Development of a Gadolinium-Boron-Conjugated Albumin for MRI-Guided Neutron Capture Therapy.

Noninvasive monitoring of boron agent biodistribution is required in advance of neutron capture therapy. In this study, we developed a gadolinium-boron-conjugated albumin (Gd-MID-BSA) for MRI-guided neutron capture therapy. Gd-MID-BSA was prepared by labeling bovine serum albumin with a maleimide-functionalized gadolinium complex and a maleimide-functionalized closo-dodecaborate orthogonally. The accumulation of Gd-MID-BSA in tumors in CT26 tumor-bearing mice reached a maximum at 24 h after the injection, as confirmed by T1-based MRI and biodistribution analysis using inductively coupled plasma optical emission spectrometry. The concentrations of boron and gadolinium in the tumors exceeded the thresholds required for boron neutron capture therapy (BNCT) and gadolinium neutron capture therapy (GdNCT), respectively. The boron concentration ratios of tumor to blood and tumor to normal tissues satisfied the clinical criteria, indicating the reduction of undesired nuclear reactions of endogenous nuclei. The molar ratio of boron to gadolinium in the tumor was close to that of Gd-MID-BSA, demonstrating that the accumulation of Gd-MID-BSA in the tumor can be evaluated by MRI. Thermal neutron irradiation with Gd-MID-BSA resulted in significant suppression of tumor growth compared to the group injected with a boron-conjugated albumin without gadolinium (MID-BSA). The neutron irradiation with Gd-MID-BSA did not cause apparent side effects. These results demonstrate that the conjugation of gadolinium and boron within the albumin molecule offers a novel strategy for enhancing the therapeutic effect of BNCT and the potential of MRI-guided neutron capture therapy as a promising treatment for malignant tumors.

Eliminating microscopic lymph node metastasis by performing pelvic lymph node dissection during radical prostatectomy for prostate cancer.

The oncological benefit of pelvic lymph node dissection (PLND) for prostate cancer (PCa) remains unclear. The therapeutic effect of PLND on the elimination of microscopic metastases during radical prostatectomy (RP) for PCa was examined in the current study. A total of 348 Japanese patients with high- or intermediate-risk PCa without lymph node metastasis, who underwent antegrade RP at the Kyushu Cancer Center (Fukuoka, Japan) between August 1998 and May 2013 were retrospectively analyzed. The patients were divided into the standard (obturator + internal iliac nodes) group and the expanded (standard + additional nodes) group according to the extent of PLND. Preoperative and postoperative characteristics were also analyzed to determine the factors associated with prostate-specific antigen (PSA) failure. Standard and expanded PLND were performed in 70.9% (247/348) and 29.1% (101/348) of cases, respectively. The results revealed that preoperative PSA levels were the only marked difference between the two groups. No differences were observed in the other preoperative and postoperative characteristics. Furthermore, the rate of PSA recurrence in each group did not differ to a statistically significant extent (P=0.3622). Reducing the area of dissection from expanded PLND to standard PLND significantly reduced the number of dissected lymph nodes (P<0.0001). Additionally, the PSA level, clinical tumor stage, Gleason score of the biopsy specimen, pathological tumor stage and extent of PLND were all associated with PSA recurrence, as determined via multivariate Cox hazards regression analysis (P=0.0177, P=0.0023, P=0.0027, P<0.0001 and P=0.0164, respectively). In high- and intermediate-risk patients without lymph node metastasis, a greater number of lymph nodes were dissected when the extent of dissection was greater. Furthermore, the extent of PLND was a significantly associated with PSA failure. The results indicated that PLND exerted a therapeutic effect by eliminating microscopic pelvic lymph node metastases that were not detected by routine pathological examinations.

Stability evaluation of Gd chelates for macromolecular MRI contrast agents.

