Profiling SLCO and SLC22 genes in the NCI-60 cancer cell lines to identify drug uptake transporters

Molecular and pharmacologic profiling of the NCI-60 cell panel offers the possibility of identifying pathways involved in drug resistance or sensitivity. Of these, decreased uptake of anticancer drugs mediated by efflux transporters represents one of the best studied mechanisms. Previous studies have also shown that uptake transporters can influence cytotoxicity by altering the cellular uptake of anticancer drugs. Using quantitative real-time PCR, we measured the mRNA expression of two solute carrier (SLC) families, the organic cation/zwitterion transporters (SLC22 family) and the organic anion transporters (SLCO family), totaling 23 genes in normal tissues and the NCI-60 cell panel. By correlating the mRNA expression pattern of the SLCO and SLC22 family member gene products with the growth-inhibitory profiles of 1,429 anticancer drugs and drug candidate compounds tested on the NCI-60 cell lines, we identified SLC proteins that are likely to play a dominant role in drug sensitivity. To substantiate some of the SLC-drug pairs for which the SLC member was predicted to be sensitizing, follow-up experiments were performed using engineered and characterized cell lines overexpressing SLC22A4 (OCTN1). As predicted by the statistical correlations, expression of SLC22A4 resulted in increased cellular uptake and heightened sensitivity to mitoxantrone and doxorubicin. Our results indicate that the gene expression database can be used to identify SLCO and SLC22 family members that confer sensitivity to cancer cells.     

Cloning and functional characterization of the multidrug resistance-associated protein (MRP1/ABCC1) from the cynomolgus monkey

The multidrug resistance-associated protein 1 (ABCC1) gene from human (hMRP1), dog (canMRP1), and mouse (muMRP1) all encode proteins that efficiently transport the endogenous MRP1 substrate glutathione-S-leukotriene C(4) and confer resistance to anticancer agents, including vincristine and etoposide. hMRP1 also confers resistance to anthracyclines, whereas this is not true of canMRP1 or muMRP1. To determine whether MRP1 from another animal species used in toxicological studies would be more functionally similar to hMRP1, we cloned and characterized two alleles of the MRP1 homologue from the cynomolgus monkey Macaca fascicularis (monMRP1). The monMRP1 cDNAs encode proteins of 1531 residues that are 98, 90, and 88% identical to hMRP1, canMRP1, and muMRP1, respectively. Stable overexpression of both monMRP1 alleles and hMRP1 in transformed human embryonic kidney cells was achieved using an episomal expression vector. Transporters encoded by both monMRP1 alleles were functionally very similar to hMRP1. monMRP1 conferred an increased resistance to vincristine and etoposide and transported glutathione-S-leukotriene C(4) into membrane vesicles. In addition, MRP1-mediated drug resistance was effectively reversed in monMRP1 and hMRP1 transfectants by LY402913, a new MRP1-selective inhibitor in the class of tricyclic isoxazoles. However, monMRP1 transporters conferred a reduced level of resistance to the anthracyclines doxorubicin, daunorubicin, and epirubicin relative to hMRP1, although resistance levels were significant relative to vector control cells. These functional differences between human and monkey MRP1 transporters will need to be considered when designing pharmacokinetic and toxicological studies for the preclinical evaluation of MRP1 modulators.     

胃癌多药耐药相关基因表达与胶滴肿瘤药物敏感的关系

目的：探讨胃癌组织中多药耐药相关基因产物P-糖蛋白（P-gp）、谷胱甘肽-S-转移酶π（GST-π）和胸苷酸合成酶（TS）的表达与胶滴肿瘤药物敏感性之间的关系。方法：收集53例手术切除胃癌患者的胃癌标本,应用胶滴肿瘤药物敏感检测技术（CD-DST）检测其对4种临床常用化学治疗药物（多柔比星、依托泊苷、氟尿嘧啶、奥沙利铂）的体外药物敏感性,并应用免疫组化法检测胃癌组织中P-gp、GST-π和TS的表达,分析其与药敏检测结果的关系。结果：P-gp、GST-π和TS在胃癌组织中的阳性表达率分别为58%、47%和40%。P-gp阳性表达者中多柔比星及依托泊苷耐药组所占比例明显高于敏感组（P〈0.05）;GST-π阳性表达者中多柔比星及奥沙利铂耐药组所占比例也明显高于敏感组（P〈0.05）;TS阳性表达者中氟尿嘧啶耐药组和敏感组所占比例差异有统计学意义（P〈0.05）。结论：P-gp、GST-π和TS高表达是胃癌对多种化学治疗药物具有耐药性的标志,结合体外药物敏感试验,将有助于临床筛选有效的化学治疗药物,实现胃癌的个体化化学治疗。     

