Their "cargo carrier" peptide called pHLIP, for pH (Low) Insertion Peptide, accumulates in the membranes of cells in acidic environments and spontaneously transfers attached molecules across the membrane. The cargo is then released by cleavage of a sulfur-sulfur bond that is only unstable if it is inside the cell.

"Our system offers a new technology for the fast and efficient delivery of drugs, imaging probes, or cell and gene regulation agents into living cells," said Donald M. Engelman, professor of molecular biophysics and biochemistry at Yale.

"pHLIP may provide a new approach for imaging, diagnosis and treatment of diseases with naturally occurring or artificially created low-pH extracellular environments, such as tumours, infarcts, stroke-afflicted tissue, atherosclerotic lesions, sites of inflammation or infection, or damaged tissue resulting from trauma."

Normal cells are surrounded by an environment with a constant pH of about 7.4, while tumour cells and sites of inflammation actively pump protons out and create an acid extracellular pH of 5.5 to 6.5.

The study shows that pHLIP entry into the cell membrane and the translocation of molecules into cells are not mediated by the usual entry pathways – endocytosis, interactions with cell receptors, or by formation of pores in cell membranes.

"By translocating a molecule into a cell and releasing it in the cytoplasm, pHLIP functions, in effect, as a nanosyringe," according to Engelman. "The peptide does not exhibit any of this structure in solution or on the cell membrane at neutral pH. However, at low pH it becomes rigid like a syringe needle, inserts into a cell membrane, and injects molecules into cells.; Source: Yale University