Yong Joo Jun

A novel micelle-encapsulated platinum(II) anticancer agent

A hydrophobic and water-insoluble platinum(II) compound, cis-(cha)(2)Pt(NO(3))(2) was encapsulated by macromolecular micelles self-assembled from an amphiphilic cyclotriphosphazene [NP(MPEG750)(GlyPheLeu)(2)Et](3) (CP750). The micelle-encapsulated platinum(II) compound exhibited outstanding pharmacokinetics in rats by showing long blood circulation and much larger systemic exposure (AUC=43.5 μgh/ml) compared with the free carboplatin (AUC=4.32 μgh/ml). Biodistribution study of the micellar platinum(II) compound using male Sprague-Dawley rats has shown excellent tumor to tissue ratios of 4.03 at 2h post injection and 4.67 at 24h post injection. Furthermore, the micellar platinum(II) compound exhibited more than 6 times higher cellular uptake in human cervical (HeLa) and lung (A549) tumor cells compared with the free platinum compound. Also it is surprising that the micellar platinum(II) compound displayed specifically high cytotoxicity against the stomach tumor cells (SNU638), which are one of the least responsive to chemotherapeutic agents currently in clinical use. The acute toxicity study has shown that the LD(50) values of free and the micellar cis-(cha)(2)Pt(NO(3))(2) are approximately 70 mg/kg and 90 mg/kg, respectively. Thus the platinum compound encapsulated by cyclotriphosphazene micelles is a promising candidate for preclinical studies.

Stable and efficient delivery of docetaxel by micelle-encapsulation using a tripodal cyclotriphosphazene amphiphile

Docetaxel micelle-encapsulated by a tripodal cyclotriphosphazene amphiphilile [NP(PEG750)(GlyPheLeu)(2)Et](3) (CP750) exhibited outstanding drug-loaded micelle stability in aqueous solution compared with the polymeric micelles assembled from linear block copolymers. Furthermore, docetaxel micelle-encapsulated by CP750 is obtainable in solvent free powder form, which is immediately soluble in any aqueous media including saline and PBS and very stable to photo-degradation even in the room light at room temperature. Although docetaxel micelle-encapsulated by CP750 did not display highly improved pharmacokinetic profile compared with Taxotere currently in clinical use, its in vivo xenograft trials exhibited excellent antitumor efficacy by showing complete tumor regression against the breast cancer cells (MDA-MB-231) at a lower dose of 5mg/kg and better efficacy against gastric cancer cells (MKN-28) compared with Taxotere. Furthermore, according to the comparative acute toxicity study, toxicities associated with Taxotere may be remarkably reduced by micelle-encapsulation of docetaxel using CP750, which afforded a much higher LD(50) value of 75 mg/kg compared with 28 mg/kg of docetaxel in Taxotere. Thus docetaxel micelle-encapsulated by CP750 has entered the stage of preclinical studies.

Tripodal amphiphiles tunable for self-assembly to polymersomes

Cyclotriphosphazenes grafted with equimolar amounts of a hydrophilic polyethylene glycol and a hydrophobic oligopeptide in cis-nongeminal way form a new class of tripodal amphiphiles allowing both intra- and intermolecular hydrophobic interactions that differ from linear block copolymer amphiphiles. It has been found in this study that the tripodal amphiphiles can be tuned for self-assembly from micelles to bilayered polymersomes by controlling the hydrophobicity of the oligopeptide grafted. For instance, the tripodal amphiphiles with an intermediate hydrophobicity (0<log P<1) (P=[solute](n-octanol)/[solute](water)) reassemble from initially formed micelles into polymersomes, whereas the trimers bearing highly hydrophobic oligopeptides (log P>1) remain as stable micelles in aqueous solution. These biodegradable polymersomes exhibit outstanding physicochemical properties required for practical drug delivery and other biomedical applications. In particular, the cyclic phosphazene trimer platinated with a hydrophobic cis-bis(cyclohexylamine)Pt-moiety forms very stable polymersomes with excellent tumor selectivity by EPR effect and seems to be a promising candidate for preclinical studies.

