Chemical elaboration of synthetic and natural bioactive compounds to improve bioavailability and activity

The project aimed to synthesize new prodrugs of bioactive molecules and new self-assembling fully biocompatible macromolecular structures as vehicles for drug delivery. Initially, I worked on the chemical modification of the phenolic group of pterostilbene – a natural bioactive polyphenol used as model in this study – in order to improve its bioavailability after oral administration. I synthesized and tested new pterostilbene derivatives using five different types of protecting groups to functionalize the hydroxyl group and convert the natural phenol, specifically, into a methylthiomethyl ether (MTM), a phosphonic ester, an alkylcarbonyloxymethyl (ACOM) ether, an alkyloxycarbonyloxymethyl (AOCOM) ether and an N-alkyl-N-alkyloxycarbonylaminomethyl (NANAOCAM) ether. The derivatives display very different chemical stability profiles. In preliminary screenings, the AOCOM and ACOM derivatives gave the best results in terms of chemical and biological stability. These compounds were thus tested in pharmacokinetic experiments in vivo. The blood concentration vs. time profiles of pterostilbene and its sulfate obtained with the ACOM prodrug were very similar to those determined after administrating pterostilbene as such. Those afforded by the AOCOM derivative showed instead a considerable shift to longer times after administration, indicating that it indeed behaves as a prodrug. During the second year, I developed two new classes of selective tumor killing agents based on the natural phenol 5-hydroxypsoralen and on the anti-leprosy drug clofazimine. The aim of this part of my project was the design, synthesis and test of novel selective inhibitors of the mitochondrial potassium channel Kv 1.3. This channel is expressed in the inner mitochondrial membrane of many types of cancer cells and its inhibition plays an important role in the induction of apoptosis. In a series of in vitro and in vivo tests three of my psoralen derivatives (patented) proved to be remarkably effective. As for the clofazimine derivatives, only a few in vitro assays have been performed so far and further in depth tests are currently under way. More recently, during the time I spent at ETH in Zürich, I worked on the design and synthesis of biocompatible polymeric micelles for drug delivery. In particular, I developed and characterized a series of novel resveratrol –OEG-co-adipate and polymethyloxazolines -co-pterostilbene based copolymers that self-assemble in water to form core-shell nanocarriers. In order to test their ability as nanocarriers I loaded them with clofazimine and studied their behavior under various experimental conditions. In the case of polyoxazolines-co-pterostilbene constructs, these preliminary tests gave encouraging results which prove the value of this approach to obtain a highly modular copolymer platform to be used for the safe delivery of its drug load into solid tumors by exploiting the Enhanced Permeability and Retention (EPR) effect