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Rib-X Maps Out Pivotal Antibiotic Trial, As Part of Built-to-Last Company Strategy

Xconomy Boston — 

Ten years have gone by since Susan Froshauer co-founded Rib-X Pharmaceuticals to create effective new antibiotics. If things break right, this will be the year her company makes some critical decisions that could ensure it lasts 10 more.

Like a lot of startup drug companies, this one is consuming a lot of time and money. The New Haven, CT-based firm raised $35 million over the past year, bringing its total financing to $158 million since its founding in 2000. Much of that cash is being set aside to test Rib-X’s lead candidate, delafloxacin, in a study of 800 patients with antibiotic-resistant infections they picked up in the hospital. If Rib-X can get help from a Big Pharma partner to start that trial on schedule this year, and it pans out, then the startup should be able to file an application to market the drug with the FDA in 2012, Froshauer says.

Rib-X’s antibiotic passed a mid-stage study of 150 patients in January 2009. The drug was well-tolerated, and helped more than 90 percent of patients become clinically cured of complex skin infections, even when more than half had dangerous and hard-to-treat MRSA infections. The treatment showed comparable effectiveness when stacked up against Pfizer’s tigecycline (Tygacil). If Rib-X can match that result in the pivotal study being planned, it could offer a new option for doctors in the constant battle against bacterial resistance. It could also be a first step for Rib-X’s transition from an R&D operation into something bigger and enduring.

“By partnering the delafloxacin asset, we’d be in a situation to continue to grow the program, and over time will allow us to have an antibiotic company,” Froshauer says.

Rib-X has been around as long as it has because of the promise of its unusual scientific approach to developing antibiotics. The vision was to use emerging technology to get high-resolution crystal structures of structures called ribosomes in bacterial cells. This is important because many different classes of antibiotics work by binding with the ribosomes. So by getting precise images, and using a proprietary computational system, Rib-X seeks to identify points where the bacteria are vulnerable, and where resistance can emerge.

While the underlying science is getting a taste of validation from clinical trials, that’s not the end goal for Rib-X as a business, Froshauer says. Other firms that have achieved some clinical validation have capitalized on that in subsequent acquisitions—San Diego-based Calixa Therapeutics, for instance, sold out last year to Lexington, MA-based Cubist Pharmaceuticals for as much as $400 million, and Paris-based Novexel was acquired by AstraZeneca for $500 million. But Froshauer doesn’t sound like she wants to go that route.

“We are an antibiotic company. We have multiple compounds coming down the pike, some advanced, some early. We have waves of programs to build a sustainable franchise. They come from a validated, performing platform that can be used for years to come,” Froshauer says.

It’s going to take more time and money before Rib-X can achieve that goal. Right now, Rib-X is really an R&D shop, with 34 of its 43 total employees in that department, Froshauer says. But if Rib-X can strike a deal to retain U.S. commercial rights to delafloxacin, and allow a partner to have commercial rights outside the U.S., that would be a feasible way for Rib-X to build up its own small sales and marketing force to focus on hospitals, Froshauer says.

Right behind delafloxacin, Rib-X has another drug candidate, radezolid, that could be on pace for an FDA application a year later in 2013, Froshauer says. That drug, a member of the class of oxazolidinones, could be in a position to compete with Pfizer’s linezolid (Zyvox), which generated $1.14 billion in worldwide sales in 2009.

Once the company has all the necessary capabilities to be independent for the long haul, then it could be in a position where it doesn’t need help from a partner, Froshauer says. The glimmer in her eye at the moment, the opportunity Rib-X might have to keep 100 percent ownership to itself, is the Rx-04 program. That’s a program in which Rib-X has designed a number of molecules against a wide variety of gram negative bacteria, including nasty drug-resistant bugs like Pseudomonas aeruginosa and Acinetobacter baumannii. The first candidate from this program is slated to enter clinical trials by the end of 2010, Froshauer says.

“There’s a lot of interest among collaborators in that program, but we want to hold onto the value,” Froshauer says. “We feel that’s the gold mine for Rib-X.”

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