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.

Modular Drug-Loaded Nanocapsules with Metal Dome Layers as a Platform for Obtaining Synergistic Therapeutic Biological Activities

Multifunctional drug-loaded polymer-metal nanocapsules have attracted increasing attention in drug delivery due to their multifunctional potential endowed by drug activity and response to physicochemical stimuli. Current chemical synthesis methods of polymer/metal capsules require specific optimization of the different components to produce particles with precise properties, being particularly complex for Janus structures combining polymers and ferromagnetic and highly reactive metals. With the aim to generate tunable synergistic nanotherapeutic actuation with enhanced drug effects, here we demonstrate a versatile hybrid chemical/physical fabrication strategy to incorporate different functional metals with tailored magnetic, optical, or chemical properties on solid drug-loaded polymer nanoparticles. As archetypical examples, we present poly(lactic-co-glycolic acid) (PLGA) nanoparticles (diameters 100-150 nm) loaded with paclitaxel, indocyanine green, or erythromycin that are half-capped by either Fe, Au, or Cu layers, respectively, with application in three biomedical models. The Fe coating on paclitaxel-loaded nanocapsules permitted efficient magnetic enhancement of the cancer spheroid assembly, with 40% reduction of the cross-section area after 24 h, as well as a higher paclitaxel effect. In addition, the Fe-PLGA nanocapsules enabled external contactless manipulation of multicellular cancer spheroids with a speed of 150 μm/s. The Au-coated and indocyanine green-loaded nanocapsules demonstrated theranostic potential and enhanced anticancer activity in vitro and in vivo due to noninvasive fluorescence imaging with long penetration near-infrared (NIR) light and simultaneous photothermal-photodynamic actuation, showing a 3.5-fold reduction in the tumor volume growth with only 5 min of NIR illumination. Finally, the Cu-coated erythromycin-loaded nanocapsules exhibited enhanced antibacterial activity with a 2.5-fold reduction in the MIC50 concentration with respect to the free or encapsulated drug. Altogether, this technology can extend a nearly unlimited combination of metals, polymers, and drugs, thus enabling the integration of magnetic, optical, and electrochemical properties in drug-loaded nanoparticles to externally control and improve a wide range of biomedical applications.