ASCLETIS-B - VOLUNTARY ANNOUNCEMENT - ASCLETIS ANNOUNCES POSITIVE RESULTS FROM 28-DAY PROOF-OF-CONCEPT CLINICAL STUDY IN U.S. FOR ASC50, A FIRST-IN-CLASS AND BEST-IN-CLASS ORAL SMALL MOLECULE IL-17A INHIBITOR FOR THE TREATMENT OF PLAQUE PSORIASIS

Ascletis Pharma Inc.

歌禮製藥有限公司

(incorporated in the Cayman Islands with limited liability)

(Stock Code: 1672)

VOLUNTARY ANNOUNCEMENT

ASCLETIS ANNOUNCES POSITIVE RESULTS FROM 28-DAY

PROOF-OF-CONCEPT CLINICAL STUDY IN U.S. FOR ASC50,

A FIRST-IN-CLASS AND BEST-IN-CLASS ORAL SMALL

MOLECULE IL-17A INHIBITOR FOR THE TREATMENT

OF PLAQUE PSORIASIS

– 48.9% placebo-adjusted reduction in psoriasis area and severity index (PASI) score achieved

in mild-to-moderate plaque psoriasis patients with once-daily 200 mg 28-day treatment.

– Steady-state elimination half-life after 28-day treatment in patients was 6.5 days, supporting

potential once-weekly oral dosing.

– Placebo-adjusted reduction in PASI score reached 65.9% in mild-to-moderate plaque psoriasis

patients 15 days after last dose (28th dose), which supports potential once-weekly oral dosing.

– Strong target engagement after 28-day dosing, indicated by elevated plasma interleukin-17A

(IL-17A) levels.

– Once-daily 200 mg 28-day treatment was safe and well tolerated with only mild adverse events observed. No alanine aminotransferase (ALT) and aspartate aminotransferase (AST)

elevations were observed. No hepatic safety signal was detected.

This announcement is made by Ascletis Pharma Inc. (the "Company" or "Ascletis", together with its subsidiaries, the "Group") on a voluntary basis for the purpose of keeping the shareholders of the Company and potential investors abreast of the latest business development of the Group.

The board (the "Board") of directors (the "Directors") of the Company announces positive results from a randomized, double-blind, placebo-controlled 28-day proof-of-concept clinical trial with ASC50 in mild-to-moderate plaque psoriasis patients in the U.S. The objectives of the Phase I study were to evaluate the safety, efficacy and pharmacokinetics of once-daily 200 mg of ASC50 after 28-day treatment in mild-to-moderate plaque psoriasis patients (NCT07024602).

Key Findings

 Achieved a placebo-adjusted reduction of 48.9% in psoriasis area and severity index (PASI)

score in mild-to-moderate plaque psoriasis patients after once-daily 200 mg 28-day treatment.  Steady-state elimination half-life after 28-day treatment in patients was 6.5 days, supporting

potential once-weekly oral dosing.

 The placebo-adjusted reduction in PASI score increased to 60.7% and 65.9% 6 days and 15 days, respectively, after the last dose (28th dose). These data support potential once-weekly

oral dosing.

 200 mg once-daily dosing demonstrated comparable reduction in PASI score to published secukinumab data (not head-to-head study). Secukinumab is the marketed interleukin-17A

(IL-17A) antibody drug.

 Strong target engagement after 28-day dosing, indicated by elevated plasma IL-17A levels.

 Once-daily 200 mg 28-day treatment was safe and well tolerated. All adverse events (AEs) were mild (Grade 1) and transient. No serious adverse events (SAEs) were reported. There was no discontinuation in the study. No alanine aminotransferase (ALT) and aspartate

aminotransferase (AST) elevations were observed. No hepatic safety signal was detected.

"Strong efficacy and encouraging safety and pharmacokinetic data from this proof-of-concept clinical trial support ASC50's potential to be a first-in-class and best-in-class oral small molecule IL-17A inhibitor, offering patients a needle-free administration option to injectable antibody therapies. ASC50's novel scaffold exhibited a steady-state elimination half-life of 6.5 days in patients, supporting the potential for once-weekly oral dosing," said Jinzi Jason Wu, Ph.D., Founder, Chairman of the Board and chief executive officer of Ascletis, "ASC50 has the potential to be a differentiated oral alternative compared to injectable antibody therapies and will benefit patients with once-weekly oral dosing."

ASC50 is an in-house discovered and developed oral small molecule inhibitor targeting IL-17A, an important biologically and commercially validated target for multiple autoimmune and inflammatory diseases, including psoriasis. ASC50 is a new chemical entity (NCE) with a novel scaffold.

Cautionary Statement required by Rule 18A.05 of the Rules Governing the Listing of

Securities on The Stock Exchange of Hong Kong Limited: We cannot guarantee that we will be able to ultimately develop, manufacture and/or commercialize ASC50 successfully.

By order of the Board

Ascletis Pharma Inc.歌禮製藥有限公司Jinzi Jason WU

Chairman

Hong Kong

September 29, 2026