NABBA project generated nanoparticles (NPs) for drug delivery based on different self-assembling biocompatible materials: lipids, polysaccharides, polymers such as polymethacrilate or polyisoprene. The materials must self-assemble in physiological medium (water) incorporating the greatest possible amount of drug. The requirement for self-assembling must be finely tuned, nature exploits liposomes, mainly composed by phospholipids in which the presence of both hydrophobic and hydrophilic moieties favour aggregation in water generating a bi-layer (Fig.3) in which both hydrophobic and hydrophilic groups can be incorporated.
Following the example of nature other polymeric biocompatible materials containing both hydrophobic and hydrophilic moieties have been developed, optimising the loading capacity and the conditions to deliver the drug. Alternatively, the self-assembly has been performed using a mixture of cationic and anionic biopolymers. The capacity to load the drug and the stability of the NPs at different pH were accurately tuned in order to allow them to release the drug at the pathological site, in the required amount. The problems faced are the following: i) how to increase the amount of drug loaded in the NP; ii) how to induce the collapse of the NPs selectively at the pathological site, in order to release the drug; iii) how to direct the NPs selectively at the pathological site (suppose the cancer cell). NABBA project developed different strategies for each problem. For example, in order to increase the amount of drug carried by the NPs, instead of encapsulate it, the drug has been covalently linked to a polymeric component, with a linkage that can be cleaved at the pathological site. Exploiting this strategy, even two different drugs can be inserted (Fig.4)
The goal to direct selectively the NPs at the pathological site, allowing them to overcome the biological barriers that stand in the way, is very difficult. The NPs have been decorated at the surface with molecules (targeting agents) selectively interacting with receptors overexpressed at the pathological sites, specifically at the vascular epithelia and tumor cell membrane. This interaction will favour the transport trough the biological barriers. In NABBA project different targeting agents have been attached at the surface on the NPs, in particular carbohydrates such as mannose that specifically interact with the mannose receptors of the dendritic cells, the cells of our immune system. The need to induce the collapse of the NPs and the release of the drug at the pathological site has been faced with different strategies, from one side the NPs were built in such a way that they collapse at specific conditions present at the pathological site (lower pH, specific enzymes, oxidative conditions). From the other side, the possibility to induce the collapse by external forces such as an ultrasound (US) (Fig.5) been focused at the pathological site, was successfully explored in the NABBA project.
In order to study the efficacy of the NPs for drug delivery, first of all in vitro models of the biological barriers and 3D microenvironments were setup for different pathologies. Then analytical methods were standardized to follow the NP fate in vitro and in vivo. Finally, the efficacy of NPs to spread into the pathological microenvironment, their capacity to overcome the biological barriers and to release the drug, were tested. NABBA project setup models of the BBB, lung epithelia and pseudomonas biofilms, and developed 3D spheroids mimicking the microenvironment of pancreatic cancer and models of lung infections.
