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Schatz CA, Zitzmann-Kolbe S, Moen I, Klotz M, Nair S, Stargard S, Bjerke RM, Wickstrøm Biseth K, Feng YZ, Indrevoll B, Cruciani V, Karlsson J, Haendler B, Nielsen CH, Alfsen MZ, Hammer S, Hennekes H, Cuthbertson A, Hagemann UB, Larsen Å. Preclinical Efficacy of a PSMA-Targeted Actinium-225 Conjugate (225Ac-Macropa-Pelgifatamab): A Targeted Alpha Therapy for Prostate Cancer. Clin Cancer Res 2024; 30:2531-2544. [PMID: 38593212 DOI: 10.1158/1078-0432.ccr-23-3746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Revised: 02/07/2024] [Accepted: 04/03/2024] [Indexed: 04/11/2024]
Abstract
PURPOSE Initially, prostate cancer responds to hormone therapy, but eventually resistance develops. Beta emitter-based prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy is approved for the treatment of metastatic castration-resistant prostate cancer. Here we introduce a targeted alpha therapy (TAT) consisting of the PSMA antibody pelgifatamab covalently linked to a macropa chelator and labeled with actinium-225 and compare its efficacy and tolerability with other TATs. EXPERIMENTAL DESIGN The in vitro characteristics and in vivo biodistribution, antitumor efficacy, and tolerability of 225Ac-macropa-pelgifatamab (225Ac-pelgi) and other TATs were investigated in cell line- and patient-derived prostate cancer xenograft models. The antitumor efficacy of 225Ac-pelgi was also investigated in combination with the androgen receptor inhibitor darolutamide. RESULTS Actinium-225-labeling of 225Ac-pelgi was efficient already at room temperature. Potent in vitro cytotoxicity was seen in PSMA-expressing (LNCaP, MDA-PCa-2b, and C4-2) but not in PSMA-negative (PC-3 and DU-145) cell lines. High tumor accumulation was seen for both 225Ac-pelgi and 225Ac-DOTA-pelgi in the MDA-PCa-2b xenograft model. In the C4-2 xenograft model, 225Ac-pelgi showed enhanced antitumor efficacy with a T/Cvolume (treatment/control) ratio of 0.10 compared with 225Ac-DOTA-pelgi, 225Ac-DOTA-J591, and 227Th-HOPO-pelgifatamab (227Th-pelgi; all at 300 kBq/kg) with T/Cvolume ratios of 0.37, 0.39, and 0.33, respectively. 225Ac-pelgi was less myelosuppressive than 227Th-pelgi. 225Ac-pelgi showed dose-dependent treatment efficacy in the patient-derived KuCaP-1 model and strong combination potential with darolutamide in both cell line- (22Rv1) and patient-derived (ST1273) xenograft models. CONCLUSIONS These results provide a strong rationale to investigate 225Ac-pelgi in patients with prostate cancer. A clinical phase I study has been initiated (NCT06052306).
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Kelly JM, Amor-Coarasa A, Ponnala S, Nikolopoulou A, Williams C, Thiele NA, Schlyer D, Wilson JJ, DiMagno SG, Babich JW. A Single Dose of 225Ac-RPS-074 Induces a Complete Tumor Response in an LNCaP Xenograft Model. J Nucl Med 2018; 60:649-655. [PMID: 30413660 DOI: 10.2967/jnumed.118.219592] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Accepted: 10/03/2018] [Indexed: 12/13/2022] Open
Abstract
Promising biochemical responses to 225Ac-prostate-specific membrane antigen (PSMA) 617, even in patients who are refractory to β-particle radiation, illustrate the potential of targeted α-therapy for the treatment of metastatic castration-resistant prostate cancer. However, side effects such as xerostomia are severe and irreversible. To fully harness the potential of targeted α-therapy, it is necessary to increase the therapeutic index of the targeted radioligands. One emerging strategy is to increase clearance half-life through enhanced binding to serum albumin. We have evaluated the albumin-binding PSMA-targeting ligand RPS-074 in a LNCaP xenograft model to determine its potential value to the treatment of prostate cancer. Methods: 225Ac-RPS-074 was evaluated in male BALB/c mice bearing LNCaP xenograft tumors. A biodistribution study was performed over 21 d to determine the dosimetry in tumors and normal tissue. The dose response was measured in groups of 7 mice using 37, 74, and 148 kBq of 225Ac-RPS-074 and compared with positive and negative control groups. Mice were sacrificed when tumor volume exceeded 1,500 mm3 Results: 225Ac-RPS-074 was labeled in greater than 98% radiochemical yield and showed high (>10% injected dose/g) and sustained accumulation in LNCaP tumors from 24 h to beyond 14 d. Signal in blood and highly vascularized tissues was evident over the first 24 h after injection and cleared by 7 d. The tumor-to-kidney ratio was 4.3 ± 0.7 at 24 h and 62.2 ± 9.5 at 14 d. A single injection of 148 kBq induced a complete response in 6 of 7 tumors, with no apparent toxic effects. Treatment with 74 kBq induced a partial response in 7 of 7 tumors, but from 42 d, 6 of 7 experienced significant regrowth. The 37-kBq group experienced a survival benefit relative to the negative control but not compared with the positive control group. Conclusion: A single dose of 148 kBq of 225Ac-RPS-074 induced a complete response in 86% of tumors, with tumor-to-normal-tissue ratios that predict an improved therapeutic index. The use of the macropa chelator enabled quantitative radiolabeling and may facilitate the clinical translation of this promising targeted α-therapeutic.
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Affiliation(s)
- James M Kelly
- Division of Radiopharmaceutical Science, Department of Radiology, Weill Cornell Medicine, New York, New York.,Molecular Imaging Innovations Institute (MI3), Department of Radiology, Weill Cornell Medicine, New York, New York
| | - Alejandro Amor-Coarasa
- Division of Radiopharmaceutical Science, Department of Radiology, Weill Cornell Medicine, New York, New York.,Molecular Imaging Innovations Institute (MI3), Department of Radiology, Weill Cornell Medicine, New York, New York
| | - Shashikanth Ponnala
- Division of Radiopharmaceutical Science, Department of Radiology, Weill Cornell Medicine, New York, New York.,Molecular Imaging Innovations Institute (MI3), Department of Radiology, Weill Cornell Medicine, New York, New York
| | - Anastasia Nikolopoulou
- Division of Radiopharmaceutical Science, Department of Radiology, Weill Cornell Medicine, New York, New York.,Citigroup Biomedical Imaging Center, Weill Cornell Medicine, New York, New York
| | - Clarence Williams
- Division of Radiopharmaceutical Science, Department of Radiology, Weill Cornell Medicine, New York, New York.,Molecular Imaging Innovations Institute (MI3), Department of Radiology, Weill Cornell Medicine, New York, New York
| | - Nikki A Thiele
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York
| | | | - Justin J Wilson
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York
| | - Stephen G DiMagno
- College of Pharmacy, University of Illinois-Chicago, Chicago, Illinois; and
| | - John W Babich
- Division of Radiopharmaceutical Science, Department of Radiology, Weill Cornell Medicine, New York, New York .,Molecular Imaging Innovations Institute (MI3), Department of Radiology, Weill Cornell Medicine, New York, New York.,Citigroup Biomedical Imaging Center, Weill Cornell Medicine, New York, New York.,Sandra and Edward Meyer Cancer Center, Weill Cornell Medicine, New York, New York
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