Background ADCs have emerged as a promising class of anticancer therapy. The choice of linker and payload in an ADC critically impacts its physiochemical properties, stability, PK/PD profile, and ultimately therapeutic index (TI) in the clinic. Monomethyl auristatin E (MMAE) is a clinically validated payload with multiple favorable attributes including broad and potent antitumor activity. On the other hand, high lipophilicity of MMAE drives the generally poor hydrophilicity and physiochemical properties of an ADC with a conventional linker such as vc-PAB. As a result, vc-PAB-MMAE (i.e. vedotin)-based ADCs are typically limited with low DAR (up to 4) and narrow TI. A novel, proprietary, protease-cleavable, and highly hydrophilic linker that can fully offset the high hydrophobicity of MMAE was developed (with the linker and MMAE collectively dubbed as LD343), and characterized in head-to-head comparisons with vedotin.

Methods Physiochemical properties and additional characteristics of LD343-based ADCs were evaluated in a range of in vitro and in vivo studies with proprietary antibodies utilized as tool mAbs. Key in vitro analyses included HIC- and SEC-HPLC, bystander effect, and plasma stability. PK, efficacy, and tolerability were evaluated in mouse or rat models.

Results LD343-based ADC (at DAR8) displayed high homogeneity and markedly improved hydrophilicity compared to the vedotin-based ADC (at DAR4) on HIC-HPLC, as well as excellent stability in plasma in vitro. LD343-based ADC produced robust bystander effect that was comparable to the vedotin-based ADC in a co-culture study with antigen-positive and negative tumor cells, suggesting no compromise on payload release from the hydrophilic linker. In the rat PK study, LD343 conferred stable PK of the ADC that is indistinguishable from the unconjugated parent mAb and superior to the vedotin-conjugate. In multiple cell-derived xenograft models in mice, LD343-based ADCs elicited sustained tumor regression that exceeded that of vedotin-based ADCs at the same or increased drug load. In the rat tolerability study, LD343 enabled an approximately 4-fold increase in the tolerated drug load, compared to vedotin, suggesting a simultaneous improvement in efficacy and tolerability.

Conclusions Comprehensive preclinical studies demonstrated that the highly hydrophilic LD343 conferred markedly improved physiochemical properties and PK/PD characteristics associated with significantly expanded TI, compared to vedotin. LD343 is a novel and highly promising MMAE-based linker-drug platform that can broadly serve many attractive targets and antibody technologies; it represents a key contribution toward developing next-generation ADCs that may further fulfill high unmet medical need.