CStone Pharmaceuticals — Capital/Financing Update 2024

Jun 4, 2024

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CStone Pharmaceuticals 基石藥業

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

VOLUNTARY ANNOUNCEMENT CSTONE ANNOUNCES PRESENTATION OF LATEST FIRST-IN-HUMAN DATA FOR CS5001 (ROR1 ADC) AT ASCO 2024

CStone Pharmaceuticals (the “ Company ” or “ CStone ”) is pleased to announce that a poster presentation of data from the first-in-human, global, multi-center, phase 1a/1b study of CS5001 (ROR1 ADC), one of the key assets in CStone Pipeline 2.0, in patients with advanced solid tumors and lymphomas has been made at the 2024 American Society of Clinical Oncology (ASCO) Annual Meeting.

Key Highlights

• The latest first-in-human study data show that CS5001 is well tolerated with promising anti-tumor activity at various dose levels in heavily pretreated, advanced solid tumors and lymphomas.

• CS5001 is the first known ROR1 antibody-drug conjugate (ADC) to demonstrate clinical anti-tumor activity in both solid tumors and lymphomas.

• Dose escalation in the global, multi-center, phase 1 trial of CS5001 is ongoing in the United States, Australia, and China, with plans to initiate dose-expansion studies in multiple tumor types soon and potential registrational trials in 2024.

• Additional up-to-date clinical data of CS5001 will be regularly disclosed at upcoming investor meetings or academic conferences, such as ESMO and ASH.

Dr. Jason Yang, CEO, President of R&D and Executive Director at CStone, said, “We are very pleased to present the first-in-human data of CS5001 at the prestigious ASCO meeting. The unique design of CS5001 has been adequately validated in clinical trial given its manageable safety and tolerability. Although the study is still in the dose-finding stage, we have already observed potent anti-tumor activity of CS5001 in various malignancies, such as diffuse large B-cell lymphoma (DLBCL), Hodgkin lymphoma, pancreatic cancer, non-small cell lung cancer (NSCLC), breast cancer, ovarian cancer, etc. It is worth noting that CS5001 is the first known ROR1 ADC to demonstrate clinical anti-tumor activity in solid tumors. We are also very excited to observe, following the cutoff date for the ASCO poster, CS5001 accumulating additional evidence of anti-tumor activity in lymphoma and solid tumors. The updated clinical data will be disclosed at subsequent investor meetings or academic conferences. The promising clinical data

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warrant further development of CS5001, a potentially best-in-class ROR1 ADC, across a broad range of cancers.”

CS5001 is a novel ROR1-targeted ADC designed with a unique pyrrolobenzodiazepine (PBD) prodrug. This first-in-human study aims to evaluate the safety, pharmacokinetics (PK), and anti-tumor activity of CS5001 in patients with advanced solid tumors and B-cell lymphomas.

The latest efficacy and safety data for CS5001 disclosed in the ASCO poster are as follows:

• As of the data cut-off date for the poster, dose-limiting toxicity (DLT) evaluation for the first nine dose levels (7 to 156 μg/kg) in Phase 1a has been completed. No DLTs were observed, and the maximum tolerated dose (MTD) was not reached.

• Most treatment-related adverse events observed were Grade 1 or 2 (per NCI-CTCAE v5.0), indicating that CS5001 was well tolerated by heavily pretreated patients with advanced solid tumors and lymphomas.

• PK data suggested dose-proportional exposure of CS5001, with similar exposure for ADC and total antibody, demonstrating excellent stability of CS5001 ADC in circulation.

• Encouraging anti-tumor activity has been observed in various solid tumors (per RECIST v1.1) and hematologic malignancies (per Lugano 2014):

• Hodgkin Lymphoma: Objective responses were observed from dose level 5 (50 μg/kg) and above, including 1 complete response (CR) and 4 partial responses (PR) among 9 evaluable patients at dose levels 5-9, achieving an objective response rate (ORR) of 55.6%.

• DLBCL: Objective responses were observed from dose level 7 (100 μg/kg) and above, including 1 CR and 2 PRs among 6 evaluable patients at dose levels 7-9, achieving an ORR of 50.0%.

