Synthesis of Passerini-3CR Polymers and Assembly into Cytocompatible Polymersomes.

The versatility of the Passerini three component reaction (Passerini-3CR) is herein exploited for the synthesis of an amphiphilic diblock copolymer, which self-assembles into polymersomes. Carboxy-functionalized poly(ethylene glycol) methyl ether is reacted with AB-type bifunctional monomers and tert-butyl isocyanide in a single process via Passerini-3CR. The resultant diblock copolymer (P1) is obtained in good yield and molar mass dispersity and is well tolerated in model cell lines. The Passerini-3CR versatility and reproducibility are shown by the synthesis of P2, P3, and P4 copolymers. The ability of the Passerini P1 polymersomes to incorporate hydrophilic molecules is verified by loading doxorubicin hydrochloride in P1DOX polymersomes. The flexibility of the synthesis is further demonstrated by simple post-functionalization with a dye, Cyanine-5 (Cy5). The obtained P1-Cy5 polymersomes rapidly internalize in 2D cell monolayers and penetrate deep into 3D spheroids of MDA-MB-231 triple-negative breast cancer cells. P1-Cy5 polymersomes injected systemically in healthy mice are well tolerated and no visible adverse effects are seen under the conditions tested. These data demonstrate that new, biodegradable, biocompatible polymersomes having properties suitable for future use in drug delivery can be easily synthesized by the Passerini-3CR.

Free drug and ROS-responsive nanoparticle delivery of synergistic doxorubicin and olaparib combinations to triple negative breast cancer models.

Combinations of the topoisomerase II inhibitor doxorubicin and the poly (ADP-ribose) polymerase inhibitor olaparib offer potential drug-drug synergy for the treatment of triple negative breast cancers (TNBC). In this study we performed in vitro screening of combinations of these drugs, administered directly or encapsulated within polymer nanoparticles, in both 2D and in 3D spheroid models of breast cancer. A variety of assays were used to evaluate drug potency, and calculations of combination index (CI) values indicated that synergistic effects of drug combinations occurred in a molar-ratio dependent manner. It is suggested that the mechanisms of synergy were related to enhancement of DNA damage as shown by the level of double-strand DNA breaks, and mechanisms of antagonism associated with mitochondrial mediated cell survival, as indicated by reactive oxygen species (ROS) generation. Enhanced drug delivery and potency was observed with nanoparticle formulations, with a greater extent of doxorubicin localised to cell nuclei as evidenced by microscopy, and higher cytotoxicity at the same time points compared to free drugs. Together, the work presented identifies specific combinations of doxorubicin and olaparib which were most effective in a panel of TNBC cell lines, explores the mechanisms by which these combined agents might act, and shows that formulation of these drug combinations into polymeric nanoparticles at specific ratios conserves synergistic action and enhanced potency in vitro compared to the free drugs.

Passerini chemistries for synthesis of polymer pro-drug and polymersome drug delivery nanoparticles.

New materials chemistries are urgently needed to overcome the limitations of existing biomedical materials in terms of preparation, functionality and versatility, and also in regards to their compatibility with biological environments. Here, we show that Passerini reactions are especially suited for the preparation of drug delivery materials, as with relatively few steps, polymers can be synthesized with functionality installed enabling drug conjugation and encapsulation, self-assembly into micellar or vesicular architectures, and with facile attachment triggerable chemistries. The polymers can be made with a variety of building blocks and assemble into nanoparticles, which are rapidly internalized in triple negative breast cancer (TNBC) cells. In addition, the polymers transport drug molecules efficiently through 3D cell cultures, and when designed with chemistries allowing pH-mediated release, exhibit greater efficacy against TNBC cells compared to the parent drug.

Reduction-responsive polymers for drug delivery in cancer therapy-Is there anything new to discover?

Among various types of stimuli-responsive drug delivery systems, reduction-responsive polymers have attracted great interest. In general, these systems have high stability in systemic circulation, however, they can respond quickly to differences in the concentrations of reducing species in specific physiological sites associated with a pathology. This is a particularly relevant strategy to target diseases in which hypoxic regions are present, as polymers which are sensitive to in-situ expressed antioxidant species can, through a local response, release a therapeutic at high concentration in the targeted site, and thus, improve the selectivity and efficacy of the treatment. At the same time, such reduction-responsive materials can also decrease the toxicity and side effects of certain drugs. To date, polymers containing disulfide linkages are the most investigated of the class of reduction-responsive nanocarriers, however, other groups such as selenide and diselenide have also been used for the same purpose. In this review article, we discussed the rationale behind the development of reduction-responsive polymers as drug delivery systems and highlight examples of recent progress. We include the most popular design methods to generate reduction-responsive polymeric carriers and their applications in cancer therapy, and question what areas may still need to be explored in a field with already a very large number of research articles. Finally, we consider the main challenges associated with the clinical translation of these nanocarriers and the future perspectives in this area. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Multi-component bioresponsive nanoparticles for synchronous delivery of docetaxel and TUBB3 siRNA to lung cancer cells.

