Amgen's PSMA Bispecific T-Cell Engager Acapatamab Tested in Advanced Prostate Cancer
Phase 1 trial of acapatamab, a PSMA-targeting bispecific T-cell engager, enrolls 212 men with metastatic castration-resistant prostate cancer.
Summary
This phase 1 clinical trial from Amgen evaluated acapatamab, a novel immunotherapy that uses bispecific T-cell engager technology to target PSMA — a protein highly expressed on prostate cancer cells. The trial enrolled 212 patients with metastatic castration-resistant prostate cancer, a difficult-to-treat late-stage disease. Researchers assessed safety, tolerability, how the drug behaves in the body, and early signs of efficacy, while also testing combination regimens with pembrolizumab and etanercept. The trial was ultimately terminated before completion. Despite its early termination, this study represents an important step in applying next-generation immunotherapy strategies to prostate cancer, a disease where durable responses to immune checkpoint therapy have historically been elusive. Results from this study continue to inform PSMA-directed therapeutic development.
Detailed Summary
Metastatic castration-resistant prostate cancer remains one of the most challenging oncologic conditions to treat, with limited long-term response rates to existing therapies. Immunotherapy has transformed outcomes in many cancers, but prostate cancer has proven largely resistant to checkpoint inhibitors alone. Bispecific T-cell engagers represent a promising next step, redirecting patients' own immune cells to attack tumor targets with precision.
This phase 1 study, sponsored by Amgen and registered in 2019, evaluated acapatamab — a half-life extended bispecific T-cell engager designed to simultaneously bind PSMA on prostate cancer cells and CD3 on T cells, triggering targeted tumor killing. The trial enrolled 212 subjects with metastatic castration-resistant prostate cancer across multiple investigational arms. In addition to acapatamab monotherapy, the trial explored combinations with pembrolizumab, an anti-PD-1 checkpoint inhibitor, and etanercept, a TNF-alpha blocker potentially included to manage cytokine-related toxicity.
The primary goals were to characterize safety and tolerability, establish the maximum tolerated dose or recommended phase 2 dose, and collect pharmacokinetic data. Early efficacy signals, likely assessed via PSA response and radiographic progression, were secondary objectives.
The trial was terminated in June 2023 before its anticipated completion, which may reflect safety concerns, interim efficacy findings, strategic portfolio decisions by Amgen, or competitive shifts in the PSMA-targeting landscape. The trial's termination does not necessarily indicate failure, but it limits interpretation of the full efficacy profile.
Despite termination, acapatamab's development adds to growing evidence that bispecific T-cell engager strategies can be rationally applied to prostate cancer. The coinvestigation of pembrolizumab and etanercept suggests the field is actively exploring ways to enhance response and manage immune-related adverse events simultaneously — a combination approach likely to shape future prostate cancer immunotherapy trials.
Key Findings
- Phase 1 trial enrolled 212 patients with metastatic castration-resistant prostate cancer across multiple arms.
- Acapatamab is a PSMA-targeting, half-life extended bispecific T-cell engager designed to recruit T cells to tumors.
- Trial tested combinations with pembrolizumab and etanercept, suggesting efforts to boost efficacy and manage toxicity.
- Trial was terminated in 2023 before completion, limiting full interpretation of safety and efficacy results.
- Study aimed to establish maximum tolerated dose and recommended phase 2 dosing for future trials.
Methodology
This was an open-label, dose-escalation phase 1 trial enrolling 212 participants with mCRPC, sponsored by Amgen. Multiple investigational arms included monotherapy and combination cohorts with pembrolizumab and etanercept. The trial ran from February 2019 to June 2023 before being terminated.
Study Limitations
The trial was terminated before completion, and no efficacy or safety results are publicly reported in the available abstract, significantly limiting clinical interpretation. This summary is based on the abstract and trial registration only — full data have not been reviewed. Reasons for termination are not disclosed, which may reflect safety, efficacy, or commercial factors.
Enjoyed this summary?
Get the latest longevity research delivered to your inbox every week.