In Theragel, the preliminary validation of the proposed delivery system has been carried out with a gel formulation based on crosslinked hyaluronic acid (HA) polymer and previously described redox-responsive gated MSNs. The presence of reductive species in the media provided a triggered release of the drug loaded into the MSNs. In an attempt to study the capability of in situ forming gels to encapsulate MSNs, a series of gels was firstly prepared with different amounts of redox-MSNs loaded with a model dye. The results showed that more than 50 mg/mL of the MSNs could be incorporated into the structure of the gels without interfering with the gelation process. In addition, the release profile of the encapsulated dye was monitored during time in the presence and absence of a model reductive species. We demonstrated that the gated MSNs keep their responsive behaviour after the encapsulation process.
To realise the full potential of the final gel formulation, the bioactivity using GBM tumor cell lines was assessed. In this case, MSNs loaded with the chemotherapeutic agent doxorubicin (DOX) was used. A cytotoxic effect dependent on the dose of gel system over time was observed, which demonstrated the sustained release of DOX from the gel loaded with responsive nanoparticles. These results successfully confirmed that the combination of in situ forming gels with responsive MSNs is a suitable strategy to design carriers for the local sustained release of chemotherapeutics. In principle, this approach can be applied to the combination any polymer and any gated MSNs.
As an attractive option to provide nanoparticles targeting to the disease, we also designed a new gated material using chlorotoxin peptide as promising capped and targeting agent. Interestingly, we determined that the peptide needs to be attached to the MSN surface following a chemical modification in one of the terminal chains of the peptide, adding a new functional group that allows to maintain the initial peptide structure during functionalization.
In parallel and as a result of our interaction with InGell Labs, we evaluated a set of polymers that are liquid at room temperature and thus injectable, which was necessary for our intended final application. Extensive release studies of both TMZ and carmustine, were carried out for all polymers. Commercial Gliadel wafers were employed as model for the release profile of carmustine. The best performing polymer was selected according to the following principles: i) maximum amount of drug released during the time of experiment, ii) limited initial burst release and iii) physical consistency of the gels.
Finally, the release of MSNs from the polymeric matrices was assessed. We compared the release profile of nanoparticles from two different gel types and studied the effect of the surface modification of MSNs on the kinetics of release. The release of the particles from the polymer was sustained in the two cases during the time of experiment. We suggested that the surface charge and the hydrophobic/hydrophilic character of the polymer was the key parameter to determine the interaction between the MSNs and the polymer and consequently the release profile. Most importantly, the influence of the MSNs in the release profile of TMZ was carefully studied. For a hydrophobic polymer, the presence of MSNs in the polymer matrix at the same time as TMZ, impaired the diffusion of the drug, and this effect was higher with surface functionalised MSNs. On the contrary, in the case of a more hydrophilic polymer, the nanoparticles competed for the hydrophilic regions in the gel, thus enhancing the diffusion of TMZ out of the polymer matrix.
