Results of a phase I dose escalation and expansion study of tegavivint (BC2059), a first-in-class TBL1 inhibitor for patients with progressive, unresectable desmoid tumor.
Authors: Cranmer Lee D. , Abdul Razak Albiruni Ryan , Ratan Ravin , Choy Edwin , George Suzanne , Liebner David A. , Stenehjem David D. , Gounder Mrinal M. 
Published: June 2022

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Background: Desmoid tumors are known to have increased nuclear β-catenin levels. Tegavivint selectively disrupts the interaction of β-catenin and TBL1/ TBLR1, resulting in specific degradation of nuclear β-catenin. The primary objectives of this study were to determine the maximum tolerated dose (MTD), safety, and preliminary efficacy of tegavivint in patients (pts) with desmoid tumors. Methods: This study ( NCT03459469) utilized an accelerated dose escalation schema for the first two dose levels followed by a 3+3 design to determine the MTD/recommended phase 2 dose (RP2D) of tegavivint, followed by a dose expansion phase. The study included adult pts with sporadic desmoid tumors that were progressive (20% increase in tumor volume, recurrent in one year from surgery, or symptomatic), unresectable, and measurable via WHO criteria. Tegavivint was administered IV weekly (three weeks on, one week off) up to two years. Results: 24 pts were enrolled. Dose escalation enrolled 17 pts in six dose levels from 0.5 - 5 mg/kg. In dose expansion, 7 additional pts were enrolled. Dose expansion cohort also included 6 pts in dose escalation that were escalated to RP2D and 3 pts treated at RP2D in dose escalation (n = 16 total). Median age was 43 years (18-66). Median time from diagnosis was 3.1 years with median of one prior systemic treatment (range 0-6). Median time on study was 9.4 months; 3 pts remain on study at data cut-off. No dose-limiting toxicities were observed; MTD was not determined. RP2D was declared at 5 mg/kg based on pharmacologically relevant plasma concentrations and preliminary efficacy. Trough plasma concentrations (Cmin) exceeded in vitro IC50 efficacy estimates at 4 mg/kg and 5 mg/kg. Median half-life was 38 hours supporting once weekly administration. Treatment-related adverse events (TRAEs) occurring in ≥20% of pts included fatigue (71%), headache (38%), nausea (33%), constipation (21%), decreased appetite (21%), and dysgeusia (21%), mostly Grade 1-2. Grade 3 TRAEs of hypophosphatemia, stomatitis, increased ALT, diarrhea, and headache occurred in 5 separate pts. There were no grade 4-5 adverse events (AEs). One serious AE of Grade 2 extravasation occurred. Objective response rate (ORR) of 17% across all dose levels and 25% at RP2D (WHO and RECIST criteria) were observed. Median duration of response was 8.1 months (range 6 to 11.8 months) with all responses ongoing. The 9-month progression free survival rate was 76% (95% CI: 54 - 90%) among all pts and 79% (95% CI: 51 – 93%) among those treated at RP2D. Patient reported outcomes and correlative science will be included in the presentation. Conclusions: Tegavivint is well tolerated with mostly Grade 1/2 AEs and no serious toxicity associated with WNT inhibition. The ORR of 25% at the RP2D warrants continued development of tegavivint in desmoid tumors. Clinical trial information: NCT03459469.