Abstract 94: Association of xCT overexpression with RTKI resistance and metastases in clear cell renal cell carcinoma
Authors: Chintala Sreenivasulu , Adelaiye-Ogala Remi , Orillion Ashley , Arisa Sreevani , Elbanna May , Damayanti Nur P. , Pili Roberto 
Published: July 2017

Abstract
Background: Cystine/glutamate exchanger xCT is a catalytic component of system xc- involved in transport of ‘conditionally indispensable’ amino acid cystine. Cystine transport is a rate limiting step for the synthesis of glutathione, a major intracellular redox regulator. Recently, we and other groups reported the overexpression of xCT and its association with drug resistance in several human cancers including bladder, glioma, breast, and colon. There are no studies to show the xCT expression in clear cell renal cell carcinoma (ccRCC) and its association with tyrosine kinase inhibitors resistance and metastasis. In the current study we have evaluated xCT expression in human ccRCC tumors arranged in tissue microarray (TMA) and determined its role in receptor tyrosine kinase inhibitor (RTKI) resistance and metastases using the patient derived tumor xenografts (PDX) models and TKI resistance ccRCC cells.
Methods: Human Renal cell carcinoma tumor nephrectomy specimens arranged in tissue microarray (TMA) were used to determine xCT expression by immunohistochemistry. Patient derived tumor xenografts (PDX) of primary, metastasis, and sunitinib resistance were used to determine the role of xCT in RCC. To understand the molecular alterations associated with RTKI resistance, we have generated sunitinib resistance 786 OR ccRCC cells and performed RNAseq analysis. To determine the xCT inhibition effect on ccRCC tumor metastases, sulfasalazine, an inhibitor of xCT was used to treat metastatic ccRCC tumor xenografts transplanted in SCID mice.
Results: Immunohistochemical evaluation of xCT in RCC TMA revealed that 70 % (19 out of 27) of the tumors express different levels of xCT. Association with tumor response to RTKI will be presented. RTKI less responsive PDX RP-R-02 was developed using the dose escalation treatment strategy and was found to have an upregulation of xCT when the tumors become less responsive to sunitinib. RNAseq analysis revealed differential gene expression of various pathway genes including lysosome biogenesis and function such as SLC7A11, HPS4, HPS5, CTSB, IFI30, PPT1, SCPEP1, TPP1, ATP6AP1L, MCOLN1, PRKAG2, and VPS18 in sunitinib resistant 786 OR cells compared to parental cells supports the role of lysosomes function in RTKI drug resistance. Furthermore, xCT inhibitor sulfasalazine treatment significantly decreased the metastasis lung nodules of RP-R-02LM in SCID mice demonstrated the xCT role in RCC tumor metastasis.
Conclusions: We found preliminary evidence that overexpression of xCT may be associated with RTKI resistance in ccRCC. These results suggest that targeting the xCT in ccRCC may reverse the resistance and enhance the efficacy of RTKI. Additional studies using larger numbers of ccRCC tumors are required to identify xCT as a potential predictive biomarker for response/resistance to RTKI in ccRCC patients.
Citation Format: Sreenivasulu Chintala, Remi Adelaiye-Ogala, Ashley Orillion, Sreevani Arisa, May Elbanna, Nur P. Damayanti, Roberto Pili. Association of xCT overexpression with RTKI resistance and metastases in clear cell renal cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 94. doi:10.1158/1538-7445.AM2017-94