KR20090126373A - 6-arm plla-peg block copolymer for micelle formation and controlled drug release - Google Patents

Abstract

PURPOSE: A 6-arm poly(L-lactide)-polyethylene block copolymer is provided to be effective for micelle formation and to control a drug release profile by controlling a chain length of poly(L-lactide) within micelle. CONSTITUTION: A micelle for drug release comprises a 6-arm poly(L-lactide)-polyethylene glycol block copolymer represented by the following chemical formula I. A method for preparing the 6-arm poly(L-lactide)-polyethylene glycol block copolymer comprises the steps of: (i) performing ring opening polymerization of L-lactide using dipentaerythritol as a starting material in the presence of a catalyst of tin octate; and (ii) conjugating carboxymethyl mono-methoxy poly(ethylene glycol) to the 6-arm poly(L-lactide).

Description

6-arm PLLA-PEG block copolymer for micelle formation and controlled drug release}

The present invention relates to a six-arm PLLA-PEG block copolymer capable of controlling micelle formation and drug release. More specifically, 6-pal PLLA prepared as a component of a polymer comprising a hydrophobic biodegradable poly-L-lactide (PLLA) and a hydrophilic polymer polyethylene glycol (PEG) as a polymer for controlling micelle formation and drug release The present invention relates to a polymer for drug delivery.

In recent decades polymers, designated multi-arm or star-forms, have attempted to utilize their various block polymers as hydrogels or micelles in the biomedical field primarily drug delivery systems. The reason for this attempt is that multi-arm polymers exhibit a small hydrodynamic size and low solution viscosity compared to linear polymers, leading to complete kidney excretion after degradation in the human body. In particular, multi-pal poly (ether-esters) have been studied for application as a substitute for Pluronic mainly due to their thermo-reversibility and biodegradability.

Choi et al. Synthesized multi-pal PEO-PLA and PEO-PCL block copolymers with four types of arms and characteristic physical properties in Macromolecules, 31, 8766 (1998). They showed that the degree of expansion and phase separation in aqueous solution changed as the number of arms varied and found useful for controlled drug delivery. Lee et al. Synthesized a multi-arm PEO-PLGA block copolymer from Polymer, 39, 4421 (1998) and tested the degradation of the polymer in vitro. As a result, 4- and 8-arm chains showed different degradation properties due to their different molecular structure compared to linear chains.

Park et al. Synthesized multi-arm PLLA-PEO block copolymers from Macromolecules, 36, 4115 (2003). His research focused on the solution properties of polymers to investigate sol-gel conversion behavior and micelles. This is described by Polym. Multi-pal PLGA-PEG block copolymers were synthesized in Chem., 44, 888 (2006) and their sol-gel transformation behavior and micelles were investigated. His study investigated the effects of temperature and concentration on micelles and sol-gel conversion behavior.

However, no study of the application of drug delivery systems has been conducted. Many previous studies have shown that polymer micelles have a drug delivery system due to their inherent properties in the body such as hydrophobic molecular dissolution, thermodynamic stability, extended drug release and suppressed rapid clearance by RES due to their size and surface properties. Has many advantages for.

The present invention thus investigates the micelleization and controlled drug release behavior from micelles of the degradable novel 6-pal PLLA-PEG copolymer and also controls the release behavior of drug encapsulated polyester chains that make up the center of micelles. The present invention has been completed by measuring the important role played by. The present invention also measures the effect of the chain length of 6-arm PLLA-PEG on micelle formation and drug release rates.

The problem to be solved by the present invention is to measure the micelleization of 6-pal PLLA-PEG copolymers and controlled drug release behavior from micelles and to control the release behavior of drug encapsulated polyester chains that form the core of micelles. To measure whether or not. It is also intended to measure the effect of the chain length of 6-arm PLLA-PEG on micelle formation and drug release rates.

An object of the present invention is a drug delivery micelle consisting of a 6-arm PLLA-PEG block copolymer represented by the following formula (I):

Equation Ⅰ

In addition, another object of the present invention is the step of (iv) ring-opening polymerization (L- lactide) using tin octoate (St-Oct) catalyst using dipentaerythritol as a starting material; Ii) preparation of the 6-arm PLLA-PEG block copolymer of formula I above, which comprises conjugating carboxymethyl mono-methoxy poly (ethylene glycol) (CMPEG) to the 6-arm PLLA obtained in step (iii). To provide a way:

On the other hand it is another object of the present invention to provide a method for controlling the drug release profile by adjusting the chain length of PLLA in the micelles.

In addition, by increasing the PLLA chain length is characterized by a more continuous control of drug release.

The effect of the present invention is to measure the micelleization of 6-pal PLLA-PEG copolymers and the controlled drug release behavior from micelles to provide the possibility of controlling the release of the encapsulated drug of the polyester chains that make up the core of the micelles. It also provides the effect of chain length of 6-pal PLLA-PEG on micelle formation and drug release rates.

