Peptide-guided targeting of GPR55 for new therapeutic strategies of cancer

Objectives G-protein-coupled receptors (GPCRs) are 'druggable' targets in cancer treatment. GPR55 was recently identified as the lysophosphatidylinositol receptor, and its expression correlates with the invasive potential of metastatic cells and bone metastasis formation1. This study aims to interfere the GPR55 function in cancer cells with peptidic binders. Methods Whole-cell-based screening of M13-phage-displayed random library2 was performed using as bait the GPR55 receptor heterologously expressed in HEK293 cells. The 7-mer insert peptides in M13-phage library were flanked by a pair of cysteine residues resulting in cyclized peptides. Binding specificity to GPR55-positive cells was verified using synthetic FITC-labelled peptides by FACS and confocal microscopy. The effect of peptide binding to GPR55 was analysed in lysphosphatidyinositol-triggered GPR55 signalling, including intracellular calcium, AKT phosphorylation, modulation of actin cytoskeleton, and receptor internalization. Anticipated data By screening M13-phage-displayed random library, we selected a peptide that binds specifically to HeLa cells expressing GPR55 and not to cells interfered for GPR55. Binding specificity of the FITC-labelled peptide was further investigated in competition assays with unlabelled peptide, and confirmed using scramble analogues. The identified peptide did not affect significantly GPR55 signalling; however, it showed a significant modulation of both basal and agonist-induced GPR55 internalization. This analysis has been extended to lymphoblastoid leukemic cells. We propose the use of GPR55-peptidic binders for in-vivo diagnosis of GPR55-positive tumor cells, specific delivery of chemotherapeutic agents to cancer cells, and direct modulation of receptor activities for therapeutic applications. 1- Ross RA (2011) Trends Pharmacol Sci 32:265-9. 2- Palmieri C et al. (2010) Blood 116:226-38.