RNA interference (RNAi) screening approach identifies agents that enhance paclitaxel activity in breast cancer cells
© Bauer et al.; licensee BioMed Central Ltd. 2010
Received: 29 March 2010
Accepted: 24 June 2010
Published: 24 June 2010
Paclitaxel is a widely used drug in the treatment of patients with locally advanced and metastatic breast cancer. However, only a small portion of patients have a complete response to paclitaxel-based chemotherapy, and many patients are resistant. Strategies that increase sensitivity and limit resistance to paclitaxel would be of clinical use, especially for patients with triple-negative breast cancer (TNBC).
We generated a gene set from overlay of the druggable genome and a collection of genomically deregulated gene transcripts in breast cancer. We used loss-of-function RNA interference (RNAi) to identify gene products in this set that, when targeted, increase paclitaxel sensitivity. Pharmacological agents that targeted the top scoring hits/genes from our RNAi screens were used in combination with paclitaxel, and the effects on the growth of various breast cancer cell lines were determined.
RNAi screens performed herein were validated by identification of genes in pathways that, when previously targeted, enhanced paclitaxel sensitivity in the pre-clinical and clinical settings. When chemical inhibitors, CCT007093 and mithramycin, against two top hits in our screen, PPMID and SP1, respectively, were used in combination with paclitaxel, we observed synergistic growth inhibition in both 2D and 3D breast cancer cell cultures. The transforming growth factor beta (TGFβ) receptor inhibitor, LY2109761, that targets the signaling pathway of another top scoring hit, TGFβ1, was synergistic with paclitaxel when used in combination on select breast cancer cell lines grown in 3D culture. We also determined the relative paclitaxel sensitivity of 22 TNBC cell lines and identified 18 drug-sensitive and four drug-resistant cell lines. Of significance, we found that both CCT007093 and mithramycin, when used in combination with paclitaxel, resulted in synergistic inhibition of the four paclitaxel-resistant TNBC cell lines.
RNAi screening can identify druggable targets and novel drug combinations that can sensitize breast cancer cells to paclitaxel. This genomic-based approach can be applied to a multitude of tumor-derived cell lines and drug treatments to generate requisite pre-clinical data for new drug combination therapies to pursue in clinical investigations.
Chemotherapy regimens containing taxanes, including docetaxel and paclitaxel, have well-established benefits in breast cancer [1, 2]. Despite improvement in the response rates with use of taxane-based drug combinations versus single agent taxanes, most patients do not have a complete response to treatment [3–6]. A partial response or resistance to paclitaxel is a major limiting factor in the successful treatment of breast cancer. Improving taxane-based chemotherapy regimens through novel drug combinations is therefore of clinical interest. Patients with tumors that lack expression of estrogen receptor (ER), progesterone receptor (PR), and HER2 amplification (triple-negative breast cancer, TNBC) are not candidates for currently available FDA-approved, targeted therapies. More efficacious combination chemotherapy is needed for these patients.
Due to its extensive use in breast cancer and other tumor types and the frequency of acquired resistance, mechanisms of taxane resistance have been investigated [7–9]. Some mechanisms identified to date include mutations of the β-tubulin gene [10, 11], expression of the tubulin binding protein tau , expression of ER [13, 14], HER2 [15, 16], BRCA1 [17, 18], and p-glycoprotein/MDR1 [19–21], among others [8, 9]. Genomic studies have also been used for predicting response to both paclitaxel and related compound docetaxel [3, 5, 6, 22, 23], but few if any genes amongst these studies overlap or have been confirmed as reliable markers or predictors of response. Despite these studies, novel therapeutic combinations with paclitaxel are being tested in clinical trials, especially in patients with advanced disease or those without clinically proven therapeutic targets such as TNBC [24–26]. Identification of gene products that when pharmacologically inhibited enhance paclitaxel sensitivity may lead to improved response rates and reduced resistance.
The advent of RNA interference (RNAi) for gene silencing allows for systematic gene and/or pathway analysis in tumor cells and an ability to uncover novel gene functions and pathways that cannot always be identified by ectopic gene expression. Several RNAi studies performed in human tumor cell lines using synthetic small interfering RNAs (siRNAs) or vector-based short hairpin RNAs (shRNAs) targeting defined gene families or genome-wide libraries have identified modulators of drug sensitivity [27–33]. These studies have unveiled novel pathways and molecules for therapeutic targeting in various tumor types and there is a great need to translate this information for clinical utility.
Genomic tumor profiling has provided us with important insights to mechanisms of tumorigenesis and translational data for clinical advances. Relative to some cancer types, there is tremendous genomic information available for breast cancers, which includes tumor DNA copy number [34–38], DNA sequence and mutations [39–44], gene expression and protein profiles [45, 46], as well as epigenetics [47, 48] and microRNAs [49, 50]. In the current study, we performed genetic loss-of-function RNAi screens to identify druggable targets involved in paclitaxel sensitivity. In our screens, we used a gene set that is comprised of the overlay of a druggable genome library with a set of genes considered to be deregulated in breast cancer (from genomic studies of human breast cancers and cell lines [37, 38]). Specific pharmacological inhibitors of the top scoring hits from our screens were used in combination with paclitaxel and the ability of the chemicals to enhance the growth inhibitory activity of paclitaxel on breast tumor-derived cell lines was analyzed. We further tested these novel paclitaxel drug combinations on four paclitaxel-resistant TNBC cell lines and for select inhibitors showed synergistic drug activity. New findings presented in this study show the feasibility of loss-of-function screening to provide biological relevance for genomic discoveries and to identify drug combinations to improve current taxane-based drug treatments in pre-clinical models for breast cancer.
Materials and methods
Reagents and resources
Paclitaxel, CCT007093, and mithramycin A (Sigma-Aldrich, St. Louis, MO, USA) were prepared in DMSO at a stock concentration of 0.1 mM, 5 mM, and 0.9 mM, respectively. LY2109761 was kindly provided by Jonathan Yingling, Lilly Research Laboratories, Indianapolis, IN, USA and prepared in DMSO at 10 mM stock concentration. The panel of candidate genes used in the shRNA screen was generated from overlay of a list of 1,778 genomically deregulated gene transcripts whose levels significantly correlated with genome copy number in breast cancer [37, 38] and a druggable genome list compiled from two sources (Open Biosystems, Huntsville, AL, USA and Qiagen, Valencia, CA, USA). Pharmacological agents were identified using several drug databases including DrugBank, Therapeutic Target Database, Comparative Toxicogenomics Database, and Ingenuity Pathway Analysis.
