Micelles Loading Research Articles

Encapsulation and covalent binding of molecular payload in enzymatically activated micellar nanocarriers.

The high selectivity and often-observed overexpression of specific disease-associated enzymes make them extremely attractive for triggering the release of hydrophobic drug or probe molecules from stimuli-responsive micellar nanocarriers. Here we utilized highly modular amphiphilic polymeric hybrids, composed of a linear hydrophilic polyethylene glycol (PEG) and an esterase-responsive hydrophobic dendron, to prepare and study two diverse strategies for loading of enzyme-responsive micelles. In the first type of micelles, hydrophobic coumarin-derived dyes were encapsulated noncovalently inside the hydrophobic core of the micelle, which was composed of lipophilic enzyme-responsive dendrons. In the second type of micellar nanocarrier the hydrophobic molecular cargo was covalently linked to the end-groups of the dendron through enzyme-cleavable bonds. These amphiphilic hybrids self-assembled into micellar nanocarriers with their cargo covalently encapsulated within the hydrophobic core. Both types of micelles were highly responsive toward the activating enzyme and released their molecular cargo upon enzymatic stimulus. Importantly, while faster release was observed with noncovalent encapsulation, higher loading capacity and slower release rate were achieved with covalent encapsulation. Our results clearly indicate the great potential of enzyme-responsive micellar delivery platforms due to the ability to tune their payload capacities and release rates by adjusting the loading strategy.

Application of micellar enhanced ultrafiltration (MEUF) process for zinc (II) removal in synthetic wastewater: Kinetics and two-parameter isotherm models

Micellar enhanced ultrafiltration (MEUF) of zinc(II) from synthetic wastewater using sodium dodecyl sulfate (SDS) at low concentration was carried out in lab scale membrane system. Initial SDS concentration below critical micelle concentration (CMC) showed marginal increment and sharp reduction in zinc(II) removal percentage above CMC. Zinc(II) removal percentage decreased from 84.67 to 82.42% when the initial zinc(II) concentration increases from 0.42 to 2.10 mM at constant SDS concentration. Various performance parameters, i.e., amount of SDS micelles, gross of surfactant, ratio of S′ to M′ (i.e., molar ratio of the SDS micelle to the zinc(II) ions), average concentration factor, volume concentration ratio, and system conversion, as function of initial SDS concentration were investigated. Pseudo-second-order kinetic equation could be used to elucidate kinetics, while Freundlich two-parameter isotherm model was apposite to describe zinc(II) adsorption on SDS micelles. Further, distribution coefficient of zinc(II) ions in micellar and aqueous pseudo-phases, micelle loading, and micelle binding constant were estimated to evaluate MEUF process.

Hydrogen-bonded and reduction-responsive micelles loading atorvastatin for therapy of breast cancer metastasis

Metastasis is one of the major obstacles for the successful therapy of breast cancer. Although increased candidate drugs targeting cancer metastasis are tested, their clinical translation is limited by either serve toxicity or low efficacy. In present work, a nano-drug delivery system loading atorvastatin calcium (Ator) was developed for the efficient suppression of the metastasis of breast cancer. The nano-drug delivery system was constructed by a amphiphilic copolymer of methoxy polyethylene glycol-s-s-vitamin E succinate (mPEG-s-s-VES, PSV), which was consisted of a hydrophilic mPEG1k segment and a hydrophobic VES head, which were conjugated with a linker bearing amide and disulfide groups simultaneously. Self-assembly of PSV and Ator formed Ator-loaded PSV micelles (ASM) with good colloidal stability, high drug loading content (up to 50%) and great encapsulation efficiency (99.09 ± 0.28%). In cellular level, it was found that the ASM could efficiently release the Ator payload into cytosol due to detachment of PEG shell at high intracellular glutathione condition. ASM could significantly inhibit the migration and invasion of 4T1 breast cancer cells with inhibitory rates of 79.2% and 88.5%, respectively. In a 4T1 orthotropic mammary tumor metastatic cancer model, it was demonstrated that ASM could completely blocked the lung and liver metastasis of breast cancer with minimal toxicity owing to enhanced Ator accumulation in tumor and lung as compared with that of free Ator. The down-regulations of metastasis-promoting MMP-9, Twist and uPA proteins were demonstrated as the main underlying mechanism. As a result, ASM could be a promising drug delivery system for the efficient therapy of breast cancer metastasis.

