Abstract 3451: XS-04: A first-in-class dual IRAK4/BTK inhibitor for the treatment of hematological malignancies

Abstract Bruton's tyrosine kinase (BTK), a critical mediator of B-cell receptor (BCR) signaling, is a validated therapeutic target found across multiple B-cell cancers. Though initially responding to treatment with a BTK inhibitor, many patients with chronic lymphocytic leukemia (CLL), mantle cell lymphoma (MCL), or Waldenström macroglobulinemia (WM) eventually progressed and clinical responses to BTK inhibitors are often poor in diffuse large B-cell lymphoma (DLBCL) patients. These highlight the need to understand the resistance mechanisms and improve responses to BTK inhibitors. The serine/threonine protein kinase IRAK4 is a key modulator of MYD88, which is found to be mutated in various aggressive B-cell lymphomas, including DLBCL. As BCR signaling and MYD88 signaling converge downstream on NF-kB activation, which plays an essential role in proliferation and survival of lymphoma cells, blockade of the two signaling pathways presents a potential therapeutic strategy. Here, we investigated the pharmacokinetic properties and anti-tumor activity of XS-04, a first-in-class dual inhibitor targeting both IRAK4 and BTK, using preclinical models of DLBCL subtypes, including tumors resistant to BTK inhibitors. XS-04 showed potent inhibition of IRAK4 and BTK kinases, with IC50 values of 0.2 and 2.9 nM, respectively. Favorable pharmacokinetic properties were also seen across multiple non-clinical species. Using in vitro anti-proliferative assays, we found that XS-04 inhibited proliferation of various DLBCL cell lines with IC50s of 30 to 40 nM. Mechanistically, XS-04 suppressed NF-kB activity in DLBCL cells and in vivo xenograft tumors, as indicated by decreased phosphorylation of IkBa. Oral dosing of XS-04 in TMD8 xenograft model led to a dose-dependent inhibition of tumor growth, which was comparable to the inhibition shown by a combination of BTK and IRAK4 inhibitors. In addition, XS-04 treatment resulted in tumor regression in a patient-derived ibrutinib-resistant MCL xenograft model, without significant changes in body weight. XS-04, a first-in-class IRAK4/BTK dual inhibitor, shows broad anti-tumor activity across preclinical models of DLBCL subtypes, including tumors resistant to BTK inhibitors. These results support XS-04 as a therapeutic candidate for the treatment of hematological malignancies. An IND submission is planned for 2023. Citation Format: Chunyan Zhao, Jianfei Wang, Aiguo Liu, Xin Gao, Yanfen Teng, Lei Liu, Yang Zhang, Xiaohong Yu. XS-04: A first-in-class dual IRAK4/BTK inhibitor for the treatment of hematological malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3451.