HeLa and MCF-7 cells were purchased from American Tissue Cell Culture (ATCC, Manassas, VA, USA) and cultured in Dulbecco's modified Eagle's medium (DMEM, Invitrogen, Carlsbad, CA, USA) supplemented with 10% fetal bovine serum, and 1% penicillin-streptomycin. All TNBC cell lines were purchased from ATCC or Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH (DSMZ, Braunschweig, Germany) and cultured as described (Additional File 1). All cells were cultured at 37°C with 5% CO2 and tested routinely for mycoplasma, using the MycoAlert Detection Kit (Cambrex, Rockland, ME, USA).
shRNA and siRNA screens
HeLa cells were plated at 20,000 cells per well (96-well plate) and 24 h later transfected with a subset of the human genome pGIPZ shRNAmir plasmid library (n = 1,078) (Open Biosystems), as provided by the Functional Genomics Shared Resource at Vanderbilt University in a one clone per well format. The next day, cells were split 1:6 into 96-well plates, allowed to attach overnight, and three plates were treated with vehicle control (DMSO) and three were treated with 5 nM paclitaxel for 24 h. Cells were washed, replaced with fresh media and incubated for an additional 72 to 96 h. Alamar Blue (Invitrogen), a dye used to detect metabolic activity in cells, was used to assay for cell viability and to identify genes that alter paclitaxel sensitivity. To identify gene targets that promote paclitaxel sensitivity or resistance, we generated a sensitivity index (SI) score for each shRNA obtained from replicate experiments after drug treatment . The SI score accounts for both the individual effect of shRNAs and the effect of drug on cell viability (see next section for description of the statistical methodology). Data from each plate were normalized to non-silencing (NS) shRNA controls that do not target any human gene, to account for plate-to-plate variability and to control for the effects of shRNA transfection. For the siRNA screen, two independent siRNAs were designed for each gene and randomly distributed in a 96-well plate. MDA-MB-231 and MDA-MB-468 cells were reverse-transfected with siRNAs complexed with lipid reagent for 48 h and subsequently split into four replicate plates. Cells were treated and measured for viability in a similar fashion as above. Transfections (that is, experiments) were performed in triplicate to allow for assessment of variation of expression data in statistical analysis.
Median centered global normalization was performed across all shRNA and siRNA plates by using the NS controls in each plate. The SI score was calculated for each of the shRNAs and siRNAs by estimating the difference between the expected and observed combined effects of shRNAs or siRNAs and paclitaxel on cell viability, as previously described . The SI scores range from -1 to 1. Positive SI scores indicate sensitizing effects and negative SI scores indicate antagonizing effects.
A bootstrap algorithm was used to estimate the variability of the mean SI level for each gene with > 3 shRNAs by randomly sampled from all shRNAs of that gene with replacement. The corresponding 95% percentile bootstrap confidence interval was calculated for each gene. Genes were taken as hits if they had a mean bootstrap in the upper quartile cutoff SI > 0.078 and the lower bound of 95% confidence interval > 0. The results of a small simulation study we carried out show that the bootstrap distribution from a very small number of shRNAs (≤3 per gene) is not reliable. Therefore, the mean SI value was calculated for the genes with ≤3 shRNAs. A more stringent cutoff (SI > 0.15) was used for hit selection among these genes. For the siRNA screen, the SI value was calculated by averaging the two siRNAs for each gene after normalization and the top hits for each cell line were selected based on the SI value of the averaged data. Correlation between experiments was estimated using Pearson's correlation coefficient. Statistical analysis was performed using R software (version 2.10.1).
Cell growth and viability assays
For cell growth assays cells were seeded at 5 × 105 cells per well of a six-well plate. The next day cells were treated with 5 μM CCT007093 or 10 nM mithramycin, ± 3 nM paclitaxel, or vehicle control (DMSO). After three days cells were collected, washed, and counted using a Coulter Counter (Beckman-Coulter, Brea, CA, USA). Cell number was plotted as a percent of cells relative to vehicle control. Cell viability assays were performed by seeding 3,000 to 8,000 cells per well of a 96-well plate. The next day, growth media was replaced with treatment media containing vehicle-DMSO or paclitaxel that was serial diluted by half-log concentrations ranging from 0.3 to 30 nM. After three days of incubation with the drug, cell viability was measured using the Alamar Blue assay (Invitrogen). Cell viability for each drug concentration was compared to vehicle-treated control. Four replicate wells from three independent experiments of each drug concentration were used to generate median-effect plots to calculate the IC50 (concentration for 50% growth inhibition) concentrations for each cell line using Calcusyn Software (Biosoft, Cambridge, United Kingdom). IC50 values for each cell line are represented with standard error.
For three-dimensional (3D) mammosphere cultures, cells were seeded on growth factor-reduced Matrigel (BD Biosciences, San Jose, CA, USA) in chamber slides as previously described [51, 52]. CCT007093, mithramycin, and LY2109761 ± paclitaxel were added to medium 24 h after cell seeding and medium was replaced every three days. Mammospheres were detached from Matrigel with dispase enzyme (BD Biosciences), trypsinized into single cell suspensions, and cell number was determined using a hemocytometer. The number of viable cells was plotted as a percent of cells relative to vehicle control.
Drug synergy analysis
Paclitaxel was combined with each of the different agents at a fixed ratio (1:1) of the individual IC50 concentrations of each drug. Drug combinations were then serial diluted (1:2) and represented as IC50, IC25, and IC12.5 concentrations, as the additive effects of both drugs. Statistical analysis of drug synergy was evaluated from the results of the Alamar Blue assays and calculated using the Chou-Talaly method  and Calcusyn Software (Biosoft). To determine synergy between two drugs, the software uses a median-effect method that determines if the drug combination produces greater effects together than expected from the summation of their individual effects. The combination index (CI) values are calculated for the different dose-effect plots (for each of the serial dilutions) based on the parameters derived from the median-effect plots of the individual drugs or drug combinations at the fixed ratios. The CI was calculated based on the assumption of mutually nonexclusive drug interactions. CI values significantly > 1 are antagonistic, not significantly different than 1 are additive, and values < 1 are synergistic. Two-sided statistical tests were used to determine if the mean CI values resulting from three independent experiments at multiple effect levels were statistically significantly different from a CI = 1.
RNAi screening for genes that sensitize cells to paclitaxel
shRNAs for each gene in our sub-library were independently transfected into HeLa cells in a 96-well-plate format and cells were split 24 h after transfection into six replicate plates. After 48 h, half of the plates (n = 3) received an IC50 concentration of paclitaxel (5 nM) and half received vehicle (DMSO) treatment. In order to detect significant differences in drug sensitivity in the assay, we allowed time for multiple cell divisions. After four days of drug treatment, cell viability was measured using an Alamar Blue assay to identify genes that alter paclitaxel sensitivity (effect of shRNA and drug). Comparison of the mean viability values of three replicates for each shRNA from the two individual screens revealed high reproducibility (r = 0.89, Pearson's correlation coefficient) (Figure 1B). We combined the results from the duplicate screens in the final analyses.
To account for plate-to-plate variability, we normalized across all the plates using non-silencing (NS) control shRNAs that were present in each plate. To identify genes that when targeted promote paclitaxel sensitivity or resistance; we generated a sensitivity index (SI) score for each shRNA obtained from replicate experiments after drug treatment, as previously described (Figure 1C) . The SI score accounts for the individual effect of shRNAs and the effect of drug on cell viability. A positive SI score is a measure of sensitivity and a negative SI score is indicative of resistance to paclitaxel treatment. In this study, we chose gene targets that are amplified/overexpressed in breast and that increase paclitaxel sensitivity (+SI value), as these are more likely to be better targets for pharmacological inhibition.
