5-alpha-reductase type I (SRD5A1) is up-regulated in non-small cell lung cancer but does not impact proliferation, cell cycle distribution or apoptosis
© Kapp et al; licensee BioMed Central Ltd. 2012
Received: 19 April 2011
Accepted: 18 January 2012
Published: 18 January 2012
Non-small cell lung cancer (NSCLC) is one of the most frequent malignancies and has a high mortality rate due to late detection and lack of efficient treatments. Identifying novel drug targets for this indication may open the way for new treatment strategies. Comparison of gene expression profiles of NSCLC and normal adjacent tissue (NAT) allowed to determine that 5-alpha-reductase type I (SRD5A1) was up-regulated in NSCLC compared to NAT. This raised the question whether SRD5A1 was involved in sustained proliferation and survival of NSCLC.
siRNA-mediated silencing of SRD5A1 was performed in A549 and NCI-H460 lung cancer cell lines in order to determine the impact on proliferation, on distribution during the different phases of the cell cycle, and on apoptosis/necrosis. In addition, lung cancer cell lines were treated with 4-azasteroids, which specifically inhibit SRD5A1 activity, and the effects on proliferation were measured. Statistical analyses using ANOVA and post-hoc Tamhane-T2-test were performed. In the case of non-parametric data, the Kruskal-Wallis test and the post-hoc Mann-Whitney-U-test were used.
The knock-down of SRDA51 expression was very efficient with the SRD5A1 transcripts being reduced to 10% of control levels. Knock-down efficiency was furthermore confirmed at the protein level. However, no effect of SRD5A1 silencing was observed in the proliferation assay, the cell cycle analysis, and the apoptosis/necrosis assay. Treatment of lung cancer cell lines with 4-azasteroids did not significantly inhibit proliferation.
In summary, the results suggest that SRD5A1 is not a crucial enzyme for the sustained proliferation of NSCLC cell lines.
Lung cancer remains one of the leading causes of morbidity and mortality in cancer patients, and its prognosis is unsatisfactory with an overall survival of 15-18% . Surgical resection promotes good long-term survival in the early stages with up to 57%-71% in stage I non-small cell lung cancer (NSCLC)  and 33-57% in stage II NSCLC . Unfortunately, late diagnosis is common due to the lack of early symptoms, which explains the low survival rates. Chemotherapy in the late stages III and IV did improve the outcome in the last decades, but only slightly from 10% in the 1980s to 15-18% nowadays. Thus, new and more effective treatment strategies are urgently needed. Several genome-wide gene expression profiling studies have been performed in the past years (reviewed by Mueller-Hagen et al. ). These analyses provide valuable diagnostic and prognostic markers as well as a basis for the discovery of novel target candidates for the therapy of NSCLC. More recently, a genome-wide expression profiling analysis of matching pairs of NSCLC and normal adjacent tissue (NAT) on Affymetrix exon arrays was performed, providing evidence for genes alternatively spliced in NSCLC .
Two main steroid 5-alpha-reductases have been identified, 5-alpha-reductase type I (SRD5A1) and 5-alpha-reductase type II (SRD5A2) . The recently described type III (SRD5A3)  was originally identified in prostate cancer tissue and acts as a polyprenol reductase involved in the N-linked glycosylation of proteins . SRD5A1 is expressed mainly in the skin from the time of puberty while SRD5A2 is the predominant enzyme in the prostate and male accessory sex glands . While SRD5A2 is an initiating factor for male pattern baldness, its germ line deficiency results in male pseudohermaphroditism, which is characterized by phenotypically female external genitalia at birth. It has been suggested that SRD5A1 and SRD5A2 are involved in the pathogenesis of polycystic ovary syndrome . So far, only few publications examined the role of 5-alpha-reductases in the lung and in lung cell lines, with partly conflicting results. Provost et al. detected only a small amount of SRD5A1 mRNA and only little enzymatic activity of SRD5A1 in A549 lung cancer cells . In a microarray analysis of different tissues, SRD5A1 expression has been described as being low in normal lung tissue . So far, there have been no reports on the expression level of SRD5A1 mRNA in NCI-H460 cells. Over-expression of SRD5A1 and SRD5A2 has been noted in breast and prostate cancer samples [13, 14].
