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Supplementary Table S4 from A Phase I Study of Acapatamab, a Half-life Extended, PSMA-Targeting Bispecific T-cell Engager for Metastatic Castration-Resistant Prostate Cancer

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posted on 2024-04-15, 07:21 authored by Tanya Dorff, Lisa G. Horvath, Karen Autio, Alice Bernard-Tessier, Matthew B. Rettig, Jean-Pascal Machiels, Mehmet A. Bilen, Martijn P. Lolkema, Nabil Adra, Sylvie Rottey, Richard Greil, Nobuaki Matsubara, Daniel S.W. Tan, Alvin Wong, Hiroji Uemura, Charlotte Lemech, Johannes Meran, Youfei Yu, Mukul Minocha, Mason McComb, Hweixian Leong Penny, Vinita Gupta, Xuguang Hu, Gabor Jurida, Hosein Kouros-Mehr, Margit M. Janát-Amsbury, Tobias Eggert, Ben Tran

Summary of treatment-related adverse events with acapatamab monotherapy occurring in ≥ 5% of patients

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ARTICLE ABSTRACT

Safety and efficacy of acapatamab, a prostate-specific membrane antigen (PSMA) x CD3 bispecific T-cell engager were evaluated in a first-in-human study in metastatic castration-resistant prostate cancer (mCRPC). Patients with mCRPC refractory to androgen receptor pathway inhibitor therapy and taxane-based chemotherapy received target acapatamab doses ranging from 0.003 to 0.9 mg in dose exploration (seven dose levels) and 0.3 mg (recommended phase II dose) in dose expansion intravenously every 2 weeks. Safety (primary objective), pharmacokinetics, and antitumor activity (secondary objectives) were assessed. In all, 133 patients (dose exploration, n = 77; dose expansion, n = 56) received acapatamab. Cytokine release syndrome (CRS) was the most common treatment-emergent adverse event seen in 97.4% and 98.2% of patients in dose exploration and dose expansion, respectively; grade ≥ 3 was seen in 23.4% and 16.1%, respectively. Most CRS events were seen in treatment cycle 1; incidence and severity decreased at/beyond cycle 2. In dose expansion, confirmed prostate-specific antigen (PSA) responses (PSA50) were seen in 30.4% of patients and radiographic partial responses in 7.4% (Response Evaluation Criteria in Solid Tumors 1.1). Median PSA progression-free survival (PFS) was 3.3 months [95% confidence interval (CI): 3.0–4.9], radiographic PFS per Prostate Cancer Clinical Trials Working Group 3 was 3.7 months (95% CI: 2.0–5.4). Acapatamab induced T-cell activation and increased cytokine production several-fold within 24 hours of initiation. Treatment-emergent antidrug antibodies were detected in 55% and impacted serum exposures in 36% of patients in dose expansion. Acapatamab was safe and tolerated and had a manageable CRS profile. Preliminary signs of efficacy with limited durable antitumor activity were observed. Acapatamab demonstrated pharmacokinetic and pharmacodynamic activity.

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