Peptide-guided targeting of GPR55 for anti-cancer therapy

// Maria Mangini 1, * , Enrico Iaccino 2, * , Maria Giovanna Mosca 1 , Selena Mimmi 2 , Rosa D’Angelo 1 , Ileana Quinto 2 , Giuseppe Scala 2 , Stefania Mariggio 1 1 Institute of Protein Biochemistry, National Research Council, Naples, Italy 2 Department of Experimental and Clinical Medicine, University ‘Magna Graecia’ of Catanzaro, Viale Europa, Localita Germaneto, 88100 Catanzaro, Italy * These authors have contributed equally to this work Correspondence to: Stefania Mariggio, email: s.mariggio@ibp.cnr.it Ileana Quinto, email: quinto@unicz.it Keywords: G-protein-coupled receptor (GPCR), GPR55, lysophosphatidylinositol (LPI), peptidic binder, phage-display screening Received: April 19, 2016 Accepted: November 21, 2016 Published: December 23, 2016 ABSTRACT Expression of the lysophosphatidylinositol receptor GPR55 correlates with invasive potential of metastatic cells and bone metastasis formation of different types of tumors. These findings suggest a role for GPR55 signaling in cancer progression, including in lymphoproliferative diseases. Here, we screened a M13-phage-displayed random library using the bait of HEK293 cells that heterologously expressed full-length HA-GPR55. We selected a set of phagotopes that carried 7-mer insert peptides flanked by a pair of cysteine residues, which resulted in cyclized peptides. Sequencing of selected phagotopes dictated the primary structure for the synthetic FITC-labeled peptide P1, which was analyzed for binding specificity to immunoprecipitated HA-GPR55, and to endogenously expressed GPR55, using cells interfered or not for GPR55, as well as for co-localization imaging with HA-GPR55 at the membrane level. The peptide P1 stimulated GPR55 endocytosis and inhibited GPR55-dependent proliferation of EHEB and DeFew cells, two human B-lymphoblastoid cell lines. Our data support the potential therapeutic application of peptide ligands of GPR55 for targeting and inhibiting growth of neoplastic cells, which overexpress GPR55 and are dependent on GPR55 signaling for their proliferation.