P204 A paclitaxel–cisplatin loaded thermosensitive hydrogel for in situ treatment of lung cancer

Background An in situ, gelling, dual drug co-delivery system (PEG-PCL-PEG/DDP + MPEG-PCL/PTX [PDMP]) was prepared through the combination of a cisplatin-containing thermosensitive hydrogel (PEG-PCL-PEG/DDP, PECE/DDP) and paclitaxel-loaded polymeric micelles (MPEG-PCL/PTX micelles). Methods PDMP was a free-flowing solution at ambient temperature and formed a non-flowing gel at body temperature, serving as a drug depot for the in situ treatment of lung cancer. The MPEG-PCL/PTX spherical micelles had a diameter of 20.1 nm and a narrow particle size distribution. Paclitaxel loading and encapsulation efficiency of micelles were 3.96 ± 0.03% and 99.18 ± 0.65%, respectively. Findings Compared with blank micelles, paclitaxel-loaded micelles showed significant tumour inhibition in A549 cells. A xenografted lung cancer model was used to evaluate the antitumour efficiency of PDMP in vivo. PDMP was effective in inhibiting tumour growth and prolonging survival time of tumour-bearing BALB/c nude mice. Immunohistochemical images also showed that tumours in the PDMP group had fewer microvessels and lower proliferation activity compared with the control group. Interpretation Prepared PDMP could have potential for in situ local treatment of lung cancer through in vitro minimal invasive injection.

Preparation and in vitro pH-responsive drug release of amphiphilic dendritic star-block copolymer complex micelles

Amphiphilic dendritic star-block copolymer PCL-b-PDMAEMA composed of poly(ε-caprolactone) and poly(2-(N,N-dimethylamino)ethyl methacrylate) was synthesized successfully. In an aqueous solution, the copolymer could simultaneously self-assemble into unimolecular micelles and multimolecular mielles with mean diameters of about 28nm and 190nm, respectively. Dynamic light scattering measurements of these copolymer micelles showed bimodal size distribution. in vitro drug release behavior of the complex micelles loading camptothecin indicated that the rate of drug release could be effectively controlled by altering the pH values of the environment. The cytotoxicity assay confirmed the low cytotoxicity of the complex micelles and the significant drug efficacy. The confocal laser scanning microscopy demonstrated that the drug-loaded micelles could penetrate the cell membrane and be internalized into cytoplasm and cell nucleus of HeLa cells. Thus, the pH-responsive dendritic PCL-b-PDMAEMA micelles could be promising drug delivery vehicles for pharmaceutical and biomedical applications.

A numerical study of the phase behaviors of drug particle/star triblock copolymer mixtures in dilute solutions for drug carrier application.

The complex microstructures of drug particle/ABA star triblock copolymer in dilute solutions have been investigated by a theoretical approach which combines the self-consistent field theory and the hybrid particle-field theory. Simulation results reveal that, when the volume fraction of drug particles is smaller than the saturation concentration, the drug particle encapsulation efficiency is 100%, and micelle loading capacity increases with increasing particle volume fraction. When the volume fraction of drug particles is equal to the saturation concentration, the micelles attain the biggest size, and micelle loading capacity reaches a maximum value which is independent of the copolymer volume fraction. When the volume fraction of drug particles is more than the saturation concentration, drug particle encapsulation efficiency decreases with increasing volume fraction of drug particles. Furthermore, it is found that the saturation concentration scales linearly with the copolymer volume fraction. The above simulation results are in good agreement with experimental results.

