SUZHOU, China, June 6, 2023 -- Transcenta Holding Limited ("Transcenta") (HKEX: 06628), a clinical stage biopharmaceutical company with fully-integrated capabilities in discovery, research, development and manufacturing of antibody-based therapeutics, 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 (TST001) 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 in≥10% 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 Q3W 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 Q3W 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 staining≥1+) 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.

“We are very encouraged by these longer follow up data. Based on other clinical trials results, we know that long term efficacy endpoints such as PFS and DOR, rather than ORR, are critical indicators of the potential of Osemitamab. We selected patients with CLDN18.2 expressing tumors, corresponding to around 55% of all cases of G/GEJ cancer, and the benefit risk of Osemitamab in combination with CAPOX in that large group of patients is extremely favorable. We look forward to initiating our Phase III trial for Osemitamab (TST001).” said Dr. Caroline Germa, Transcenta’s Executive Vice President, Global Medicine Development and Chief Medical Officer. 

The full text of posters is available on Transcenta's website: https://www.transcenta.com/Scientific_Publications.html