Bioresponsive nanoparticles (NPs) are of interest for anticancer nanomedicines, owing to the possibility to 'design in' selective modulation of drug release at target sites. Here we describe the double emulsion formulation of redox-responsive NPs based on modified polyethylene glycol (PEG)-co-poly(lactic-co-glycolic acid) (PLGA) block copolymers and oligo (ß-aminoesters) (OBAE), both of which contained disulfide linkages, for the co-delivery of a cytotoxic small molecule drug and a nucleic acid. In particular, we focused our attention on docetaxel (DTX) and a siRNA against TUBB3, a gene that encodes for ßIII-tubulin, in order to have a synergistic effect in the treatment of lung cancer. Spherical NPs of around 150 nm with negative zeta potential and high loading efficiencies of both drugs were obtained. Stability and release studies showed "on demand" drug release under reducing conditions. Unloaded NPs containing PEG-disulfide-PLGA and OBAE were well-tolerated by lung cancer cells, thus masking the intrinsic cytotoxicity of OBAE, while for intracellular siRNA delivery, redox responsive NPs demonstrated a higher cell internalization with a preferential cytoplasmic accumulation of siRNA, with a subsequent fast gene-silencing efficiency. The viability of cells treated with combined DTX/TUBB3-siRNA NPs significantly decreased as compared to NPs loaded only with DTX, thus showing an efficient combined anticancer effect, due to a substantial reduction of ß-tubulin expression. Finally, in an in vivo feasibility study employing an orthotopic lung cancer model, NPs formulated with an anti-luciferase siRNA distributed throughout the lungs following oro-tracheal administration, and demonstrated effective gene knockdown and no apparent cytotoxicity. Taken together, these results show that the double emulsion formulated redox responsive PEG-PLGA and OBAE systems represent a promising new therapeutic approach for the local combined chemo- and gene-therapy of lung cancer.

Fluorophore Selection and Incorporation Contribute to Permeation and Distribution Behaviors of Hyperbranched Polymers in Multi-Cellular Tumor Spheroids and Xenograft Tumor Models.

Improving our understanding of how design choices in materials synthesis impact biological outcomes is of critical importance in the development of nanomedicines. Here, we show that fluorophore labeling of polymer nanomedicine candidates significantly alters their transport and cell association in multi-cellular tumor spheroids and their penetration in breast cancer xenografts, dependent on the type of the fluorophore and their positioning within the macromolecular structure. These data show the critical importance of the biomaterials structure and architecture in their tissue distribution and intracellular trafficking, which in turn govern their potential therapeutic efficacy. The broader implication of these findings suggests that when developing materials for medical applications, great care should be taken early on in the design process as relatively simple choices may have downstream impacts that could potentially skew preclinical biology data.

Effects of Polymer 3D Architecture, Size, and Chemistry on Biological Transport and Drug Delivery In Vitro and in Orthotopic Triple Negative Breast Cancer Models.

The size, shape, and underlying chemistries of drug delivery particles are key parameters which govern their ultimate performance in vivo. Responsive particles are desirable for triggered drug delivery, achievable through architecture change and biodegradation to control in vivo fate. Here, polymeric materials are synthesized with linear, hyperbranched, star, and micellar-like architectures based on 2-hydroxypropyl methacrylamide (HPMA), and the effects of 3D architecture and redox-responsive biodegradation on biological transport are investigated. Variations in "stealth" behavior between the materials are quantified in vitro and in vivo, whereby reduction-responsive hyperbranched polymers most successfully avoid accumulation within the liver, and none of the materials target the spleen or lungs. Functionalization of selected architectures with doxorubicin (DOX) demonstrates enhanced efficacy over the free drug in 2D and 3D in vitro models, and enhanced efficacy in vivo in a highly aggressive orthotopic breast cancer model when dosed over schedules accounting for the biodistribution of the carriers. These data show it is possible to direct materials of the same chemistries into different cellular and physiological regions via modulation of their 3D architectures, and thus the work overall provides valuable new insight into how nanoparticle architecture and programmed degradation can be tailored to elicit specific biological responses for drug delivery.

Synthesis of micellar-like terpolymer nanoparticles with reductively-cleavable cross-links and evaluation of efficacy in 2D and 3D models of triple negative breast cancer.

