CStone Pharmaceuticals — Capital/Financing Update 2019

May 2, 2019

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CStone Pharmaceuticals

基 石 藥 業

(Incorporated in the Cayman Islands with limited liability) ( Stock Code: 2616 )

VOLUNTARY ANNOUNCEMENT

CSTONE AND NUMAB ANNOUNCE EXCLUSIVE REGIONAL LICENSING AGREEMENT FOR ND021, A MULTI-FUNCTIONAL DRUG CANDIDATE AND POTENTIAL NEXT-GENERATION IMMUNOTHERAPY

CStone Pharmaceuticals (the “ Company ” or “ CStone ”) today announces that the Company has recently entered into an exclusive regional licensing agreement (the “ Licensing Agreement ”) with Numab Therapeutics AG (“ Numab ”) for the development and commercialization of ND021, a potential best-in-class monovalent, tri-specific antibody-based molecule targeting PD-L1, 4-1BB, and human serum albumin (HSA).

The Company will fund the research and development of ND021 up to completion of an initial Phase Ib clinical trial pursuant to the terms of the Licensing Agreement dated April 26, 2019. In exchange, the Company obtains exclusive rights from Numab to develop and commercialize ND021 in Greater China (including mainland China, Hong Kong, Macau and Taiwan), South Korea and Singapore. Numab retains all ND021 rights for the rest of the world. Upon completion of the Company’s funding period, no further financial obligations will be owed by either party. This collaboration provides the Company with its first access to Numab’s novel multispecific technology platform and Numab the opportunity to bring this innovative drug candidate into Greater China, South Korea and Singapore.

Discovered and engineered using Numab’s proprietary λcap™ technology and MATCH™ platform, ND021 is a late-preclinical-stage, monovalent, tri-specific antibody-based molecule (scMATCH3™) that simultaneously targets PD-L1, 4-1BB, and HSA. ND021 is designed to bind to 4-1BB and activate T cells only when engaging with PD-L1 on the surface of tumor cells, potentially preventing liver toxicities observed in patients treated with conventional 4-1BB-agonistic antibodies.

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Compared to other PD-L1/4-1BB bispecific antibody candidates, ND021’s unique monovalent structure and ultra-high-affinity PD-L1-binding is expected to lead to a significantly broader safety window and higher efficacy. Furthermore, half-life extension via the HAS-binding motif in ND021 enables convenient dosing schedules for patients. ND021 is anticipated to be effective against tumors with a wide range of PD-L1 expression-levels and may overcome primary and/or acquired resistance to anti-PD-1/PD-L1 therapies. Therefore, ND021 represents a leading class of next-generation cancer immunotherapies and a new backbone molecule for combinations.

Dr. Frank Ningjun Jiang, chairman, executive director and chief executive officer of CStone, commented: “This collaboration with Numab further strengthens our position as a leading immuno-oncology player in China and commitment to our immuno-oncology combination strategy. We look forward to joining global simultaneous development to bring this novel therapy to patients in China and beyond as soon as possible.”

Dr. David Urech, chief executive officer of Numab, said: “We are very happy to join forces with CStone to accelerate the progress of ND021 in the clinic. In addition to blocking PD-L1-mediated immune-suppression, ND021 has a novel design that tethers potent T cell co-stimulation to the engagement of PD-L1-positive cancer cells, in order to generate focused anti-cancer immune-responses and a favorable risk/benefit profile. We believe this drug candidate has the potential to become an important treatment option for cancer patients around the world.”

About ND021

ND021 is a next-generation PD-L1/4-1BB/HSA monovalent tri-specific scMATCH3™ that potently blocks PD-L1/PD-1 signaling while eliciting tumor-restricted co-stimulation of 4-1BB+ cells. In preclinical models, ND021 was well tolerated and induced exquisite antitumoral effects. Its unique, rationally designed molecular architecture and binding properties endow ND021 with several advantageous features that may translate into significant clinical benefit in a broad population of cancer patients.

About CStone

CStone is a biopharmaceutical company focused on developing and commercializing innovative immunooncology and precision medicine 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 with a strategic emphasis on immuno-oncology combination therapies. Currently, 4 late-stage candidates are at or near 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, please visit: www.cstonepharma.com.

About Numab

Numab is a biopharmaceutical company discovering and developing next-generation therapies for cancer and auto-immune disease. Numab applies its proprietary antibody discovery engine, Fv-stabilizing λcap™

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technology and MATCH™ platform to generate highly versatile multi-specific antibodies with best-in-class properties. Multi-specific MATCH molecules comprise antibody Fvs with fully human frameworks, are highly stable and readily accommodate plug-and-play engineering of novel mechanisms of action (e.g., tumortargeting T cell-engagers), with superior efficacy and favorable safety profiles.

For more information about Numab Therapeutics, please visit: www.numab.com.

By order of the Board CStone Pharmaceuticals Dr. Frank Ningjun Jiang Chairman

Suzhou, People’s Republic of China, May 2, 2019

As at the date of this announcement, the Board of Directors of the Company comprises Dr. Frank Ningjun Jiang as Chairman and Executive Director, Dr. Wei Li, Mr. Qun Zhao, Mr. Xiaomeng Tong, Mr. Guobin Zhang and Dr. Lian Yong Chen as non-executive Directors, and Dr. Paul Herbert Chew, Mr. Ting Yuk Anthony Wu and Mr. Hongbin Sun as independent non-executive Directors.

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