Published OnlineFirst May 16, 2012; DOI: 10.1158/1535-7163.MCT-12-0215 Molecular Cancer Therapeutic Discovery Therapeutics New Use for an Old Drug: Inhibiting ABCG2 with Sorafenib Yinxiang Wei1,3, Yuanfang Ma3, Qing Zhao1,4, Zhiguang Ren1,3, Yan Li1, Tingjun Hou2, and Hui Peng1 Abstract Human ABCG2, a member of the ATP-binding cassette transporter superfamily, represents a promising target for sensitizing MDR in cancer chemotherapy. Although lots of ABCG2 inhibitors were identified, none of them has been tested clinically, maybe because of several problems such as toxicity or safety and pharma- cokinetic uncertainty of compounds with novel chemical structures. One efficient solution is to rediscover new uses for existing drugs with known pharmacokinetics and safety profiles. Here, we found the new use for sorafenib, which has a dual-mode action by inducing ABCG2 degradation in lysosome in addition to inhibiting its function. Previously, we reported some novel dual-acting ABCG2 inhibitors that showed closer similarity to degradation-induced mechanism of action. On the basis of these ABCG2 inhibitors with diverse chemical structures, we developed a pharmacophore model for identifying the critical pharmacophore features necessary for dual-acting ABCG2 inhibitors. Sorafenib forms impressive alignment with the pharmacophore hypothesis, supporting the argument that sorafenib is a potential ABCG2 inhibitor. This is the first article that sorafenib may be a good candidate for chemosensitizing agent targeting ABCG2-mediated MDR. This study may facilitate the rediscovery of new functions of structurally diverse old drugs and provide a more effective and safe way of sensitizing MDR in cancer chemotherapy. Mol Cancer Ther; 11(8); 1693–702. Ó2012 AACR. Introduction of its nucleotide-binding domain at the amino terminus MDR is a major reason for the failure of clinical treat- and transmembrane at the carboxyl terminus. Human ment of cancer and characterized by decreased cellular ABCG2 mediates concurrent resistance to the commonly sensitivities to a broad range of chemotherapeutic agents used chemotherapeutic agents, such as mitoxantrone due, at least mostly, to the overexpression of efflux trans- (MX), topotecan, and 7-ethyl-10-hydroxycamptothecin port protein on the plasma membrane of cancer cells. (SN-38), by pumping these drugs out of the tumor cells Three major human ATP-binding cassette (ABC) trans- and thus lowering their cytotoxic effects. Indeed, several porters have been specialized to play a key role in the clinical studies have clearly shown that ABCG2 overex- clinical development of MDR, including P-glycoprotein pression correlates with poor clinical responses in both (MDR1/ABCB1), MDR protein 1 (MRP1/ABCC1), and adult and childhood leukemia patients (2, 3). Therefore, breast cancer resistance protein (BCRP/ABCG2; ref. 1). the overexpression of ABCG2 in cancer cells has Unlike ABCC1 and ABCB1, human ABCG2 has been been an important target of the efficacy of anticancer considered a half-transporter with a unique arrangement agents (4). To date, many ABCG2 inhibitors with diverse chemical structures have been found or developed, but none of Authors' Affiliations: 1Department of Molecular Immunology, Institute of them has been tested clinically. It would not be surprising Basic Medical Sciences, Beijing; 2Institute of Functional Nano & Soft if clinical use of ABCG2 inhibitors with novel chemical Materials (FUNSOM) and Jiangsu Key Laboratory for Carbon-Based Func- structures may have unexpected effects due to several tional Materials & Devices, Soochow University, Suzhou, Jiangsu; 3Institute of Immunology, Medical School of Henan University, Kaifeng, Henan; and problems, such as toxicity or safety and pharmacokinetic 4Medical School of Nankai University, Tianjin, China uncertainty of the compound. Although most small mol- Note: Supplementary data for this article are available at Molecular Cancer ecule tyrosine kinase inhibitors (TKI) are competitive or Therapeutics Online (http://mct.aacrjournals.org/). high-affinity substrates of ABCG2 (5), some of them, such as apatinib (6), sunitinib (7), lapatinib (8), erlotinib (9), Y. Wei and Y. Ma contributed equally to this work. gefitinib (10), imatinib (11), nilotinib (12), and vandetanib Corresponding Authors: Hui Peng, Department of Molecular Immunolo- gy, Institute of Basic Medical Sciences, 27 Taiping Road, Beijing 100850, (13), have been reported to be inhibitors or modulators. China. Phone: 86-10-66931326; Fax: 86-10-68159436; E-mail: These TKIs seem to inhibit the function of ABCG2 trans- [email protected]; and Tingjun Hou, Institute of Functional Nano & porter by directly interacting with this transporter, there- Soft Materials (FUNSOM) and Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, 199 Ren-ai Road, by completely reversing the MDR of cancer cells (14). Suzhou, Jiangsu 215123, China. Phone: 86-512-65882039; E-mail: Furthermore, the MDR reversal action seems to be unre- [email protected] or [email protected] lated to the expression level of ABCG2. Despite the fact doi: 10.1158/1535-7163.MCT-12-0215 that underlying mechanisms are still not clear, simulta- Ó2012 American Association for Cancer Research. neous administrations of TKIs with chemotherapeutic www.aacrjournals.org 1693 Downloaded from mct.aacrjournals.org on September 23, 2021. © 2012 American Association for Cancer Research. Published OnlineFirst May 16, 2012; DOI: 10.1158/1535-7163.MCT-12-0215 Wei et al. agents, mainly refer to substrates of ABCG2, might be Cell culture, treatments, and lysate preparations applicable to clinical practice. Regardless, these possibil- The human chronic myelogenous leukemia cell ities are still needed to evaluate effectiveness in the future line K562 and its drug-selected cell line K562/A02 (17) clinic. Therefore, these joint works for many years have were kindly provided by Prof. Dongsheng Xiong (Insti- led to further progress in identifying new functions of old tute of Hematology & Blood Diseases Hospital, CAMS & drugs already used in the clinic and become one of the PUMC, China). HEK293-transfected sublines HEK293/ practicable solutions in the fast affordable MDR chemo- Vec (18), HEK293/ABCC1 (19), and HEK293/ABCG2 (20) sensitizer development. were obtained from Prof. Jian-ting Zhang (Indiana Uni- In our previous studies, we reported, for the first time, versity Simon Cancer Center, Indianapolis, IN). The a novel dual-acting ABCG2 inhibitor (15), PZ-39, and human breast cancer cell line MCF-7 and the mitoxan- identified 2 types of ABCG2 inhibitors with one inhibit- trone selected MDR cell line MCF-7/MX (21) were kindly ing only ABCG2 function (static) and the other inducing provided by Dr. E. Schneider (Wadsworth Center, ABCG2 degradation in lysosome in addition to inhibit- Albany, NY). All cell lines from gifts were cultured as ing its function (dynamic) (16). The discovery of dynamic previously described and frozen into multiple aliquots. inhibitors that induce ABCG2 degradation may, there- All cells were passaged for 4 months or less before the fore, assist in establishing a new strategy for the reversal renewal from frozen, early-passage stocks. All cell lines of ABCG2-mediated MDR in cancer chemotherapy. In were periodically authenticated by morphologic inspec- this study, an old drug, sorafenib was identified as a tion. For analysis of ABCG2 degradation, HEK293/ potential ABCG2 inhibitor, showing closer similarity to ABCG2 cells were first treated with 10 nmol/L bafilomy- degradation-induced mechanism of action. On the basis cin A1 or 2 mmol/L MG-132 for 24 hours followed by of these reported dynamic ABCG2 inhibitors, we devel- treatment with 2.5 mmol/L sorafenib for 3 days and oped a pharmacophore model to identify the critical collection of cell lysates. Lysate preparation was carried pharmacophore features necessary for inhibitor-induced out as described previously (15). ABCG2 degradation. The hypothesis model was also mapped very well with the corresponding functional Western blot and fluorescence-activated cell sorting groups of sorafenib, supporting the argument that sor- analyses afenib is a potential ABCG2 dynamic inhibitor. This is Western blot and fluorescence-activated cell sorting the first report that sorafenib may be a good candidate (FACS) analyses of drug accumulation were carried for further evaluation as chemosensitizing agent target- out exactly as we previously described (15, 20). To ing ABCG2-mediated MDR. This study may facilitate the determine the conformational change of ABCG2 fol- rediscovery of new functions of structurally diverse old lowing treatment with ABCG2 inhibitors, HEK293/ drugs and provide a more effective and safe way of ABCG2 cells were incubated with 0.5 and 2.5 mmol/L reversing MDR in cancer chemotherapy. sorafenib at 37C for 10 minutes before PE-conjugated 5D3 antibody (1:20 dilution) was added and incubated for 30 minutes. The cells were then washed 3 times Materials and Methods and analyzed by FACS. Materials All electrophoresis reagents, protein concentration Real-time reverse transcriptase-PCR and assay kit, and polyvinylidene difluoride membranes were cytotoxicity assay purchased from Bio-Rad. Adriamycin, topotecan, and RNA extraction and real-time reverse transcriptase mitoxantrone were from Zhejiang Hisun Pharmaceutical PCR (RT-PCR) were carried out as we described previ- Co., Ltd., Huangshi Feiyun Pharmaceutical Co., Ltd., and ously (15). The sequences of ABCG2 primers are 50-TCAT- Jiangsu