Linear-dendrimer type methoxy-poly (ethylene glycol)-b-poly (ɛ-caprolactone) copolymer micelles for the delivery of curcumin

Purpose: To improve curcumin’s pharmacokinetic, in vitro cytotoxicity and release property.Methods: A novel linear-dendrimer methoxy-poly (ethylene glycol)-b-poly (ɛ-caprolactone) copolymer was synthesized through O-alkylation, basic hydrolysis and ring-opening polymerization reaction with methoxy-poly (ethylene glycol), epichlorohydrin and ɛ-caprolactone as raw materials. Its structure was characterized by 1H-NMR and GPC. The copolymer’s hemolysis and micellar encapsulation for curcumin by thin-film hydration were studied. Curcumin-loaded micelles were evaluated by use of in vitro release, FT-IR and X-ray diffraction. Curcumin-loaded micelles’ in vitro cytotoxic activities against Hela and HT-29 cells were done, and its pharmacokinetic parameters were also carried out.Results: Curcumin was encapsulated into the micelles with 92.54% of entrapment efficiency and 12.84% of drug loading in amorphous forms. The dissolubility of nanoparticulate curcumin was 1.70 × 105 times higher than that of curcumin in water. The obtained copolymer showed no hemolysis. In vitro drug release study indicated that, in all cases, the kinetics was adjusted well to the Makoid–Banakar model ( = 0.9984). In addition, data were analyzed by the Korsmeyer–Peppas model, n values were 0.43, indicating that the drug release was accomplished by the combination diffusion and polymer chain relaxation. The cytotoxicity experiment indicated that the nanoparticulate curcumin kept up its potent anti-cancer activities. The pharmacokinetic results showed that the MRT0–∞, t1/2z and AUC0–∞ of Curcumin-loaded micelles were 1.64, 6.54 and 4.67 times higher than that of CUR control solution.Conclusions: The copolymeric micelles loading curcumin might act as a delivery vehicle for CUR.

Multi-targeted inhibition of tumor growth and lung metastasis by redox-sensitive shell crosslinked micelles loading disulfiram

Metastasis, the main cause of cancer related deaths, remains the greatest challenge in cancer treatment. Disulfiram (DSF), which has multi-targeted anti-tumor activity, was encapsulated into redox-sensitive shell crosslinked micelles to achieve intracellular targeted delivery and finally inhibit tumor growth and metastasis. The crosslinked micelles demonstrated good stability in circulation and specifically released DSF under a reductive environment that mimicked the intracellular conditions of tumor cells. As a result, the DSF-loaded redox-sensitive shell crosslinked micelles (DCMs) dramatically inhibited cell proliferation, induced cell apoptosis and suppressed cell invasion, as well as impairing tube formation of HMEC-1 cells. In addition, the DCMs could accumulate in tumor tissue and stay there for a long time, thereby causing significant inhibition of 4T1 tumor growth and marked prevention in lung metastasis of 4T1 tumors. These results suggested that DCMs could be a promising delivery system in inhibiting the growth and metastasis of breast cancer.

Study on solubilization capability of various Gemini micelles in micellar-enhanced ultrafiltration of phenol-contaminated waters

A systematic study has been conducted to have an insight into the separation efficiency of phenol with the help of Gemini surfactants and conventional nonionic surfactant in their single and mixed systems using micellar-enhanced ultrafiltration (MEUF). A flat sheet membrane with a total effective area of 0.08 m2 and a molecular weight cut-off of 10 kDa, was selected in this investigate. The effects of feed component (surfactant concentration for single surfactant system and mixed ratio for mixed surfactant system) on solubilization and filtration efficiency were researched. Some related parameters were used to estimate the performance of various surfactant systems, such as distribution coefficient (D), the phenol concentration in micellar phase (Pm), the surfactant concentration in micellar phase (Sm), the micelle loading (Lm), and the equilibrium distribution constant (K). With the increase of feed surfactant concentration or the addition of nonionic surfactant, the degree of solubilization of phenol enhances, leading to the decrease of permeate concentration and the augment of retentate concentration. Consequently, D, Pm, and Sm increases. The addition of nonionic surfactant has positive effects to recounterbalance the interior structure and improve the micellar solubilization power for phenol. Both the single and mixed C12-2-16 systems have higher D, Pm, and Sm values than these of C12-2-12, due to the longer length alkyl chain and more optimized structure. Lm and K are the significant indicators for evaluating the effectiveness of dissolving phenol. Irreversible fouling was almost eliminated with a series of cleaning solution in a short time. There results from the laboratory-scale experiments could be very useful in selection of the suitable surfactant systems for raising efficiency and could serve as valuable guide for MEUF in industrial application.

