Targeting the Tumor Microenvironment with Fluorescence-Activatable Bispecific Endoglin/Fibroblast Activation Protein Targeting Liposomes.

Felista L Tansi,Ronny Rüger,Markus Rabenhold,Frank Steiniger,Alfred Fahr,Roland E Kontermann,Ingrid Hilger,Ulf K Teichgräber,Ansgar M Kollmeier

doi:10.3390/pharmaceutics12040370

Abstract

Liposomes are biocompatible nanocarriers with promising features for targeted delivery of contrast agents and drugs into the tumor microenvironment, for imaging and therapy purposes. Liposome-based simultaneous targeting of tumor associated fibroblast and the vasculature is promising, but the heterogeneity of tumors entails a thorough validation of suitable markers for targeted delivery. Thus, we elucidated the potential of bispecific liposomes targeting the fibroblast activation protein (FAP) on tumor stromal fibroblasts, together with endoglin which is overexpressed on tumor neovascular cells and some neoplastic cells. Fluorescence-quenched liposomes were prepared by hydrating a lipid film with a high concentration of the self-quenching near-infrared fluorescent dye, DY-676-COOH, to enable fluorescence detection exclusively upon liposomal degradation and subsequent activation. A non-quenched green fluorescent phospholipid was embedded in the liposomal surface to fluorescence-track intact liposomes. FAP- and murine endoglin-specific single chain antibody fragments were coupled to the liposomal surface, and the liposomal potentials validated in tumor cells and mice models. The bispecific liposomes revealed strong fluorescence quenching, activatability, and selectivity for target cells and delivered the encapsulated dye selectively into tumor vessels and tumor associated fibroblasts in xenografted mice models and enabled their fluorescence imaging. Furthermore, detection of swollen lymph nodes during intra-operative simulations was possible. Thus, the bispecific liposomes have potentials for targeted delivery into the tumor microenvironment and for image-guided surgery.

Highlights

Liposomes are highly biocompatible organic nanovesicles with a high drug payload capacity [1] and flexibility for modifications, whereby different substances including genes, proteins, therapeutic drugs and contrast agents are encapsulated in the aqueous interior or embedded in the lipid bilayer [1,2,3]
We elucidated the potential of bispecific liposomes targeting the fibroblast activation protein (FAP) on tumor stromal fibroblasts, together with endoglin which is overexpressed on tumor neovascular cells and some neoplastic cells
Considering the beneficial features of FAP and endoglin as target markers and previous works where we demonstrated tumor imaging based on the use of activatable mono-specific liposomes, we sought to elucidate the feasibility of targeting FAP and endoglin simultaneously, with activatable bispecific liposomes

Summary

Introduction

Liposomes are highly biocompatible organic nanovesicles with a high drug payload capacity [1] and flexibility for modifications, whereby different substances including genes, proteins, therapeutic drugs and contrast agents are encapsulated in the aqueous interior or embedded in the lipid bilayer [1,2,3]. The clinical use of non-targeted PEGylated liposomes for the delivery of chemotherapeutics [4] greatly relies on the enhanced permeability and retention (EPR)-effect and the level of phagocytic tumor associated macrophages (TAMs) available in the tumor stroma [5]. This passive liposomal delivery has greatly increased the efficacy of tumor treatment as compared to the free chemotherapeutic drugs, they still have limitations. We hypothesized that endowing liposomes with ligands that are selective for more universal tumor markers found in a diverse spectrum of tumor types could be beneficial for many patients

Methods

Results

Conclusion