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CHENGDU, China, Oct. 20, 2025 /PRNewswire/ — Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd. (the “Company”) announced that at the 2025 European Society for Medical Oncology (ESMO) Congress held in Berlin, Germany, Results from a Phase 3 study of the Company’s human epidermal growth factor receptor 2 (HER2)-directed ADC trastuzumab botidotin (also known as A166) trastuzumab botidotin versus trastuzumab emtansine (T-DM1) in HER2-positive unresectable or metastatic BC was presented as an oral report by Professor Xichun Hu from Fudan University Shanghai Cancer Center (Presentation # LBA24, Proffered paper session 1: Breast cancer, metastatic).
Molecular structure of trastuzumab botidotin
Trastuzumab botidotin is a HER2-targeted ADC composed of a cytotoxic drug (Duostatin-5, anti-microtubule agent) with site-specific conjugation to trastuzumab via a stable protease-cleavable valine-citrulline linker. The unique linker is stable in plasma and selectively cleaved by lysosomal cathepsin B that is up-regulated in cancer cells.
In this study, a total of 365 patients with HER2+ unresectable or metastatic BC who had received at least one prior anti-HER2 therapy were randomized (1:1) to receive trastuzumab botidotin or T-DM1. 53% of patients had received ≥2 lines of anti-HER2 therapy, 61% of patients had HER2 Immunohistochemistry (IHC) 3+, and 60% of patients had been treated with TKIs, particularly pyrotinib (56%). As of April 26, 2025, median follow-up was 14.9 months.
Median PFS was significantly longer in trastuzumab botidotin than in T-DM1 (11.1 months vs 4.4 months; HR: 0.39, 95% CI, 0.30-0.51, p<0.0001). PFS benefit with trastuzumab botidotin was consistently observed regardless of prior lines of anti-HER2 therapy (HR 0.36, 95% CI, 0.25-0.53, for 1 prior line; HR 0.39, 95% CI, 0.28-0.56, for ≥2 prior lines).
ORR by blinded independent central review (BICR) was 76.9% vs 53.0%.
A trend toward benefit in OS was observed in trastuzumab botidotin (HR 0.62; 95% CI, 0.38-1.03).
Grade ≥3 treatment emergent adverse events (TEAEs) occurred in 69.8% of patients in trastuzumab botidotin and 63.7% in T-DM1. The most common TEAEs associated with dose reduction were ocular AEs for trastuzumab botidotin, and were platelet count decreased for trastuzumab emtansine. Only two patients permanently discontinued trastuzumab botidotin due to TEAE. No on-treatment deaths were observed in trastuzumab botidotin, compared with 1.6% in T-DM1, all of which were considered unrelated to treatment.
As a conclusion, this second head-to-head trial comparing T-DM1 with other anti-HER2 regimens demonstrated that trastuzumab botidotin statistically improved PFS with an ORR of 76.9% vs 53.0%. PFS benefit with trastuzumab botidotin was consistently observed regardless of prior lines of anti-HER2 therapy. Ocular AEs were also manageable.
“Professor Xichun Hu, National Lead Principal Investigator from Fudan University Shanghai Cancer Center:”Trastuzumab botidotin effectively balances safety and efficacy through its unique molecular design, reducing the incidence of interstitial lung disease and hematologic toxicity. According to research data, trastuzumab botidotin demonstrated significant survival benefits in the pivotal Phase III trial, with an overall manageable safety profile, providing a new important treatment option for pretreated HER2+ BC patients. These positive results also offer robust evidence-based support for personalized treatment and updates to clinical practice guidelines.”
About Trastuzumab botidotin
Trastuzumab botidotin is a differentiated HER2 ADC to treat advanced HER2+ solid tumors. As an innovative HER2 ADC developed by the Company, it conjugates a novel, monomethyl auristatin F (MMAF) derivative (a highly cytotoxic tubulin inhibitor, Duo-5) via a stable, enzyme-cleavable linker to a HER2 monoclonal antibody with a DAR of 2. Trastuzumab botidotin specifically binds to HER2 on the surface of tumor cells and is internalized by tumor cells, releasing the toxin molecule Duo-5 inside the cell. Duo-5 induces tumor cell cycle arrest in the G2/M phase, leading to tumor cell apoptosis. After targeting HER2, trastuzumab botidotin can also inhibit the HER2 signaling pathway; it has antibody-dependent cell-mediated cytotoxicity (ADCC) activity.
Based on the results of a multi-center, randomized, open-label, controlled, Phase 3 KL166-III-06 study, trastuzumab botidotin was approved for marketing by the NMPA in for adult patients with unresectable or metastatic HER2 positive BC who have received one or more prior anti-HER2 therapy. At a pre-specified interim analysis, trastuzumab botidotin demonstrated a statistically significant and clinically meaningful improvement in the primary endpoint of PFS as assessed by the BICR compared with T-DM1[; the beneficial trend for OS of trastuzumab botidotin was also observed.
Currently, the Company has initiated an open, multi-center Phase 2 clinical study of trastuzumab botidotin in the treatment of HER2+ unresectable or metastatic BC that previously received a topoisomerase inhibitor ADC.
About Kelun-Biotech
Kelun-Biotech (6990.HK) is a holding subsidiary of Kelun Pharmaceutical (002422.SZ), which focuses on the R&D, manufacturing, commercialization and global collaboration of innovative biological drugs and small molecule drugs. The company focuses on major disease areas such as solid tumors, autoimmune, inflammatory, and metabolic diseases, and in establishing a globalized drug development and industrialization platform to address the unmet medical needs in China and the rest of world. The Company is committed to becoming a leading global enterprise in the field of innovative drugs. At present, the Company has more than 30 ongoing key innovative drug projects, of which 4 projects have been approved for marketing, 1 projects are in the NDA stage and more than 10 projects are in the clinical stage. The company has established one of the world’s leading proprietary ADC and novel DC platforms, OptiDC™, and has 1 ADC project approved for marketing and multiple ADC and novel DC assets in clinical or preclinical research stage. For more information, please visit https://kelun-biotech.com/.