In preliminary studies with Affymetrix GeneChips, SRD5A1 was identified as up-regulated in NSCLC compared to NAT. The hypothesis was developed that SRD5A1 was possibly involved in sustaining the proliferation in NSCLC cell lines. In order to analyze this, knock-down of SRD5A1 expression was performed and the effects on cell growth, cell cycle distribution, apoptosis, and necrosis were determined. In addition, the impact of blocking the enzymatic activity of SRD5A1 with compounds selective for SRD5A1 such as 4-azasteroids was studied.
Lung cancer samples and NAT were obtained with informed consent from patients treated at the Department of General, Vascular and Thoracic Surgery and at the Institute of Pathology, Charité, Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany .
Cell lines and culture
The human NSCLC cell lines A549 and NCI-H460 (H460) were obtained from ATCC (ATCC, Manassas, VA, USA). Both cell lines were cultured in DMEM/Ham's F12 medium (Biochrom AG, Berlin, Germany) supplemented with 2 mM L-glutamine (Invitrogen, Carlsbad, CA, USA), 100 units/ml penicillin G and 100 μg/ml streptomycin (Invitrogen). Also, fetal calf serum (FCS; Biochrom AG), which contains 0.03 ng/ml testosterone, was added to a final concentration of 10%. The cells were grown at 37.0°C, in 5% CO2 and 95% relative humidity.
Affymetrix microarray analysis
RNA was transcribed into cRNA and hybridized onto Affymetrix GeneChip HG-U133Plus2.0 The hybridization intensities on each array were calculated with the MAS5.0 summarization algorithm. The refined and summarized data were loaded into the CoBi database (Genedata, Basel, CH). The analysis of the probeset-specific signal intensities was performed with the Genedata Expressionist Version 6.1 software (Genedata, Basel, CH). The dataset was normalized using Central Tendency Median Normalization. The Genedata software was used for Principal Component Analysis (PCA) and statistical tests. SRD5A1 expression was analyzed using the in-house available Array Northern database . Here, the expression values for a specific gene were displayed as a bar graph of the geometric mean values of the expression value on an arbitrary scale over all samples belonging to a specific class (e.g. tissue or organ type, cell line). For a number of organs, the expression levels in corresponding cancer samples are additionally shown. First, the expression data were transformed into logarithmic scale, then a calculation of the arithmetic mean and standard deviation was performed. Afterwards, the mean values were transformed to mean +/- standard deviation on a linear scale.
siRNA knock-down studies
Human SRD5A1 specific and mismatch (mm) siRNAs.
Lipofectamine™ 2000 (Invitrogen) and OPTI-MEM I (Invitrogen) were used for the transfection of siRNA into cultured cells. BLOCK-iT™ Fluorescent Oligo (Invitrogen) was used to visualize successful transfection via fluorescence microscopy. The lowest amount of siRNA required for a consistent knock-down of SRD5A1 was determined to be 10 pmol. For transfection, 5 μl of Lipofectamine™ 2000 were used per well of a six-well culture plate (TPP, Trasadingen, Switzerland). In order to reduce possible toxic effects, the amount of Lipofectamine™ 2000 was lowered to 2.5 μl per well in the course of the experiments.
