CStone submits new drug application for the targeted therapy avapritinib in Taiwan for the treatment of adults with advanced PDGFRA exon 18 mutant gastrointestinal stromal tumor

SUZHOU, China, March 27, 2020

"Within just one year, CStone has submitted NDAs for two first-in-class targeted-therapies, demonstrating our commitment to addressing urgent clinical needs and the Company's rapid transformation toward commercialization," said Dr. Frank Jiang, Chairman and CEO of CStone. "GIST is a rare tumor type, and PDGFRA D842V mutant GIST is resistant to currently approved therapies in Greater China. In addition to Taiwan, we plan to submit an NDA for the same indication in Mainland China in the first half of this year with the goal of benefitting more patients suffering from this devastating condition."

"Avapritinib is an investigational, orally available, potent, and selective inhibitor of KIT and PDGFRA. In January this year, avapritinib received an approval from the U.S. FDA for the treatment of adults with unresectable or metastatic PDGFRA exon 18 mutant GIST and became the first and only U.S. FDA-approved targeted therapy for this indication," said Dr. Jason Yang, Chief Medical Officer of CStone. "Clinical data submitted to the TFDA show unprecedented antitumor activity of avapritinib in advanced GIST patients with a PDGFRA exon 18 mutation, including PDGFRA D842V mutations, with an overall response rate (ORR) of 84% and most adverse events reported as Grade 1 or 2. In addition, the median duration of response (DOR) was not reached and 61% of these patients had a DOR ≥6 months. "

GIST is the most common mesenchymal tumor of the GI tract, and it is most prevalent in patients aged 50 to 80. Around 90% of all GIST cases are associated with dysregulated cell growth due to mutations in KIT and PDGFRA tyrosine kinases. As GIST patients do not respond well to chemotherapy and radiotherapy, current treatment for advanced GIST is primarily based on sequential treatment with tyrosine kinase inhibitors (TKIs). However, GIST patients harboring PDGFRA D842V mutations are not sensitive to existing approved TKIs in Greater China, with studies showing an ORR of 0%, a median progression-free survival of just three to five months, and a median overall survival of about 15 months^[1]. Similarly, these approved therapies have shown limited effects against other rare PDGFRA exon 18 mutations.

CStone Pharmaceuticals and Blueprint Medicines have an exclusive collaboration and license agreement for the development and commercialization of avapritinib and certain other drug candidates in Mainland China, Hong Kong, Macau and Taiwan. Blueprint Medicines retains development and commercial rights for these licensed products in the rest of the world.

About Avapritinib

Avapritinib is an investigational, selective and potent inhibitor of KIT and PDGFRA mutant kinases. It is a type 1 inhibitor that works by directly binding to the active kinase conformation from which mutant KIT and PDGFRA signal. Avapritinib has demonstrated inhibition of a broad range of KIT and PDGFRA mutations associated with GIST, including potent clinical activity against activation loop mutations that are associated with resistance to currently approved therapies in Greater China.