Optimization of Amphiphilic Miktoarm Star Copolymers for Anticancer

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Controlled Release and Delivery Systems

Optimization of Amphiphilic Miktoarm Star Copolymers for Anti-Cancer Drug Delivery Mingqi Wang, Xiaolong Zhang, Han Peng, Mingkui Zhang, Xianshuo Zhang, Zhe Liu, Liwei Ma, and Hua Wei ACS Biomater. Sci. Eng., Just Accepted Manuscript • DOI: 10.1021/acsbiomaterials.8b00678 • Publication Date (Web): 12 Jul 2018 Downloaded from http://pubs.acs.org on July 14, 2018

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ACS Biomaterials Science & Engineering

Optimization of Amphiphilic Miktoarm Star Copolymers for Anti-Cancer Drug Delivery

Mingqi Wang, Xiaolong Zhang, Han Peng, Mingkui Zhang, Xianshuo Zhang, Zhe Liu, Liwei Ma, and Hua Wei*

State Key Laboratory of Applied Organic Chemistry, Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, Gansu 730000, China

*Corresponding author E-mail address: [email protected] (H. Wei)

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ACS Biomaterials Science & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract: The preparation of various types of miktoarm star polymers with precisely controlled structures (A2B, ABC, AB2C2, etc.) has made significant progress due to the considerable advances in the synthetic strategies including multi-step protections/deprotections, orthogonality, and integration of different polymerization techniques. However, compared to the well-developed synthesis methodologies, the investigations on miktoarm star copolymers as drug delivery vehicles remain relatively unexplored, especially for the relationship of their branched structures and properties as drug delivery systems. To elucidate this structure-property relationship of amphiphilic miktoarm star polymers, we prepared four different amphiphilic miktoarm star copolymers with the respectively identical molecular weights (MWs) of hydrophilic and hydrophobic

moieties but different star structures using

heteroinitiators that were synthesized by protection/deprotection strategies for integrated ring-opening polymerization (ROP) of hydrophobic ε-caprolactone (ε-CL) and atom transfer radical polymerization (ATRP) of hydrophilic oligo (ethylene glycol) monomethyl ether methacrylate (OEGMA). Further screening of an optimal formulation for anti-cancer drug delivery by the stability of micelles, in vitro drug loading capacity, drug release properties, cellular uptake efficacy, and cytotoxicity of doxorubicin (DOX)-loaded micelles showed that PCL3POEGMA1 micelles possessed the lowest critical micelle concentration (CMC), the highest drug loading content (DLC), and enhanced therapeutic efficiency for DOX release of all the synthesized four star copolymer constructs. This study thus provides preliminary guidelines and


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rationalities for the construction of amphiphilic miktoarm star polymers toward enhanced anti-cancer drug delivery. Keywords: miktoarm star copolymers; amphiphilicity; anti-cancer drug delivery; micelle stability; drug-loading capacity; therapeutic efficacy



Introduction Polymers with advanced topologies show unique properties and excellent performance for various potential applications that could never be realized by the traditional linear counterparts.1 Branched polymers including dendrimers, cyclic brush polymers, and star-shaped polymers represent intriguing species for both fundamental investigations and biomedical applications due to a compact structure with small dimension, an ability to form unimolecular micelles with enhanced stability, and a multivalent surface for various functionalities. Star-shaped polymers integrate the relative ease synthesis of linear polymers and the advantages of branched structures mentioned above, therefore they have drawn considerable attention during the past several decades. Miktoarm star polymers, also termed as asymmetric star polymers or heteroarm star polymers, are star-shaped polymers with certain amount of different polymer arms radiating from a core.2-4 The different polymer arms generally vary by chemical identity and/or chain length. The rapid and considerable advances in the synthetic strategies including multi-step protections/deprotections, orthogonality, and integration of different polymerization techniques have enabled the preparation of various types of miktoarm star polymers with precisely controlled structures (A2B, ABC, AB2C2, etc.).5-9 For example, Takuya Isono et al. recently reported the preparation of AB2 and AB3 -type miktoarm star copolymers consisting of maltoheptaose and poly(ε-caprolactone) (PCL).10 Although several new types of miktoarm star copolymers with either a sugar core11,12 or pH-responsive arms13,14 have been developed and evaluated for drug delivery applications, the investigations


