The FDA has issued a complete response letter (CRL) to Sesen Bio regarding its biologics license application (BLA) for Vicineum (oportuzumab monatox-qqrs) for the treatment of patients with BCG-unresponsive non-muscle invasive bladder cancer (NMIBC).1
The CRL requests additional clinical/statistical data and analyses for the treatment. The company plans to meet with the FDA as soon as possible to discuss a path forward for regulatory approval.
“We are deeply disappointed by this unexpected result, and it is an unfortunate day for patients suffering from BCG-unresponsive NMIBC,” Thomas Cannell, DVM, president and chief executive officer of Sesen, stated in a press release. “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.”
The protein fusion drug Vicineum consists of an epithelial cell adhesion molecule (EpCAM)-specific antibody fragment that is fused to , Pseudomonas Exotoxin A, a potent inhibitor of protein synthesis.
In preliminary findings from the pivotal phase 3 VISTA trial (NCT02449239), Vicineum showed positive antitumor activity in patients with high-risk, BCG-unresponsive NMIBC. One of the primary end points of the study was complete response (CR), and across 2 of the 3 study cohorts, patients with carcinoma in situ who had received prior BCG therapy achieved a CR rate of 28% at 6 months and 17% at 12 months.2,3
The open-label, single-arm, multicenter VISTA trial enrolled adult patients with carcinoma in situ and/or high-grade (Ta and T1) papillary disease who were unresponsive to prior treatment with BCG with or without interferon. Participants were required to have completed at least 2 courses of full-dose BCG, with at least 5 doses in the first course and 2 doses in the second course, and experienced disease recurrence within 30 weeks from last BCG treatment for those with papillary NMIBC, or within 50 weeks for those with CIS.
The trial included 133 patients, who were places into 1 of 3 cohorts: patients with carcinoma in situ with or without papillary disease that was refractory or the patient had recurred within 6 months of adequate BCG treatment; patients with carcinoma in situ with or without papillary disease that recurred between 6 and 11 months of BCG treatment; and patients with papillary disease only that recurred within 6 months of BCG treatment.
The study design consisted of a screening period, a 12-week induction phase, and a maintenance phase of up to 21 cycles of treatment, for a total of 104 weeks of treatment. Vicineum at 30 mg in 50 mL of saline was instilled into the bladder 2 hours on a schedule of 2 times per week for 6 weeks in the induction phase, followed by weekly for 6 weeks followed by every 2 weeks for up to 2 years as the maintenance phase. The coprimary end points of the trial are CR rate and the duration of response (DOR) in the first cohort.
In the first cohort of 82 evaluable patients who completed the induction phase, the CR rate was 39% at 3 months, 26% at 6 months, and 17% at 12 months. In the second cohort of 7 evaluable patients who completed the induction phase, the CR rate was 57% at 3 months, 57% at 6 months, and 14% at 12 months.
The median DOR in the first cohort was 273 days among 86 patients. An ad-hoc analysis of patients from both cohorts 1 and 2 (n = 93) showed that among patients who achieved a CR at 3 months, 52% had a CR for 12 months or more. The median time to disease recurrence in patients in the third cohort (n = 40) was 402 days.
More than 75% of patients treated with Vicineum across the 3 cohorts were estimated to remain cystectomy-free at 3 years, 90% were estimated to remain progression-free for 2 years or more, 29% were estimated to remain event free at 1 year, and 96% were estimated to have an overall survival of 2 years or more.
Regarding safety, 95% of all adverse events (AEs) were grade 1 or 2. Serious AEs were observed in 14% of patients. Four patients discontinued treatment due to an AE.
1. Sesen Bio Announces FDA Acceptance and Priority Review of its Biologics License Application for Vicineum. https://bwnews.pr/3jSeBwz. Posted online August 13, 2021. Accessed August 13, 2021.
2. Sesen Bio Reports Positive, Preliminary Data Update from Phase 3 VISTA Trial for High-Risk Non-Muscle Invasive Bladder Cancer [press release]. Cambridge, MA: Sesen Bio; August 8, 2019. https://bit.ly/2OM9LEB. Accessed February 17, 2021.
3. Dickstein R, Wu N, Cowan B, et al. Phase 3 study of Vicinium in BCG-unresponsive non-muscle invasive bladder cancer: initial results. J Urol. 2018;199(4S; abstr LBA27):e1167. doi: 10.1016/j.juro.2018.03.099