Zwitterionic polymeric micelles that undergo a pH-triggered positive charge for enhanced cellular uptake

Inducing pH control over the critical micelle concentration of zwitterionic surfactants via polyacids adsorption: Effect of chain length and structure

HYPOTHESIS

The critical concentration above which micelles form from zwitterionic surfactant solutions and their thermodynamic stability is affected by the interaction with weak Brønsted polyacid chains (A_n) via the formation of charged hydrogen bonds between the latter and anionic moieties.

EXPERIMENTS

The interaction between zwitterionic micelles and polyacids capable of forming hydrogen bonds, and its dependence on the environmental pH and polymer structure, has been studied with constant-pH simulations and a restricted primitive model for all electrolytes.

FINDINGS

At low pH, the formation of polyacid/micelle complexes is witnessed independently of the polymer size or structure, so that the concentration above which micelles form is substantially decreased compared to polyacid-free cases. Upon rising pH, polymer desorption takes place within a narrow range of pH values, its location markedly depending on the size and structure of polyacids, and on the relative disposition between headgroup charged moieties. Thus, the desorption onset for long linear polyacids (A₆₀) interacting with sulphobetainic headgroups is roughly two pH units higher than for six decameric chains (6A₁₀) adsorbed onto micelles bearing phosphorylcholinic headgroups. This effect, together with the preferential desorption of chain ends at intermediate pH, may be exploited for drug delivery purposes or building advanced metamaterials.

Hypoxia-responsive pullulan-based nanoparticles as erlotinib carriers

A hypoxia-responsive pullulan-based co-polymer was developed to assess its efficacy to deliver erlotinib (ERL) to the cervical cancer cells. Upon exposure to hypoxic condition, the synthesized and structurally characterized co-polymer i.e. succinyl pullulan-g-6-(2-nitroimidazole) hexylamine (Pull-SA-HA-NI) exhibited a hypochromic shift in the UV spectra and alteration in its self-assembled structures as compared to the control co-polymer, succinyl pullulan-g-hexylamine (Pull-SA-HA). Its corresponding ERL-loaded nanoparticles (NPs) displayed an attenuated crystallinity of pure ERL with excellent drug-trapping capacity (DEE, 94.23 ± 1.36%) and acceptable zeta potential (+39.21 ± 1.09 mV) and diameter (84.10 ± 2.10 nm) values. These also evidenced a faster drug release profile under hypoxic condition relative to the normoxic condition. The cellular internalization of the NPs was mediated through the energy-dependent endocytic process, which could utilize its multiple pathways (i.e., macropinocytosis, clathrin- and caveolae-mediated endocytosis). The ERL-loaded NPs suppressed HeLa cell proliferation and induced apoptosis more efficiently than the pristine drug.

Peptide dendrimers as potentiators of conventional chemotherapy in the treatment of pancreatic cancer in a mouse model

Chemotherapy is the recommended treatment for patients with advanced pancreatic ductal adenocarcinoma (PDAC). However, efficacy of traditional chemotherapy is not satisfactory due to the presence of a dense dysplastic tumor stroma which prevents drug accumulation in and deep penetration into tumors. To overcome these obstacles, we designed and synthesized peptide dendrimers as potentiators of conventional chemotherapy. The dendrimers markedly promoted free doxorubicin accumulation and penetration deeply into 3D multicellular PDAC tumor cultures upon co-incubation. Co-administration of the dendrimer and doxorubicin into PDAC tumor xenograft-bearing mice greatly increased the doxorubicin concentration in the tumor. In addition, the dendrimer also promoted free doxorubicin internalization into PDAC cells upon co-incubation in media mimicking tumor microenvironment. Finally, a significant enhancement in the anticancer efficacy of doxorubicin and gemcitabine when either of the drugs was individually co-administered with the dendrimer into PDAC tumor xenograft-bearing mice was observed. This was especially pronounced for the combination treatment with the dendrimer and gemcitabine, resulting in a tumor weight decrease to 12.9% compared to the treatment with gemcitabine alone. This can be attributed to the combination of the multi-functionalities of the dendrimer, i.e., promoting free drug accumulation and penetration deeply into tumors and internalization into cancer cells.