OBJECTIVE: We try to establish designs for the macromolecular agents possessing high Gd3+-chelating stability, because free Gd3+ ion released from Gd chelates is known as a risk factor to cause toxic side effects and a safety concern. MATERIALS AND METHODS: We prepared three types of Gd-based macromolecular MRI contrast agents from a synthetic polymer (poly(glutamic acid) homopolymer or poly(ethylene glycol)-b-poly(lysine) block copolymer) and a chelating moiety (DO3A or DOTA) having two strategic designs for high chelate stability. Then, we examine the in vitro Gd3+-chelate stability of these macromolecular MRI contrast agents. RESULTS: The prepared macromolecular agents exhibited the same or higher Gd3+-chelate stability as/than did Gd-DOTA that possesses the highest Gd3+-chelate stability among the approved small-MW Gd-chelate MRI contrast agent. DISCUSSION: Our macromolecular design was considered to work well for high Gd3+-chelate stability.

Toxicity and immunogenicity concerns related to PEGylated-micelle carrier systems: a review.

Polymeric-micelle carrier systems have emerged as a novel drug-carrier system and have been actively studied for anticancer drug targeting. In contrast, toxicological and immunological concerns related to not only polymeric-micelle carrier systems, but also other nanocarrier systems, have received little attention owing to researchers' focus on therapeutic effects. However, in recent clinical contexts, biopharmaceuticals' effects on immune responses have come to light, requiring that researchers substantively explore the potential negative side effects of nanocarrier systems and of therapeutic proteins in order to develop nanocarrier systems suitable for clinical use. The present review describes current insights into both toxicological and immunological issues regarding polymeric-micelle carrier systems. The review focuses on immunogenicity issues of polymeric-micelle carrier systems possessing poly(ethylene glycol) (PEG). We conclude that PEG-related immunogenicity is deeply related to characteristics of a counterpart block of PEG-conjugates, and we propose future directions for addressing this unresolved issue.

PEG-poly(L-lysine)-based polymeric micelle MRI contrast agent: Feasibility study of a Gd-micelle contrast agent for MR lymphography.

PURPOSE: To investigate the feasibility of polymeric micelle of poly(ethyleneglycol) (PEG)-b-poly(L-lysine-DOTA) (Gd-micelle) as a contrast agent for magnetic resonance lymphography (MRL). MATERIALS AND METHODS: Twenty-four female BALB/c mice were randomly divided into four groups of six mice each. Among them, mice of two groups were injected of complete Freund's adjuvant to obtain inflamed lymph nodes. We subcutaneously injected 0.5 µmol Gd per mouse of Gd-micelle or gadofluorine P in the right rear footpad. Identical 3D T1 -weighted gradient-echo imaging (1T MRI system) were subsequently obtained to create time-intensity curves of the right popliteal, sacral, and lumbar-aortic lymph nodes and to measure the contrast ratios (CRs). The peak CR, area under the curve (AUC), and elimination half-life (T1/2 ) of CR of the popliteal lymph node were assessed by two-way factorial analysis of variance. We also performed a qualitative assessment of normal and inflamed lymph node at three timepoints. RESULTS: The mean peak CR of Gd-micelle was 2.64 and 1.89 for gadofluorine P in normal mice, and 3.48 and 2.73 in the inflamed lymph node. Statistically, peak CR was higher for Gd-micelle (P = 0.004). In addition, the AUC was larger (P < 0.001) and T1/2 was longer (P < 0.001) for Gd-micelle. In qualitative assessment, Gd-micelle demonstrated the same or higher scores in every lymph node, and demonstrated a higher score in lumbar-aortic lymph node of a 360-minute image (P = 0.006) and in inflamed lymph node of a 360-minute image (P = 0.009). CONCLUSION: Compared to gadofluorine P, Gd-micelle showed higher and more prolonged enhancement in MRL imaging in normal and inflamed lymph nodes. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:238-245.

A polymeric micelle magnetic resonance imaging (MRI) contrast agent reveals blood-brain barrier (BBB) permeability for macromolecules in cerebral ischemia-reperfusion injury.

