Sponsor: Amgen (industry)
Phase: 3
Start date: Dec. 9, 2024
Planned enrollment: 675
Xaluritamig (AMG 509) is an investigational, first‑in‑class bispecific T‑cell–engaging antibody being developed for prostate cancer. It targets the prostate cancer antigen STEAP1 and CD3 on T cells. Initial human data in metastatic castration‑resistant prostate cancer (mCRPC) show antitumor activity with a safety profile characterized by mostly early, manageable cytokine release syndrome (CRS). A global phase 1 program is ongoing across late‑ and earlier‑stage settings, and Amgen has initiated/enrolled additional phase 1b studies and a phase 3 trial in post‑taxane mCRPC. (aacrjournals.org, ichgcp.net, cdek.pharmacy.purdue.edu, amgen.com)
First‑in‑human, phase 1 (NCT04221542) monotherapy dose‑exploration/optimization in heavily pretreated mCRPC: - Across all dose cohorts (n≈97): confirmed PSA50 response in 49% and RECIST v1.1 objective response rate (ORR) 24% among patients with measurable disease. (aacrjournals.org, pubmed.ncbi.nlm.nih.gov) - At target doses ≥0.75 mg: PSA50 59% and ORR 41%. (aacrjournals.org)
Longer follow‑up and dose‑optimization (ESMO 2024 and company summary): - In dose‑exploration cohorts, median overall survival (OS) ~17–18 months with longer follow‑up; higher‑depth PSA90 response correlated with improved survival. (oncologypro.esmo.org, nasdaq.com) - In a randomized dose‑expansion comparing target doses (0.75 mg vs 1.5 mg), the 1.5 mg regimen improved efficacy and was selected for further development (recommended for phase 3). (oncologypro.esmo.org, nasdaq.com)
Notes: Reported response and safety figures are from early‑phase studies in heavily pretreated mCRPC and may evolve with ongoing dose‑expansion, optimization, and phase 3 evaluation. (aacrjournals.org, oncologypro.esmo.org, amgen.com)
Last updated: Sep 2025
Goal: Compare overall survival of xaluritamig versus investigator’s choice of cabazitaxel or a second androgen receptor–directed therapy (abiraterone or enzalutamide) in post-taxane metastatic castration-resistant prostate cancer (mCRPC).
Patients: Adults with histologically confirmed prostate adenocarcinoma and mCRPC, at least one measurable or bone lesion, evidence of progression per PCWG3 criteria, castrate testosterone levels while on continuous ADT or after orchiectomy, prior progression on at least one AR-directed therapy, and exactly one prior taxane in the mCRPC setting (docetaxel in mHSPC allowed in addition). ECOG 0–1 and adequate organ function required. Key exclusions include prior STEAP1-targeted therapy, recent anticancer therapy, recent PSMA-RLT (unless <2 cycles), recent radionuclide or palliative radiotherapy without recovery, active concurrent systemic anticancer therapies, and history of CNS metastases other than treated, asymptomatic, stable dural disease.
Design: Phase 3, open-label, multicenter, randomized trial with approximately 675 participants allocated to xaluritamig versus investigator’s choice of cabazitaxel or second AR-directed therapy. Primary purpose is treatment; analyses will compare survival and key efficacy and patient-reported endpoints between arms with blinded independent central review for radiographic endpoints.
Treatments: Xaluritamig (AMG 509) administered by intravenous infusion. Xaluritamig is an investigational, first-in-class bispecific T-cell–engaging antibody targeting STEAP1 on prostate cancer cells and CD3 on T cells, using an XmAb 2+1 format to enhance STEAP1 avidity with a reduced-effector Fc. In phase 1 mCRPC studies, xaluritamig demonstrated antitumor activity (approximate PSA50 49% overall; higher responses at target doses) with a safety profile notable for mostly early, manageable cytokine release syndrome mitigated by step-up dosing and premedication; a 1.5 mg target regimen was selected for further development. Comparator arm: cabazitaxel IV or a second AR-directed therapy (abiraterone or enzalutamide) given per standard dosing at investigator discretion.
Outcomes: Primary endpoint is overall survival. Key secondary endpoints include rPFS by PCWG3-modified RECIST v1.1 per blinded independent central review, objective response rate, duration of response, disease control rate, time to response, time to first symptomatic skeletal event, safety and tolerability (TEAEs), patient-reported outcomes (BPI-SF pain measures, FACT-P, EQ-5D-5L, PRO-CTCAE), PSA50 and PSA90 response rates, and pharmacokinetics and immunogenicity of xaluritamig (Cmax, Tmax, Cmin, AUC, accumulation, half-life, anti-drug antibodies). Assessments are planned for up to approximately 43 months.
