Efficacy and Selectivity of FGF2-Saporin Cytosolically Delivered by PCI in Cells Overexpressing FGFR1.

Aurora K Vikan,Pål K Selbo,Michal Kostas,Jørgen Wesche,Ellen Margrethe Haugsten

doi:10.3390/cells10061476

Aurora K Vikan, Pål K Selbo + Show 3 more

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https://doi.org/10.3390/cells10061476

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Abstract

Fibroblast growth factor receptors (FGFRs) have become an attractive target in cancer research and therapy due to their implication in several cancers. Limitations of current treatment options require a need for additional, more specific and potent strategies to overcome cancers driven by FGFRs. Photochemical internalization (PCI) is a light-controlled method for cytosolic delivery of drugs that are entrapped in endosomes and lysosomes. We here evaluated the efficacy and selectivity of PCI of FGF2-saporin (FGF-SAP) in cells overexpressing FGFR1. FGF-SAP is a conjugate of FGF2 and the highly cytotoxic ribosome-inactivating protein (RIP) saporin, which is used as payload to eliminate cancer cells. Evaluation of the targeting effect of PCI of FGF-SAP was done by comparing the cytotoxic response in osteosarcoma cells with very low levels of FGFR1 (U2OS) to cells overexpressing FGFR1 (U2OS-R1). We demonstrate that PCI greatly enhances cytotoxicity of the drug showing efficient cell killing at pM concentrations of the drug in U2OS-R1 cells. However, U2OS cells were also sensitive to the toxin after PCI. Binding experiments using confocal microscopy and Western blotting techniques indicate that FGF-SAP is taken up by cells through heparan sulfate proteoglycans (HSPGs) in U2OS cells. We further show that the cytotoxicity of FGF-SAP in U2OS cells was reduced when cells were co-treated with heparin to compete out binding to HSPG, demonstrating that the cytotoxic effect was due to internalization by HSPGs. We conclude that to prevent off-target effects of FGF-based toxins, it will be necessary to circumvent binding to HSPGs, for example by mutating the binding site of FGF2 to HSPGs.

Highlights

Over a century ago Paul Ehrlich introduced the concept of “the magic bullet”
To investigate the specificity of Photochemical internalization (PCI) of FGF-SAP towards cells overexpressing Fibroblast growth factor receptors (FGFRs), we chose to use a cellular model system consisting of cells stably expressing FGFR1 (U2OSR1) and compare the efficiency in these cells to the parental cell line (U2OS) with very low of all FGFRs (FGFR1-4) [38]
We evaluated PCI of FGF-SAP as a strategy to target and achieve cytotoxic effects aimed at cancer cells overexpressing FGFRs

Summary

Introduction

Over a century ago Paul Ehrlich introduced the concept of “the magic bullet”. The idea was to develop a drug that would precisely target disease-causing agents [1]. Much effort has been done to develop drugs that target cancer cells. Treatment is often impaired by nonspecific drug distribution, lack of specificity to the target site, and acquired resistance [2,3]. Several strategies can be employed for targeted drug delivery. One such strategy is to exploit the expression of specific receptors on the surface of cancer cells. Discrimination between healthy and cancerous tissue is possible by applying a targeting ligand that binds efficiently to these surface markers [3]. By coupling a ligand to a toxic moiety, receptor–ligand interaction triggering endocytosis can deliver a drug to the target site [3,4]. Among the very few antibody–drug conjugates (ADCs) that have been approved by the U.S Food and Drug Administration (FDA) are, for example, brentuximab vedotin (AdcetrisTM) for treatment of relapsed Hodkin’s lymphoma and systemic anaplastic large cell lymphoma [5], and ado-trastuzumab ematisine (KadcylaTM)

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