Abstract 6069: Discovery and preclinical development of orally bioavailable potent BTK degrader, and its early clinical development for the treatment of relapsed and refractory B-cell malignancies

Abstract Background: Bruton tyrosine kinase (BTK) is an important signaling hub that activates the B-cell receptor (BCR) signaling cascade, which is critical for growth and survival of B-cell lymphoma or leukemia. BTK inhibitors have shown anti-tumor activity in patients with B-NHL. However, nearly half of the patients on current BTK inhibitors discontinue the treatment due to adverse effects and/or mutation-induced drug resistance. A degrader is a heterobifunctional chemical compound aimed at eliminating disease-causing proteins, rather than simply inhibiting proteins’ enzymatic function, through the ubiquitin-proteasome system (UPS) -mediated protein degradation. This approach offers a unique solution for addressing relapse or refractory disease by removing overexpressed and mutated proteins, unlike traditional inhibitors. We thus designed UBX-382, a degrader targeting BTK. Results: UBX-382 showed superior degradation activity for both wild-type (WT) and mutant BTK proteins in a single-digit nanomolar range of half-maximal degradation concentration when compared to the competing degrader programs in diffuse large B-cell lymphoma cell line. UBX-382 effectively addressed 7 out of 8 previously reported resistant BTK mutants in in vitro experiments and outperformed ibrutinib, ARQ-531, and MT-802 in inhibiting tumor growth in murine xenograft models harboring WT or C481S mutant BTK-expressing TMD-8 cells. Remarkably, oral dosing of UBX-382 for 2 weeks led to complete tumor regression in 3 and 10 mg/kg groups in murine xenograft models. Following this, further optimization was carried out for potency and PK profile. We nominated the candidate for IND filing and are planning a phase 1 clinical trial. For the first-in-human, open-label, multicenter, phase 1 study, patients in part 1 (dose escalation with BOIN design) had R/R B-cell malignancies and had received at least 2 prior therapies. The candidate will be administered orally at 5 mg once daily followed by 2 days, for a 7-day schedule over 28-day cycles. Part 2 (dose expansion) consisted of disease-specific cohorts, including CLL/SLL, DLBCL, MCL, FL, MZL, and WM. The primary endpoints were safety and tolerability, along with the definition of the maximum tolerated dose. Secondary endpoints included pharmacokinetics/pharmacodynamics and preliminary efficacy. Conclusions: We have discovered potent BTK degrader exhibiting excellent anti-tumor activity in vitro and in vivo. In pre-clinical safety studies, the candidate of UBX demonstrated an acceptable safety profile. The candidate of UBX is currently preparing phase 1 clinical trials for hematological malignancies. Citation Format: Song Hee Lee, Sun-Mi Yoo, Ye Seul Lim, Han Wool Kim, Je Ho Ryu, Jong Hwan Lim. Discovery and preclinical development of orally bioavailable potent BTK degrader, and its early clinical development for the treatment of relapsed and refractory B-cell malignancies abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6069.