Paclitaxel sensitivity index for indicated genes from shRNA screen
> 3 clones mean SI > 0.078
< 3 clones mean SI > 0.150
0.154 to 0.242
0.135 to 0.242
0.110 to 0.265
0.121 to 0.287
0.120 to 0.241
0.075 to 0.259
0.006 to 0.345
0.085 to 0.186
0.080 to 0.198
0.081 to 0.205
0.087 to 0.378
0.080 to 0.138
0.053 to 0.175
0.019 to 0.170
0.022 to 0.168
0.030 to 0.140
0.016 to 0.137
-0.061 to -0.021
To determine if the results of the shRNA screen were reproducible in breast cancer cells, we validated the top 36 high-confidence hits (genes) from the shRNA screen that were amplified/overexpressed in breast cancer and had positive SI values (Table 1). Some of the genes selected are targets of agents that have not been tested for efficacy in combination with paclitaxel in the preclinical setting and are of biological relevance and interest (for example, transforming growth factor beta (TGFβ) signaling). Two independent siRNA oligos were designed for each of the 36 genes selected and reverse-transfected into two TNBC cell lines, MDA-MB-231 and MDA-MB-468. Duplicate experiments were performed and resulted in high reproducibility (correlation coefficients approximately 0.70 to 0.80, data not shown).
Top gene targets from siRNA screen that increase paclitaxel sensitivity and the corresponding chemical inhibitors
Previous combination with paclitaxel
thioxanthen-9-one; CCT007093; anti-estrogens*
NVP-AEW541; 9-cis-retinoic acid*; raloxifene*
erlotinib; gefitinib; cetuximab
LY2109761; LY2157299; SD-208
mithramycin; arsenic trioxide*
To ensure that drug sensitivity correlated with relative decreases in gene expression and to eliminate any possible off-target effects from shRNAs and siRNAs, we used Dharmacon ON-TARGETplus individual and pooled siRNAs as a third independent RNAi approach on select positive hits and our results with PPMID are shown as an example. ON-TARGETplus siRNAs for a top hit, PPM1D, were transfected in two breast cancer cell lines, MCF-7 and MDA-MB-468. PPM1D knockdown was measured at 48 h after transfection by quantitative real-time PCR. Three of the four individual and the pooled ON-TARGETplus siRNAs for PPM1D showed > 80% reduction in PPM1D mRNA levels in MCF-7 cells and > 60% reduction in MDA-MB-468 cells (Additional File 2). Importantly, knockdown of PPM1D was correlated with increased paclitaxel sensitivity over a range of paclitaxel doses in both cell lines (Additional File 2). The use of multiple shRNAs and validation with independent siRNAs limited the likelihood that the observed sensitivity was due to off-target effects.
Candidate pharmacological inhibitors that enhance paclitaxel sensitivity
A primary goal of this study was to identify gene targets that are druggable, to which pharmacological agents have been developed, and that can be used in novel combinations with paclitaxel in preclinical studies. The list of top hits from the validation siRNA screen for both cell lines is shown in Table 2 with associated chemical agents identified using in silico drug databases (see Materials and Methods). In some cases, agents linked to genes in the list represent FDA-approved drugs, some of which have already been successfully used in combination with paclitaxel (for example, FRAP1; rapamycin [58, 59], EGFR; erlotinib [54, 60, 61]). Gene targets with inhibitors known to enhance paclitaxel sensitivity both in preclinical [62–67] and clinical models [54, 58, 61, 68, 69] (noted in Table 2) were not studied further; however, their discovery validated our RNAi screening approach. We also did not pursue hits that had non-specific inhibitors and those that had no available agents despite being considered druggable (for example, MARK1); however, those gene targets still remain of interest. Since some hits are involved in intricate signaling pathways, there could be other drug targetable molecules within the same pathway, which could impact paclitaxel sensitivity. For example, a top hit in our screen, RPS6KB1, is downstream of mTOR and PI3K, two prominent signaling pathways in breast cancer with known direct inhibitors, rapamycin and LY294002, and that have been shown to sensitize cells to paclitaxel [59, 70].
Three gene targets from our list were of particular interest. These genes encode proteins to which agents have been developed and thus we could test the compounds in combination with paclitaxel for biological effect. The first was PPM1D, a member of the PP2C family of serine/theronine protein phosphatases, and a known negative regulator of cell stress response pathways including those regulated by p53, CHEK1, and p38 MAP kinase . PPM1D is amplified and overexpressed in breast cancers [72, 73] and inhibition of its activity, through use of small molecules such as CCT007093, inhibits the growth of tumor cell lines that overexpress PPM1D [74, 75]. The second gene target of interest was SP1, a constitutively expressed transcription factor that regulates basal promoter activity of many housekeeping genes. SP1-binding activity has been shown to be higher in human breast carcinomas than in normal tissues and may play a role in tumorigenesis by regulating the expression of genes involved in angiogenesis, cell growth, and apoptosis resistance [76, 77]. Mithramycin A binds to dsDNA and inhibits SP1 binding sites (GC-rich regions of promoters) thus inhibiting SP1 transcriptional activity . Finally, TGFβ1 is a ligand that regulates a signaling pathway that becomes deregulated in many types of malignancies including breast cancer . TGFβ1 can act in a paracrine manner to promote tumor growth and can activate PI3K/AKT, a signaling program associated with drug resistance . Thus, the ligand TGFβ1 and its receptors TGFβ receptor (TGFβR) type I and II have been pursued as anti-cancer targets. LY2109761 is a small molecule inhibitor of TGFβR I and II and has been shown to inhibit tumor cell migration, invasion, as well as suppressing metastasis in vivo [80–82].
Pharmacological agents enhance paclitaxel cell growth inhibition of breast cancer cells
Novel drug combinations with paclitaxel inhibit 3D growth of breast cancer cell lines
CCT007093 and mithramycin synergistically enhance paclitaxel activity in paclitaxel-sensitive and -resistance TNBC cell lines
There are currently no targeted therapies for patients with TNBC. Frequently, patients with this type of breast cancer receive paclitaxel, due to its initial effects and higher response rates as compared to other chemotherapies . However, not all patients have a complete response and those that are resistant or have residual disease after initial or secondary chemotherapy have a worse prognosis and outcome [83, 84]. In addition, TNBC patients that initially respond to chemotherapy have a higher incidence and faster relapse compared to patients with non-TNBC . Thus, improving the effect of initial paclitaxel treatment is an important goal in successfully treating patients with TNBC until more improved and/or targeted therapies are developed.
CCT007093 was synergistic with paclitaxel (average CI value significantly < 1, P < 0.05) in two paclitaxel-sensitive cell lines, MDA-MB-468 and MDA-MB-231, average CI value of 0.56 and 0.38, respectively, and in two of the four paclitaxel-resistant cell lines CAL120 (average CI = 0.89) and HDQP1 (average CI = 0.65) (Figure 4B). CCT007093 was additive with paclitaxel in the two other paclitaxel-resistant cell lines SW527 and MT3 (average CI values not significantly different than 1 (P > 0.05)). Mithramycin was synergistic with paclitaxel in the two paclitaxel-sensitive lines MDA-MB-468 and MDA-MB-231, average CI value of 0.66 and 0.54, respectively, and the paclitaxel-resistant cell line HDQP1 average CI value 0.87. However, mithramycin and paclitaxel were antagonistic, average CI values significantly > 1, in reducing cell viability at high effective drug doses (IC50 and IC25) in the paclitaxel-resistant lines CAL120, SW527 and MT3 (Figure 4B). Collectively these data indicate that novel drug combinations with paclitaxel can effectively reduce cell viability of select paclitaxel-sensitive and importantly, paclitaxel-resistant TNBC cell lines.
