Poly(L-histidine)-PEG block copolymer micelles and pH-induced destabilization

Proteases in cutaneous malignant melanoma: relevance as biomarker and therapeutic target

Cutaneous malignant melanoma is the most aggressive skin cancer. It is also the most rapidly spreading cancer in terms of worldwide incidence. Although it is detected by simple inspection and can be relatively easily removed or treated, differential diagnosis to other melanocytic lesions, lack of prognostic markers, and no efficient treatment of advanced melanoma pose problems. Detection and targeting of proteases may represent a useful tool since they play a role in tumor cell metabolism, invasion, angiogenesis and metastasis. This review gives an overview of the role of proteases in development and progression of cutaneous malignant melanoma. In addition, regulation, activation, and interaction of proteases and their inhibitors are explained for tumors in general. The potential use of proteases as differential markers for melanoma mimicking melanocytic lesions, as biomarkers in tissues, and as prognostic serum markers is discussed. Current and future possibilities to target tumor proteases in therapy are presented.

Polymeric micelles in anticancer therapy: targeting, imaging and triggered release

Micelles are colloidal particles with a size around 5-100 nm which are currently under investigation as carriers for hydrophobic drugs in anticancer therapy. Currently, five micellar formulations for anticancer therapy are under clinical evaluation, of which Genexol-PM has been FDA approved for use in patients with breast cancer. Micelle-based drug delivery, however, can be improved in different ways. Targeting ligands can be attached to the micelles which specifically recognize and bind to receptors overexpressed in tumor cells, and chelation or incorporation of imaging moieties enables tracking micelles in vivo for biodistribution studies. Moreover, pH-, thermo-, ultrasound-, or light-sensitive block copolymers allow for controlled micelle dissociation and triggered drug release. The combination of these approaches will further improve specificity and efficacy of micelle-based drug delivery and brings the development of a 'magic bullet' a major step forward.

Stimulus-responsive macromolecules and nanoparticles for cancer drug delivery

Nanoparticles and macromolecular carriers have been widely used to increase the efficacy of chemotherapeutics, largely through passive accumulation provided by the enhanced permeability and retention effect. Stimulus-responsive peptide and polymer vehicles can further enhance the efficacy of antitumor therapeutics compared with the administration of free drug by three mechanisms: increasing the overall accumulation within solid tumors; providing a homogeneous spatial distribution in tumor tissues; and increasing the intracellular localization of anticancer therapeutics. This article highlights recent developments in 'smart' - stimulus-responsive - peptide, polymer and lipid drug carriers designed to enhance the localization and efficacy of therapeutic payloads as compared with free drug.

Binary mixing of micelles using Pluronics for a nano-sized drug delivery system

Pluronics with different structural compositions and properties are used for several applications, including drug delivery systems. We developed a binary mixing system with two Pluronics, L121/P123, as a nano-sized drug delivery carrier. The lamellar-forming Pluronic L121 (0.1 wt%) was incorporated with Pluronic P123 to produce nano-sized dispersions (in case of 0.1 and 0.5 wt% P123) with high stability due to Pluronic P123 and high solubilization capacity due to Pluronic L121. The binary systems were spherical and less than 200-nm diameter, with high thermodynamic stability (at least 2 weeks) in aqueous solution. The CMC of the binary system was located in the middle of the CMC of each polymer. In particular, the solubilization capacity of the binary system (0.1/0.1 wt%) was higher than mono-systems of P123. The main advantage of binary systems is overcoming limitations of mono systems to allow tailored mixing of block copolymers with different physicochemical characteristics. These nano-sized systems may have potential as anticancer drug delivery systems with simple preparation method, high stability, and high loading capacity.

