The study also yields hope because the potential protease inhibitors identified have a high degree of what Cantley called “bioavailability,” or effectiveness in reaching target sites. The molecules that stopped the spread of anthrax toxin in the clinical study are between 0.5 and 5 micrometers in size—small enough to be able to permeate a human cell membrane.

The small size of the molecules also signifies an increased likelihood that humans could orally ingest a drug made up of these molecules without suffering acute side effects, said Cantley. Moreover, smaller molecules are generally less costly to synthesize into drugs, Cantley said.

The protease inhibitors identified by the study were discovered by utilizing technology developed in 2001 by Cantley and Benjamin E. Turk, another Beth Israel scientist and an HMS research fellow in medicine.

The technology, called a “mixture-based peptide library,” enables the screening of billions of peptides to narrow the field of potential protease inhibitors.

Cantley said that because there was little known about anthrax at the time that this technology was developed, his team focused on finding potential inhibitors of anthrax lethal factor.

Although Cantley said that he was aware of the potential for the use of anthrax as a biological weapon when he began the study, he acknowledged that the Sept. 11 terrorist attacks increased the immediate importance of his research.

“We were working on this study in the spring of 2001 and had made quite a bit of progress,” he said. “We got the grant to continue to fund our work just at the time that the letters [containing anthrax] hit.”

—Staff writer Alan J. Tabak can be reached at tabak@fas.harvard.edu.