Our RNAi screen represents a directed approach to identifying breast cancer relevant, druggable targets to enhance drug sensitivity. The screen was validated by our finding that several of the positive hits are genes that are known targets of paclitaxel sensitivity and have been clinically targeted in combination with taxanes [54, 58, 61, 68, 69]. We identified additional novel gene targets and respective agents that were not previously identified by drug sensitivity RNAi screens or whose inhibitors were not previously combined with paclitaxel.
We found PPM1D as a target for paclitaxel sensitivity in our RNAi screens and in follow-up studies observed synergistic inhibition of tumor cell growth with use of the PPM1D inhibitor CCT007093 in high PPM1D, wild-type p53 expressing MCF-7 cells. The oncogenic activity of PPM1D expression is attributed to its phosphatase activity and ability to deregulate tumor suppressor genes such as p53, Chk1, and p38 . PPM1D contributes to the development of human cancers by suppressing p53 activation and thus has been an attractive therapeutic target in tumors that overexpress PPM1D and those with wild-type functional p53 activity . Indeed, others have found that suppression of PPM1D expression by RNAi inhibits proliferation and induces apoptosis in breast cancer cell lines with wild-type p53 (BT-474) and those with PPM1D amplification (MCF-7 and ZR-75-1) . However, the effect of inhibition of PPM1D on tumor cell growth and drug sensitivity is not limited to tumor cells that harbor these amplifications as we observed synergistic or additive activity of CCT007093 with paclitaxel in TNBC cell lines (MDA-MB-231 and MDA-MB-468, mutant p53 cell lines) including some paclitaxel-resistant lines. Likewise, Belova et al. identified chemical compounds that inhibit PPM1D activity and showed that these compounds could significantly inhibit tumor cell growth in MCF-7 cells and those with low PPM1D, mutant p53 expression MDA-MB-231 . Interestingly, PPM1D inhibitors in both of these cell lines were able to potentiate the effects of doxorubicin but failed to enhance activity in other cell lines (MDA-MB-361) .
We found that mithramycin, an inhibitor of SP1 binding, could synergize with paclitaxel in some TNBC (basal-like) cell lines, MDA-MB-231, MDA-MB-468, and HDQP1. SP1 is a zinc finger transcription factor important in the regulation of genes involved in cell survival, growth and differentiation, and tumor development and progression . SP1 cooperates with other prominent transcription factors including oncogenes such as MYC, which may contribute to tumor cell proliferation and growth [87, 88]. MYC has recently been shown to have elevated activity and gene signatures present in basal-like TNBCs [89, 90]. Thus, inhibiting SP1 binding with mithramycin may block oncogenic transcriptional activity and cooperate with anti-mitotic agents such as paclitaxel to inhibit tumor cell growth. In addition, SP1 is a potent transactivator of IGF-IR and EGFR, two prominent genes overexpressed in breast cancer cells (for example, MDA-MB-468) and both of which were identified as hits in our screen [91, 92].
Despite extensive preclinical studies aimed at therapeutically targeting the TGFβ signaling pathway, there is a lack of reports in which TGFβ inhibitors are combined with paclitaxel. We found that the TGFβR inhibitor LY2109761 is synergistic with paclitaxel in breast cancer cells grown in 3D cultures but not 2D cultures, indicating the importance of performing drug combination in more than one growth context. TGFβ protects mammary epithelial cells from apoptosis in the absence of serum, which may be through activation of the PI3K/AKT cell survival pathway [80, 93]. Thus, inhibition of TGFβ may sensitize cells that are grown in low-serum and/or anchorage-independent 3D conditions to apoptosis-inducing agents like paclitaxel. In support of this, others have shown that inhibition of TGFβ in human breast carcinoma cells grown in 3D cultures that secrete high levels of TGFβ increases the cytotoxic response to ionizing radiation and several chemotherapeutic drugs, namely cisplatin . Likewise, inhibition of TGFβ can prevent radiation-induced acceleration of metastatic cancer progression [95, 96]. On the contrary, Ahmed et al. showed that the loss of the ECM protein TGFβI is sufficient to induce specific resistance to paclitaxel and mitotic spindle abnormalities in ovarian cancer cells . In ovarian and breast tumor specimens, TGFβI expression was shown to be tightly co-regulated with other genes that induce paclitaxel sensitivity, such as the adhesion glycoprotein, THBS1 .
The mechanism by which inhibition of TGFβ signaling cooperates with paclitaxel is not well understood. Intracellular TGFβ signaling proteins Smad2 and Smad3 bind microtubules, and upon TGFβ stimulation, these transcription factors dissociate from microtubules, are phosphorylated and relocate to the nucleus . TGFβ signaling may serve as a growth promoter and/or enabling changes in tumor cell adhesion, migration, and host-tumor interactions . Thus, loss of TGFβ signaling may sensitize cells to paclitaxel, an agent that can also alter adhesion and migration due to significant changes in microtubule dynamics that are required for these biological activities.
The ever-increasing volume of genomic information paired with bioinformatic and biostatistical analyses is making genotype-driven health care a reality. The tremendous amount of tumor-derived genomic information available now, and after completion of several large-scale cancer sequencing efforts, combined with biological validation of mutations to determine relevant drivers, will allow for much more facile identification of new targets for drug discovery, as well as more precise alignment of patients with a particular targeted therapy. Validation of putative drug targets through loss-of-function screening, similar to that performed herein, will likely be a frequently used approach to generate requisite pre-clinical data to investigate novel single agent and drug combinations. The exciting challenge ahead of us is to integrate the ever-expanding genomic information as quickly as possible for human benefit.
We used a genomic-based approach that included loss-of-function RNAi screening to identify druggable targets involved in paclitaxel sensitivity in breast cancer cells. We identified pharmacological agents that target hits from our screens, several which sensitized breast cancer cells to paclitaxel. A potential translation of our discoveries is new treatment options for patients with TNBC disease, those without current clinically proven targeted therapies. In summary, we provide a platform in which integrated genomic information can be rationally used to design functional screens to identify druggable targets to improve current treatments or to discover novel cancer treatment strategies.
Dulbecco's modified Eagle's medium
concentration that inhibits growth compared to control
short hairpin RNA
small interfering RNA
triple-negative breast cancer.
