Breaking Through the Barrier: New methods in determining drug efficacy

Many promising drugs are developed every year, but very few of them are approved for human treatment. One major obstacle in the drug approval process is effectively delivering a drug into a cell and monitoring how much crosses the biological membrane. Recently, a group at Yale University led by chemistry professor Alanna Schepartz and molecular biophysics and biochemistry professor Elizabeth Rhoades has found a way to determine exactly how many molecules of a peptide-like drug end up in the cytosol that fills a cell.

Efficient mechanisms of delivering drugs into cells could be a major step towards elimination of prominent diseases that affect millions worldwide. The new method coming out of Yale research will allow drug developers to accurately identify the trafficking efficiency of certain drugs to the cell interior. It will also help optimize the chemical structures of drugs, and it will supplement our understanding of the cellular systems that regulate traffic across the cell membrane. Schepartz and Rhoades have opened the door to a new frontier in drug delivery, and it all started with observations of arginine.

Previously, the team had found that although many small proteins containing four to six copies of the amino acid arginine are taken up by cells, very few of these proteins actually end up in the cytosol. A majority attempt to cross the cell membrane but are kept constrained in capsules. The few exceptions have a precise configuration of five arginines in what is termed the penta-arg motif. This configuration stimulates a vesicle to release the encapsulated protein into the cell interior. The penta-arg motif thus makes it into the cytosol.

Prior methods of testing cytosolic uptake of these molecules were ineffective. The new method developed by Yale researchers, called fluorescence correlation spectroscopy, detects the traffic into a cell’s interior when fluorescently tagged molecules diffuse across a predetermined volume. “Knowing precisely how much of a peptide-like molecule makes it to the cytosol helps design better-trafficking molecules,” Schepartz said.

The past 20 years have seen a continual interest in developing methods to assist molecules in crossing biological membranes. Schepartz and Rhoades have contributed a major finding to this field, a method that has many potential applications in disease therapy.