Correlation of PI3K upregulation with NOTCH2 mutations in ibrutinib-resistant mantle cell lymphoma.

Abstract

e20065 Background: PI3K dysregulation has been linked to ibrutinib resistance in mantle cell lymphoma (MCL); however, the investigation of PI3K signaling as an important ibrutinib resistance mechanism has been rarely assessed in clinical samples. Therefore, we sought to more fully characterize PI3K dysregulation in ibrutinib-sensitive and -resistant MCL clinical samples at the genomic and transcriptomic levels. Methods: Whole exome sequencing (WES; n = 41) and RNA-seq (n = 93) were performed on fresh peripheral blood, apheresis, or biopsy patient primary samples. All analysis was performed using the BostonGene automated pipeline. Results: To evaluate ibrutinib resistance in MCL, we compared the activity of 11 cellular pathways calculated by PROGENy between ibrutinib-sensitive and -resistant MCL. The PI3K pathway was the most differentially expressed between the two groups (q < 0.005; > 1 median absolute deviation in ibrutinib-resistant MCL). Increased PI3K pathway expression in the ibrutinib-resistant MCL tumors strongly correlated with hyperproliferation (r = 0.49; p = 6e-07). Both hyperproliferation and enriched PI3K expression associated with more frequent NOTCH2 somatic mutations (~22% ibrutinib-resistant MCL with high PI3K expression (p = 0.004) and hyperproliferation (p = 0.003)) that generate a premature stop codon in the PEST domain, likely resulting in hyperactive NOTCH2. Frequent TP53 mutations were identified in ibrutinib-resistant MCL tumors (58%; 3-fold greater vs ibrutinib-sensitive tumors; p = 0.02) based on our cohort and the Agarwal et al., 2019, Nature Medicine cohort. PI3K signaling is a known p53 activator, which may lead to a compensatory tumor suppressive mechanism, indicating that PI3K activation may induce mutational pressure on TP53 to promote MCL survival. VH gene usage variability of the B-cell receptor (BCR), the inducer of PI3K signaling, was not different between ibrutinib-sensitive and -resistant MCL, suggesting that diverse BCR expression does not underlie enriched ibrutinib-resistant MCL PI3K expression. Conclusions: PI3K inhibitors have resulted in underwhelming MCL clinical outcomes; yet, the advent of next-generation PI3K inhibitors such as copanlisib with potentially greater efficacy and less toxicity warrants the continued investigation of PI3K signaling in ibrutinib-resistant MCL. We identified a strong correlation between gain-of-function NOTCH2 mutations and enriched PI3K signaling, suggesting that dual inhibition of NOTCH and PI3K may overcome ibrutinib resistance in MCL.