This work was supported by the National Institutes of Health Grants: CA009385-25 (Bauer); CA62212 (Arteaga); CA95131 (Specialized Program of Research Excellence in Breast Cancer); CA105436 and CA070856 (Pietenpol), ES00267, and CA68485 (core services)
- Hortobagyi G: Docetaxel in breast cancer and a rationale for combination therapy. Oncology (Williston Park). 1997, 11: 11-15.Google Scholar
- Hortobagyi GN: Paclitaxel-based combination chemotherapy for breast cancer. Oncology (Williston Park). 1997, 11: 29-37.Google Scholar
- Ayers M, Symmans WF, Stec J, Damokosh AI, Clark E, Hess K, Lecocke M, Metivier J, Booser D, Ibrahim N, Valero V, Royce M, Arun B, Whitman G, Ross J, Sneige N, Hortobagyi GN, Pusztai L: Gene expression profiles predict complete pathologic response to neoadjuvant paclitaxel and fluorouracil, doxorubicin, and cyclophosphamide chemotherapy in breast cancer. J Clin Oncol. 2004, 22: 2284-2293. 10.1200/JCO.2004.05.166.PubMedView ArticleGoogle Scholar
- Dressman HK, Hans C, Bild A, Olson JA, Rosen E, Marcom PK, Liotcheva VB, Jones EL, Vujaskovic Z, Marks J, Dewhirst MW, West M, Nevins JR, Blackwell K: Gene expression profiles of multiple breast cancer phenotypes and response to neoadjuvant chemotherapy. Clin Cancer Res. 2006, 12: 819-826. 10.1158/1078-0432.CCR-05-1447.PubMedView ArticleGoogle Scholar
- Hess KR, Anderson K, Symmans WF, Valero V, Ibrahim N, Mejia JA, Booser D, Theriault RL, Buzdar AU, Dempsey PJ, Rouzier R, Sneige N, Ross JS, Vidaurre T, Gomez HL, Hortobagyi GN, Pusztai L: Pharmacogenomic predictor of sensitivity to preoperative chemotherapy with paclitaxel and fluorouracil, doxorubicin, and cyclophosphamide in breast cancer. J Clin Oncol. 2006, 24: 4236-4244. 10.1200/JCO.2006.05.6861.PubMedView ArticleGoogle Scholar
- Thuerigen O, Schneeweiss A, Toedt G, Warnat P, Hahn M, Kramer H, Brors B, Rudlowski C, Benner A, Schuetz F, Tews B, Eils R, Sinn HP, Sohn C, Lichter P: Gene expression signature predicting pathologic complete response with gemcitabine, epirubicin, and docetaxel in primary breast cancer. J Clin Oncol. 2006, 24: 1839-1845. 10.1200/JCO.2005.04.7019.PubMedView ArticleGoogle Scholar
- McGrogan BT, Gilmartin B, Carney DN, McCann A: Taxanes, microtubules and chemoresistant breast cancer. Biochim Biophys Acta. 2008, 1785: 96-132.PubMedGoogle Scholar
- Noguchi S: Predictive factors for response to docetaxel in human breast cancers. Cancer Sci. 2006, 97: 813-820. 10.1111/j.1349-7006.2006.00265.x.PubMedView ArticleGoogle Scholar
- Villeneuve DJ, Hembruff SL, Veitch Z, Cecchetto M, Dew WA, Parissenti AM: cDNA microarray analysis of isogenic paclitaxel-and doxorubicin-resistant breast tumor cell lines reveals distinct drug-specific genetic signatures of resistance. Breast Cancer Res Treat. 2006, 96: 17-39. 10.1007/s10549-005-9026-6.PubMedView ArticleGoogle Scholar
- Burkhart CA, Kavallaris M, Band Horwitz S: The role of beta-tubulin isotypes in resistance to antimitotic drugs. Biochim Biophys Acta. 2001, 1471: O1-9.PubMedGoogle Scholar
- Hasegawa S, Miyoshi Y, Egawa C, Ishitobi M, Tamaki Y, Monden M, Noguchi S: Mutational analysis of the class I beta-tubulin gene in human breast cancer. Int J Cancer. 2002, 101: 46-51. 10.1002/ijc.10575.PubMedView ArticleGoogle Scholar
- Rouzier R, Rajan R, Wagner P, Hess KR, Gold DL, Stec J, Ayers M, Ross JS, Zhang P, Buchholz TA, Kuerer H, Green M, Arun B, Hortobagyi GN, Symmans WF, Pusztai L: Microtubule-associated protein tau: a marker of paclitaxel sensitivity in breast cancer. Proc Natl Acad Sci USA. 2005, 102: 8315-8320. 10.1073/pnas.0408974102.PubMedPubMed CentralView ArticleGoogle Scholar
- Estevez LG, Cuevas JM, Anton A, Florian J, Lopez-Vega JM, Velasco A, Lobo F, Herrero A, Fortes J: Weekly docetaxel as neoadjuvant chemotherapy for stage II and III breast cancer: efficacy and correlation with biological markers in a phase II, multicenter study. Clin Cancer Res. 2003, 9: 686-692.PubMedGoogle Scholar
- Tham YL, Gomez LF, Mohsin S, Gutierrez MC, Weiss H, Hilsenbeck SG, Elledge RM, Chamness GC, Osborne CK, Allred DC, Chang JC: Clinical response to neoadjuvant docetaxel predicts improved outcome in patients with large locally advanced breast cancers. Breast Cancer Res Treat. 2005, 94: 279-284. 10.1007/s10549-005-9020-z.PubMedView ArticleGoogle Scholar
- Learn PA, Yeh IT, McNutt M, Chisholm GB, Pollock BH, Rousseau DL, Sharkey FE, Cruz AB, Kahlenberg MS: HER-2/neu expression as a predictor of response to neoadjuvant docetaxel in patients with operable breast carcinoma. Cancer. 2005, 103: 2252-2260. 10.1002/cncr.21037.PubMedView ArticleGoogle Scholar
- Yu D, Jing T, Liu B, Yao J, Tan M, McDonnell TJ, Hung MC: Overexpression of ErbB2 blocks Taxol-induced apoptosis by upregulation of p21Cip1, which inhibits p34Cdc2 kinase. Mol Cell. 1998, 2: 581-591. 10.1016/S1097-2765(00)80157-4.PubMedView ArticleGoogle Scholar
- Lafarge S, Sylvain V, Ferrara M, Bignon YJ: Inhibition of BRCA1 leads to increased chemoresistance to microtubule-interfering agents, an effect that involves the JNK pathway. Oncogene. 2001, 20: 6597-6606. 10.1038/sj.onc.1204812.PubMedView ArticleGoogle Scholar
- Zhou C, Smith JL, Liu J: Role of BRCA1 in cellular resistance to paclitaxel and ionizing radiation in an ovarian cancer cell line carrying a defective BRCA1. Oncogene. 2003, 22: 2396-2404. 10.1038/sj.onc.1206319.PubMedView ArticleGoogle Scholar
- Brooks TA, Minderman H, O'Loughlin KL, Pera P, Ojima I, Baer MR, Bernacki RJ: Taxane-based reversal agents modulate drug resistance mediated by P-glycoprotein, multidrug resistance protein, and breast cancer resistance protein. Mol Cancer Ther. 2003, 2: 1195-1205.PubMedGoogle Scholar
- Mechetner E, Kyshtoobayeva A, Zonis S, Kim H, Stroup R, Garcia R, Parker RJ, Fruehauf JP: Levels of multidrug resistance (MDR1) P-glycoprotein expression by human breast cancer correlate with in vitro resistance to taxol and doxorubicin. Clin Cancer Res. 1998, 4: 389-398.PubMedGoogle Scholar
- Shabbits JA, Mayer LD: P-glycoprotein modulates ceramide-mediated sensitivity of human breast cancer cells to tubulin-binding anticancer drugs. Mol Cancer Ther. 2002, 1: 205-213.PubMedGoogle Scholar
- Chang JC, Wooten EC, Tsimelzon A, Hilsenbeck SG, Gutierrez MC, Elledge R, Mohsin S, Osborne CK, Chamness GC, Allred DC, O'Connell P: Gene expression profiling for the prediction of therapeutic response to docetaxel in patients with breast cancer. Lancet. 2003, 362: 362-369. 10.1016/S0140-6736(03)14023-8.PubMedView ArticleGoogle Scholar
- Iwao-Koizumi K, Matoba R, Ueno N, Kim SJ, Ando A, Miyoshi Y, Maeda E, Noguchi S, Kato K: Prediction of docetaxel response in human breast cancer by gene expression profiling. J Clin Oncol. 2005, 23: 422-431. 10.1200/JCO.2005.09.078.PubMedView ArticleGoogle Scholar
- Bauer JA, Chakravarthy AB, Rosenbluth JM, Mi D, Seeley EH, De Matos Granja-Ingram N, Olivares MG, Kelley MC, Mayer IA, Meszoely IM, Means-Powell JA, Johnson KN, Tsai CJ, Ayers GD, Sanders ME, Schneider RJ, Formenti SC, Caprioli RM, Pietenpol JA: Identification of markers of taxane sensitivity using proteomic and genomic analyses of breast tumors from patients receiving neoadjuvant paclitaxel and radiation. Clin Cancer Res. 16: 681-690. 10.1158/1078-0432.CCR-09-1091.
