Alphamab Oncology Announces Anti-HER2 Biparatopic ADC JSKN003 Obtained Orphan Drug Designation from the U.S. FDA for the Treatment of GC/GEJ

Alphamab Oncology (stock code: 9966.HK) announced that anti-HER2 biparatopic antibody-drug conjugate (ADC) JSKN003 has been granted Orphan Drug Designation (ODD) by the U.S. Food and Drug Administration (FDA) for the treatment of gastric cancer and gastroesophageal junction cancer (GC/GEJ).

GC/GEJ is the fifth most common cancer and the fifth leading cause of cancer death worldwide. According to the 2022 Global Cancer Statistics report released by the International Agency for Research on Cancer (IARC), a subsidiary of the World Health Organization, there are approximately 960,000 new cases diagnosed and 660,000 deaths worldwide annually. In the U.S., the SEER database model predicts that there will be 26,890 new cases and 10,880 new deaths of GC/GEJ in 2024, with a five-year overall survival rate of less than 40%. Fluoropyrimidine and platinum-based regimens are commonly used as first-line treatments. Available second-line or later-line treatment options include paclitaxel plus ramucirumab, paclitaxel, docetaxel or irinotecan monotherapy, and best supportive care, with objective response rates of approximately 15-25%. The median overall survival is approximately 8-9 months for second-line treatment and 4-6 months for later lines.

JSKN003 is an anti-HER2 biparatopic ADC developed inhouse with Alphamab's proprietary glycan-specific conjugation platform. The antibody molecule KN026 is site-specifically modified via enzyme catalytic reaction and click chemistry to achieve a drug-to-antibody ratio (DAR) of approximately 4. It can bind HER2 on the surface of tumor cells, and release topoisomerase I inhibitors (TOPIi) through cellular endocytosis, thereby exert anti-tumor effects. Compared with its ADC counterparts, JSKN003 demonstrated better serum stability and stronger bystander effect, which effectively expands the therapeutic window. Research results from the Phase I clinical study JSKN003-101 (NCT05494918) conducted in Australia and the Phase I/II clinical study JSKN003-102 (NCT05744427) in China have demonstrated favorable tolerability and safety profile, with promising efficacy of JSKN003 in heavily pretreated patients with advanced solid tumors, especially in patients with high HER2-expressing gastrointestinal tumors. Detailed data were presented at the 2024 European Society for Medical Oncology (ESMO) Congress for the first time and subsequently updated at the 2025 Annual Meeting of American Society of Clinical Oncology (ASCO) in June 2025.

The "Orphan Drug Designation", originated from the Orphan Drug Act (ODA), is a U.S. FDA initiative aimed at encouraging the development of innovative drugs for the treatment of diseases affecting fewer than 200,000 people in the U.S. The designation of JSKN003 will be beneficial to obtain relevant policy supports for subsequent research and development, registration, and commercialization in the U.S., including funding for research and development costs, tax credits for clinical trial expenditures, waiver of prescription drug user fee, accelerated review and approval processes, and, upon approval, the potential for seven years of market exclusivity in the U.S.

About JSKN003

JSKN003 is a bispecific ADC developed based on KN026 using Alphamab's proprietary glycan-specific conjugation platform. JSKN003 can bind HER2 on the surface of tumor cells and release topoisomerase I inhibitors (TOPIi) through cellular endocytosis, thereby exerting anti-tumor effects. Compared with its ADC counterparts, JSKN003 demonstrated better serum stability and stronger bystander effect, which effectively expands the therapeutic window.

Results of multiple clinical studies at various stages of JSKN003 in China and Australia have demonstrated favorable safety profile, with promising efficacy of JSKN003 in heavily pretreated patients with advanced solid tumors, especially in patients with platinum-resistant ovarian cancer (PROC), HER2-expressing breast cancer (BC), or high HER2-expressing solid tumors. JSKN003 was granted breakthrough therapy designation by CDE. The designation is for the treatment of platinum-resistant recurrent epithelial ovarian cancer, primary peritoneal cancer, or fallopian tube cancer. Three Phase III clinical studies of JSKN003 for the treatment of HER2-low expressing BC, PROC, and HER2-positive BC as well as multiple exploratory Phase II clinical studies are currently undergoing smoothly.

In September 2024, the Company entered a licensing agreement with JMT-Bio Technology Co., Ltd. ("JMT-Bio"), a wholly-owned subsidiary of CSPC Pharmaceutical Group Co., Ltd. ("CSPC") (stock code: 1093.HK), pursuant to which, JMT-Bio was granted the exclusive license and sublicense rights to develop, sell, offer for sale and commercialize JSKN003, for the treatment of tumor-related indications (the "Field") in mainland China (excluding Hong Kong, Macau or Taiwan) (the "Territory") and become the sole marketing authorization holder for JSKN003 for the Field in the Territory. Alphamab retains the sole right to supply JSKN003.

About Alphamab Oncology

Alphamab Oncology is an innovative biopharmaceutical company focusing on oncology therapeutics. On December 12, 2019, the Company was successfully listed on the Main Board of the Hong Kong Stock Exchange, trading under the stock code 9966.

By leveraging its proprietary core technology platforms including single-domain antibodies, bispecific antibodies, glycan-specific conjugation, linker-payload, dual-payload antibody conjugation, and subcutaneous high concentration formulation for biologics, the Company has established a product portfolio with differentiated innovation and global competitiveness, covering cutting-edge areas such as antibody-drug conjugates (ADCs), bispecific antibodies, and single-domain antibodies.

The Company has one product approved for marketing (Envafolimab, the world's first subcutaneously injectable PD-(L)1 inhibitor), which has made a significant breakthrough in the convenience and accessibility of cancer treatment. Additionally, the Company has multiple bispecific antibodies and bispecific ADCs in clinical stage, while rapidly advancing the preclinical pipeline prioritizing bispecific ADCs and dual-payload ADCs. Multiple strategic collaborations based on innovative products or technology platforms have been established with partners such as CSPC, ArriVent, and Glenmark.

Our overarching mission is to make cancer manageable and curable by addressing unmet clinical needs in oncology. Alphamab Oncology is continuously dedicated to the development of effective, safe, and globally competitive anti-tumor drugs, delivering China-innovated cancer therapies to benefit patients worldwide.