Abstract 451: Proteomic profiling of the unfolded protein response identifies patients benefiting from bortezomib in pediatric acute myeloid leukemia
Authors: Hoff Fieke W. , Qiu Yihua , Hu Wendy , Qutub Amina A. , Gamis Alon S. , Aplenc Richard , Kolb E Anders , Alonzo Todd A. , Bont Eveline SJM de , Kornblau Steven M. , Horton Terzah 
Published: August 2018

Abstract
Background: The unfolded protein response (UPR) is a cellular stress response triggered by accumulation of misfolded proteins in the endoplasmatic reticulum. Bortezomib is a proteasome inhibitor that triggers the UPR. Our goal was to globally assess the expression and activation of cell stress proteins, including the UPR, and to determine if proteins in the UPR pathway are prognostic of clinical response or predictive of bortezomib resistance in pediatric acute myeloid leukemia (AML).
Methods: We analyzed 5 UPR proteins (CAV1, EIF2S1, EIF2S1.pS51, ERN1, and GRP78) involved in the UPR by reverse phase protein arrays (RPPA) in ‘‘bulk'' (CD3-/19-) AML cells from 505 de novo pediatric AML patients who participated in the Children's Oncology Group AAML1031 phase 3 clinical trial. Progeny clustering was used to identify subgroups of patients (protein clusters) based on similar protein expression. Clusters were correlated with outcome, as well as patient characteristics.
Results: Four UPR protein clusters (C1-4) were recognized based on relative protein expression levels. UPR clusters were correlated with cytogenetics (high risk underrepresented in C3+C4, P&lt;0.001), MLL-rearrangement (low in C3, p&lt;0.001), t(8;21) (enriched in C3, p&lt;0.001) and the CEPBA (low in C3+C4, p= 0.023). In patients treated with standard therapy, cytarabine/daunorubicin/etopside (ADE), protein clusters were prognostic for overall survival (OS) (p=0.024) and event-free survival (EFS) (p=0.003), with C2 having an unfavorable prognosis (OS estimate C2: 55% vs. 73-80% for C1, C3+C4 at 4yr). Multivariate Cox regression analysis identified C2 as independent prognostic variable for EFS (p=0.009). Adding bortezomib (ADE+B) did not show an outcome difference overall (p=0.65). However, the response of patients in C2 improved with the addition of bortezomib (ADE: 46% 4yr-OS vs. 65% with ADE+B, Fisher's exact: p=0.014). This cluster was characterized by relative low levels of CAV1 and ERN1, in combination with slightly elevated expression of EIF2S1, EIFS2S1.pS51 and reduced GRP78 compared to normal CD34+ cells.
Conclusion: We analyzed UPR in pediatric AML and identified four protein clusters that were prognostic of OS and EFS. We were able to identify a subgroup of patients that benefited from the addition of bortezomib to ADE chemotherapy. We hypothesize that patients with low UPR activation are more susceptible to protein cell stress, and protein cell stress susceptibility is amplified by the addition of bortezomib with ADE. This suggests that certain subsets of pediatric AML patients benefit from the ADE+B therapy. The use of UPR screening could identify patients who would benefit from ADE+B therapy.
Citation Format: Fieke W. Hoff, Yihua Qiu, Wendy Hu, Amina A. Qutub, Alon S. Gamis, Richard Aplenc, E Anders Kolb, Todd A. Alonzo, Eveline SJM de Bont, Steven M. Kornblau, Terzah Horton. Proteomic profiling of the unfolded protein response identifies patients benefiting from bortezomib in pediatric acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 451.