Organic Anion Transporting Polypeptide 1B3 Expression Research Articles

Near-Infrared Fluorescence Imaging of miRNA Using a Transmembrane Polypeptide-Based Genetic Reporter.

MicroRNAs (miRNAs) are small noncoding RNAs that play important regulatory roles in multiple biological processes. Many miRNAs exhibit unique expression patterns and are considered as theranostic biomarkers in a variety of human diseases. A reporter system that is capable of imaging miRNA in vivo is crucial for investigating miRNA biology. In the present study, an organic anion-transporting polypeptide 1B3 (OATP1B3)-based genetic switch system is designed and optimized to achieve near-infrared fluorescent imaging of miRNA by the uptake of indocyanine green (ICG) dye. The reporter system, named miR-ON-OB3, is shown to be efficient to regulate the expression of OATP1B3 in mammalian cells. Notably, the results indicate that the system is of high sensitivity for near-infrared fluorescence imaging of both exogenous and endogenous miRNA in mammalian cells. Moreover, the system is proved to be functional for real-time near-infrared fluorescence imaging of miRNA in living mice. This study establishes a novel genetic encoded reporter for near-infrared fluorescence imaging of miRNA, which may provide a potential tool for in vivo imaging of miRNA in clinical applications due to the clinical availability of ICG.

Relevance of the organic anion transporting polypeptide 1B3 (OATP1B3) in the personalized pharmacological treatment of hepatocellular carcinoma

Although pharmacological treatment is the best option for most patients with advanced hepatocellular carcinoma (HCC), its success is very limited, partly due to reduced uptake and enhanced efflux of antitumor drugs. Here we have explored the usefulness of vectorizing drugs towards the organic anion transporting polypeptide 1B3 (OATP1B3) to enhance their efficacy against HCC cells. In silico studies (RNA-Seq data, 11 cohorts) and immunohistochemistry analyses revealed a marked interindividual variability, together with general downregulation but still expression of OATP1B3 in the plasma membrane of HCC cells. The measurement of mRNA variants in 20 HCC samples showed the almost absence of the cancer-type variant (Ct-OATP1B3) together with marked predominance of the liver-type variant (Lt-OATP1B3). In Lt-OATP1B3-expressing cells, the screening of 37 chemotherapeutical drugs and 17 tyrosine kinase receptors inhibitors (TKIs) revealed that 10 classical anticancer drugs and 12 TKIs were able to inhibit Lt-OATP1B3-mediated transport. Lt-OATP1B3-expressing cells were more sensitive than Mock parental cells (transduced with empty lentiviral vectors) to some Lt-OATP1B3 substrates (paclitaxel and the bile acid-cisplatin derivative Bamet-UD2), but not to cisplatin, which is not transported by Lt-OATP1B3. This enhanced response was abolished by competition with taurocholic acid, a known Lt-OATP1B3 substrate. Tumors subcutaneously generated in immunodeficient mice by Lt-OATP1B3-expressing HCC cells were more sensitive to Bamet-UD2 than those derived from Mock cells. In conclusion, Lt-OATP1B3 expression should be screened before deciding the use of anticancer drugs substrates of this carrier in the personalized treatment of HCC. Moreover, Lt-OATP1B3-mediated uptake must be considered when designing novel anti-HCC targeted drugs.

Dynamic CT and Gadoxetic Acid-enhanced MRI Characteristics of P53-mutated Hepatocellular Carcinoma.