Hereinafter, the present invention will be described in more detail.

¹ H NMR spectra provide structural information of the synthesized polymer. Characteristic peak peaks of the 6-arm PLLA chain were found at 1.55 and 5.1 ppm, respectively, indicating successful polymerization of L-lactide. Also two peak peaks assigned to both methylenes in dipentaerithritol were observed at 3.28 and 4.16 ppm. These signals can be estimated by comparing the ratio of peak regions to the molecular weight of the synthesized 6-pal PLLA.

PEG conjugation to 6-pal PLLA was confirmed by the loss of signal for both methylene protons of PEG adjacent to the ester bond (-OCH ₂ CH ₂ COO-) at 4.23 ppm. FT IR spectra of 6-arm PLLA, 6-arm PLLA-PEG and CMPEG are shown in FIG. 1.

As shown in FIG. 1 (a), the FT IR spectrum of 6-arm PLLA-PEG, 6-arm PLLA-PEG was PLLA at ˜1,750 cm ^{−1, which} was not shown in FIG. 1 (c), the FT IR spectrum for CM PEG. It showed a distinct carbonyl extension band for the block and showed a strong band of methylene group for PEG at ˜2,900 cm ⁻¹ , which is not shown in FIG. 1 (b), the FT IR spectrum for 6-pal PLLA. The six-arm PLLA-PEG also provided two weakened peaks assigned to the CH bend signal of the PEG segment at about 1560 cm ⁻¹ and 1630 cm ⁻¹ . The signal was not shown in FIG. 1 (b), which is an FT IR spectrum representing 6-arm PLLA, but strong in FIG. 1 (c), which is an FT IR spectrum for CM PEG.

The molecular weights of the polymers obtained by gel permeation chromatography are shown in Table 1.

Six-arm PLLA series with different molecular weights were synthesized and provided molecular weights of 3,800, 4,500 and 6,000 and exhibited nearly similar PDI of 1.24. Conjugation of CMPEG to each 6-arm PLLA gave three kinds of 6-arm PLLA-PEG, exhibiting nearly identical PDI of 1.32-1.35. Molecular weight data indicate that polymerization of L-lactide to 6-pal PLLA and conjugation of PEG to 6-pal PLLA performed well. However, the PDI of 6-arm PLLA-PEG was somewhat higher than that of 6-arm PLLA. This means that the molecular weight distribution of 6-pal PLLA-PEG was somewhat increased after conjugation of PEG compared to 6-pal PLLA. This result is evidenced by the 6-pal PLLA 4.5 K-PEG 5K conjugated with longer CMPEG showing higher PDI.

Critical micelle concentration (CMC) data is shown in Table 2.

For 2,000 PEG chain lengths, the critical micelle concentration value decreased with increasing molecular weight of PLLA. These results indicate that more hydrophobic chains are effective for micelle formation, which is consistent with the case of Pluronic and other amphiphilic star-shaped copolymers.

This explanation also shows that the six-arm PLLA-PEG with longer PEG chains (6-arm PLLA 4.5 K-PEG 5K) has a higher threshold than the shorter PEG chain (6-arm PLLA 4.5 K-PEG 2K). It was demonstrated that the red micelle concentration value. The micelle size was found to be between about 100-200 nm.

In particular, the hydrodynamic size (diameter diameter of micelles) was reduced after encapsulation of the IMC, indicating that the integration of the IMC's micelle structure into the hydrophobic core produces smaller structures during micelles. The loading content and efficiency of IMC are also shown in Table 2. They tended to show higher values in more hydrophobic chains. This tendency is because hydrophobic IMC is more suitable to integrate into the larger space of the hydrophobic core of micelles.

The IMC release profile of the 6-arm PLLA-PEG is shown in FIG. 2. The profile demonstrated that more hydrophobic 6-arm copolymers with longer PLLA chains apparently released the loaded IMCs under the conditions of the same PEG chain. This indicates that the hydrophobic PLLA chain plays an important role in releasing the loaded IMC. It can be concluded that hydrophobic PLLA retards the release of IMC from hydrophobic cores consisting predominantly of PLLA.

Furthermore, among the two copolymers with the same PLLA chain length, the inclusion of PEG 5K in contrast to PEG 2K showed a strong conversion of cumulative release percentage to high values in the middle of the release period. This can be explained by the hydrophilicity of PEG in aqueous solution. Hydrophilic PEG chains make up the shell of the micelle structure that is hydrated under an aqueous environment.

A new series of 6-arm PLLA-PEG copolymers was synthesized for drug delivery systems. Such block copolymers were prepared by conjugating PEG to 6-pal PLLA. Six-armed PLLA-PEG formed micelles in aqueous solution and exhibited different sizes and IMC loading efficiencies by varying the PLLA chain length. The overall release profile of IMC from 6-pal PLLA-PEG micelles showed no initial rapid increase but an extended release time. In particular, 6-arm PLLA-PEG micelles with long PLLA chains showed more sustained release behavior. The release rate of the IMC can be controlled by the chain length of the PLLA, which can be controlled.