Blood-brain barrier (BBB) opening is a key phenomenon for understanding ischemia-reperfusion injuries that are directly linked to hemorrhagic transformation. The recombinant human tissue-type plasminogen activator (rtPA) increases the risk of symptomatic intracranial hemorrhages. Recent imaging technologies have advanced our understanding of pathological BBB disorders; however, an ongoing challenge in the pre-"rtPA treatment" stage is the task of developing a rigorous method for hemorrhage-risk assessments. Therefore, we examined a novel method for assessment of rtPA-extravasation through a hyper-permeable BBB. To examine the image diagnosis of rtPA-extravasation for a rat transient occlusion-reperfusion model, in this study we used a polymeric micelle MRI contrast-agent (Gd-micelles). Specifically, we used two MRI contrast agents at 1h after reperfusion. Gd-micelles provided very clear contrast images in 15.5±10.3% of the ischemic hemisphere at 30min after i.v. injection, whereas a classic gadolinium chelate MRI contrast agent provided no satisfactorily clear images. The obtained images indicate both the hyper-permeable BBB area for macromolecules and the distribution area of macromolecules in the ischemic hemisphere. Owing to their large molecular weight, Gd-micelles remained in the ischemic hemisphere through the hyper-permeable BBB. Our results indicate the feasibility of a novel clinical diagnosis for evaluating rtPA-related hemorrhage risks.

Photo Irradiation-Induced Core Crosslinked Poly(ethylene glycol)-block-poly(aspartic acid) Micelles: Optimization of Block Copolymer Synthesis and Characterization of Core Crosslinked Micelles.

We used photo irradiation to design core crosslinked polymeric micelles whose only significant physico-chemical change was in their physico-chemical stability, which helps elucidate poly(ethylene glycol) (PEG)-related immunogenicity. Synthetic routes and compositions of PEG-b-poly(aspartic acid) block copolymers were optimized with the control of n-alkyl chain length and photo-sensitive chalcone moieties. The conjugation ratio between n-alkyl chain and the chalcone moieties was controlled, and upon the mild photo irradiation of polymeric micelles, permanent crosslink proceeded in the micelle cores. In the optimized condition, the core crosslinked (CCL) micelles exhibited no dissociation while the non-CCL micelles exhibited dissociation. These results indicate that the photo-crosslinking reactions in the inner core were successful. A gel-permeation chromatography (GPC) measurement revealed a difference between the micellar-formation stability of CCL micelles and that of the non-CCL micelles. GPC experiments revealed that the CCL micelles were more stable than the non-CCL micelles. Our research also revealed that photo-crosslinking reactions did not change the core property for drug encapsulation. In conclusion, the prepared CCL micelles exhibited the same diameter, the same formula, and the same inner-core properties for drug encapsulation as did the non-CCL micelles. Moreover, the CCL micelles exhibited non-dissociable micelle formation, while the non-CCL micelles exhibited dissociation into single block copolymers.

Exploring the relationship between anti-PEG IgM behaviors and PEGylated nanoparticles and its significance for accelerated blood clearance.

Surface PEGylation on nanoparticles has greatly helped prolong their blood circulation half-lives. However, The injection of PEGylated nanoparticles into mice induced poly(ethylene glycol) (PEG)-specific IgM antibodies (anti-PEG IgMs), significantly changing PEG-liposomes' pharmacokinetics. In this study, we used various PEG-conjugates to conduct a mechanistic study of anti-PEG IgMs' binding behavior. The conventional belief has been that anti-PEG IgMs bind to PEG main chains; however, our findings reveal that anti-PEG IgMs did not bind to PEG main chains, whereas anti-PEG IgMs did bind to PEG-hydrophobic polymer blocks. The insertion of a hydrophilic polymer between each PEG chain and each hydrophobic polymer block suppressed anti-PEG IgMs' binding. We prove here that hydrophobic blocks are essential to anti-PEG IgMs' binding, and also that anti-PEG IgMs do not bind to intact PEGs without hydrophobic moiety. These results support our conclusion that anti-PEG IgMs exhibit specificity to PEG; however, the presence of a hydrophobic block at a proximity position from each PEG chain is essential for the binding. Also in the present study, we elucidate relations between anti-PEG IgMs and PEGylated nanoparticles. In one of our previous studies, anti-PEG IgMs scarcely affected the pharmacokinetics of PEG-b-poly(ß-benzyl l-aspartate) block copolymer (PEG-PBLA) micelles, whereas anti-PEG IgMs significantly decreased PEG-liposomes' blood circulation half-life. Finally, we found that the ratio of anti-PEG IgM molecules to PEG-liposome particles is critical to these pharmacokinetic changes, and that a 10-fold increase in the number of anti-PEG IgM molecules permitted them to capture the PEG-liposome particles, thus leading to the aforementioned changes.

