Apomaghemite as a doxorubicin carrier for anticancer drug delivery
Graphical abstract
We report here the successful co-encapsulation of 6 nm-maghemite nanoparticles and doxorubicin molecules in the apoferritin capsid. This drug delivery system reaches a drug release period of 10 to 25 days depending on the environmental conditions.
Introduction
Cancer is one of the leading causes of mortality worldwide. For this reason, tremendous efforts in biomedical research have been devoted to clinical therapy and anticancer drug new formulations [1], [2]. Nevertheless, most chemotherapeutics have in common nonspecific tissue biodistribution and drug resistance, so that high doses are needed to increase selectivity. To get over these problems, nanoparticle-mediated drug delivery has emerged as a promising therapeutic methodology for the treatment of cancer [1], [2], [3], [4]. In this regard, multifunctional nanoparticles, including nanocomposites [5], liposomes [6], dendrimers [7], polymers [8], micelles [9] ceramics [10], viruses [11] and protein capsids [12], have been employed as nanocarriers for drug delivery. These nanoplatforms could allow decreasing the dose to the patient (high drug loadings in a small container) and control release, so that succeeding the problems of drug selectivity [13].
Doxorubicin (DOX) is a well-known anthracycline antibiotic which has shown great efficacy against a range of carcinomas. However, this widely used anti-tumor drug is also associated with several common drawbacks, such as poor selectivity and high cardiotoxicities. Therefore, it is crucial to develop novel DOX-targeted and delivery systems to optimize efficiency and minimize toxicity [11].
In contrast to the development and use of separate materials for diagnosis and therapy, theranostics combine these two objectives into one “probe”, which has the potential to overcome undesirable differences in biodistribution and selectivity that currently exist between distinct imaging and therapeutic agents [14].
Even though a wide variety of nanostructures has been shown efficient to host, carry and release drugs in vitro, an in vivo evaluation of biodistribution of these nanocarriers is necessary, which can be performed by a non-invasive technique as MRI. One strategy to address this issue involves the simultaneous incorporation of magnetic nanoparticles and the drug in the same nanocarrier, so obtaining the so-called theranostic agents [15], [16], [17], [18], [19]. In this sense, magnetite and/or maghemite (Fe3O4/γ–Fe2O3) nanoparticles have been used extensively as a paradigmatic magnetic material for MRI in the biomedical field.
Apoferritin, the empty ferritin protein, is a spherical protein shell composed of 24 subunits surrounding an aqueous cavity with a diameter of about 8 nm. This hollow protein can be loaded with different metallic and non-metallic species, as reported by our group and many others [20], [21], [22], [23]. Apoferritin protein is a good candidate as a theranostic platform due to its small size, biocompatibility and nonimmunogenic behavior [24], [25], [26].
In this context, we have recently reported the successful preparation of long-circulating maghemite nanoparticles coated with apoferritin protein capsids, which are effective for MR imaging of the liver for 45 days [27]. These so-called apomaghemites (Apomag) represent a new generation of long-term MRI contrast agents that could allow both an initial diagnosis and also provide information in real time of the progress and efficiency of a medical treatment. All these features prompted us to investigate the possibility of incorporating some anticancer drugs to apomaghemite with the aim of obtaining an MRI agent capable of delivering a therapeutic drug.
Section snippets
Preparation of the maghemite colloid
Magnetite was synthesized with slight modifications to Massart's method [23] by coprecipitation of Fe2 + and Fe3 + salts in 1:2 stoichiometric ratio. Briefly, magnetite nanoparticles were prepared by coprecipitation of Fe2 + [(NH4)2Fe(SO4)2] and Fe3 + [Fe(NO3)3] salts in stoichiometry of 0.5. By adjusting both pH (11.0 for 6 nm nanoparticles) and ionic strength (1 M NaNO3), the size of the resulting magnetite nanoparticles can be controlled [27]. All solutions were carefully deaerated with argon
Results and discussion
One of the most powerful strategies to optimize the efficiency of anticancer drugs is its encapsulation in a nanocarrier. DOX for instance, exhibits side effects when administrated in conventional formulations, i.e. cardiotoxicity and multidrug resistance. For this reason, the development of new nanocarriers to encapsulate and delivery DOX is required.
We have used two different approaches to incorporate DOX into apoferritin. In the first approach, DOX was co-encapsulated with maghemite using a
Conclusions
The ultimate goal of theranostics is to gain the ability to image and monitor the diseased tissue, and drug efficacy with the long-term hope of tuning the therapy and dose in a control manner.
The simultaneous loading of maghemite nanoparticles and DOX has been achieved using co-encapsulation and surface-binding methods. The DOX co-encapsulation method is better suited for sustained drug release over time. The resulting magnetic hybrid display good MRI contrast properties, as reported by our
Abbreviations
- Apo
apoferritin protein
- ApoDOX
doxorubicin encapsulated into the apoferritin protein
- Apomag
maghemite nanoparticles encapsulated by the apoferritin protein
- DLS
dynamic light scattering
- DOX
doxorubicin hydrochloride
- DOX-Apomag
doxorubicin and maghemite nanoparticles co-encapsulated by the apoferritin protein
- DOX-Apomag sb
doxorubicin bound to the surface protein of apomaghemite
- MCF7
human breast cancer cells
- MCF10A
normal breast cells
- MTS
Acknowledgments
This work was funded by the Junta de Andalucía (Project P11-FQM-8136) and by MINECO (Projects CTQ2012-32236).
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