Supramolecular Conjugated Polymer Systems with Controlled

Jan 6, 2017 - Infections of antibiotic-resistant pathogens have caused a series of public health crises across the world. According to the latest publ...
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Supramolecular Conjugated Polymer Systems with Controlled Antibacterial Activity Haotian Bai, Hongyi Zhang, Rong Hu, Hui Chen, Fengting Lv, Libing Liu, and Shu Wang Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b04469 • Publication Date (Web): 06 Jan 2017 Downloaded from http://pubs.acs.org on January 6, 2017

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Supramolecular Conjugated Polymer Systems with Controlled Antibacterial Activity a

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Haotian Baia, Hongyi Zhangb, Rong Hua, Hui Chena, Fengting Lv *, Libing Liu , and Shu Wang * a

Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China b Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, U.S.A. ABSTRACT: Infections of antibiotic-resistant pathogens nowadays have caused series of public health crises across the world. According to our latest published reports, antibiotic switch has been recognized as a potential strategy to control antibacterial activity for combating the serious drug-resistance. Thus, it is anticipated that more effective antibiotic switches should be obtained by further exploring the developed strategies. Here, we report an improved pretreatment strategy using surfactant (Triton X-100) for constructing effective supramolecular antibiotic switch based on poly(fluorene-co-phenylene) derivative (PFP) and cucurbit[7] uril (CB[7]), which can regulate the aggregation state of polymers before supramolecular self-assembly process. Triton X-100 can regulate the aggregation states of conjugated polymers, which is used to successfully realize the reversible control of bactericidal activity of PFP in dark and under white light irradiation by the supramolecular assembly/disassembly between PFP and CB [7]. Specialized antibiotic switches are significantly important to fight with pathogenic infections and solve drug-resistance crisis in the future. 1. INTRODUCTION The emergence of antibiotic resistance nowadays has been rising to dangerously high levels all around the world.1-3 According to the published reports of World Health Organization (WHO), methicillin resistant staphylococcus aureus (MRSA) caused the death of a 12 years old schoolboy from Southern California, and a resistant type of E. coli infected an egyptian businessman when he beats leukaemia.4 Currently, severe bacterial infections has caused the death of around 2 million children annually.5 Such reallife examples resulted from antibiotic resistance, which has been one of the biggest crises to global health today. Moreover, both overusing and misusing of antibiotics are the primary causes of the development of resistant pathogens.6,7 Since penicillin was discovered accidently by Fleming in 1928,8 drug development as a traditional strategy for solving antibiotic resistance has been continuing for almost 100 years. However, these traditional strategies cost a lot of money and require a long process from experimental study to marketing and clinical application.9 Thus developing neoteric strategies and drugs is significant to solve the crisis of resistant pathogens, including new antibiotics, antimicrobial peptides and artificial nanoparticles

etc.1,3,9-11 “Antibiotic switch”, as one of the most promising candidates has proved to control antibacterial activity by supramolecular assembly /disassembly between cationic conjugated polymers and CB[7] reversibly, which means we can prevent the indiscriminate use of antibiotics and reduce accumulation in environment as well.12,13-15 Scientists and clinicians in crossdisciplinary field have a long way to go to design and construct various antibiotic switches. Cationic conjugated polymers with quaternary ammonium (QA) side chains are conveniently synthesized and stable in different media chemically and physically. Most of them have the ability to sensitize the surrounding oxygen to produce reactive oxygen species (ROS).12 In our latest research, we have found that the bacterial killing ability of poly(phenylene vinylene) derivative (PPV) could be controlled efficaciously by just adding CB[7] and amantadine (AD).12,14 Recently, poly(fluorene-co-phenylene) derivative (PFP), which is a class of important cationic conjugated polymers16-18, was used to construct supramolecular probes with CB[7] for detecting different bacteria and fungi through different interaction manners toward pathogens before and after disassembly.19 Inspired by the aforemention-

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Scheme 1. (a) The schematic supramolecular assembly process between PFP and CB[7], and the disassembly process of PFP/CB[7] complex by adding AD solution. (b) The schematic antibacterial process of the antibiotic switch with or without pretreatment of Triton X-100.

ed works, we want to explore whether PFP can also be used to construct antibiotic switch with CB[7] for combating the serious drug-resistance, since different conjugated polymers have both diverse degree of aggregation state due to various π-conjugated backbones, water solubility and different thermodynamic phenomenon during supramolecular self-assemble with CB[7].20 Here, we described an improved method for constructing supramolecular antibiotic switch for reversi-

bly controlling antibacterial activity of PFP, utilizing the disaggregating effect of Triton X-100 (polyoxyethylene octyl phenyl ether, a nonionic surfactant commonly used in biological work)2123 , and the supramolecular assembly and disassembly process between active sites of PFP and CB[7]. As shown in Scheme 1b, without the pretreatment of Triton X-100, PFP cannot construct the effective antibiotic switch. On the contrary, by the pretreatment with Triton X-100 (0.06%), 2

