Yuan Yao ¹ Yiyi Yan ² Vera J. Suman ³ Courtney L. Erskine ⁴ Anastasios Dimou ¹ Lisa A. Kottschade ¹ Svetomir N. Markovic ^1,4 Robert R. McWilliams ¹ Heather N. Montane ¹ Matthew S. Block ^1,4*

• ¹ Department of Oncology, Mayo Clinic, Rochester, Minnesota, United States
• ² Division of Hematology and Oncology, Mayo Clinic, Jacksonville, United States
• ³ Division of Clinical Trials and Biostatistics, Department of Quantitative Health Sciences, Mayo Clinic, Rochester, United States
• ⁴ Department of Immunology, Mayo Clinic, Rochester, Michigan, United States

Background: Immune checkpoint inhibitors (ICIs) have been transformative in the treatment of patients with metastatic melanoma, but primary and secondary resistance to ICIs is common. One mechanism for ICI resistance is the skewing of the immune response from a cytotoxic (Th1) to a chronic inflammatory (Th2) profile. The small molecule ibrutinib inhibits Bruton's Tyrosine Kinase (BTK) and Interleukin-2-inducible T-cell Kinase (ITK), a key regulator of Th2 immunity. Therefore, combining ibrutinib and pembrolizumab could potentially induce an increase in Th1 immunity in melanoma patients. We hypothesized that the combination would be well-tolerated and might benefit patients with metastatic melanoma. The primary aim of this phase I study was to evaluate the safety, tolerability, maximum tolerated dose (MTD) of ibrutinib in combination with pembrolizumab in patients with metastatic melanoma. Methods: A 3+3 phase I clinical trial was conducted. Pembrolizumab (200 mg/kg every 3 weeks) was combined with ibrutinib, administered orally (140 mg daily, 280 mg daily, or 420 mg daily). Patients were treated until disease progression, intolerability, or patient decision to discontinue. Blood samples were collected after each cycle of treatment for immunophenotyping and Th1/Th2 polarity assessment. Results: Between January 31, 2017 and January 9, 2023, 17 patients enrolled. The MTD of ibrutinib/pembrolizumab was 420 mg daily. The adverse events leading to discontinuation included: grade 4 ALT and AST increase (1 pt, DL0); grade 4 ALT increase with grade 3 AST increase (1 pt, DL1); and grade 3 hyponatremia, hypoxia, and rash (1 pt, DL1). Three of the 16 patients treated had objective responses (2 partial responses, 1 complete response) lasting over 8 months. The median progression-free survival was 3 months, and median overall survival was 1.8 years. The combination did not result in consistent increases in Th1 immune polarity. In conclusion, the maximum tolerated dose of ibrutinib in combination with pembrolizumab in patients with advanced or metastatic melanoma was 420 mg by mouth once daily. The combination was well-tolerated but did not result in a consistent increase in Th1 immune polarity; further investigation is needed to assess the relative clinical efficacy of this approach. (Funded by Pharmacyclics; ClinicalTrials.gov number: NCT03021460)