Comparative study of paclitaxel physically encapsulated in and chemically conjugated with PEG-PLA

Synthesis of Polyethylene Glycol-Poly(glycerol carbonate) Block Copolymeric Micelles as Surfactant-Free Drug Delivery Systems

We report the synthesis of block copolymers of monomethoxylated polyethylene glycol and poly(glycerol carbonate) (mPEG-b-PGC) via the ring-opening polymerization of benzyl glycidyl ether, monomethoxylated polyethylene glycol, and carbon dioxide using a cobalt salen catalyst. The resulting block copolymers display high polymer/cyclic carbonate selectivity (>99%) and, if two oxirane monomers are used, random incorporation into the polymer feed. The resulting diblock mPEG-b-PGC polymer shows promise as a nanocarrier for surfactant-free, sustained chemotherapeutic delivery. mPEG-b-PGC, with paclitaxel conjugated to the pendant primary alcohol of the glycerol polymer backbone, readily forms 175 nm diameter particles in solution and contains 4.6 wt % paclitaxel (PTX), which is released over 42 days. The mPEG-b-PGC polymer itself is noncytotoxic, whereas the PTX-loaded nanoparticles are cytotoxic to lung, breast, and ovarian cancer cell lines.

Cisplatin and paclitaxel co-delivery nanosystem for ovarian cancer chemotherapy

We have designed and developed an effective drug delivery system using biocompatible polymer of poly (ethylene glycol)-polyaspartic acid (mPEG-PAsp) for co-loading the chemotherapy drugs paclitaxel (PTX) and cisplatin (CP) in one nano-vehicle. This study aimed to improve the anti-cancer efficacy of combinations of chemotherapy drugs and reduce their side effects. mPEG-PAsp-(PTX/Pt) nano-micelles disperse well in aqueous solution and have a narrow size distribution (37.8 ± 3.2 nm) in dynamic light scattering (DLS). Drug release profiles found that CP released at pH 5.5 was significantly faster than that at pH 7.4. MPEG-PAsp-(PTX/Pt) nano-micelles displayed a significantly higher tumor inhibitory effect than mPEG-PAsp-PTX nano-micelles when the polymer concentrations reached 50 μg/mL. Our data indicated that polymer micelles of mPEG-PAsp loaded with the combined drug exert synergistic anti-tumor efficacy on SKOV3 ovarian cells via different action mechanisms. Results from our studies suggested that mPEG-PAsp-(PTX/Pt) nano-micelles are promising alternatives for carrying and improving the delivery of therapeutic drugs with different water solubilities.

Clinical developments of antitumor polymer therapeutics

Polymer therapeutics encompasses polymer-drug conjugates that are nano-sized, multicomponent constructs already in the clinic as antitumor compounds, either as single agents or in combination with other organic drug scaffolds. Nanoparticle-based polymer-conjugated therapeutics are poised to become a leading delivery strategy for cancer treatments as they exhibit prolonged half-life, higher stability and selectivity, water solubility, longer clearance time, lower immunogenicity and antigenicity and often also specific targeting to tissues or cells. Compared to free drugs, polymer-tethered drugs preferentially accumulate in the tumor sites unlike conventional chemotherapy which does not discriminate between the cancer cells and healthy cells, thereby causing severe side-effects. It is also desirable that the drug reaches its site of action at a particular concentration and the therapeutic dose remains constant over a sufficiently long period of time. This can be achieved by opting for new formulations possessing polymeric systems of drug carriers. However, many challenges still remain unanswered in polymeric drug conjugates which need to be readdressed and therefore, can broaden the scope of this field. This review highlights some of the antitumor polymer therapeutics including polymer-drug conjugates, polymeric micelles, polymeric liposomes and other polymeric nanoparticles that are currently under investigation.

Building the design, translation and development principles of polymeric nanomedicines using the case of clinically advanced poly(lactide(glycolide))-poly(ethylene glycol) nanotechnology as a model: An industrial viewpoint

The design of the first polymeric nanoparticles could be traced back to the 1970s, and has thereafter received considerable attention, as evidenced by the significant increase of the number of articles and patents in this area. This review article is an attempt to take advantage of the existing literature on the clinically tested and commercialized biodegradable PLA(G)A-PEG nanotechnology as a model to propose quality building and outline translation and development principles for polymeric nano-medicines. We built such an approach from various building blocks including material design, nano-assembly - i.e. physicochemistry of drug/nano-object association in the pharmaceutical process, and release in relevant biological environment - characterization and identification of the quality attributes related to the biopharmaceutical properties. More specifically, as envisaged in a translational approach, the reported data on PLA(G)A-PEG nanotechnology have been structured into packages to evidence the links between the structure, physicochemical properties, and the in vitro and in vivo performances of the nanoparticles. The integration of these bodies of knowledge to build the CMC (Chemistry Manufacturing and Controls) quality management strategy and finally support the translation to proof of concept in human, and anticipation of the industrialization takes into account the specific requirements and biopharmaceutical features attached to the administration route. From this approach, some gaps are identified for the industrial development of such nanotechnology-based products, and the expected improvements are discussed. The viewpoint provided in this article is expected to shed light on design, translation and pharmaceutical development to realize their full potential for future clinical applications.