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on miktoarm star copolymers as drug delivery vehicles remain limited to a formulation with only one predetermined star structure. Since our recent studies have disclosed significant effect of the branched structure on the stability, drug-loading capacity, and therapeutic efficacy of the homoarm star copolymers-based micelles,15,16 it remains unclear whether the heteroarm star copolymer reported in the literature was the optimal formulation for controlled drug release because, to our knowledge, such structure-properties relationship of the miktoarm star copolymers hasn’t been elucidated so far. To address this issue and to provide preliminary guidelines and rationalities for the fabrication of amphiphilic miktoarm star copolymers for drug delivery applications, we reported in this study the preparation of four different amphiphilic miktoarm star copolymers with the respectively identical MWs of hydrophilic and hydrophobic moieties but different star structures using heteroinitiators that were synthesized by protection/deprotection strategies for integrated ring-opening polymerization (ROP) of hydrophobic ε-caprolactone (ε-CL) and atom transfer radical polymerization (ATRP) of hydrophilic oligo (ethylene glycol) monomethyl ether methacrylate (OEGMA). Further screening of an optimal formulation for anti-cancer drug delivery by the stability of micelles, in vitro drug loading capacity, and cytotoxicity of doxorubicin (DOX)-loaded micelles was performed.

Experimental Section Materials



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ε-CL and triethyl orthoacetate were purchased from Sigma-Aldrich, and were dried over CaH2 and distilled under reduced pressure prior to use. OEGMA (Mn=300 g/mol and 3~4 pendent EO units) from Sigma-Aldrich was purified by passing through a column filled with basic alumina to remove the inhibitor. Pentaerythritol, stannous(II) octanoate

(Sn(Oct)2),

1,1,1-tri(hydroxymethyl)ethane,

triethylamine

(TEA)

,

2-bromoisobutyryl bromide, and copper(I) bromide (CuBr) were purchased from Sigma-Aldrich and used as received. N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDETA) was supplied by Aladdin. 2,2-Dimethoxypropane, p-toluenesulfonic acid monohydrate, Dowex 50wx4 200-400 mesh, N, N'-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP) were purchased from J&K and used as received. Tetrahydrofuran (THF) and toluene were purified by refluxing over sodium and distilled prior to use. All other reagents and solvents were used without further purification. The synthesis procedures of PCL and POEGMA arms were conducted following our previous study.15 For simplicity, the detailed feed amounts of chemicals and solvents for the synthesis of various miktoinitiators and polymers were provided in the supporting information.

Preparation of Various

Bromo-Terminated PCL-Based Macro-initiators,

PCLnBrm PCL2Br1

was

prepared

by

ROP

of

ε-CL

3-hydroxy-2-(hydroxymethyl)-2-methylpropyl-2-bromo-2-methylpropanoate17,18

using as

the initiator (Yield, 70%). 1H NMR [400 MHz, (CDCl3)] (Figure S1(a)): 0.89 ppm (s,


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3H), 1.93 ppm (s, 6H), 3.59 ppm (d, 4H), 4.24 ppm (s, 2H), 2.90 ppm (broad peak, s, 2H). 13C NMR [400 MHz, (CDCl3)]: δ (ppm) 16.69, 30.69, 41.03, 55.74, 67.36, 67.91, 76.58, 77.00, 77.43, 172.38. was

PCL2Br2

prepared

using

2,2-bis(hydroxymethyl)propane-1,3-diylbis(2-bromo-2-methylpropanoate)18,19 as the initiator (Yield, 72%). 1H NMR [400 MHz, (CDCl3)] (Figure S2(a)): 1.93 ppm (s, 12H), 3.71 ppm (s, 4H), 4.26 ppm (s, 2H), 2.92 ppm (broad peak, s,2H).

13

C NMR

[400 MHz, (CDCl3)]: δ (ppm) 31.02, 46.04, 56.04, 62.82, 64.18, 77.18, 77.50, 77.82, 172.42. PCL1Br3

was

prepared

using

3-hydroxy-2,2-bis(hydroxymethyl)propyl

2-bromo-2-methylpropanoate as the initiator (Yield, 75%). 1H NMR [400 MHz, (CDCl3)] (Figure S3(a)): 1.95 ppm (s, 18H), 3.71ppm (s, 2H), 4.31 ppm (s,4H).