Background Imaging markers of hepatocellular carcinoma (HCC) on the basis of molecular classification are important for predicting malignancy grade and prognosis. P53-mutated HCC is a major aggressive subtype; however, its imaging characteristics have not been clarified. Purpose To clarify the imaging characteristics of P53-mutated HCC at dynamic CT and gadoxetic acid-enhanced MRI that are correlated with its clinical features, pathologic findings, and prognosis. Materials and Methods In this retrospective single-center study, patients with surgically resected HCC between January 2015 and May 2018 in a university hospital were evaluated. HCC was classified into P53-mutated HCC and non-P53-mutated HCC using immunostaining. Dynamic CT and gadoxetic acid-enhanced MRI findings, clinical features, pathologic findings, and prognosis were compared using Mann-Whitney test, χ2 test, multivariable regression analysis, receiver operating characteristic analysis, Kaplan-Meier method, and log-rank test. Immunohistochemical expression of P53, organic anion transporting polypeptide 1B3 (OATP1B3), and CD34 were evaluated, and the correlations were analyzed using the Pearson correlation test. Results In total, 149 patients (mean age, 67 years ± 9 [SD]; 103 men) with 173 HCCs were evaluated. P53-mutated HCC (n = 28) demonstrated higher serum α-fetoprotein (median, 127.5 ng/mL vs 5.5 ng/mL; P < .001), larger size (40.4 mm ± 29.7 vs 26.4 mm ± 20.5; P = .001), and higher rates of poorly differentiated HCC (22 of 28 [79%] vs 24 of 145 [17%]; P < .001). Dilated vasculature in the arterial phase of dynamic CT (odds ratio, 14; 95% CI: 3, 80; P = .002) and a lower relative enhancement ratio in the hepatobiliary phase (odds ratio, 0.05; 95% CI: 0.01, 0.34; cutoff value, 0.69; P = .002) independently predicted P53-mutated HCC. OATP1B3 expression and P53 expression were inversely correlated (P = .002; R = -0.24). Five-year overall survival was worse for P53-mutated HCC (50.0% vs 72.6%; P = .02). Conclusion Dilated vasculature at the arterial phase of dynamic CT and a lower relative enhancement ratio at the hepatobiliary phase of gadoxetic acid-enhanced MRI were useful markers for P53-mutated hepatocellular carcinoma with poor prognosis. © RSNA, 2022 Online supplemental material is available for this article.

Gd-EOB-DTPA-enhanced MRI in Hepatocellular Carcinoma : Molecular and Genetic Background

Hepatobiliary specific contrast medium Gd-EOB-DTPA-enhanced MRI (EOB-MRI) is excellent for the detection and characterization of nodular lesions and plays an important role in the diagnosis of hepatocellular carcinoma (HCC). Gd-EOB-DTPA is received by normal hepatocytes, and then, excreted into bile ducts, under mediation by hepatocyte membrane transporters. The expression of uptake transporter organic anion transporting polypeptide 1B3 (OATP1B3) correlates with the enhancement ratio in the hepatobiliary phase of HCC. Consequently, OATP1B3 is the main uptake transporter of Gd-EOB-DTPA in HCC. The hepatobiliary phase of EOB-MRI can sensitively detect pathologically early HCC as a hypointense nodule, because the OATP1B3 expression decreases at an early stage of multistep hepatocarcinogenesis. Hypervascular HCC commonly presents hypointensity in the hepatobiliary phase with the decrease in the OATP1B3 expression ; however, approximately 10% of HCC atypically demonstrates hyperintensity, owing to OATP1B3 overexpression. HCC presenting hyperintensity in the hepatobiliary phase is a unique genetic subtype of HCC with a biologically less aggressive nature and mature hepatocyte-like molecular/genetic features. The interaction between β-catenin signaling and hepatocyte nuclear factor (HNF) 4α may plays an important role in the OATP1B3 expression and less aggressive biological nature of the hyperintense HCC in the hepatobiliary phase. Thus, EOB-MRI is crucial for the detection and characterization of HCC as well as for personalized medicine, such as an imaging biomarker.

Low expression of organic anion-transporting polypeptide 1B3 predicts a poor prognosis in hepatocellular carcinoma

ObjectiveTo detect the expression level of organic anion-transporting polypeptide 1B3 (OATP1B3) in hepatocellular carcinoma (HCC) and to determine the relationship between OATP1B3 expression, clinicopathological features, and prognosis.MethodsImmunohistochemical (IHC) staining was performed to detect the expression of OATP1B3 in 131 HCC specimens and in 89 adjacent nontumorous tissues. Moreover, the expression levels of OATP1B3 in 30 pairs of tumor and matched adjacent nontumorous tissues were detected by quantitative real-time polymerase chain reaction, and 34 pairs of tumor and matched adjacent nontumorous tissues were detected by Western blotting. The χ2 test was applied to analyze the correlation between OATP1B3 expression and the clinical parameters of HCC patients. The prognostic value of OATP1B3 in HCC patients was estimated by Kaplan-Meier survival analysis and the Cox stepwise proportional hazards model.ResultsCompared with that in adjacent nontumorous tissues (25.8%, 23/89), OATP1B3 expression was significantly downregulated in tumor tissues (59.5%, 78/131) (P < 0.0001). Moreover, OATP1B3 expression was markedly correlated with tumor size, recurrence, tumor differentiation, and tumor node metastasis (TNM) stage (P < 0.05 for each). However, age, sex, tumor capsule status, HBsAg, cirrhosis, tumor number, vascular invasion, and serum alpha fetoprotein were not associated with OATP1B3 expression. The overall survival (OS) and disease-free survival (DFS) of HCC patients who had high expression of OATP1B3 were significantly longer than those of patients with low expression (33.0% vs 12.9%, P = 0.001; 18.8% vs 5.3%, P < 0.0001). Cox multivariate analysis showed that OATP1B3, invasion, and TNM stage (P < 0.05 for each) were independent prognostic factors of OS in HCC patients and that OATP1B3 and TNM stage (both P < 0.05) were independent prognostic factors of DFS in HCC patients.ConclusionsThe expression of OATP1B3 in HCC patients was significantly lower than that in adjacent nontumorous tissues. OATP1B3 expression may be a potential prognostic marker in HCC patients.

