TY - JOUR T1 - Preclinical Evaluation of <sup>213</sup>Bi- and <sup>225</sup>Ac-Labeled Low-Molecular-Weight Compounds for Radiopharmaceutical Therapy of Prostate Cancer JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 980 LP - 988 DO - 10.2967/jnumed.120.256388 VL - 62 IS - 7 AU - Sangeeta Ray Banerjee AU - Ala Lisok AU - Il Minn AU - Anders Josefsson AU - Vivek Kumar AU - Mary Brummet AU - Srikanth Boinapally AU - Cory Brayton AU - Ronnie C. Mease AU - George Sgouros AU - Robert F. Hobbs AU - Martin G. Pomper Y1 - 2021/07/01 UR - http://jnm.snmjournals.org/content/62/7/980.abstract N2 - Prostate-specific membrane antigen (PSMA)–targeted radiopharmaceutical therapy is a new option for patients with advanced prostate cancer refractory to other treatments. Previously, we synthesized a β-particle–emitting low-molecular-weight compound, 177Lu-L1 which demonstrated reduced off-target effects in a xenograft model of prostate cancer. Here, we leveraged that scaffold to synthesize α-particle–emitting analogs of L1, 213Bi-L1 and 225Ac-L1, to evaluate their safety and cell kill effect in PSMA-positive (+) xenograft models. Methods: The radiochemical synthesis, cell uptake, cell kill, and biodistribution of 213Bi-L1 and 225Ac-L1 were evaluated. The efficacy of 225Ac-L1 was determined in human PSMA+ subcutaneous and micrometastatic models. Subacute toxicity at 8 wk and chronic toxicity at 1 y after administration were evaluated for 225Ac-L1. The absorbed radiation dose of 225Ac-L1 was determined using the biodistribution data and α-camera imaging. Results: 213Bi- and 225Ac-L1 demonstrated specific cell uptake and cell kill in PSMA+ cells. The biodistribution of 213Bi-L1 and 225Ac-L1 revealed specific uptake of radioactivity within PSMA+ lesions. Treatment studies of 225Ac-L1 demonstrated activity-dependent, specific inhibition of tumor growth in the PSMA+ flank tumor model. 225Ac-L1 also showed an increased survival benefit in the micrometastatic model compared with 177Lu-L1. Activity-escalated acute and chronic toxicity studies of 225Ac-L1 revealed off-target radiotoxicity, mainly in kidneys and liver. The estimated maximum tolerated activity was about 1 MBq/kg. α-Camera imaging of 225Ac-L1 revealed high renal cortical accumulation at 2 h followed by fast clearance at 24 h. Conclusion: 225Ac-L1 demonstrated activity-dependent efficacy with minimal treatment-related organ radiotoxicity. 225Ac-L1 is a promising therapeutic for further clinical evaluation. ER -