Determination of polymeric micelles' structural characteristics, and effect of the characteristics on pharmacokinetic behaviors.

We evaluated structural factors characterizing PEG-b-P(Asp-Bzl) micelles including core size, aggregation number (Nagg), and core surface PEG density by means of small-angle X-ray scattering (SAXS), field flow fractionation with multi-angle light scattering (FFF-MALS) analysis, and DLS. Furthermore, we evaluated the stability of PEG-b-P(Asp-Bzl) micelles by means of GPC. This paper reports the correlation between the evaluated micelles' structural factors and the micelles' behaviors including the micelles' in vivo pharmacokinetic behaviors. One micelle PEG(12)-b-P(Asp-Bzl) (PEG=12,000) exhibited a high core surface density (~0.99 chain/nm(2)). In these circumstances, PEG(12)-b-P(Asp-Bzl) micelles exhibited a highly stretched PEG brush form. However, the evaluated core surface PEG densities could not fully explain the micelles' in vivo pharmacokinetic behaviors. In contrast, GPC will become a strong tool for predicting PEG(12)-b-P(Asp-Bzl) micelles' in vivo behaviors, as well as the micelles' in vitro behaviors. The stability results correlated strongly with the area-under-the-curve (AUC) values of PEG-b-P(Asp-Bzl) micelles' in vivo pharmacokinetics. Finally, we evaluated PEG(12)-b-P(Asp-Bzl) micelles' most effective structural factor for determining the micelles' behaviors, and the micelles' outermost shell surface's PEG density (DOS, PEG) correlated with the micelles' behaviors. We revealed that the evaluated DOS, PEG is the most important factor for understanding PEG(12)-b-P(Asp-Bzl) micelles' behaviors.

Effects of silica and titanium oxide particles on a human neural stem cell line: morphology, mitochondrial activity, and gene expression of differentiation markers.

Several in vivo studies suggest that nanoparticles (smaller than 100 nm) have the ability to reach the brain tissue. Moreover, some nanoparticles can penetrate into the brains of murine fetuses through the placenta by intravenous administration to pregnant mice. However, it is not clear whether the penetrated nanoparticles affect neurogenesis or brain function. To evaluate its effects on neural stem cells, we assayed a human neural stem cell (hNSCs) line exposed in vitro to three types of silica particles (30 nm, 70 nm, and <44 µm) and two types of titanium oxide particles (80 nm and < 44 µm). Our results show that hNSCs aggregated and exhibited abnormal morphology when exposed to the particles at concentrations = 0.1 mg/mL for 7 days. Moreover, all the particles affected the gene expression of Nestin (stem cell marker) and neurofilament heavy polypeptide (NF-H, neuron marker) at 0.1 mg/mL. In contrast, only 30-nm silica particles at 1.0 mg/mL significantly reduced mitochondrial activity. Notably, 30-nm silica particles exhibited acute membrane permeability at concentrations =62.5 µg/mL in 24 h. Although these concentrations are higher than the expected concentrations of nanoparticles in the brain from in vivo experiments in a short period, these thresholds may indicate the potential toxicity of accumulated particles for long-term usage or continuous exposure.

Folate-targeted gadolinium-lipid-based nanoparticles as a bimodal contrast agent for tumor fluorescent and magnetic resonance imaging.

To enhance tumor magnetic resonance imaging (MRI) signals via the selective accumulation of contrast agents, we prepared folate-modified gadolinium-lipid-based nanoparticles as MRI contrast agents. Folate-modified nanoparticles were comprised of polyethylene glycol (PEG)-lipid, gadolinium diethylenetriamine pentaacetic acid lipid, cationic cholesterol derivatives, folate-conjugated PEG-lipid, and Cy7-PEG-lipid. Folate receptor-mediated cellular nanoparticle association was examined in KB cells, which overexpress the folate receptor. The biodistribution of nanoparticles after their intravenous injection into KB tumor-bearing mice was measured. Mice were imaged through in vivo fluorescence imaging and MRI 24 h after nanoparticle injection, and the intensity enhancement of the tumor MRI signal was evaluated. Increased cellular association of folate-modified nanoparticles was inhibited by excess free folic acid, indicating that nanoparticle association was folate receptor-mediated. Irrespective of folate modification, the amount of nanoparticles in blood 24 h after injection was ca. 10% of the injected dose. Compared with non-modified nanoparticles, folate-modified nanoparticles exhibited significant accumulation in tumor tissues without altering other biodistribution, as well as enhanced tumor fluorescence and MRI signal intensity. The results support the feasibility of MRI- and in vivo fluorescence imaging-based tumor visualization using folate-modified nanoparticles and provide opportunities to develop folate targeting-based imaging applications.