Spontaneous formation of temperature-responsive assemblies by molecular recognition of a β-cyclodextrin containing block copolymer and poly(N-isopropylacrylamide)

We report the construction of novel temperature-responsive assemblies based on a double hydrophilic block copolymer (consisting of a PEG block and a β-cyclodextrin-containing block, PEG-b-PCD) and poly(N-isopropylacrylamide) (PNIPAm). Thus formed nano-assemblies exhibit a spherical morphology and have a temperature-responsive loose core. The driving force for the formation of these assemblies was found to be the inclusion complexation interaction between the hydrophobic cavity of β-cyclodextrin and the isopropyl group of PNIPAm. The particle size of these assemblies changed reversibly in response to the external temperature change. The particle size also changed with the PNIPAm/PEG-b-PCD weight ratio. A model hydrophobic drug (indomethacin) was loaded into these assemblies with a high efficiency. An in vitro release study showed that the payload could be released in a sustained manner after an initial burst release. The release rate could be switched between high and low in an ON/OFF fashion by temperature. These results demonstrate that the nano-assemblies have high potential for applications in controlled drug delivery and biomedicine when temperature responsiveness is desired.

Nanodiamond as the pH-responsive vehicle for an anticancer drug

Cis-dichlorodiammineplatinum(II) (CDDP, cisplatin), a widely used anticancer drug, is successfully loaded onto nanodiamond (ND) by adsorption and complexation. The CDDP-ND composite is characterized by IR spectroscopy, atomic absorption spectroscopy, thermogravimetric analysis, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. CDDP is released from the composite in phosphate-buffered saline (PBS) of pH 6.0 at a rate higher than in PBS of pH 7.4. Therefore, it is predicted that the ND vehicle would deliver low concentrations of CDDP in the blood, but release much more drug after integration into the acidic cytoplasm, thereby reducing toxic side effects. The complexation between CDDP and the carboxyl groups on the ND surface is responsible for the pH-responsive release property. The drug released from the composite retains the same cytotoxicity as free CDDP against human cervical cancer cells.

Advances in polymeric micelles for drug delivery and tumor targeting

A plethora of formulation techniques have been reported in the literature for targeting drugs to specific sites. Polymeric micelles (PMs) can be targeted to tumor sites by passive as well as active mechanisms. Some inherent properties of PMs, including size in the nanorange, stability in plasma, longevity in vivo, and pathological characteristics of tumor allow PMs to be targeted to the tumor site by a passive mechanism called the enhanced permeability and retention effect. PMs formed from an amphiphilic block copolymer are suitable for encapsulation of poorly water-soluble, hydrophobic anticancer drugs. Other characteristics of PMs such as separate functionality at the outer shell are useful for targeting the anticancer drug to tumor by active mechanisms. PMs can be conjugated with many ligands such as antibody fragments, epidermal growth factors, α(2)-glycoprotein, transferrin, and folate to target micelles to cancer cells. Application of heat or ultrasound are the alternative methods to enhance drug accumulation in tumoral cells. Targeting using micelles can also be directed toward tumor angiogenesis, which is a potentially promising target for anticancer drugs. PMs have been used for the delivery of many anticancer agents in preclinical and clinical studies. This review summarizes recently available information regarding targeting of anticancer drugs to the tumor site using PMs.

pH-dependent hemolysis of biocompatible imidazole-grafted polyaspartamide derivatives

A series of novel, pH-sensitive, endosomolytic polymers based on imidazole-grafted polyaspartamide were synthesized to characterize the pH-sensitive membrane fusion properties of red blood cells and their toxicity to L929 cells. All imidazole-containing polymers exhibited strong cationic characteristics under acidic conditions, as well as a high buffering effect in the pH range 5-7. In the presence of O-(2-aminoethyl)-O'-methylpolyethylene glycol and 1-(3-aminopropyl)imidazole-grafted polyaspartamide (MPEG/API-g-PASPAM) systems red blood cells agglutinated below pH 6.5 without any hemolytic effect. The octadecylamine, O-(2-aminoethyl)-O'-methylpolyethylene glycol and 1-(3-aminopropyl)imidazole-grafted polyaspartamide (C18/MPEG/API-g-PASPAM) systems, however, displayed considerable hemolytic behavior below pH 6.5, but no hemolysis occurred above this pH. It can be concluded from these results that not only the pH-sensitive imidazole group, but also the hydrophobic octadecyl chain plays a critical role in membrane fusion. The hypothetical mechanism of this fusion involves both ionic and hydrophobic interactions between the polymers and lipid bilayers.