- Juul N, Szallasi Z, Eklund AC, Li Q, Burrell RA, Gerlinger M, Valero V, Andreopoulou E, Esteva FJ, Symmans WF, Desmedt C, Haibe-Kains B, Sotiriou C, Pusztai L, Swanton C: Assessment of an RNA interference screen-derived mitotic and ceramide pathway metagene as a predictor of response to neoadjuvant paclitaxel for primary triple-negative breast cancer: a retrospective analysis of five clinical trials. Lancet Oncol. 2010, 11: 358-65. 10.1016/S1470-2045(10)70018-8.PubMedView ArticleGoogle Scholar
- Schwartz J: Current combination chemotherapy regimens for metastatic breast cancer. Am J Health Syst Pharm. 2009, 66: S3-8. 10.2146/ajhp090438.PubMedView ArticleGoogle Scholar
- Bartz SR, Zhang Z, Burchard J, Imakura M, Martin M, Palmieri A, Needham R, Guo J, Gordon M, Chung N, Warrener P, Jackson AL, Carleton M, Oatley M, Locco L, Santini F, Smith T, Kunapuli P, Ferrer M, Strulovici B, Friend SH, Linsley PS: Small interfering RNA screens reveal enhanced cisplatin cytotoxicity in tumor cells having both BRCA network and TP53 disruptions. Mol Cell Biol. 2006, 26: 9377-9386. 10.1128/MCB.01229-06.PubMedPubMed CentralView ArticleGoogle Scholar
- Honma K, Iwao-Koizumi K, Takeshita F, Yamamoto Y, Yoshida T, Nishio K, Nagahara S, Kato K, Ochiya T: RPN2 gene confers docetaxel resistance in breast cancer. Nat Med. 2008, 14: 939-948. 10.1038/nm.1858.PubMedView ArticleGoogle Scholar
- Ji D, Deeds SL, Weinstein EJ: A screen of shRNAs targeting tumor suppressor genes to identify factors involved in A549 paclitaxel sensitivity. Oncol Rep. 2007, 18: 1499-1505.PubMedGoogle Scholar
- MacKeigan JP, Murphy LO, Blenis J: Sensitized RNAi screen of human kinases and phosphatases identifies new regulators of apoptosis and chemoresistance. Nat Cell Biol. 2005, 7: 591-600. 10.1038/ncb1258.PubMedView ArticleGoogle Scholar
- Menendez JA, Vellon L, Colomer R, Lupu R: Pharmacological and small interference RNA-mediated inhibition of breast cancer-associated fatty acid synthase (oncogenic antigen-519) synergistically enhances Taxol (paclitaxel)-induced cytotoxicity. Int J Cancer. 2005, 115: 19-35. 10.1002/ijc.20754.PubMedView ArticleGoogle Scholar
- Swanton C, Marani M, Pardo O, Warne PH, Kelly G, Sahai E, Elustondo F, Chang J, Temple J, Ahmed AA, Brenton JD, Downward J, Nicke B: Regulators of mitotic arrest and ceramide metabolism are determinants of sensitivity to paclitaxel and other chemotherapeutic drugs. Cancer Cell. 2007, 11: 498-512. 10.1016/j.ccr.2007.04.011.PubMedView ArticleGoogle Scholar
- Whitehurst AW, Bodemann BO, Cardenas J, Ferguson D, Girard L, Peyton M, Minna JD, Michnoff C, Hao W, Roth MG, Xie XJ, White MA: Synthetic lethal screen identification of chemosensitizer loci in cancer cells. Nature. 2007, 446: 815-819. 10.1038/nature05697.PubMedView ArticleGoogle Scholar
- Adelaide J, Finetti P, Bekhouche I, Repellini L, Geneix J, Sircoulomb F, Charafe-Jauffret E, Cervera N, Desplans J, Parzy D, Schoenmakers E, Viens P, Jacquemier J, Birnbaum D, Bertucci F, Chaffanet M: Integrated profiling of basal and luminal breast cancers. Cancer Res. 2007, 67: 11565-11575. 10.1158/0008-5472.CAN-07-2536.PubMedView ArticleGoogle Scholar
- Bergamaschi A, Kim YH, Wang P, Sorlie T, Hernandez-Boussard T, Lonning PE, Tibshirani R, Borresen-Dale AL, Pollack JR: Distinct patterns of DNA copy number alteration are associated with different clinicopathological features and gene-expression subtypes of breast cancer. Genes Chromosomes Cancer. 2006, 45: 1033-1040. 10.1002/gcc.20366.PubMedView ArticleGoogle Scholar
- Han W, Jung EM, Cho J, Lee JW, Hwang KT, Yang SJ, Kang JJ, Bae JY, Jeon YK, Park IA, Nicolau M, Jeffrey SS, Noh DY: DNA copy number alterations and expression of relevant genes in triple-negative breast cancer. Genes Chromosomes Cancer. 2008, 47: 490-499. 10.1002/gcc.20550.PubMedView ArticleGoogle Scholar
- Neve RM, Chin K, Fridlyand J, Yeh J, Baehner FL, Fevr T, Clark L, Bayani N, Coppe JP, Tong F, Speed T, Spellman PT, DeVries S, Lapuk A, Wang NJ, Kuo WL, Stilwell JL, Pinkel D, Albertson DG, Waldman FM, McCormick F, Dickson RB, Johnson MD, Lippman M, Ethier S, Gazdar A, Gray JW: A collection of breast cancer cell lines for the study of functionally distinct cancer subtypes. Cancer Cell. 2006, 10: 515-527. 10.1016/j.ccr.2006.10.008.PubMedPubMed CentralView ArticleGoogle Scholar
