A Study of FG-3246 in Participants With Metastatic Castration-Resistant Prostate Cancer (mCRPC)

Open to males ages 18 years and up

• Participant must have histological, and/or cytological confirmation of prostate adenocarcinoma.
• Participant with safely accessible tumor lesion must agree to biopsy of a primary or metastatic lesion during screening. Alternatively, participant may provide an archival biopsy of a primary or metastatic lesion that was taken after castration resistance developed and within 1 year prior to randomization.
• Participant must have serum testosterone levels <50 nanograms (ng)/deciliter (dL) during screening.
• Participant is required to have progressed on one prior treatment with a second generation ARSI (abiraterone acetate, enzalutamide, apalutamide, or darolutamide) initiated in either the castration-sensitive or castration-resistant setting.
• Participant must have progressive mCRPC following last treatment at screening.
• Participant must have ≥1 metastatic lesion that is present on baseline Computed Tomography (CT), Magnetic Resonance Imaging (MRI), or bone scan obtained ≤28 days prior to randomization.
• Participant must have adequate organ function during screening and reconfirmed on Study Day -1 or Day 1.

• Participant has received previous treatment with a therapeutic targeting CD46.
• Participant has small cell neuroendocrine carcinoma (pure or mixed) or any other non-adenocarcinoma component on prior or current histologic evaluation of primary or metastatic lesion.
• Participant has received more than one prior second-generation ARSI in any setting.
• Participant has received any systemic anticancer therapy (for example, hormonal therapy, chemotherapy, immunotherapy, radioligand therapy, or biological therapy [including monoclonal antibodies], including investigational therapy) within 28 days prior to randomization.
• Participant has received any prior radiation therapy within 28 days prior to randomization.
• Participant has a known actionable mutation or gene alteration, for example, BRCA1 mutation, for which approved therapies are available, for example, PARP inhibitors, unless these therapies are not appropriate for the participant as determined by the investigator or the participant refuses such therapy.
• Participant has National Cancer institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) ≥Grade 2 peripheral neuropathy at the time of screening from any etiology.
• Participant has received any prior chemotherapy; however, one prior taxane-based chemotherapy in the castration-sensitive setting is allowed if completed >12 months before randomization.
• Participant has known hypersensitivity to the components of FG-3246 or its analogs or a history of allergic or anaphylactic reaction to human, humanized, or chimeric monoclonal antibodies.
• Participant has diagnosis with any other malignancy in the past 5 years, except for adequately treated basal cell or squamous cell carcinoma of the skin.
• Participant requires treatment with a strong cytochrome P450 3A4 (CYP3A4) inhibitor or inducer drug that cannot be safely discontinued.

NOTE: Other protocol-defined inclusion/exclusion may apply.