Abstract LB236: HP-002: A brain-penetrant PROTAC that demonstrated potent anti-proliferation activities on multiple BTK mutant

Abstract Introduction: Bruton's Tyrosine Kinase(BTK) inhibitors are widely used in the clinic to treat patients with B-cell malignancies. Acquired resistance mutations, however, can reduce or eliminate their efficacy and represent a growing challenge. Mutations at C481 dramatically reduce the binding of covalent BTK inhibitors, whereas other clinically observed mutations such as T474l and L528W accumulated as the approval of the next-generation BTK inhibitors and reduced or eliminated their activities. Some “kinase-dead” mutations can abolish BTK kinase activity while retaining intact BCR signaling and BTK-dependent growth. Compared with traditional small molecule inhibitors, target protein degraders (TPD) have shown great advantages in overcoming acquired resistances by removing the overactive kinase with all of its functions once and for all. Here, we have identified a brain-penetrant BTK PROTAC HP-002 with superior anti-proliferation potency against cells harboring diverse BTK mutants. Results: HP-002 can effectively degrade BTK in cancer cell lines with DC50 = 0.09 nM. In lymphoma cells e.g. REC-1 and TMD8, HP-002 demonstrated 2-digit pM IC50 with up to ∼10-fold more potent than NX-5948 and BGB-16673. In cells harboring mutated BTK (e.g. C481S/F, T474I, L528W), HP-002 demonstrated 5∼20-fold improved anti-proliferation potency compared to NX-5948. The superior target protein degradation could be attributed to the ∼ 20-fold improvement in the CRBN binding compared to NX-5948. In proteomic analysis assay, HP-002 can selectively degrade BTK over 7000 proteins while does not show effects on any known neo-substrates (e.g. IKZF 1/3, CK1a, SALL4, or GSPT1. ). In the PK/PD experiments (on mouse, rat, and NHP), HP-002 shows excellent pharmacokinetic properties and BTK degradation activity in vivo. In the TMD8 ABC-DLBCL CDX model, HP-002 (9 mpk, PO, QD) demonstrated complete tumor regression by 21 days (100% CR) and the lowest effective dosage at 1 mpk QD. The protein level of BTK was measured by the WB, indicating that HP-002 (3 mpk, PO, QD) leads to ∼50% BTK degradation in mouse’s brain tissue, compared to <15% in NX-5948 (3 mpk, PO, QD). Conclusion: HP-002 is a potent and highly selective BTK degrader against BTK-WT and multiple BTK inhibitor-resistant mutations. Brain penetration was observed in the TMD8 xenograft tumor model with deeper BTK down-regulation on the HP-002 treatment and robust tumor growth inhibition. With no significant safety risk findings in the preliminary rat and NHP DRF studies, HP-002 is currently under IND-enabling development. Citation Format: Dihuang Wang, Zheng Xu, Liwei Deng, Kefeng Zhang, Liwen Zhao. HP-002: A brain-penetrant PROTAC that demonstrated potent anti-proliferation activities on multiple BTK mutant [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB236.