- Chin K, DeVries S, Fridlyand J, Spellman PT, Roydasgupta R, Kuo WL, Lapuk A, Neve RM, Qian Z, Ryder T, Chen F, Feiler H, Tokuyasu T, Kingsley C, Dairkee S, Meng Z, Chew K, Pinkel D, Jain A, Ljung BM, Esserman L, Albertson DG, Waldman FM, Gray JW: Genomic and transcriptional aberrations linked to breast cancer pathophysiologies. Cancer Cell. 2006, 10: 529-541. 10.1016/j.ccr.2006.10.009.PubMedView ArticleGoogle Scholar
- Leary RJ, Lin JC, Cummins J, Boca S, Wood LD, Parsons DW, Jones S, Sjoblom T, Park BH, Parsons R, Willis J, Dawson D, Willson JK, Nikolskaya T, Nikolsky Y, Kopelovich L, Papadopoulos N, Pennacchio LA, Wang TL, Markowitz SD, Parmigiani G, Kinzler KW, Vogelstein B, Velculescu VE: Integrated analysis of homozygous deletions, focal amplifications, and sequence alterations in breast and colorectal cancers. Proc Natl Acad Sci USA. 2008, 105: 16224-16229. 10.1073/pnas.0808041105.PubMedPubMed CentralView ArticleGoogle Scholar
- Shah SP, Morin RD, Khattra J, Prentice L, Pugh T, Burleigh A, Delaney A, Gelmon K, Guliany R, Senz J, Steidl C, Holt RA, Jones S, Sun M, Leung G, Moore R, Severson T, Taylor GA, Teschendorff AE, Tse K, Turashvili G, Varhol R, Warren RL, Watson P, Zhao Y, Caldas C, Huntsman D, Hirst M, Marra MA, Aparicio S: Mutational evolution in a lobular breast tumour profiled at single nucleotide resolution. Nature. 2009, 461: 809-813. 10.1038/nature08489.PubMedView ArticleGoogle Scholar
- Stephens PJ, McBride DJ, Lin ML, Varela I, Pleasance ED, Simpson JT, Stebbings LA, Leroy C, Edkins S, Mudie LJ, Greenman CD, Jia M, Latimer C, Teague JW, Lau KW, Burton J, Quail MA, Swerdlow H, Churcher C, Natrajan R, Sieuwerts AM, Martens JW, Silver DP, Langerod A, Russnes HE, Foekens JA, Reis-Filho JS, van 't Veer L, Richardson AL, Borresen-Dale AL, et al: Complex landscapes of somatic rearrangement in human breast cancer genomes. Nature. 2009, 462: 1005-1010. 10.1038/nature08645.PubMedPubMed CentralView ArticleGoogle Scholar
- Nikolsky Y, Sviridov E, Yao J, Dosymbekov D, Ustyansky V, Kaznacheev V, Dezso Z, Mulvey L, Macconaill LE, Winckler W, Serebryiskaya T, Nikolskaya T, Polyak K: Genome-wide functional synergy between amplified and mutated genes in human breast cancer. Cancer Res. 2008, 68: 9532-9540. 10.1158/0008-5472.CAN-08-3082.PubMedView ArticleGoogle Scholar
- Sjoblom T, Jones S, Wood LD, Parsons DW, Lin J, Barber TD, Mandelker D, Leary RJ, Ptak J, Silliman N, Szabo S, Buckhaults P, Farrell C, Meeh P, Markowitz SD, Willis J, Dawson D, Willson JK, Gazdar AF, Hartigan J, Wu L, Liu C, Parmigiani G, Park BH, Bachman KE, Papadopoulos N, Vogelstein B, Kinzler KW, Velculescu VE: The consensus coding sequences of human breast and colorectal cancers. Science. 2006, 314: 268-274. 10.1126/science.1133427.PubMedView ArticleGoogle Scholar
- Wood LD, Parsons DW, Jones S, Lin J, Sjoblom T, Leary RJ, Shen D, Boca SM, Barber T, Ptak J, Silliman N, Szabo S, Dezso Z, Ustyanksky V, Nikolskaya T, Nikolsky Y, Karchin R, Wilson PA, Kaminker JS, Zhang Z, Croshaw R, Willis J, Dawson D, Shipitsin M, Willson JK, Sukumar S, Polyak K, Park BH, Pethiyagoda CL, Pant PV, et al: The genomic landscapes of human breast and colorectal cancers. Science. 2007, 318: 1108-1113. 10.1126/science.1145720.PubMedView ArticleGoogle Scholar
- Boyd ZS, Wu QJ, O'Brien C, Spoerke J, Savage H, Fielder PJ, Amler L, Yan Y, Lackner MR: Proteomic analysis of breast cancer molecular subtypes and biomarkers of response to targeted kinase inhibitors using reverse-phase protein microarrays. Mol Cancer Ther. 2008, 7: 3695-3706. 10.1158/1535-7163.MCT-08-0810.PubMedView ArticleGoogle Scholar
- Hennessy BT, Gonzalez-Angulo AM, Stemke-Hale K, Gilcrease MZ, Krishnamurthy S, Lee JS, Fridlyand J, Sahin A, Agarwal R, Joy C, Liu W, Stivers D, Baggerly K, Carey M, Lluch A, Monteagudo C, He X, Weigman V, Fan C, Palazzo J, Hortobagyi GN, Nolden LK, Wang NJ, Valero V, Gray JW, Perou CM, Mills GB: Characterization of a naturally occurring breast cancer subset enriched in epithelial-to-mesenchymal transition and stem cell characteristics. Cancer Res. 2009, 69: 4116-4124. 10.1158/0008-5472.CAN-08-3441.PubMedPubMed CentralView ArticleGoogle Scholar
- Ruike Y, Imanaka Y, Sato F, Shimizu K, Tsujimoto G: Genome-wide analysis of aberrant methylation in human breast cancer cells using methyl-DNA immunoprecipitation combined with high-throughput sequencing. BMC Genomics. 11: 137-10.1186/1471-2164-11-137.
- Andrews J, Kennette W, Pilon J, Hodgson A, Tuck AB, Chambers AF, Rodenhiser DI: Multi-platform whole-genome microarray analyses refine the epigenetic signature of breast cancer metastasis with gene expression and copy number. PLoS One. 5: e8665-10.1371/journal.pone.0008665.