Reversal of multidrug resistance by small interfering RNA (siRNA) in doxorubicin-resistant MCF-7 breast cancer cells

Purpose

Resistance to anticancer drugs is a serious obstacle to cancer chemotherapy. A common form of multidrug resistance (MDR) is caused by the overexpression of transmembrane transporter proteins P-glycoprotein (P-gp) and multidrug resistance-associated protein-1 (MRP1), encoded by MDR1 and MRP1 genes, respectively. These proteins lead to reduced intracellular drug concentration and decreased cytotoxicity by means of their ability to pump the drugs out of the cells. Breast cancer tumor resistance is mainly associated with overexpression of P-gp/MDR1. Although some chemical MDR modulators aim to overcome MDR by interfering functioning of P-gp, their toxicities limit their usage in clinics. Consequently, RNA interference mediated sequence specific inhibition of the expression of P-gp/MDR1 mRNA may be an efficient tool to reverse MDR phenotype and increase the success of chemotherapy. Aim of this study was resensitizing doxorubicin-resistant breast cancer cells to anticancer agent doxorubicin by selective downregulation of P-gp/MDR1 mRNA.

Methods

The effect of the selected MDR1 siRNA, and MRP1 expression after MDR1 silencing was determined by qPCR analysis. Intracellular drug accumulation and localization was investigated by confocal laser scanning microscopy after treatment with MDR1 siRNA. XTT cell proliferation assay was performed to determine the effect of MDR1 silencing on doxorubicin sensitivity.

Results

The results demonstrated that approximately 90% gene silencing occurred by the selected siRNA targeting MDR1 mRNA. However, the level of MRP1 mRNA did not change after MDR1 downregulation. Silencing of P-gp encoding MDR1 gene resulted in almost complete restoration of the intracellular doxorubicin accumulation and relocalization of the drug in the nuclei. Introduction of siRNA resulted in about 70% resensitization to doxorubicin.

Conclusions

Selected siRNA duplex was shown to effectively inhibit MDR1 gene expression, restore doxorubicin accumulation and localization, and enhance chemosensitivity of resistant cells, which makes it a suitable candidate for therapeutic applications.     

Pharmacogenetics of ATP-binding cassette transporters in cancer and chemotherapy

The ATP-binding cassette (ABC) transporters belong to the largest known transporter gene family and translocate a variety of substrates including chemotherapy agents. ABC multidrug transporter expression has been implicated in tumor cell resistance to anticancer therapy, altered disposition of chemotherapy drugs, and associated chemotherapy toxicity. More recently, genetic heterogeneity has been described in a number of the ABC transporter genes, including ABC transporters that contribute to the pharmacokinetics and/or pharmacodynamics of chemotherapy drugs. The role of these transporters and their naturally occurring genetic polymorphisms in cancer and chemotherapy is reviewed.     

Chemosensitivity profile of cancer cell lines and identification of genes determining chemosensitivity by an integrated bioinformatical approach using cDNA arrays

We have established a panel of 45 human cancer cell lines (JFCR-45) to explore genes that determine the chemosensitivity of these cell lines to anticancer drugs. JFCR-45 comprises cancer cell lines derived from tumors of three different organs: breast, liver, and stomach. The inclusion of cell lines derived from gastric and hepatic cancers is a major point of novelty of this study. We determined the concentration of 53 anticancer drugs that could induce 50% growth inhibition (GI50) in each cell line. Cluster analysis using the GI50s indicated that JFCR-45 could allow classification of the drugs based on their modes of action, which coincides with previous findings in NCI-60 and JFCR-39. We next investigated gene expression in JFCR-45 and developed an integrated database of chemosensitivity and gene expression in this panel of cell lines. We applied a correlation analysis between gene expression profiles and chemosensitivity profiles, which revealed many candidate genes related to the sensitivity of cancer cells to anticancer drugs. To identify genes that directly determine chemosensitivity, we further tested the ability of these candidate genes to alter sensitivity to anticancer drugs after individually overexpressing each gene in human fibrosarcoma HT1080. We observed that transfection of HT1080 cells with the HSPA1A and JUN genes actually enhanced the sensitivity to mitomycin C, suggesting the direct participation of these genes in mitomycin C sensitivity. These results suggest that an integrated bioinformatical approach using chemosensitivity and gene expression profiling is useful for the identification of genes determining chemosensitivity of cancer cells.     

