Positive Topline Results from Japan Phase III Clinical Study (Period 1) of Fostamatinib for Chronic Immune Thrombocytopenic Purpura

Kissei Pharmaceutical Co., Ltd. (Head Office: Matsumoto, Nagano, Japan; Chairman and CEO: Mutsuo Kanzawa; "Kissei") today announced that the primary endpoint was achieved in a Japan Phase III Clinical Study (Period 1) for the treatment of adult chronic immune thrombocytopenic purpura with fostamatinib (generic name, Product Code: R788) licensed from Rigel Pharmaceuticals, Inc. (Head Office: USA, President and CEO: Raul Rodriguez; "Rigel") .

Fostamatinib is an oral spleen tyrosine kinase (SYK) inhibitor discovered by Rigel. Kissei acquired the development and commercialization rights for Japan, China, Korea and Taiwan in October 2018 and conducted the Phase III clinical study in Japan.

In this Phase III study, 34 patients with chronic immune thrombocytopenic purpura have been enrolled. The study consists of 3 periods: a placebo-controlled double-blind period for 24 weeks (Period 1), an extension treatment period in which fostamatinib is continuously administered for up to 52 weeks (Period 2), and a long-term treatment period (Period 3), to examine the efficacy and safety of fostamatinib in twice daily oral administration. In Period 1, the primary endpoint is "achievement rate of stable platelet response (ratio of patients with platelet count ≥50,000/μL at 4 of 6 visits from week 14 to week 24)".

The analysis for Period 1 showed the primary endpoint was significantly higher in the fostamatinib group than in the placebo group . In the fostamatinib group, the safety profile was consistent with other clinical trials, with no new or unusual safety issues observed. Kissei is currently conducting a detailed analysis of Period 1. The treatment in Period 2 is ongoing.

Kissei strives to provide new treatment options by engaging in R&D in the field of rare diseases, including chronic immune thrombocytopenic purpura.

This event has negligible effects on Kissei's consolidated business forecasts for the fiscal year ending in March 2022.

《 Reference 》

ITP is a disease which causes serious bleeding events and bruising due to a decrease in platelet counts below 100,000/μL, despite the absence of other obvious illnesses and medications that cause thrombocytopenia. ITP is classified into "acute ITP" in which the platelet count recovers normally within 6 months from the onset and "chronic ITP" in which thrombocytopenia continues for 6 months or more depending on the course of the medical condition. Fostamatinib is a treatment for chronic ITP.

The clinical symptoms of ITP include subcutaneous bleeding (petechiae or purpura) as well as bleeding from the gums or nose, blood in the urine or stool, and intracranial bleeding.

ITP is designated as an "intractable disease" by the Minister of Health, Labour and Welfare. The number of patients with ITP is estimated to be approximately 17,000* and 2.16 per 100,000** people are newly diagnosed with ITP every year in Japan. While the cause of ITP has still not been definitively elucidated, it is believed that the platelet count is decreased as a result of the production of autoantibodies against platelets, leading to the destruction of platelets by macrophages in the spleen. ITP is currently treated with corticosteroids or thrombopoietin (TPO) receptor agonists as well as surgical removal of the spleen.

*: Estimated based on the number of patients having certificates issued for specific disease treatment (designated intractable disease)

**: Int J Hematol, 2011, 93: 329-35

Fostamatinib is an oral spleen tyrosine kinase (SYK) inhibitor that suppresses platelet destruction by macrophages and platelet depletion. Thereby, improving the bleeding symptoms caused by immune thrombocytopenic purpura (ITP).

Fostamatinib has been granted orphan drug status in the United States and Japan. It was approved by the US Food and Drug Administration in April 2018 for the treatment of adult patients with chronic ITP and launched in May 2018 in the United States. Subsequently, fostamatinib has been launched in Canada and some European countries including Germany. Kissei entered into sublicense agreements in June 2021 and August 2021 for the rights to develop and commercialize fostamatinib in South Korea and China respectively, which are the Kissei territories.

Rigel Pharmaceuticals, Inc., is a biotechnology company dedicated to developing and commercializing novel small molecule drugs that significantly improve the lives of patients with hematologic disorders, cancer and rare immune diseases. Rigel's pioneering research focuses on signaling pathways that are critical to disease mechanisms. Rigel is headquartered in South San Francisco, California, U.S.A. For more details, please visit www.rigel.com.