Triple negative or basal-like breast cancer (TNBC) is characterised by aggressive progression, lack of standard therapies and poorer overall survival rates for patients. The bad prognosis, high rate of relapse and resistance against anticancer drugs have been associated with a highly abnormal loss of redox control in TNBC cells. Here, we developed docetaxel (DTX)-loaded micellar-like nanoparticles (MLNPs), designed to address the aberrant TNBC biology through the placement of redox responsive cross-links designed into a terpolymer. The MLNPs were derived from poly(ethyleneglycol)-b-poly(lactide)-co-poly(N3-α-ε-caprolactone) with a disulfide linker pendant from the caprolactone regions in order to cross-link adjacent chains. The terpolymer contained both polylactide and polycaprolactone to provide a balance of accessibility to reductive agents necessary to ensure stability in transit, but rapid micellar breakdown and concomitant drug release, when in breast cancer cells with increased levels of reducing agents. The empty MLNPs did not show any cytotoxicity in vitro in 2D monolayers of MDA-MB-231 (triple negative breast cancer), MCF7 (breast cancer) and MCF10A (normal breast epithelial cell line), whereas DTX-loaded reducible crosslinked MLNPs exhibited higher cytotoxicity against TNBC and breast cancer cells which present high intracellular levels of glutathione. Crosslinked and non-crosslinked MLNPs showed high and concentration-dependent cellular uptake in monolayers and tumour spheroids, including when assessed in co-cultures of TNBC cells and cancer-associated fibroblasts. DTX loaded crosslinked MLNPs showed the highest efficacy against 3D spheroids of TNBC, in addition the MLNPs also induced higher levels of apoptosis, as assessed by annexin V/PI assays and increased caspase 3/7 activity in MDA-MB-231 cells in comparison to cells treated with DTX-loaded un-crosslinked MLNP (used as a control) and free DTX. Taken together these data demonstrate that the terpolymer micellar-like nanoparticles with reducible crosslinks have high efficacy in both 2D and 3D in vitro cancer models by targeting the aberrant biology, i.e. loss of redox control of this type of tumour, thus may be promising and effective carrier systems for future clinical applications in TNBC.

Dual bioresponsive antibiotic and quorum sensing inhibitor combination nanoparticles for treatment of Pseudomonas aeruginosa biofilms in vitro and ex vivo.

Many debilitating infections result from persistent microbial biofilms that do not respond to conventional antibiotic regimens. A potential method to treat such chronic infections is to combine agents which interfere with bacterial biofilm development together with an antibiotic in a single formulation. Here, we explore the use of a new bioresponsive polymer formulation derived from specifically modified alginate nanoparticles (NPs) in order to deliver ciprofloxacin (CIP) in combination with the quorum sensing inhibitor (QSI) 3-amino-7-chloro-2-nonylquinazolin-4(3H)-one (ACNQ) to mature Pseudomonas aeruginosa biofilms. The alginate NPs were engineered to incorporate a pH-responsive linker between the polysaccharide backbone and the QSI, and to encapsulate CIP via charge-charge interactions of the positively-charged drug with the carboxyl residues of the alginate matrix. In this way, a dual-action release of antibiotic and QSI was designed for the low-pH regions of a biofilm, involving cleavage of the QSI-linker to the alginate matrix and reduced charge-charge interactions between CIP and the polysaccharide as the alginate carboxyl side-chains protonated. When tested in a biofilm model the concomitant release of CIP + QSI from the pH-responsive nanoparticles significantly reduced the viability of the biofilm compared with CIP treatment alone. In addition, the alginate NPs were shown to penetrate deeply into P. aeruginosa biofilms, which we attribute in part to the charges of the NPs and the release of the QSI agent. Finally, we tested the formulation in both a 2D keratinocyte and a 3D ex vivo skin infection model. The dual-action bio-responsive QSI and CIP release nanoparticles effectively cleared the infection in the latter, suggesting considerable promise for combination therapeutics which prevent biofilm formation as well as effectively killing mature P. aeruginosa biofilms.

Bioreducible cross-linked core polymer micelles enhance in vitro activity of methotrexate in breast cancer cells.

Polymer micelles have emerged as promising carriers for controlled release applications, however, several limitations of micelle-based drug delivery have also been reported. To address these issues, we have synthesized a functional biodegradable and cytocompatible block copolymer based on methoxypoly(ethyleneglycol)-b-poly(ε-caprolactone-co-α-azido-ε-caprolactone) (mPEG-b-poly(εCL-co-αN3εCL)) as a precursor of reduction sensitive core-crosslinked micelles. The synthesized polymer was formulated as micelles using a dialysis method and loaded with the anti-inflammatory and anti-cancer drug methotrexate (MTX). The micellar cores were subsequently crosslinked at their pendent azides by a redox-responsive bis(alkyne). The size distributions and morphology of the polymer micelles were assessed using dynamic light scattering (DLS) and transmission electron microscopy, and drug release assays were performed under simplified (serum free) physiological and reductive conditions. Cellular uptake studies in human breast cancer cells were performed using Oregon-green loaded core-crosslinked micelles. The MTX-loaded core-crosslinked micelles were assessed for their effects on metabolic activity in human breast cancer (MCF-7) cells by evaluating the reduction of the dye MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. The apoptosis inducing potential of MTX-loaded core-crosslinked micelles was analysed using Hoechst/propidium iodide (PI) and annexin-V/PI assays. The data from these experiments indicated that drug release from these cross-linked micelles can be controlled and that the redox-responsive micelles are more effective carriers for MTX than non-crosslinked analogues and the free drug in the cell-lines tested.