Folate-Conjugated Polymer Micelles with pH-Triggered Drug Release Properties

Folate has been applied as a targeting moiety for various anticancer drug-delivery agents to avoid non-specific attack of normal tissues as well as to increase cellular uptake at the target tumor cells. Polymer micelles made of poly[(D,L-lactide)-co-glycolide)]-poly(ethylene glycol)-folate (PLGA-PEG-FOL) was fabricated as a tumor targeting carrier for encapsulating the anticancer drug doxorubicin. To accelerate the drug release in the endosome after folate-mediated cellular uptake, pH-sensitive poly(β-amino ester)-PEG-FOL (PAE-PEG-FOL) was added together with PLGA-PEG-FOL to form mixed micelles. The results showed that the drug release can be triggered at different pH due to the ionization of PAE. The IC(50) of PLGA-PEG-FOL micelles is 0.46 × 10(-6) M. With 20% PAE in the mixed micelles (20:80 mixed micelles), the IC(50) decreases to 0.34 × 10(-6) M, which is comparable to that of pure PAE-PEG-FOL micelles at pH 7.4. As a result of the pH sensitivity, the PAE-PEG-FOL micelles are not stable at pH 6.5 or lower, and the drug may be released from the micelles into the extracellular environment before uptake by the cells. The 20:80 mixed micelles are relatively stable at this condition. As a result, the micelles retain more drug in the micelles for a higher degree of cellular uptake by folate receptor-mediated endocytosis, and exhibit higher cytotoxicity.

Tumour and dendrimers: a review on drug delivery aspects

Tumour is a morbid state, characterized by spontaneous outgrowth of an abnormal mass of cells. The evolution of tumours is random, disorganized, a condition of numerous mutations. The properties are biased and incompletely comprehended. It is a malignant or benign condition that encompasses its own rules of morphogenesis, an immortal state that elucidates different physiology. It is a pathological crisis that still haunts the minds of scientists, physicians and patients, a complete cure of which is still a dream to be realized. The unpredictable microenvironment of cancerous cells in all of its existing forms i.e. leukaemic cells, solid tumours and sarcomas is well documented. This phenomenon expressed by cancerous sites in the body poses various obstacles towards drug efficacy. Thus, it has become necessary to address briefly the issues relating to tumour physiology, its vasculature and angiogenesis. The information could provide insight towards the development of tumour-targeted drug delivery. The salient features regarding these have been discussed.

Folate mediated histidine derivative of quaternised chitosan as a gene delivery vector

Folate targeted gene delivery vectors showed enhanced accumulation in folate receptor expressing tumor model. In the present work, the water solubility and transfection efficiency of chitosans were improved by modifying the depolymerised trimethylated chitosans with histidine moiety. Folate mediated targeting was induced by conjugating poly(ethylene glycol)-folate (PEG-FA) on histidine modified chitosan polymer having low molecular weight of 15 kDa and high degree of quaternisation (HTFP15-H). The zeta potential and size of the HTFP15-H/pDNA nanoparticles were determined using dynamic light scattering technique and the results were confirmed by transmission electron microscopy (TEM). The morphology of the nanoparticles was found spherical in shape having core-shell nanostructure. The HTFP15-H derivative found to buffer in the pH range from 10 to 4. The blood compatibility in terms of percentage hemolysis, erythrocyte aggregation and also by platelet activation was found to be significantly improved compared to the control vector PEI. At a concentration of 10 microg the derivative promote the cell growth up to 139% compared to control at normal cell growing conditions. The transfection efficiency in KB cell line, which over expresses the folate receptor (FR) in presence of 10% fetal bovine serum (FBS) was also found to be comparable to the control. Moreover the enhanced cellular and nuclear uptake due to the conjugation of both folic acid and histidine makes it a potential vector for gene delivery applications.