p16基因表达在卵巢癌分化程度诊断及化疗疗效判断中的意义

目的:研究p16基因的表达在卵巢癌的生物学特性的诊断以及化疗预后的判断中的意义。方法:采用免疫组化检测78例上皮性卵巢癌患者p16的表达,其中52例予以4～6个疗程以铂类为主的TP联合化疗,26例予以4～6个疗程的拓扑替康单药治疗,分析p16的表达与癌细胞多种生物学特性之间的关系以及与化疗疗效之间的关系。结果:52.6%的卵巢癌p16阴性表达,并且与癌细胞的分化程度呈明显相关性。采用TP方案的铂类联合化疗,其疗效与癌细胞p16表达无相关性(P>0.05),而采用拓扑替康单药化疗,p16阳性表达的患者其疗效明显好于p16阴性组的疗效(P<0.05)。结论:卵巢癌中高频率的p16基因活性缺失与癌细胞的分化程度密切相关,检测p16基因表达有可能作为癌细胞分化及恶性度的判断指标。此外,p16基因表达可能影响肿瘤细胞对部分化疗药物的敏感性,这对于指导临床肿瘤化疗方案的选择具有重要的参考意义,并可能用于患者化疗预后的判断。     

S3核糖体蛋白基因的过表达与K562/DOX细胞耐药性的关系

目的 观察S3核糖体蛋白（S3rp)基因表达的改变对白血病耐药性的影响。通过RT－PCR方法获得含S3rp基因完整开放阅读框架（ORF）的cRNA，并将其克隆到pGEM-T Easy载体里，然后通过亚克隆方法将pGEM-T Easy重组质粒里的S3rp cDNA片段克隆到真核表达载体pcDNA3.1( )中，分别构建正向插入和反向插入的S3rp cDNA重组质粒，进行基因转染。将正义S3rp cDNA真核表达质粒转染K562细胞，使其S3rp基因表达增加，观察其对化疗药物敏感性的改变；将反义S3rp cDNA真核表达质粒转染具有多药耐药（MDR）表型的K562／DOX细胞，阻碍其S3rp基因的表达，观察其对化疗药物耐药性的改变。结果 转染正义S3rp cDNA真核表达质粒后，K562细胞对阿霉素的耐药性比未转染的K562细胞增强5．8倍；转染反义S3rp cDNA真核表达质粒后，K562／DOX细胞对阿霉素的耐药性比未转染的K562／DOX细胞降低69％。结论 S3rp基因过表达在K562／DOX细胞耐药性的形成中起重要作用。     

小片段干扰RNA抑制人肝癌细胞株中YAP基因表达的研究

目的:研究用小片段干扰RNA(small interfering RNA,siRNA)抑制肝癌细胞株中YAP(yes-associated protein)表达后肝癌细胞株对阿霉素(adriamycin,ADM)的敏感性变化。方法:设计YAP基因的siRNA序列,用脂质体LipofectamineTM2000将siRNA转染至4株肝癌细胞株PLC/PRF/5、Huh-7、MHCC97H、MHCC97L中,在荧光显微镜下观察并采用蛋白免疫印迹(Western blotting)法检测肝癌细胞株中YAP的表达。将细胞以不同浓度的ADM处理后,采用四甲基偶氮唑蓝(methyl thialzolyl tetrazolium,MTT)比色法检测细胞的存活率。结果:成功构建针对YAP的siRNA表达载体。Western blotting结果显示,肝癌细胞株经特异性siRNA转染后,YAP蛋白的表达受到抑制,表明RNA干扰(RNA interference,RNAi)能特异、有效地抑制肝癌细胞株中YAP的表达。MTT结果显示,转染YAP siRNA后肝癌细胞株的存活率受到明显抑制。结论:siRNA抑制肝癌细胞株中YAP的表达可增强肝癌细胞株对ADM的敏感性。     