Synthesis and properties of a new micellar polyphosphazene–platinum(II) conjugate drug

Aiming at tumor targeting delivery of oxaliplatin using polymer therapy, a new monomeric platinum(II) complex (dach)Pt[HEDM] (dach: trans-(±)-1,2-diaminocyclohexane; HEDM: 2-hydroxyethoxydiethylmalate) was designed to include the antitumor moiety (dach)Pt and HEDM as a linker to the polyphosphazene backbone. This monomeric Pt-complex could easily be grafted to the PEGylated polyphosphazene backbone to prepare a novel polyphosphazene-Pt conjugate, [NP(MPEG550)(dach)Pt(EM)]n [MPEG550: methoxy poly(ethylene glycol) with an average molecular weight of 550; EM: ethoxymalate]. This amphiphilic polyphosphazene-Pt conjugate was found to self-assemble into stable polymeric micelles of a mean diameter of 130nm, which is suitable for passive tumor targeting by enhanced permeability and retention (EPR) effect. Pharmacokinetic study of this polymer conjugate exhibited long blood circulation as expected and longer half-life (t1/2β=9.52h) compared with oxaliplatin (3.47h), and much larger AUC (area under the curve) value (25,831ng·h/mL) compared with oxaliplatin (1194ng·h/mL). Biodistribution study of the polymer conjugate has shown excellent tumor selectivity with the tumor to tissue ratio of 3.84 at 2h post injection and 11.7 at 24h post injection probably due to the EPR effect of the polymer conjugate while no tumor selectivity was observed for monomeric oxaliplatin. Furthermore, accumulation of this polymer conjugate in kidney was much lower compared with oxaliplatin. Also the nude mouse xenograft trial of the polymer conjugate has shown higher antitumor efficacy compared with oxaliplatin.

Design of a novel theranostic nanomedicine: synthesis and physicochemical properties of a biocompatible polyphosphazene–platinum(II) conjugate

To develop a theranostic nanomedicine involving the antitumor-active moiety (dach)Pt(II) (dach: trans-(±)-1,2-diaminocyclohexane) of oxaliplatin (OX), a new biocompatible polyphosphazene carrier polymer was designed by grafting with a methoxy poly(ethylene glycol) (MPEG) to increase duration of circulation in the blood and with aminoethanol (AE) as a spacer group. The antitumor (dach)Pt moiety was conjugated to the carrier polymer using cis-aconitic acid (AA) as a linker, resulting in a polymer conjugate formulated as [NP(MPEG550)(AE-AA)Pt(dach)]n, named “Polyplatin” (PP). PP was found to self-assemble into very stable polymeric nanoparticles with a mean diameter of 55.1 nm and a critical aggregation concentration of 18.5 mg/L in saline. PP could easily be labeled with a fluorescence dye such as Cy5.5 for imaging studies. The time-dependent ex vivo image studies on organ distributions and clearance of Cy-labeled PP have shown that PP accumulated in the tumor with high selectivity by the enhanced permeability and retention effect but was cleared out from all the major organs including the liver in about 4 weeks postinjection. Another time-dependent bioimaging study on distribution and clearance of PP in mouse kidney using laser ablation inductively coupled plasma mass spectroscopy has shown that PP accumulates much less in kidney and is more rapidly excreted than monomeric OX, which is in accord with the very low acute toxicity of PP as shown by its high LD50 value of more than 2000 mg/kg. The pharmacokinetic study of PP has shown that it has a much longer half-life (t1/2β) of 13.3 hours compared with the 5.21 hours of OX and about a 20 times higher area under the curve value of 42,850.8 ng h/mL compared with the 2,320.4 ng h/mL of OX. The nude mouse xenograft trials of PP against the gastric MKN-28 tumor cell line exhibited remarkably better tumor efficacy compared with OX at the higher tolerated dose, with lower systemic toxicity.

Synthesis and physicochemical properties of new tripodal amphiphiles bearing fatty acids as a hydrophobic group

Saturated fatty acids (FA) were grafted using tyrosine as a spacer group to the cyclotriphosphazene ring along with equimolar hydrophilic methoxy poly(ethylene glycol) (MPEG) in cis-nongeminal way. Seven new cyclotriphosphazene amphiphiles were prepared from combinations of hydrophilic MPEGs with different molecular weights of 350, 550, 750 and 1000 and four different fatty acids of different hydrophobicity including lauric, myristic, palmitic and stearic acids. These steric amphiphiles bearing fatty acids as a hydrophobic group were found to form more stable micelles with very low critical micelle concentrations (CMC) (2.95-7.80mg/L) compared with oligopeptide analogues, and their highly hydrophobic core environment is unique and potentially useful for various biomedical applications.

