Development of [²²⁵ac]ac-psma-i&t for targeted alpha therapy according to gmp guidelines for treatment of mcrpc

Recently, promising results of the antitumor effects were observed in patients with metastatic castration-resistant prostate cancer treated with177Lu-labeled PSMA-ligands. Radionu-clide therapy efficacy may even be improved by using the alpha emitter Ac-225. Higher efficacy is claimed due to high linear energy transfer specifically towards PSMA positive cells, causing more double-strand breaks. This study aims to manufacture [225Ac]Ac-PSMA-I&T according to good manufacturing practice guidelines for the translation of [225Ac]Ac-PSMA-I&T into a clinical phase 1 dose escalation study. Quencher addition during labeling was investigated. Quality control of [225Ac]Ac-PSMA-I&T was based on measurement of Fr-221 (218 keV), in equilibrium with Ac-225 in approximately six half-lives of Fr-221 (T12 = 4.8 min). Radio-(i)TLC methods were utilized for identification of the different radiochemical forms, gamma counter for concentration determination, and HPGe-detector for the detection of the radiochemical yield. Radiochemical purity was determined by HPLC. The final patient dose was prepared and diluted with an optimized concentration of quenchers as during labeling, with an activity of 8–12 MBq (±5%), pH > 5.5, 100 ± 20 µg/dose, PSMA-I&T, radiochemical yield >95%, radiochemical purity >90% (up to 3 h), endotoxin levels of <5 EU/mL, osmolarity of 2100 mOsmol, and is produced according to current guidelines. The start of the phase I dose escalation study is planned in the near future

Development of alpha particle emitting radionuclide therapy according to GMP guidelines for treatment of mCRPC

Introduction: Patients with metastatic castration resistant prostate cancer (mCRPC) have a poor prognosis. Recently, promising results of antitumor effects were observed in patients with mCRPC treated with Lutetium-177 linked to PSMA. Efficacy of radionuclide therapy might improve with the alpha emitting radionuclide actinium-225 (Ac-225). Ac-225 surfaced as a candidate radionuclide for targeted alpha-particle therapy (TAT) due to the preferable characteristics regarding high LET energies, deposit of the energy at a close range and an appropriate half-life for treatment (T½=9.92 days). Therefore, [225Ac]Ac-PSMA-I&T emerged as a possible  effective treatment of mCRPC. Objectives: The aim of this study is to manufacture [225Ac] Ac-PSMA-I&T according to Good Manufacturing Practice (GMP) guidelines for the translation of [225Ac]Ac-PSMA-I&T (8-12 MBq) into the clinic, for a phase I dose escalation study. Methods: Labelling of PSMA-I&T with Ac-225 was optimized to ensure stability and release criteria. Labelling solution before heating consisted of 15 MBq Ac-225 (~25L 0.1M HCl), 180g/300L PSMAI&T in 0.1M TRIS buffer (pH 9) and 180L ultrapure water. After labelling, 500L ascorbate (pH5.8) and 15 L 4mg/mL DTPA were added. For first labelling, SPE Sep-pak C18 purification was performed to identify and quantify radiolysed PSMA-I&T. Quencher addition (1M ascorbate (pH5.8) 0-100L) during labelling was evaluated. Quality control of [225Ac]Ac-PSMA-I&T is based on measurement of Fransium-221 (Fr-221, 218KeV), which forms an equilibrium with Ac-225 in ~6 T½ of Fr-221 (4.8 min). Detection methods of Ac-225 (Fr-221) are validated according to EANM guidelines. Radio-(I)TLC methods are utilized for identification of different chemical forms. Separation methods; sodium citrate (0.5M pH5) and acetonitrile/water (50:50v/v) are evaluated. Radio-(I)TLC methods  identified free Ac-225, [225Ac]Ac-DTPA and [225Ac]Ac-DTPA (0.5M sodium citrate, pH5). The gamma counter is used for concentration quantification (kBq/L) and HPLC fractions measurement. RCY results are confirmed by HPGe-detector. RCP is determined by HPLC. [225Ac]Ac-PSMA-I&T for injection is prepared by addition of an equal ratio quencher as after stabilization, addition of ethanol (5% final concentration) and saline solution, followed by sterile filtration. Final patient dose is confirmed by dose calibrator. Results: SPE Sep-pak C18 purification confirmed presence of radiolysed [225Ac]Ac-PSMA-I&T (RCP ~82%). After introduction of quencher (100L 1M ascorbate, pH5.8) during labelling, stability increased (RCP >90%). Quality control radio-(I)TLC (Optimal separation method sodium citrate (0.5M, pH 5)), resulted in a RCY >95%, which is confirmed by HPGe detector. Stability could be maintained with a RCP >90% up to 3 hours after labelling (HPLC). After dilution into saline, stability decreased rapidly. Therefore, dilution of labelling solution for injection was prepared by addition equal ratio quencher as after stabilization. [225Ac]Ac-PSMA-I&T (8-12 MBq) solution for injection is produced, containing ~100 g PSMA-I&T per dose. Conclusion: [225Ac]Ac-PSMA-I&T has been produced according to GMP guidelines, conform the release criteria: RCY > 95% and RCP > 90% up to 3 hours after synthesis. The final patient dose [225Ac] Ac-PSMA-I&T (8-12 MBq, 5 mL) allows the start of the phase I dose escalation study, which is planned in the near future