Characterization of the breast cancer resistance protein (BCRP/ABCG2) in clear cell renal cell carcinoma.

The efflux transporter breast cancer resistance protein BCRP/ABCG2 is well-known for its contribution to multi-drug resistance in cancer. Its relevance in cancer biology independent from drug efflux remains largely elusive. Our study aimed at elucidating the biological relevance and regulatory mechanisms of BCRP/ABCG2 in clear cell renal cell carcinoma (ccRCC) and disease progression. Two independent ccRCC-cohorts [Cohort 1 (KIRC/TCGA): n = 453, Cohort 2: n = 64] were investigated to elucidate BCRP/ABCG2 mRNA and protein expression and their association with survival. The impact of BCRP/ABCG2 on response to sunitinib treatment was investigated in two independent sunitinib-treated ccRCC-cohorts based on mRNA levels. Moreover, underlying regulatory mechanisms for interindividual variability of BCRP/ABCG2 expression were systematically assessed. Owing to redundant functional properties, mRNA and protein expression of the multidrug resistance protein MDR1/ABCB1 were additionally evaluated in these cohorts. In independent ccRCC-cohorts, low BCRP/ABCG2 and MDR1/ABCB1 mRNA and protein expression were associated with severity (e.g., tumor stage) of ccRCC and poor cancer-specific survival. BCRP/ABCG2 and MDR1/ABCB1 mRNA expression were linked to decreased progression-free survival after sunitinib treatment. Germline and somatic variants influenced interindividual variability of BCRP/ABCG2 expression only moderately. miR-212-3p and miR-132-3p were identified to regulate BCRP/ABCG2 posttranscriptionally by interaction with the ABCG2 3'UTR as confirmed through reporter gene assays in RCC cell lines. In summary, BCRP/ABCG2 expression in ccRCC underlies considerable interindividual variability with impact on patient survival and response to sunitinib treatment. While germline or somatic genetic variants and DNA methylation cannot explain aberrant BCRP/ABCG2 expression, miR-212-3p and miR-132-3p were identified to contribute to posttranscriptional regulation of BCRP/ABCG2.

Metabolic and Lipidomic Reprogramming in Renal Cell Carcinoma Subtypes Reflects Regions of Tumor Origin.

BACKGROUND: Renal cell carcinoma (RCC) consists of prognostic distinct subtypes derived from different cells of origin (eg, clear cell RCC [ccRCC], papillary RCC [papRCC], and chromophobe RCC [chRCC]). ccRCC is characterized by lipid accumulation and metabolic alterations, whereas data on metabolic alterations in non-ccRCC are limited. OBJECTIVE: We assessed metabolic alterations and the lipid composition of RCC subtypes and ccRCC-derived metastases. Moreover, we elucidated the potential of metabolites/lipids for subtype classification and identification of therapeutic targets. DESIGN, SETTING, AND PARTICIPANTS: Metabolomic/lipidomic profiles were quantified in ccRCC (n=58), chRCC (n=19), papRCC (n=14), corresponding nontumor tissues, and metastases (n=9) through a targeted metabolomic approach. Transcriptome profiling was performed in corresponding samples and compared with expression data of The Cancer Genome Atlas cohorts (patients with ccRCC, n=452; patients with papRCC, n=260; and patients with chRCC, n=59). OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: In addition to cluster analyses, metabolomic/transcriptomic data were analyzed to evaluate metabolic differences of ccRCC and chRCC using Welch's t test or paired t test as appropriate. Where indicated, p values were adjusted for multiple testing using Bonferroni or Benjamini-Hochberg correction. RESULTS AND LIMITATIONS: Based on their metabolic profiles, RCC subtypes clustered into two groups separating ccRCC and papRCC from chRCC, which mainly reflected the different cells of origin. ccRCC-derived metastases clustered with primary ccRCCs. In addition to differences in certain lipids (lysophosphatidylcholines and sphingomyelins), the coregulation network of lipids differed between ccRCC and chRCC. Consideration of metabolic gene expression indicated, for example, alterations of the polyamine pathway at metabolite and transcript levels. In vitro treatment of RCC cells with the ornithine-decarboxylase inhibitor difluoromethylornithine resulted in reduced cell viability and mitochondrial activity. Further evaluation of clinical utility was limited by the retrospective study design and cohort size. CONCLUSIONS: In summary, we provide novel insight into the metabolic profiles of ccRCC and non-ccRCC, thereby confirming the different ontogeny of RCC subtypes. Quantification of differentially regulated metabolites/lipids improves classification of RCC with an impact on the identification of novel therapeutic targets. PATIENT SUMMARY: Several subtypes of renal cell carcinoma (RCC) with different metastatic potentials and prognoses exist. In the present study, we provide novel insight into the metabolism of these different subtypes, which improves classification of subtypes and helps identify novel targets for RCC therapy.

