A phase I study of ontuxizumab, a humanized monoclonal antibody targeting endosialin, in Japanese patients with solid tumors

Background We conducted a first-in-Japanese, phase I study of ontuxizumab, a humanized, anti-endosialin monoclonal antibody, to confirm its tolerability, safety, and pharmacokinetics, and identify exploratory efficacy. Methods This was a multicenter, multiple-dose, open-label study in Japanese patients aged ≥20 years with solid tumors, including gastric cancer (GC) or advanced hepatocellular carcinoma (HCC), who had failed standard chemotherapy. The study comprised two parts: part 1 (dose-escalation; ontuxizumab 2-12 mg/kg weekly) and part 2 (cohort-expansion; 4 or 8 mg/kg weekly, or 12 mg/kg biweekly). Results Fifteen patients were treated in part 1, and 31 in part 2 (16 patients with GC and 15 with HCC). In part 1, the most common treatment-related, treatment-emergent adverse event (TEAE) was fatigue (20%); no patients had grade ≥ 3 treatment-related TEAEs. In part 2, the most common treatment-related TEAEs were constipation, malaise, hiccups, and increased bilirubin; treatment-related grade 3 TEAEs occurred in two patients with HCC. In part 1, no patients achieved a partial response, and 6/15 (40%) had stable disease (SD). In part 2, 2/15 patients (13.3%) with GC and 8/15 (53.3%) with HCC had SD. Tumor shrinkage was observed in 5/15 HCC patients (33.3%). Conclusions Ontuxizumab, up to a dosage of 12 mg/kg weekly, was generally safe and well tolerated in this population, with no dose-limiting toxicities. The maximum tolerated dose was not reached; 8 mg/kg weekly or 12 mg/kg biweekly were the recommended dosages. We observed long-term disease stabilization in GC and extraskeletal chondrosarcoma, and tumor shrinkage in gastrointestinal stromal tumor and HCC. Trial registration: NCT01773434 ( ClinicalTrials.gov ).

A phase 2 study of ontuxizumab, a monoclonal antibody targeting endosialin, in metastatic melanoma

Objectives Ontuxizumab (MORAB-004) is a first-in-class monoclonal antibody that interferes with endosialin function, which is important in tumor stromal cell function, angiogenesis, and tumor growth. This Phase 2 study evaluated the 24-week progression-free survival (PFS) value, pharmacokinetics, and tolerability of 2 doses of ontuxizumab in patients with metastatic melanoma. Patients and methods Patients with metastatic melanoma and disease progression after receiving at least 1 prior systemic treatment were randomized to receive ontuxizumab (2 or 4 mg/kg) weekly, without dose change, until disease progression. Results Seventy-six patients received at least 1 dose of ontuxizumab (40 received 2 mg/kg, 36 received 4 mg/kg). The primary endpoint, 24-week PFS value, was 11.4% (95% Confidence Interval [CI]: 5.3%-19.9%) for all patients (13.5% for 2 mg/kg and 8.9% for 4 mg/kg). The median PFS for all patients was 8.3 weeks (95% CI: 8.1-12.3 weeks). One patient receiving 4 mg/kg had a partial response, as measured by Response Evaluation Criteria in Solid Tumors v1.1. Twenty-seven of 66 response evaluable patients (40.9%) had stable disease. The median overall survival was 31.0 weeks (95% CI: 28.3-44.0 weeks). The most common adverse events overall were headache (55.3%), fatigue (48.7%), chills (42.1%), and nausea (36.8%), mostly grade 1 or 2. Conclusions Ontuxizumab at both doses was well tolerated. The 24-week PFS value was 11.4% among all ontuxizumab-treated patients. The overall response rate was 3.1% at the 4 mg/kg dose, with clinical benefit achieved in 42.4% of response evaluable patients. Efficacy of single-agent ontuxizumab at these doses in melanoma was low.

Development of 89Zr-Ontuxizumab for in vivo TEM-1/endosialin PET applications

PURPOSE

The complexity of sarcoma has led to the need for patient selection via in vivo biomarkers. Tumor endothelial marker-1 (TEM-1) is a cell surface marker expressed by the tumor microenvironment. Currently MORAb-004 (Ontuxizumab), an anti-TEM-1 humanized monoclonal antibody, is in sarcoma clinical trials. Development of positron emission tomography (PET) for in vivo TEM-1 expression may allow for stratification of patients, potentially enhancing clinical outcomes seen with Ontuxizumab.

RESULTS

Characterization of cell lines revealed clear differences in TEM-1 expression. One high expressing (RD-ES) and one low expressing (LUPI) cell line were xenografted, and mice were injected with 89Zr-Ontuxizumab. PET imaging post-injection revealed that TEM-1 was highly expressed and readily detectable in vivo only in RD-ES. In vivo biodistribution studies confirmed high radiopharmaceutical uptake in tumor relative to normal organs.

EXPERIMENTAL DESIGN

Sarcoma cell lines were characterized for TEM-1 expression. Ontuxizumab was labeled with 89Zr and evaluated for immunoreactivity preservation. 89Zr-Ontuxizumab was injected into mice with high or null expressing TEM-1 xenografts. In vivo PET imaging experiments were performed.

CONCLUSION

89Zr-Ontuxizumab can be used in vivo to determine high versus low TEM-1 expression. Reliable PET imaging of TEM-1 in sarcoma patients may allow for identification of patients that will attain the greatest benefit from anti-TEM-1 therapy.