On June 30, 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, reported progression free survival (PFS) data by CLDN18.2 expression level from Phase I/II study of Osemitamab (TST001) plus Capecitabine and Oxaliplatin (CAPOX) as the first-line treatment of advanced gastric/gastroesophageal junction (G/GEJ) cancer at ESMO (Free ESMO Whitepaper) World Congress on Gastrointestinal Cancer 2023. These data will support the upcoming global Phase III pivotal trial to be initiated in the second half of 2023.

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Title

Osemitamab (TST001) plus Capecitabine and Oxaliplatin (CAPOX) as the First-Line Treatment of Advanced G/GEJ Cancer – Updated Efficacy Data per Claudin 18.2 Expression Level from Study TranStar102/TST001-1002-Cohort C.

Study Design

The efficacy and safety of Osemitamab (TST001) plus CAPOX as the first-line treatment for patients with advanced G/GEJ cancer was explored in a dose escalation and expansion Phase I/II study in China (Cohort C of TranStar102, NCT04495296). In the expansion phase (except 8 patients from a safety run-in), CLDN18.2 positive was required, which is defined as IHC membrane staining ≥10% tumor cells with ≥1+ intensity per LDT assay, selecting approximately 55% of the screened patients.

Study Results

As of April 21, 2023, a total number of 64 patients were dosed with Osemitamab (TST001) in combination with CAPOX, 15 patients received Osemitamab (TST001) at doses ranging from 1 to 8 mg/kg Q3W in the dose escalation and 49 patients at 6 mg/kg in the dose expansion. The median follow-up was 195 days.
41 out of 49 patients in the dose expansion at 6mg/kg had CLDN18.2 positive tumor (High: n=9, Medium: n=13, Low: n=19), 8 patients didn’t get their tumor tested (unknown CLDN18.2 expression). The baseline demographics of this dose expansion are similar to that of the overall population published on 2023 ASCO (Free ASCO Whitepaper) (abstract 4046*). There are no clinically significant differences in baseline characteristics across different CLDN18.2 expression levels.
The safety profile of Osemitamab (TST001) is mainly characterized by manageable on-target off-tumor effects and has been presented during at ASCO (Free ASCO Whitepaper) 2023 (abstract 4046*). Most of these AEs are of grade 1 or 2 and occurred during the first 2 cycles.
At the cut-off date of April 21, 2023, 26 out of 64 patients had progression disease or death, with an estimated median progression-free survival (PFS) 9.5 months. There was no clear trend between progression-free survival and the CLDN18.2 expression levels.
"Appropriately selecting the patients is critical to optimize the benefit/risk of treatment with Osemitamab (TST001). Using our proprietary CLDN18.2 assay, we have selected 55% of the G/GEJ cancer patients and shown that the lower expressors amongst these patients derive the same level of durable benefit than the higher expressors. This is a key differentiation and a significant dataset supporting our Phase III design globally." said Dr. Caroline Germa, Transcenta’s Executive Vice President, Global Medicine Development and Chief Medical Officer.

About Osemitamab (TST001)

Osemitamab (TST001) is a high affinity humanized anti- CLDN18.2 monoclonal antibody with enhanced antibody-dependent cellular cytotoxicity ("ADCC"). It has shown potent anti-tumor activities in tumor xenograft models. Osemitamab (TST001) is the second most advanced CLDN18.2 targeting antibody being developed globally. Osemitamab (TST001) was generated using Transcenta’s Immune Tolerance Breaking Technology (IMTB) platform. Osemitamab (TST001) kills CLDN18.2 expressing tumor cells by mechanisms of ADCC. Leveraging advanced bioprocessing technology, the fucose content of Osemitamab (TST001) was significantly reduced during the production, which further enhanced NK cells mediated ADCC activity of Osemitamab (TST001). Clinical trials for Osemitamab (TST001) are ongoing in the U.S. and China (NCT05190575, NCT04396821, NCT04495296, NCT05608785 / CTR20201281). Osemitamab (TST001) was granted Orphan Drug Designation in the U.S. by FDA for the treatment of patients with gastric or gastroesophageal junction (G/GEJ) and pancreatic cancer.