Cross-Linked Polymeric Nanogel Formulations of 5‘-Triphosphates of Nucleoside Analogues:  Role of the Cellular Membrane in Drug Release

Abstract

Activation of cytotoxic nucleoside analogs in vivo depends primarily on their cell-specific phosphorylation. Anticancer chemotherapy using nucleoside analogs may be significantly enhanced by intracellular administration of active phosphorylated drugs. However, the cellular transport of anionic compounds is very ineffective and restricted by many drug efflux transporters. Recently developed cationic nanogel carriers can encapsulate large amounts of nucleoside 5′-triphosphates that form polyionic complexes with protonated amino groups on the polyethylenimine backbone of the nanogels. In this paper, 5′-triphosphate of an antiviral nucleoside analog, 3′-azido-2′,3′-dideoxythymidine (AZT), was efficiently synthesized and its complexes with nanogels were obtained and evaluated as potential cytotoxic drug formulations for treatment of human breast carcinoma cells. A selective phosphorylating reagent, tris-imidazolylphosphate, was used to convert AZT into the nucleoside analog 5′-triphosphate using a one-pot procedure. The corresponding 3′-azidothymidine 5′-triphosphate (AZTTP) was isolated with high yield (75%). Nanogels encapsulated up to 30% of AZTTP by weight by mixing solutions of the carrier and the drug. The AZTTP/nanogel formulation showed enhanced cytotoxicity in two breast cancer cell lines, MCF-7 and MDA-MB-231, demonstrating the IC 50 values 130-200 times lower than those values for AZT alone. Exact mechanism of drug release from nanogels remains unclear. One mechanism could involve interaction with negatively charged counterions. A high affinity of nanogels to isolated cellular membranes has been observed, especially for nanogels made of amphiphilic block copolymer, Pluronic® P85. Cellular trafficking of nanogel particles, contrasted by PEI-coordinated copper(II) ions, was studied by transmission electron microscopy (TEM), which revealed membranotropic properties of nanogels. A substantial release of encapsulated drug was observed following interactions of drug-loaded nanogels with cellular membranes. A drug release mechanism triggered by interaction of the drugloaded nanogels with phospholipid bilayer is proposed. The results illustrate therapeutic potential of the phosphorylated nucleoside analogs formulated in nanosized crosslinked polymeric carriers for cancer chemotherapy.

Polymeric nanogel formulations of nucleoside analogs

“…Previously, a putative mechanism of drug release (Figure 3) including interaction of nanogel cationic network with negatively charged phospholipids and other components of the cellular membrane has been suggested [43]. Membranotropic properties of nanogels were clearly illustrated recently by dose-dependent interactions of tritium-labelled nanogels with isolated cellular membranes, and by direct visualisation of these events using transmi sion electron and atomic force microscopy [47]. These findings could clearly be observed in a cellular system of rhodamine-labelled nanogels loaded with a fluorescein-labelled ATP (Figure 4).…”

Nanomedicine in the diagnosis and therapy of neurodegenerative disorders

“…Nanogels are nanosized networks of cross-linked polymers that often combine ionic and nonionic chains, such as polyethyleneimine (PEI) and PEG [140,142,240,241] or poly(acrylic acid) and Pluronic ® [238]. Such networks swell in water and can incorporate through ionic interactions of oppositely charged molecules such as oligonucleotides, siRNA, DNA, proteins and low molecular mass drugs.…”

“…Such networks swell in water and can incorporate through ionic interactions of oppositely charged molecules such as oligonucleotides, siRNA, DNA, proteins and low molecular mass drugs. Their loading proceeds with very high capacities (up to 40-60% wt) not achieved with conventional nanoparticles [140,191,237,238,[240][241][242]. Because of solubility of PEG chains, individual collapsed nanogel particles do not phase separate and form stable dispersions.…”

Curcumin-Combretastatin Nanocells as Breast Cancer Cytotoxic and Antiangiogenic Agent

“…Based on this assumption we selected the nanoparticles ranging in size between 100 and 200 nm for loading with curcumin. Curcumin was encapsulated into polymeric-based carrier, the colloidal nanogels, a recently developed by Dr. Vinogradov and his colleagues a new family of carriers for encapsulation and delivery of drugs and biomacromolecules (31)(32)(33)(34)(35)(36)(37)(38). Colloidal microgels have recently received attention as environmentally responsive systems and now are increasingly used in applications as carriers for therapeutic drugs and diagnostic agents.…”