CStone Pharmaceuticals announced the presentation of preclinical research findings for three internally developed drug candidates at the American Association for Cancer Research (AACR) Annual Meeting held from April 17 to 22, 2026. The presented candidates include CS5007 (an EGFR/HER3 ADC), CS5006 (an ITGB4 ADC), and CS5008 (a DLL3/SSTR2 ADC).

All three candidates were developed using CStone's proprietary antibody-drug conjugate (ADC) technology platform, which features high stability and precise drug release. The platform utilizes the company's proprietary CSL20 linker, noted for its high hydrophilicity, which enhances circulatory stability. It enables efficient, tumor-selective payload release through a tandem cleavage mechanism involving beta-glucuronidase and cathepsin. The platform employs Exatecan as the payload, a clinically validated, potent topoisomerase I inhibitor known for its strong bystander effect, which helps reduce susceptibility to multidrug resistance.

CS5007 is a bispecific ADC composed of an anti-EGFR/HER3 human IgG1 antibody, the proprietary CSL20 linker, and the Exatecan payload. It uses a semi-random conjugation method, achieving an average drug-to-antibody ratio (DAR) of approximately 4. The company plans to submit an Investigational New Drug (IND) application for CS5007 in the first half of 2026. The planned CS5007-101 study is a monotherapy dose-escalation and expansion trial designed to evaluate the safety and identify the recommended Phase 2 dose (RP2D) in approximately 70 patients with advanced solid tumors who have progressed after standard therapy, are ineligible for standard treatment, or lack effective treatment options. Key preclinical data indicate that CS5007 exhibits high binding affinity, mediates rapid internalization in tumor cells with varying levels of EGFR and HER3 expression, effectively blocks downstream signaling, and demonstrates potent anti-tumor activity and a favorable safety and pharmacokinetic (PK) profile, supported by a strong bystander effect. These comprehensive preclinical results provide a solid scientific foundation for its further clinical development in solid tumors.

CS5006 is a potential first-in-class ADC targeting the novel target ITGB4. It consists of an anti-ITGB4 human IgG1 antibody, the CSL20 linker, and the Exatecan payload, with a semi-random conjugation yielding an average DAR of about 4. Preclinical studies show CS5006 induces rapid and deep internalization, leading to potent and specific killing of ITGB4-positive cells and clearance of negative cells via its bystander effect, demonstrating broad and profound anti-tumor activity in CDX models. In non-human primates (NHPs), it showed expected highest non-severely toxic dose (HNSTD) and half-life. The candidate also features high antibody yield, strong ADC stability, and good developability. This data strongly supports its clinical development, with an IND application anticipated in the second half of 2026.

CS5008 is a bispecific ADC targeting DLL3 and SSTR2, built with the respective human IgG1 antibody, the CSL20 linker, and Exatecan, and has an average DAR of around 4. Preclinical evidence indicates CS5008 achieves efficient, specific killing of tumor cells with varying DLL3/SSTR2 expression levels through rapid, deep internalization, showing broad and potent in vivo anti-tumor efficacy in CDX models. It demonstrated good tolerability and excellent PK properties in NHPs, alongside high antibody yield, strong stability, and favorable developability. This robust preclinical dataset provides substantial scientific rationale for advancing CS5008 into clinical development for solid tumors, including SCLC and neuroendocrine cancers (NECs), with an IND application planned for the latter half of 2026.