核糖体蛋白L6对K562/A02细胞耐药性及凋亡的影响

本研究观察核糖体蛋白L6（RPL6）基因表达的改变对白血病细胞耐药性的作用及其可能的机制。通过RT-PCR方法获得RPL6 cDNA序列,用真核表达载体pcDNA3.1（＋）分别构建正向插入和反向插入的RPL6 cDNA重组质粒。以脂质体将正义RPL6 cDNA真核表达质粒转染K562细胞,将反义RPL6 cDNA真核表达质粒转染K562/AO2细胞。以MTT、流式细胞术和荧光分光光度计观察RPL6对化疗药物耐药性、凋亡和caspase-3的作用。结果表明：转染正义RPL6 cDNA真核表达质粒后,K562细胞对阿霉素的耐药性增强到原来的325%,凋亡和caspase-3活性明显降低（P〈0.005）;转染反义RPL6 cDNA真核表达质粒后,K562/A02细胞对阿霉素的耐药性降低原来的38%;凋亡和caspase-3活性明显增加（P〈0.005）。结论：RPL6基因过表达通过改变药物诱导的凋亡在K562/A02细胞耐药性的形成中起重要作用。     

Gene expression profiles do not consistently predict the clinical treatment response in locally advanced breast cancer

Neoadjuvant treatment offers an opportunity to correlate molecular variables to treatment response and to explore mechanisms of drug resistance in vivo. Here, we present a statistical analysis of large-scale gene expression patterns and their relationship to response following neoadjuvant chemotherapy in locally advanced breast cancers. We analyzed cDNA expression data from 81 tumors from two patient series, one treated with doxorubicin alone (51) and the other treated with 5-fluorouracil and mitomycin (30), and both were previously studied for correlations between TP53 status and response to therapy. We observed a low frequency of progressive disease within the luminal A subtype from both series (2 of 36 versus 13 of 45 patients; P = 0.0089) and a high frequency of progressive disease among patients with luminal B type tumors treated with doxorubicin (5 of 8 patients; P = 0.0078); however, aside from these two observations, no other consistent associations between response to chemotherapy and tumor subtype were observed. These specific associations could possibly be explained by covariance with TP53 mutation status, which also correlated with tumor subtype. Using supervised analysis, we could not uncover a gene profile that could reliably (>70% accuracy and specificity) predict response to either treatment regimen.     

Study of therapy resistance in cancer cells with functional proteome analysis.

Different types of cancer are naturally resistant to many anticancer drugs. Additionally, these tumours develop acquired drug resistance, which includes the classical multidrug resistance (MDR) accompanied by the synthesis of P-glycoprotein, a member of the superfamily of ATP-binding cassette (ABC) transporters. Furthermore, atypical MDR is mediated by several different, some unknown, mechanisms. To overcome chemoresistance problems, antineoplastic drugs are often combined with other modes of therapy, e.g. hyperthermia, where good response has been reported in several experimental tumour models and in advanced cancer patients. The success of this combined anticancer treatment may be limited by an increase in chemoresistance and thermoresistance. A model system to study resistance phenomena is the use of chemoresistant and thermoresistant cancer cell lines. We have established chemoresistant cancer cell lines (gastric and pancreatic carcinoma, fibrosarcoma, melanoma) and now thermoresistant cell lines derived from gastric and pancreatic carcinoma cells and their counterparts that were resistant towards daunorubicin (classical MDR) and mitoxantrone (atypical MDR). Using proteomics, in this paper we evaluate the drug resistance of chemoresistant melanoma cells (parental cell line MeWo and sublines exhibiting drug resistance towards etoposide, cisplatin, fotemustine and vindesine) as a paradigm for analysis of drug resistance phenomena. Additionally, we investigate heat resistance and the interaction of chemoresistance and thermoresistance to identify common pathways using the parental and drug resistant stomach cancer cell lines EPG85-257, EPG85-257RNOV, EPG85-257RDB and their thermoresistant counterparts. Possible implications of differential protein expression will be discussed.     