Gadoxetic acid-enhanced MR imaging for hepatocellular carcinoma: molecular and genetic background.

Gadoxetic acid-enhanced magnetic resonance imaging (MRI) plays important roles in diagnosis of hepatic lesions because of its superiority in the detectability of small lesions, its differentiation ability, and its utility for the early diagnosis of hepatocellular carcinoma (HCC). In HCC, expression of organic anion transporting polypeptide (OATP) 1B3 correlates with the enhancement ratio in the hepatobiliary phase. Gadoxetic acid-enhanced MRI, an indirect molecular imaging method, reflects OATP1B3 expression in HCC. OATP1B3 expression gradually decreases from the dysplastic nodule stage to advanced HCC. Decreased expression is a sensitive marker of multistep hepatocarcinogenesis, especially in the early stages. Hypervascular HCCs commonly show hypointensity in the hepatobiliary phase corresponding to a decrease in OATP1B3; however, approximately 10% of HCCs show hyperintensity due to OATP1B3 overexpression. This hyperintense HCC shows less aggressive biological features and has a better prognosis than hypointense HCC. Hyperintense HCC can be classified into a genetic subtype of HCC with a mature hepatocyte-like molecular expression. OATP1B3 expression and the less aggressive nature of hyperintense HCC are regulated by the molecular interaction of β-catenin signaling and hepatocyte nuclear factor 4α, a tumor suppressor factor. Gadoxetic acid-enhanced MR imaging has the potential to be an imaging biomarker for HCC. KEY POINTS: • The hepatobiliary phase is a sensitive indirect indicator of organic anion transporting polypeptide1B3 (OATP1B3) expression in hepatocellular carcinoma (HCC). • The OATP1B3 expression, namely, enhancement in the hepatobiliary phase, decreases from the very early stage of hepatocarcinogenesis, contributing to early diagnosis of HCC. • HCC showing hyperintensity on the hepatobiliary phase is a peculiar genetic subtype of HCC with OATP1B3 overexpression, a less aggressive nature, and mature hepatocyte-like molecular/genetic features.

Central bisectionectomy for hepatocellular carcinoma in a patient with indocyanine green excretory defect associated with reduced expression of the liver transporter.

BackgroundIndocyanine green (ICG) excretory defect is a dye excretory disorder, and it is characterized by the selective impairment of plasma ICG clearance with normal liver histology. The pathophysiology involves selective loss of active transporters for ICG in the hepatic cell membrane. Several cases of hepatectomy in patients with ICG excretory defect have been reported, but the expression of hepatic transporters involved in ICG excretory defect has not been examined in these cases.Case presentationAn 81-year-old man who was hepatitis B and C virus negative was admitted to our hospital with a diagnosis of HCC. Abdominal computed tomography revealed an 8-cm-diameter tumor in hepatic segments 4 and 8. The retention rate of ICG at 15 min (ICGR15), which has been used to evaluate hepatic functional reserve, was markedly elevated (79.1 %), whereas other liver function test results, were normal. Therefore, we diagnosed the patient with HCC with an ICG excretory defect, and considered major hepatectomy. Central bisectionectomy was performed, and the postoperative course was uneventful. Microscopic examination of the resected specimen showed moderately differentiated HCC. Immunohistochemical staining and polymerase chain reaction analysis of a non-neoplastic site of the resected specimen showed very few expression of the organic anion-transporting polypeptide 1B3 (OATP1B3), which is usually expressed on the basolateral membrane of human hepatocytes and mediates the uptake of ICG.ConclusionsIn this case, we present a case of hepatectomy for HCC in a patient with ICG excretory defect, which may be attributable to a congenital disorder of OATP1B3 expression; however, an ICG excretory defect did not seem to have any effect on the short-term prognosis after hepatectomy.