13

C

NMR [400 MHz, (CDCl3)]: δ (ppm) 30.74, 54.18, 55.51,60.91, 63.31, 76.80, 77.11, 77.43, 171.50. PCL3Br1

was

prepared

using

4-hydroxy-2,2-bis(hydroxymethyl)butyl

2-bromo-2-methylpropanoate20,21 as the initiator (Yield, 79%). 1H NMR [400 MHz, (CDCl3)] (Figure 1a): 1.93 ppm (s, 18H), 3.71ppm (s, 6H), 4.29 ppm (s,2H).

13

C

NMR [400 MHz, (CDCl3)]: δ (ppm) 31.14, 46.17, 56.18,63.66, 64.96, 77.18, 77.50, 77.82, 172.97.

Synthesis of Various Amphiphilic Miktoarm Star Copolymers, PCLnPOEGMAm



PCLnPOEGMAm was synthesized by ATRP using PCLnBrm as the macroinitiator and CuBr/PMDETA as the catalyst. PCL2POEGMA1 (Yield, 76%, Figure S1(b)), PCL2POEGMA2 (Yield, 80%, Figure S2(b)), PCL1POEGMA3 (Yield, 84%, Figure S3(b)), PCL3POEGMA1 (Yield, 84%, Figure 1b).

Characterization of Polymers The composition, molecular weight (MW) and polydispersity index (PDI) of synthesized polymers were determined by

1

H NMR and the size exclusion

chromatography and multi-angle laser light scattering (SEC-MALLS) analyses.22

Preparation and Characterization of Self-Assembled Micelles Classical dialysis method22 was used to prepare the micelle solutions of various miktoarm copolymers. TEM, DLS, and Critical Micelle Concentration (CMC) measurements were conducted following the reported procedures.15,22

In Vitro Drug Loading and Drug Release In vitro drug loading and drug release study was performed following the reported procedures.15,22

In Vitro Biological Assays HeLa cells (kindly provided by Stem Cell Bank, Chinese Academy of Sciences) were maintained in complete growth medium, and cultured as a monolayer in a 37 °C, 5%


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CO2 environment. Medium was replaced every 2−3 days. Cells were passaged at ∼70−80% confluence by incubation with Trypsin-EDTA followed by resuspension in complete growth medium. Confocal imaging was conducted on a Nikon A1R confocal microscope following the reported procedures.22,23 Cellular uptake efficiency was quantified by flow cytometry (FCM).23 The cytotoxicities of various formulations were evaluated in vitro using the MTS assay.22-24

Results and Discussion Synthesis and Characterization of Four Amphiphilic Miktoarm Star Copolymers, PCL2POEGMA1, PCL2POEGMA2, PCL3POEGMA1 and PCL1POEGMA3. Four well-defined amphiphilic miktoarm star copolymers, PCLnPOEGMAm with the respectively identical degree of polymerization values (DPs) for the hydrophilic POEGMA and hydrophobic PCL moieties but different degree of branching (DB) were designed and synthesized by using four miktoinitiators as the core template. The four miktoinitiators were prepared by the protection/deprotection strategies using pentaerythritol and 1,1,1-tri(hydroxymethyl)ethane as the starting materials in this study (Scheme 1).25 The DPs of PCL segment and POEGMA moiety were both determined by 1H NMR analysis to be approximately 40 for all the four miktoarm star copolymers. Taking PCL3POEGMA1 for example, the DP of PCL was determined to be 39 by comparing the ratio of the integrated intensity of peak f assigned to the methylene



protons adjacent to the terminal hydroxyl group to that of peak a and e attributed to the methylene protons adjacent to carbonyl groups (Figure 1a). The presence of all the characteristic signals of PCL and POEGMA blocks in the 1H NMR spectrum (Figure 1b) of PCL3POEGMA1 indicates successful preparation of target amphiphilic miktoarm star copolymer. The DP of POEGMA block was calculated to be 40 according to our previous study.15 Successful synthesis of well-defined miktoarm PCLnPOEGMAm copolymers is also verified by SEC-MALLS analysis (Figure 2), which reveals unimodal and symmetrical SEC elution peaks with narrow distributions for all the synthesized polymers. The results demonstrate well-controlled ROP and ATRP processes.26-28 The MWs, PDIs and DPs of all the synthesized polymers are summarized in Table 1.


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Scheme 1. Synthesis of (a) PCL2POEGMA1, (b) PCL2POEGMA2, (c) PCL3POEGMA1, and (d) PCL1POEGMA3 amphiphilic miktoarm star copolymers.



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Table 1. Summary of MW, PDI, and DP of various PCLnBrm and miktoarm PCLnPOEGMAm copolymers.