Expression analysis by quantitative real-time PCR (qRT-PCR)
RNA was extracted with the RNeasy® Mini Kit (Qiagen, Hilden, Germany), followed by digestion of genomic DNA using the RNase free DNase-Set (Qiagen). RNA content was measured by spectrophotometry. The cDNA synthesis was conducted with SuperScript™ III First-Strand Synthesis System for RT-PCR (Invitrogen) using 1 μg of the extracted total RNA. The cDNA was analyzed in a multiplex analysis using TaqMan® Universal PCR MasterMix and specific primers for SRD5A1 or the internal controls (Applied Biosystems, Foster City, CA, USA). The primers specific for SRD5A1 had the Assay ID: Hs00602694_mH, reporter dye FAM). Cyclophilin A served as the endogenous control and had the reference 4310883E (VIC/TAMRA Probe, Primer Limited). The reagents were assembled in MicroAmp™ Fast Optical 96-Well Reaction Plates (Applied Biosystems) and the PCR reaction was conducted in a 7500 Fast Real-Time PCR System (Applied Biosystems). The regular RT-PCR program was used and the read-out was set to automatic threshold (Ct). Each cell culture sample was measured in triplicates, non-template controls were included to detect potential contamination. In order to apply the ΔΔCt method, a validation experiment according to the protocol provided by Applied Biosystems  was conducted first, to demonstrate that multiplex analysis of SRD5A1 and cyclophilin was feasible. The validation experiment was successful with an absolute value of the slope of ΔCt vs. log input of RNA being < 0.1 (-0,07, data not shown). The qRT-PCR protocol from Applied Biosystems  and the publication by Yuan et al  describe the ΔΔCt-method used for analysis of the real-time PCR data. In brief, the cycle number at the Ct for the target gene (SRD5A1) was subtracted by the Ct of the reference gene (cyclophilin A) to give the ΔCt value. The ΔCt of the treated sample was then subtracted from the ΔCt of the untreated sample to give ΔΔCt. The exponential function of 2-ΔΔCt represents the relative amount of the target gene in the treated sample compared to the target gene in the untreated control.
Expression levels of SRD5A1 in NSCLC and NAT samples as measured by qRT-PCR.
The cells were suspended in M-PER buffer (Pierce Biotechnology, Rockford, IL, USA) for protein extraction. The protein lysate was then run on NuPAGE 12% Bis-Tris Gel (Invitrogen) and blotted onto PVDF membranes (Invitrogen). The membranes were then rinsed with 0.1% Tween® 20 (Carl Roth GmbH + Co. KG, Karlsruhe, Germany) and blocked with 5% milk powder (Carl Roth GmbH). Rabbit polyclonal anti-5-alpha-reductase 1 H-105 (Santa Cruz Biotechnology, Inc., Santa Cruz, CA, USA) and goat anti-SRD5A1 / 5-alpha-reductase antibodies (Everest Biotech Ltd., Upper Heyford, UK) were used with the respective secondary antibodies for detection of SRD5A1. Mouse anti-GAPDH antibody (Advanced Immunochemical, Long Beach, CA, USA) was used as loading control. The two anti-SRD5A1 antibodies either resulted in no bands detected on the immunoblot or multiple non-specific bands and could not be used for determination of SRD5A1 protein levels after knock-down. A plasmid containing a cDNA of the human SRD5A1 gene with a V5-epitope at the C-terminus was therefore used to overexpress SRD5A1 in the two lung cancer cell lines and a mouse monoclonal anti-V5 antibody (Invitrogen) was used for detection. A sheep ECL Anti-Mouse IgG, Horseradish Peroxidase-Linked Antibody (Amersham Biosciences, GE Healthcare Bio-Sciences AB, Uppsala, Sweden) was used as a secondary antibody. The immunoblot was developed with Western Lightning Reagent (PerkinElmer Inc., Waltham, MA, USA) on Amersham Hyperfilm ECL (GE Healthcare Life Sciences, Munich, Germany) in a Curix 60 device (Agfa, Mortsel, Belgium). The immunoblots were analyzed with the ImageJ software (by Waynde Rasband (NIH), Washington D.C., USA) according to the protocol by Miller .
Plasmid transformation, purification and transfection
Due to the difficulties in quantifying the reduction of SRD5A1 protein with commercially available SRD5A1 antibodies, an immunoblot with antibodies against the V5 epitope was performed. The expression construct was generated by cloning human SRD5A1 cDNA into the pcDNA/V5-His vector (Invitrogen), for details see Additional File 2. Plasmid transformation was conducted with XL1-Blue Supercompetent Cells (Stratagene, Santa Clara, CA, USA) and the heat-shock method at 42°C for 45 s. Cells were then cooled and incubated on agar plates at 37°C overnight. Single colonies were selected and transferred into LB-medium containing ampicillin and shaken at 37° overnight. The cells were then centrifuged and processed with the QIAfilter Plasmid Kit (QIAGEN) to extract recombinant plasmid. Purified plasmid (0.5 μg) was then transfected into A549 and NCI-H460 cells using 5 μl of Lipofectamine™ 2000. In order to verify successful transfection, a GFP-containing plasmid was transfected in a separate well and fluorescence microscopy was conducted the next day. After 24 h, the cells were transfected with siRNAs following the method described above using 10 μl siRNA and 3.75 μl Lipofectamine™ 2000. The cells were harvested 24 h and 48 h after siRNA transfection.
