In clinical trials, QS-21A has been shown to significantly improve the body's immune response in vaccine therapies against aggressive diseases such as melanoma, breast cancer, small-cell lung cancer, prostate cancer, HIV-1 and malaria. An extract from the bark of the South American tree Quillaja saponaria Molina, QS-21A is available only in small quantities.
"Now that we have synthesized this remarkable molecule and confirmed its structure, we are in a position to examine how it works and investigate ways to improve its performance," said David Y. Gin, a professor of chemistry at Illinois. Gin and his collaborators describe their work in a paper that has been accepted for publication in the Journal of the American Chemical Society, and posted on its Web site.
An extremely powerful adjuvant, QS-21A enhances the potency of antigens introduced in the body to elicit an immune response, allowing for lower vaccine doses with greater effectiveness. The molecule could therefore save patients money on expensive drugs and stretch limited supplies of antigens and vaccines.
Gin and his collaborators are now exploring ways to improve the molecule. By investigating structure activity relationships, they want to strip away nonessential structures, leaving a simpler and more potent core.
"One frequent problem encountered with vaccines is ensuring that the vaccine is potent enough to elicit a strong immune response," Gin said. "We will continue looking for ways to produce new molecules similar to QS-21A that will enhance the body's natural immune response to eradicate diseases."