Evaluation of micellar enhanced ultrafiltration for removing methylene blue and cadmium ion simultaneously with mixed surfactants

Micellar enhanced ultrafiltration (MEUF) has been extensively applied to the separation of organic solutes or heavy metal ions from water, but the feasibility and efficiency of removing them simultaneously via MEUF have been seldom researched. In this study, simultaneous removal of methylene blue (MB) and cadmium ion (Cd2+) with MEUF by the binary mixture of sodium dodecylsulfate (SDS) and polyoxyethylene octyl phenyl ether (TritonX-100) was investigated. The critical micelle concentration (CMC) of mixed surfactants was considered. Retentions of MB and Cd2+, flux decay, and three parameters, namely distribution coefficient (D), micelle loading (L), and micelle binding constant (K) were discussed to assess the efficiency of MEUF process. The higher mole ratio of TritonX-100 exhibited lower CMC value but more intensified flux decay. Within a certain range, the addition of TritonX-100 was in favor of MB and Cd2+ removal. The presence of Cd2+ could promote the rejection of MB by increasing the micelles in the retentate but had no influence on the unit binding capacity of micelles and the relative affinity of MB for micelles. The presence of MB could also increase Cd2+ rejection with little influence on the unit binding capacity of micelles.

The Influence of Drug Loading on Caveolin-1 Mediated Intracellular Internalization of Doxorubicin Nanomicelles in vitro

Despite the considerable progress made in the field of anticancer nanomedicine, the influence of the physicochemical characteristics of the nanoconstructs on their internalization and cytotoxicity towards specific cancer cells remains to be fully understood. The aim of this in vitro study was to examine the factors influencing the potency of styrene maleic acid (SMA-Dox) micelles loaded with doxorubicin in a range of 4.4% to 28.4% using breast cancer and prostate cancer cell lines. A significant difference in cytotoxicity relative to micelle loading was observed and correlated with the expression level of caveolin-1. The expression level of caveolin-1 has previously been associated with advanced, aggressive cancer subtypes. For example, SMA-Dox micelles were shown to co-localize with caveolin-1 in PC3 cells and this colocalization was disrupted by treatment with the caveolin-1 inhibitor, genistein. The results of this study are indicative that the micelle loading and cellular expression of caveolin-1 modulates the relative cytotoxicity of nanoconstructs of different loading against breast and prostate cancer cell lines in vitro. The expression level of caveolin-1 is a factor to consider when developing nanoconstructs for the treatment of breast and prostate cancers.

Homopolymers as nanocarriers for the loading of block copolymer micelles with metal salts: a facile way to large-scale ordered arrays of transition-metal nanoparticles

A new and facile approach is presented for generating quasi-regular patterns of transition metal-based nanoparticles on flat substrates exploiting polystyrene-block-poly2vinyl pyridine (PS-b-P2VP) micelles as intermediate templates. Direct loading of such micellar nanoreactors by polar transition metal salts in solution usually results in nanoparticle ensembles exhibiting only short range order accompanied by broad distributions of particle size and inter-particle distance. Here, we demonstrate that the use of P2VP homopolymers of appropriate length as molecular carriers to transport precursor salts into the micellar cores can significantly increase the degree of lateral order within the final nanoparticle arrays combined with a decrease in spreading in particle size. Thus, a significantly extended range of materials is now available which can be exploited to study fundamental properties at the transition from clusters to solids by means of well-organized, well-separated, size-selected metal and metal oxide nanostructures.