Polymer

Mna (kDa)

Mnb (kDa)

Mna of

Mna of

hydrophilic

hydrophobic

chain (kDa)

chain (kDa)

PDIb

PCL2Br1

4.7

7.1

1.25

-

-

PCL2POEGMA1

17.0

17.1

1.33

4.7

12.3

PCL2Br2

4.7

6.8

1.09

-

-

PCL2POEGMA2

16.7

16.4

1.11

4.9

11.8

PCL1Br3

5.1

6.3

1.20

-

-

PCL1POEGMA3

17.1

17.6

1.23

5.1

12.0

PCL3Br1

4.9

6.2

1.18

-

-

PCL3POEGMA1

16.8

16.0

1.11

4.9

11.9

a

Determined by 1H NMR; bDetermined by SEC-MALLS


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Figure 1. 1H NMR spectra of PCL3Br1 (a) and PCL3POEGMA1 (b) in CDCl3.



Figure 2. SEC elution traces (dRI signals) of PCL2POEGMA1 (a), PCL2POEGMA2 (b), PCL3POEGMA1 (c), and PCL1POEGMA3 (d) using DMF as an eluent.

Size and Morphology of Self-Assembled Micelles The micelle size affects significantly the its performance for drug delivery.29-31 It has been repeatedly highlighted that a relatively small size (< 200 nm) can contribute to reduced nonspecific uptake by the Reticuloendothelial System (RES), decreased renal excretion, and enhanced permeability and retention (EPR) effect to realize passive tumor targeting of nanocarriers.32,33 The capacity of the synthesized four amphiphilic miktoarm star copolymers to form micelles was evaluated using pyrene as a fluorescence probe (Figure 3).34-36 Interestingly, PCL3POEGMA1, all of the tested


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four polymers, apparently exhibits the lowest CMC value, indicating the greatest ability of its self-assembled micelles. Note that the larger CMC of the three-miktoarm star copolymer (PCL2POEGMA1) than those of the three four-miktoarm star analogues (PCL2POEGMA2, PCL3POEGMA1 and PCL1POEGMA3) probably implies the greater stability of four-miktoarm star copolymers. We have a particular research interest in developing (hyper)branched polymers for drug delivery applications. A series of amphiphilic homostar and heterostar copolymers with identical polymer compositions but different star architectures were synthesized and optimized for anticancer drug delivery in our previous15 and current studies, respectively. Interestingly, both investigations revealed that the four-arm star copolymers showed the greater stability relative to the three-arm analogues.



Figure 3. Plots of I373 in the fluorescence spectra as a function of logarithm of

polymer concentration, PCL2POEGMA1 (a), PCL2POEGMA2 (b), PCL3POEGMA1 (c), and PCL1POEGMA3 (d).

Next, DLS and TEM measurements were used to determine the average hydrodynamic size and morphology of the self-assembled micelles at a polymer concentration of 0.5 mg/mL (Figure 4), which is well above the determined CMCs. The micelles of PCL3POEGMA1 show the smallest size among all the tested four polymeric micelles, probably suggesting the three-arm star PCL with the highest DB promotes the formation of more compact hydrophobic core domain of PCL3POEGMA1 micelles relative to those of the other micelle analogues. The larger mean sizes of PCL2POEGMA2-bassed micelles than those of the three four-miktoarm copolymers (PCL2POEGMA2, PCL3POEGMA1 and PCL1POEGMA3)-based micelle analogues imply that a higher DB results in a smaller dimension of the self-assembled micelles. Such trends are in good agreement with the CMC data. TEM observation reveals the formation of well-dispersed micelles with regularly spherical shape for all the four amphiphilic miktoarm star copolymers. The average sizes observed by TEM are approximately 20 nm, which are smaller than that determined by DLS.15,37


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Figure 4. Size distributions and TEM images of micelles self-assembled from PCL2POEGMA1 (a & c), PCL2POEGMA2 (b & d), PCL3POEGMA1 (e & g), and PCL1POEGMA3 (f & h) in water at a polymer concentration of 0.5 mg/mL.

