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 by Amgen for prostate cancer, primarily metastatic castration‑resistant prostate cancer (mCRPC). A Phase 1 first‑in‑human study has reported antitumor activity and defined dose‑limiting toxicities; a global Phase 3 trial in post‑taxane mCRPC is recruiting. (pubmed.ncbi.nlm.nih.gov)
Xaluritamig is a STEAP1×CD3 “XmAb 2+1” T‑cell engager with two STEAP1‑binding domains and one CD3‑binding domain. It redirects T cells to lyse STEAP1‑expressing tumor cells and was engineered for avidity‑dependent activity, favoring tumor cells with high STEAP1 expression over normal tissues. Preclinical data showed potent T cell–dependent cytotoxicity and tumor regressions in prostate cancer models. (aacrjournals.org)
Phase 1 (dose exploration; monotherapy, mostly taxane‑pretreated mCRPC): - N=97 treated across weekly or Q2W dosing; median age 67. Confirmed PSA50 responses in 49% overall; at target doses ≥0.75 mg, PSA50 59% and objective response rate (ORR) 41% in RECIST‑evaluable disease. Overall ORR 24%. (pubmed.ncbi.nlm.nih.gov) - ESMO 2023 interim presentation (same study) reported, among 67 RECIST‑evaluable patients, 24% confirmed partial responses and 48% stable disease; at higher dose levels (n=37), 41% PR and 38% SD. PSA50 achieved by 47% overall and 54% at higher doses; PSA90 by 27% overall. (oncologypro.esmo.org)
A randomized Phase 3 study (XALute; NCT06691984) is comparing xaluritamig against cabazitaxel or a second androgen receptor–directed therapy (enzalutamide or abiraterone) with overall survival as the primary endpoint; the trial opened in December 2024 and is recruiting. (cdek.pharmacy.purdue.edu)
In the Phase 1 dose‑exploration study (N=97): - Most common treatment‑related adverse events: cytokine release syndrome (CRS) 72%, fatigue 45%, myalgia 34%; CRS was predominantly grade 1–2, occurred mainly in cycle 1, and was mitigated with premedication and step‑dosing. Maximum tolerated dose identified as 1.5 mg IV weekly using a 3‑step dose. (pubmed.ncbi.nlm.nih.gov) - ESMO 2023 interim reported grade ≥3 CRS in about 2% (1 event grade 3); other frequent events included pyrexia and anemia. Treatment‑related adverse events leading to discontinuation occurred in 17.5% of patients in the presented dataset. (oncologypro.esmo.org)
Preliminary pharmacokinetics showed dose‑proportional exposure with a terminal half‑life of approximately 3–4 days. (oncologypro.esmo.org)
Last updated: Oct 2025
Goal: Compare overall survival of xaluritamig versus investigator’s choice of cabazitaxel or a second androgen receptor–directed therapy in post‑taxane metastatic castration‑resistant prostate cancer (mCRPC).
Patients: Adults with histologically confirmed prostate adenocarcinoma, metastatic castration‑resistant disease with at least one measurable or bone lesion, and evidence of progression per PCWG3. All must be castrate (testosterone <50 ng/dL), have ECOG 0–1, prior progression on at least one AR‑directed agent (enzalutamide, abiraterone, apalutamide, or darolutamide), and have received exactly one taxane in the mCRPC setting; docetaxel in mHSPC is allowed. Key exclusions include prior STEAP1‑targeted therapy, recent anticancer therapy, recent or extensive PSMA radioligand therapy, recent radionuclide therapy, active CNS metastases (stable treated dural metastases allowed), and unresolved >grade 1 toxicities.
Design: Phase 3, open‑label, multicenter, randomized study (allocation 1:1) enrolling approximately 675 participants after chemotherapy in the mCRPC setting. Primary intent is superiority on overall survival. Stratification factors are expected to include prior therapies and disease characteristics; imaging assessments will be centrally reviewed for key efficacy endpoints.
Treatments: Experimental: Xaluritamig administered as intravenous infusion. Xaluritamig (AMG 509) is a first‑in‑class bispecific T‑cell–engaging antibody that binds STEAP1 on prostate cancer cells and CD3 on T cells, using an XmAb 2+1 format to enhance STEAP1 avidity with reduced Fc effector function. Early phase 1 studies in heavily pretreated mCRPC reported PSA50 responses around 49% overall and higher at target doses, with objective responses by RECIST in patients with measurable disease; cytokine release syndrome, typically early and manageable with step‑up dosing and premedication, is the most common adverse event. The 1.5 mg target regimen showed improved activity and an acceptable safety profile and was advanced to phase 3. Control: Investigator’s choice of cabazitaxel IV, or a second AR‑directed therapy (abiraterone or enzalutamide) per standard dosing and labeling.
Outcomes: Primary endpoint: overall survival. Key secondary endpoints include radiographic progression‑free survival by BICR using PCWG3‑modified RECIST v1.1, 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, EQ‑5D‑5L, FACT‑P including time to worsening and improvement), PSA50 and PSA90 response rates, and xaluritamig pharmacokinetics and immunogenicity (Cmax, Tmax, Cmin, AUC, accumulation, half‑life, anti‑drug antibodies). Follow‑up for efficacy and safety is planned for up to approximately 43 months.
Burden on patient: Moderate. Participants will require regular clinic visits for IV infusions, especially in the xaluritamig arm where step‑up dosing and early‑cycle monitoring for cytokine release syndrome may necessitate longer or more frequent visits during initial cycles. Imaging for rPFS by BICR will involve periodic CT/MRI and bone scans at standard mCRPC intervals, comparable to usual care. Safety assessments, laboratory monitoring, and comprehensive PRO instruments add time but are routine for phase 3 mCRPC trials. The xaluritamig arm includes pharmacokinetic and immunogenicity blood draws that increase visit duration and blood sampling, mainly in early cycles; control‑arm burden varies by choice of cabazitaxel IV (higher infusion‑visit burden) versus oral ARDT (lower visit burden). Overall travel and testing are greater than standard oral therapy alone but similar to other phase 3 IV‑based mCRPC studies.
Last updated: Oct 2025
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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