Encapsulation of an Anti-tumor Chelator in Polymeric Nanoparticles: Development, Optimization, and Assessment

Neoplastic cells require extensive amounts of iron, a vital element for normal cellular growth, for supporting their rapid proliferation. Metal chelators that have long been used to remove heavy metals from the body, have also been utilized in treatment of neurodegenerative diseases and cancer. Thiosemicarbazones are a novel class of chelators that bind to both iron and copper and have been explored for cancer therapy. Di-2-pyridylketone-4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC), a second-generation thiosemicarbazone, has proven to be a particularly promising anti-proliferative agent. However, this chelator has only been explored in its free from in previous studies, limiting its applications. To further advance the application of DpC as a chemotherapeutic, here we aim to develop and optimize a formulation of DpC-loaded nanoparticles (NPs) by using poly(lactic-co-glycolic acid) (PLGA), an FDA-approved biodegradable polymeric material. To this end, we prepared DpC-encapsulated PLGA NPs (PLGA-DpC-NPs) via the nanoprecipitation method and investigated the effect various parameters had on the resultant NPs, including drug-to-polymer ratio, injection rate, stirring rate, and surfactant type and concentration used during nanoprecipitation. The NPs were characterized for size distribution, zeta potential, encapsulation efficiency, and loading capacity to determine the optimal fabrication conditions. Next, we studied the drug release from PLGA-DpC-NPs and the particles’ colloidal and serum stability. Discharge of DpC from NPs showed a more rapid release when NPs were made with PVA than those made with F-127, reaching ~ 90% released after 48 hours compared to ~ 70% released, respectively. All the examined NP formulations showed stability for 24 hours under physiological conditions. Finally, we assessed the in vitro toxicity of PLGA-DpC-NPs against various types of cancer cells. These DpC-loaded NPs were highly toxic with IC50 values of ~ 51 nM, 83 nM, and 178 nM in malignant human breast cancer, human glioblastoma, and human colorectal adenocarcinoma, respectively. This study is the first to report the encapsulation of DpC in a nanocarrier that may advance the use of this anti-proliferative chelator in oncological treatments in the future.