0.10 to 17 nM. 203Pb-L1–203Pb-L5 were synthesized in high radiochemical yield and specific activity. Whole-body clearance of 203Pb-L1–203Pb-L5 was fast. The absorbed dose coefficients (mGy/kBq) of the tumor and kidneys were highest for 203Pb-L5 (31.0, 15.2) and lowest for 203Pb-L2 (8.0, 4.2). The tumor-to-kidney absorbed dose ratio was higher for 203Pb-L3 (3.2) and 203Pb-L4 (3.6) than for the other agents, but with lower tumor-to-blood ratios. PSMA(+) tumor lesions were visualized through SPECT/CT as early as 0.5 h after injection. A proof-of-concept therapy study with a single administration of 212Pb-L2 demonstrated dose-dependent inhibition of tumor growth in the PSMA(+) flank tumor model. 212Pb-L2 also demonstrated an increased survival benefit in the micrometastatic model compared with 177Lu-PSMA-617. Long-term toxicity studies in healthy, immunocompetent CD-1 mice revealed kidney as the dose-limiting organ. Conclusion: 203Pb-L1–203Pb-L5 demonstrated favorable pharmacokinetics for 212Pb-based TRT. The antitumor efficacy of 212Pb-L2 supports the corresponding 203Pb/212Pb theranostic pair for PSMA-based α-particle TRT in advanced PC. ER -