Cancer-type Organic Anion Transporting Polypeptide 1B3: Current Knowledge of the Gene Structure, Expression Profile, Functional Implications and Future Perspectives.

Human organic anion transporting polypeptide 1B3 (OATP1B3) is a hepatocyte drug transporter that facilitates uptake of various therapeutic drugs from the circulatory system. Shortly after its initial identification in the liver, OATP1B3 expression was also reported in various solid cancer tissues. In the years since that time, it has been presumed that the OATP1B3 expressed in cancer tissues is identical to that expressed in the liver. However, we have recently identified a new OATP1B3 mRNA variant in cancer tissues, which we have named cancer-type OATP1B3 (Ct-OATP1B3). Given that the identification of Ct-OAT1B3 as a bona fide cancer-associated isoform revises a longstanding study premise, it is essential to fully elucidate the molecular function of Ct-OATP1B3 in cancer cells. Based on the predicted Ct-OATP1B3 protein structure, it is reasonable to assume that it functions as a transporter, but there are a number of ongoing arguments regarding Ct-OATP1B3 protein expression and its functions. With the above points in mind, this review will summarize current knowledge of Ct-OATP1B3 mRNA expression features in cancer tissues and its proposed, yet currently controversial, functions. Based on that background, our future perspectives related to Ct-OATP1B3 studies will also be presented.

Role of OATP1B3 in the transport of bile acids assessed using first-trimester trophoblasts.

The aim of this study was to investigate the transport of two kinds of bile acids by organic anion transporting polypeptide 1B3 (OATP1B3) using first-trimester trophoblasts. The mechanisms of damage to fetuses with intrahepatic cholestasis of pregnancy were investigated, providing new potential strategies for targeted therapies aimed at reducing fetal risk. The expression of OATP1B3 was knocked down by lentiviral vector-mediated RNA interference, and silencing efficiency was assessed using real-time polymerase chain reaction and Western blotting. The cytotoxicity of two bile acids (glycocholic acid [GCA] and glycochenodeoxycholic acid [GCDCA]) was assessed using the MTT method. Transport of bile acids was assessed by establishing an in vitro trophoblast monolayer model using polyester Transwell-clear inserts, and the concentration of bile acids in the upper compartment was assessed using high-pressure liquid chromatography. GCA and GCDCA (10 and 20 μM) were not cytotoxic to the SWAN cell line (P > 0.05). RNAi treatment decreased the mRNA and protein expressions of OATP1B3 by 94.42% and 49.51%, respectively (P < 0.05). The bile acid transport curves were similar in the control and negative RNAi groups, whereas those in the RNAi group differed significantly from those in the control and negative RNAi groups. The concentration of GCA and GCDCA in the upper compartment was significantly lower in the RNAi group than in the control and negative RNAi groups. OATP1B3 expression in trophoblasts was confirmed indirectly by its ability to transport the bile acids GCA and GCDCA.

OATP1B3 expression is strongly associated with Wnt/β-catenin signalling and represents the transporter of gadoxetic acid in hepatocellular carcinoma

