Study With [225Ac]Ac-FL-020 in mCRPC Participants

Inclusion Criteria:

1. Histologically or cytologically confirmed metastatic CRPC.

2. Age ≥ 18 years.

3. Signed informed consent, and able and willing to comply with protocol requirementsprior to any study procedures.

4. All patients are required to have one or more positive lesions detected byPSMA-PET/CT scan

5. Documented progression of the disease based on the Investigator judgement

6. Eastern Cooperative Oncology Group (ECOG) performance status of 0-1.

7. Have a castrate serum testosterone < 50 ng/dL or <1.7 nmol/L. Patients must continueprimary androgen deprivation with an LHRH analogue (agonist/antagonist) if they havenot undergone bilateral orchiectomy.

8. Have previously been treated with at least one of the following:

9. Androgen receptor signaling inhibitor (such as enzalutamide).

10. CYP 17 inhibitor (such as abiraterone acetate).

11. Patients must have been previously treated with at least 1, but no more than 2previous taxane regimens.

12. Adequate organ function as defined by:

13. Absolute neutrophil count (ANC) ≥2 x 10^9/L (2000/µL),

14. Hemoglobin ≥10.0 g/dL,

15. Platelets ≥90 x 10^9/L (90 000/µL),

16. Serum albumin >3g/dL

17. Aspartate aminotransferase (AST) ≤2.5 x ULN; alanine aminotransferase (ALT) ≤2.5 x ULN (AST, ALT ≤5 x ULN if liver metastases are present),

18. ALP ≤2.5 x ULN (ALP ≤5.0 x ULN, if liver or bone metastases are present),

19. Serum total bilirubin ≤1.5 x ULN (≤5 x ULN if liver metastases present)

20. Creatinine clearance ≥60 mL/min calculated using a standard Cockcroft and Gaultformula.

21. Q wave to T wave (QT) interval corrected for heart rate (QTc) <470 ms

Exclusion Criteria:

1. Patients with known brain metastases.

2. Grade 3 Cystitis infective and non-infective.

3. Severe acute or chronic medical or psychiatric conditions or laboratory abnormalitythat may increase the risk associated with the study participation or the studytreatment administration or may interfere with the interpretation of study resultsand, in the judgment of the Investigator, would make the patient inappropriate forenrollment in this study.

4. Previous treatment with Actinium-225, Strontium-89, Samarium-153, Rhenium-186,Rhenium-188, or hemi-body irradiation or any other radionuclide therapy except [177Lu]Lu-PSMA-617 or Radium-223.

5. Radium-223 within 6 months prior to the first study treatment administration.

6. [177Lu]-Lu-PSMA-617 within 6 weeks prior to first study treatment administration.Adverse events related to [177Lu]Lu-PSMA-617 are required to be either resolved orof grade 1 prior to the first study treatment administration.

7. Any systemic anti-cancer therapy (e.g., chemotherapy, immunotherapy or biologicaltherapy [including monoclonal antibodies]) within 6 weeks prior to the first studytreatment administration. Patients on a stable bisphosphonate or denosumab regimenfor 30 days prior to first study treatment administration are eligible.

8. Any investigational agents within 6 weeks prior to the first study treatmentadministration.

9. Radiotherapy: external beam radiotherapy that encompasses >30% of bone marrowcompleted less than 6 weeks or focal radiation completed less than 2 weeks, prior tothe first study treatment administration.

10. Major surgery (not including placement of vascular access device or tumor biopsies)within 6 weeks prior to first dose of the study treatment, or no recovery from sideeffects of such intervention.

11. Symptomatic cord compression, or clinical or radiologic findings indicative ofimpending cord compression.

12. Known hypersensitivity to the components of the study therapy or its analogs.

13. Enrollment in another interventional clinical study.

14. Known history of myelodysplastic syndrome.