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the antibacterial ability of PFP can be turned off by adding CB[7] and be turned on again with the addition of AD. With the aid of Triton X-100, we could change the aggregation degree of conjugated polymers to effectively proceed supramolecular assembly/disassembly, and the biological function for killing pathogens was kept at the same time. Moreover, the regulation of antibacterial ability of PFP both in dark and under white light irradiation was realized. It is believed that the pretreatment strategy is very helpful for constructing more effective antibiotic switches of polymers and treating pathogenic infections of antibiotic-resistance over the long haul. 2. Results and discussion. The PFP was synthesized by pervious reports16 and PFP/CB[7] complex was constructed by mixing the aqueous solution of PFP and CB[7] as the published reports.12,19 As shown in Figure 1a, compared with PFP alone, the emission intensity of PFP/CB[7] complex increased distinctly, which demonstrated that CB[7] had changed the spatial conformation and reduced the aggregation degree of PFP. After adding AD into the solution of PFP/CB[7] complex, the fluorescence intensity

of PFP/CB[7] decreased partly, owing to the formation of AD/CB[7] by competitive replacement. However, it was still higher than that of PFP, which indicated that the aggregation state of polymers partly recovered to the original condition. In order to further verify that the emission fluorescence intensity enhancement of PFP/CB[7] complex was the result of the decrease of aggregation degree, Triton X-100 as a general surfactant which can be used to reduce the aggregation was added into the PFP solution. Figure 1a illustrates that Triton X-100 (0.06%) can also reduce the aggregation of PFP markedly, and the increased fluorescence intensity reveals that the aggregation state of PFP treated with Triton X-100 is looser than those of both PFP/CB[7] complex and PFP/CB[7] with AD. To further demonstrate that Triton X-100 could decrease the aggregation degree of PFP, zeta potential (ζ) and size distribution measurements were conducted by using Dynamic Light Scattering (DLS). As shown in Figure 1c and 1d, after the addition of Triton X-100, the size of PFP decreased distinctly, which means that Triton X-100 enhanced the dispersion of PFP in aqueous. Thus, we speculated that the looser structure of polymers exposed more QA side chains and had better sterilization ability. A tra-

Figure 1. (a) The fluorescence spectra of PFP with different treatments in water and the concentration of PFP in every sample is 15 µΜ in Repetitive Units (RUs). [PFP]:[CB[7]]=1:20, [CB[7]] : [AD]=1:5. (b) The size and zeta potential (ζ) of PFP and PFP with 0.06% Triton X-100. [PFP]=15 µΜ in RUs . (c, d) Size distribution histograms of PFP with and without Triton-X100. 3 ACS Paragon Plus Environment

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ditional plate counting method was employed to investigate the antibacterial activity changes of PFP/CB[7] complex before and after the addition of AD. These results showed that CB[7] did not decrease the bacteria-killing ability of PFP expectedly. As shown in Figure 2a, the killing efficiency of PFP/CB[7] complex (58%) was higher than that of PFP alone (49%). After the disassembly process of PFP/CB[7] complex by adding AD, the killing efficiency (60%) had no obvious change, which was quite different from that of PPV with QA side chains, whose killing bacterial ability can be controlled by CB[7] and AD.12,14 According to our previous research, CB[7] could be used to turn-off the bactericidal ability of PPV with QA side chains by supramolecular assembly, because CB[7] could encapsulate and prevent the QA side chains from binding and inserting into negatively charged membrane of bacteria. Owing to a more stable formation of CB[7]/AD, after adding AD, the QA side chains could be released again by competitive replacement and the biocidal activity of PPV recovered. However, PFP has totally different π-conjugated backbones and water solubility compared to PPV. Fluorescence spectra (Figure 1a) revealed that during the encapsulation process of QA side-chains with CB[7], the aggregation state of PFP was inhibited

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distinctly by CB[7] as bulk “noncovalent building blocks”, which induced more QA side chains protruded to the outside. Meanwhile, heat absorption phenomena during self-assemble between PFP and CB[7]17 also proved the result of change in fluorescence intensity. However, isothermal titration calorimetry (ITC) results quantificationally elucidate that the binding stoichiometry between PFP and CB[7] was 0.235, which means that CB[7] could not encapsulate all the side chains. Because of the steric hindrance caused by the close distance QA side chains, PFP/CB[7] complex had low aggregation degree and more effective QA side chains which could insert into the membrane of bacteria and therefore caused a little enhancement of killing bacteria ability comparing with the pristine PFP.5,24 Moreover, the aggregation state of PFP partly recovered to its initial state induced by the addition of AD, while some QA side chains without encapsulation were still free compared with the pristine PFP, which caused the increase of microbicidal efficacy. Thus, by single addition of CB[7] and AD, we cannot obtain effective supramolecular antibiotic switch based on PFP, and it is necessary to explore an improved strategy to regulate the antibacterial ability of PFP.

