Optimization of the Single Emulsion Method for Encapsulation of a Cancer Drug in Nanoparticles

Functionalizing Thiosemicarbazones for Covalent Conjugation

Thiosemicarbazones (TSCs) with their modular character (thiosemicarbazides + carbonyl compound) allow broad variation of up to four substituents on the main R1R2C=N(1)-NH-C(S)-N(4)R3R4 core and are thus interesting tools for the formation of conjugates or the functionalization of nanoparticles (NPs). In this work, di-2-pyridyl ketone was introduced for the coordination of metals and 9-anthraldehyde for luminescence as R1 and R2 to TSCs. R3 and R4 substituents were varied for the formation of conjugates. Amino acids were introduced at the N4 position to produce [R1R2TSC-spacer-amino acid] conjugates. Further, functions such as phosphonic acid (R-P(O)(OH)2), D-glucose, o-hydroquinone, OH, and thiol (SH) were introduced at the N4 position producing [R1R2TSC-spacer-anchor group] conjugates for direct NP anchoring. Phenyl, cyclohexyl, benzyl, ethyl and methyl were used as spacer units. Both phenyl phosphonic acid TSC derivatives were bound on TiO2 NPs as a first example of direct NP anchoring. [R1R2TSC-spacer-end group] conjugates including OH, S-Bn (Bn = benzyl), NH-Boc (Boc = tert-butyloxycarbonyl), COOtBu, C≡CH, or N3 end groups were synthesized for potential covalent binding to functional molecules or functionalized NPs through amide, ester, or triazole functions. The synthesis of the thiosemicarbazides H2NNH-C(S)-NR3R4 starting from amines, including amino acids, SCCl2 or CS2, and hydrazine and their condensation with dipyridyl ketone and anthraldehyde led to 34 new TSC derivatives. They were synthesized in up to six steps with overall yields ranging from 10 to 85% and were characterized by a combination of nuclear magnetic resonance spectroscopy and mass spectrometry. UV-vis absorption and photoluminescence spectroscopy allowed us to easily trace the dipyridyl imine and anthracene chromophores.

Examining the Anti-Tumor Activity of Dp44mT-Loaded Nanoparticles In Vitro

We have recently reported encapsulating an antitumor iron chelator, Dp44mT (Di-2-pyridylketone-4,4dimethyl-3-thiosemicarbazone), in nanoparticles (NPs) of poly(lactic-co-glycolic acid) (PLGA). In this paper, we examine the effectiveness of this nano-formulation, referred to as Dp44mT-NPs, against several cancer cell lines in vitro; specifically, we evaluate the cytotoxicity of this formulation in glioma (U87, U251), breast (MCF7), and colorectal (HT29) cancer cell lines. Cell viability results from treatment of glioma cells with Dp44mT-NPs for 24-72 hrs revealed that these NPs were highly toxic towards these malignant cells with very low IC₅₀ values (<100 nM). Although addition of a PEG (poly(ethylene glycol)) layer to the surface of NPs reduced their toxicity in glioma cells, they remained highly toxic towards these cells (IC₅₀ of 135-210 nM). Dp44mT-NPs were also toxic towards breast MCF7 and colorectal HT29 cells, but at higher dosages (IC₅₀ >1 µM) compared to glioma cells. Addition of PEG to these NPs, again lowered their toxicity in these cells. Varying the percentage of PEG on NPs resulted in changes in their cytotoxicity, highlighting the necessity of further optimization of this parameter. This study, overall, demonstrates the therapeutic potential of Dp44mT-NPs against different malignant cells, with particularly promising results in highly-aggressive glioma tumor cells.