Clinical and Functional Relevance of the Monocarboxylate Transporter Family in Disease Pathophysiology and Drug Therapy.

The solute carrier (SLC) SLC16 gene family comprises 14 members and encodes for monocarboxylate transporters (MCTs), which mediate the absorption and distribution of monocarboxylic compounds across plasma membranes. As the knowledge about their physiological function, activity, and regulation increases, their involvement and contribution to cancer and other diseases become increasingly evident. Moreover, promising opportunities for therapeutic interventions by directly targeting their endogenous functions or by exploiting their ability to deliver drugs to specific organ sites emerge.

Selective Inhibition of the Lactate Transporter MCT4 Reduces Growth of Invasive Bladder Cancer.

The significance of lactate transporters has been recognized in various cancer types, but their role in urothelial carcinoma remains mostly unknown. The aim of this study was to investigate the functional importance of the monocarboxylate transporter (MCT) 4 in preclinical models of urothelial carcinoma and to assess its relevance in patient tumors. The association of MCT4 expression with molecular subtypes and outcome was determined in The Cancer Genome Atlas (TCGA) cohort and two independent cohorts of patients with urothelial carcinoma. Silencing of MCT4 was performed using siRNAs in urothelial carcinoma cell lines. Effects of MCT4 inhibition on cell growth, apoptosis, and production of reactive oxygen species (ROS) were assessed. Moreover, effects on lactate efflux were determined. The in vivo effects of MCT4 silencing were assessed in an orthotopic xenograft model. MCT4 expression was higher in the basal subtype. Decreased MCT4 methylation and increased RNA and protein expression were associated with worse overall survival (OS). Inhibition of MCT4 led to a reduction in cell growth, induction of apoptosis, and an increased synthesis of ROS. MCT4 inhibition resulted in intracellular accumulation of lactate. In vivo, stable knockdown of MCT4 reduced tumor growth. The expression of MCT4 in urothelial carcinoma is associated with features of aggressive tumor biology and portends a poor prognosis. Inhibition of MCT4 results in decreased tumor growth in vitro and in vivo Targeting lactate metabolism via MCT4 therefore provides a promising therapeutic approach for invasive urothelial carcinoma, especially in the basal subtype.

Methylomes of renal cell lines and tumors or metastases differ significantly with impact on pharmacogenes.

Current therapies for metastatic clear cell renal cell carcinoma (ccRCC) show limited efficacy. Drug efficacy, typically investigated in preclinical cell line models during drug development, is influenced by pharmacogenes involved in targeting and disposition of drugs. Here we show through genome-wide DNA methylation profiling, that methylation patterns are concordant between primary ccRCC and macro-metastases irrespective of metastatic sites (rs ≥ 0.92). However, 195,038 (41%) of all investigated CpG sites, including sites within pharmacogenes, were differentially methylated (adjusted P < 0.05) in five established RCC cell lines compared to primary tumors, resulting in altered transcriptional expression. Exemplarily, gene-specific analyses of DNA methylation, mRNA and protein expression demonstrate lack of expression of the clinically important drug transporter OCT2 (encoded by SLC22A2) in cell lines due to hypermethylation compared to tumors or metastases. Our findings provide evidence that RCC cell lines are of limited benefit for prediction of drug effects due to epigenetic alterations. Similar epigenetic landscape of ccRCC-metastases and tumors opens new avenue for future therapeutic strategies.

MCT4 surpasses the prognostic relevance of the ancillary protein CD147 in clear cell renal cell carcinoma.

UNLABELLED: Cluster of differentiation 147 (CD147/BSG) is a transmembrane glycoprotein mediating oncogenic processes partly through its role as binding partner for monocarboxylate transporter MCT4/SLC16A3. As demonstrated for MCT4, CD147 is proposed to be associated with progression in clear cell renal cell carcinoma (ccRCC). In this study, we evaluated the prognostic relevance of CD147 in comparison to MCT4/SLC16A3 expression and DNA methylation. METHODS: CD147 protein expression was assessed in two independent ccRCC-cohorts (n = 186, n = 59) by immunohistochemical staining of tissue microarrays and subsequent manual as well as automated software-supported scoring (Tissue Studio, Definien sAG). Epigenetic regulation of CD147 was investigated using RNAseq and DNA methylation data of The Cancer Genome Atlas. These results were validated in our cohort. Relevance of prognostic models for cancer-specific survival, comprising CD147 and MCT4 expression or SLC16A3 DNA methylation, was compared using chi-square statistics. RESULTS: CD147 protein expression generated with Tissue Studio correlated significantly with those from manual scoring (P < 0.0001, rS = 0.85), indicating feasibility of software-based evaluation exemplarily for the membrane protein CD147 in ccRCC. Association of CD147 expression with patient outcome differed between cohorts. DNA methylation in the CD147/BSG promoter was not associated with expression. Comparison of prognostic relevance of CD147/BSG and MCT4/SLC16A3, showed higher significance for MCT4 expression and superior prognostic power for DNA methylation at specific CpG-sites in the SLC16A3 promoter (e.g. CD147 protein: P = 0.7780,Harrell's c-index = 53.7% vs. DNA methylation: P = 0.0076, Harrell's c-index = 80.0%). CONCLUSIONS: Prognostic significance of CD147 protein expression could not surpass that of MCT4, especially of SLC16A3 DNA methylation, corroborating the role of MCT4 as prognostic biomarker for ccRCC.

