The board of directors of Transcenta Holding Limited announced that the Company has presented updated data of Cohort C from a phase I/IIa, multi-center study of Osemitamab (TST001) in combination with Capecitabine and Oxaliplatin (CAPOX) as a first-line treatment of advanced G/GEJ cancer at 2023 American Society of Clinical Oncology (ASCO) Annual Meeting. The data showed that Osemitamab has durable anti-tumor activity in all the study population including both high and low to median CLDN18.2-expressing gastric cancer. These data will support the upcoming global Phase III pivotal trial to be initiated in the second half of 2023.

Adding an anti-claudin18.2 (CLDN18.2) antibody to a chemotherapy is a clinically validated approach for patients with high CLDN18.2 expressing gastric tumors. Osemitamab (TST001) is a potential best-in-class humanized antibody with higher CLDN18.2 binding affinity and lower fucose, resulting in enhanced antibody-dependent cellular cytotoxicity (ADCC) activity. Pre-clinical studies showed that Osemitamab (TST001) has stronger tumor growth inhibition effect than the Zolbetuximab (IMAB362)-analog at the same dose, regardless of CLDN18.2 expression levels.

Title: Osemitamab (TST001) in Combination with Capecitabine and Oxaliplatin (CAPOX) as a First-Line Treatment of Advanced G/GEJ Cancer-updated Data of Cohort C from a Phase I/IIa, Multi-center Study (TranStar102/TST001-1002) Study Design: Transtar-102 (NCT04495296) is an ongoing Phase I/II, open-label, multi-cohort, multi-center clinical study in China to evaluate the efficacy and safety of Osemitamab (TST001) plus CAPOX as a first-line treatment for Chinese patients with unresectable locally advanced or metastatic G/GEJ cancer who had not received prior systemic treatment for advanced disease. Positive CLDN18.2 expression (membranous staining 1+ intensity in10% of tumor cells) as assessed centrally using the LDT assay was required in the expansion phase only. Safety Results: As of April 21, 2023, 15 patients received Osemitamab (TST001) in the escalation phase and 49 patients at dose of 6mg/kg Third Quarter W in the expansion group.

Treatment-emergent adverse events (TEAEs) were mostly grade 1-2 and the most common TEAEs include nausea, hypoalbuminemia, anemia and vomiting. Only one patient experienced grade 3 nausea and vomiting at the dose of 6mg/kg, one patient experienced grade 3 hypoalbuminemia at the dose of 8mg/kg. There were no grade 4 adverse events.

Efficacy Results: As of April 21, 2023, among the 49 patients of 6mg/kg Third Quarter W dose expansion group, 42 patients had measurable lesions and at least one post treatment tumor assessment, 28 (66.7%) achieved partial response. Estimated median duration of response was 9.9 months in 34 responders from all dose groups. Estimated median progression-free survival was 9.5 months from all dose groups.

Conclusions: The safety profile of Osemitamab (TST001) is mainly characterized by manageable on-target, off-tumor side effects; most of these AEs are of grade 1 or 2. The addition of Osemitamab (TST001) to CAPOX for first-line treatment of CLDN18.2 expressing (10% tumor cells with membrane staining1+) patients with G/GEJ cancer leads to improved efficacy outcomes as compared to historical controls, with no trend to lower efficacy with lower levels of expression.