On September 13, 2021 Harbour BioMed ("HBM", HKEX: 02142) reported that positive results from its phase I dose escalation clinical trial of HBM4003 in solid tumors in Australia (the "phase I study") (Press release, Harbour BioMed, SEP 13, 2021, View Source [SID1234587652]). The clinical data abstract has been presented by way of an e-poster at the 2021 European Society for Medical Oncology (ESMO) (Free ESMO Whitepaper) Congress.

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The data received from the phase I study, as the first clinical evidence of next generation anti-CTLA-4 fully human heavy-chain only antibody (HCAb) in solid tumors, showed favorable safety and encouraging efficacy profile of HBM4003. All treatment-related adverse events (TRAEs) to the extent discovered during the phase I study were manageable and reversible. The initial anti-tumor efficacy of HBM4003 monotherapy was encouraging, especially two respondents who underwent multiple therapies responded to HBM4003 monotherapy.

The Phase I Study Design

The phase I study is an open-label, multi-center study on subjects with solid tumors to receive HBM4003 at dose levels of 0.3mg/kg QW (28-day cycle), 0.45mg/kg Q3W (21-day cycle), and 0.6mg/kg Q3W (21-day cycle). The primary endpoint for the dose escalation stage is proportion of patients with dose-limiting toxicity (DLT).

Key Results of the Phase I Study

(i) 20 patients with advanced solid tumors have been treated at four Australian sites where the phase I study was conducted, with 13 out of 20 patients (65%) having received 2 or more prior regimens and with 8 patients (40%) having received PD-1 treatment.
(ii) HBM4003 treatment demonstrated favorable safety profile. No toxicity reported was related to lung, kidney, heart or endocrine system.
(iii) A dosage of 0.45 mg/kg Q3W was recommended as the phase II dose for dose expansion.
(iv) A total of 15 patients had post-treatment tumor assessments. One hepatocellular carcinoma (HCC) patient had confirmed partial response (PR) and another prostate cancer patient achieved a prostate surface antigen (PSA) response with tumor remaining stable disease (SD) up to 24 weeks. Nine patients had SD with tumor shrinkage in 3 patients.
(v) For the HCC patient with PR, extended clinical benefit was observed after treatment discontinuation. Tumor reduction reached 64.4% for target lesions and non-target lesions were no longer detectable 16 weeks after the last dose.

"We are extremely pleased to announce the positive results of this study at ESMO (Free ESMO Whitepaper) Congress 2021, one of the top international academic conferences. The anti-tumor efficacy of HBM4003 with the good safety profile and tolerability is encouraging. With high expectations on the promising therapeutic value of HBM4003, the Company has proceeded with multiple global phase Ib/IIa trials in solid tumors." said Dr. Jingsong Wang, Founder, Chairman and CEO of Harbour BioMed.

About HBM4003

HBM4003 is a fully human anti-CTLA-4 monoclonal heavy chain only antibody (HCAb) generated from Harbour Mice. By enhancing antibody-dependent cell cytotoxicity (ADCC) killing activity, HBM4003 has demonstrated significantly improved depletion specific to high CTLA-4 Treg cells in tumor tissues. The potent anti-tumor efficacy and differentiated pharmacokinetics with durable pharmacodynamic effect presents 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 combo-therapy.