Etherified pullulan-polyethylenimine based nanoscaffolds improved chemosensitivity of erlotinib on hypoxic cancer cells

The current research endeavor aimed to accomplish hypoxia-responsive polyethyleneimine-conjugated carboxymethyl pullulan-based co-polymer (CMP-HA-NI-PEI-NBA) bearing nitroaromatic subunits to efficiently deliver erlotinib (ERL) to reverse its hypoxia-induced resistance in cancer cells. As compared to a control co-polymer (CMP-HA-MI-PEI-BA) devoid of hypoxia-sensitive moieties, this scaffold demonstrated a hypochromic shift in the UV spectra and rapid dismantling of its self-assembled architecture upon exposure to simulated hypoxic condition. The hypoxia-responsive co-polymer encapsulated ERL with desirable loading capacity (DEE, 63.05 ± 2.59%), causing attenuated drug crystallinity. The drug release rate of the scaffold under reducing condition was faster relative to that of non-reducing environment. Their cellular uptake occurred through an energy-dependent endocytic process, which could exploit its caveolae/lipid raft-mediated internalization pathway. The ERL-loaded scaffolds more efficiently induced apoptosis and suppressed the proliferation of drug-resistant hypoxic HeLa cells than the pristine ERL. Hence, this study presented a promising drug delivery nanoplatform to overcome hypoxia-evoked ERL resistance.

Doxorubicin-loaded natural daptomycin micelles with enhanced targeting and anti-tumor effect in vivo

Development of a simple method to enhance targeting and anti-tumor effect of the chemotherapeutic agents in vivo is a major problem. Amphipathic and natural daptomycin is biocompatible antibacterial polypeptide used in clinical practice. Herein, doxorubicin (DOX) was stabilized by zwitterionic daptomycin (Dap) micelles in aqueous solution to form a zwitterionic nanodrug (Dap-DOX micelles). The hydrodynamic size and zeta potential of Dap-DOX micelles were 85 nm and -10 mV, respectively. The study on the controlled release showed that more DOX molecules were released from Dap-DOX micelles at acidic condition of tumor tissue than that at neutral condition of normal tissue which was due to pH responsiveness of Dap-DOX micelles. Dap-DOX micelles exhibited good stability in fibrinogen solution. Moreover, MTT studies showed that Dap-DOX micelles had higher cytotoxicity than free DOX. Notably, the results of flow cytometry indicated that the average fluorescence intensity of Dap-DOX micelle-treated cells was higher than that of free DOX-treated cells, and acidic conditions were more favorable for Dap-DOX micelles than normal pH in cell uptake assay. More importantly, Dap-DOX micelles were biocompatible in vivo based on the changes of weight and blood indexes of mice. Dap-DOX micelles were selectively accumulated at tumor sites in vivo through EPR effect, which reduced the toxicity of free DOX and achieved excellent tumor inhibition effect. The tumor inhibition rate of Dap-DOX micelles reached 96%. Dap-DOX micelles also effectively inhibited the growth of bacterial. Taken together, Dap-based drug delivery systems are promising and effective in cancer therapy.

Co-administration of a branched arginine-rich polymer enhances the anti-cancer efficacy of doxorubicin

The severe side-effects and drug resistance development of conventional chemotherapy are mainly caused by poor tumor penetration as well as nonspecific biodistribution and insufficient cellular uptake of drugs. Herein a branched arginine-rich polymer was synthesized and co-administration of this polymer with doxorubicin, a model drug of chemotherapeutic agents, overcame simultaneously the three obstacles shown above. Co-incubation of the polymer promoted doxorubicin penetration deeply into multicellular tumor spheroids and internalization into cancer cells. Upon co-injection of the polymer with doxorubicin into tumor-bearing mice, the enhanced drug accumulation in and deep penetration into tumor tissue were observed compared to injection of doxorubicin alone. A combined therapy of doxorubicin and the polymer in the treatment of tumor-bearing mice showed a marked enhancement in anticancer efficacy compared to doxorubicin alone. Notably, the treatment with the combination regime reduced the doxorubicin dose to one fifth without reducing the antitumor efficacy compared to the treatment with doxorubicin alone. The possible mechanism of action of the polymer was postulated, in which the guanidinium groups of arginine residues in the polymer may play a pivotal role in the action.

