Background: IRAK4, a serine/threonine kinase, was identified as a therapeutic target in hematological malignancies. IRAK4-mediated activation of NF-kappaB could play an important role in NF-kappaB-regulated survival and chemoresistance of cancer cells. CA-4948, a first-in-class small molecule inhibitor of IRAK4, has been tested in Phase 1 clinical trial with evidence of clinical activity in Non-Hodgkin's Lymphoma (NHL) patients. To support the development of companion diagnostic for CA-4948, we developed an immunohistochemical (IHC) assay and explored expression of potential biomarkers of response to CA-4948 in tumor biopsy samples obtained from NHL patients.

Materials and Methods: IHC assay was developed and used for analysis of NF-kappaB p-p50 and p-IRAK1 expression in tumor biopsy samples obtained from 14 patients with NHL. Patients were defined according to their clinical response to CA-4948 treatment: stable disease (SD), 6 cases and progressive disease (PD), 8 cases.

Results: We found nuclear and/or cytoplasmic expression of NF-kappaB p-p50 in all 6 SD cases treated with 50 mg QD (2 cases, tumor regression), 50 mg BID (1 case), 200 mg BID (1 case, tumor regression) and 400 mg BID (2 cases). Expression of NF-kappaB p-p50 was not detected in 7 of 8 cases with PD including patients treated with 50 mg QD (1 case), 100 mg QD (1 case), 100 mg BID (3 cases), 200 mg BID (1 case) and 400 mg BID (1 case). We found statistically significant correlation between expression of NF-kappaB p-p50 in tumor biopsy and SD in NHL patients treated with CA-4948 (p<0.05). Analysis of NF-kappaB p-p50 expression in paired tumor biopsy samples (3 cases) collected before and after the treatment with CA-4948 revealed a significant downregulation of NF-kappaB p-p50 expression in tumors obtained from CA-4948-treated NHL patients. In support of our in vivo findings, our in vitro experiments demonstrated that expression of NF-kappaB p-p50 was depleted in 3D lymphoma organoids treated with a clinically relevant concentration of CA-4948. Our results support further development of NF-kappaB p-p50 as a potential predictive and pharmacodynamic biomarker of IRAK4 inhibitor CA-4948. We found that expression of p-IRAK1 in tumor biopsies was not correlated with clinical response.

Conclusions: Although the cohort size is small, our findings suggest that expression of NF-kappaB p-p50 can serve as biomarker to predict SD in response to the treatment with IRAK4 inhibitor CA-4948 in NHL patients. NF-kappaB p-p50 selection strategy might be used in future clinical trials to identify NHL patients which are most likely to respond to CA-4948 in combination with chemotherapy or targeted therapeutics.

Citation Format: Andrey Ugolkov, Maria Samson, Rosanna Hok, Reinhard von Roemeling, Robert Martell. Identification of NF-kappaB phospho-p50 as a predictive biomarker for IRAK4 inhibitor CA-4948 in patients with non-Hodgkin's lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 385.