Burden on patient: Moderate. Participants will require regular clinic visits for IV administration, especially early cycle monitoring for cytokine release syndrome with potential step-up dosing and premedications. Imaging for rPFS with BICR, serial PSA testing, frequent safety labs, and comprehensive PRO questionnaires add to visit time but are consistent with advanced mCRPC trials. The xaluritamig arm may include additional pharmacokinetic and immunogenicity blood draws, particularly in early cycles, increasing chair time and venipuncture frequency. Oral comparator options may lessen visit burden, whereas cabazitaxel involves infusion visits similar to xaluritamig. Travel demands are typical for phase 3 oncology studies, without mandated biopsies or highly intensive procedures reported.
Inclusion Criteria:
* Participant has provided informed consent prior to initiation of any study-specific activities/procedures.
* Age ≥ 18 years (or ≥ legal age within the country if it is older than 18 years) at the time of signing the informed consent.
* Participant must have histological, pathological, and/or cytological confirmation of adenocarcinoma of the prostate. Mixed histologies (eg, adenocarcinoma with neuroendocrine component) are not permitted.
* mCRPC with ≥ 1 metastatic lesion that is present on baseline computed tomography (CT), magnetic resonance imaging (MRI), or bone scan imaging obtained within 28 days prior to enrollment.
* Evidence of progressive disease, defined as 1 or more PCWG3 criteria:
* Serum PSA progression defined as 2 consecutive increases in PSA over a previous reference value measured at least 1 week prior. The minimal start value is 2.0 ng/mL.
* Soft-tissue progression defined as an increase ≥ 20% in the sum of the diameter (SOD) (short axis for nodal lesions and long axis for non-nodal lesions) of all target lesions based on the smallest SOD since treatment started or the appearance of one or more new lesions or unequivocal progression of existing non-target lesions.
* Progression of bone disease: defined by the appearance of at least 2 new bone lesion(s) by bone scan (as per the 2+2 PCWG3 criteria).
* Participants must have had a prior orchiectomy and/or ongoing androgen-deprivation therapy and a castrate level of serum testosterone (\< 50 ng/dL or \< 1.7 nmol/L).
* Prior progression on at least one ARDT (enzalutamide, abiraterone, apalutamide, darolutamide).
* Prior treatment with only one taxane therapy in the mCRPC setting. Note: Prior treatment with docetaxel in the metastatic hormone-sensitive prostate cancer (mHSPC) setting is permitted; however, participants must have also received one, and only one, taxane therapy in the mCRPC setting.
* Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 or 1.
* Adequate organ function.
Key Exclusion Criteria:
Prior \& Concomitant Therapy:
* Prior six transmembrane epithelial antigen of the prostate 1 (STEAP1)-targeted therapy.
* Any anticancer therapy, immunotherapy, or investigational agent within 4 weeks prior to the first dose of study treatment, not including androgen suppression therapy (eg, luteinizing hormone-releasing hormone/gonadotropin-releasing hormone \[LHRH/GnRH\] analogue \[agonist/antagonist\]).
* Prior Prostate-Specific Membrane Antigen (PSMA) radioligand therapy (RLT) within 3 months of the first dose of study treatment unless participants received \< 2 cycles of therapy.
* Prior palliative radiotherapy within 2 weeks of first dose of study treatment. Participants must have recovered from all radiation-related toxicities.
* Concurrent cytotoxic chemotherapy, ARDT, immunotherapy, radioligand therapy, PARP inhibitor, biological therapy, investigational therapy. Note: Prior treatment with a PARP inhibitor is permitted as long as not within 4 weeks before first dose of study treatment.
* Prior radionuclide therapy (Radium-223) within 2 months of first dose of study treatment.
* Treatment with live and live-attenuated vaccines within 4 weeks before the first dose of study treatment.
Disease Related:
* Participants with a history of central nervous system (CNS) metastasis. Note: Participants with treated, asymptomatic, and clinically stable dural metastases are eligible.
* Unresolved toxicities from prior anti-tumor therapy not having resolved to CTCAE version 5.0 events grade above 1 or baseline, with the exception of alopecia or toxicities that are stable and well controlled AND there is an agreement to allow inclusion by both the investigator and the sponsor.
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