Bortezomib is significantly beneficial for de novo pediatric AML patients with low phosphorylation of the NF-κB subunit RelA.

Purpose: The addition of the proteasome inhibitor (PI) bortezomib to standard chemotherapy (ADE: cytarabine [Ara-C], daunorubicin, and etoposide) did not improve overall outcome of pediatric AML patients in the Children's Oncology Group AAML1031 phase 3 randomized clinical trial (AAML1031) . Bortezomib prevents protein degradation, including RelA via the intracellular NF-kB pathway. In this study, we hypothesized that subgroups of pediatric AML patients benefitting from standard therapy plus bortezomib (ADEB) could be identified based on pre-treatment RelA expression and phosphorylation status.
Experimental Design: RelA-total and phosphorylation at serine 536 (RelA-pSer ⁵³⁶ ) were measured in 483 patient samples using reverse phase protein array technology.
Results: In ADEB-treated patients, low-RelA-pSer ⁵³⁶ was favorably prognostic when compared to high-RelA-pSer ⁵³⁶ (3-yr overall survival (OS): 81% vs. 68%, p = 0.032; relapse risk (RR): 30% vs. 49%, p = 0.004). Among low-RelA-pSer ⁵³⁶ patients, RR significantly decreased with ADEB compared to ADE (RR: 30% vs. 44%, p = 0.035). Correlation between RelA-pSer ⁵³⁶ and 295 other assayed proteins identified a strong correlation with HSF1-pSer ³²⁶ , another protein previously identified as modifying ADEB response. The combination of low-RelA-pSer ⁵³⁶ and low-HSF1-pSer ³²⁶ was a significant predictor of ADEB response (3-yr OS: 86% vs. 67%, p = 0.013).
Conclusion and Clinical Relevance: Bortezomib may improve clinical outcome in a subgroup of AML patients identified by low-RelA-pSer ⁵³⁶ and low-HSF1-pSer ³²⁶ .
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