Multifunctional nanoassemblies of block copolymers for future cancer therapy

Nanoassemblies from amphiphilic block copolymers are promising nanomedicine platforms for cancer diagnosis and therapy due to their relatively small size, high loading capacity of drugs, controlled drug release, in vivo stability and prolonged blood circulation. Recent clinical trials with self-assembled polymeric micelles incorporating anticancer drugs have shown improved antitumor activity and decreased side effects encouraging the further development of nanoassemblies for drug delivery. This review summarizes recent approaches considering stimuli-responsive, multifunctionality and more advanced architectures, such as vesicles or worm-like micelles, for tumor-specific drug and gene delivery.

Environment-responsive multifunctional liposomes

Liposomal nanocarriers anchored with a cell-penetrating peptide and a pH-sensitive PEG-shield where later has ability to provide simultaneously better systemic circulation and site-specific exposure of cell penetrating peptide. PEG chains were incorporated into the liposome membrane via the PEG-attached phosphatidylethanolamine (PE) residue with PEG and PE being conjugated with the lowered pH-degradable hydrazone bond (PEG-HZ-PE), while cell-penetrating peptide (TATp) was added as TATp-PEG-PE conjugate. Under normal conditions, liposome-grafted PEG "shielded" liposome-attached TATp moieties, since the PEG spacer for TATp attachment (PEG(1000)) was shorter than protective PEG(2000). PEGylated liposomes accumulate in targets via the EPR effect, but inside the "acidified" tumor or ischemic tissues lose their PEG coating because of the lowered pH-induced hydrolysis of HZ and penetrate inside cells via the now-exposed TATp moieties. pH-responsive behavior of these constructs is successfully tested in cell cultures in vitro as well as in tumors in experimental mice in vivo. These nanocarriers also showed enhanced pGFP transfection efficiency upon intratumoral administration in mice, compared to control pH nonsensitive counterpart. These results can be considered as an important step in the development of tumor-specific stimuli-sensitive drug and gene delivery systems.

Passive and active drug targeting: drug delivery to tumors as an example

The paradigm of using nanoparticulate pharmaceutical carriers has been well established over the past decade, both in pharmaceutical research and in the clinical setting. Drug carriers are expected to stay in the blood for long time, accumulate in pathological sites with affected and leaky vasculature (tumors, inflammations, and infarcted areas) via the enhanced permeability and retention (EPR) effect, and facilitate targeted delivery of specific ligand-modified drugs and drug carriers into poorly accessible areas. Among various approaches to specifically target drug-loaded carrier systems to required pathological sites in the body, two seem to be most advanced--passive (EPR effect-mediated) targeting, based on the longevity of the pharmaceutical carrier in the blood and its accumulation in pathological sites with compromised vasculature, and active targeting, based on the attachment of specific ligands to the surface of pharmaceutical carriers to recognize and bind pathological cells. Here, we will consider and discuss these two targeting approaches using tumor targeting as an example.

In vivo evaluation of doxorubicin-loaded polymeric micelles targeting folate receptors and early endosomal pH in drug-resistant ovarian cancer