The present invention will be described in more detail with reference to the following examples. However, these examples do not limit the scope of the present invention.

Example 1 Synthesis of 6-Pal PLLA-PEG Copolymer

The 6-arm PLLA-PEG copolymer was synthesized via the simple route shown in Scheme I.

Scheme Ⅰ. Synthetic route of 6-arm PLLA-PEG

Six-arm PLLA was synthesized by mass-opening polymerization of L-lactide with dipentaerythritol as the six-arm initiator and tin octoate (St-Oct) as the catalyst. Briefly pure L-lactide (15 g, 104.1 mmol) and dipentaerythritol (1.5 g, 12.4 mmol) were placed in a dry glass ampoule containing a Teflon-coated magnetic stir bar and St-Oct (0.21 g, 0.52 mmol) was added as catalyst. The mixture was stirred under vacuum at 130 ° C. for 6 hours, then dissolved in chloroform, filtered, precipitated in n-hexane and dried under vacuum. The molar ratio of L-lactide to St-Oct was fixed at 200. Carboxymethyl mono-methoxy poly (ethylene glycol) (CMPEG) was synthesized as shown in S. Zalipsky, Bioconjugate Chem., 6, 150 (1995). The prepared CMPEG was then conjugated to 6-pal PLLA to provide 6-pal PLLA-PEG. 6-pal PLLA (5.5 g, 1.0 mmol), CMPEG (12.1 g, 6.04 mmol), DCC (1.25 g, 6.04 mmol) and DMAP (0.15 g, 1.21 mmol) are dissolved in 200 ml of anhydrous methylene chloride and N ₂ Stir at room temperature for 48 hours under air. The reaction mixture was subjected to a number of processes including filtration, crystallization and tutu to produce powdered compounds.

Example 2 Structural Analysis of 6-Arm PLLA-PEG

The structures of the synthesized 6-arm PLLA, CMPEG, 6-arm PLLA-PEG were confirmed by FT-IR (Nicolet Magma-IR 550) and ¹ H-NMR (400 MHz, Varian). GPC (M616LC System, Waters) was used to obtain the molecular weight and polydispersity index (PDI) of the polymer.

Example 3 micelle formation

Micelles incorporating IMC were prepared in 6-pal PLLA-PEG by the following solvent evaporation method. First, 6-pal PLLA-PEG and IMC were solvent in distilled water and ethanol, respectively. Secondly IMC solution was added to the 6-pal PLLA-PEG solution. Finally the mixed solution was shaken at 37 ° C. at 50 rpm for 24 hours and then dried at 60 ° C. overnight. The remaining IMC was completely removed by centrifugation (4,000 rpm, 10 minutes) and the separated micelle solution was sonicated and lyophilized. The content of IMC loaded in micelles was measured by measuring the UV absorbance of IMC at 318 nm and the loading efficiency (LE) was calculated by the measured weight ratio of IMC to micelles loaded with IMC. Critical micelle concentrations (CMC) of micelles were analyzed with pyrene as probes by fluorescence measurements (FP-6500, JASCO). The diameter and size distribution of the micelles were measured by a dynamic light scattering (DLS) analyzer (FPAR-100, Photal). Intensity autocorrelation data were measured at a scattering angle of 160 Hz at 25 ° C. for 120 seconds.

The release behavior of IMC from micelles was observed by the following procedure. IMC loaded on micelles was released at 37 ° C. for 35 days in 0.01 M phosphate buffered saline (PBS, pH 7.4). At the time measured, the released IMC in the micelle solution was measured and fresh PBS was added.

1 shows the FT-IR spectra of (a) 6-arm PLLA-PEG, (b) 6-arm PLLA and (c) CMPEG.

2 shows the release profile of IMC from 6-arm PLLA-PEG micelles. PLLA 3.8 K-PEG 2K (black circles), PLLA 4.5 K-PEG 2K (white circles), PLLA 4.5 K-PEG 5K (black squares), and PLLA 6 K-PEG 2K (white squares).

Claims (4)

Drug delivery micelles consisting of a 6-arm PLLA-PEG block copolymer represented by Formula I:

Equation Ⅰ V) ring-opening polymerization of L-lactide in the presence of a tin octoate (St-Oct) catalyst with dipentaerythritol as starting material; Ii) preparation of the 6-arm PLLA-PEG block copolymer of formula I above, which comprises conjugating carboxymethyl mono-methoxy poly (ethylene glycol) (CMPEG) to the 6-arm PLLA obtained in step (iii). Way:

Method of controlling drug release profile by controlling chain length of PLLA in micelles of claim 1 4. The method of claim 3, wherein the drug release is controlled more continuously by increasing the PLLA chain length.

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