Discovery and Preclinical Evaluation of PBX-7016, a Methylenedioxy-Camptothecin Payload for Antibody-Drug Conjugates with Enhanced Therapeutic Potential

Camptothecin derivatives have become cornerstone payloads in antibody–drug conjugates (ADCs), with recent clinical success driving continued optimization to improve therapeutic efficacy and safety. Herein, we present the development of PBX-7016 (14), a novel methylenedioxy-camptothecin analog. Hybrid molecules combining FL118 and Exatecan pharmacophores were synthesized and tested in vitro, yielding three lead compounds characterized by dual Topo1 inhibition and antiapoptotic protein suppression. Functional evaluation of ADC constructs incorporating these payloads validated physicochemical compatibility with antibody conjugation, target-dependent cytotoxicity, and antibody-like pharmacokinetics. When benchmarked against Enhertu, these ADCs showed superior bystander killing and in vivo efficacy across multiple xenograft models. Furthermore, PBX-7016–based ADCs maintained strong efficacy against various tumor-associated antigens, demonstrating therapeutic versatility. Notably, in vitro ADME profiling and rodent toxicology studies confirmed a favorable safety profile and good tolerability. PBX-7016 represents a differentiated camptothecin payload with strong translational promise, and its ADCs are currently advancing through Phase I trials.