The second generation of pH-sensitive micelles composed of poly(l-histidine-co-l-phenlyalanine(16 mol %))(MW:5K)-b-PEG(MW:2K) and poly(l-lactic acid)(MW:3K)-b-PEG(MW:2K)-folate (80/20 wt/wt %) was previously optimized by physicochemical and in vitro tests for both folate receptor and early endosomal pH targeting (pH approximately 6.0). In this study, the therapeutic efficacy of the doxorubicin (DOX)-loaded micelles (DOX loading content: 20 wt %) was evaluated using in vivo tests. Multidrug-resistant (MDR) ovarian tumor-xenografted mouse models were employed. The skin-fold dorsal window chamber model was applied for visualization of extravasation and drug retention for the initial one hour after iv injection. Noninvasive imaging followed, providing evidence of drug accumulation in the tumor after the first hour. The biodistribution study further supported the long circulation of the drug carrier, tumor-selective accumulation and intracellular drug delivery. Comprehensive tumor growth inhibition experiments examined the collective efficacy of the pH-sensitive micelles. The micelle formulation effectively suppressed the growth of existing MDR tumors in mice for at least 50 days by three iv injections at a 3-day interval at a dose of 10 mg of DOX/kg. The body weight of the animals treated with the test micelle formulation gradually increased over the experimental time period, rather than decreasing. The micelle formulation was superior to its first generation, which targeted pH 6.8 and folate receptor.

Environment-Responsive Polymers for Coating of Pharmaceutical Nanocarriers(,)

Polyethylene glycol derivatives, such as block copolymers of polyethylene glycol and diacyllipids (for example, phosphatidylethanolamine) are widely used for surface modification of various pharmaceutical carriers in order to impart them longevity in the body. To make polyethylene glycol detachable from the surface of pharmaceutical carrier and facilitate the interaction of the carrier with target cells when in pathological zone, we have prepared a set of polyethylene glycol-phosphatidylethanolamine block copolymers with the pH sensitive hydrazone bond between polyethylene glycol and phosphatidylethanolamine, which destabilizes at lowered pH values typical for tumors and inflammation zones. We have demonstrated that the stability of the hydrazone bond at normal physiological pH (7.4) as well as the rate of its hydrolysis at pH 6 and below strongly depend on the type of substitutions at this bond. Using aliphatic and aromatic aldehydes and ketones, polyethylene glycol-phosphatidylethanolamine block copolymers were prepared with different stabilities and degradation rates, which can be useful in constructing stimuli-sensitive pharmaceutical carriers.

pH-sensitive nanoparticles self-assembled from a novel class of biodegradable amphiphilic copolymers based on chitosan

A new type of biodegradable amphiphilic graft copolymers, PEG-g-hexanoyl chitosan, was synthesized by a facile scheme. The self-assemble properties of the copolymers were studied by TEM, fluorometry and dynamic light scattering. It was found that spherical nanoparticles of the copolymers could be formed through dialysis method. With the increase of PEG content in the copolymers, the average diameter of the nanoparticles decreased from about 180 to 40 nm. PEG fraction in the copolymers has little effect on the copolymer CAC. The micellization of the copolymers was strongly dependent of the medium pH. When pH was lowered from 7.2 to 6.8, the average diameter of the nanoparticles dramatically changed from about 180 to 60 nm.

Engineered polymers for advanced drug delivery

Engineered polymers have been utilized for developing advanced drug delivery systems. The development of such polymers has caused advances in polymer chemistry, which, in turn, has resulted in smart polymers that can respond to changes in environmental condition such as temperature, pH, and biomolecules. The responses vary widely from swelling/deswelling to degradation. Drug-polymer conjugates and drug-containing nano/micro-particles have been used for drug targeting. Engineered polymers and polymeric systems have also been used in new areas, such as molecular imaging as well as in nanotechnology. This review examines the engineered polymers that have been used as traditional drug delivery systems and as more recent applications in nanotechnology.

Multifunctional and stimuli-sensitive pharmaceutical nanocarriers

Currently used pharmaceutical nanocarriers, such as liposomes, micelles, and polymeric nanoparticles, demonstrate a broad variety of useful properties, such as longevity in the body; specific targeting to certain disease sites; enhanced intracellular penetration; contrast properties allowing for direct carrier visualization in vivo; stimuli-sensitivity, and others. Some of those pharmaceutical carriers have already made their way into clinic, while others are still under preclinical development. In certain cases, the pharmaceutical nanocarriers combine several of the listed properties. Long-circulating immunoliposomes capable of prolonged residence in the blood and specific target recognition represent one of the examples of this kind. The engineering of multifunctional pharmaceutical nanocarriers combining several useful properties in one particle can significantly enhance the efficacy of many therapeutic and diagnostic protocols. This paper considers the current status and possible future directions in the emerging area of multifunctional nanocarriers with primary attention on the combination of such properties as longevity, targetability, intracellular penetration, contrast loading, and stimuli-sensitivity.