• In solid tumors, multiple PRs and stable diseases (SDs) with reduced tumor burden were emerging from dose level 7 (100 μg/kg) and above, notably in NSCLC (1 PR and 3 SDs), pancreatic cancer (1 PR), triple-negative breast cancer (TNBC; 1 SD), and ovarian cancer (1 SD). Based on the efficacy trends observed, more potent anti-tumor activity is expected in patients with solid tumors as the dose increases.

To date, the phase 1a dose escalation in the reported study remains ongoing, with parallel backfilling of additional patients at selected higher doses to determine preliminary phase 2 recommended dose (RP2D) and to evaluate the relationship between ROR1 expression and efficacy. Phase 1b will be initiated in the near term in multiple indications for dose optimization, followed by initiation of potential pivotal trials by the end of 2024.

About CS5001 (ROR1 ADC)

CS5001 is a clinical-stage antibody-drug conjugate (“ADC”) targeting ROR1 (receptor tyrosine kinaselike orphan receptor 1). CS5001 has been uniquely designed with proprietary tumor-cleavable linker and pyrrolobenzodiazepine (“PBD”) prodrug. Only after reaching the tumor, the linker and prodrug are cleaved to release the PBD toxin, resulting in lethal DNA cross-links in cancer cells. The use of the linker plus PBD prodrug effectively helps addressing the toxicity problem associated with traditional PBD payloads, leading to a better safety profile. CS5001 has demonstrated complete tumor suppression in several preclinical cancer models and demonstrated favorable serum half-life and pharmacokinetic characteristics. CS5001 is a promising candidate drug with precision treatment potential in both hematologic tumors and malignant solid tumors. Additionally, CS5001 utilizes site-specific conjugation for a precise drug antibody ratio of which enables homogeneous production and large-scale manufacturing.

In October 2020, CStone signed a licensing agreement with LigaChem Biosciences, Inc. (LCB) for the development and commercialization of CS5001 which was originally generated by collaboration of LCB

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and ABL Bio, both South Korea-based leading biotech companies. Under the agreement, CStone obtained the exclusive global right to develop and commercialize CS5001 outside the Republic of Korea.

About CStone

CStone (HKEX: 2616), established in late 2015, is an innovation-driven biopharmaceutical company, focused on the research and development of anti-cancer therapies. Dedicated to addressing patients’ unmet medical needs in China and worldwide, the company has made significant strides since its inception. To date, the company has successfully launched 4 innovative drugs and secured approvals for 14 New Drug Applications (NDAs) covering 9 indications. The company’s pipeline is balanced by 12 promising candidates, featuring potentially first-in-class or best-in-class antibody-drug conjugates (ADCs), multispecific antibodies, immunotherapies and precision medicines. CStone also prides itself on a management team with comprehensive experiences and capabilities that span the entire drug development spectrum, from preclinical and translational researches to clinical development, drug manufacturing, business development, and commercialization.

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

Cautionary Statement required by Rule 18A.05 of the Listing Rules: THE COMPANY CANNOT GUARANTEE THAT WE MAY BE ABLE TO ULTIMATELY DEVELOP AND MARKET CS5001 SUCCESSFULLY. Shareholders of the Company and potential investors are advised to exercise due care when dealing in the shares of the Company.

Forward Looking Statement

There is no assurance that any forward-looking statements regarding the business development of the Group in this announcement or any of the matters set out herein are attainable, will actually occur or will be realized or are complete or accurate. The financial and other data relating to the Group as disclosed in this announcement has also not been audited or reviewed by its auditors. Shareholders and/or potential investors of the Company are advised to exercise caution when dealing in the securities of the Company and not to place any excessive reliance on the information disclosed herein. Any shareholder or potential investor who is in doubt is advised to seek advice from professional advisors.

By Order of the Board CStone Pharmaceuticals Dr. Wei Li Chairman

Suzhou, the People’s Republic of China, June 4, 2024

As at the date of this announcement, the board of directors of the Company comprises Dr. Wei Li as Chairman and non-executive director, Dr. Jianxin Yang as executive director, Mr. Kenneth Walton Hitchner III, Mr. Xianghong Lin and Mr. Edward Hu 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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