Abstract 297: Activity of carfilzomib (CFZ) alone and in combination with cytarabine and chloroquine diphosphate (CHQ) in acute myeloid leukemia (AML)
Authors: Peng Mao Yu , Abaza Yasmin , Conklin Dylan , Euw Erika Von , Mead Monica , Timmerman John , Slamon Dennis , Larson Sarah 
Published: August 2019

Abstract
Background: Despite the recent advances in AML with the emergence of multiple targeted therapies, patient outcomes remain poor, particularly in the relapsed/refractory setting underscoring the need for novel therapeutic strategies. Proteasome inhibitors (PIs) have antitumor activity in AML through inhibition of the nuclear factor κB pathway and induction of apoptosis with multiple clinical trials showing promising activity of bortezomib particularly when combined with other cytotoxic agents (Csizmar 2016). CFZ, a second-generation PI, has preferential preclinical activity in AML compared to bortezomib and is therefore an agent of interest in AML therapy (van der Helm 2015). Here we assessed the activity of CFZ alone and in combination with cytarabine and the autophagy inhibitor CHQ in AML cell lines.
Methods: After screening 18 AML cell lines, 3 sensitive: KASUMI1, ML2, and MV411, and 3 resistant cell lines: AML193, THP1, and NOMO1, were selected for further analysis using an IC50 cutoff for CFZ of 10 nM. Apoptosis, cell cycle, and cell senescence analysis were performed after 72 hours of CFZ exposure at 10 nM. Combination assays using CFZ 10 nM, cytarabine 200 nM, and CHQ 20 µM were performed to evaluate for potential interaction in the form of antagonism or potentiation. Proteomic analysis was performed at baseline using reverse phase protein assay (RPPA) and confirmed with western blot analysis.
Results: Single-agent CFZ induced apoptosis in sensitive cell lines with apoptotic rates increasing by 85% to 95%; while apoptotic rates remained unchanged in resistant cell lines. Similarly, CFZ resulted in G0/G1 cell cycle arrest in sensitive but not resistant AML cell lines. Lack of difference in cellular senescence confirmed apoptosis and cell cycle arrest as the major mechanisms of CFZ-induced growth inhibition in AML cell lines. No antagonism was noted when CFZ 10 nM was combined with cytarabine (200 nM). RPPA revealed that AML cell lines with low expression of autophagy related proteins are more sensitive to proteasome inhibition with CFZ treatment compared to resistant cell lines. This was confirmed with western blot which showed upregulation of the autophagy related proteins in resistant cell lines upon exposure to CFZ. However, sensitive cell lines did not upregulate autophagy pathways which may lead to cell cycle arrest and apoptosis. Inhibiting autophagy with CHQ sensitized CFZ resistant lines to CFZ treatment.
Conclusion: CFZ demonstrated single agent activity in human AML cell lines and upregulation of autophagy may contribute to resistance to CFZ which can be overcome using autophagy inhibitors such as CHQ. These results support the development of CFZ and autophagy inhibitor-based combinations for AML.
Citation Format: Mao Yu Peng, Yasmin Abaza, Dylan Conklin, Erika Von Euw, Monica Mead, John Timmerman, Dennis Slamon, Sarah Larson. Activity of carfilzomib (CFZ) alone and in combination with cytarabine and chloroquine diphosphate (CHQ) in acute myeloid leukemia (AML) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 297.