[Utilization of polymeric micelle magnetic resonance imaging (MRI) contrast agent for theranostic system].

We applied a polymeric micelle carrier system for the targeting of a magnetic resonance imaging (MRI) contrast agent. Prepared polymeric micelle MRI contrast agent exhibited a long circulation characteristic in blood, and considerable amount of the contrast agent was found to accumulate in colon 26 solid tumor by the EPR effect. The signal intensities of tumor area showed 2-folds increase in T1-weighted images at 24 h after i.v. injection. To observe enhancement of the EPR effect by Cderiv pretreatment on tumor targeting, we used the contrast agent for the evaluation by means of MRI. Cderiv pretreatment significantly enhanced tumor accumulation of the contrast agent. Interestingly, very high signal intensity in tumor region was found at 24 h after the contrast agent injection in Cderiv pretreated mice. The contrast agent visualized a microenvironmental change in tumor. These results indicate that the contrast agent exhibits potential use for tumor diagnostic agent. To combine with a polymeric micelle carrier system for therapeutic agent, the usage of the combination makes a new concept of "theranostic" for a better cancer treatment.

Polymeric micelles possessing polyethyleneglycol as outer shell and their unique behaviors in accelerated blood clearance phenomenon.

Polymeric micelles are assemblies of synthetic polymers and have been studied and developed as drug carriers for targeting. Polymeric micelles are composed of the inner core and the outer shell, and typically form from AB-type block copolymers in which two polymer blocks are connected in a tandem form. Polyethyleneglycol (PEG) has been most commonly used as one polymer block composing the outer shell. This review describes the reasons that PEG is used for the outer shell of the polymeric micelle carrier systems. On the other hand, accelerated blood clearance (ABC) phenomenon is a well-known immunological response of PEG-coated liposomes. Since the ABC phenomenon greatly influences targeting functions of carrier systems, elaborative studies on polymeric micelles' ABC phenomenon have been done, and revealed different behaviors of the polymeric micelle systems from those of PEG-coated liposomes. These studies indicate that polymeric micelle systems are highly feasible tools for contrast agent targeting as well as theranostics.

Hydrophobic molecules infiltrating into the poly(ethylene glycol) domain of the core/shell interface of a polymeric micelle: evidence obtained with anomalous small-angle X-ray scattering.

Polymeric micelles have been extensively studied as nanoscale drug carriers. Knowing the inner structure of polymeric micelles that encapsulate hydrophobic drugs is important to design effective carriers. In our study, the hydrophobic compound tetrabromocathecol (TBC) was chosen as a drug-equivalent model molecule. The bromine atoms in TBC act as probes in anomalous small-angle X-ray scattering (ASAXS) allowing for its localization in the polymeric micelles whose shape and size were determined by normal small-angle X-ray scattering (SAXS). Light scattering measurements coupled with field flow fractionation were also carried out to determine the aggregation number of micelles. A core-corona spherical model was used to explain the shape of the micelles, while the distribution of bromine atoms was explained with a hard-sphere model. Interestingly, the radius of the spherical region populated with bromine atoms was larger than the one of the sphere corresponding to the hydrophobic core of the micelle. This result suggests that the TBC molecules infiltrate the PEG hydrophilic domain in the vicinity of the core/shell interface. The results of light scattering and SAXS indicate that the PEG chains at the shell region are densely packed, and thus the PEG domain close to the interface has enough hydrophobicity to tolerate the presence of hydrophobic compounds.

Hydrophobic blocks of PEG-conjugates play a significant role in the accelerated blood clearance (ABC) phenomenon.