24 h, 48 h and 72 h after transfection of siRNAs, AlamarBlue (BioSource Europe, Nivelles, Belgium) was added to the cultured cells which were then incubated for 1 h 45 min before being measured in a Victor3 1420 Multilabel Counter (Perkin Elmer Inc.) (excitation 530 nm, emission 590 nm). The results were compared to the 24 h time-point of non-treated control cells and are displayed as percentage.
Cell cycle analysis
24 h, 48 h and 72 h after transfection with siRNAs, cells were collected, washed twice with PBS, fixed in 70% ethanol and frozen overnight. After thawing, RNase A (Sigma-Aldrich, St. Louis, MO, USA) and propidium iodide (Sigma-Aldrich) were added. Distribution in the cell cycle was analyzed on a FACSCalibur (BD Biosciences, San Jose, CA, USA) flow cytometer using the CellQuest Pro software (BD Biosciences). A total of 10,000 cells was counted per treatment group.
24 h, 48 h and 72 h after transfection with siRNAs, cells were collected and washed with PBS. The Annexin V-FITC Apoptosis Detection Kit I (BD Biosciences) was used for detection of apoptosis and necrosis. In brief, the cells were washed with PBS and afterwards with Annexin Binding Buffer. After centrifugation, the supernatant was discarded, Binding Buffer as well as Annexin V-FITC and propidium iodide were added to the cells which were incubated for 15 min at room temperature in the dark. After incubation, Binding Buffer was added and the analyses were performed in the flow cytometer mentioned above, with 10,000 cells being counted per treatment group.
Three 17-methylene-4-azasteroids (see Additional File 3) inhibiting SRD5A1 selectively  (ZK-879, ZK-924, ZK-425 ; Jenapharm GmbH, Jena, Germany) and Finasteride (Sigma), a SRD5A2 inhibitor, were diluted in ethanol to concentrations ranging from 10-5 M to 10-9 M. The fully synthetic sagopilone (ZK-EPO) (Bayer HealthCare, Berlin, Germany), a microtubule inhibitor , was used as positive control for proliferation inhibition at concentrations ranging from 10-7 M to 10-9 M. The viability of the cells was assessed in the proliferation assay described above at 24 h, 72 h, and 120 h. Ethanol diluted at the appropriate concentration was used as vehicle control.
Statistical analyses of cell culture experiments
For parametrical data, a two-tailed one-factor ANOVA was conducted, with Dunnett's test in case of equal variances and Tamhane's T2 in case of unequal variances. If the data were non-parametric, a Kruskal-Wallis-Test was performed, the post-hoc analysis was done with a Mann-Whitney-U-Test. The threshold for significant results was p < 0.05. Significant results are indicated in the legends of the figures. All experiments except flow cytometry were conducted three times, each one with three replicates. Flow cytometry analyses were conducted three times, each one with one sample (10,000 analyzed cells), making the calculation of a p-value not useful but giving reliable results based on approximately 30,000 analyzed cells.
Expression analysis of SRD5A1 in lung tumor samples and cell lines
In order to further substantiate these data, clinical samples from 23 additional lung cancer patients were analyzed. One tumor sample was obtained from each patient and in 9 cases an NAT sample was available as well. Following RNA extraction and cDNA synthesis, qRT-PCR was performed using two different primer sets specific for SRD5A1. In parallel, the expression levels for the housekeeping gene cyclophilin A and for 18S rRNA were determined. Comparison of the measured Ct values showed that for these samples also, there was a significantly higher expression of SRD5A1 in lung tumors than in NAT (p = 0.0007 for SRD5A1 primer pair #1, p = 0.0011 for SRD5A1 primer pair #2; Table 2). Conversely, the levels of cyclophilin A and of 18S rRNA did not differ significantly between both groups (p = 0.3008 and p = 0.6570, respectively; Table 2).
