A Phase Ib/II Open-label Study of AMO959 With Lutetium (177Lu) Vipivotide Tetraxetan (AAA617) in Combination With ARPI in Adult Participants With PSMA-positive mCRPC

Incidence of dose limiting toxicities (DLTs) with AMO959 in combination with AAA617 +/- ARPI A dose-limiting toxicity (DLT) is defined as an adverse event or abnormal laboratory value assessed as unrelated to disease, disease progression, inter-current illness/injury, or concomitant medications that occurs within the evaluation period and meets any of the criteria specified in the protocol. The National Cancer Institute Common Terminology Criteria for Adverse events (NCI CTCAE) version 5.0 will be used for all grading.

Incidence of adverse events by type, frequency, and severity, as graded by the NCI CTCAE version 5.0.

The number of participants with dose adjustments (reductions, interruption, or permanent discontinuation).

Dose intensity (computed as the ratio of actual cumulative dose received and actual duration of exposure) and the relative dose intensity (computed as the ratio of dose intensity and planned dose intensity).

Duration of exposure (in months) to each study drug.

Biochemical response (PSA50), defined as the proportion of participants who achieved a ≥ 50% decrease in PSA from baseline at any time during the treatment period prior to start of new anti-cancer therapy that is confirmed by a second PSA measurement ≥ 4 weeks later.

PSA90 response is defined as the proportion of participants who have achieved a ≥ 90% decrease in PSA from baseline at any time during the treatment period prior to start of new anti-cancer therapy that is confirmed by a second PSA measurement ≥4 weeks later.

PSA50 response is defined as the proportion of participants who have achieved a ≥ 50% decrease in PSA from baseline at any time during the treatment period prior to the start of new anti-cancer therapy, confirmed by a second PSA measurement ≥4 weeks later.

Radiographic progression- free survival (rPFS) is defined as the time from the date of start of study treatment (Phase Ib) / randomization (Phase II) to the date of first documented radiographic disease progression using conventional imaging and Prostate Cancer Working Group 3 (PCWG3)-modified RECIST v1.1 criteria (Scher et al 2016) or death due to any cause, whichever occurs first.

Overall Response Rate (ORR) is defined as the proportion of participants with best overall response (BOR) of confirmed complete response (CR) or partial response (PR) in soft tissue based on tumor response data and according to PCWG3-modified RECIST v1.1, in the absence of bone progression as per PCWG3.

Disease control rate (DCR) is defined as the proportion of participants with a BOR of confirmed CR or PR, stable disease (SD) or Non-CR/Non- progressive disease (PD) in soft tissue based on tumor response data and according to PCWG3-modified RECIST v1.1, in the absence of bone progression as per PCWG3.

Duration of Response (DoR) is defined as the duration of time between the date of first documented response (CR or PR) according to PCWG3- modified RECIST v1.1, in the absence of bone progression as per PCWG3, based on tumor response data and the date of first documented radiographic progression in soft tissue or death due to any cause, whichever occurs first.

Overall Survival (OS) is defined as the time from the date of start of study treatment (Phase Ib) / randomization (Phase II) to the date of death due to any cause.

Time to soft tissue progression (TTSTP) is defined as time from randomization to the date of first documented radiographic soft tissue progression per PCWG3-modified RECIST v1.1.

AMO959 pharmacokinetic (PK) samples will be obtained and evaluated in all participants at all dose levels by treatment arms

AAA617 pharmacokinetic (PK) samples will be obtained and evaluated in all participants at all dose levels by treatment arms

Time Activity Curves (TAC) will be generated by plotting concentrations against time.

The organ absorbed radiation dose and effective radiation dose will be evaluated.

Incidence of adverse events by type, frequency, and severity, as graded by the NCI CTCAE version 5.0.

The number of participants with dose adjustments (reductions, interruption, or permanent discontinuation).

Dose intensity (computed as the ratio of actual cumulative dose received and actual duration of exposure) and the relative dose intensity (computed as the ratio of dose intensity and planned dose intensity).

Duration of exposure (in months) to each study drug.

Radiographic Progression Free Survival (rPFS) by Positron Emission Tomography (PET) (rPFS- PET) is defined as the time from the date of randomization to first documented radiographic disease progression (an increase in PSMA-positive tumor volume ≥ 20% from baseline and new PSMA-positive malignant lesions) using PSMA PET/CT imaging (Seifert et al 2023, Gafita et al 2023) or death due to any cause, whichever occurs first.

Change from baseline in FACT-P PCS refers to the difference in a patient's score on the Prostate Cancer Subscale (PCS) of the Functional Assessment of Cancer Therapy-Prostate (FACT-P) questionnaire between the start of a study (baseline) and subsequent time points.

Time to worsening on the Worst Pain defined as the time from the date of randomization to the first occurrence of worsening on the Brief Pain Inventory - Short Form (BPI-SF) Worst Pain item of at least 30% increase from baseline or a minimum of 2 points increase from baseline or death due to any cause, whichever occurs first.

Time to first symptomatic skeletal event (TTSSE) is defined as the time from the date of randomization to the date of first new symptomatic pathological bone fracture, spinal cord compression, tumor-related orthopedic surgical intervention, or requirement for radiation therapy to relieve bone pain, or death due to any cause, whichever occurs first.