Antibodies and peptides directed against the switch regions of RAS can disrupt interactions with its downstream effector proteins, blocking downstream pro-tumorigenic signaling. However, these biologic therapies are unable to reach the intracellular environment. We have overcome this problem using peptidic molecular guidance system (MGSs) that have the unique ability to bind specifically to epithelial-derived cancer cells, and upon binding, trigger rapid internalization and trafficking to a specific subcellular location. Using an unbiased phage display approach, we have identified a series of cancer-specific MGSs that deliver cargo to discrete subcellular locations. Chemical optimization results in MGSs with 1-10 nM affinity for their cellular target, serum stability >48 hours, and 50-1000-fold specificity for cancer cells compared to normal control cells. The rate of MGS internalization is rapid with t1/2 of 10-30 minutes, achieving intracellular concentrations up to 1.5 µM. Using these MGSs as delivery agents, we have delivered a function blocking RAS antibody (Y13-259), resulting in a reduction of p-ERK and apoptosis in KRAS mutant cell lines. The effect is MGS dependent, and confocal microscopy indicates co-localization of KRAS and the antibody indicating target engagement. The MGS-Antibody homes to tumors in an animal model resulting in significant suppression in tumor growth compared to untreated animals. Free MAb does not impact tumor growth. Using MGSs to delivery MAb for intracellular targets is paradigm change for immunotherapy and represents a new approach for controlling intracellular protein-protein interactions. Combination of these cancer-specific delivery agents with effectors of RAS signaling, such as antibodies and other biologics, has therapeutic potential for KRAS-driven cancers.