Silica Cross-linked Micelles Loading with Silicon Nanoparticles: Preparation and Characterization

A new family of luminescent and stable silicon-based nanoparticles (NPs), silica cross-linked pluronic F127 (PF127) micelles loaded with decyl capped silicon nanoparticles (decyl-SiNPs), were synthesized in aqueous media. The decyl-SiNPs were prepared by first liberating hydride terminated SiNPs (H-SiNPs) from a porous silicon matrix followed by their functionalization via hydrosilylation with 1-decene under photochemical activation. The silicon-based NPs exhibit bright photoluminescence (PL) with a quantum yield of ∼3.8% and peaking at ∼2.0 eV, which lies within the transmission window that is useful for biological imaging. They display a hydrodynamic size of ∼25 nm with exterior polyethylene oxide (PEO) blocks stretching out in aqueous media. Chloroform was found to quench the excitation at energy above 4.9 eV by shielding the incident light or relaxing the charge carriers, which highlights that caution against solvent interference should be taken when performing the studies on PL origin and luminescence efficiency of SiNPs. For PF127, the blocks of hydrophilic PEO participate in the PL quenching, while poly(propylene oxide) (PPO) does not. The colloidal solution displays excellent PL stability against salt (NaCl) and temperature but is susceptible to basic solution at pH above 9.

Flow-Directed Loading of Block Copolymer Micelles with Hydrophobic Probes in a Gas–Liquid Microreactor

We investigate the loading efficiencies of two chemically distinct hydrophobic fluorescent probes, pyrene and naphthalene, for self-assembly and loading of polystyrene-block-poly(acrylic acid) (PS-b-PAA) micelles in gas-liquid segmented microfluidic reactors under different chemical and flow conditions. On-chip loading efficiencies are compared to values obtained via off-chip dropwise water addition to a solution of copolymer and probe. On-chip, probe loading efficiencies depend strongly on the chemical probe, initial solvent, water content, and flow rate. For pyrene and naphthalene probes, maximum on-chip loading efficiencies of 73 ± 6% and 11 ± 3%, respectively, are obtained, in both cases using the more polar solvent (DMF), an intermediate water content (2 wt % above critical), and a low flow rate (∼5 μL/min); these values are compared to 81 ± 6% and 48 ± 2%, respectively, for off-chip loading. On-chip loading shows a significant improvement over the off-chip process where shear-induced formation of smaller micelles enables increased encapsulation of probe. As well, we show that on-chip loading allows off-chip release kinetics to be controlled via flow rate: compared to vehicles produced at ∼5 μL/min, pyrene release kinetics from vehicles produced at ∼50 μL/min showed a longer initial period of burst release, followed by slow release over a longer total period. These results demonstrate the necessity to match probes, solvents, and running conditions to achieve effective loading, which is essential information for further developing these on-chip platforms for manufacturing drug delivery formulations.

Development and evaluation of fast forming nano-composite hydrogel for ocular delivery of diclofenac

In this paper, a fast forming nano-composite hydrogel was developed for potential application in ocular drug delivery. The optical transmission (OT) as well as rheological properties of nano-composite hydrogel was characterized. The developed nano-composite hydrogel given a high diclofenac micelles loading and provided a sustained release manner of diclofenac within 6h. The developed nano-composite hydrogel formulation was administrated into the eye as flowable solution, quickly forming a hydrogel that is able to resist of the blinking and flushing of tear, yet resulting in the prolonged residence time of pre-corneal. In vivo eye irritation test suggested that the developed nano-composite hydrogel was none-eye irritation might be suitable for various ocular applications. In vivo pharmacokinetic study indicated that the developed nano-composite hydrogel could significantly increase the bioavailability of diclofenac and maintain the concentration of diclofenac in aqueous humor above MEC at least 24h after administration as compared with that of the commercial diclofenac sodium eye drops, which might be able to reduce the frequency of administration for patients.

Synthesis and characterization of low-toxicity N-caprinoyl-N-trimethyl chitosan as self-assembled micelles carriers for osthole