Novel pH-responsive nanoparticles

In this work we report a new type of pH-responsive micelle-like nanoparticle. Reversible nanoscale structures are formed in solutions of a pH-sensitive hydrophobic polyelectrolyte, poly( N-methacryloyl- l-valine) or poly( N-methacryloyl- l-phenylalanine), and nonionic surfactant (Brij 98) in the presence of hydrochloric acid. The influence of composition and pH on particles size and shape was investigated by a variety of methods. An entity's size and polydispersity could be varied in a broad range making them a perspective candidate as a drug carrier. Unlike the case of typical micelles, our results indicate the presence of cavities in the formed particles. A hypothetical model of a nanoparticle and mechanism of formation are proposed.

Doxorubicin loaded pH-sensitive micelle: antitumoral efficacy against ovarian A2780/DOXR tumor

PURPOSE

To evaluate pH-sensitive mixed micelles for multidrug resistant (MDR) ovarian tumor targeting and optical imaging of solid tumors.

METHOD

Doxorubicin (DOX) encapsulated pH-sensitive mixed micelles composed of poly(L-histidine)(MW 5K)-b-PEG(MW 2K) and poly(L-lactic acid)(3K)-b-PEG (2K)-folate (PHSM-f) were prepared. Folate receptor-mediated endocytosis, drug uptake, endosomal disruption and cell viability were investigated at the cellular level. For in vivo tumor growth inhibition tests, multidrug resistant ovarian A2780/DOX(R) xenografted nude mice were used. Optical imaging was performed by using a Cy5.5 fluorescence dye-labeled mixed micelle system. Cy5.5 fluorescence intensity at the tumor site was measured in KB epidermoid xenografted nude mice.

RESULTS

In vitro cell viability and drug distribution in the cytoplasm demonstrated the significantly superior efficacy of PHSM-f to free DOX and a control sample of DOX loaded pH-insensitive micelle composed of poly(L-lactic acid)(3K)-b-PEG(2K)/poly(L-lactic acid)(3K)-b-PEG(2K)-folate (80/20 wt/wt%) (PHIM-f). The mechanisms of these results were proved by folate receptor mediated endocytosis of micelle and endosomal disruption function by it. In addition, the optical imaging demonstrated the future application of the diagnositic area. PHSM-f inhibited the growth of multidrug resistant ovarian tumors efficiently in mice, with minimum weight loss.

CONCLUSIONS

The pH-sensitive mixed micelle system demonstrates effective antitumor efficacy against the multidrug resistant ovarian tumor A2780/DOX(R).

Physicochemical aspects of doxorubicin-loaded pH-sensitive polymeric micelle formulations from a mixture of poly(L-histidine)-b-poly(ethylene glycol)/poly(L-lactide)-b-poly(ethylene glycol) [corrected]

In this study, doxorubicin (DOX) was physically incorporated into pH-sensitive micelles made from a mixture of poly(L-histidine)-b-poly(ethylene glycol)/poly(L-lactide)-b-poly(ethylene glycol) (75/25, wt.%). The DOX-loaded mixed micelles were formulated using dialysis methods and optimal DOX incorporation was achieved at a drug/polymer feed ratio of 0.2 (wt./wt.) when a proper amount of aqueous phase (0.2, v./v.) was added into the common solvent (DMSO) solution, followed by dialysis at 4 degrees C. Based on the results obtained from dynamic light scattering, UV-Vis absorption, and fluorescence experiments, it was demonstrated that the encapsulated drugs were mainly located inside the hydrophobic micelle cores, well protected and inaccessible to the exterior molecules. Under in vitro conditions, although the microstructure of the micelles was altered below pH 8.0 by the encapsulated drugs, the drug-loaded micelles still exhibited a desirable ability to control the drug release in response to tumor extracellular pH.

