A First-in-Class mAb (BI-1607) Targeting FcγRIIB: Preclinical Data and First-in-Human Studies in Patients with HER2-Positive Advanced Solid Tumors.

PURPOSE: BI-1607 is a human mAb that specifically blocks FcγRIIB, the sole inhibitory Fc receptor and master regulator of humoral and innate immune homeostasis. These studies evaluated preclinical antitumor activity using a BI-1607 murine surrogate (mBI-1607) and the safety, tolerability, pharmacokinetics, and pharmacodynamics of the compound in combination with trastuzumab in patients with HER2-positive advanced solid tumors (NCT05555251).

PATIENTS AND

METHODS

Immunocompetent syngeneic mouse breast tumor (TUBO) and melanoma (B16-F10) models were used to evaluate in vivo antitumor activity in combination (anti-HER2 and anti-gp75). Ascending doses of BI-1607 administered intravenously every 3 weeks in combination with trastuzumab were evaluated in 18 patients with HER2-positive cancer. The primary objective was to assess the safety and tolerability of BI-1607 by determining dose-limiting toxicities and the maximum tolerated dose or maximum administered dose and identifying a recommended phase 2 dose.

RESULTS

mBI-1607 enhanced tumor-targeting antibody efficacy and animal survival. BI-1607/trastuzumab was well tolerated, with dose-limiting toxicity (rash) in one patient (5.6%) at 900 mg; the maximum tolerated dose was not reached. Treatment-emergent adverse events grade ≥3 occurred in five patients (28%), including exanthema, increase in liver enzymes, urticaria, acute kidney injury, and aggravated condition. Overall best response was stable disease, observed in seven of the nine evaluable patients (78%). BI-1607 exhibits linear pharmacokinetics for doses above 500 mg, and full receptor saturation was observed throughout the 21 days at 700 mg. No antidrug antibodies were observed.

CONCLUSIONS

The enhancing effect on tumor direct-targeting antibodies observed preclinically, together with the favorable safety profile in patients, supports further investigation of BI-1607.