Design of theranostic nanomedicine (II): synthesis and physicochemical properties of a biocompatible polyphosphazene–docetaxel conjugate

To prepare an efficient theranostic polyphosphazene–docetaxel (DTX) conjugate, a new drug delivery system was designed by grafting a multifunctional lysine ethylester (LysOEt) as a spacer group along with methoxy poly(ethylene glycol) (MPEG) to the polyphosphazene backbone ([NP]n), and then DTX was conjugated to the carrier polymer using acid-cleavable cis-aconitic acid (AA) as a linker. The resultant polyphosphazene–DTX conjugate, formulated as [NP(MPEG550)3(Lys-OEt)(AA)(DTX)]n and named “Polytaxel”, exhibited high water solubility and stability by forming stable polymeric micelles as shown in its transmission electron microscopy image and dynamic light scattering measurements. Another important aspect of Polytaxel is that it can easily be labeled with various imaging agents using the lysine amino group, enabling studies on various aspects, such as its organ distribution, tumor-targeting properties, pharmacokinetics, toxicity, and excretion. The pharmacokinetics of Polytaxel was remarkably improved, with prolonged elimination half-life and enhanced area under the curve. Ex vivo imaging study of cyanine dye-labeled Polytaxel showed that intravenously injected Polytaxel is long circulating in the blood stream and selectively accumulates in tumor tissues. Polytaxel distributed in other organs was cleared from all major organs at ~6 weeks after injection. The in vitro study of DTX release from the carrier polymer showed that >95% of conjugated DTX was released at pH 5.4 over a period of 7 days. Xenograft trials of Polytaxel using nude mice against the human gastric tumor cell line MKN-28 showed complete tumor regression, with low systemic toxicity. Polytaxel is currently in preclinical study.

Abstract A116: Stable and efficient delivery of docetaxel by micelle encapsulation using a tripodal cyclotriphosphazene amphiphile.

Docetaxel, a semi-synthetic analogue of paclitaxel, is currently one of the most important chemotherapeutic agents, since it is clinically very efficacious against a variety of tumors. Docetaxel is known to be more potent than paclitaxel, but its photo-instability causes more inconveniences in drug storage and patient treatment compared with paclitaxel. Docetaxel is solubilized in aqueous solution by formulation using a surfactant polysorbate 80 (Tween 80). Docetaxel in such a formulation named Taxotere is known to cause several adverse effects. Therefore, a great deal of efforts has been devoted to replace the surfactant polysorbate 80 with polymeric micelles composed of linear amphiphilic block copolymers. However, most of the linear block copolymers exposed commonly a few critical problems for practical application, and in particular, docetaxel-loaded polymeric micelles are not stable enough to hold the drug component in the micelle core and drug precipitates mostly within 24 h after drug loading. We have recently developed a novel class of cyclotriphosphazene micelles of a general formula [N=P(X)(Y)]3 prepared by stepwise substitutions of cyclic chlorophosphazene [N=PCl2]3 with equimolar hydrophilic (X) and hydrophobic (Y) nucleophiles in cis-nongeminal way. In particular, the tripodal amphiphiles with a methoxy poly(ethylene glycol) as a hydrophilic group and a linear oligopeptide as a hydrophobic group have been found to self-assemble into very stable spherical micelles with a mean diameter less than 10 nm and a CMC value of 5 mg/L in aqueous solution. Docetaxel micelle-encapsulated by a tripodal amphiphilile [NP(PEG750)(GlyPheLeu)2Et]3 (CP750) exhibited outstanding drug-loaded micelle stability in aqueous solution compared with the polymeric micelles assembled from linear block copolymers. Furthermore, docetaxel micelle-encapsulated by CP750 is obtainable in solvent free powder form, which is immediately soluble in any aqueous media including saline and PBS and very stable to photo-degradation even in the room light at room temperature. Docetaxel micelle-encapsulated by CP750 displayed significantly improved pharmacokinetic profile compared with Taxotere currently in clinical use. Furthermore, its in vivo xenograft trials exhibited outstanding antitumor efficacy by showing complete tumor regression against the breast cancer cells (MDA-MB-231) at a low dose of 5 mg/kg, which is only 1/3 of the optimum dose of Taxotere. Furthermore, according to the acute toxicity study, docetaxel micelle-encapsulated by CP750 exhibited a much higher LD50 value of 75 mg/kg compared with 28 mg/kg of docetaxel in Taxotere. Thus docetaxel micelle-encapsulated by CP750 has entered the stage of preclinical studies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A116.