Finally we determined the expression of SRD5A1 in cell lines originating from NSCLC. Similar transcript levels were measured in A549, NCI-H322, NCI-H460 and LXF-289 cells (Figure 2C).
Expression analysis of SRD5A1 in other tumors
SRD5A1 knock-down efficiency at the mRNA level
SRD5A1 knock-down efficiency at the protein level
Cell cycle analysis
Dysregulated expression of discrete sets of genes is frequently observed in many tumor types, including lung cancer [26–28]. In case an over-expressed gene is causally involved in cancer growth, its specific blockade may show clinical benefit. This is preferentially achieved by small molecule or antibody approaches. More recently, targets with little druggability have been addressed by RNA interference in order to reduce expression levels, and first clinical successes have been reported [29, 30].
Elevated levels of SRD5A1 and SRD5A2 have been reported in prostate cancer and a correlation with the severity of the disease linked to increased dihydrotestosterone levels was documented . SRD5A1 and SRD5A2 are also consistently over-expressed in breast cancer, which increases the levels of progesterone metabolites possibly involved in cell proliferation . Indeed, we found SRD5A1 to be markedly elevated in prostate and breast cancer, and also in several breast cancer cell lines.
The main finding of the present study is that SRD5A1 is significantly over-expressed in NSCLC. This was observed in clinical samples originating from two different patient populations which were analyzed either by microarray hybridization or by qRT-PCR. High expression of SRD5A1 expression was furthermore measured in the lung cancer cell lines A549 and NCI-H460. A study was therefore initiated to determine whether SRD5A1 played a determinant role in lung cancer cell proliferation. For that, conditions for an efficient silencing of SRD5A1 expression in these two cell lines via RNA interference were first established. Proliferation assays and flow cytometry analyses were then conducted. In addition, three SRD5A1 inhibitors were used for chemosensitivity assays in order to determine if any anti-proliferative effects could be observed.
Knock-down of SRD5A1 was conducted with the lowest amount of siRNA still providing an effective reduction of expression levels . With as little as 10 pmol siRNA per well of a six-well culture dish, a very good knock-down to under 20% of SRD5A1 mRNA in all cases and under 10% of SRD5A1 mRNA in most cases, when compared to the untreated control, was achieved. Higher amounts of siRNA (50 and 100 pmol) did not result in a more effective knock-down. The concentration of 10 pmol per well was therefore used for all following experiments.
Beside the knock-down of target gene expression, reduction of the target protein levels needs additionally to be proven . Despite an effective knock-down of mRNA, the target protein can persist in the cells, for example due to a long half-life of the protein. The half-life of SRD5A1 has been calculated to be 20-30 h in CHO cells by Russell and Wilson . Due to non-specific binding, the two commercially available SRD5A1 antibodies could not be used to quantify SRD5A1 protein levels after siRNA treatment. To determine in an indirect way whether the three selected siRNAs indeed decreased the SRD5A1 protein content of the cells, over-expression of SRD5A1-V5 was conducted together with siRNA transfection. In A549 cells, a knock-down was clearly observed after 24 h, the estimated half-life of SRD5A1-V5 being approximately 12 h, and thus significantly shorter than what was observed previously in CHO cells. Knock-down of over-expressed SRD5A1-V5 at the protein level was also achieved in NCI-H460 lung cancer cells, the estimated half-life being approximately 20-30 h.
