CStone Pharmaceuticals has received the US Food and Drug Administration (FDA) clearance for its investigational new drug (IND) application, enabling the company to initiate a Phase II clinical trial of CS2009, its trispecific antibody, in patients with advanced solid tumours.

The ongoing global trial uses a parallel, multi-cohort expansion design. It will examine the safety, efficacy, pharmacokinetics and tolerability of CS2009 as both monotherapy and in combination regimens.

Recruitment is ongoing in China and Australia, with IND clearance now obtained in the US.

A total of 15 cohorts are planned across nine solid tumour indications, including cervical cancer (CC), extensive-stage small cell lung cancer (ES-SCLC), gastric or gastroesophageal junction cancer (GC/GEJC), ovarian cancer (PROC), and triple-negative breast cancer (TNBC).

CS2009 is an antibody targeting programmed cell death protein 1 (PD-1), vascular endothelial growth factor A (VEGFA), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4).

According to CStone, it is designed to deliver anti-tumour effects on multiple fronts by combining three clinically validated targets within a single agent.

CStone CEO, R&D president and executive director Dr Jason Yang said: “This milestone follows a productive interaction with the agency, during which they reviewed our comprehensive Phase I data, including safety and anti-tumour activity data collected during dose escalation and expansion, and provided alignment on key elements of the Phase II study design, including dose optimisation and expansion strategies.

“We are now actively advancing the CS2009 clinical programme globally and look forward to sharing further updates as the study progresses.”

In March 2025, CStone dosed the first subject in the multi-centre Phase I trial of CS2009.