Novel amphiphilic chitosan derivatives (N-caprinoyl-N-trimethyl chitosan [CA-TMC]) were synthesized by grafting the hydrophobic moiety caprinoyl (CA) and hydrophilic moiety trimethyl chitosan to prepare carriers with good compatibility for poorly soluble drugs. Based on self-assembly, CA-TMC can form micelles with sizes ranging from 136 nm to 212 nm. The critical aggregation concentration increased from 0.6 mg • L−1 to 88 mg • L−1 with decrease in the degree of CA substitution. Osthole (OST) could be easily encapsulated into the CA-TMC micelles. The highest entrapment efficiency and drug loading of OST-loaded CA-TMC micelles(OST/CA-TMC) were 79.1% and 19.1%, respectively. The antitumor efficacy results show that OST/CA-TMC micelles have significant antitumor activity on Hela and MCF-7 cells, with a 50% of cell growth inhibition (IC50) of 35.8 and 46.7 μg. mL−1, respectively. Cell apoptosis was the main effect on cell death of Hela and MCF-7 cells after OST administration. The blank micelles did not affect apoptosis or cell death of Hela and MCF-7 cells. The fluorescence imaging results indicated that OST/CA-TMC micelles could be easily uptaken by Hela and MCF-7 cells and could localize in the cell nuclei. These findings suggest that CA-TMC micelles are promising carriers for OST delivery in cancer therapy.

Acid-triggered core cross-linked nanomicelles for targeted drug delivery and magnetic resonance imaging in liver cancer cells

PurposeTo research the acid-triggered core cross-linked folate-poly(ethylene glycol)-b-poly[N-(N′,N′-diisopropylaminoethyl) glutamine] (folated-PEG-P[GA-DIP]) amphiphilic block copolymer for targeted drug delivery and magnetic resonance imaging (MRI) in liver cancer cells.MethodsAs an appropriate receptor of protons, the N,N-diisopropyl tertiary amine group (DIP) was chosen to conjugate with the side carboxyl groups of poly(ethylene glycol)-b-poly (L-glutamic acid) to obtain PEG-P(GA-DIP) amphiphilic block copolymers. By ultrasonic emulsification, PEG-P(GA-DIP) could be self-assembled to form nanosized micelles loading doxorubicin (DOX) and superparamagnetic iron oxide nanoparticles (SPIONs) in aqueous solution. When PEG-P(GA-DIP) nanomicelles were combined with folic acid, the targeted effect of folated-PEG-P(GA-DIP) nanomicelles was evident in the fluorescence and MRI results.ResultsTo further increase the loading efficiency and the cell-uptake of encapsulated drugs (DOX and SPIONs), DIP (pKa≈6.3) groups were linked with ~50% of the side carboxyl groups of poly(L-glutamic acid) (PGA), to generate the core cross-linking under neutral or weakly acidic conditions. Under the acidic condition (eg, endosome/lysosome), the carboxyl groups were neutralized to facilitate disassembly of the P(GA-DIP) blocks’ cross-linking, for duly accelerating the encapsulated drug release. Combined with the tumor-targeting effect of folic acid, specific drug delivery to the liver cancer cells and MRI diagnosis of these cells were greatly enhanced.ConclusionAcid-triggered and folate-decorated nanomicelles encapsulating SPIONs and DOX, facilitate the targeted MRI diagnosis and therapeutic effects in tumors.

Pharmacokinetic Evaluation of a DSPE-PEG2000 Micellar Formulation of Ridaforolimus in Rat

The rapamycin analog, ridaforolimus, has demonstrated potent anti-proliferative effects in cancer treatment, and it currently is being evaluated in a range of clinical cancer studies. Ridaforolimus is an extremely lipophilic compound with limited aqueous solubility, which may benefit from formulation with polymeric micelles. Herein, we report the encapsulation of ridaforolimus in 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-methoxy-poly(ethylene glycol 2000) (DSPE-PEG2000) via a solvent extraction technique. Micelle loading greatly improved the solubility of ridaforolimus by approximately 40 times from 200 μg/mL to 8.9 mg/mL. The diameters of the drug-loaded micelles were 33 ± 15 nm indicating they are of appropriate size to accumulate within the tumor site via the enhanced permeability and retention (EPR) effect. The DSPE-PEG2000 micelle formulation was dosed intravenously to rats at 10 mg/kg and compared to a control of ridaforolimus in ethanol/PEG 400. The micelle significantly increased the half-life of ridaforolimus by 170% and decreased the clearance by 58%, which is consistent with improved retention of the drug in the plasma by the micelle formulation.