After establishing the optimal conditions for knock-down of SRD5A1, functional assays were conducted. In proliferation assays using AlamarBlue, no differences between target siRNA-treated groups and control groups were observed. Flow cytometry was performed to check for more subtle effects. Differences between the different treatment groups could neither be identified in cell cycle distribution nor in the apoptosis/necrosis assay. In the chemosensitivity assays, the only observable inhibition of proliferation occurred in the group treated with 10-5 M ZK425 in A549 cells. As the other concentrations did not result in any inhibition of proliferation, this is likely to represent a non-specific effect linked to the very high concentration of compound used. In view of these results, it is unlikely that SRD5A1 contributes significantly to the proliferation of NSCLC. The conduction of similar experiments in cell lines originating from lung SCC is planned (e.g. in NCI-H520 or SW-900 cells), since an up-regulation of SRD5A1 has been observed in tissue samples of SCC as well. Before that, up-regulation of SRD5A1 needs to be confirmed in candidate cell lines.
On the other hand, it cannot be excluded that the conditions used here did not allow the proper assessment of the role of SRD5A1 in lung cancer. Cultivating cells in monolayers alters their requirements for growth factors and stimulatory agents, and gene expression profiling studies show significant differences in comparison to cells cultivated in three-dimensional conditions (e.g. spheroid-forming cells), which may better reflect the situation in the tumor [32, 33]. Also, the signals originating from neighboring stromal cells and from the extra-cellular matrix influence the pathways that are essential for tumor cell growth [34, 35]. In view of the availability of selective SRD5A1 inhibitors, one might consider in vivo testing in nude mice xenografted with human lung tumor models as a more sophisticated approach to address these points.
SRD5A1 was found to be up-regulated in NSCLC by microarray analysis and qRT-PCR. To elucidate whether SRD5A1 levels influenced the proliferation of NSCLC cells, knock-down experiments with specific siRNAs were conducted in A549 and NCI-H460 lung cancer cells. Despite efficient knock-down, no changes in proliferation, cell cycle distribution or apoptosis/necrosis were observed. Moreover, blockade of the enzymatic activity of SRD5A1 with three specific inhibitors did not reduce proliferation of A549 and NCI-H460 cells. In summary, SRD5A1 knock-down or inhibition does not affect proliferation of the NSCLC cell lines analyzed.
List of abbreviations
fetal calf serum
normal adjacent tissue
non-small cell lung cancer
principal component analysis
quantitative real-time PCR
squamous cell carcinoma
5-alpha-reductase type I
5-alpha-reductase type II
5-alpha-reductase type III.
The experiments were conducted at the laboratories of and were funded by Bayer HealthCare. We thank Jörn Krätzschmar, Henrik Seidel and Gabriele Leder of Bayer HealthCare for their support. We are indebted to Hannes-Friedrich Ulbrich of Bayer HealthCare for statistical analysis of the SRD5A1 expression levels determined by qRT-PCR in patients' samples.
- RKI Krebs in Deutschland 2005/2006-Häufigkeiten und Trends. [http://www.rki.de/nn_1869836/DE/Content/GBE/DachdokKrebs/KID/kid__node.html?__nnn=true]
- Smythe WR: Treatment of stage I non-small cell lung carcinoma. Chest. 2003, 123: 181S-187S. 10.1378/chest.123.1_suppl.181S.View ArticlePubMed