NRF2/ABCB1-mediated efflux and PARP1-mediated dampening of DNA damage contribute to doxorubicin resistance in chronic hypoxic HepG2 cells

Transarterial chemoembolization (TACE)-induced hypoxia can trigger residual liver cancer cells to present a more aggressive phenotype associated with chemoresistance, but the underlying mechanisms are still unknown. In this study, the human liver cancer cell line HepG2 was pre-cultured in different oxygen environments to examine the possible mechanisms of hypoxia-induced doxorubicin resistance. Our study showed that HepG2 cells pre-cultured in a chronic intermittent hypoxic environment exhibited significant resistance to doxorubicin, evidenced by increased intracellular doxorubicin efflux, relatively higher cell proliferation, lower apoptosis, and decreased DNA damage. These changes were accompanied by high levels of NRF2 and ABCB1 under conditions of both chronic and acute hypoxia and PARP1 gene expression only under conditions of chronic hypoxia. SiRNA-mediated silencing of NRF2 gene expression downregulated the expression of ABCB1 and increased the intracellular doxorubicin accumulation and cell apoptosis both in acute and chronic hypoxic HepG2 cells. Moreover, silencing of PARP1 gene expression increased the doxorubicin-induced DNA damage and cell apoptosis in chronic hypoxic cells. On the basis of these findings, we concluded that NRF2/ABCB1-mediated efflux and PARP1-mediated DNA repair contribute to doxorubicin resistance in chronic hypoxic HepG2 cells.     

Drug-induced apoptosis in hepatoma cells is mediated by the CD95 (APO-1/Fas) receptor/ligand system and involves activation of wild-type p53.

Chemotherapeutic drugs are cytotoxic by induction of apoptosis in drug-sensitive cells. We investigated the mechanism of bleomycin-induced cytotoxicity in hepatoma cells. At concentrations present in the sera of patients during therapy, bleomycin induced transient accumulation of nuclear wild-type (wt) p53 and upregulated expression of cell surface CD95 (APO-1/Fas) receptor in hepatoma cells carrying wt p53 (HepG2). Bleomycin did not increase CD95 in hepatoma cells with mutated p53 (Huh7) or in hepatoma cells which were p53-/- (Hep3B). In addition, sensitivity towards CD95-mediated apoptosis was also increased in wt p53 positive HepG2 cells. Microinjection of wt p53 cDNA into HepG2 cells had the same effect. In contrast, bleomycin did not enhance susceptibility towards CD95-mediated apoptosis in Huh7 and in Hep3B cells. Furthermore, bleomycin treatment of HepG2 cells increased CD95 ligand (CD95L) mRNA expression. Most notably, bleomycin-induced apoptosis in HepG2 cells was almost completely inhibited by antibodies which interfere with CD95 receptor/ligand interaction. These data suggest that apoptosis induced by bleomycin is mediated, at least in part, by p53-dependent stimulation of the CD95 receptor/ligand system. The same applies to other anti-cancer drugs such as cisplatin and methotrexate. These data may have major consequences for drug treatment of cancer and the explanation of drug sensitivity and resistance.     

miR-198 通过靶向ZEB2 调控EMT 过程抑制肝癌细胞增殖和迁移的机制研究

目的 探讨微小核糖核酸-198（miR-198）在肝细胞癌（hepatocellular carcinoma,HCC）组织细胞中的表达及其对癌细胞增殖、迁移的影响及其相关机制。方法 采用qRT-PCR 检测miR-198 在HCC 组织及细胞(HepG2,Hep3G,MHCC97H,Huh7) 中的表达情况;采用脂质体2000 向Huh7 细胞中单独转染miR-198 mimics,共转染miR-198 mimics 和pcDNA3.1-ZEB2;生物信息学网站预测miR-198 的潜在靶基因,采用双荧光素酶报告基因实验进行验证;采用Western blot 检测E 盒结合锌指蛋白2（E-box binding zinc finger protein 2, ZEB2）及上皮-间质转化（epithelialmesenchymaltransformation, EMT）相关蛋白表达;CCK-8 法和细胞划痕实验检测Huh7 细胞增殖和迁移能力。结果 20 例HCC 组织中miR-198相对表达量（0.354±0.022）明显低于邻近正常组织（4.762±1.135）,差异有统计学意义（t=17.365,P＜ 0.001）。HCC细胞系HepG2（0.589±0.103）,Hep3G（0.495±0.086）,MHCC97H（0.558±0.056）和Huh7（0.362±0.045）中miR-198 相对表达量较正常肝细胞LO2（1.823±0.125）显著降低（t=17.159,18.466,17.590,20.315,均P ＜ 0.05）。miR-198 mimics 组细胞增殖（0.398±0.146 vs 0.691±0.213）和迁移能力（20.012±2.103 vs 84.032±6.512）较对照组明显降低（t=1.965,52.459,均P ＜ 0.001）。miR-198 mimics 组细胞中E-cadherin 表达较对照组明显升高,N-cadherin和Vimentin 表达较对照组明显降低（t=18.478,17.550,19.706,均P ＜ 0.01）。ZEB2 是miR-198 的靶基因,miR-198负调控ZEB2。20 例HCC 组织中ZEB2 相对表达量（3.621±1.143）明显高于邻近正常组织（ 0.736±0.030）,差异有统计学意义（t=11.284,P ＜ 0.001）,与miR-198 表达呈负相关（r=-0.702,P ＜ 0.05）。共转染过表达ZEB2 逆转了miR-198 mimics 对HCC 细胞增殖、迁移和EMT 的抑制作用。结论 miR-198 在HCC 组织和细胞中表达下调,miR-198 通过靶向负调控ZEB2 的表达抑制Huh7 细胞的增殖和迁移。     

