Targeted nanomedicine for reprogramming the tumor innate immune system: From bench to bedside.

Tumor-associated innate immune cells such as tumor-associated macrophages, neutrophils, dendritic cells play a crucial role in tumor progression, angiogenesis and metastasis. These cells also control the efficacy of chemotherapy and immunotherapy by inducing drug resistance and immunosuppression, leading to therapeutic failures. Therefore, targeting the tumor-associated innate immune cells has gained high attention for the development of effective cancer therapy. Nanomedicine based strategies to target these cells are highly relevant and can be used to reprogram these cells. In this review, we discuss the fundamental roles of the tumor-associated innate immune cells in the tumor microenvironment and different strategies to modulate them. Then, nanomedicine-based strategies to target different tumor innate immune cells are explained in detail. While the clinical development of the targeted nanomedicine remains a great challenge in practice, we have provided our perspectives on various factors such as pharmaceutical aspects, preclinical testing and biological aspects which are crucial to consider before translating these targeting strategies to clinics.

Evaluation of paclitaxel-loaded polymeric nanoparticles in 3D tumor model: impact of tumor stroma on penetration and efficacy.

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.

Repositioning the antihistamine ebastine as an intracellular siRNA delivery enhancer.

Small interfering RNAs (siRNAs) are promising therapeutics for the treatment of human diseases via the induction of sequence-specific gene silencing. To be functional, siRNAs require cytosolic delivery into target cells. However, state-of-the-art delivery systems mediate cellular entry through endocytosis and suffer from ineffective endosomal escape, routing a substantial fraction of the siRNA towards the lysosomal compartment. Cationic amphiphilic drugs (CADs) have been described to improve cytosolic siRNA delivery by the transient induction of lysosomal membrane permeabilization. In this work, we evaluated ebastine, an antihistamine CAD, for its ability to enhance cytosolic release of siRNA in a non-small cell lung cancer model. In particular, we demonstrated that ebastine can improve the siRNA-mediated gene silencing efficiency of a polymeric nanogel by 40-fold, outperforming other CAD compounds. Additionally, ebastine substantially enhanced gene knockdown of a cholesterol-conjugated siRNA, in two-dimensional (2D) cell culture as well as in three-dimensional (3D) tumor spheroids. Finally, ebastine could strongly promote siRNA delivery of lipid nanoparticles (LNPs) composed of a pH-dependent switchable ionizable lipid and with stable PEGylation, in contrast to state-of-the-art LNP formulations. Altogether, we identified ebastine as a potent and versatile siRNA delivery enhancer in cancer cells, which offers opportunities for drug combination therapy in oncology.

Cancer immune therapy using engineered ?tail-flipping' nanoliposomes targeting alternatively activated macrophages.

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.

Novel 3D µtissues Mimicking the Fibrotic Stroma in Pancreatic Cancer to Study Cellular Interactions and Stroma-Modulating Therapeutics.

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.