Theranostics 2018, Vol. 8, Issue 6 1591 Ivyspring International Publisher Theranostics 2018; 8(6): 1591-1606. doi: 10.7150/thno.22430 Research Paper Bioinspired Multifunctional Melanin-Based Nanoliposome for Photoacoustic/Magnetic Resonance Imaging-Guided Efficient Photothermal Ablation of Cancer Liang Zhang1*, Danli Sheng2*, Dong Wang1, Yuanzhi Yao3, Ke Yang1, Zhigang Wang2, Liming Deng2, Yu Chen4 1. Department of Ultrasound, The First Affiliated Hospital of Chongqing Medical University, Chongqing 400016, P. R. China; 2. Institute of Ultrasound Imaging, The Second Affiliated Hospital of Chongqing Medical University, Chongqing, 400010, P. R. China; 3. Department of Ultrasound, Chongqing Cancer Hospital, Chongqing Cancer Institute, Chongqing Cancer Center, Chongqing 400030, P. R. China; 4. State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, P. R. China. * These two authors contributed equally to this work. Corresponding authors: D. Wang ([email protected]); Y. Chen ([email protected]) © Ivyspring International Publisher. This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/). See http://ivyspring.com/terms for full terms and conditions. Received: 2017.08.18; Accepted: 2017.12.08; Published: 2018.02.07 Abstract Background: The construction of theranostic nanosystems with concurrently high biosafety and therapeutic performance is a challenge but has great significance for the clinical translation of nanomedicine for combating cancer. Methods: Bio-inspired melanin-based nanoliposomes (Lip-Mel) as theranostic agents were constructed for simultaneous photoacoustic (PA) imaging- and T1-weighted magnetic resonance (MR) imaging-guided photothermal ablation of tumors, which was demonstrated both in vitro and in vivo. The high biosafety of Lip-Mel was also systematically evaluated. Results: The achieved Lip-Mel nanoliposomes demonstrated their imaging capability for both PA -1 -1 and T1-weighted MR imaging (r1 = 0.25 mM ·s ) both in vitro and in vivo, providing the potential for therapeutic guidance and monitoring. Importantly, the desirable photothermal-conversion efficiency of the as-prepared Lip-Mel achieved complete eradication of tumors in breast cancer-bearing mice, exhibiting remarkable photothermal-based therapeutic performance. In particular, the efficient encapsulation of melanin into the PEGylated liposome mitigated the potential toxicity of melanin and improved the photothermal performance of the loaded melanin. Systematic in vivo biosafety evaluations demonstrated the high biocompatibility of Lip-Mel at a high dose of 100 mg/kg. Conclusion: In this work, we reported a bioinspired strategy where melanin, a natural product in the human body, is encapsulated into PEGylated nanoliposomes for efficient theranostics with high biocompatibility. This work provides a new strategy for creating desirable theranostic agents with concurrent high biocompatibility and satisfactory theranostic performance through the use of materials that totally originate from biosystems. Key words: Melanin, Liposome, Photoacoustic imaging, MRI, Photothermal ablation, Nanomedicine Introduction Theranostic nanomedicine has been developing cancer in the past decades [1-4]. A large number of rapidly for early diagnosis and efficient therapy of inorganic, organic, and organic-inorganic hybrid http://www.thno.org Theranostics 2018, Vol. 8, Issue 6 1592 theranostic nanoagents have been explored for or side effects of nanoagents by prolonging their versatile biomedical applications, including gold circulation and increase the passive accumulation of nanoparticles (Au NPs) [5, 6], quantum dots (QDs) [7, delivered therapeutic agents [37, 38]. 8], India ink [9], superparamagnetic iron oxide (SPIO) To develop a novel melanin-based theranostic [10, 11], carbon-based nanomaterials [12, 13], nanomedicine, we herein successfully constructed synthetic dye-based nanocarriers (e.g., ICG, IR780) melanin-based nanoliposome-PEG (Lip-Mel) by a [14-17], etc. As these nanoagents are optical absorbers, facile trichloromethane-injection and freeze-drying when stimulated by laser irradiation at specific wave- strategy. Melanin was entrapped in nanolipo- lengths, they can generate noninvasive photoacoustic some-PEG to mitigate its toxicity, improve contrast enhancement, heat tissues to higher phagocytosis by tumor cells and enhance the PTT temperatures, and even cause thermal damage. effect. The physiochemical properties of Lip-Mel were However, the further clinical implementation of these systematically characterized. In particular, these nanoagents is hindered by biosafety issues because of Lip-Mel nanosystems were developed as contrast their poor