On the distribution of hydrophilic polyelectrolytes and their counterions around zwitterionic micelles: the possible impact on the charge density in solution

Despite their charge neutrality, micelles composed of surfactants with zwitterionic headgroups selectively accumulate anions at their hydrophobic core/solution interphase due to electrostatic interactions if headgroup positive moieties are the innermost. This tendency may be markedly enhanced if polyions substitute simple ions. To investigate this possibility, solutions composed of zwitterionic micelles and hydrophilic polyanions have been investigated with Monte Carlo simulations representing the studied systems via primitive electrolyte models. Structural and energetic properties are obtained to highlight the impact of connecting simple ions into polyions on the interactions between electrolytes and micelles. Despite the latter, polyanions conserve their conformational properties. A marked increase in the concentration of charged species inside the micellar corona is, instead, found when polyions are present independently of their charge sign or the headgroup structure. Thus, polyelectrolytes act as "shuttle" for all charged species, with the potential of increasing reactions rates involving the latter due to mass effects. Besides, results for the polyions/micelles mixing free energy and Helmholtz energy profiles indicate that the critical micelle concentration is impacted minimally by hydrophilic polyelectrolytes, an outcome agreeing with experiments. This finding is entirely due to weak enthalpic effects while mixing hydrophilic polyions and micelles. A strong reduction in the screening of the micelle negative charge, acquired following the adsorption of anions in the corona and due to counterions layering just outside it (the so called "chameleon effect"), is forecasted when polyanions substitute monovalent anions.

Interface crosslinked mPEG-b-PAGE-b-PCL triblock copolymer micelles with high stability for anticancer drug delivery

The stability of polymeric micelles is a key property for anticancer drug delivery. In this study, a novel amphiphilic triblock copolymer, methoxy poly(ethylene glycol)-b-poly(allyl glycidyl ether)-b-poly(ε-caprolactone) (mPEG-b-PAGE-b-PCL), with different hydrophobic lengths was designed and synthesized using the combination of two successive ring-opening polymerizations. The products were characterized using ¹H NMR and gel permeation chromatography (GPC). The triblock copolymers could self-assemble into micelles to encapsulate doxorubicin (DOX). The diameter of the DOX-loaded micelles increased from 63 to 92 nm with increasing PCL block length in the copolymer composition. The interface of the mPEG-b-PAGE-b-PCL micelles was crosslinked by a thiol-ene reaction with 1,4-butanedithiol. The stability, drug release and in vitro cytotoxicity of the DOX-loaded micelles were studied. The results showed that the DOX-loaded micelles could be effectively endocytosed by cancer cells and have good antitumor efficacy. In addition, the crosslinked micelles (CLMs) had better tumor accumulation than the noncrosslinked micelles (NCLMs) after intravenous injection using the lipophilic dye DiR.

Biomimetic phosphorylcholine strategy to improve the hemocompatibility of pH-responsive micelles containing tertiary amino groups

pH-responsive nanocarriers such as polymeric micelles that self-assemble from amphiphilic copolymers containing amino groups have been limited by their significant effects on the blood and thus compromise of their hemocompatibility due to the amino group-induced positive charges. Here we report a biomimetic phosphorylcholine strategy to improve the hemocompatibility of the pH-responsive micelles with positive charges. Amphiphilic copolymers containing different number of tertiary amino groups were synthesized in five steps through ring opening polymerization, azide reaction, thio-bromo "Click" chemistry, and atom transfer radical polymerization to self-assemble biomimetic phosphorylcholine micelles with pH-responsiveness, which shown no significant effects on red blood cells, coagulation, and platelet activation. Moreover, albumin adsorption on the micelles was significantly lower than that of polycaprolactone-methoxypolyethylene glycol (PCL-mPEG) control, and in terms of immune cells, the micelles showed controllable phagocytosis that dependent on the number of tertiary amino groups, in which the one containing four tertiary amino groups in its corresponding copolymer remains had a lower phagocytosis by whole blood leukocyte than that of PCL-mPEG. Based on these results, the hemocompatibility related mechanism of the micelles was discussed and proposed. Our findings demonstrated that this biomimetic phosphorylcholine is a promising strategy to improve the hemocompatibility of the positively charged nanocarriers.

Anti-biofouling therapeutic nanoparticles with removable shell and highly efficient internalization by cancer cells

Cationic gelatin nanoparticles ((+)nGNPs) were prepared by in situ polymerization upon the surfaces of monodispersed gelatin nanoparticles (GNPs) using N-(3-Aminopropyl)methacrylamide (APm) as monomer, which were then decorated with doxorubicin terminated poly(2-methylacryloyloxyethyl phosphorylcholine) (DOX-pMPC) via EDC/NHS conjugation to obtain core-shell nanoparticles ((+)nGNPs@DOX-pMPC) for cancer therapy. The non-fouling pMPC shell could effectively shield the positively charged surface of inner nanoparticle and prevent non-specific protein adsorption, thus endowing the materials with potential for long-acting cancer treatment. Furthermore, the acyl hydrazone bond connecting DOX and pMPC chain could be easily hydrolyzed in the weakly acidic tumor microenvironment. After decladding of the pMPC shell, electropositive (+)nGNPs carrying the drugs can be effectively internalized by cancer cells to induce apoptosis, avoiding undesirable hindrance caused by the superhydrophilic outer layer. On combining the above properties, this drug delivery system can be a promising candidate for long-acting, low-toxicity and high-efficiency cancer therapy.

