Abstract

Conventional chemotherapy using small molecular weight anticancer drugs presents many side effects due to poor specificities and aqueous solubility. To overcome the limitations, polymer-based drug delivery systems (PDDS) have been emerged for targeted delivery of therapeutic agents. Upon introduction of stimuli-responsive platform, the drugs can be released in controlled manner at the targeted tumor site providing enhanced drug efficacy and reduced toxicity. Stimuli-responsive degradation platform involves incorporation of covalent linkages that can be cleaved in response to external stimuli. The external stimuli can be found in altered microenvironment in pathophysiological tissues. For example, elevated levels of esterase and reactive oxygen species (ROS) are found in cancer tumor cells. As esters can be cleaved by the esterase and sulfides can be oxidized by the ROS, esters and sulfides can be incorporated to polymer to exhibit esterase and oxidation-responsive properties.
Size is an important consideration for the design of drug delivery systems. Ideally, the size should be ranged from 50 to 150 nm for optimal biodistributions and targeting ability. Microfluidic process provides high degree of control over the size of NPs. Chapter 2 examines size tunability of the dual enzyme- and oxidation-responsive polyester-based nanoparticulates (DPE-NPs) using a microfluidic instrument for cancer therapy. The DPE-NPs can be fabricated by using the polyester and polymeric stabilizer. The size of NPs can be influenced by changing the variables such as microfluidic parameters (total flow rate and organic/aqueous flow rate ratio) and formulation parameters (molecular weight of polyesters, concentration of nanoparticles, and nature and amount of stabilizers). In addition to size of NPs, it turns out that these parameters have an effect on colloidal stability. The results obtained from dual stimuli-responsive degradation and in vitro experiments with an enhanced cellular uptake demonstrate that the DPE-NPs can offer a versatile platform for the development of drug delivery systems.
Chapter 3 describes biological assessment of DPE-NPs as effective tumor-targeting intracellular nanocarriers. Doxorubicin (Dox), a clinically used anticancer drug, was incorporated into DPE-NPs stabilized with PEG and Brij S20. They exhibited excellent colloidal stability and as well as in pseudo-physiological conditions without any aggregation. They were destabilized in response to esterase that cleaved ester linkages and to hydrogen peroxide that oxidized sulfides. Such disruption led to an enhanced release of encapsulated therapeutics. For biological perspectives, the DPE-NPs were assessed in vitro using HeLa cervical cancer cells as a model. The results from MTT assay, epifluorescence microscope, flow cytometry, and cellular entry assay suggest that the dual responses triggered the intracellular release of the Dox to prohibit the cell proliferation followed by a rapid internalization through caveolae-mediated endocytosis. Further evaluation on 3D HeLa multicellular tumor spheroid (MCTS) indicated that the penetration ability of Dox was significantly enhanced when encapsulated in DPE NPs, suggesting that such deep penetration could be effective in vivo.