CAMBRIDGE, Mass., ROTTERDAM, Netherlands and SUZHOU, China, Oct. 9, 2024 /PRNewswire/ -- Harbour BioMed (the "Company"; HKEX: 02142), a global biopharmaceutical company committed to the discovery, development, and commercialization of novel antibody therapeutics focusing on oncology and immunology, today announced the online publication of the results from its phase I clinical trial of porustobart (HBM4003), the Company's first-in-class fully human heavy chain antibody targeting CTLA-4. The trial evaluated porustobart in combination with the anti-PD-1 antibody toripalimab for the treatment of advanced solid tumors, with a particular focus on melanoma. These results were published in the Journal for ImmunoTherapy of Cancer (IF=10.3, 2023).

This multicenter, open-label phase I trial was led by Dr. Jun Guo, Chief Physician of the Department of Melanoma and Soft Tissue Sarcoma at Beijing Cancer Hospital. The data demonstrated that the combination of porustobart and toripalimab had a manageable safety profile with no new safety signals in the treatment of solid tumors. Initial results also indicated promising antitumor activity, particularly in PD-1 treatment-naïve mucosal melanoma.

Dual immunotherapy combining anti-CTLA-4 and anti-PD-1 antibodies is currently approved as a frontline treatment for several solid tumors, including melanoma, renal cell carcinoma, and non-small cell lung cancer. However, the high toxicity associated with anti-CTLA-4 antibodies has limited their broader use. Porustobart, a next-generation fully human anti-CTLA-4 antibody developed using the HCAb Harbour Mice^® platform, is the first of its kind to enter clinical development globally. Its unique properties offer the potential to overcome the efficacy and toxicity challenges of conventional anti-CTLA-4 therapies, making it a promising candidate in the field of cancer immunotherapy.

The phase I trial was conducted in two stages: a dose-escalation phase (Part 1) and a dose-expansion phase (Part 2). A total of 40 patients received treatment aimed at evaluating the safety, pharmacokinetics, immunogenicity, and preliminary efficacy of the combination therapy for the treatment of solid tumors, with a particular focus on melanoma.

Safety Results

Among the 40 patients who received study treatment, 10 (25.0%) patients reported grade ≥3 treatment-related adverse events (TRAEs). The commonly reported TRAEs were rash (30.0%), abnormal liver function (30.0%), leukopenia (25.0%), and fever (20.0%). Additionally, 5 (12.5%) patients experienced immune-related adverse events (irAEs) with maximum severity of Grade 3. No Grade 4 or 5 irAEs occurred.

Efficacy Results

Efficacy was evaluated in 32 melanoma patients treated with the recommended phase II dose (RP2D) of porustobart 0.3 mg/kg combined with toripalimab 240 mg every three weeks (Q3W), and who had available post-baseline imaging data. The objective response rate (ORR) was 33.3% in the anti-PD-1/PD-L1 treatment-naïve subgroup. For patients with mucosal melanoma, the ORR in this anti-PD-1/PD-L1 treatment-naïve subgroup was 40.0%. A high baseline Treg/CD4+ ratio in the tumor was identified as an independent predictive factor for immunotherapy efficacy.

In summary, the combination of porustobart 0.3 mg/kg with toripalimab 240 mg Q3W demonstrated promising antitumor activity and manageable safety in patients with advanced melanoma, including the difficult-to-treat mucosal subtypes. Further studies are needed to confirm these findings, particularly in patients with mucosal melanoma.

"We are encouraged by the positive results from our phase I study of porustobart in combination with an anti-PD-1 antibody, which has shown a favorable safety profile and early signs of clinical activity," said Dr. Jingsong Wang, Founder, Chairman and CEO of Harbour BioMed. "Porustobart is the first internally developed molecule generated from our HCAb Harbour Mice^® platform. We look forward to moving forward with further studies to fully explore the potential of this combination in addressing unmet medical needs and ultimately making a meaningful difference in patients' lives."

About Porustobart

Porustobart (HBM4003) is a fully human anti-CTLA-4 monoclonal heavy chain only antibody (HCAb) generated from Harbour Mice^®. It is the first fully human heavy-chain-only monoclonal antibody entered into clinical stage globally. By enhancing antibody-dependent cell cytotoxicity (ADCC) killing activity, porustobart has demonstrated significantly improved depletion specific to high CTLA-4 expressing Treg cells in tumor tissues. The potent anti-tumor efficacy and differentiated pharmacokinetics with durable pharmacodynamic effect present a favorable product profile. This novel and differentiated mechanism of action has the potential to improve efficacy while significantly reducing the toxicity of the drug in monotherapy and combination therapy.

About Harbour BioMed

Harbour BioMed (HKEX: 02142) is a global biopharmaceutical company committed to the discovery, development, and commercialization of novel antibody therapeutics focusing on immunology and oncology. The Company is building its robust portfolio and differentiated pipeline through internal R&D capability, collaborations with co-discovery and co-development partners, and select acquisitions.

The proprietary antibody technology platforms Harbour Mice^® generates fully human monoclonal antibodies in two heavy and two light chains (H2L2) format, as well as heavy chain only (HCAb) format. Building upon the HCAb antibodies, the HCAb-based immune cell engagers (HBICE^®) bispecific antibody technology is capable of delivering tumor-killing effects unachievable by traditional combination therapies. Integrating Harbour Mice^®, and HBICE^® with a single B cell cloning platform, our antibody discovery engine is highly unique and efficient for the development of next-generation therapeutic antibodies. For further information, please refer to www.harbourbiomed.com.

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