biodegradability and unclear biocompat- agents for dual-mode contrast-enhanced PAI and ibility [18, 19]. To solve this critical biosafety issue, MRI, providing the potential for therapeutic guidance theranostic nanoplatforms synthesized from and monitoring. The high photothermal-conversion endogenous ingredients from living organisms have efficiency of Lip-Mel successfully achieved efficient attracted tremendous attention in theranostic ablation of tumor tissue. nanomedicine for further clinical translation [20-22]. Melanin, mainly presenting in the skin, hair Materials and Methods follicles and eyes, is an endogenous biological Materials pigment with intrinsic optical absorption capability [23, 24]. Recent progress has preliminarily Melanin and propidium iodide (PI) were demonstrated that melanin-based nanoparticles could purchased from Sigma Aldrich (St. Louis, MO, USA). serve as multifunctional contrast agents for both 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine photoacoustic imaging (PAI) [25-27] and magnetic (DPPC), 1,2-distearoyl-sn-glycero-3-phosphoethanol- resonance imaging (MRI) [26-29]. Such melanin-based amine-N-[methoxy (polyethylene glycol)-2000] (DS contrast agents possess desirable biosafety and PE-mPEG2000) and cholesterol were purchased from mitigate side effects. Therefore, a melanin-based Avanti Polar Lipids, Inc. (Alabaster, AL, USA). nanoplatform with endogenous composition could Calcein acetoxymethyl ester (Calcein-AM) was show great promise in diagnostic imaging based on its purchased from Santa Cruz Biotechnology (TX, USA). optical properties and satisfactory biocompatibility. Cell Counting Kit-8 (CCK-8) was purchased from Photothermal therapy (PTT) is a noninvasive Dojindo (Japan). 1,1'-dioctadecyl-3,3,3',3'-tetramethyl- therapeutic modality for tumor therapy, featuring a indocarbocyanine perchlorate (DiI), 2-(4-Amidino- short recovery period, low recurrence rate, and phenyl)-6-indolecarbamidinedihydrochloride (DAPI) real-time temperature monitoring, showing superior and 1,1’-dioctadecyl-3,3,3’,3’-tetramethylindotricarbo- characteristics compared to conventional surgery and cyanine iodide (DiR) were obtained from Beyotime chemotherapy [30, 31]. Typically, within the tumor Technology. Deionized water was obtained from a tissue, PTT agents absorb near infrared (NIR) light Millipore water purification system. All reagents were and convert light energy into heat, eventually leading used without further purification. to irreversible cell damage (apoptosis and coagulative Synthesis of Lip-Mel and Lip necrosis of tumor cells) and tumor ablation [30-32]. In Lip-Mel and Lip were prepared by a particular, melanin, as a potential PTT agent, has trichloromethane-injection and freeze-drying demonstrated high photothermal conversion strategy. First, a certain mass of hybrid lipid (12 mg efficiency [33]; but, melanin delivery has not been DPPC, 4 mg DSPE-mPEG2000 and 4 mg cholesterol) satisfactorily effective to achieve high PTT efficiency. was dissolved into 20 mL trichloromethane (CHCl3). Nanoliposomes, as a potential drug carrier Melanin granule (2 mg) was dissolved in 5 mL nanosystem, have the advantages of tunable drug ammonium hydroxide (NH3·H2O), and then loading, easy metabolism, prolonged biological ammonia was volatilized completely by rotary half-life and low toxicity [34, 35]. In particular, evaporation in a water bath at 55 oC. The prepared PEGylation of liposomes (PEG: polyethylene glycol) melanin solution (2 mL) was then transferred into a can increase the bioavailability of drugs or 100 mL round-bottomed flask in a water bath at 65 oC nanoagents by overcoming the critical issue of quick with a magnetic stirrer. Then, the trichloromethane- elimination by the mononuclear phagocyte system lipid solution was contained into a 20 mL syringe and (MPS) in systemic circulation [36], minimize toxicity was added dropwise into the above melanin aqueous http://www.thno.org Theranostics 2018, Vol. 8, Issue 6 1593 solution at a flow rate of 0.1 mL/min monitored by a Cell culture and MDA-MB-231 tumor-bearing high-precision syringe pump (Baoding Longer mice model Precision Pump Co., Ltd, China). After the removal of The human breast cancer MDA-MB-231 cell line the trichloromethane, self-assembled phospholipids was obtained from Institute of Ultrasound Imaging, formed the liposomes with melanin aqueous solution Chongqing Medical University (Chongqing, China) in the core. The formed melanin-loaded liposome was and cultured in high glucose dulbecco's modified then homogenized using an ultrasonic probe (Sonics eagle medium (DMEM) supplemented with 10% fetal & Materials Inc., USA) at 100 W for 2 min. The