Translocating cell‐impermeable molecules through the plasma membrane of cancer cells

Abstract

We have discovered a novel approach to specifically target tumors based on their acidity. Our method is based on pHLIP (pH Low Insertion Peptide) ‐ a peptide that is soluble at physiological pH and inserts across lipid bilayers as a transmembrane helix at acidic pH. Unlike other strategies, pHLIP can simultaneously target tumors, carry a cargo linked to its C‐terminus and translocate the payload across the plasma membrane. In drug design, a constraint has been to create molecules that are sufficiently hydrophobic and small to traverse membranes (Log P from ‐0.4 to +5.6 and MW of 160 to 480 g.mol‐1). As a result, a broad range of cell‐impermeable molecules is excluded from drug design and discovery. Our goal is to define the properties of cell‐impermeable cargo molecules linked to pHLIP to guide the use of this novel delivery system. In this study, peptides linked to the C‐terminus of pHLIP served as model cargos. These peptides follow a host‐guest model, where single amino acids can be modified to allow the fine adjustment of cargo properties and were designed to be membrane‐impermeable. We show that pHLIP can successfully translocate such membrane‐impermeable cargos (Log P < ‐2.5; MW ≈ 800) across lipid bilayers and cancer cell membranes. Thus, pHLIP can broaden the useful range of polarity and size of potential therapeutic agents as well as targeting them to tumors.Support: NIH CA133890 and GM073857