Stability of Self-Assembled Micelles To investigate the stability of self-assembled micelles in salt conditions, the size of micelles was also examined in the physiological condition (PBS, pH 7.4, 150 mM) by DLS at a polymer concentration of 0.5 mg/mL (Figure S4). The average diameters of micelles formed by PCL2POEGMA1, PCL2POEGMA2 and PCL3POEGMA1 show insignificant change irrespective of medium shift (water vs PBS), supporting their apparent stability. However, the PCL1POEGMA3 micelles exhibit significantly increased size from 56.56 nm in water to 73.20 nm in PBS, which indicates the occurrence of somewhat aggregation and instability of PCL1POEGMA3 micelles in salt medium. The better salt stability of PCL2POEGMA1, PCL2POEGMA2 and PCL3POEGMA1 micelles relative to that of PCL1POEGMA3 counterparts implies that a branched PCL moiety results in the greater stability of self-assembled micelles than a linear PCL block with an identical MW.

In Vitro Drug Loading Doxorubicin (DOX) was encapsulated within the micelle core following the classical dialysis method.21 The DLC and EE of PCL2POEGMA1, PCL2POEGMA2, PCL3POEGMA1, PCL1POEGMA3 micelles are 4.36% and 34.3%, 5.69% and 52.6%,


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8.14% and 62.9%, 4.50% and 39.8% respectively. Of all the four micelle formulations, PCL3POEGMA1 micelles possess the highest DLC and EE values. The branched PCL moiety with the highest DB of three is believed to contribute significantly to the greatest drug loading capacity of PCL3POEGMA1 micelles, likely due to the highest micelle stability as well as the stronger hydrophobic interactions reflected by CMC and DLS data.

In Vitro Drug Release Next, in vitro DOX release profiles of four miktoarm copolymers-based DOX-loaded micelles were evaluated in the physiological condition (PBS, pH 7.4, 150 mM) and in an acidic medium (SSC, pH 5.0, 150 mM) at 37 °C (Figure 5). For all the micelle constructs, incubation at the tumor intracellular pH of 5.0 clearly promoted drug release compared to the cumulative drug release at the extracellular pH of 7.4 within 72 h, which is attributed to the increased solubility of DOX in an acidic medium. Similar phenomena were also reported in the previous in vitro drug release studies.37-39 It is important to note that the cumulative drug release of the four miktoarm copolymers-based micelles shows an increased trend following the order of PCL1POEGMA3> PCL3POEGMA1> PCL2POEGMA2> PCL2POEGMA1 in 72 h at pH 5.0. The fastest drug release of DOX-loaded PCL1POEGMA3 micelle is likely relevant to its instability in contrast to the stability of the other three micelles revealed by DLS.



Figure 5. In vitro drug release profiles of DOX-loaded micelles of PCL2POEGMA1, PCL2POEGMA2, PCL3POEGMA1, PCL1POEGMA3 at different pHs of 7.4 and 5.0, at 37 oC.

Cellular Uptake Study Confocal imaging was further used to qualitatively investigate the intracellular trafficking of four miktoarm star copolymers-based micelles. DOX fluorescence was clearly observed in the cytoplasm and/or nuclei incubated with various micelles for 4 h (Figure 6), which suggests that all the miktoarm star copolymers-based micelles could transport efficiently the anticancer drug into the cancer cells.23,40


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Figure 6. Confocal imaging of free DOX (A), PCL2POEGMA1 (B), PCL2POEGMA2 (C), PCL3POEGMA1 (D) and PCL1POEGMA3 (E) uptake in HeLa cells (nuclei stained blue with DAPI). Note that cells were treated with polymer or free drug at 25%



of their respective IC50 values to minimize cell death.23

The cellular uptake efficiency of four DOX-loaded miktoarm star copolymers-based micelles was further quantified using flow cytometry (Figure 7). It is important to note that the DOX concentration was indeed fixed at 22 µg/mL for all the samples in the quantitative flow cytometry analysis, which is different from the various DOX concentrations at 25% of their respective IC50 values adopted for different samples in the confocal imaging.23 The mean fluorescence intensity of HeLa cells treated with various DOX-loaded micelles was clearly observed in 4 h. The cells treated with DOX-loaded micelles all presented much higher fluorescence intensity than the cells treated with free DOX, which demonstrates that all the miktoarm star copolymers-based micelles are able to transport the anticancer drug into the cancer cells with high efficacy compared to the free drug. The results agree roughly with the confocal observation. The highest DOX fluorescence recorded for DOX-loaded PCL1POEGMA3 micelle is likely attributed to its fastest drug release at pH 5.0 of the four formulations. For the remaining three DOX-loaded micelle constructs, the mean fluorescence intensities show a slightly increased trend following the order of PCL2POEGMA1> PCL3POEGMA1> PCL2POEGMA2 without statistical significance between each group, probably suggesting the insignificant effect of the miktoarm structures on the cellular uptake efficiency of the DOX-loaded stabilized micelles.


