MRSA: RIP?

It's just before noon in a narrow lab at Tufts School of Veterinary Medicine in North Grafton, Mass., and Naomi Balaban and her postdoc Kiran Madanahally have just opened a package they've waited two months for. The package, from a genomics company in Iceland, is the microarray analysis of a knockout Bacillus cereus bacterium deficient in one protein in a signaling pathway that produces enterotoxins. "These results are fantastic," says Madanahally, staring at the computer screen in front of him. "Really?" Balaban says as she quickly strides to where Madanahally sits. Balaban's eyes light up as her smile widens. The screen shows a graph containing a cluster of rainbow-colored dots along a regression line, with several dots slung at the bottom right of the screen, to which Madanahally is pointing. "Those are the toxins," he says. Balaban grips his shoulder in excitement: "That's amazing." The dots represent genes expressed in the bacteria, with the height of the dots indicating expression level. The dots at the bottom of the screen represent the genes associated with toxins, which were, as the scientists had hoped, down-regulated. But it's not Bacillus that Balaban is primarily concerned with. The new results concern a signaling pathway homologous to one found in Staphylococcus aureus, the bacteria that Balaban has worked on for more than 15 years, and one that has recently gripped the country with concern over methicillin-resistant Staphylococcus aureus (MRSA). Balaban has found that the protein complex in Staph and other bacteria that produce toxins is highly conserved, and these new results are strong evidence that this complex can be knocked down. Bacteria are present on all surfaces, including human skin, where all the varieties usually maintain equilibrium. When resources start running out at a particular locale, bacteria start producing toxins that help them repel other local bacteria, or spread by burrowing into host skin. In 1992, Balaban began working on the pathway that signals toxin production in Staph. When the bacteria are high enough in quantity they form a biofilm and begin producing a molecule called RAP. The accumulation of enough RAP activates a signal transduction pathway that leads to the production of toxins via the expression of RNAIII. Along the signaling pathway but before RNAIII expression, RAP phosphorylates another molecule, called the target of RAP (TRAP), which in turn activates the agr molecule. Researchers named these two interactions "quorum" sensing. While RAP is responsible for upregulating toxin production, Balaban discovered that another molecule, RNAIII-inhibiting peptide, or RIP, is responsible for downregulating the process by blocking the phosphorylation of TRAP. Although scientists had already identified RIP, Balaban and her former mentor, Richard Novick, now at New York University School of Medicine, discovered in 1999 that RIP naturally downregulated toxin production in non-pathogenic Staph populations. Her work has continued to demonstrate both in vivo and in vitro the effectiveness of RIP in preventing and treating Staph biofilm formation and enterotoxin production -- a paper last June in Antimicrobial Agents and Chemotherapy (51:2226-9, 2007) demonstrated that when administered to rats in multiple doses or in combination with antibiotics, RIP significantly reduced the accumulation of MRSA biofilm. Balaban believes that RIP therapeutics will not cause antagonistic resistance in bacteria leading to antibiotic resistant strains like MRSA. As opposed to antibiotics which target and kill bacteria, prompting them to thicken biofilm layers and devise other antibiotic-resistant measures, RIP therapy is "like Prozac for the bacteria," she says. By knocking out the toxin signaling pathway that bacteria use to deter neighbors and disperse, RIP makes the bacteria think they are alone in their microenvironment, and do not need to spread. Thus, in combination with antibiotic treatment, RIP may lessen bacteria defenses. "Happy bacteria tend not to mutate as much." Meanwhile, others are trying to find other treatments for, especially, antibiotic-resistant Staph. A group from Scripps Research Institute recently devised an antibody that targets the agr molecule (Chem. Biol., 14:1119-27, 2007). But the action of this antibody in vivo is not yet known, and it is not effective against all strains of Staph. Even though Balaban has known that the RIP treatment works since the early 1990s, bringing the therapeutic to market has been markedly slow. One clinician has been running human trials with successful data, Balaban says, but she won't give his name or hospital affiliation. In 2005, a small biotech company called Centegen licensed all of Balaban's patents for RIP, and has continued to develop the compound, called CEN-101. So far the company has been able to raise enough money from private investors to get the compound through preclinical testing and hopes to have an investigational new drug application filed by the end of this year, according to Centegen CEO Paul Abrams. But for Balaban, this isn't fast enough. The government reported last October that there are 90,000 deaths a year from drug-resistant Staph in the United States -- five times the number of deaths from HIV in North America. "I've known for 15 years that RIP works," she says. "And meanwhile a million people have died."

MRSA: RIP?

A Tufts biologist devises a strategy she says can save the tens of thousands of people infected each year with the deadly "superbug"

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