Intracellular MUC1 Peptides Inhibit Cancer Progression

Purpose: During cancer progression, the oncoprotein MUC1 binds β-catenin while simultaneously inhibiting the degradation of the epidermal growth factor receptor (EGFR), resulting in enhanced transformation and metastasis. The purpose of this study was to design a peptide-based therapy that would block these intracellular protein-protein interactions as a treatment for metastatic breast cancer. Experimental Design: The amino acid residues responsible for these interactions lie in tandem in the cytoplasmic domain of MUC1, and we have targeted this sequence to produce a MUC1 peptide that blocks the protumorigenic functions of MUC1. We designed the MUC1 inhibitory peptide (MIP) to block the intracellular interactions between MUC1/β-catenin and MUC1/EGFR. To allow for cellular uptake we synthesized MIP adjacent to the protein transduction domain, PTD4 (PMIP). Results: We have found that PMIP acts in a dominant-negative fashion, blocking both MUC1/β-catenin and MUC1/EGFR interactions. In addition, PMIP induces ligand-dependent reduction of EGFR levels. These effects correspond to a significant reduction in proliferation, migration, and invasion of metastatic breast cancer cells in vitro, and inhibition of tumor growth and recurrence in an established MDA-MB-231 immunocompromised (SCID) mouse model. Importantly, PMIP also inhibits genetically driven breast cancer progression, as injection of tumor-bearing MMTV-pyV mT transgenic mice with PMIP results in tumor regression and a significant inhibition of tumor growth rate. Conclusions: These data show that intracellular MUC1 peptides possess significant antitumor activity and have important clinical applications in the treatment of cancer.