Although
Sophiris Bio plans to continue development, investors weren’t enthused, letting stock
plunge more than 38 percent after the company
released mixed results from its Phase IIb clinical trial of topsalysin in prostate cancer.
Topsalysin (PRX302) is a first-in-class, pore-forming protein. It was being evaluated in localized prostate cancer in a Phase IIb trial, in patients who received a second dose of the drug. On the positive side, the drug appears to be safe and generally well-tolerated.
In earlier data, 27 percent of patients (10/37) showed a clinical response six months after a single dose of the drug. Six of the 10 patients that had a response showed complete ablation of their tumor.
Also, after the single administration, 41 percent of patients had a partial response, which was defined as a reduction in Maximum Cancer Core Length (MCCL) and/or Gleason pattern, but the targeted lesion was still evaluated as clinically significant. About a third, 32 percent, of patients didn’t respond to treatment.
No benefit was observed after a second administration of the drug.
“We remain encouraged by both the safety and biopsy data from the first administration of topsalysin and are working with Sophiris to design a protocol for a potential Phase III registration study using a single administration of topsalysin,” stated Mark Emberton, principal investigator of the trial and Dean of the University College London Faculty of Medical Sciences. “These data show that 27 percent of the patients who received a single administration of topsalysin may avoid or delay the need for alternative treatment for their localized prostate cancer.”
Emberton went on to say, “Taking into account the observed efficacy and safety profile to date following a single administration, we believe urologists would welcome a treatment like topsalysin for men with clinically-significant localized prostate cancer.”
The company indicates that it plans to move into Phase III development. They are finalizing the Phase III study design and plan to submit it first to the European regulatory agencies, then to the U.S. Food and Drug Administration (FDA). They are also looking for a partner to help fund the larger trial.
“We are equally focused on determining the best path forward for funding a potential Phase III study and continue to engage in business development discussions as part of this effort,” stated Randall E. Woods, president and chief executive officer of Sophiris. “We are also encouraged to see such strong interest from the medical community in the development of a focal treatment for clinically-significant localized prostate cancer.”
Another aspect of the trial was to determine if it was safe to re-administer topsalysin, and to see if any additional clinical benefit would come from it six months after the initial treatment. The study did find that there were no particular new safety signals.
One patient, however, died from a sudden cardiac event after the second dose. Review of the patient’s medical records, autopsy findings and serology results find that topsalysin was not related to the death.
However, the company concluded there were no clinical advantages to the second treatment.
“While we are disappointed that no additional ablation occurred following a second administration of topsalysin, we had already planned the Phase III study around a single administration and will continue to move forward accordingly, while we continue to evaluate the potential benefit of a second dose separately,” stated Emberton. “The results from the second administration in no way impacts our excitement about topsalysin as a potential targeted focal therapy in localized prostate cancer.”
Although investors would seem to disagree with Emberton’s assessment, it needs to also be placed in the
context of the overall stock market. The Nasdaq Composite Index yesterday was down 125 points, erasing all of the year’s gains, and the Dow Jones
dropped 508 points and S&P 500 lost 2.1 percent, hitting its lowest level of the year.
