Abstract 4634: Inhibitory-κB kinase alpha as a biomarker and therapeutic target in colorectal cancer
Authors: Pennel Kathryn A. , McKenzie Molly , Lian Guang-Yu , Quinn Jean A. , Al-Badran Sara Samir Foad , Roxburgh Campbell S. , Mackay Simon P. , Birch Joanna , Edwards Joanne 
Published: March 2024

Abstract
Introduction/Aims: Colorectal cancer (CRC) remains a leading cause of cancer-related mortality. The canonical NF-κB pathway driven by IKKβ has been implicated in CRC development and progression, however less research has focused on non-canonical NF-κB signaling, regulated by inhibitory-κB kinase alpha (IKKα). This project aimed to assess IKKα, phospho-IKKα (pIKKαs176) and IKKβ expression in a retrospective CRC cohort to establish association with survival outcomes. Subsequently, this project aimed to determine the effect of abrogating IKKα activity without perturbing the canonical NF-κB pathway controlled by IKKβ using a first-in-class selective IKKα inhibitor in vitro/ex vivo.
Methods: Immunohistochemical staining for IKKα/pIKKα s176/IKKβ was performed using tissue microarrays from a CRC patient cohort (n=787). QuPath® software was used to semi-quantitively assess expression levels and scores were analyzed for association with cancer-specific survival (CSS). CRC cell lines (n=3), patient-derived organoids (PDOs; n=5) and patient-derived explants (n=5) were treated with novel IKKα inhibitor SU1644 and assessed for cell viability and proliferation.
Results: Positive staining for IKKα, pIKKαs176 and IKKβ was detected in tumor specimens. High cytoplasmic expression of IKKα within tumor cells was associated with reduced CSS in patients with right-sided colon cancer (HR=3.091, 95%CI; 1.128-9.467, log rank p=0.021). Conversely, high IKKβ expression was a marker of good prognosis (HR=0.627, 95%CI; 0.457-0.861, log rank p=0.004). A high ratio of IKKα to IKKβ was associated with reduced CSS in the full cohort (HR=1.404, 95%CI; 1.050-1.879, log rank p=0.021) and this was potentiated in right-sided colon cases (HR=1.772, 95%CI; 1.107-2.837, log rank p=0.016). Selective inhibition of IKKα using 1µM SU1644 in vitro caused a significant reduction in HT29 colony formation (p=0.012) and cell viability (p=0.039). PDOs showed altered cell morphology, reduced cell viability and proliferation when treated with SU1644. In the patient-derived explant model, Ki67 expression was reduced in tumor explants treated with SU1644.
Conclusions: These data establish high cytoplasmic IKKα expression within tumor cells as a marker of poor prognosis in CRC and conversely high IKKβ expression as a marker of good prognosis. This highlights the importance of development of selective IKKα inhibitor SU1644. IKKα inhibition using SU1644 demonstrated anti-cancer activity in recapitulative CRC disease models.
Citation Format: Kathryn A. Pennel, Molly McKenzie, Guang-Yu Lian, Jean A. Quinn, Sara Samir Foad Al-Badran, Campbell S. Roxburgh, Simon P. Mackay, Joanna Birch, Joanne Edwards. Inhibitory-κB kinase alpha as a biomarker and therapeutic target in colorectal cancer [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(6_Suppl):Abstract nr 4634.