Transcenta Releases Encouraging Interim Safety and Efficacy Data of the TST001 (Osemitamab) and Chemotherapy Combination Expansion Cohort for First Line Claudin18.2 Positive Gastric Cancer at ESMO Congress 2022

• In first line treatment of advanced or metastatic G/GEJ cancer, early interim data of the first 15 patients with measurable disease receiving the combination of TST001 (Osemitamab) with CAPOX demonstrated a partial response rate of 73.3% and a disease control rate of 100% per RECIST1.1.
• Based on these encouraging data, the TST001 (Osemitamab) program is further accelerated and Health Authority consultations are being initiated. A global phase III clinical program of TST001 (Osemitamab) for the first line treatment of locally advanced or metastatic Claudin18.2 positive G/GEJ cancer is currently being planned.

SUZHOU, China, Sept. 12, 2022 /PRNewswire/ -- 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, announces that interim safety and efficacy data of dose expansion cohort from the phase I/II study of TST001 (Osemitamab), a humanized ADCC-enhanced anti-Claudin18.2 monoclonal antibody, in combination with Capecitabine and Oxaliplatin (CAPOX) as a first line treatment of locally advanced or metastatic gastric or gastroesophageal junction (G/GEJ) cancer was presented in a poster at the European Society for Medical Oncology (ESMO) Congress 2022.

As of August 4, 2022, 51 patients were enrolled and dosed including 36 patients treated with TST001 (Osemitamab) plus CAPOX at 6mg/kg Q3W in the expansion phase (median follow up of 65 days). Among the 15 patients with measurable disease and at least one post-treatment tumor assessment, 11 (73.3%) achieved partial response and four (26.7%) achieved stable disease as the best overall tumor response per RECIST1.1, resulting in a disease control rate of 100%. Six out of the eight patients with medium or high Claudin18.2 expression, and five out of the five patients with unknown Claudin18.2 expression achieved partial response.

All 51 enrolled patients were evaluated for safety and tolerability. Treatment-emergent adverse events (TEAEs) regardless of causality were mostly grade 1-2, including nausea, hypoalbuminemia, anemia, vomiting, platelet count decreased. Twelve (23.5%) patients experienced dose delay, five (9.8%) experienced dose reduction and no patient experienced discontinuation due to treatment-related adverse events (TRAEs).

These data suggest that TST001 (Osemitamab) in combination with CAPOX as the first line treatment of patients with Claudin18.2 positive G/GEJ cancer is well tolerated and encouraging anti-tumor activities have been observed. Transcenta has also developed a proprietary IHC assay to select patients with Claudin18.2 expressing tumors for registration enabling studies. A phase III trial is being planned.

"Chemotherapy is still the main treatment of advanced or metastatic G/GEJ cancer, however, it has limited efficacy. We are pleased to see that TST001 (Osemitamab) combined CAPOX showed good tolerability and promising efficacy in a broad gastric cancer patient population with tumors expressing either medium level or high level of Claudin18.2 expression." said Professor Lin Shen from Beijing Cancer Hospital, the principal investigator. "We look forward to further confirming its clinical benefits through confirmatory studies and bringing a more effective and accessible treatment option for patients with G/GEJ cancer."

"We are extremely encouraged by the early efficacy data we have observed in first line G/GEJ

cancer when adding our differentiated Claudin18.2 antibody, TST001 (Osemitamab) to standard of care chemotherapy. These initial results also support our plans to explore the potential of TST001 (Osemitamab) in G/GEJ cancer with other combinations as well as in other indications. As data continue to mature, we will share them with health authorities with the intent to initiate a confirmatory program in Claudin18.2 selected G/GEJ patients." said Dr. Caroline Germa, Transcenta's Executive Vice President, Global Medicine Development and Chief Medical Officer.

About TST001 (Osemitamab)

TST001 (Osemitamab) is a high affinity humanized anti-Claudin18.2 monoclonal antibody with enhanced antibody-dependent cellular cytotoxicity ("ADCC") and complement-dependent cytotoxicity ("CDC") activities and potent anti-tumor activities in tumor xenograft models. TST001 (Osemitamab) is the second most advanced Claudin18.2 targeting antibody being developed globally. TST001 (Osemitamab) is generated using Transcenta's Immune Tolerance Breaking Technology (IMTB) platform. TST001 (Osemitamab) kills Claudin18.2 expressing tumor cells by mechanisms of ADCC and CDC. Leveraging advanced bioprocessing technology, the fucose content of TST001 (Osemitamab) was significantly reduced during the production, which further enhanced NK cells mediated ADCC activity of TST001 (Osemitamab). Clinical trials for TST001 (Osemitamab) are ongoing in the U.S. and China (NCT04396821, NCT04495296/CTR20201281). TST001 (Osemitamab) was granted Orphan Drug Designation in the U.S. by FDA for the treatment of patients with gastric or gastroesophageal junction (G/GEJ) cancer.

About Transcenta Holding Limited

Transcenta (HKEX: 06628) is a clinical stage biopharmaceutical company with fully integrated capabilities in antibody-based biotherapeutics discovery, research, development and manufacturing.

Transcenta has established global footprint, with Headquarters and Discovery, Clinical and Translational Research Center in Suzhou, Process and Product Development Center and Manufacturing Facility in Hangzhou, and Clinical Development Centers in Princeton, US and in Beijing, Shanghai and Guangzhou of China, and External Partnering Center in Boston and Los Angeles, US. Transcenta has also initiated the construction of the Group Headquarters and the second high-end biopharmaceutical facility with ICB as its core technology in Suzhou Industrial Park. Transcenta is developing ten therapeutic antibody molecules for oncology and selected non-oncology indications including bone and kidney disorders.

For more information, please visit www.transcenta.com and https://www.linkedin.com/company/transcenta.

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SOURCE Transcenta Holding Limited