Recruitment for PROter A206T-G01-001 (NCT03490838) was halted in Phase I by sponsor decision. Phase II expansion portion of the study was never initiated.

This Phase 1/2 study is intended to investigate the safety, tolerability, and radiation dosimetry of 177Lu-PSMA-R2 and further assess preliminary efficacy data in patients with metastatic castration-resistant prostate cancer (mCRPC). The Phase 1 portion of the study will determine the recommended dose of 177Lu-PSMA-R2 for radio-ligand therapy (RLT) of mCRPC, and the Phase 2 portion will expand into approximately 60 patients documenting the preliminary activity (anti-tumor response) of repeated treatments administered, continuing safety assessments and collecting QoL data.

Recruitment for PROter A206T-G01-001 (NCT03490838) was halted in Phase I by sponsor decision. Phase II expansion portion of the study was never initiated. Importantly, this recruitment halt was not a consequence of any safety concern. Ongoing patients at the time of recruitment halt continued per protocol and completed the 1 year safety follow-up prior to early study termination.

The primary objective of the Phase I portion of the study to assess the safety and tolerability of 177Lu-PSMA-R2 and to assess Dose Limiting Toxicities (DLTs) and determine the maximum tolerated dose (MTD) (if reached) and the recommended Phase II dose was not reached due to early recruitment halt.

Inclusion Criteria:

• Male patients, 18 years of age or older

• Signed and dated written ICF by the patient or legally acceptable representative prior to any study-specific procedures

• Histologically confirmed adenocarcinoma of the prostate

• Serum testosterone levels < 50 ng/dL after surgical or continued chemical castration

• Metastatic disease documented by CT/MRI or bone scan (not older than 28 days at enrollment) revealing at least one metastatic lymph-node, visceral metastasis and/or bone metastasis

• Positive 68Ga-PSMA-R2 PET/CT scan for central eligibility assessment. Patients who receive 68Ga-PSMA-R2 as part of separate clinical protocol are eligible (must meet all study eligibility criteria)

• Documented progressive mCRPC on or after the last systemic treatment administered for the advanced disease including metastatic disease. Disease progression defined as increasing serum PSA (per PCWG3), radiological progression or ≥ 2 new bone lesions.

• Must have received prior systemic treatment for mCRPC including CYP17 inhibitors and/or androgen-pathway inhibitors (i.e. abiraterone and/or enzalutamide when available) and one and no more than one line of chemotherapy for the advanced disease (unless ineligible (unfit) to receive chemotherapy).

• At least 28 days elapsed between last anti-cancer treatment administration and the initiation of study treatment (except for Luteinizing Hormone-releasing Hormone [LHRH] or Gonadotropin-releasing Hormone [GnRH]), or resolution of all previous treatment related toxicities to CTCAE version 5.0 grade of ≤ 1 (except for chemotherapy induced alopecia and grade 2 peripheral neuropathy or grade 2 urinary frequency which are allowed). Prior major surgery must be at least 12 weeks prior to study entry.

• Eastern cooperative oncology group (ECOG) performance status of 0-2 with a life expectancy ≥ 6 months

• Adequate bone marrow reserve and organ function as demonstrated by complete blood count, and biochemistry in blood and urine at baseline

  1. Platelet count of >100 x10e9/L
  2. White blood cell (WBC) count > 3,000/mL
  3. Neutrophil count > 1,500/mL
  4. Hemoglobin ≥ 10 g/dL
  5. Serum creatinine < 1.5 x upper limit normal (ULN) or estimated glomerular filtration rate (GFR) > 50 mL/min based upon Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) equation. Patients with estimated GFR between 50 - 60 mL/min at baseline will require a 99mTc-DTPA GFR test and only patients with non-obstructive pathology will be included in the study.
  6. Total bilirubin < 3 x ULN (except if confirmed history of Gilbert's disease)
  7. Baseline serum albumin > 30 g/L
  8. Aspartate aminotransferase (AST) < 3 times the ULN

• For male patients with partners of childbearing potential, agreement to use barrier contraceptive method (condom) and to continue its use for 6 months from receiving the last dose of IP

Exclusion Criteria:

• Pathological finding consistent with small cell, neuroendocrine carcinoma of the prostate or any other histology different than adenocarcinoma.

• Diffuse bone-marrow involvement (i.e. "superscan" defined as bone scintigraphy in which there is excessive skeletal radioisotope uptake [>20 bone lesions] in relation to soft tissues along with absent or faint activity in the genitourinary tract due to diffuse bone/ bone marrow metastases)

• Prior exposure to radioligand therapy radioisotope therapy (e.g. 89Sr), systemic radiotherapy or 223Ra-therapy.

• Current severe urinary incontinence, hydronephrosis, severe voiding dysfunction, any level of urinary obstruction requiring indwelling/condom catheters

• Spinal cord compression or brain metastases

• Uncontrolled pain that results in patient's lack of compliance with the imaging procedures

• Uncontrolled cardiovascular history, defined as:

  • Congestive heart failure (New York Heart Association [NYHA] II, III, IV)
  • Mean resting corrected QT interval (QTc) >450 millisecond (msec), obtained from 3 ECGs recordings, using the screening clinic ECG machine-derived QTc value.
  • Any clinically important abnormalities in rhythm, conduction, or morphology of resting ECG (e.g., complete left bundle branch block, third-degree heart block, second-degree heart block, PR interval >250 msec).
  • Any factor increasing the risk of QTc prolongation or risk of arrhythmic events such as heart failure, hypokalemia, congenital long QT syndrome, family history of long QT syndrome, or unexplained sudden death under 40 years of age in first-degree relatives, or any concomitant medication known to prolong the QT interval.

• Other known co-existing malignancies except non-melanoma skin cancer or low grade superficial bladder cancer unless definitively treated and proven no evidence of recurrence for 5 years.

• History of deep vein thrombosis and/or pulmonary embolism within 4 weeks of enrollment.

• Known incompatibility to CT or PET scans.

• Any evidence of severe or uncontrolled systemic or psychiatric diseases, including uncontrolled hypertension and active bleeding diatheses, which in the Investigator's opinion makes it undesirable for the patient to participate in the trial or which would jeopardize compliance with the protocol

• Active infection including human immunodeficiency virus (HIV) and untreated hepatitis B, and hepatitis C. Screening for chronic conditions is not required.

• Patients who have received any investigational treatment agent within the last 28 days.

• Known allergies, hypersensitivity, or intolerance to the IP or its excipients

• Known history of myelodysplastic syndrome/leukemia at any time

• Patient is unlikely to comply with study procedures, restrictions and requirements and judged by the Investigator that the patient is not suitable for participation in the study.