Viventia Biotech, Inc.

Sesen Bio received some bad news Friday afternoon that it said was “unexpected,” briefly slashing shares by more than 80% and below $1 for the first time in nearly a year. The biotech reported it received a CRL from the FDA regarding its bladder cancer candidate Vicineum, an antibody-drug conjugate acquired in the company’s buyout of Toronto-based Viventia back in 2016. Trading was halted for about an hour on Friday, with Sesen entering the halt at about $6 per share and emerging battered with a $0.86 stock price. Ahead of the closing bell, Sesen shares recovered modest gains to close at $2.11, down 57% from Friday’s open. Expectations had swirled among investors leading up to the PDUFA date, scheduled for next Wednesday, as Sesen’s stock price rose about 43% from Thursday’s open to Friday’s halt. “We are deeply disappointed by this unexpected result, and it is an unfortunate day for patients suffering from BCG-unresponsive NMIBC,” CEO Thomas Cannell said in a statement. “We remain dedicated to our mission to save and improve the lives of patients by bringing new treatment options to patients, and we intend to work closely with the FDA to understand next steps.” Sesen described the reason for the CRL as a combination of manufacturing issues and requests for more data and statistical analyses. The Cambridge, MA-based company plans to meet with the FDA “as soon as possible” and said regulators provided recommendations for how to boost the data package. Vicineum uses a recombinant fusion protein attached to a genetically engineered peptide, with researchers aiming to target specific antigens on the surface of tumor cells to treat cancers. The FDA had given Sesen priority review for the program back in February, with Cannell saying at the time Sesen understood the agency’s guidance “very clearly” and “found the review process to be collaborative and engaging.” Sesen had submitted data from an open-label Phase III study that enrolled 133 patients with high-risk, BCG-unresponsive non-muscle invasive bladder cancer. The patients had previously been on BCG immunotherapy, and the most recent data came from 93 individuals whose cancer had not spread from the bladder into the muscle or other tissue. Sesen reported that 39% of those patients achieved a complete response after three months, with follow-ups at six, nine and 12 months seeing CRs of 28%, 21% and 15%, respectively. Vicineum had given Sesen new life after a former lead program failed twice and was subsequently licensed out to Roche. But Friday’s news sent Sesen back into deep penny-stock territory, and it remains to be seen how or whether the biotech plans to re-work its datasets and CMC issues to the FDA’s liking. In anticipation of a potential approval, Sesen had been launching significant commercial efforts over the last several months, efforts that ramped up in recent weeks and now may need to be paused. The biotech reported it had completed hiring about 60 new sales reps at the end of July — representing 97% of its sales force — and hired a new assistant general counsel and chief compliance officer as the calendar turned to August. As recently as July 14, Sesen painted a positive picture following a meeting with the FDA.

After years spent in the penny stock range, Sesen Bio has nabbed a long-awaited FDA review for its antibody-drug conjugate bladder cancer program. Thomas Cannell The FDA will give an accelerated audit to Sesen and its bladder cancer candidate Vicineum, an antibody-drug conjugate acquired in the company’s buyout of Toronto-based Viventia back in 2016. Sesen is penciled in for an Aug 18 PDUFA, and there is no adcomm on the docket right now, the company said. “We have been meeting with the FDA regularly for the past two years on the application for Vicineum,” CEO Thomas Cannell said in a statement. “We understand the FDA’s position and guidance very clearly and have found the review process to be collaborative and engaging.” News of the priority review ostensibly pleased investors, sending Sesen $SESN shares up more than 10% in early Tuesday trading. The idea behind the experimental drug is to use a recombinant fusion protein, attached to a genetically engineered peptide, to target specific antigens on the surface of tumor cells. It seeks out what are called epithelial cell adhesion molecule antigens, or EpCAM, that are overexpressed in NMIBC and uses the peptide tether to allow for minimal spillover toxicity. Sesen applied for Vicineum to treat high-risk, BCG-unresponsive non-muscle invasive bladder cancer and submitted data from a 133-patient Phase III trial, which is still conducting the follow-up stage. Patients in the single-arm Phase III trial had previously been on BCG immunotherapy, a standard treatment that doesn’t always work. The most recent batch of efficacy data, which came from 93 patients with cancer that had not spread from the bladder into muscle or other tissue, showed the program had a complete response rate of 39% after three months. Later data also showed complete responses at the 6-, 9- and 12- month periods. Respectively, those time frames resulted in rates of 28%, 21% and 15%. The program’s safety data, which appeared to spook investors three years ago when top-line results were first released, showed that 78% of side effects were designated as Grade 1 or Grade 2. But there were four treatment-related side effects noted at the time, including acute kidney injury, renal failure and cholestatic hepatitis. Those events, which sent the company’s stock down about 23% after the initial announcement, don’t seem to have regulators worried, however. With Tuesday’s news, Sesen is preparing to submit data to European regulators in the next one to two months. The company is also waiting to hear back from Chinese health authorities over a possible approval of their IND application. Bladder cancer isn’t the only area Sesen is seeking to treat with Vicineum. The company is also looking at squamous cell carcinoma of the head and neck, having completed a Phase II trial in the US. Sesen is also looking at Vicineum combination partners, studying the program with AstraZeneca’s Imfinzi in the same indication as the NMIBC monotherapy. The candidate has given Sesen new life after its former lead program failed twice and it completed a deal to license out its remaining program to Roche.