CStone Pharmaceuticals is set to initiate a Phase III clinical trial to study its avapritinib drug candidate as a third-line treatment for KIT-driven gastrointestinal stromal tumours (GIST).

The Chinese company has secured the National Medical Products Administration (NMPA) approval to conduct the trial in China.

Avapritinib is an oral, potent and highly selective KIT and PDGFRα inhibitor. Preclinical data demonstrated that the therapeutic is active against a broad spectrum of KIT and PDGFRα mutations.

CStone Pharmaceuticals signed an exclusive collaboration and licence agreement with US-based Blueprint Medicines for the development and commercialisation of avapritinib and additional drug candidates in Greater China.

Blueprint Medicines is also developing avapritinib for advanced GIST and advanced systemic mastocytosis (ASM).

“Avapritinib is the only inhibitor of KIT and PDGFRα D842V mutant kinases under clinical development in China at present.”

The new trial will be performed as part of the global VOYAGER Phase III trial designed to assess avapritinib, compared to the current standard of care regorafenib, in GIST patients who had prior therapy with imatinib and one or two additional tyrosine kinase inhibitors (TKIs).

Intended to study avapritinib’s safety and efficacy, the new trial will monitor progression-free survival as the primary efficacy endpoint.

CStone Pharmaceuticals chief medical officer Jason Yang said: “Avapritinib is the only inhibitor of KIT and PDGFRα D842V mutant kinases under clinical development in China at present.

“We aim to advance the Phase III VOYAGER study for avapritinib rapidly to benefit Chinese patients with KIT-mutated GIST. We are also planning trials of avapritinib for the treatment of earlier lines of GIST and systemic mastocytosis.”

The drug candidate was previously investigated at 300mg and 400mg doses in the Phase I NAVIGATOR trial, which involved 109 fourth-line or later GIST patients.

Of the total participants, one experienced complete response and 21 achieved partial response when treated with avapritinib.