Targeted saponin nanoparticles as a novel tool to enhance the efficacy of tumor-specific toxin therapy by pH dependent trigger

• Applicant: Mayank Thakur, Ph.D.
• Subject Area: Pharmacy
• Term: from 2012 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 228859562

Saporin (Sap-3) based targeted toxins together with particular saponins (Spn) (glycosylated triterpenoids) is proven to have highly augmented, tumor cell specific toxic effects. This synergistic augmentation is found to be more than a million fold in vitro and specific to the tumor cell types. However, specificity is maintained by the targeted toxin while the saponins are widely distributed in the body. Therefore, dose finding and the application scheme of two different routes at different time intervals are major problems. A basic strategy to prepare target specific saponin nanoparticles is therefore warranted, from an in vivo perspective. It is envisaged to develop a bio-degradable nanocarrier which is able to deliver the saponin with or without toxin specifically to the tumor cell. These actively targeted nanoparticles would release the saponin and/or the targeted toxin in a pH dependent manner thus certifying a release inside the endo/lysosomes where the synergistic effect takes place and providing a sure-shot specific tumor cell toxicity. Salient features of the proposed project are as follows.a. The first novel objective is to prepare completely biodegradable and bio-compatible nanoparticles of saponins with proven toxicity enhancement effects. The toxin would be entrapped inside a matrix that would specifically carry the toxin to desired tumor site via ligand-receptor mediated targeting and both components would thus be delivered at the same time for synergistic augmentation of toxin efficacy. b. The second objective is the development of a pH sensitive core having a swelling (at endo/lysosomal pH)-shrinking (at cytosolic pH) core entrapping the toxicity enhancing saponins. The swelling of the shell at acidic pH of endo/lysosomes would lead to the target site-specific release of saponin from the core. The swelling shrinking behavior would be optimally adjusted via chemical modification to control the release pattern of saponins in the vicinity of the tumor to provide a sustained effect. c. A third approach would be to prepare EGFR targeted nanosized particles or vesicles using biocompatible polymer viz. double cross-linked pH sensitive chitosan. Saponins would be entrapped in the core of the chitosan matrix. This strategy would give the flexibility of choosing different natural polymers as basis for utilizing saponins in therapeutics thus reducing hemolytic and inflammatory effects. The prepared systems will be tested for selectivity and specificity to tumor cells in vitro. Most potent and stable systems would thereafter be tested in vivo in a BALB/c and nude mouse model. It is notable that the proposed system is highly flexible, the targeting moiety (EGF) can be replaced by a monoclonal antibody or another targeting domain, and the toxin can be replaced by other toxins or therapeutic modalities. pH dependent release would be a significant step ahead to mitigate the problems with the endosomal escape of therapeutic substances.

• DFG Programme: Research Grants