Chemoinducible gene therapy: a strategy to enhance doxorubicin antitumor activity

A replication-defective adenoviral vector, Ad.Egr-TNF.11D, was engineered by ligating the CArG (CC(A/T)6GG) elements of the Egr-1 gene promoter upstream to a cDNA encoding human tumor necrosis factor-alpha. We report here that Ad.Egr-TNF.11D is activated by the clinically important anticancer agents cisplatin, cyclophosphamide, doxorubicin, 5-fluorouracil, gemcitabine, and paclitaxel. N-acetylcysteine, a free radical scavenger, blocked induction of tumor necrosis factor-alpha by anticancer agents, supporting a role for reactive oxygen intermediates in activation of the CArG sequences. Importantly, resistance of PC-3 human prostate carcinoma and PROb rat colon carcinoma tumors to doxorubicin in vivo was reversed by combining doxorubicin with Ad.Egr-TNF and resulted in significant antitumor effects. Treatment with Ad.Egr-TNF.11D has been associated with inhibition of tumor angiogenesis. In this context, a significant decrease in tumor microvessel density was observed following combined treatment with doxorubicin and Ad.Egr-TNF.11D as compared with either agent alone. These data show that Ad.Egr-TNF.11D is activated by diverse anticancer drugs.     

Novel acrylonitrile derivatives, YHO-13177 and YHO-13351, reverse BCRP/ABCG2-mediated drug resistance in vitro and in vivo

Breast cancer resistance protein (BCRP/ABCG2) confers resistance to anticancer drugs such as 7-ethyl-10-hydroxycamptothecin (SN-38, an active metabolite of irinotecan), mitoxantrone, and topotecan. In this study, we examined the reversing effects of YHO-13177, a novel acrylonitrile derivative, and its water-soluble diethylaminoacetate prodrug YHO-13351 on the BCRP-mediated drug resistance. YHO-13177 potentiated the cytotoxicity of SN-38, mitoxantrone, and topotecan in both BCRP-transduced human colon cancer HCT116 (HCT116/BCRP) cells and SN-38-resistant human lung cancer A549 (A549/SN4) cells that express BCRP, but had little effect in the parental cells. In addition, YHO-13177 potentiated the cytotoxicity of SN-38 in human lung cancer NCI-H460 and NCI-H23, myeloma RPMI-8226, and pancreatic cancer AsPC-1 cells that intrinsically expressed BCRP. In contrast, it had no effect on P-glycoprotein-mediated paclitaxel resistance in MDR1-transduced human leukemia K562 cells and multidrug resistance-related protein 1-mediated doxorubicin resistance in MRP1-transfected human epidermoid cancer KB-3-1 cells. YHO-13177 increased the intracellular accumulation of Hoechst 33342, a substrate of BCRP, at 30 minutes and partially suppressed the expression of BCRP protein at more than 24 hours after its treatment in both HCT116/BCRP and A549/SN4 cells. In mice, YHO-13351 was rapidly converted into YHO-13177 after its oral or intravenous administration. Coadministration of irinotecan with YHO-13351 significantly increased the survival time of mice inoculated with BCRP-transduced murine leukemia P388 cells and suppressed the tumor growth in an HCT116/BCRP xenograft model, whereas irinotecan alone had little effect in these tumor models. These findings suggest that YHO-13351, a prodrug of YHO-13177, could be clinically useful for reversing BCRP-mediated drug resistance in cancer chemotherapy.