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

PURPOSE

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 AND METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Xaluritamig, a STEAP1 × CD3 XmAb 2+1 Immune Therapy for Metastatic Castration-Resistant Prostate Cancer: Results from Dose Exploration in a First-in-Human Study

Xaluritamig (AMG 509) is a six-transmembrane epithelial antigen of the prostate 1 (STEAP1)-targeted T-cell engager designed to facilitate lysis of STEAP1-expressing cancer cells, such as those in advanced prostate cancer. This first-in-human study reports monotherapy dose exploration for patients with metastatic castration-resistant prostate cancer (mCRPC), primarily taxane pretreated. Ninety-seven patients received ≥1 intravenous dose ranging from 0.001 to 2.0 mg weekly or every 2 weeks. MTD was identified as 1.5 mg i.v. weekly via a 3-step dose. The most common treatment-related adverse events were cytokine release syndrome (CRS; 72%), fatigue (45%), and myalgia (34%). CRS occurred primarily during cycle 1 and improved with premedication and step dosing. Prostate-specific antigen (PSA) and RECIST responses across cohorts were encouraging [49% PSA50; 24% objective response rate (ORR)], with greater frequency at target doses ≥0.75 mg (59% PSA50; 41% ORR). Xaluritamig is a novel immunotherapy for prostate cancer that has shown encouraging results supporting further development.

SIGNIFICANCE

Xaluritamig demonstrated encouraging responses (PSA and RECIST) compared with historical established treatments for patients with late-line mCRPC. This study provides proof of concept for T-cell engagers as a potential treatment for prostate cancer, validates STEAP1 as a target, and supports further clinical investigation of xaluritamig in prostate cancer. See related commentary by Hage Chehade et al., p. 20. See related article by Nolan-Stevaux et al., p. 90. This article is featured in Selected Articles from This Issue, p. 5.

Long-term Survival of High-Risk Pediatric Patients With Primitive Neuroectodermal Tumors Treated With Antineoplastons A10 and AS2-1

Primitive neuroectodermal tumors (PNETs) are usually successfully treated with craniospinal radiation and chemotherapy; however, difficulties with standard treatment can be encountered in very young children, in adult patients at high risk of complication from standard treatment, and in patients with recurrent tumors. Thirteen children, either with recurrent disease or high risk, were treated in phase II studies with antineoplastons (ANP). The median age of patients was 5 years, 7 months (range, 1-11). Medulloblastoma was diagnosed in 8 patients, pineoblastoma in 3 patients, and other PNET in 2 patients. Previous treatments included surgery in 12 patients (1 had biopsy only, suboccipital craniotomy), chemotherapy in 6 patients, and radiation therapy in 6 patients. Six patients had not received prior chemotherapy or radiation. The treatment consisted of intravenous infusions of 2 formulations of ANP, A10 and AS2-1, and was administered for an average of 20 months. The average dosage of A10 was 10.3 g/kg/d and of AS2-1 was 0.38 g/kg/d. Complete response was accomplished in 23%, partial response in 8%, stable disease in 31%, and progressive disease in 38% of cases. Six patients (46%) survived more than 5 years from initiation of ANP; 5 were not treated earlier with radiation therapy or chemotherapy. The serious side effects included single occurrences of fever, granulocytopenia, and anemia. The study is ongoing and accruing additional patients. The percentage of patients’ response is lower than for standard treatment of favorable PNET, but long-term survival in poor-risk cases and reduced toxicity makes ANP promising for very young children, patients at high risk of complication of standard therapy, and patients with recurrent tumors.

Long-term survival and complete response of a patient with recurrent diffuse intrinsic brain stem glioblastoma multiforme

Recurrent diffuse intrinsic brain stem glioblastoma multiforme carries an extremely poor prognosis and a median survival of less than 7 months. In this article, the authors report good results in a 40-year-old man diagnosed with glioblastoma multiforme who received antineoplastons. The patient's brain tumor was diagnosed in May 1999, and he subsequently underwent subtotal tumor resection and standard radiation therapy. Magnetic resonance imaging and positron emission tomography scans documented his tumor recurrence. Approximately 2 months after completion of radiation therapy, he was admitted for administration of intravenous antineoplastons A10 and AS2-1 through a subclavian venous catheter by intermittent bolus injections 6 times per day using a portable pump. Administration of antineoplastons A10 and AS2-1 was over 655 consecutive days with the exception of a few short interruptions. The maximum dosage of A10 was 8.15 g/kg/d and AS2-1 0.35 g/kg/d. Antineoplastons A10 and AS2-1 administration was very well tolerated with only mild reversible side effects. Follow-up magnetic resonance imaging and positron emission tomography scans revealed decrease and eventually disappearance of the tumor. A complete response was documented after approximately 1 year of antineoplastons A10 and AS2-1 administration. More than 4 years later, off antineoplastons A10 and AS2-1, the patient is tumor free, able to carry on normal activities, and works full-time, and his Karnofsky Performance Status increased from 50 to 100. Extensive phase II trials with antineoplastons A10 and AS2-1 in patients with glioblastoma multiforme are nearing completion. These trials may provide more data regarding the efficacy of antineoplastons A10 and AS2-1 in the treatment of glioblastoma multiforme in untreated patients compared to the results in those patients with tumor recurrence after radiation therapy.

Response of pain to static magnetic fields in postpolio patients: a double-blind pilot study

OBJECTIVE

To determine if the chronic pain frequently presented by postpolio patients can be relieved by application of magnetic fields applied directly over an identified pain trigger point.

DESIGN

Double-blind randomized clinical trial.

SETTING

The postpolio clinic of a large rehabilitation hospital.

PATIENTS

Fifty patients with diagnosed postpolio syndrome who reported muscular or arthritic-like pain.

INTERVENTION

Application of active or placebo 300 to 500 Gauss magnetic devices to the affected area for 45 minutes.

MAIN OUTCOME MEASURE

Score on the McGill Pain Questionnaire.

RESULTS

Patients who received the active device experienced an average pain score decrease of 4.4 +/- 3.1 (p < .0001) on a 10-point scale. Those with the placebo devices experienced a decrease of 1.1 +/- 1.6 points (p < .005). The proportion of patients in the active-device group who reported a pain score decrease greater than the average placebo effect was 76%, compared with 19% in the placebo-device group (p < .0001).

CONCLUSIONS

The application of a device delivering static magnetic fields of 300 to 500 Gauss over a pain trigger point results in significant and prompt relief of pain in postpolio subjects.