Exatecan Antibody Drug Conjugates Based on a Hydrophilic Polysarcosine Drug-Linker Platform

Abstract

We herein report the development and evaluation of a novel HER2-targeting antibody–drug conjugate (ADC) based on the topoisomerase I inhibitor payload exatecan, using our hydrophilic monodisperse polysarcosine (PSAR) drug-linker platform (PSARlink). In vitro and in vivo experiments were conducted in breast and gastric cancer models to characterize this original ADC and gain insight about the drug-linker structure–activity relationship. The inclusion of the PSAR hydrophobicity masking entity efficiently reduced the overall hydrophobicity of the conjugate and yielded an ADC sharing the same pharmacokinetic profile as the unconjugated antibody despite the high drug-load of the camptothecin-derived payload (drug–antibody ratio of 8). Tra-Exa-PSAR10 demonstrated strong anti-tumor activity at 1 mg/kg in an NCI-N87 xenograft model, outperforming the FDA-approved ADC DS-8201a (Enhertu), while being well tolerated in mice at a dose of 100 mg/kg. In vitro experiments showed that this exatecan-based ADC demonstrated higher bystander killing effect than DS-8201a and overcame resistance to T-DM1 (Kadcyla) in preclinical HER2+ breast and esophageal models, suggesting potential activity in heterogeneous and resistant tumors. In summary, the polysarcosine-based hydrophobicity masking approach allowsfor the generation of highly conjugated exatecan-based ADCs having excellent physicochemical properties, an improved pharmacokinetic profile, and potent in vivo anti-tumor activity.

Sequence-Defined Synthetic Polymers for New-Generation Functional Biomaterials

“…It is worth mentioning that the pharmacokinetics and tolerability of ADCs are greatly affected by drug-to-antibody ratios (DARs) of the conjugates, with typical values of 2–4, whereas a higher DAR commonly increases the overall hydrophobicity of ADCs, compromising their therapeutic efficacy . To resolve this issue, hydrophilic homopolymers have been attempted to construct homogeneous ADCs with defined sequence or high DARs. , Specifically, discrete polysarcosine-based linkers as hydrophobicity masking motifs were synthesized to formulate β-glucuronidase-sensitive ADCs with a DAR of 8 (Figure b) . Chain-length-dependent pharmacokinetic properties and in vivo antitumor activities were further investigated, revealing an optimal length of polysarcosines (i.e., dodecamer).…”

“…194 To resolve this issue, hydrophilic homopolymers have been attempted to construct homogeneous ADCs with defined sequence 195 or high DARs. 196,197 Specifically, discrete polysarcosine-based linkers as hydrophobicity masking motifs were synthesized to formulate β-glucuronidase-sensitive ADCs with a DAR of 8 (Figure 8b). 196 Chain-length-dependent pharmacokinetic properties and in vivo antitumor activities were further investigated, revealing an optimal length of polysarcosines (i.e., dodecamer).…”

Novel ADCs and Strategies to Overcome Resistance to Anti-HER2 ADCs

“…In addition to the anti-HER2 ADCs under clinical development that have been discussed above, several anti-HER2 ADCs that include cleavable linkers, new conjugation techniques, specific conjugation sites, increased DAR, and/or new cytotoxic agents that possess bystander cytotoxic effect are currently being developed. Those changes improve the stability and efficacy of ADCs compared to T-DM1, and therefore improve their activity in tumors with heterogeneous HER2 expression and/or resistance to T-DM1 [ 125 , 148 , 149 , 150 ].…”

“…Tra-Exa-PSAR10 is a novel ADC anti-HER2 generated by a specific technology called hydrophilic monodisperse polysarcosine (PSAR) drug-linker platform (PSARlink) [ 149 ]. With this technology, Coniln and colleagues conjugated trastuzumab to the topoisomerase I inhibitor payload exatecan, achieving a DAR of 8.…”

Antibody-Drug Conjugates: Functional Principles and Applications in Oncology and Beyond

“…The hydrophilic composition of linker provides adequate polarity and stability and solubilizes typically hydrophobic payloads [47]. This masking through hydrophilic monodisperse polysarcosine drug-linker configuration (PSARlink) sensitive to β-glucuronidase, was applied in the production of novel high-DAR ADCs, against T-DM1-resistant cells [48]. Non-cleavable linkers display greater stability than cleavable ones, remaining intact through proteolytic, acidic and reductive conditions.…”