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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - THERAGEL (Development of a chemotherapeutic gel for glioblastoma multiforme treatment)

Teaser

Summary

The Theragel project was designed to create a novel therapy for the treatment of glioblastoma multiforme (GBM), the most aggressive and common form of brain cancer. GBM typically results in death in the first 15 months after diagnosis. It accounts for 15.4% of all primary brain tumours and its relative survival estimates are quite low; 5% of patients survive five years post diagnosis. The average incidence of GBM in Europe is approximately 3.2 per 100,000 individuals. Moreover, an increase is projected for the number of patients newly diagnosed with GBM (35,420 new cases are predicted in 2033). For the better chances of survival and the wellbeing of the patients, there is a great need for new strategies to obtain more efficient treatments.
Nowadays, the current standard of care for GBM comprises surgical resection followed by a combination of implantation of carmustine wafers (GliadelÂ®) and concomitant temozolomide (TMZ) administered systemically. This administration process increases the likelihood of unwanted side effects and sometimes it is not effective due to the restrictive nature of the blood brain barrier. In addition, the cytotoxic effects of carmustine are hindered by poor surface contact with the tumour, large diffusion distances through brain tissues and increased risk of side-effects. Therefore, the state-of-the-art is far from optimal and new strategies are warranted to deliver therapies with higher efficacy and low toxicity.
Due to the treatment limitations, the main objective of the Theragel project was the development of a safe, innovative and effective delivery system for the local administration of chemotherapeutic drugs into a specific area of the brain. In particular, I have designed a novel delivery system combining an injectable polymer matrix containing the antitumoral drug TMZ, and gated mesoporous silica nanoparticles (MSNs) loaded with another chemotherapeutic compound. The polymer matrix was designed to provide a sustained release of TMZ and MSNs, with the intention to selectively deliver the cargo in GBM cells.

Work performed

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.

Final results

The results delivered by THERAGEL constitute a solid proof of the strong capabilities of local delivery systems based on the conbination of injectable polymers and MSNs to meet the needs of brain tumor treatment. The controlled and local administration of cytotoxic drugs by using smart depots will offer translatable alternatives able to provide cost-effective treatments with significant impact in near future advanced therapies