Solute carrier transporter and drug-related nephrotoxicity: the impact of proximal tubule cell models for preclinical research.

INTRODUCTION: The final excretion step of several drugs is facilitated by membrane transporters of the Solute carrier (SLC) family expressed in the proximal tubules of the kidney. Membrane transporters contribute substantially to the pharmacokinetic profile of drugs and play important roles in drug-induced nephrotoxicity. Different cell models have been applied as tools for the assessment of nephrotoxic effects caused by drugs. AREAS COVERED: This review gives an overview over clinically relevant SLC transporters involved in the renal elimination of drug agents and their specific role in drug-induced nephrotoxicity. Most widely applied cell models are described and their advantages and limitations are outlined. EXPERT OPINION: In vitro cell culture models (e.g., continuous and primary renal cell lines, polarized cell monolayers) represent valuable tools for early assessment of the nephrotoxic potential of drugs. Since SLC transporters contribute to drug excretion in a large part, in vitro cell culture models might be very helpful to study transport pathways and/or potential drug-drug interactions at an early stage of the drug development process to predict nephrotoxic effects.

Metformin and cancer: from the old medicine cabinet to pharmacological pitfalls and prospects.

Metformin is a biguanide derivative used in the treatment of type II diabetes (T2D) and one of the world's most widely prescribed drugs. Owing to its safety profile, it has been recently promoted for a range of other indications, particularly for its role in cancer prevention. There is evidence from studies in diabetic cohorts, as well as laboratory studies, that the action of metformin depends on a balance between the concentration and duration of exposure, which depends crucially on cell- and tissue-specific pharmacological factors. Mechanistic studies have revealed the involvement of increasingly complex pathways. Yet, there are several missing links regarding the role of drug transporters and drug-drug interactions, as well as the expression levels of transporters in normal versus tumor tissues, which may affect patient exposure and dosing when metformin is used in cancer prevention. This review highlights the current knowledge on metformin action and pharmacology, including novel insights into genomic factors, with a specific focus on cancer prevention. Furthermore, future challenges that may influence therapeutic outcome will be discussed.

DNA methylation of the SLC16A3 promoter regulates expression of the human lactate transporter MCT4 in renal cancer with consequences for clinical outcome.

PURPOSE: The monocarboxylate transporter 4 (MCT4) is a metabolic target in tumor biology because it mediates lactate transport across membranes resulting in antiapoptotic effects. Cell experiments support the importance of MCT4 in clear cell renal cell carcinoma (ccRCC). In this study, we assessed the prognostic potential of MCT4 expression in ccRCC and its epigenetic regulation by DNA methylation as novel predictive marker for patient outcome using independent ccRCC cohorts. EXPERIMENTAL DESIGN: MCT4 protein expression was quantified in 207 ccRCC and corresponding nontumor tissues. Data of an independent ccRCC cohort from The Cancer Genome Atlas (TCGA) were analyzed on MCT4 mRNA (n = 482) and DNA methylation (n = 283) level. The findings on MCT4 expression and DNA methylation in the SLC16A3 promoter were validated in a third cohort (n = 64). Promoter activity assays were conducted in four RCC cell lines. RESULTS: MCT4 protein expression was upregulated (P < 0.0001) in ccRCC and showed significant association with cancer-related death. Upregulation of MCT4 mRNA expression (P < 0.00001) was confirmed in the TCGA cohort. Single CpG sites correlated inversely with mRNA expression and were associated with overall survival in Kaplan-Meier analyses [HR = 0.39; 95% confidence interval (CI), 0.24-0.64; P[log-rank] = 1.23e(-04)]. Promoter activity studies confirmed MCT4 regulation by DNA methylation. The significant correlation between MCT4 protein and gene expression or DNA methylation at single CpG sites was validated in a third cohort. Again, higher methylation at individual CpG sites was associated with prolonged survival [HR = 0.05; 95% CI, 0.01-0.40; P[log-rank] = 6.91e(-05)]. CONCLUSION: We identified SLC16A3 promoter DNA methylation as a novel epigenetic mechanism for MCT4 regulation in ccRCC with first evidence of a biological rationale for prognosis and clinical outcome.