- Scott WJ, Howington J, Movsas B: Treatment of stage II non-small cell lung cancer. Chest. 2003, 123: 188S-201S. 10.1378/chest.123.1_suppl.188S.View ArticlePubMed
- Müller-Hagen G, Beinert T, Sommer A: Aspects of lung cancer gene expression profiling. Curr Opin Drug Discov Devel. 2004, 7: 290-303.PubMed
- Langer W, Sohler F, Leder G, Beckmann G, Seidel H, Grone J, Hummel M, Sommer A: Exon Array Analysis using re-defined probe sets results in reliable identification of alternatively spliced genes in non-small cell lung cancer. BMC Genomics. 2010, 11: 676-10.1186/1471-2164-11-676.PubMed CentralView ArticlePubMed
- Schmidt LJ, Tindall DJ: Steroid 5 α-reductase inhibitors targeting BPH and prostate cancer. J Steroid Biochem Mol Biol. 2011, 125: 32-38. 10.1016/j.jsbmb.2010.09.003.View ArticlePubMed
- Uemura M, Tamura K, Chung S, Honma S, Okuyama A, Nakamura Y, Nakagawa H: Novel 5 alpha-steroid reductase (SRD5A3, type-3) is overexpressed in hormone-refractory prostate cancer. Cancer Sci. 2008, 99: 81-86.PubMed
- Cantagrel V, Lefeber DJ, Ng BG, Guan Z, Silhavy JL, Bielas SL, Lehle L, Hombauer H, Adamowicz M, Swiezewska E, De Brouwer AP, Blümel P, Sykut-Cegielska J, Houliston S, Swistun D, Ali BR, Dobyns WB, Babovic-Vuksanovic D, van Bokhoven H, Wevers RA, Raetz CRH, Freeze HH, Morava E, Al-Gazali L, Gleeson JG: SRD5A3 is required for converting polyprenol to dolichol and is mutated in a congenital glycosylation disorder. Cell. 2010, 142: 203-217. 10.1016/j.cell.2010.06.001.PubMed CentralView ArticlePubMed
- Thigpen AE, Silver RI, Guileyardo JM, Casey ML, McConnell JD, Russell DW: Tissue distribution and ontogeny of steroid 5 alpha-reductase isozyme expression. J Clin Invest. 1993, 92: 903-910. 10.1172/JCI116665.PubMed CentralView ArticlePubMed
- Jakimiuk AJ, Weitsman SR, Magoffin DA: 5alpha-reductase activity in women with polycystic ovary syndrome. J Clin Endocrinol Metab. 1999, 84: 2414-2418. 10.1210/jc.84.7.2414.PubMed
- Provost PR, Blomquist CH, Godin C, Huang XF, Flamand N, Luu-The V, Nadeau D, Tremblay Y: Androgen formation and metabolism in the pulmonary epithelial cell line A549: expression of 17beta-hydroxysteroid dehydrogenase type 5 and 3alpha-hydroxysteroid dehydrogenase type 3. Endocrinology. 2000, 141: 2786-2794. 10.1210/en.141.8.2786.PubMed
- Wu C, Orozco C, Boyer J, Leglise M, Goodale J, Batalov S, Hodge CL, Haase J, Janes J, Huss JW, Su AI: BioGPS: an extensible and customizable portal for querying and organizing gene annotation resources. Genome Biol. 2009, 10: R130-10.1186/gb-2009-10-11-r130.PubMed CentralView ArticlePubMed
- Lewis MJ, Wiebe JP, Heathcote JG: Expression of progesterone metabolizing enzyme genes (AKR1C1, AKR1C2, AKR1C3, SRD5A1, SRD5A2) is altered in human breast carcinoma. BMC Cancer. 2004, 4: 27-27. 10.1186/1471-2407-4-27.PubMed CentralView ArticlePubMed
- Das K, Lorena PDN, Ng LK, Lim D, Shen L, Siow WY, Teh M, Reichardt JKV, Salto-Tellez M: Differential expression of steroid 5alpha-reductase isozymes and association with disease severity and angiogenic genes predict their biological role in prostate cancer. Endocr Relat Cancer. 2010, 17: 757-770. 10.1677/ERC-10-0022.View ArticlePubMed
- Egner U, Krätzschmar J, Kreft B, Pohlenz H-D, Schneider M: The target discovery process. Chembiochem. 2005, 6: 468-479. 10.1002/cbic.200400158.View ArticlePubMed
- Applied Biosystems: Guide to Performing Relative Quantitation of Gene Expression Using Real-Time Quantitative PCR. 2008
- Yuan JS, Reed A, Chen F, Stewart CN: Statistical analysis of real-time PCR data. BMC Bioinformatics. 2006, 7: 85-10.1186/1471-2105-7-85.PubMed CentralView ArticlePubMed
