ARTEMIS-002: Phase 2 study of HS-20093 in patients with relapsed or refractory osteosarcoma.

11507 Background: Patients (pts) with relapsed and refractory (R/R) osteosarcoma have a poor prognosis with limited therapeutic options. HS-20093 is a novel antibody-drug conjugate (ADC) targeting B7-H3, which showed preliminary anti-tumor activity in phase 1 ARTEMIS-001 study (NCT05276609). Here we report results in R/R osteosarcoma pts treated with HS-20093 from ARTEMIS-002 study (NCT05830123). Methods: ARTEMIS-002 trial is an open label, two-arm phase 2 trial in pts with R/R osteosarcoma or other sarcomas progressed upon standard systemic treatment. Based on the results of the phase 1 trial that the maximum tolerated dose was 12 mg/kg once every 3 weeks (Q3W) intravenous infusion, the osteosarcoma pts in the phase 2 trial were randomized to receiving HS-20093 either at 8 mg/kg or 12 mg/kg Q3W at a ratio of 1:1. The primary endpoint was objective response rate (ORR) according to RECIST1.1. B7-H3 expression was retrospectively evaluated by IHC in osteosarcoma FFPE tissue. Results: A total of 34 pts with R/R osteosarcoma were enrolled from June to December in 2023, receiving HS-20093 at the dose of either 8.0 mg/kg (N = 15) or 12.0 mg/kg (N = 19). Median age was 21.5 years (range: 18~65). At baseline, most pts were evaluated with clinical stage IV disease (32/34, 94.1%) and pulmonary metastasis (28/34, 82.4%). Twenty-two pts (64.7%) had received ≥3 prior lines therapy. Twenty-six pts (76.5%) had received 4 types of standard chemotherapies consisting of platinum, anthracyclines, ifosfamide and methotrexate. Treatment emergent adverse event (TEAEs) occurred in 33 pts (97.1%). The common grade 3/4 TEAEs (≥5%) were: neutropenia, leukopenia, thrombocytopenia, lymphopenia and anemia. The incidences of discontinuations, dose withhold and dose reductions were 2.9%, 11.8% and 23.5%, respectively. There was no TEAE leading to death. As of cut-off date (25 December, 2023), the median follow-up time was 4.1 months (95% CI: 1.4~5.5) among 21 response-evaluable pts (11 treated with 8 mg/kg and 10 with 12.0 mg/kg). The ORR of 12.0 mg/kg HS-20093 was 20.0%. Two confirmed partial responses were observed in pts with 12.0 mg/kg and remained on response until last follow-up, of which the longest duration of response was 4.0 months. The disease control rate was 81.8% (9/11) and 100% (10/10) in pts with 8 mg/kg and 12.0 mg/kg. The median progression-free survival of all 21 pts was not mature. B7-H3 is highly expressed in osteosarcoma with median H-score 185 (0~260). No correlation was observed between tumor response and B7-H3 expression level. The PK exposure of HS-20093 ADC, total Ab and payload increased with dose, approximately proportional to dose, with a half-life of 4 to 6 days, and no or minor accumulation after multiple doses of Q3W. Conclusions: The data has demonstrated that HS-20093 exhibited promising antitumor activity with acceptable toxicity in pts of heavily-pretreated R/R osteosarcoma. The enrollment of ARTEMIS-002 is continuing. Clinical trial information: NCT05830123 .