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 -- CStone Pharmaceuticals ("CStone" or the "Company",HKEX: 2616) today announced that the Company has submitted a New Drug Application (NDA) to the Taiwan Food and Drug Administration (TFDA) for avapritinib,a precision therapy being developed for the treatment of gastrointestinal stromal tumor (GIST),and had received priority review designation from the TFDA on March 9,2020. This NDA is for the indication of adult patients with unresectable or metastatic GIST harboring a platelet-derived growth factor receptor alpha (PDGFRA) exon 18 mutation,including PDGFRA D842V mutations. Discovered by CStone's partner,Blueprint Medicines,avapritinib is the second drug candidate for which CStone has submitted an NDA.

"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.

Blueprint Medicines is pursuing a broad clinical development program for avapritinib across multiple lines of GIST treatment,as well as for advanced,smoldering and indolent systemic mastocytosis.

Avapritinib is a kinase inhibitor approved by the U.S. FDA under the brand name AYVAKIT™ for the treatment of adults with unresectable or metastatic GIST harboring a PDGFRA exon 18 mutation,including PDGFRA D842V mutations.

Avapritinib is not approved for the treatment of any other indication in the U.S. or for the treatment of any indication by the TFDA in Taiwan,by the National Medical Products Administration in China or by any other health authority in any other jurisdiction.

About CStone

CStone Pharmaceuticals (HKEX: 2616) is a biopharmaceutical company focused on developing and commercializing innovative immuno-oncology and precision medicines to address the unmet medical needs of cancer patients in China and worldwide. Established in 2015,CStone has assembled a world-class management team with extensive experience in innovative drug development,clinical research,and commercialization. The company has built an oncology-focused pipeline of 15 drug candidates with a strategic emphasis on immuno-oncology combination therapies. Currently,5 late-stage candidates are at pivotal trials. With an experienced team,a rich pipeline,a robust clinical development-driven business model and substantial funding,CStone's vision is to become globally recognized as a leading Chinese biopharmaceutical company by bringing innovative oncology therapies to cancer patients worldwide.

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

Forward-looking Statement

The forward-looking statements made in this article relate only to the events or information as of the date on which the statements are made in this article. Except as required by law,we undertake no obligation to update or revise publicly any forward-looking statements,whether as a result of new information,future events or otherwise,after the date on which the statements are made or to reflect the occurrence of unanticipated events. You should read this article completely and with the understanding that our actual future results or performance may be materially different from what we expect. In this article,statements of,or references to,our intentions or those of any of our Directors or our Company are made as of the date of this article. Any of these intentions may alter in light of future development.

References

1. Cassier PA,Fumagalli E,Rutkowski P,Schoffski P,Van Glabbeke M,Debiec-Rychter M,et al. Outcome of patients with platelet-derived growth factor receptor alpha-mutated gastrointestinal stromal tumors in the tyrosine kinase inhibitor era. Clin Cancer Res. 2012;18(16):4458-64.

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