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protein’s function. If that piece is cleaved off, Ekman says the protein is activated—becoming highly toxic to cells that are close to it.
The particular genius of PRX302 is that the company genetically modified proaerolysin so that only one enzyme—the Prostate Specific Antigen (PSA)—can cleave the carboxyl group from the protein. Ekman says the approach makes the drug highly specific for two reasons—“the PSA is found only on the surface of prostate cells and nowhere else in the body” and because PRX302 is deposited by an ultrasound-guided injection in the area where the prostate meets the ureter. He says the process of injecting the drug is similar to taking a biopsy of the prostate, an outpatient procedure done about 350,000 times a year in the United States.
Once on the surface of the prostate, the drug activates PRX302, causing the protein to drill into the prostate’s cell walls, triggering a programmed cell death known as apoptosis. The toxic effects of the PRX302 protein, he says, cannot be activated elsewhere in the body, Ekman says. The drug’s enzymatic activity appears to have no impact on nerves in the prostate, unlike most conventional treatments, and removes about 15-20 percent of the prostate in the area in closest proximity to the ureter, Ekman says.
“The ureter is completely untouched by the toxin because it’s not coated with PSA, Ekman says. “That part of the prostate is the part that compresses the ureter and makes it difficult to [urinate], so the pressure is alleviated.”
A Sophiris spokesman says the company met the primary endpoint in a randomized mid-stage trial. Of 126 patients treated so far, the company says it has seen no drug-related sexual side effects. The effects of PRX302 lasts at least six months, and Sophiris plans to present its 12-month data in another month or so, Ekman says.
Ekman, who was the president of R&D at Elan before joining Sofinnova in 2008, has more than 28 years in drug development as a senior executive and research scientist. He says the next step involves meeting with FDA regulators this summer to determine the design of final-stage clinical trials. “It will be probably two Phase 3 trials, in the ballpark of 500 to 600 patients in each trial,” Ekman says.
The company also will need to raise additional capital to conduct the pivotal trials. “We are prepared to make the stock available on stock markets other than the Toronto Stock Exchange,” Ekman says, adding that he can’t discuss those plans in detail.
He’s keen to move forward, though. “The commercial opportunity is important,” Ekman says, and I’m at a stage where I want to spend my time in developing meaningful drugs in areas of substantial unmet medical need.” He explains that the current standard of care for treating enlarged prostates involves prescribing alpha-blockers to relax the membrane surrounding the prostrate or some kind of surgery. “So the unmet need is large, and clearly—if the data holds up in the Phase 3 trials—this drug has a blockbuster potential over time.”