Abstract
The physicochemical properties of stimuli-responsive polymers change with physical or biological signals, such as pH, enzyme concentrations, and temperature. These polymers have attracted considerable attention in the field of drug delivery. The drug carrier system, which was revolutionized by the introduction of these polymers, has recently provided a new paradigm of maximizing the therapeutic activity of drugs. This review highlights recent studies regarding stimuli-responsive drug carriers tailor-made for effective cytosolic drug delivery, with particular emphasis on tumor treatment.
Highlights
The targeting of a cytotoxic agent to solid tumors entails the passive accumulation of nano-sized drug carriers around solid tumor tissues, followed by active internalization into tumor cells [1,2,3,4,5,6,7,8,9,10,11,12]
The leaky characteristics of tumor blood vessels, which result from hypervasculature, defective vascular architecture, and a variety of permeability enhancing mediators secreted from tumor cells, are attributed to the enhanced extravasation of a given nano-sized drug carrier into a tumor site from circulation in the blood [12,13,14]
Active internalization is generally thought to occur with drug carriers that are directed by a monoclonal antibody binding to a tumor associated surface antigen, or by the binding of a ligand to its corresponding receptor on the surface of tumor cells [15,16,17,18,19]
Summary
The targeting of a cytotoxic agent to solid tumors entails the passive accumulation of nano-sized drug carriers around solid tumor tissues, followed by active internalization into tumor cells [1,2,3,4,5,6,7,8,9,10,11,12]. Nano-sized drug carriers that respond to physical or biological signals, such as pH, temperature, and enzyme expression, have been extensively evaluated for achieving spatial site-specific drug delivery [26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50]. DNA, short-interfering RNA (siRNA), and oligonucleotides (ODN), are not covered here, because a number of review articles regarding cytosolic gene delivery have already been reported
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