Overcoming acquired and intrinsic resistance with an integrated ADC platform

Antibody-drug conjugates (ADCs) emerged as a transformative class of targeted therapeutics, reforming the treatment landscape for a growing number of malignancies by integrating benefits from the specificity of antibodies and the potent cytotoxicity of payloads. Despite the remarkable clinical successes, development of acquired and intrinsic resistance poses a fundamental challenge limiting the long-term potential in a considerable proportion of patients. Various mechanisms have been reported to cause ADC resistance, including alterations in target antigen, impaired ADC internalization, efflux of the cytotoxic payload, dysregulation of lysosomal function and insensitivity to payload etc. Elucidating this complex biology is crucial for developing novel ADCs, identifying biomarkers for patient stratification and exploring strategies to overcome resistance. This is not only a scientific need but also an important clinical imperative. The current study describes an integrated platform recapitulating different clinical scenarios of ADC resistance. Models with acquired resistance were developed by either long-term in vivo induction on responsive CDX models or by establishing PDX from post-treatment relapsed patient tumors. Models with intrinsic resistance were first identified by screening ADC responses across a panel of target-positive models, followed by subsequent mechanism studies, such as PD examination, sequencing and ex vivo analysis. An Her2- and Trop2-positive gastric PDX shown clear resistance (TGI < 10%) to trastuzumab deruxtecan and sacituzumab govitecan, two clinically used Her2 and Trop2 ADCs respectively, limited response (TGI 10-30%) to Herceptin and no response to Dxd treatment. This result suggests its intrinsic resistance is largely due to the unresponsiveness to payload end. Further study on double-humanized PDX (PDX established on humanized mice) shown significant tumor growth inhibition (TGI > 65%) when treated with anti-PD1 antibody, implicating the clinical benefit of combining immune checkpoint inhibitors with ADCs. In addition to in vivo models featuring ADC resistance, multiple in vitro platforms were established to enable rapid assessment of ADC in terms of sensitivity and toxicity. A tissue culture assay using clinical samples allows ADC evaluation and comparative screening of combination strategies over a panel of patient tumors. In addition, the well-known ocular toxicity associated with multiple clinically used ADCs can be recapitulated by a cell-based assay using human corneal epithelial cells. On this platform, belantamab mafodotin, trodelvy and T-DM1 demonstrated consistent high, medium and low cytotoxicity respectively. The integration of above-mentioned platforms facilitates a deep understanding of resistance mechanisms and promotes the development of ADCs that are better aligned with clinical needs, with the ultimate goal of overcoming resistance.