Mustang Bio has received Orphan Drug Designation from the FDA for its MB-101 CAR-T therapy targeting IL13Rα2 for the treatment of recurrent diffuse and anaplastic astrocytoma and glioblastoma (GBM). The designation provides seven years of market exclusivity post-approval, independent of intellectual property protection, along with tax credits for clinical trials and prescription drug user fee waivers.
Clinical Results Show Promise in Challenging Disease
Phase 1 trial data published in Nature Medicine demonstrated encouraging efficacy signals for MB-101 in treating one of oncology's most difficult targets. Among evaluable patients, 50% achieved stable disease or better, including two partial responses and two complete responses. Notably, the complete responses lasted 7.5 and 66+ months respectively, representing remarkable durability in a disease where median survival is typically 15 months.
The complete responses occurred in patients with pre-existing "hot tumors" characterized by high intratumoral CD3+ T cells. Of 57 patients evaluable for survival in the City of Hope Phase 1 study, these two complete responses were observed in a cohort of three patients with the "hottest" tumors prior to treatment with MB-101.
Combination Strategy Targets Tumor Microenvironment
Mustang Bio is advancing MB-109, a combination therapy that pairs MB-101 with MB-108, an HSV-1 oncolytic virus that previously received its own Orphan Drug Designation. The combination strategy leverages MB-108 to reshape the tumor microenvironment and convert "cold" tumors into "hot" ones, potentially improving MB-101's efficacy.
Preclinical data presented at the American Association for Cancer Research Annual Meeting in 2022 supported this combination approach. MB-108 works by infecting tumor cells, which leads to recruitment of endogenous CD8+ and CD3+ T cells, creating an inflamed tumor microenvironment. This potentially allows MB-101 CAR-T cells to better infiltrate throughout the tumor mass and undergo activation for enhanced tumor cell killing.
Regulatory Advantages and Market Potential
The FDA's designation was broader than the indication originally proposed by Mustang Bio, expanding the therapy's addressable market beyond just recurrent cases to include all malignant gliomas. With GBM affecting approximately 13,000 U.S. patients annually, the broader coverage of other high-grade astrocytomas further increases the potential patient population.
"We are thrilled that MB-101 received Orphan Drug Designation on time and with a designation that is broader than the indication proposed," said Manuel Litchman, M.D., President and Chief Executive Officer of Mustang Bio. "The Orphan Drug Designation for MB-101, coupled with the Orphan Drug Designation granted previously for MB-108, is strong validation for our science."
Development Path Forward
Phase 1 clinical trials continue to enroll patients, with MB-101 being studied at City of Hope and MB-108 at The University of Alabama at Birmingham. Both therapies have demonstrated tolerability in recurrent GBM patients according to data presented separately.
The company notes that its ability to further develop the MB-109 combination program for recurrent GBM and high-grade astrocytomas is contingent upon raising additional funding and/or establishing a strategic partnership. Mustang Bio currently maintains a solid balance sheet with cash exceeding debt obligations.
