Sonus Pharmaceuticals, Inc. has announced the failure of its TOCOSOL® Paclitaxel breast cancer drug that it was developing with partner Bayer Schering Pharma AG. The company has made public the results of its Phase III trial which were quite unsatisfactory, as the new drug proved less efficient and with more side effects than the current equivalent, Taxol. Phase III trial results showed the ORR (objective response rate) for TOCOSOL Paclitaxel was 37% versus 45% for Taxol for the treatment of women with metastatic breast cancer.

In addition, the TOCOSOL Paclitaxel had significantly more side effects, such as neutropenia and febrile neutropenia.

"We are profoundly surprised and disappointed that TOCOSOL Paclitaxel did not achieve the primary endpoint of this pivotal trial, particularly given the efficacy and safety results from previous clinical studies of our drug," said Michael A. Martino, President and Chief Executive Officer of Sonus. He was referring to the Phase II results which have shown promising anti-tumor activity in breast, non-small cell lung, bladder and ovarian cancers.

Sonus and Bayer Schering Pharma are thus closing all clinical trials of Tocosol Paclitaxel, the biotechnology company said in their statement. After the announcement, its stocks crashed as investors sought to rid of their shares. However, the company still has another cancer product in development, using the same TOCOSOL technology, which is a special vitamin E-based emulsion formulation meant to increase effectiveness. However, in Paclitaxel the TOCOSOL formulation lowered the efficiency instead of improving it.

"We are extremely disappointed with the outcome," said Michael Martino, Sonus's chief executive officer, on a conference call. "We don't know what went wrong and why."

They also have TOCOSOL Camptothecin (SN2310 Injectable Emulsion), a formulation which has proved better anti-tumor effects in preclinical studies when compared to irinotecan.

TOCOSOL® Paclitaxel is a vitamin E-based emulsion formulation of paclitaxel, a mitotic inhibitor used for some time in cancer chemotherapy. It is better known for its brand name, Taxol. TOCOSOL Paclitaxel allows for shorter infusion times (15 minutes) than classic Paclitaxel and does not require any reconstitution or dilution prior to administration.