Radio-synthesis of protein-gold nanoparticles for theranostics applications

CONSTANZA Y. FLORES; ESTEFANIA ACHILLI; MARIANO GRASSELLI; SILVIA ALONSO

Viena

Encuentro; Meeting of the IAEA?s Coordinated Research Project (CRP); 2015

IAEA

Breast cancer is the tumor with the highest incidence and mortality of women in the world; it is for this reason that many investigations are aimed to therapeutic drug design strategies for diagnosis and treatment. Tremendous advances have been made in the treatment, prevention and early detection of these malignancies; however none of the current therapies are specifically able to cover all the variants of these diseases that differ in their histopathology characteristics and genomic and genetic variations (Gupta, G. P. & Massagué, 2006). For example, 90% of breast cancers without detectable metastases in lymphatic nodes are treated systemically with chemotherapy, although 70-80% of these patients will not develop distant metastasis and therefore suffer from the serious side-effects of this treatment (Van?t Veer et al., 2002). Furthermore, many of the available drugs are not able to reach the site of metastases (Schroeder et al., 2012). For this reason there is a new approach in the development of novel therapeutic strategies which allow high degree of specificity and spatial extent of the tumors even after metastasis spread. This approach is addressed by the nanotechnology (Schroeder et al., 2012).The use of nanotechnology in medicine, also called nanomedicine, is based on the generation of nanostructures, such as nanoparticles (NP), with particular physicochemical characteristics able to be easily detected and some therapeutic loads in the same structure, combining therapeutic and diagnostic functions. Additionally, these NPs have increased efficiency relative their containing therapeutic entity. This is because they can be targeted to specific tumor tissues given its pharmacokinetics, pharmacodynamics and enhanced intracellular activation. These characteristics will depend on the size and surface properties of the NPs.NPs size of currently used in anti-cancer therapy varies between 10-100 nm. An advantage of the use of NPs in such therapies is that the tumor vasculature has higher permeation for macromolecules, in addition to the poorly functionality of lymphatic system in the surround media, NPs accumulate in tumors leading to phenomenon known as ?Effect of enhanced permeability and retention? also called EPR (Nagy et al., 2012; Dvorak et al., 1988). The surface of the NPs has a pivotal role in the fate within the body given by the interactions between it and the local environment. Furthermore, by the covalent attachment of targeting ligands gives rise to specific interactions between target cells and NPs. For example, these aggregates can bind to cell receptors such as the transferrin receptor, which is often over-expressed in many tumors. This functionality will allow the NP to enter the cell via receptor-mediated endocytosis.The use of NPs as anti-cancer therapeutic strategy has multiple benefits over conventional cancer treatments. First, the NPs are capable of carrying a large quantity of drug, protecting them from degradation, and without affecting the pharmacokinetics and biodistribution of the NPs. Secondly, the NPs are large enough to contain multiple ligands on its surface enabling addressing multivalent binding to cellular receptors. Third, a single NP may contain multiple types of drugs, resulting in a simultaneous application in a controlled manner. Fourthly, the activity of the drug can be modulated by the release mechanism designed for it, for example when the drug is activated in higher concentrations inside the cell. Fifth, the use of NP mechanisms could prevent multi-drug resistance as it does not involve the action of protein carriers to income of the drug into the cell. Finally, the combined actions of all these properties achieved by the NP design could minimize unwanted side effects and increase the drug effectiveness (Schroeder et al., 2012).The use of NPs in anticancer strategies has proven to be more effective than drugs alone. Advantages, such as carrying a therapeutic agent into liposomes having a half-life 100 times higher compared to its free form and a significant reduction in toxicity caused by the free drug have been reached. However, this liposome does not provide good intracellular release, which has limited the potentiality for multi-drug resistant cancers and besides it has not cell targeting (Davis et al., 2008)There are different types of NPs according to their chemical composition. First NPs reported were synthetized by conjugation of synthetic polymers with oncologic drugs, followed by liposomes and Albumin NP (Alb-NP) were developed later (Petros & DeSimone, 2010). In order to enhance the NP entrance into the intracellular milieu, compounds such as PEG were included. There are also NPs developed based on inorganic components such as gold, iron oxide and other metals (Kumar, 2007). Current NP therapeutic strategies are based on multifunctional properties, focused on combining both therapeutic and imaging agents within the same particle. For example, gold NPs (Au-NP) have two major advantages in this context; they are not able to undergo oxidation and can, very efficiently, transform electromagnetic energy (visible/NIR) into thermal energy. Furthermore, as a very stable and human body is capable of tolerating an amount of grams of this material without side-effects (Nie & Chen, 2012). More recently, the possibility of using the isotope 198-Au as raw material to Au?NP synthesis, can generate a nanomaterial with radioactive properties, which can emits beta and gamma radiation to the milieu, performing a theranostic tool (therapy and diagnosis properties) (Janib et al., 2010; Xie et al., 2010; Park et al., 2012).Our laboratory has been recently report a new preparation of protein NPs using globular proteins, more specifically Albumin (Alb). Previous results from our research group demonstrated Alb aggregation can be stabilized by the formation of intermolecular covalent bonds generated by hydrogen abstraction of free radicals generated by solvent radiolysis. Tailoring size can be done by changing the reaction medium with a yield higher than 90%. However, and perhaps the most important property is that Alb-NP maintains the three dimensional structure of constitute proteins according to spectroscopic studies. The potential of ionizing radiation for generating nanostructures in a simple and straightforward manner has been demonstrated. In this report a novel NP preparation is described which involves the preparation of a core/shell Au/Alb-NP. Thus, the novel NPs should have advantages of both materials, such as biocompatibility, drug transport and simple detection.