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Figure 7. Quantitive measurements of the mean fluorescence intensity after incubation with free DOX, DOX-loaded micelles of PCL1POEGMA3, PCL2POEGMA1, PCL3POEGMA1, and PCL2POEGMA2 in HeLa cells via flow cytometry (4 h incubation, DOX concentration = 22 µg/mL, and 10000 cells were counted). The data were expressed as mean ± SD, n = 3.

In Vitro Cytotoxicity Study The cytotoxicities of various micelles to HeLa cells were assessed by MTS cell viability assay (Figure 8). The blank micelles are non-toxic to HeLa cells (with cell viability above 80%) up to a concentration of 40.0 mg/ml (Figure S5). The half maximal inhibitory concentration (IC50) values of free DOX, DOX-loaded PCL2POEGMA1, PCL2POEGMA2, PCL3POEGMA1 and PCL1POEGMA3 micelles are summarized in Table 2. All the DOX-loaded micelles exhibit a less cytotoxic



activity than the free DOX, which is possibly associated with the release kinetics of free DOX from the micelle constructs.23,40 An exceptional low IC50 was recorded for the DOX-loaded PCL1POEGMA3 micelle, which is similar to the results of flow cytometry analysis and is ascribed to its fastest drug release at pH 5.0 of the four formulations. Among the other three stabilized micelle constructs, the DOX-loaded PCL3POEGMA1 micelle shows the greatest therapeutic efficacy (the lowest IC50), likely attributed to its faster drug release relative to the other two micelle constructs and its highest DLC.

Figure 8. In vitro cytotoxicity of DOX-loaded micelles of PCL2POEGMA1, PCL2POEGMA2, PCL3POEGMA1, PCL1POEGMA3 and free DOX in HeLa cells.


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Table 2. Summary of IC50 values for free DOX, and DOX-loaded micelles of four amphiphilic miktoarm star copolymers. The data were expressed as mean ± SD,

n=3.

Samples

PCL2POEG

PCL2POEG

PCL3POEG

PCL1POEG

MA1

MA2

MA1

MA3

82.71 ±8.86

72.45 ±2.34

62.96 ±5.60

22.00 ±1.11

Free DOX

IC50 3.04 ± 0.25 (µg/mL)

Conclusions In summary, we fabricated successfully four miktoarm amphiphilic star copolymers, PCL2POEGMA1, PCL2POEGMA2, PCL3POEGMA1 and PCL1POEGMA3 using integrated ROP and ATRP techniques starting from four small miktoarm initiators. Further screening of an optimal formulation for anti-cancer drug delivery revealed that PCL3POEGMA1 micelles possessed the lowest CMC, the highest DLC, and enhanced therapeutic efficiency for DOX release of all the synthesized four miktoarm copolymers due to the star PCL moiety with the highest DB. This study thus reveals that the topology of amphiphilic miktoarm star copolymers played a critical role in the their properties and performance as drug delivery systems, and that a branched hydrophobic segment with a higher DB value resulted in the greater therapeutic efficacy than the linear and low branched analogues with an identical MW.



AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ORCID Hua Wei: 0000-0002-5139-9387 Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS The authors acknowledge the financial support from the National Natural Science Foundation of China (51473072 and 21504035), the Thousand Young Talent Program, and the Open Research Fund of State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences.

ASSOCIATED CONTENT Supporting information Detailed feed amounts of chemicals and solvents for the synthesis of various miktoinitiators and polymers, additional 1H NMR spectra, salt stability determined by DLS, and in vitro cytotoxicity study of blank micelles are available in Figure S1-S5.

References


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(1) Enders, S.; Langenbach, K.; Schrader, P.; Zeiner, T. Phase Diagrams for Systems Containing

Hyperbranched

Polymers.

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2012,

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Optimization of Amphiphilic Miktoarm Star Copolymers for Anti-Cancer Drug Delivery

Mingqi Wang, Xiaolong Zhang, Han Peng, Mingkui Zhang, Xianshuo Zhang, Zhe Liu, Liwei Ma, and Hua Wei*


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Optimization of Amphiphilic Miktoarm Star Copolymers for Anticancer

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