Abstract 4679: Acquisition of cytarabine resistance leads to increased glucocorticoid sensitivity in AML
Authors: Malani Disha , Murumägi Astrid , Yadav Bhagwan , Kontro Mika , Eldfors Samuli , Kumar Ashwini , Wennerberg Krister , Heckman Caroline , Porkka Kimmo , Wolf Maija , Aittokallio Tero , Kallioniemi Olli 
Published: July 2016

Abstract
Acquired resistance to standard chemotherapeutic agents, such as cytarabine, is a major challenge in the treatment of acute myeloid leukemia (AML). Here, we hypothesized that development of resistance to one chemotherapeutic agent may lead to increased sensitivity to other drugs. Hence, we sought to identify novel drug vulnerabilities that arise during the development of cytarabine resistance using both cytarabine resistant AML cell lines and samples from AML patients who had relapsed during cytarabine containing chemotherapy.
We developed resistant variants of AML cell lines MOLM-13 and SHI-1 by long-term drug treatment with increasing doses of cytarabine. Profiling data from the in vitro generated cytarabine resistant cell line variants were systematically compared with corresponding data from 31 chemorefractory AML patient samples. All samples were subjected to genomic and transcriptomic profiling and high-throughput drug sensitivity and resistance testing with a panel of 250 chemical compounds (each in five doses).
Cytarabine resistant AML cell line variants and patient samples showed co-resistance to other nucleoside analogues, such as cladribine, clofarabine and gemcitabine. Genomic profiling showed deletion of the deoxycytidine kinase gene DCK, a well-known genetic lesion related to cytarabine resistance, in both MOLM-13 and SHI-1 cytarabine resistant cell lines and in one chemorefractory AML patient. Importantly, comprehensive drug testing revealed that cytarabine resistant SHI-1 cell variants developed increased sensitivity to glucocorticoids, such as dexamethasone, methylprednisolone and prednisolone when compared to parental cells. This was accompanied by up-regulation of the glucocorticoid receptor NR3C1. We also observed acquisition of glucocorticoid sensitivity in paired samples from two AML patient cases who had relapsed after cytarabine containing chemotherapy. Systematic ex vivo drug testing of 31 relapsed and chemorefractory AML patient samples showed high sensitivity to dexamethasone in five (20%) and to prednisolone and methylprednisolone in four (13%) patient samples.
In conclusion, our results from both cytarabine resistant AML cell lines and chemorefractory patient samples indicate that a subset of AML samples develop sensitivity to glucocorticoids. This novel finding indicates the need of detailed investigation of glucocorticoid efficacy in the clinic.
Citation Format: Disha Malani, Astrid Murumägi, Bhagwan Yadav, Mika Kontro, Samuli Eldfors, Ashwini Kumar, Krister Wennerberg, Caroline Heckman, Kimmo Porkka, Maija Wolf, Tero Aittokallio, Olli Kallioniemi. Acquisition of cytarabine resistance leads to increased glucocorticoid sensitivity in AML. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4679.