Quantitative Membrane Proteomics for Discovery of Actionable Drug Targets at the Surface of RAS-Driven Human Cancer Cells.

With the advent of promising lung cancer immunotherapies targeting proteins at the cell surface of RAS-driven human cancers, the mass spectrometry (MS)-based surfaceomics remains a feasible strategy for therapeutic target discovery. This chapter describes a protocol for discovery of druggable protein targets at the surface of RAS-driven human cancer cells. This method relies on bottom-up MS-based quantitative surfaceomics that employs in parallel, targeted hydrazide-based cell-surface glycoproteomics and global shotgun membrane proteomics to enable unbiased quantitative profiling of thousands of cell surface membrane proteins. A large-scale molecular map of the KRAS surface was attained, resulting in confident detection and quantitation of more than 500 cell surface membrane proteins that were found to be unique or upregulated at the surface of cells harboring the KRAS mutant. A multistep bioinformatic progression revealed a subset of unique and/or significantly upregulated proteins as priority drug targets selected for orthogonal cross-validation using immunofluorescence, structured illumination microscopy, and western blotting. Among cross-validated targets, CUB domain containing protein 1 (CDCP1) and basigin (BSG-CD147) were selected as leading targets due to their involvement in cell adhesion and migration, consistent with the KRAS malignant phenotype as revealed by scanning electron microscopy and phenotypic cancer cell assays. Follow-up studies confirmed CDCP1 as an actionable therapeutic target, resulting in development of recombinant antibodies capable of killing KRAS-transformed cancer cells in preclinical setting. The present MS-based surfaceomics workflow represents a powerful drug target discovery platform that enables development of innovative immunotherapeutics (e.g., antibody drug conjugate against CDCP1) for attacking oncogenic RAS-driven cancers at the cell surface.