Assessing factors for predictive response to ADC targets in clinical tissue for companion diagnostic development.

Abstract

e22187 Background: One premise of antibody-drug conjugates (ADC) is that the bound mAb-antigen complex on the cell surface will internalize and be metabolized by lysosomal proteases to release the free drug. Thus, the efficacy of an ADC is dependent not only on the presence of cell surface antigens, but also intact delivery of the conjugated drug. In most cases, the biological mechanisms behind these processes have not been elucidated. Furthermore, the extracellular stability of the ADC may be affected by the activity of the target proteases in the tumor microenvironment outside of the lysozome. These concepts are especially important for CDx approaches, which would ideally account not only for the degree of cell surface expression of the target, but also receptor internalization and potential effects of tumor microenvironment. Although in vitro approaches exist to measure these attributes, there are no clinically amenable approaches to measure these critical parameters. Methods: Flagship Biosciences has invented several proprietary approaches for measuring critical properties of the therapeutic target on the cell surface or inside the cell, as well as properties of the TME which could be used to predict efficacy to an ADC using FFPE biopsies. These image analysis approaches have been designed specifically in context of ADC CDx programs to: 1) Accurately define cell surface target expression independent of cytoplasmic expression; 2) Assess critical factors in the TME which may affect delivery of the drug to the intracellular target; and 3) Multiplex these evaluations for an integrative answer to be derived from a typical clinical biopsy. Results: The measurement of cytoplasm/membrane localization was evaluated on several hundred tissue sections, and the methodology was found to be highly reproducible, with coefficients of variation lower than that observed by manual pathologist accessment. Conclusions: Our approach discretely measures endpoints of cell surface biomarker prevalence, biomarker membrane/cytoplasmic ratio, heterogeneity, stromal contribution, inflammatory environment, and other important cell-by-cell outputs from a single FFPE slide in the context of typical drug discovery.