In the current era of emerging molecular targeted drugs, it is necessary to identify before treatment the specific subclass to which a tumour belongs. Gadoxetic acid is a liver-specific contrast agent that is preferentially taken up by hepatocytes. Therefore, gadoxetic acid-enhanced magnetic resonance imaging (EOB-MRI) should provide precise molecular information about hepatocellular carcinomas (HCCs). The aim of this study was to investigate the transporters of gadoxetic acid in HCC comprehensively and to analyse the molecular regulatory mechanism of such transporters. Expression levels of transporters, transcriptional factors and Wnt target genes in clinical samples were examined by quantitative real-time reverse transcription polymerase chain reaction and immunohistochemistry. LiCl treatment of the HCC cell line KYN-2 was conducted in vitro to assess the effects of Wnt signalling activity. Comprehensive analyses of transporter mRNAs and protein expressions revealed that the organic anion transporting polypeptide 1B3 (OATP1B3) had the strongest correlation with tumour enhancement in hepatobiliary-phase images of EOB-MRI. Association analysis with OATP1B3 expression revealed significant correlation with the expression of Wnt/β-catenin target genes. Further, LiCl treatment induced OATP1B3 mRNA expression in KYN-2 cells, indicating a strong association between OATP1B3 expression and Wnt/β-catenin signalling. The sensitivity and specificity to predict Wnt/β-catenin-activated HCC using tumour enhancement in EOB-MRI were 78.9% and 81.7%, respectively. OATP1B3 was confirmed as the most important transporter mediating HCC enhancement in EOB-MRI. OATP1B3 expression showed a strong association with the expression of Wnt/β-catenin target genes, therefore, OATP1B3-upregulated HCC likely represents a specific subclass of Wnt/β-catenin-activated HCC.

A Cancer-Specific Variant of the SLCO1B3 Gene Encodes a Novel Human Organic Anion Transporting Polypeptide 1B3 (OATP1B3) Localized Mainly in the Cytoplasm of Colon and Pancreatic Cancer Cells

OATP1B3 is a member of the OATP (organic anion transporting polypeptides) superfamily, responsible for mediating the transport of numerous endogenous and xenobiotic substances. Although initially reported to be exclusively expressed in the liver, several studies reported that OATP1B3 is frequently expressed in multiple types of cancers and may be associated with differing clinical outcomes. However, a detailed investigation on the expression and function of OATP1B3 protein in cancer has been lacking. In this study, we confirmed that colon and pancreatic cancer cells express variant forms of OATP1B3, different from OATP1B3 wild-type (WT) expressed in the normal liver. OATP1B3 variant 1 (V1), the most prevalent form among the variants, contains alternative exonic sequences (exon 2a) instead of exons 1 and 2 present in OATP1B3 WT. The translated product of OATP1B3 V1 is almost identical to OATP1B3 WT, with exception to the first 28 amino acids at the N-terminus. Exogenous expression of OATP1B3 V1 revealed that OATP1B3 V1 undergoes post-translational modifications and proteasomal degradation to a differing extent compared to OATP1B3 WT. OATP1B3 V1 showed only modest transport activity toward cholecystokin-8 (CCK-8, a prototype OATP1B3 substrate) in contrast to OATP1B3 WT showing a markedly efficient uptake of CCK-8. Consistent with these results, OATP1B3 V1 was localized mainly in the cytoplasm with a much lower extent of trafficking to the surface membrane compared to OATP1B3 WT. In summary, our results demonstrate that colon and pancreatic cancer cells express variant forms of OATP1B3 with only limited transport activity and different subcellular localization compared to OATP1B3 WT. These observed differences at the molecular and functional levels will be important considerations for further investigations of the biological and clinical significance of OATP1B3 expression in cancer.

Abstract 1848: Expression of an androgen transporter, organic anion transporting polypeptide 1B3, impacts progression and treatment of prostate cancer

Abstract Organic anion transporting polypeptides (OATPs) are membrane transporters that facilitate the movement of large substrates into cells. One family member, organic anion transporting polypeptide 1B3 (OATP1B3) is aberrantly overexpressed in prostate cancer and has been shown to influx both endogenous small molecules and chemotherapy reagents. Our hypothesis is that the OATP1B3 affects tumor growth by influxing testosterone. However, little is known about the cause of OATP1B3 expression in cancer and the impact of OATP1B3 transport on tumor growth. Therefore, we completed a study investigating putative hypoxia elements in the OATP1B3 promoter region, characterizing the impact of OATP1B3 androgen transport on prostate cancer growth, and examining the effect of OATP1B3 on the efficacy of standard prostate cancer treatments. The results showed that OATP1B3 co-localized with HIF 1-alpha in prostate cancer tissues from patients, correlated significantly to HIF1A in xenograft tumors under castration (P=0.005), and confirmed HIF-1alpha elements in the SLCO1B3 promoter region. In addition, radioactive transport assays with Xenopus oocytes showed that OATP1B3 transports testosterone and dihydrotestosterone 50- to 250-fold over passive diffusion at low physiological concentrations. A prostate cancer cell line expressing OATP1B3 grew faster than untransfected in response to androgens at all concentrations. Finally, OATP1B3 increased cell sensitivity to docetaxel treatment. In summary, these data show that hypoxia and castration increases OATP1B3 expression in cancer, OATP1B3-mediated androgen transport significantly impacts prostate cancer growth and OATP1B3 impacts the efficacy of docetaxel. These data provides evidence that OATP1B3 impacts prostate cancer growth and treatment. Future studies could screen for specific inhibitors of OATP1B3-mediated androgen transport. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1848. doi:1538-7445.AM2012-1848

