Family of pH (low) insertion peptides for tumor targeting

Abstract

Cancer is a complex disease with a range of genetic and biochemical markers within and among tumors, but a general tumor characteristic is extracellular acidity, which is associated with tumor growth and development. Acidosis could be a universal marker for cancer imaging and the delivery of therapeutic molecules, but its promise as a cancer biomarker has not been fully realized in the clinic. We have discovered a unique approach for the targeting of acidic tissue using the pH-sensitive folding and transmembrane insertion of pH (low) insertion peptide (pHLIP). The essence of the molecular mechanism has been elucidated, but the principles of design need to be understood for optimal clinical applications. Here, we report on a library of 16 rationally designed pHLIP variants. We show how the tuning of the biophysical properties of peptide-lipid bilayer interactions alters tumor targeting, distribution in organs, and blood clearance. Lead compounds for PET/single photon emission computed tomography and fluorescence imaging/MRI were identified, and targeting specificity was shown by use of noninserting variants. Finally, we present our current understanding of the main principles of pHLIP design.membrane-associated folding | tumor acidity | thermodynamics | kinetics | diagnostics

Enhancement of radiation effect on cancer cells by gold-pHLIP

“…The delivery approach we propose is based on the energy of membrane-associated folding of peptides from the pHLIP family to target cellular membranes in a pHdependent manner (22,24,37). At pH < 7.0, pHLIPs insert into the lipid bilayer of the membrane, which is accompanied by a coil-helix transition and formation of a transmembrane helix.…”

“…The pH-sensitive targeting agents we are developing are based on the action of a family of pHLIPs (pH Low-Insertion Peptides), which can "sense" acidity at the surface of cancer cells and deliver diagnostic and therapeutic molecules to tumors of different origins (20)(21)(22)(23)(24)(25). It was shown that pHLIP can promote fusion of liposomes with cancer cells and cellular delivery of various payloads (26,27), including small gold nanoparticles (26).…”

Targeted imaging of urothelium carcinoma in human bladders by an ICG pHLIP peptide ex vivo

“…Thus, acidity may provide a universal biomarker for tumor targeting that is not subject to the selection of resistant cell lines (10). pH low insertion peptides (pHLIPs) are a class of membrane-binding peptides that specifically target acidic cells in vitro and in vivo (11) by inserting across cellular membranes when the extracellular pH is low (12). pHLIPs conjugated with fluorescent dyes have been used to differentiate normal from neoplastic tissue in various animal tumor models (12)(13)(14)(15) and in human biopsy head and neck samples (16,17).…”

“…pH low insertion peptides (pHLIPs) are a class of membrane-binding peptides that specifically target acidic cells in vitro and in vivo (11) by inserting across cellular membranes when the extracellular pH is low (12). pHLIPs conjugated with fluorescent dyes have been used to differentiate normal from neoplastic tissue in various animal tumor models (12)(13)(14)(15) and in human biopsy head and neck samples (16,17). This report uses an indocyanine green (ICG) pHLIP conjugate for the diagnosis of urothelial carcinoma and precancerous lesions in fresh human radical cystectomy samples ex vivo and points the way toward a wide range of diagnostic and therapeutic alternatives.…”

An in vitro study on the detection of ovarian cancer using a novel pH-specific targeting polypyrrole nanocontrasting agent.

“…To exploit the acidic extracellular pH as a targeting strategy for our polypyrrole nanocontrasting agent, we utilized a V7 pHLIP (pH Low Insertion Peptide), which changes conformation in response to its environment. In neutral pHe (7.2-7.4), it maintains a globular form and transforms to a transmembrane alpha-helix at acidic pHe conditions (6.4-6.8), this then allows the conjugated particle to insert and anchor into tumor cells [31][32][33].…”