Alternatively-activated, M2-like tumor-associated macrophages (TAM) strongly contribute to tumor growth, invasiveness and metastasis. Technologies to disable the pro-tumorigenic function of these TAMs are of high interest to immunotherapy research. Here we show that by designing engineered nanoliposomes bio-mimicking peroxidated phospholipids that are recognised and internalised by scavenger receptors, TAMs can be targeted. Incorporation of phospholipids possessing a terminal carboxylate group at the sn-2 position into nanoliposome bilayers drives their uptake by M2 macrophages with high specificity. Molecular dynamics simulation of the lipid bilayer predicts flipping of the sn-2 tail towards the aqueous phase, while molecular docking data indicates interaction of the tail with Scavenger Receptor Class B type 1 (SR-B1). In vivo, the engineered nanoliposomes are distributed specifically to M2-like macrophages and, upon delivery of the STAT6 inhibitor (AS1517499), zoledronic acid or muramyl tripeptide, these cells promote reduction of the premetastatic niche and/or tumor growth. Altogether, we demonstrate the efficiency and versatility of our engineered “tail-flipping” nanoliposomes in a pre-clinical model, which paves the way to their development as cancer immunotherapeutics in humans.

Since tumor stroma poses as a barrier to achieve efficacy of nanomedicines, it is essential to evaluate nano-chemotherapeutics in stroma-mimicking 3D models that reliably predict their behavior regarding these hurdles limiting efficacy. In this study, we evaluated the effect of paclitaxel-loaded polymeric micelles (PTX-PMCs) and polymeric nanoparticles (PTX-PNPs) in a tumor stroma–mimicking 3D in vitro model. PTX-PMCs (77 nm) based on a amphiphilic block copolymer of mPEG-b-p(HPMAm-Bz) and PTX-PNPs (159 nm) based on poly(lactic-co-glycolic acid) were prepared, which had an encapsulation efficiency (EE%) of 81 ± 15% and 45 ± 8%, respectively. 3D homospheroids of mouse 4T1 breast cancer cells and heterospheroids of NIH3T3 fibroblasts and 4T1 (5:1 ratio) were prepared and characterized with high content two-photon microscopy and immunostaining. Data showed an induction of epithelial-mesenchymal transition (α-SMA) in both homo- and heterospheroids, while ECM (collagen) deposition only in heterospheroids. Two-photon imaging revealed that both fluorescently labeled PMCs and PNPs penetrated into the core of homospheroids and only PMCs penetrated into heterospheroids. Furthermore, PTX-PMCs, PTX-PNPs, and free PTX induced cytotoxicity in tumor cells and fibroblasts grown as monolayer, but these effects were substantially reduced in 3D models, in particular in heterospheroids. Gene expression analysis showed that heterospheroids had a significant increase of drug resistance markers (Bcl2, Abgc2) compared to 2D or 3D monocultures. Altogether, this study shows that the efficacy of nanotherapeutics is challenged by stroma-induced poor penetration and development of resistant phenotype. Therefore, this tumor stroma–mimicking 3D model can provide an excellent platform to study penetration and effects of nanotherapeutics before in vivo studies. Graphical Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive tumor type with low patient survival due to the low efficacy of current treatment options. Cancer-associated fibroblasts (CAFs) in the tumor microenvironment (TME) create a dense fibrotic environment around the tumor cells, preventing therapies from reaching their target. Novel 3D in vitro models are needed that mimic this fibrotic barrier for the development of therapies in a biologically relevant environment. Here, novel PDAC microtissues (µtissues) consisting of pancreatic cancer cell core surrounded by a CAF-laden collagen gel are presented, that is based on the cells own contractility to form a hard-to-penetrate barrier. The contraction of CAFs is demonstrated facilitating the embedding of tumor cells in the center of the µtissue as observed in patients. The µtissues displayed a PDAC-relevant gene expression by comparing their gene profile with transcriptomic patient data. Furthermore, the CAF-dependent proliferation of cancer cells is presented, as well as the suitability of the µtissues to serve as a platform for the screening of CAF-modulating therapies in combination with other (nano)therapies. It is envisioned that these PDAC µtissues can serve as a high-throughput platform for studying cellular interactions in PDAC and for evaluating different treatment strategies in the future.

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