Recent progress in tumor pH targeting nanotechnology

pH-sensitive polymeric micelles and nanogels have recently been developed to target slightly acidic extracellular pH environment of solid tumors. The pH targeting approach is regarded as a more general strategy than conventional specific tumor cell surface targeting approaches, because the acidic tumor microclimate is most common in solid tumors. When nanosystems are combined with triggered release mechanisms by endosomal or lysosomal acidity plus endosomolytic capability, the nanocarriers demonstrated to overcome multidrug resistance of various tumors. This review highlights recent progress of the pH-sensitive nanotechnology developed in Bae research group.

Super pH-sensitive multifunctional polymeric micelle for tumor pH(e) specific TAT exposure and multidrug resistance

As an alternative to cell specific cancer targeting strategies (which are often afflicted with the heterogeneity of cancer cells as with most biological systems), a novel polymeric micelle constitute of two block copolymers of poly(L-lactic acid)-b-poly(ethylene glycol)-b-poly(L-histidine)-TAT (transactivator of transcription) and poly(L-histidine)-b-poly(ethylene glycol) was developed. The micelle formed via the dialysis method was approximately 95 nm in diameter and contained 15 wt.% of doxorubicin (DOX) by weight. The micelle surface hides TAT during circulation, which has the strong capability to translocate the micelle into cells, and exposes TAT at a slightly acidic tumor extracellular pH to facilitate the internalization process. The micelle core was engineered for disintegration in early endosomal pH of tumor cells, quickly releasing DOX. The ionization process of the block copolymers and ionized polymers assisted in disrupting the endosomal membrane. This processes permitted high DOX concentrations in the cytosol and its target site of the nucleus, thus increasing DOX potency in various wild and multidrug resistant (MDR) cell lines (3.8-8.8 times lower IC50 than free DOX, depending on cell line). When tested with the xenografted tumors of human ovarian tumor drug-resistant A2780/AD, human breast tumor drug-sensitive MCF-7, human lung tumor A549 and human epidermoid tumor KB in a nude mice model, all tumors significantly regressed in size by three bolus injections at a dose of DOX 10 mg equivalent/kg body per injection of DOX-loaded micelle at three day interval, while minimum weight loss was observed. This approach may replace the need for cell-specific antibodies or targeting ligands, thereby providing a general strategy for solid tumor targeting.

L-histidine-based pH-sensitive anticancer drug carrier micelle: reconstitution and brief evaluation of its systemic toxicity

A doxorubicin (DOX)-carrier micellar system consisting of poly(histidine)(5K)-b-poly(ethylene glycol)(2K) and poly(l-lactic acid)(3K)-b-PEG(2K)-folate has been developed targeting the early endosomal pH and it have been convincingly proved that intracellular high dose strategy using such micelles is effective in overcoming multidrug resistance (MDR) of cancer cells. Due to the low DOX concentrations in the micelle solution obtained by dialysis and the lack of long-term stability of the micelles, stable and lyophilized micelle formulations were the subject of investigation reported here by using excipients of sucrose, PEG or Pluronic. The reconstituted micelle solutions were examined by particle size, pH sensitivity, and cytotoxicity for MDR cells and the results were compared with the non-lyophilized micelles. Among tested excipients, Pluronic F127 (33 wt%) added to the polymer/drug solution prior to dialysis resulted in a reconstituted product stable for a week and presented equivalent benefits as the fresh micelle formulation. The blank micelles did not present any apparent systemic toxicity in mice up to 2400 mg/kg i.v. injection (800 mg/kg day) for 3 days). The brief toxicity of reconstituted DOX loaded micelles was examined by the maximum tolerated dose (MTD), which was approximately 7.5-fold higher than free DOX and guaranteeing further animal toxicity and efficacy study.