CStone Pharmaceuticals Unveils Breakthrough Preclinical Data on Three Proprietary ADCs at AACR 2026

Hong Kong, April 20, 2026 — CStone Pharmaceuticals (HKEX: 2616) has made a significant announcement that may have material implications for shareholders and investors. The Company presented promising preclinical data for three of its novel or differentiated antibody-drug conjugates (ADCs) — CS5007 (EGFR/HER3), CS5006 (ITGB4), and CS5008 (DLL3/SSTR2) — at the prestigious American Association for Cancer Research (AACR) Annual Meeting 2026. All three ADCs are developed from CStone’s proprietary ADC technology platform and are poised to advance into clinical trials, representing potentially transformative treatments for various solid tumors.

Key Highlights from the Announcement

• First-in-class and Bispecific ADCs: CStone’s ADC portfolio leverages a proprietary hydrophilic CSL20 linker for high stability and precise payload release, using the potent topoisomerase I inhibitor exatecan. These innovations are aimed at overcoming tumor heterogeneity and resistance mechanisms, which are major challenges in cancer therapy.
• Preclinical Data Shows Broad Anti-Tumor Activity, PK/PD Superiority, and Favorable Safety: The data across all three ADCs demonstrate potent anti-tumor effects in various in vitro and in vivo models, superior pharmacokinetics and pharmacodynamics (PK/PD), and broad safety windows in animal studies.
• Clinical Advancement Plans: CStone intends to file IND (Investigational New Drug) applications for the three ADCs beginning in the first half of 2026 for CS5007, and in the second half of 2026 for CS5006 and CS5008, paving the way for human clinical trials.

Detailed Pipeline Asset Summaries

CS5007 — EGFR/HER3 Bispecific ADC

• Target and Mechanism: EGFR and HER3 are frequently co-overexpressed oncogenic drivers in human epithelial cancers. Current EGFR-targeted therapies are limited by resistance via HER3 signaling. CS5007 is designed to synergistically bind both EGFR and HER3, blocking almost all HER family receptor complexes (except HER2 homodimers), thus overcoming resistance and tumor heterogeneity.
• Structure: CS5007 comprises an anti-EGFR/HER3 IgG1 antibody, CSL20 linker, and exatecan payload (DAR ~4).
• Preclinical Data Highlights:
  • Superior Stability: Outperforms trastuzumab deruxtecan (DS-8201) in plasma stability; less than 0.5% free payload release after 7 days, minimizing off-target toxicity.
  • Dual Pathway Blockade: Potent inhibition of Akt and MAPK signaling, outperforming competitor SI-B001. Blocks both EGFR and HER3/Akt signaling, even under ligand-stimulated conditions.
  • Rapid Internalization: Efficient drug delivery, including through HER3 pathway in EGFR-low cells, ensuring broad tumor coverage.
  • Broad-Spectrum In Vitro Efficacy: Nanomolar-level cell killing across NSCLC, SCC, CRC, pancreatic, and breast cancer lines.
  • Bystander Killing Effect: Demonstrated ability to eliminate both antigen-positive and adjacent antigen-negative tumor cells, addressing tumor heterogeneity.
  • In Vivo Tumor Regression: Effectiveness in multiple xenograft models, including osimertinib-resistant NSCLC (EGFR C797S mutation) and low-EGFR/high-HER3 tumors.
  • PK/PD Superiority: Longer half-life (~20 hours vs. 10 hours for competitor BL-B01D1) and greater in vivo potency at equivalent exposure.
  • Favorable Safety: No lethal toxicity in non-human primates up to 30 mg/kg; only high-dose skin toxicity observed. Half-life in NHPs ~2 days; in human FcRn transgenic mice ~2.5–8 days.
• Clinical Plans: IND filing in H1 2026; first-in-human study to enroll ~70 adults with advanced solid tumors, evaluating safety and recommended Phase II dose.

