Filamentous, mixed micelles of triblock copolymers enhance tumor localization of indocyanine green in a murine xenograft model.

Polymeric micelles formed by the self-assembly of amphiphilic block copolymers can be used to encapsulate hydrophobic drugs for tumor-delivery applications. Filamentous carriers with high aspect ratios offer potential advantages over spherical carriers, including prolonged circulation times. In this work, mixed micelles composed of poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) and Pluronic F-127 (PF-127) were used to encapsulate a near-infrared fluorophore. The micelle formulations were assessed for tumor accumulation after tail vein injection to xenograft tumor-bearing mice by noninvasive optical imaging. The mixed micelle formulation that facilitated the highest tumor accumulation was shown by cryo-electron microscopy to be filamentous in structure compared to spherical structures of pure PF-127 micelles. In addition, increased dye loading efficiency and dye stability were attained in this mixed micelle formulation compared to pure PEO-PHB-PEO micelles. Therefore, the optimized PEO-PHB-PEO/PF-127 mixed micelle formulation offers advantages for cancer delivery over micelles formed from the individual copolymer components.

Evaluation of temperature-sensitive, indocyanine green-encapsulating micelles for noninvasive near-infrared tumor imaging.

PURPOSE: Indocyanine green (ICG), an FDA-approved near infrared (NIR) dye, has potential application as a contrast agent for tumor detection. Because ICG binds strongly to plasma proteins and exhibits aqueous, photo, and thermal instability, its current applications are largely limited to monitoring blood flow. To address these issues, ICG was encapsulated and stabilized within polymeric micelles formed from the thermo-sensitive block copolymer Pluronic F-127, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), to increase the stability and circulation time of ICG. METHODS: ICG-loaded Pluronic micelles were prepared at various concentrations of Pluronic and ICG and characterized by determining particle sizes, dye loading efficiency, and the kinetics of dye degradation. Förster resonance energy transfer spectroscopy was employed to monitor the stability of Pluronic micelles in physiological solutions. The plasma clearance kinetics and biodistribution of ICG-loaded micelles was also determined after intravenous delivery to CT-26 colon carcinoma tumor-bearing mice, and NIR whole-body imaging was performed for tumor detection. RESULTS: The Pluronic F-127 micelles showed efficient ICG loading, small size, stabilized ICG fluorescence, and prolonged circulation in vivo. Solid tumors in mice were specifically visualized after intravenous administration of ICG-loaded micelles. CONCLUSIONS: These materials are therefore promising formulations for noninvasive NIR tumor imaging applications.

Poly(lactic-co-glycolic) acid microspheres encapsulated in Pluronic F-127 prolong hirudin delivery and improve functional recovery from a demyelination lesion.

Components of the blood have been proposed as potential therapeutic targets for improving cellular regeneration after injury and neurodegenerative disease. In this work, thrombin is shown to increase endogenous neural progenitor proliferation in the intact murine spinal cord. A local injection of heparin before a spinal cord injury reduces cell proliferation and astrogliogenesis associated with scarring. We sought to create depot-formulations of PLGA microsphere and Pluronic F-127 for sustained local delivery of two thrombin inhibitors, heparin and hirudin. Each hydrogel depot-formulation showed delayed drug release compared to microspheres or hydrogel alone. Animals with a lateral demyelination lesion showed a reduction in CD68+ macrophages when treated with hirudin-loaded PLGA/F-127 gels compared to control and heparin-treated animals. Moreover, hirudin-loaded materials showed an accelerated recovery in coordinated stepping and increased oligodendrocyte densities. Together, these data demonstrate that controlled delivery of hirudin accelerates functional recovery from a demyelination lesion in the spinal cord.

pH-dependent, thermosensitive polymeric nanocarriers for drug delivery to solid tumors.

Polymeric micelles are promising carriers for anti-cancer agents due to their small size, ease of assembly, and versatility for functionalization. A current challenge in the use of polymeric micelles is the sensitive balance that must be achieved between stability during prolonged blood circulation and release of active drug at the tumor site. Stimuli-responsive materials provide a mechanism for triggered drug release in the acidic tumor and intracellular microenvironments. In this work, we synthesized a series of dual pH- and temperature-responsive block copolymers containing a poly(ε-caprolactone) (PCL) hydrophobic block with a poly(triethylene glycol) block that were copolymerized with an amino acid-functionalized monomer. The block copolymers formed micellar structures in aqueous solutions. An optimized polymer that was functionalized with 6-aminocaproic acid (ACA) possessed pH-sensitive phase transitions at mildly acidic pH and body temperature. Doxorubicin-loaded micelles formed from these polymers were stable at blood pH (~7.4) and showed increased drug release at acidic pH. In addition, these micelles displayed more potent anti-cancer activity than free doxorubicin when tested in a tumor xenograft model in mice.

The delivery of doxorubicin to 3-D multicellular spheroids and tumors in a murine xenograft model using tumor-penetrating triblock polymeric micelles.

Doxorubicin (DOX) is an effective chemotherapeutic against a wide range of solid tumors. However, its clinical use is limited by severe side effects such as cardiotoxicity as well as inherent and acquired drug resistance of tumors. DOX encapsulation within self-assembled polymeric micelles has the potential to decrease the systemic distribution of free drug and enhance the drug accumulation in the tumor via the enhanced permeability and retention (EPR). In this study, DOX was encapsulated in micelles composed of poly (ethylene oxide)-poly [(R)-3-hydroxybutyrate]-poly (ethylene oxide) (PEO-PHB-PEO) triblock copolymers. Micelle size, DOX loading and DOX release were characterized. To evaluate DOX activity, micelles were tested in both monolayer cell cultures and three-dimensional (3-D) multicellular spheroids (MCS) that mimic solid tumors. Antitumor activity in vivo was further studied with tumor-bearing mice. The micelles improved the efficiency of Dox penetration in 3-D MCS compared with free DOX. Efficient cell killing by Dox-micelles in both monolayer cells and 3-D MCS was also demonstrated. Finally, DOX-loaded micelles mediate efficient tumor delivery from tail vein injections to tumor-bearing mice with much less toxicity compared with free DOX.