Development of l-Lysine Based Biodegradable Polyurethanes and Their Dual-Responsive Amphiphilic Nanocarriers for Drug Delivery to Cancer Cells

Abstract

The present investigation reports the development of new classes of l-lysine based polyurethanes by a solvent and isocyanate free melt transurethane polycondensation approach. New enzyme and thermo-dual responsive amphiphilic polyurethane nanocarriers were developed for the delivery of drugs both at the intracellular level and at cancer tissue temperature. Multifunctional l-lysine monomers were tailor-made by suitably converting the amine functionalities into urethanes (or carbamates) while masking the carboxylic acid functional unit as amide pendants. The l-lysine monomers underwent melt transurethane polymerization with diols at 150 °C in the presence of catalyst to produce high molecular weight linear polyurethanes. Further, a new amphiphilic l-lysine monomer was designed with a PEG-350 chain as a pendant, and this monomer upon polymerization yielded well-defined amphiphilic aliphatic polyurethanes (APUs). The APU was found to undergo core–shell type self-assembly in aqueous medium to produce nanoparticles of size <175 nm and exhibited excellent encapsulation capabilities for anticancer drugs such as doxorubicin (DOX). The APU nanocarriers showed thermoresponsiveness from clear to turbid solution above the lower critical solution temperature (LCST) at 41–43 °C corresponding to cancer tissue temperature. At the extracellular level, the thermal-stimuli responsiveness (stimuli-1) in the APU nanocarrier was employed as trigger to deliver the DOX at cancer tissue temperature. At the intracellular level, the aliphatic urethane linkages in the APU backbone underwent lysosomal enzymatic-biodegradation (stimuli-2) to deliver DOX. Cytotoxicity studies revealed that the APU nanoparticles were not toxic to cells up to 80.0 μg/mL whereas their DOX-loaded nanoparticles accomplished more than 90% cell death in breast cancer (MCF 7) cells. Confocal microscopy and flow cytometry analysis confirmed that the l-lysine based polymer nanoparticles were readily taken up and internalized in the cancer cells. Live cell imaging using lysotracker was done to prove the intracellular biodegradation of the APU nanocarriers.