Second dose of Sophiris’ prostate cancer drug proves futile, shares crash

Following a patient death that was ruled unrelated to the study drug, Sophiris Bio continued testing a second administration of its experimental drug in patients with prostate cancer who responded well to the first round of dosing. That faith was in vain, as re-treatment with the drug, topsalysin, failed to confer additional benefit in the Phase IIb study, obliterating the San-Diego-based company’s shares $SPHS after the bell on Monday.

Previously, the biotech had reported that 10 out of 37 patients with localized prostate cancer in the trial demonstrated a clinical response six months following a single administration of topsalysin — and that 6 of those 10 responders experienced complete ablation of their tumor. On Monday, the company updated its results from the mid-stage trial saying that the 10 responders who received a secondary administration of the drug did not derive additional benefit, according to a targeted biopsy conducted on them six months after re-treatment.

Shares of the company, which said it was formulating a design for a Phase III study for submission to US and EU regulators, cratered about 40% after-market.

In June, the company temporarily halted secondary dosing in patients who had responded well to the first administration of the drug, after a patient suddenly died. By August, Sophiris said it would resume dosing after researchers concluded the drug had not caused the death.

Mark Emberton

On Monday, lead study investigator Mark Emberton said that “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.” Meanwhile, the company did not provide any details on reaction to the second dose, other than to say it had not introduced any additional benefit.

Topsalysin is designed to be activated only by enzymatically-active prostate specific antigen (PSA), which is overproduced in patients with prostate cancer. The drug is being developed as an option for patients to delay or even prevent aggressive surgeries such as radical prostatectomy, which comes with sexual side-effects and urinary incontinence. The drug’s safety profile could potentially allow it to position itself between non-invasive therapeutic options and invasive surgical procedure, while also reducing or preventing the off-target effects, HC Wainwright’s Joseph Pantginis wrote in a note last month.

Other than skin cancer, prostate cancer is the most common cancer in American men, according to the American Cancer Society.

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