Measuring Tumor Aggressiveness and Targeting Metastatic Lesions with Fluorescent pHLIP

Abstract

Purpose Malignant cancer foci develop acidic extracellular environments. Mild acidic conditions trigger insertion and folding of the pH (low) insertion peptide (pHLIP™) across a cellular membrane, enabling targeting of such lesions. Procedures We employed optical imaging to follow targeting by fluorescent pHLIP given i.v. in mice. For visualization, Cy5.5 and Alexa750 were covalently attached to the N terminus of pHLIP, which stays outside of a cell membrane after transmembrane insertion. Results We demonstrate that pHLIP targets: (a) tumors of different origins established by subcutaneous injection of cancer cells, (b) spontaneous prostate tumors in TRAMP mice and (c) metastatic lesions in lung. pHLIP accumulation in tumors correlates with tumor aggressiveness. Within a tumor, it stains extracellular spaces and cellular membranes. Conclusions Tissue acidity can be detected by pHLIP peptide insertion and used to diagnose primary tumors, metastatic lesions, and lipid bodies in necrotic tissues. The ability of pHLIP to differentially bind metastatic and non-metastatic tumors may provide a new approach for evaluating cancer prognosis.

Extracellular acidity strengthens mesenchymal stem cells to promote melanoma progression

“…Now, pH-sensitive PET radiotracers may be used for in vivo measurement of tumor pH, a water-soluble membrane peptide that inserts and folds across a cellular membrane lipid bilayer in response to low pH has been synthetized and used to detect tissue acidity and to diagnose primary tumors and metastatic lesions. 19 Because melanoma represents one of the most aggressive human cancer able to metastasize to multiple sites, and, as most solid tumors, shows extracellular acidosis, we decided to elucidate whether acidity affects cross-talk between MSC and melanoma cells, also to disclose new evil liaisons promoting melanoma progression and, possibly, to offer new strategies for therapy. We found that melanoma cells injected into immunodeficient mice together with MSC exposed to a low pH (pH 6.7) medium generate tumors with a higher growth rate than melanoma cells injected alone or together with MSC grown in standard pH medium.…”

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

“…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.…”

pH-controlled delivery of luminescent europium coated nanoparticles into platelets

“…The pHLIP mechanism of action has been determined in liposomes (17) and has been used in cells for the delivery of fluorescent molecules (18). Furthermore, there is significant interest in this peptide as a probe or drug delivery system for cancerous cells and in inflammatory arthritis because of the low extracellular pH associated with these regions (18)(19)(20)(21)(22).…”