BL-B01D1, a first-in-class EGFRxHER3 bispecific antibody-drug conjugate (ADC), in patients with locally advanced or metastatic solid tumor: Results from a first-in-human phase 1 study

3001 Background: BL-B01D1 is a first-in-class novel ADC consisting of an EGFRxHER3 bispecific antibody linked to a novel TOP-I inhibitor payload via a cleavable linker. We now present safety/efficacy results from a FIH phase I study of BL-B01D1. Methods: This study included patients (pts) with locally advanced or metastatic solid tumors. For dose escalation (D-ESC, i3+3), BL-B01D1 was administered intravenously at doses of 0.27, 1.5, 3.0 mg/kg QW, 2.5, 3.0, 3.5mg/kg D1D8 Q3W or 4.5, 5.0, 6.0 mg/kg D1 Q3W. A subset of pts were enrolled into dose-expansion (D-EXP) at Q3W regimens. Results: As of Dec 31, 2022, 150 pts were enrolled and received at least one dose (D-ESC, n=25; D-EXP, n=125). DLTs were neutropenia, febrile neutropenia and thrombocytopenia at 3.0mg/kg QW and 3.5mg/kg D1D8 Q3W. The MTDs were determined to be 3.0mg/kg D1D8 Q3W and 6.0mg/kg D1 Q3W. D-EXP was carried out at 2.5, 3.0mg/kg D1D8 Q3W and 4.5, 5.0, 6.0 mg/kg D1 Q3W. 144 pts were enrolled across all Q3W dose levels (D-ESC and D-EXP), including 89 NSCLC, 7 SCLC, 27 nasopharyngeal cancer (NPC), 19 HNSCC and 2 others. Most common TRAEs (>10%, all grade / ≥ G3) were leukopenia (60%/30%), neutropenia (51%/34%), anemia (45%/15%), thrombocytopenia (44%/19%), alopecia (30%/0%), nausea (29%/<1%), vomiting (28%/0%), asthenia (21%/<1%), decreased appetite (22%/<1%), asthenia (21%/<1%), hypophagia (16%/0%), diarrhoea (15%/2%), mouth ulceration (15%/<1%), rash (13%/0%). No ILD was observed. 122 pts were evaluable for efficacy (at least 1 tumor assessment). PK and other details will be updated in the meeting. Conclusions: BL-B01D1 demonstrated encouraging efficacy in heavily pretreated metastatic/locally advanced solid tumors, especially in pts with EGFRm NSCLC. The safety profile showed adequate safety and tolerability. Clinical trial information: NCT05194982 . [Table: see text]