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 <b>PBX-7016</b> (14), a novel methylenedioxy-camptothecin analog. Hybrid molecules combining FL118 and Exatecan pharmacophores were synthesized and tested <i>in vitro</i>, 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 <i>in vivo</i> efficacy across multiple xenograft models. Furthermore, PBX-7016-based ADCs maintained strong efficacy against various tumor-associated antigens, demonstrating therapeutic versatility. Notably, <i>in vitro</i> ADME profiling and rodent toxicology studies confirmed a favorable safety profile and good tolerability. <b>PBX-7016</b> represents a differentiated camptothecin payload with strong translational promise, and its ADCs are currently advancing through Phase I trials.