Researchers manipulate DNA in bacterial gene cluster in step toward making new anti-cancer drug

By Lorraine Cichowski and Kevin Reynolds

RICHMOND, Va. – A U.S. and Japanese team of researchers led by Virginia Commonwealth University has produced a mutant version of a bacteria found naturally in soil and plants that makes a powerful natural product that is of interest to scientists for creating a new class of anti-tumor drugs.

The work, published in the Sept. 12 issue of the Journal of Biological Chemistry, represents the first cloning and analysis of a biosynthetic gene cluster responsible for production of the potent antibiotic phoslactomycin by a Streptomyces bacteria. 

"This process is an exciting new area of drug discovery," said Kevin A. Reynolds, Ph.D., professor of medicinal chemistry in VCU's School of Pharmacy and a vice director of VCU's Institute for Structural Biology and Drug Discovery. Reynolds was the lead author on the article.

"Instead of having chemists make drugs through synthetic methods, we can change the genome to make a new version of a drug using naturally occurring processes," said Reynolds, an internationally recognized expert in combinational biosynthesis, which is the process of combining and exchanging genes from different organisms to make new natural products. "The approach is an alternative to any other kind of drug design because we're making compounds that are difficult to synthesize and that may be extremely difficult to find in nature."

Phoslactomycin (PLM) and the related natural product fostriecin have attracted interest from scientists in recent years because of their antifungal and anti-tumor activity.  These antibiotics, which are generated by bacteria, have a unique and selective mechanism of action that scientists are exploring in their pursuit of a new class of antiviral and anti-tumor agents.  Unfortunately, PLM and fostriecin compounds produced in native bacteria have proven to be unstable and are generated in low yields and multiple forms.  Until now, those problems have blocked further development of the compounds and prompted numerous efforts to produce members of the class of compounds synthetically. 

In the VCU biosynthesis experiment, researchers grew a strain of Streptomyces and identified and subsequently sequenced and analyzed the entire gene cluster responsible for making phoslactomycin (PLM).  They then reengineered the biosynthetic process by deleting one of the genes in the cluster and generated a mutant strain of Streptomyces, which selectively made one PLM product in an amount six times higher than the wild-type strain.  The biosynthetic solution simultaneously overcame two of the hurdles associated with development of this class of compounds – low yields and multiple forms.   

"Cloning of the PLM biosynthetic gene cluster sets the stage for genetically engineered production of novel analogs with improved stability, activity and selectivity," Reynolds said. "This work represents a complementary approach to the widespread synthetic approaches directed toward this class of compounds. Having the bacteria generate the drug is also a more economical means of manufacture."

Reynolds and his colleagues at VCU are conducting additional gene disruption studies to identify the exact role of selected genes in PLM biosynthesis in order to make more potent and selective drugs.

The research was supported by a grant from the National Institutes of Health.