CS5006 — ITGB4-Targeting ADC

• Target and Rationale: ITGB4, part of the α6β4 integrin heterodimer, is highly expressed in multiple solid tumors (CRC, NSCLC, HNSCC, ESCC) and plays a central role in tumor progression and resistance to PD-1 immunotherapy.
• Structure: Humanized anti-ITGB4 IgG1 antibody, CSL20 linker, exatecan payload (DAR ~4).
• Preclinical Data Highlights:
  • Excellent Stability: Less than 0.6% free payload released after 7 days in human/monkey serum.
  • Rapid Internalization: Deep internalization on ITGB4-positive tumor cells.
  • Potent, Specific Killing: Nanomolar, antigen-dependent cytotoxicity correlating with ITGB4 expression.
  • Bystander Effect: Kills adjacent ITGB4-negative cells via bystander effect.
  • Broad In Vivo Efficacy: Tumor regression in NSCLC, breast, colorectal, squamous cell, urothelial, esophageal, and gastric cancer models.
  • Favorable PK/Safety: Half-life ~3.5 days in NHPs; highest non-severe toxic dose (HNSTD) 45 mg/kg.
• Clinical Plans: IND filing targeted for H2 2026.

CS5008 — DLL3/SSTR2 Bispecific ADC

• Target and Rationale: DLL3 and SSTR2 are frequently overexpressed in small cell lung cancer (SCLC) and neuroendocrine tumors (NETs/NECs). Dual targeting addresses tumor heterogeneity and resistance, especially relevant given SCLC’s tendency for rapid therapy resistance and molecular subtype switching.
• Structure: Bispecific anti-DLL3/SSTR2 IgG1 antibody, CSL20 linker, exatecan payload (DAR ~4).
• Preclinical Data Highlights:
  • High Serum Stability: Less than 0.5% toxin release after 7 days at 37°C in human and monkey serum.
  • Rapid Internalization: High antigen-dependent internalization in SCLC and NET cell lines, superior to mono-specific ADCs.
  • Potent, Antigen-Dependent Killing: Activity correlates with DLL3/SSTR2 expression levels.
  • Broad and Potent In Vivo Efficacy: Tumor regression in various SCLC models, including DLL3-negative tumors, outperforming mono-specific comparators.
  • Favorable PK/Safety: Half-life ~14 days in cynomolgus monkeys; HNSTD 60 mg/kg with no lethal toxicity observed.
  • Resistance Overcoming Strategy: Dual targeting has the potential to overcome SCLC subtype switching resistance, a major clinical challenge.
• Clinical Plans: IND filing planned for H2 2026.

Potential Share Price Impact and Shareholder Considerations

• These data represent a significant step forward in CStone’s pipeline and highlight the Company’s advancement into next-generation ADCs, a highly competitive and high-value oncology segment.
• If translated into clinical success, these assets could substantially increase CStone’s addressable market and revenue potential, making this news potentially price-sensitive and impactful for share value.
• The Company has already demonstrated robust CMC (chemistry, manufacturing, and controls) profiles for these ADCs, supporting future development and commercialization.
• Risk Factors: CStone cautions that there is no guarantee the Company will ultimately be able to develop or market CS5007, CS5006, or CS5008 successfully. Shareholders and potential investors should closely monitor the progress of these assets, as setbacks in clinical development or regulatory approval could negatively affect share value.

About CStone Pharmaceuticals

CStone (HKEX: 2616), founded in 2015, is an innovation-driven biopharmaceutical company focusing on oncology, immunology, inflammation, and other key disease areas. The Company has launched 4 innovative drugs and secured 21 new drug applications for 9 indications. CStone’s pipeline now includes 16 clinical-stage candidates, with a strong emphasis on ADCs and multispecific antibodies.

The management team brings comprehensive expertise across drug development, clinical research, manufacturing, and commercialization.

For more information, visit www.cstonepharma.com.

Disclaimer: This article is based on information disclosed by CStone Pharmaceuticals as of April 20, 2026. Forward-looking statements contained herein are subject to risks and uncertainties, and there is no guarantee of ultimate clinical or commercial success for CS5007, CS5006, or CS5008. Readers should exercise due diligence and consult professional advisors before making investment decisions. The financial and other data cited have not been audited or reviewed by the Company’s auditors.

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