3-D Tumor Model Improves Anticancer Drug Testing
(Paper of Special Interest)
One of the early steps in assessing whether a new molecule or formulation is a potential anticancer agent is to treat layers of cancer cells with the drug candidate and observe whether the drug kills the cells. Although this approach has value, drugs that are active in such a two-dimensional (2-D) system often show far less activity as anticancer agents once they are tested in mice or other animals. Cancer researchers believe that the discrepancy betweenin vitro and in vivo results arises in large part because tumors are not 2-D, but three-dimensional (3-D), objects. Indeed, studies have shown that cells grown in three dimensions differ greatly in their response to external stimuli compared with the responses seen in 2-D systems.
In an attempt to develop a better drug-testing system, Vinod Labhasetwar, Ph.D., and his colleagues at the Cleveland Clinic and at his former institution, the University of Nebraska Medical Center, have used the principles of tissue engineering to develop surface-engineered, large, porous, and biodegradable polymer microparticles to serve as a scaffold for the 3-D growth of tumor cells. After numerous experiments, the investigators determined that the microspheres that were best at encouraging tumor growth were made of 5 percent polyvinyl alcohol and 1.25 percent chitosan, a natural protein isolated from shrimp shells. The results of this study appear in the journal Molecular Pharmacology.
Cells added to the microspheres began growing over this scaffold by first spreading over the surface of the microsphere and then growing though the scaffold, forming a 3-D tumor-like structure. Cells grown in three dimensions produced twice as much collagen as cells grown in two dimensions. Collagen growth is a measure of how much extracellular matrix cells produce; extracellular matrix plays a critical role in the life of a tumor. The investigators also found that 3-D-grown cells exhibited a far different gene expression profile from their 2-D counterparts. In particular, genes involved in protein binding, cell membrane composition, and signal transduction were expressed at significantly higher levels by cells grown in the 3-D system.
Once these 3-D structures formed, the investigators then tested the behavior and activity of anticancer agents and compared the results with those obtained using 2-D assay systems. These experiments showed that the dose needed to kill half the cells in each system was between 12-fold and 23-fold higher in the 3-D system. Additional studies showed that 3-D cells took up significantly less drug than did their 2-D counterparts, largely because drug diffused through the mass of cells at a much slower rate than in a 2-D layer of cells.
This work is detailed in the paper “3-D Tumor Model for In Vitro Evaluation of Anticancer Drugs.” An abstract of this paper is available through PubMed.