Abstract 3739: Nuclear hormone receptors modulate imatinib resistance in chronic myeloid leukemia (CML)
Authors: Rajamani Bharathi M. , Karathedath Sreeja , Illangeswaran Raveen Stephen , Benjamin Esther Sathya Bama , Mathews Vikram , Abraham Aby , Balasubramanian Poonkuzhali 
Published: August 2018

Despite the impressive success of molecular targeted therapy in chronic myeloid leukemia (CML) with tyrosine kinase inhibitors (TKI) such as imatinib (IM), a proportion of patients exhibit suboptimal response and intolerance to the drug. While the mechanism by which resistance or intolerance develops is not completely clear, it is possible that several secondary modifiers could determine disease progression and drug response in CML. Nuclear Hormone Receptors-NHRs are attractive but less explored therapeutic targets in myeloid leukemia. The impressive success of treatment with ATRA, a RAR ligand, in the treatment of APL has not been translated to other myeloid leukemia subtypes. Recently, Prost et al., 2015 showed that Peroxisome proliferator-activated receptor-γ agonist Pioglitazone eliminates the residual CML stem cell pool and these patients remained in complete molecular response even after withdrawal of IM. The role of other NHRs in CML TKI resistance has not been explored extensively.

Based on the in-vitro drug sensitivity data, CML cell lines KU812, EM2 were grouped as sensitive (IC50-0.15 & 2.29uM) and Lama84, KCL22 were grouped as resistant (IC50-54.45 & 66uM) to IM. The NHRs and coregulators that are differentially expressed between IM sensitive and resistant cell lines were identified using NHR RT2 PCR profiler array (SAbiosciences). Based on +2 fold cutoff, the differentially expressed NHRs between test and control group were identified. Eight NHRs (AHR, AR, ESR1, ESRRG, PPARγ, RXRA, RXRB & THRA) were upregulated in the sensitive compared to the resistant cell lines, which was further validated by qRT-PCR.

To understand the effect of these NHRs in sensitizing resistant CML cells to Imatinib, KCL22 and Lama84 cells were pretreated with NHR ligands, followed by increasing concentrations of Imatinib (5µM-100µM). Ligands of RXR (9-cis retinoic acid), AR (testosterone) and ESRRG1 (GSK4716) significantly improved IM sensitivity by increasing the RNA expression of IM influx transporter hOCT1, which was also reported by Wang et al., 2012; Austin et al., 2014 using ligands for RXR, PXR and PPARγ. Pretreatment with these ligands did not have significant effect on the mRNA expression of BCR-ABL, but there was increased inhibition of the BCR-ABL downstream targets such as pCRKL, pSTAT5 and pAKT at the protein level in combination with IM. The AR, RXR & ESRRG ligands significantly decreased the IC50 to IM (p&lt;0.0001) in primary CML cells (n=22) in combination with IM. We also observed significant sensitization of primary samples (n=7) to IM when used in combination with clinically available RXR and AR ligands isotretinoin (p=0.0011) & stanozolol (p=0.0054). Our finding suggests that NHR ligands, especially RXR, AR & ESRRG when used in combination with IM could overcome resistance. Further studies are warranted to confirm the mechanistic effects of these ligands in modulating drug resistance in CML.

Citation Format: Bharathi M. Rajamani, Sreeja Karathedath, Raveen Stephen Illangeswaran, Esther Sathya Bama Benjamin, Vikram Mathews, Aby Abraham, Poonkuzhali Balasubramanian. Nuclear hormone receptors modulate imatinib resistance in chronic myeloid leukemia (CML) [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 3739.