Compound the first selective inhibitor of protein phospholipase D (PLD), an enzyme that has been implicated in several human cancers including breast, kidney, stomach and colon.
New inhibitors, published in a recent issue of the journal Nature Chemical Biology, block invasive migration of breast cancer cells, supporting their further development as antimetastatic agents. They will also be useful tools for understanding the complex role of PLD in cell physiology, said N. Alex Brown, Ph.D., professor of pharmacology and one of the leaders of the team.
"PLD is associated with a number of fundamental cellular processes such as secretion, migration, growth and proliferation. But the lack of selective inhibitors indeed interfere with the ability of biologists to study this important enzyme," Brown said.
There are two related "isoforms" of PLD: PLD1 and PLD2. Both PLD enzymes produce phosphatidic acid, the key lipid metabolism and signaling molecule. But what if the two PLDs have different roles is an open question, which is a new isoform-selective inhibitors can now be used for the solution.
Brown and his colleagues found that PLD is important invasive migration of breast cancer cells in culture using a genetic tool called small interfering RNA (siRNA).
"When we had evidence of siRNA and other techniques that blocking PLD led to dramatic consequences blocking of metastatic invasion in breast cancer cells, we were very motivated to try to make the isoform-selective inhibitors," Brown said.
Craig Lindsley, Ph.D., a medicinal chemist who joined the faculty of Vanderbilt after five years at Merck Research Laboratories, and his group used a previously described inhibitor of PLD as a starting point for chemical process called diversity directed synthesis. The team screened the compounds obtained by the activity against PLD1 and PLD2 using in vitro and cell-screening tools developed in the laboratory of Brown.
"Without these high-quality screening tests and rapid turnover, this process is not going to work," said Lindsley, an associate professor of pharmacology and chemistry.Scientists were able to obtain compounds that selectively inhibits PLD1 or PLD2, and other compounds that inhibit both isoforms.
"With the connections we made, we can almost choose the range at which we would like to suppress the various isoforms, something that has never before been possible," Lindsley said.
Scientists have shown that the compounds act directly on the enzymes PLD (using purified proteins), and they showed that they blocked the invasive behavior of migration from three different lines of breast cancer.
"These inhibitors are key tools that we really have to probe biology, and we are obviously hoping to develop them for therapeutic use too," added Brown. "Not only did Craig excellent chemist, but he did not know that the compounds that have the potential to become drugs, and it was a very positive impact on this cooperation."
By focusing on FPGA, Brown, Lindsley, and their colleagues have the torch forward for the enzyme, which was famously characterized by Vanderbilt. John Exton, MD, Ph.D., professor of molecular physiology and biophysics and pharmacology, has been elected to the National Academy of Sciences for his work on PPB.
Scientists now will be to optimize their new compounds in vivo studies and give them characteristics consistent with being good medicine. They are also expanding their research in other areas of biology, in addition to studying inhibitors in models of breast cancer, they will learn how they work in cell systems that model of brain tumors, rheumatoid arthritis and viral infections.