Injections of poly(ethylene glycol)-modified liposomes (PEG-liposomes) cause rapid clearance of the second dose of PEG-liposomes. This phenomenon is known as the accelerated blood clearance (ABC) phenomenon. Previous studies have suggested that PEG-specific IgM (anti-PEG IgM) can play a major role in the ABC phenomenon. In our previous study, however, a PEG-shell-possessing polymeric micelle with hydrophilic inner core (PEG-P(Lys-DOTA-Gd) micelle) did not induce the ABC phenomenon nor the IgM responses, and exhibited no change in its plasma concentration in PEG-liposome-injected mice. In the present paper, we studied the ABC-phenomenon in more detail by comparing the behaviors between PEG-liposomes, PEG-P(Lys-DOTA-Gd) micelle, and hydrophobic-core-possessing PEG-PBLA micelles. We demonstrated that the PEG-PBLA micelle induced similar IgM responses as observed in PEG-liposome; however, the second dose of PEG-PBLA micelle exhibited no decreases in their plasma concentration, while the second dose of PEG-liposome did exhibit rapid clearances. Furthermore, we did not observe any PEG main chain specific IgM in PEG-liposome injected mice by sandwich ELISA which can measure more specific IgM to the PEG main chain theoretically. These results suggested that the induced IgM recognizes an interface between PEG chain and hydrophobic chain, rather than PEG main chain, and the anti-PEG IgM hypothesis should be re-evaluated.

Partial splenic embolisation using n-butyl cyanoacrylate: intraprocedural evaluation by magnetic resonance imaging.

OBJECTIVES: To evaluate the use of diffusion-weighted imaging (DWI) for estimating infarcted splenic volume during partial splenic embolisation (PSE) using n-butyl cyanoacrylate (NBCA). METHODS: Twenty consecutive patients (57.2 ± 11.7 years) with hypersplenism underwent PSE. Intrasplenic branches were embolised using NBCA via a 2.1-French microcatheter aiming at infarction of 50 to 80 % of total splenic volume. Immediately after PSE, signal intensities (SI) of embolised and non-embolised splenic parenchyma were measured on DWI. Semi-automated volumetry (SAV) on DWI was compared with conventional manual volumetry (MV) on contrast-enhanced CT 1 week after PSE. Platelet counts were recorded before and after PSE. RESULTS: The SI on DWI in the embolised parenchyma decreased significantly (P < 0.01) to 24.7 ± 8.1 % as compared to non-embolised parenchyma. SAV and MV showed a strong correlation (r = 0.913 before PSE, r = 0.935 after PSE, P < 0.01) and significant (P < 0.01) reduction of normal splenic volume was demonstrated on both SAV (71.9 ± 12.4 %) and MV (73.6 ± 9.3 %) after PSE. Based on the initial SAV, three patients (15 %) underwent additional branch embolisation to reach sufficient infarction volume. Platelet counts elevated significantly (522.8 ± 209.1 %, P < 0.01) by 2 weeks after PSE. No serious complication was observed. CONCLUSION: Immediate SI changes on DWI after PSE allowed semi-automated splenic volumetry on site. KEY POINTS: • Partial splenic embolisation (PSE) is an important interventional technique for hypersplenism • Diffusion-weighted MR reveals an immediate decrease in signal in the embolised parenchyma • Such signal reduction permits semi-automated splenic volumetry on site. • This allows precise quantification of the amount of parenchyma infarcted, avoiding additional PSE.

Development of high boron content liposomes and their promising antitumor effect for neutron capture therapy of cancers.

Mercaptoundecahydrododecaborate (BSH)-encapsulating 10% distearoyl boron lipid (DSBL) liposomes were developed as a boron delivery vehicle for neutron capture therapy. The current approach is unique because the liposome shell itself possesses cytocidal potential in addition to its encapsulated agents. BSH-encapsulating 10% DSBL liposomes have high boron content (B/P ratio: 2.6) that enables us to prepare liposome solution with 5000 ppm boron concentration. BSH-encapsulating 10% DSBL liposomes displayed excellent boron delivery efficacy to tumor: boron concentrations reached 174, 93, and 32 ppm at doses of 50, 30, and 15 mg B/kg, respectively. Magnescope was also encapsulated in the 10% DSBL liposomes and the real-time biodistribution of the Magnescope-encapsulating DSBL liposomes was measured in a living body using MRI. Significant antitumor effect was observed in mice injected with BSH-encapsulating 10% DSBL liposomes even at the dose of 15 mg B/kg; the tumor completely disappeared three weeks after thermal neutron irradiation ((1.5-1.8) × 10(12) neutrons/cm(2)). The current results enabled us to reduce the total dose of liposomes to less than one-fifth compared with that of the BSH-encapsulating liposomes without reducing the efficacy of boron neutron capture therapy (BNCT).

