pHLIP (pH Low Insertion Peptide) Technology for Cancer Diagnosis and Treatment

The combined effort of the three laboratories of Dr. Oleg Andreev (URI), Dr. Yana Reshetnyak (URI) and Dr. Donald Engelman (Yale University) directed toward the development of pHLIP nanotechnology platform for cancer imaging and treatment. pHLIP technology is based on the action of the pH (Low) Insertion Peptide (pHLIP) - a water-soluble membrane peptide that interacts weakly with a cell membrane at neutral pH, without insertion into the lipid bilayer, whereas at slightly acidic pH (<7.0) pHLIP inserts into the cell membrane and forms a stable transmembrane alpha-helix. The pHLIP-nanotechnology platform can be used in two ways:

pH-selective targeting of therapeutic or imaging agents to solid tumors, where they are tethered to the surfaces of cancer cells.

pH-selective targeting of tumor cells with cytoplasmic delivery of cargo molecules attached to the pHLIP C-terminus via a cleavable bond.

Acting as a monomer, pHLIP can inject and release cargo molecules attached to the pHLIP C-terminus via an S-S bond that is cleaved in the cytoplasm. Among the successfully injected molecules are the organic dyes, phalloidin (a polar, cyclic peptide of more than 1 kDa), and 12-mer and 18-mer peptide nucleic acids (PNAs). If cargo molecules are attached to the pHLIP N-terminus via a non-cleavable bond, pHLIP can tether them to the surfaces of cells in acidic tissues. The pH-selective insertion and folding of pHLIP into membranes has been used to target acidic tissue in vivo, including tumors and sites of inflammation. The pathway of pHLIP entry into the membrane and the translocation of molecules into cells is not mediated by endocytosis, but by interactions with cell receptors or by formation of pores in the cell membrane. We have shown that pHLIP insertion is associated with the protonation of Asp residues, which leads to an increase in pHLIP hydrophobicity that immediately (within seconds) triggers the insertion of the peptide into a cell membrane. The insertion is accompanied by the release of about 2 kcal/mol of energy, which is used to move cell-impermeable cargo molecules through the lipid bilayer of membrane into the cell.

alt pHLIP 

Schematic representation of pHLIP-cargo interactions with the membrane of cells in healthy and diseased tissue.