Figure 2. (a) The photographs of colony forming units (CFU) for E. coli on LB agar plate in dark for 20min. (b) CFU reduction of antibiotic switch based on PFP without pretreament. (c) CFU reduction of antibiotic switch based on PFP treated with 0.06% Triton X-100. [PFP] = 15 µΜ in RUs, [PFP] : [CB[7]] =1:20, [CB[7]] : [AD]=1:5. 4 ACS Paragon Plus Environment

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To acquire reversible regulation of antibacterial ability, pretreatment strategy was utilized to change the aggregation state before supramolecular assembly/disassembly. As shown in Figure 2, Triton X-100 was applied to enhance the dispersion of PFP in water and highlight the encapsulated role of CB[7] before the supramolecular regulation. In the sterilization experiment, as displayed in Figure 2c, the result demonstrated that Triton X-100 could actually reduce the aggregation degree of PFP at the same time; the released QA side chains could effectively improve the bacteria-killing ability (77%). CB[7] could also encapsulate the released QA side chains and turn-

off the killing bacteria ability effectively (The inhibition ratio declined to 61%). As expected, upon the addition of AD into the bacteria treated with PFP/CB[7], the bacteria-killing efficiency was turned-on again (The inhibition ratio recovered to 91%). It should be also noted that Triton X-100 (0.06%) and AD (0.15 mM) had no effect on the growth of pathogens (Figure S1). By the process of assembly and disassembly, we successfully constructed the desirable supramolecular antibiotic switch based on PFP treated with Triton X-100, and simultaneously realized the reversible control of antibacterial activity without irradiation.

Figure 3. (a) Fluorescence intensity of DCF in the presence of PFP treated with 0.06% Triton X-100 before and after assembly, as well as adding AD upon white light irradiation (1 mW/cm2, for 0-5 min). (b) CFU reduction of antibiotic switch based on PFP with 0.06% Triton X-100 under white light irradiation. (c) The photographs of CFU for E. coli on LB agar plate under white light irradiation (45 mW/cm2) for 10 min. [PFP] = 15µΜ in RUs, [PFP]:[CB[7]] = 1:20 [CB[7]] : [AD] = 1:5. It is well known that water-soluble conjugated polymers (WSCPs) can sensitize surrounding oxygen to produce ROS upon illumination for killing pathogens.25-27 Thus, we also studied the antibacterial regulation of PFP/CB[7] supramolecular complex with pretreatment of Triton X-

100 upon white light irradiation. Primarily, 2,7dichlorofluoresceindiacetate (DCFH-DA), which could be converted into highly fluorescent 2,7dichlorofluorescein (DCF, quantum yield=90%) in the presence of ROS, was utilized to study the ROS production. As shown in Figure 3a, the flo5

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rescence intensity increased from 515 nm to 565 nm dramatically within 5 minutes upon white light irradiation (1 mW/cm2). It demonstrated that PFP in Triton X-100 solution (0.06%) could also sensitize the surrounding oxygen and CB[7] could prevent the releasing of ROS. After the replacement process of PFP by AD, the ROS generation ability of PFP/CB[7]was fully recovered to the pristine PFP. The antibacterial experiments upon white light irradiation (45 mW/cm2) for 10 min were performed as well. As Figure 3b shown, PFP treated with 0.06% Triton X-100 could kill 79% E .coli, while only 60% bacteria were killed by PFP/CB[7] complex. As expected, the inhibition ratio of PFP/CB[7] towards E .coli was recovered to 92% with the addition of AD. It is worth noting that the antibacterial mechanism of the PFP supramolecular antibiotic switch in dark and under irradiation are totally different. In dark the bactericidal effect was realized owing to the QA side chains of polymers, since QA could attach to and insert into the membrane of bacteria. But under white light irradiation, it was depended mainly on the bactericidal ROS, which was generated by sensitizing oxygen in the presence of the backbone of polymers. The sterilization experiment result under white light irradiation was the synergy effect of the backbone and the side chains. 3. CONCLUSION We have successfully used pretreatment strategy by using Triton X-100 for constructing a supramolecular antibiotic switch based on the selfassembly and the disassembly between PFP and CB[7], which was applied for controlling the antibacterial ability reversibly both in dark and under white light irradiation. By changing the aggregation state of polymers before supramolecular assembly and disassembly, the antibacterial function retains as well, and it does not require any additional chemical modification. This pretreatment strategy will contribute to constructing effective antibiotic switches of polymers, whose antibiotic activity cannot be controlled by the only addition of CB[7] and AD. The pretreatment strategy is general for other polymers with similar structure properties and is very helpful to construct more antibiotic switches for fighting with

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pathogenic infections and solving drug-resistance crisis. 

ASSOCIATED CONTENT

Supporting Information. Experimental procedures and additional Figures S1. This material is available free of charge via the Internet at http://pubs.acs.org/. 

AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected] [email protected] (L.L.). 

(S.W.);

ACKNOWLEDGEMENTS

The authors are grateful to the National Natural Science Foundation of China (Nos. 21533012, 91527306, 21373243), and Strategic Priority Research Program of the Chinese Academy of Sciences (XDA09030306). 

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