Abstract P6-11-11: Multistage Delivery of Paclitaxel: Increased Drug Stability and Sustained Release Results in Enhanced Efficacy in Breast Cancer

Abstract Background: A significant challenge for effectively treating cancer is overcoming biological barriers that reduce circulation times and increase degradation of possible treatments. We established an innovative approach to address this issue by embedding drug-containing nanoparticles within the pores of a larger mesoporous silicon particle (MSP) in order to optimize site-specific localization and release of therapeutic agents. The objective is to develop a nanotherapeutic-based multistage platform for breast cancer treatment, wherein paclitaxel, a mitotic inhibitor used in the treatment of breast tumors, will be loaded into polymeric micelles, which in turn will be loaded within MSPs. We hypothesize that this nested incorporation of drugs within MSPs, combined with enhanced tumor transport, will result in a more pronounced and sustained antitumor effect. Materials and Methods: Micelles were assembled from amphiphilic block copolymers consisting of poly(ethylene glycol)-poly(∈-caprolactone) (PEG-PCL, MW = 5k-5k). Nanoparticle size, zeta potential, and morphology was determined, and PTX loading and release kinetics from micelles analyzed. Drug-containing micelles were incorporated into MSPs by a previously established dry-loading method, wherein nanoparticles were incorporated into pores via capillary action. Loading of fluorescent micelles was used to verify loading within MSPs via fluorescence microscopy and flow cytometry analysis. Sulforhodamine B assays were used to evaluate the in vitro antitumor efficacy of the platform in MCF-7 and MDA-MB-468 breast cancer cells. In vivo efficacy was evaluated in MDA-MB-468 breast tumors in female nu/nu mice. Results: Resulting micelles had an average size of 20 nm, as confirmed through TEM, with paclitaxel loaded into micelles very effectively. Release kinetics showed that 50% of the drug was released within 4 hours and 80% released within 24 hours. Loading of micelles into MSPs depended largely on electrostatic interactions, with micelles loading better within pores of MSPs displaying increased positive charge. Micelle loading into MSPs was successful as demonstrated by flow cytometry, and release was significantly retarded (< 30% of drug released over 4 d). Incubation of micelle-containing MSPs with breast cancer cells in vitro showed that MSPs could be internalized by cells, after which a sustained and delayed release of the payload was observed in cells. Breast tumors treated with MSPs demonstrated sustained tumor suppression (169 mm3 compared to initial starting volume of 200 mm3) at day 35 following a single injection. It is important to note that sustained tumor efficacy was achieved with nanoparticle and free drug formulations, however, with the caveat of repeated administrations. Discussion: A novel multistage approach to chemotherapy effectively allows a secondary payload to be loaded and preserved within the MSPs until reaching the tumor site. This prevents premature release of the drug and allows for a sustained release which may potentially result in fewer patient side effects. Future studies will involve loading of multiple nanoparticle types into MSPs and addition of targeting and diagnostic components. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-11-11.

Drug Loading of Polymeric Micelles

To gain mechanistic insights into drug loading and lyophilization of polymeric micelles. PEGylated poly-4-(vinylpyridine) micelles were loaded with dexamethasone. Three different methods were applied and compared: O/W emulsion, direct dialysis, cosolvent evaporation. Micellar dispersions with the highest drug load were lyophilized with varying lyoprotectors: sucrose, trehalose, maltose, a polyvinylpyrrolidine derivative, and β-cyclodextrin derivatives. For comparison, other PEGylated block copolymer micelles (PEGylated polylactic acid, polylactic acid-co-glycolic acid, polycaprolactone) were freeze-dried. Drug loading via direct dialysis from acetone was a less effective loading method which led to dexamethasone loads <2% w/w. O/W emulsion technique from dichlormethane increased drug load up to ~13% w/w; optimized cosolvent evaporation increased load up to ~19% w/w. An important step for cosolvent evaporation was solubility screen of the drug prior to preparation. Loading was maintained upon lyophilization with β-cyclodextrins which proved to be versatile stabilizers for other block copolymer micelles. Careful solvent selection prior to cosolvent evaporation was a beneficial approach to load hydrophobic drugs into polymeric micelles. Moreover, β-cyclodextrins could be used as versatile lyoprotectors for these micelles.