ESMO 2025: CStone Discloses Phase I Data for CS2009 (PD-1/VEGF/CTLA-4 Trispecific Antibody)

SUZHOU, China, Oct. 19, 2025 /PRNewswire/ -- CStone Pharmaceuticals ("CStone," HKEX: 2616),  an innovation-driven biopharmaceutical company focused on the research and development of therapies for oncology, autoimmune/inflammation, and other key disease areas, today announced the first disclosure of preliminary Phase I data for CS2009 (a PD-1/VEGF/CTLA-4 trispecific antibody) and the Phase Ib study design for CS5001 (a ROR1-targeted Antibody-Drug Conjugate [ADC]) at the 2025 European Society for Medical Oncology (ESMO) Annual Congress.

Key Highlights of CS2009 Poster Presentation:

This also represents the first known clinical data publication of a PD-1/VEGF/CTLA-4 trispecific antibody to date.

CS2009-101 is a multi-regional phase Ⅰ study currently ongoing in Australia and China. The study evaluates the safety, tolerability, pharmacokinetics (PK)/ pharmacodynamics (PD), and antitumor activity of CS2009 in patients with advanced solid tumors.

Patients baseline characteristics:

1. As of the data cutoff date, 72 patients with advanced solid tumors treated across 6 dose levels (DL1-6, 1-45 mg/kg); 72.2% remain on treatment.
2. Heavily pretreated population: over 51% received prior immuno-oncology (IO) therapies. Median follow-up: only 1.9 months (range 0.1-6.7 months) at data cutoff.

Favorable safety and tolerability:

1. Dose escalation completed with no dose-limiting toxicity (DLT) reported; maximum tolerated dose (MTD) not reached.
2. No Grade 4 or 5 treatment-related adverse event (TRAE) observed. Incidence of Grade ≥3 TRAEs, immune-related AEs (irAEs), and VEGF-related TRAEs was 13.9%, 4.2%, and 2.8%, respectively.
3. Only 1 treatment-emergent adverse event (TEAE) leading to drug permanent discontinuation observed (at DL4 [20 mg/kg]; 1.4% incidence).

Promising antitumor activity and high disease control rate (DCR):

CS2009 demonstrated encouraging anti-tumor activities across tumor types. As of the cutoff date, the overall follow-up duration remained limited, particularly in higher-dose cohorts where the majority patients had yet to reach the protocol-specified time point of post-baseline tumor assessment:

1. 49/72 patients underwent at least one post-baseline tumor assessment by data cutoff.
2. Despite limited follow-up duration, anti-tumor activity was observed across all dose levels with dose-dependent uptrend:
   • Among all 49 evaluable patients, overall response rate (ORR) was 12.2%; DCR was 71.4%. Efficacy data remains immature; with additional follow-up beyond the poster data cutoff, ORR was further improved to 14.3%.
   • Higher ORR (25.0%) at tentative recommended Phase 2 dose (RP2D, 30 mg/kg) and higher dose.
3. Promising efficacy signals were observed across multiple tumor types within the short follow-up period:
   • Non-Small Cell Lung Cancer (NSCLC): ORR: 11.8%, DCR: 82.4%; Post-ESMO update: stable disease (SD)-to-partial response (PR) conversion observed, ORR further elevated to 17.6%; In AGA-negative subgroup, ORR reached 25%;
   • Ovarian Cancer (OC): ORR: 16.7%, DCR: 66.7%;
   • Triple-Negative Breast Cancer (TNBC): ORR: 25.0%, DCR: 75.0%;
   • Non–Clear Cell Renal Cell Carcinoma (nccRCC): ORR: 33.3%, DCR: 100.0%;
   • Soft Tissue Sarcoma (STS): ORR: 11.1%, DCR: 66.7%.

Favorable PK and PD profiles:

1. Linear PK with half-life of 6-8 days supported every-three-week (Q3W) dosing, with no significant accumulation observed at cycle 3.
2. PD profile demonstrated saturated receptor occupancy and robust T-cell activation/proliferation confirming PD-1/CTLA-4 blockade and deep and sustained VEGFA neutralization.
   • Receptor occupancy of PD-1/CTLA-4 on peripheral T cells reached saturation throughout dosing interval at doses ≥20 mg/kg.
   • On cycle 1 day 8, CS2009 induced notable, dose-dependent upregulation of Ki67 (proliferation due to PD-1 and CTLA-4 blockade) and ICOS (activation due to CTLA-4 blockade) expression on both CD4+ and CD8+ T cells, collectively demonstrating effective PD-1 and CTLA-4 inhibition.
   • Serum-free VEGFA reduced deeply and rapidly across all dose levels, and the effect sustained throughout dose intervals.

CStone has initiated Phase Ⅱ dose expansion study in first-line patients with selected tum or  types for dose optimization and to generate data supporting registration trials in first-line NSCLC and other tumors as monotherapy or in combination therapies.

CS2009 Data Review Conference Call:

CStone will host an investor meeting to discuss presented data and future clinical development plan. The Company cordially invites all investors to attend this conference call.

Chinese-language session:

• Date & Time: Monday, October 20, 2025, at 2:00 p.m. (Beijing Time)/2:00 a.m. (US Eastern Time)
• Registration Link: Registration is required, please sign up via the link: https://s.comein.cn/iq2y9krs

English-language session:

• Date & Time: Monday, October 20, 2025, at 9:00 p.m. (Beijing Time)/9:00 a.m. (US Eastern Time)
• Registration Link: The Zoom meeting link will be sent to you by email after registration via the below link. You may join the meeting by clicking the link in email: https://us06web.zoom.us/webinar/register/WN_PO-SYEhNScyOdlU1p75MdQ

Key Highlights of CS5001 ePoster Presentation:

1. CS5001 phase Ib study aims to determine the RP2D and further evaluate the safety, tolerability, PK, and efficacy of CS5001 as a monotherapy and in combination with systemic therapies in selected tumor types.
2. In monotherapy cohorts, Cohorts A-D enroll patients with chronic lymphocytic leukemia and other B-cell lymphomas, and Cohort I enrolls patients with ROR1-positive solid tumors. In combination therapy cohorts (E-H), CS5001 will be administered with standard systemic therapies (R-GemOx, R2 or R-CHOP) or with sugemalimab (an anti-PD-L1 monoclonal antibody). 
3. Patient enrollment for CS5001 Phase Ib study commenced in December 2024 and is currently advancing smoothly at 30 sites across Australia, the United States, and China.

About CStone

CStone (HKEX: 2616), established in late 2015, is an innovation-driven biopharmaceutical company focused on the research and development of therapies for oncology, autoimmune/inflammation, and other key disease areas. Dedicated to addressing patients' unmet medical needs in China and globally, the Company has made significant strides since its inception. To date, the Company has successfully launched 4 innovative drugs and secured approvals for 16 new drug applications covering 9 indications. The company's pipeline is balanced by 16 promising candidates, featuring potentially first-in-class or best-in-class antibody-drug conjugates (ADCs), multispecific antibodies, immunotherapies and precision medicines. CStone also prides itself on a management team with comprehensive experiences and capabilities that span the entire drug development spectrum, from preclinical and translational research to clinical development, drug manufacturing, business development, and commercialization.

For more information about CStone, please visit: www.cstonepharma.com.

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SOURCE CStone Pharmaceuticals