Composition dependence of the micellar architecture made from poly(ethylene glycol)-block-poly(partially benzyl-esterified aspartic acid).

Poly(ethylene glycol)-block-poly(partially benzyl-esterified aspartic acid), denoted by PEG-P(Asp(Bzl)), is one of the most examined blockcopolymers for drug carriers. However, little is known about fundamental physical properties. Nine samples of PEG-P(Asp(Bzl)) with different benzylation fractions (F(Bzl)) and aspartic chain lengths (DP(Asp)) were synthesized, and the aggregation number (N(agg)), core radius (R(C)), and other structural parameters were determined with combination of light scattering and synchrotron X-ray small-angle scattering. The major factor to determine N(agg) and R(C) was found to be F(Bzl), i.e., the hydrophobic nature of the core, even though F(Bzl) was changed in the relatively small composition range from 66 to 89 mol %. When we compared the data for the same F(Bzl), the scaling theory was consistent with the core chain length dependence of both core and micelle sizes. The overcrowding nature of the tethered PEG chains on the micelles was increased about 1.3-2.9 times with increasing N(agg) compared with the unperturbed state in solutions.

Size-dependent induction of accelerated blood clearance phenomenon by repeated injections of polymeric micelles.

An accelerated blood clearance (ABC) phenomenon is induced by repeated injections of poly(ethylene glycol)-modified (PEGylated) liposomes. We previously indicated that the phenomenon was induced by polymeric micelles possessing PEG chains like as liposomes, although, the induction mechanism of the ABC phenomenon is not fully elucidated. In the present study, we investigate whether repeat-injection of the polymeric micelles having PEG chains trigger the phenomenon or not. Two polymeric micelles, PM-30 (polymeric micelles with 33.6nm in diameter) and PM-75 (76.2nm), were prepared with PEG-poly[Asp(pentyl)] and PEG-poly[Asp(nonyl)], respectively. We firstly examined the ABC-triggering effect of these micelles, and observed that both polymeric micelles, especially PM-75, induced the production of anti-PEG IgM antibody in treated mice. Then, PM-30 or PM-75 was preadministered into mice as a preconditioning. Seven days later, AlexaFluor594-labeled PM-30 or PM-75 was administered to determine the susceptibility of the phenomenon. As a result, rapid clearance of AlexaFluor594-labeled PM-75 from the bloodstream and accumulation in the liver were observed in PM-75 pretreated mice. Although, the ABC phenomenon of AlexaFluor594-labeled PM-30 was less obvious in PM-30 pretreated mice. Our present results indicated that the repeated injections of polymeric micelles caused the ABC phenomenon in a size-dependent manner.

Ladder oligo(m-aniline)s: derivatives of azaacenes with cross-conjugated π-systems.

We describe the synthesis and electronic properties of ladder oligomers of poly(m-aniline) that may be considered as derivatives of azaacenes with cross-conjugated π-systems. Syntheses of ladder oligo(m-aniline)s with 9 and 13 collinearly fused six-membered rings employed Pd-catalyzed aminations and Friedel-Crafts-based ring closures. Structures were confirmed by either X-ray crystallography or correlations between DFT-computed and experimental spectroscopic data such as (1)H, (13)C, and (15)N NMR chemical shifts and electronic absorption spectra. All compounds have planar "azaacene" moieties. The experimental band gaps E(g) ≈ 3.5-3.65 eV, determined by the UV-vis absorption onsets, were in agreement with the TD-DFT-computed vertical excitation energies to the S(1) state. Fluorescence quantum yields of up to 20% were found. Electrochemically estimated HOMO energies of -4.8 eV suggested propensity for a facile one-electron oxidation and just sufficient environmental stability toward oxygen (O(2)). For two oligomers with "tetraazanonacene" moieties, potentials of E(4+/3+) ≈ 1.6-1.7 V vs SCE were determined for four-electron oxidation to the corresponding tetraradical tetracations.