- Quantifying western blots without expensive commercial quantification software. [http://www.lukemiller.org/journal/2007/08/quantifying-western-blots-without.html]
- Aggarwal S, Thareja S, Verma A, Bhardwaj TR, Kumar M: An overview on 5alpha-reductase inhibitors. Steroids. 2010, 75: 109-153. 10.1016/j.steroids.2009.10.005.View ArticlePubMed
- Menzenbach B, Droescher P, Hillisch A, Elger W, Schweikert H, Schöllkopf K: Methylene-4-azasteroids (WO 2003020744). 2003
- Klar U, Hoffmann J, Giurescu M: Sagopilone (ZK-EPO): from a natural product to a fully synthetic clinical development candidate. Expert Opin Investig Drugs. 2008, 17: 1735-1748. 10.1517/13543722.214.171.1245.View ArticlePubMed
- Hammer S, Sommer A, Fichtner I, Becker M, Rolff J, Merk J, Klar U, Hoffmann J: Comparative profiling of the novel epothilone, sagopilone, in xenografts derived from primary non-small cell lung cancer. Clin Cancer Res. 2010, 16: 1452-1465. 10.1158/1078-0432.CCR-09-2455.View ArticlePubMed
- Russell DW, Wilson JD: Steroid 5 alpha-reductase: two genes/two enzymes. Annu Rev Biochem. 1994, 63: 25-61. 10.1146/annurev.bi.63.070194.000325.View ArticlePubMed
- Semizarov D, Frost L, Sarthy A, Kroeger P, Halbert DN, Fesik SW: Specificity of short interfering RNA determined through gene expression signatures. Proc Natl Acad Sci USA. 2003, 100: 6347-52. 10.1073/pnas.1131959100.PubMed CentralView ArticlePubMed
- Chatterjee-Kishore M, Miller CP: Exploring the sounds of silence: RNAi-mediated gene silencing for target identification and validation. Drug Discov Today. 2005, 10: 1559-65. 10.1016/S1359-6446(05)03623-8.View ArticlePubMed
- Santos ES, Perez CA, Raez LE: How is gene-expression profiling going to challenge the future management of lung cancer?. Future Oncol. 2009, 5: 827-835. 10.2217/fon.09.60.View ArticlePubMed
- Zhu C-Q, Pintilie M, John T, Strumpf D, Shepherd FA, Der SD, Jurisica I, Tsao M-S: Understanding prognostic gene expression signatures in lung cancer. Clin Lung Cancer. 2009, 10: 331-340. 10.3816/CLC.2009.n.045.View ArticlePubMed
- Agulló-Ortuño MT, López-Ríos F, Paz-Ares L: Lung cancer genomic signatures. J Thorac Oncol. 2010, 5: 1673-1691. 10.1097/JTO.0b013e3181f1900e.View ArticlePubMed
- Alvarez-Salas LM: Nucleic acids as therapeutic agents. Curr Top Med Chem. 2008, 8: 1379-1404. 10.2174/156802608786141133.View ArticlePubMed
- Sioud M: Promises and challenges in developing RNAi as a research tool and therapy. Methods Mol Biol. 2011, 703: 173-187. 10.1007/978-1-59745-248-9_12.View ArticlePubMed
- Huppi K, Martin SE, Caplen NJ: Defining and assaying RNAi in mammalian cells. Mol Cell. 2005, 17: 1-10.View ArticlePubMed
- Elliott NT, Yuan F: A review of three-dimensional in vitro tissue models for drug discovery and transport studies. J Pharm Sci. 2011, 100: 59-74. 10.1002/jps.22257.View ArticlePubMed
- Hirschhaeuser F, Menne H, Dittfeld C, West J, Mueller-Klieser W, Kunz-Schughart LA: Multicellular tumor spheroids: an underestimated tool is catching up again. J Biotechnol. 2010, 148: 3-15. 10.1016/j.jbiotec.2010.01.012.View ArticlePubMed
- Shekhar MPV: Drug resistance: challenges to effective therapy. Curr Cancer Drug Targets. 2011, 11: 613-623.View ArticlePubMed
- Bremnes RM, Dønnem T, Al-Saad S, Al-Shibli K, Andersen S, Sirera R, Camps C, Marinez I, Busund L-T: The role of tumor stroma in cancer progression and prognosis: emphasis on carcinoma-associated fibroblasts and non-small cell lung cancer. J Thorac Oncol. 2011, 6: 209-217. 10.1097/JTO.0b013e3181f8a1bd.View ArticlePubMed
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.