Rib-X Pharma, and Its Lead Antibiotic, Gear Up for Prime Time

Xconomy Boston — 

Rib-X Pharmaceuticals is gearing up to reveal mid-stage clinical results for its lead antibiotic that could advance the heavily backed biotech firm to a point at which larger drug companies often want a piece of the action.

New Haven, CT-based Rib-X, which has raised $123 million in private capital since it was founded in 2001, plans to report on two Phase 2 trials of its antibiotic, radezolid, at the Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) in Washington, D.C., late this month. Radezolid, which was tested in separate studies as a treatment for types of pneumonia and skin infections, is a small molecule designed with Rib-X’s proprietary computational system that identifies points of vulnerability and sources of antibiotic resistance in infection-causing bacteria.

Rib-X CEO Susan Froshauer foresees a day when her company’s technology could offer physicians a variety of antibiotic options to accurately target different infections. “The platform ensures a sustainable franchise,” Froshauer says. “We can do this over and over again, and we have now validated that by getting our own molecule through Phase 2.”

Froshauer, a former executive in the strategic alliance group of drug giant Pfizer (NYSE:PFE), is very much in pitch mode when she talks about the progress of her small company. Though she prefers not to discuss specifics of the Phase 2 studies—the results of which are under wraps until the ICAAC meeting from October 25 to 28—she says the firm is in active discussions with potential partners. (Given her connections at Pfizer, which markets the antibiotic linezolid, I asked her whether she was in partnership talks with her former employer. She didn’t bite.)

Speaking of the Pfizer antibiotic, Froshauer describes her firm’s radezolid as a next-generation linezolid. Sold under the trade name Zyvox, linezolid is Pfizer’s lucrative answer to antibiotic-resistant bugs that cause forms of pneumonia and skin infections, generating revenue of $944 million in 2007, up 21 percent from the prior year, according to Pfizer. But bacteria learn quickly, and strains resistant even to linezolid have emerged over the past several years. Froshauer says that her lead antibiotic has shown an ability to fight such linezolid-resistant bugs, and the Phase 2 trials her firm is about to showcase put the two antibiotics head-to-head.

Radezolid isn’t the only clinical candidate in Rib-X’s pipeline. Delafloxacin, the No. 2 antibiotic in the company’s pipeline, is in a Phase 2 study for skin and soft-tissue infections. The firm’s computer-based discovery platform has yielded two other antibiotics slated to enter clinical trials by the end of this year, Froshauer says. She also notes that the firm has put its discovery system to work on identifying a drug to treat an antibiotic-resistant bug, called acinetobacter, which has gained notoriety recently for infecting U.S. soldiers in Iraq.

Still, the bill to advance an antibiotic or any other drug into late-stage development is typically too high for a privately held biotech to foot on its own. Froshauer, who acknowledged that her company is unlikely to seek a near-term initial public offering due to the poor IPO climate, says Rib-X in the process of raising another round of private capital from existing investors. She notes that the largest investor in Rib-X is Warburg Pincus, an international private equity investment firm. (Warburg, which says it has invested $29 billion across several sectors over the years, is also a founding partner of recently launched Boston investment fund Constitution Medical Investors.)

Despite the expected influx of dollars in the next round, the exact amount of which the CEO declined to disclose, Froshauer says her company will “look to next year for the significant partnerships to offset [spending] on these core programs.”