Improved antitumor activity and reduced myocardial toxicity of doxorubicin encapsulated in MPEG-PCL nanoparticles

Doxorubicin (Dox) is a broad-spectrum antitumor drug used for the treatment of many types of malignant tumors. Although it possesses powerful antitumor activity, its clinical application is seriously encumbered by its unselective distribution and systemic toxicities, particularly myocardial toxicity. Thus, it is imperative to modify Dox to decrease its systemic toxicities and improve its therapeutic index. In the present study, we adopted a novel type of monomethoxy poly(ethylene glycol)-poly(ε-caprolactone) (MPEG-PCL) micelles to encapsulate Dox to prepare Dox-loaded MPEG-PCL (Dox/MPEG-PCL) nanoparticles by a controllable self-assembly process. The cellular uptake efficiency and cell proliferation inhibition of the Dox/MPEG-PCL nanoparticles were examined. The antitumor activity of the Dox/MPEG-PCL nanoparticles was tested on a multiple pulmonary metastasis model of melanoma on C57BL/6 mice. Systemic toxicities and survival time were compared between the mice treated with the Dox/MPEG-PCL nanoparticles and free Dox. The potential myocardial toxicity of the Dox/MPEG-PCL nanoparticles was investigated using a prolonged observation period. Encapsulation of Dox in MPEG-PCL nanoparticles significantly improved the cellular uptake and cell proliferation inhibition of Dox in vivo. Intravenous injection of Dox/MPEG-PCL nanoparticles obtained significant inhibition of the growth and metastasis of melanoma in the lung and prolonged survival time compared with free Dox (P<0.05). The Dox/MPEG-PCL nanoparticles did not show obvious additional systemic toxicities compared with free Dox during the treatment time. During the prolonged observation period, obvious decreased cardiac toxicity was observed in the Dox/MPEG-PCL nanoparticle-treated mice compared with that observed in the free Dox-treated mice. These results indicated that encapsulating Dox with MPEG-PCL micelles could significantly promote its antitumor activity and reduce its toxicity to the myocardium.

Biodegradable pH-sensitive polyurethane micelles with different polyethylene glycol (PEG) locations for anti-cancer drug carrier applications

Biodegradable pH sensitive polyurethane micelles with a dense brush like coating of PEG were prepared. The PTX-loaded PEG-g-PU-3 micelles exhibited potent cytotoxicity against H460 cancer cells compared to PEG-b-PU-3 and PEG-c-PU-3 micelles.

Inulin-Ethylenediamine Coated SPIONs Magnetoplexes: A Promising Tool for Improving siRNA Delivery

PURPOSE

An inulin based polycation (Inu-EDA) has been synthesized by the grafting of ethylenediamine molecules onto inulin backbone. The obtained inulin copolymer has been though to coat SPIONs (IC-SPIONs) and obtain stable magnetoplexes by complexation of IC-SPIONs with a model duplexed siRNA, for improving oligonucleotide transfection efficiency.

METHODS

The physical-chemical characteristics of IC-SPIONs and IC-SPIONs/siRNA magnetoplexes have been investigated by scanning and transmission electron microscopies, dynamic light scattering, FT-IR and qualitative surface elementary analysis. Cell compatibility and internalization in vitro of IC-SPIONs have been evaluated by MTS and fluorescence microscopy respectively on cancer (HCT116) and normal human (16HBE) cells. The efficiency of gene silencing effect of magnetoplexes was studied on both tumoral (JHH6) and non tumoral (16HBE) cell lines also by applying an external magnet.

RESULTS

IC-SPIONs showed dimension of 30 nm and resulted cytocompatible on the tested cell lines; in the presence of an external magnet, the magnetic force enhanced the IC-SPIONs uptake inside cells. Magnetically improved transfection was observed in 16HBE cells under magnetofective conditions, in accordance with the IC-SPIONs uptake enhancement in the presence of an external magnet.

CONCLUSIONS

These findings support the potential application of this system as a magnetically targeted drug delivery system. Graphical Abstract Magnetically improved siRNA transfection in cells under magnetofective conditions upon uptake enhancement of IC-SPIONs in the presence of an external magnet.