Synthesis of Polylactide-Based Core-Shell Interface Cross-Linked Micelles for Anticancer Drug Delivery

Well-defined poly(ethylene glycol)-b-allyl functional polylactide-b-polylactides (PEG-APLA-PLAs) are synthesized through sequential ring-opening polymerization. PEG-APLA-PLAs that have amphiphilic properties and reactive allyl side chains on their intermediate blocks are successfully transferred to core-shell interface cross-linked micelles (ICMs) by micellization and UV-initiated irradiation. ICMs have demonstrated enhanced colloidal stability in physiological-mimicking media. Hydrophobic molecules such as Nile Red or doxorubicin (Dox) are readily loaded into ICMs; the resulting drug-ICM formulations possess slow and sustained drug release profiles under physiological-mimicking conditions. ICMs exhibit negligible cytotoxicity in human uterine sarcoma cancer cells by using biodegradable aliphatic polyester as the hydrophobic segments. Relative to free Dox, Dox-loaded ICMs show a reduced cytotoxicity due to the late intracellular release of Dox from ICMs. Overall, ICMs represent a new type of biodegradable cross-linked micelle and can be employed as a promising platform for delivering a broad variety of hydrophobic drugs.

PEG based anti-cancer drug conjugated prodrug micelles for the delivery of anti-cancer agents

Development of polymer prodrug conjugates has evolved recently in the nano-medicine field for cancer diagnosis and treatment. This review focuses on the development of different types of PEG based polymer drug conjugates used for the delivery of anti-cancer agents.

Poly(d,l-lactic acid)-block-poly(N-(2-hydroxypropyl)methacrylamide) nanoparticles for overcoming accelerated blood clearance and achieving efficient anti-tumor therapy

The substitution of PEG with PHPMA maintained the long circulation of PDLLA-b-PEG and alleviated the accelerated blood clearance (ABC).

Self-assembled 20-nm (64)Cu-micelles enhance accumulation in rat glioblastoma

There is an urgent need to develop nanocarriers for the treatment of glioblastoma multiforme (GBM). Using co-registered positron emission tomography (PET) and magnetic resonance (MR) images, here we performed systematic studies to investigate how a nanocarrier's size affects the pharmacokinetics and biodistribution in rodents with a GBM xenograft. In particular, highly stable, long-circulating three-helix micelles (3HM), based on a coiled-coil protein tertiary structure, were evaluated as an alternative to larger nanocarriers. While the circulation half-life of the 3HM was similar to 110-nm PEGylated liposomes (t1/2=15.5 and 16.5h, respectively), the 20-nm micelles greatly enhanced accumulation within a U87MG xenograft in nu/nu rats after intravenous injection. After accounting for tumor blood volume, the extravasated nanoparticles were quantified from the PET images, yielding ~0.77%ID/cm(3) for the micelles and 0.45%ID/cm(3) for the liposomes. For GBM lesions with a volume greater than 100mm(3), 3HM accumulation was enhanced both within the detectable tumor and in the surrounding brain parenchyma. Further, the nanoparticle accumulation was shown to extend to the margins of the GBM xenograft. In summary, 3HM provides an attractive nanovehicle for carrying treatment to GBM.

Polymeric micelles and nanoemulsions as tumor-targeted drug carriers: Insight through intravital imaging

Intravital imaging of nanoparticle extravasation and tumor accumulation has revealed, for the first time, detailed features of carrier and drug behavior in circulation and tissue that suggest new directions for optimization of drug nanocarriers. Using intravital fluorescent microscopy, the extent of the extravasation, diffusion in the tissue, internalization by tissue cells, and uptake by the RES system were studied for polymeric micelles, nanoemulsions, and nanoemulsion-encapsulated drug. Discrimination of vascular and tissue compartments in the processes of micelle and nanodroplet extravasation and tissue accumulation was possible. A simple 1-D continuum model was suggested that allowed discriminating between various kinetic regimes of nanocarrier (or released drug) internalization in tumors of various sizes and cell density. The extravasation and tumor cell internalization occurred much faster for polymeric micelles than for nanoemulsion droplets. Fast micelle internalization resulted in the formation of a perivascular fluorescent coating around blood vessels. A new mechanism of micelle extravasation and internalization was suggested, based on the fast extravasation and internalization rates of copolymer unimers while maintaining micelle/unimer equilibrium in the circulation. The data suggested that to be therapeutically effective, nanoparticles with high internalization rate should manifest fast diffusion in the tumor tissue in order to avoid generation of concentration gradients that induce drug resistance. However an extra-fast diffusion should be avoided as it may result in the flow of extravasated nanoparticles from the tumor to normal organs, which would compromise targeting efficiency. The extravasation kinetics were different for nanodroplets and nanodroplet-encapsulated drug F-PTX suggesting a premature release of some fraction of the drug from the carrier. In conclusion, the development of an "ideal" drug carrier should involve the optimization of both drug retention and carrier diffusion parameters.