Functional Consequences of Genetic Variations in the Human Organic Anion Transporting Polypeptide 1B3 (OATP1B3) in the Korean Population

The objectives of this study were to investigate the allele frequencies and linkage disequilibrium (LD) in the organic anion transporting polypeptide 1B3 (OATP1B3) in the Korean population and to examine the functional consequences. Using samples from 48 Koreans, direct sequencing was carried out to determine the allele frequencies and LD of OATP1B3 in a representative Korean population. Thirty-six genetic variations in the transporter were found in Koreans; among them, five undocumented variations (i.e.,-6436G>C in the 5'-upstream region, 26A>C and 586A>G in the protein coding region, and IVS6-72A>T and IVS12-80A>T in intron regions) were identified. In the upstream region, -5035G>A was found to have lowered gene expression, as determined by a reporter gene assay, suggesting that this variation reduces the expression of OATP1B3 in humans. The functional relevance of the genetic variations in the protein coding region was determined by an uptake study involving representative substrates in human embryonic kidney 293 cells expressing wild type or variant forms. Variations involving 699G>A showed a reduced uptake activity for testosterone, but not for estradiol 17β-d-glucuronide or methotrexate, indicating that the functional impact of the variations is substrate specific. Considering the kinetic relevance of OATP1B3, the functionally affected variations may be therapeutically important.

Abstract B28: Organic anion transporting polypeptide 1B3 as a novel biomarker for hypoxia in prostate cancer.

Abstract The organic anion transporting polypeptide 1B3 (OATP1B3) is aberrantly expressed in prostate cancer. We showed that OATP1B3 expression correlated to Gleason score in primary prostate cancer samples. As a transporter, OATP1B3 functions to influx both endogenous small molecules and xenobiotics. We also demonstrated that decreased survival and decreased progression in patients with prostate cancer was associated with a polymorphism in SLCO1B3, the gene encoding OATP1B3. However, OATP1B3 has not been validated as a clinical biomarker and the cause of expression in cancer is unknown. The purpose of this study was to identify a molecular regulation that explains OATP1B3 expression in cancer. In this study, we show that hypoxia increases the transcriptional and translational expression of OATP1B3 in cancer, that hypoxia-inducible factor 1-alpha (HIF1-alpha) binds putative hypoxia response elements in the SLCO1B3 promoter region by chromatin immunoprecipitation, and show co-localization of hypoxia and OATP1B3 by immunohistochemistry in clinical tissue samples. Additionally, cooperation between androgen- and hypoxia-signaling pathways explains the increased expression of OATP1B3 in prostate cancer xenografts under castration conditions. These data provide a foundation for the use of OATP1B3 as a biomarker of cancerous disease. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B28.

Organic anion transporting polypeptide 1B3 (OATP1B3) is overexpressed in colorectal tumors and is a predictor of clinical outcome

OATP1B3 is an organic anion transporting polypeptide (OATP) that functions as a multispecific transporter in the normal liver. We examined the expression and clinical significance of OATP1B3 in colon cancers in tissue microarrays. Immunohistochemistry was used to assess OATP1B3 protein expression in paraffinized colon tumor tissue microarrays. OATP1B3 immunostaining was evaluated by location and intensity. Relationships between OATP1B3 expression, known prognostic variables and clinical outcomes were examined. 278 colon tumor samples of all stages were evaluated for OATP1B3 expression. OATP1B3 immunostaining was detectable in the majority (56%) of the tumor samples. Higher OATP1B3 expression was seen in lower stage tumors (p = 0.003) and lower grade (p = 0.004) tumors, but was not predictive of 5-year survival or tumor recurrence as an independent variable. Within individual tumor grades, OATP1B3 expression was associated with improved 5-year survival, but not recurrence in patients with poorly differentiated tumors. OATP1B3 expression was seen in the majority of colon tumors and may be a marker of lower grade and lower stage tumors and may predict for improved outcome in certain tumors.