Abstract 4439: Ero1L is a determinant of resistance to bortezomib and collateral sensitivity to MTI-101-induced cell death in myeloma
Authors: Emmons Michael , Hazlehurst Lori , Escherich Steven , McLaughlin Mark , Cuevas Javier , Sullivan Daniel 
Published: August 2015

Abstract
Our laboratory previously reported that the novel first-in-class peptidometitc, referred to as MTI-101, binds a CD44/ITGA4-containing complex and induces necrotic cell death in multiple myeloma cells. In this presentation, we worked towards further elucidating the mechanism of action of MTI-101. To this end, we examined changes in gene expression between samples that are either resistant or sensitive to MTI-101 using both an isogenic acquired resistant cell line model and primary myeloma patient specimens. Using cell line models we show that the acquisition of resistance to this class of compounds correlates with changes in genes predicted to regulate Ca2+ homeostasis. Changes included decreased expression of the IP3 receptor(IP3R) isoform 3, phospholipase C (PLC)-β, and SERCA3 channel, as well as decreased expression of the plasma membrane Ca2+ channels TRPC1 and TRPM7. Moreover, we show that MTI-101 treatment evokes a robust and sustained increase in intracellular Ca2+ levels, a phenotype that as predicted was attenuated in the drug-resistant cell line. Blocking Ca2+ release from the IP3R as well as blocking influx of Ca2+ from plasma membrane channels inhibited the MTI-101 induced Ca2+ response. We are also able to inhibit MTI-101 induced cell death by pharmacologically blocking release of Ca2+ from the IP3 receptor and blocking uptake by the mitochondria. Importantly, and consistent with what we previously reported with the linear analog HYD-1, MTI-101 is more potent in specimens obtained from relapsed patients compared to newly diagnosed patients. This differential response to MTI-101 treatment was used to compare baseline GEP in these primary myeloma samples. Using this strategy we show that in primary multiple myeloma specimens, the sensitivity to MTI-101 significantly correlates with increased levels of the thiol oxidase Ero1L. Ero1L has been shown by others to regulate Ca2+ release from the IP3R. Mechanistically, we demonstrate that reducing the expression of Ero1L is sufficient to confer resistance to MTI-101, a finding that correlates with attenuation of MTI-101-induced Ca2+ levels. Moreover, reducing the expression of Ero1L was sufficient to cause increased sensitivity to bortezomib-induced cell death. Importantly, a retrospective analysis of relapsed specimens showed that increased Ero1L levels were found to be a poor prognostic marker for response to bortezomib. Together, our data indicate that Ero1L is a prognostic marker for resistance to bortezomib and may account for the increased sensitivity to MTI-101 in relapsed multiple myeloma specimens. As MTI-101 induces cell death by the deregulation of Ca2+, we speculate that alterations in Ca2+ signaling may play a role in the progression of multiple myeloma.
Citation Format: Michael Emmons, Lori Hazlehurst, Steven Escherich, Mark McLaughlin, Javier Cuevas, Daniel Sullivan. Ero1L is a determinant of resistance to bortezomib and collateral sensitivity to MTI-101-induced cell death in myeloma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4439. doi:10.1158/1538-7445.AM2015-4439