Drug delivery vehicles on a nano-engineering perspective

Nanoengineered drug delivery systems (nDDS) have been successfully used as clinical tools for not only modulation of pharmacological drug release profile but also specific targeting of diseased tissues. Until now, encapsulation of anti-cancer molecules such as paclitaxel, vincristin and doxorubicin has been the main target of nDDS, whereby liposomes and polymer-drug conjugates remained as the most popular group of nDDS used for this purpose. The success reached by these nanocarriers can be imitated by careful selection and optimization of the different factors that affect drug release profile (i.e. type of biomaterial, size, system architecture, and biodegradability mechanisms) along with the selection of an appropriate manufacture technique that does not compromise the desired release profile, while it also offers possibilities to scale up for future industrialization. This review focuses from an engineering perspective on the different parameters that should be considered before and during the design of new nDDS, and the different manufacturing techniques available, in such a way to ensure success in clinical application.

Rational design of multifunctional upconversion nanocrystals/polymer nanocomposites for cisplatin (IV) delivery and biomedical imaging

By combining upconversion nanoparticles with the cisplatin (IV) prodrug we have demonstrated that a stable and multifunctional drug delivery system can be designed that will both reduce the drawbacks of cisplatin and give insight in to its in vitro/in vivo imaging. The up/down-conversion fluorescence are detectable and show obvious co-localization, demonstrating that the nanoparticles are rather stable inside cells and retain the UCNPs and block copolymer.

Biodegradable polymer - cisplatin(IV) conjugate as a pro-drug of cisplatin(II)

A Pt(IV) complex was covalently conjugated to a new biodegradable amphiphilic tri-block copolymer, MPEG-b-PCL-b-PLL, which contains pendant amino groups, to form a polymeric pro-drug of cisplatin(II), MPEG-b-PCL-b-PLL/Pt(IV). The conjugate was assembled into nano-micelles. The Pt(IV) complex, the polymer carrier and the conjugate were characterized systematically. In vitro release experiments showed that drug release from the polymer-Pt(IV) micelles follows an acid responsive and oxidation-reduction sensitive kinetics. HPLC-ICP-MS analysis revealed that cisplatin(II) can be released from the conjugate under an acidic plus a reductive condition which is available inside a cancerous cell. In vitro MTT assay demonstrated that the polymer-Pt(IV) micelles display higher cytotoxicity against SKOV-3 tumor cells than both cisplatin(II) and Pt(IV) complex. This enhanced cytotoxicity is attributed to effective internalization of the micelles by the cells via endocytosis mechanism, which was observed by fluorescence imaging and by direct determination of the platinum uptake by the cells. This polymer-Pt(IV) conjugate is a promising polymeric pro-drug of cisplatin in micellar form. It can protect the Pt(IV) complex against blood clearance. It can enter cancerous cells via endocytosis mechanism and then cisplatin(II) can be released. Therefore, this polymeric pro-drug of cisplatin is expected to find clinical applications in the future.

Encapsulation and release of Amphotericin B from an ABC triblock fluorous copolymer

PURPOSE

PEG-phospholipid-based micelles have been successfully used for the solubilization of several hydrophobic drugs but generally lack sustained stability in blood. Our novel PEG-Fluorocarbon-DSPE polymers were designed to increase stability and improve time-release properties of drug-loaded micelles.

METHODS

Novel ABC fluorous copolymers were synthesized, characterized, and used for encapsulation release of amphotericin B. FRET studies were used to study micelle stability.

RESULTS

The micelles formed by the new polymers showed lower critical micelle concentrations and higher viscosity cores than those formed by the polymers lacking the fluorous block. FRET studies indicated that fluorocarbon-containing micelles had increased stability in presence of human serum. Physicochemical properties and in vitro release profile of micelles loaded with Amphotericin B (AmB) were studied.

CONCLUSIONS

The effect of PEG length and fluorocarbon incorporation were investigated. The shorter hydrophilic PEG2K induced greater stability than PEG5K by decreasing the proportion of hydrophilic block of the polymer. The fluorocarbon placed between hydrophilic and hydrophobic block formed a fluorous shell contributing to the enhanced thermodynamic stability of micelles and to the drug sustained release. Polymer mPEG2K-F(10)-DSPE, bearing both a fluorocarbon block and a shorter mPEG, showed the greatest stability and the longest half-life for AmB release.