Tumor Environment Changed by Combretastatin Derivative (Cderiv) Pretreatment That Leads to Effective Tumor Targeting, MRI Studies, and Antitumor Activity of Polymeric Micelle Carrier Systems

Combretastatins: An Overview of Structure, Probable Mechanisms of Action and Potential Applications

Combretastatins are a class of closely related stilbenes (combretastatins A), dihydrostilbenes (combretastatins B), phenanthrenes (combretastatins C) and macrocyclic lactones (combretastatins D) found in the bark of Combretum caffrum (Eckl. & Zeyh.) Kuntze, commonly known as the South African bush willow. Some of the compounds in this series have been shown to be among the most potent antitubulin agents known. Due to their structural simplicity many analogs have also been synthesized. Combretastatin A4 phosphate is the most frequently tested compounds in preclinical and clinical trials. It is a water-soluble prodrug that the body can rapidly metabolize to combretastatin A4, which exhibits anti-tumor properties. In addition, in vitro and in vivo studies on combretastatins have determined that these compounds also have antioxidant, anti-inflammatory and antimicrobial effects. Nano-based formulations of natural or synthetic active agents such as combretastatin A4 phosphate exhibit several clear advantages, including improved low water solubility, prolonged circulation, drug targeting properties, enhanced efficiency, as well as fewer side effects. In this review, a synopsis of the recent literature exploring the combretastatins, their potential effects and nanoformulations as lead compounds in clinical applications is provided.

Nanoformulation-based sequential combination cancer therapy

Although combining two or more treatments is regarded as an indispensable approach for effectively treating cancer, the traditional cocktail-based combination therapies are seriously limited by coordination issues that fail to account for differences in the pharmacokinetics and action sites of each drug. The careful manipulation of dosing regimens, such as by the sequential application of combination treatments, may satisfy the temporal and spatial needs of each drug and achieve successful combination antitumor therapy. Nanotechnology-based carriers might be the best tools for sequential combination therapy, as they can be loaded with multiple cargos and may provide targeted and sustained delivery to target tumor cells. Single nanoformulations capable of sequentially releasing drugs have shown synergistic anticancer activity, such as by sensitizing tumor cells through cascaded drug delivery or remodeling the tumor vasculature and microenvironment to enhance the tumor distribution of nanotherapeutics. This review highlights the use of nanotechnology-based multistage drug delivery for cancer treatment, focusing on the ability of such formulations to enhance antitumor efficacy by applying sequential treatment and modulating dosing regimens, which are challenges currently being faced in the clinic.

Polyethylenimine incorporation into hydrogel nanomatrices for enhancing nanoparticle-assisted chemotherapy

Addition of polyethylenimine into drug loaded hydrogel nanoparticle leads to enhanced cellular uptake, better ability to control drug release and deliver drugs to the cytosol, while evading the endosomes.

[Utilization of polymeric micelle magnetic resonance imaging (MRI) contrast agent for theranostic system]

We applied a polymeric micelle carrier system for the targeting of a magnetic resonance imaging (MRI) contrast agent. Prepared polymeric micelle MRI contrast agent exhibited a long circulation characteristic in blood, and considerable amount of the contrast agent was found to accumulate in colon 26 solid tumor by the EPR effect. The signal intensities of tumor area showed 2-folds increase in T1-weighted images at 24 h after i.v. injection. To observe enhancement of the EPR effect by Cderiv pretreatment on tumor targeting, we used the contrast agent for the evaluation by means of MRI. Cderiv pretreatment significantly enhanced tumor accumulation of the contrast agent. Interestingly, very high signal intensity in tumor region was found at 24 h after the contrast agent injection in Cderiv pretreated mice. The contrast agent visualized a microenvironmental change in tumor. These results indicate that the contrast agent exhibits potential use for tumor diagnostic agent. To combine with a polymeric micelle carrier system for therapeutic agent, the usage of the combination makes a new concept of "theranostic" for a better cancer treatment.