- Iorio MV, Ferracin M, Liu CG, Veronese A, Spizzo R, Sabbioni S, Magri E, Pedriali M, Fabbri M, Campiglio M, Menard S, Palazzo JP, Rosenberg A, Musiani P, Volinia S, Nenci I, Calin GA, Querzoli P, Negrini M, Croce CM: MicroRNA gene expression deregulation in human breast cancer. Cancer Res. 2005, 65: 7065-7070. 10.1158/0008-5472.CAN-05-1783.PubMedView ArticleGoogle Scholar
- Mattie MD, Benz CC, Bowers J, Sensinger K, Wong L, Scott GK, Fedele V, Ginzinger D, Getts R, Haqq C: Optimized high-throughput microRNA expression profiling provides novel biomarker assessment of clinical prostate and breast cancer biopsies. Mol Cancer. 2006, 5: 24-10.1186/1476-4598-5-24.PubMedPubMed CentralView ArticleGoogle Scholar
- Debnath J, Muthuswamy SK, Brugge JS: Morphogenesis and oncogenesis of MCF-10A mammary epithelial acini grown in three-dimensional basement membrane cultures. Methods. 2003, 30: 256-268. 10.1016/S1046-2023(03)00032-X.PubMedView ArticleGoogle Scholar
- Lee GY, Kenny PA, Lee EH, Bissell MJ: Three-dimensional culture models of normal and malignant breast epithelial cells. Nat Methods. 2007, 4: 359-365. 10.1038/nmeth1015.PubMedPubMed CentralView ArticleGoogle Scholar
- Chou TC, Talalay P: Quantitative analysis of dose-effect relationships: the combined effects of multiple drugs or enzyme inhibitors. Adv Enzyme Regul. 1984, 22: 27-55. 10.1016/0065-2571(84)90007-4.PubMedView ArticleGoogle Scholar
- Modi S, D'Andrea G, Norton L, Yao TJ, Caravelli J, Rosen PP, Hudis C, Seidman AD: A phase I study of cetuximab/paclitaxel in patients with advanced-stage breast cancer. Clin Breast Cancer. 2006, 7: 270-277. 10.3816/CBC.2006.n.040.PubMedView ArticleGoogle Scholar
- Finn RS, Press MF, Dering J, Arbushites M, Koehler M, Oliva C, Williams LS, Di Leo A: Estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2 (HER2), and epidermal growth factor receptor expression and benefit from lapatinib in a randomized trial of paclitaxel with lapatinib or placebo as first-line treatment in HER2-negative or unknown metastatic breast cancer. J Clin Oncol. 2009, 27: 3908-3915. 10.1200/JCO.2008.18.1925.PubMedPubMed CentralView ArticleGoogle Scholar
- Di Leo A, Gomez HL, Aziz Z, Zvirbule Z, Bines J, Arbushites MC, Guerrera SF, Koehler M, Oliva C, Stein SH, Williams LS, Dering J, Finn RS, Press MF: Phase III, double-blind, randomized study comparing lapatinib plus paclitaxel with placebo plus paclitaxel as first-line treatment for metastatic breast cancer. J Clin Oncol. 2008, 26: 5544-5552. 10.1200/JCO.2008.16.2578.PubMedPubMed CentralView ArticleGoogle Scholar
- Dai CL, Tiwari AK, Wu CP, Su XD, Wang SR, Liu DG, Ashby CR, Huang Y, Robey RW, Liang YJ, Chen LM, Shi CJ, Ambudkar SV, Chen ZS, Fu LW: Lapatinib (Tykerb, GW572016) reverses multidrug resistance in cancer cells by inhibiting the activity of ATP-binding cassette subfamily B member 1 and G member 2. Cancer Res. 2008, 68: 7905-7914. 10.1158/0008-5472.CAN-08-0499.PubMedPubMed CentralView ArticleGoogle Scholar
- Campone M, Levy V, Bourbouloux E, Berton Rigaud D, Bootle D, Dutreix C, Zoellner U, Shand N, Calvo F, Raymond E: Safety and pharmacokinetics of paclitaxel and the oral mTOR inhibitor everolimus in advanced solid tumours. Br J Cancer. 2009, 100: 315-321. 10.1038/sj.bjc.6604851.PubMedPubMed CentralView ArticleGoogle Scholar
- Mondesire WH, Jian W, Zhang H, Ensor J, Hung MC, Mills GB, Meric-Bernstam F: Targeting mammalian target of rapamycin synergistically enhances chemotherapy-induced cytotoxicity in breast cancer cells. Clin Cancer Res. 2004, 10: 7031-7042. 10.1158/1078-0432.CCR-04-0361.PubMedView ArticleGoogle Scholar
- Dai Q, Ling YH, Lia M, Zou YY, Kroog G, Iwata KK, Perez-Soler R: Enhanced sensitivity to the HER1/epidermal growth factor receptor tyrosine kinase inhibitor erlotinib hydrochloride in chemotherapy-resistant tumor cell lines. Clin Cancer Res. 2005, 11: 1572-1578. 10.1158/1078-0432.CCR-04-0993.PubMedView ArticleGoogle Scholar
- Fountzilas G, Pectasides D, Kalogera-Fountzila A, Skarlos D, Kalofonos HP, Papadimitriou C, Bafaloukos D, Lambropoulos S, Papadopoulos S, Kourea H, Markopoulos C, Linardou H, Mavroudis D, Briasoulis E, Pavlidis N, Razis E, Kosmidis P, Gogas H: Paclitaxel and carboplatin as first-line chemotherapy combined with gefitinib (IRESSA) in patients with advanced breast cancer: a phase I/II study conducted by the Hellenic Cooperative Oncology Group. Breast Cancer Res Treat. 2005, 92: 1-9. 10.1007/s10549-005-0322-y.PubMedView ArticleGoogle Scholar
- Schafer-Hales K, Iaconelli J, Snyder JP, Prussia A, Nettles JH, El-Naggar A, Khuri FR, Giannakakou P, Marcus AI: Farnesyl transferase inhibitors impair chromosomal maintenance in cell lines and human tumors by compromising CENP-E and CENP-F function. Mol Cancer Ther. 2007, 6: 1317-1328. 10.1158/1535-7163.MCT-06-0703.PubMedView ArticleGoogle Scholar
- Shoemaker AR, Oleksijew A, Bauch J, Belli BA, Borre T, Bruncko M, Deckwirth T, Frost DJ, Jarvis K, Joseph MK, Marsh K, McClellan W, Nellans H, Ng S, Nimmer P, O'Connor JM, Oltersdorf T, Qing W, Shen W, Stavropoulos J, Tahir SK, Wang B, Warner R, Zhang H, Fesik SW, Rosenberg SH, Elmore SW: A small-molecule inhibitor of Bcl-XL potentiates the activity of cytotoxic drugs in vitro and in vivo. Cancer Res. 2006, 66: 8731-8739. 10.1158/0008-5472.CAN-06-0367.PubMedView ArticleGoogle Scholar
- Kutuk O, Letai A: Alteration of the mitochondrial apoptotic pathway is key to acquired paclitaxel resistance and can be reversed by ABT-737. Cancer Res. 2008, 68: 7985-7994. 10.1158/0008-5472.CAN-08-1418.PubMedPubMed CentralView ArticleGoogle Scholar
- Xu R, Sato N, Yanai K, Akiyoshi T, Nagai S, Wada J, Koga K, Mibu R, Nakamura M, Katano M: Enhancement of paclitaxel-induced apoptosis by inhibition of mitogen-activated protein kinase pathway in colon cancer cells. Anticancer Res. 2009, 29: 261-270.PubMedGoogle Scholar
- MacKeigan JP, Collins TS, Ting JP: MEK inhibition enhances paclitaxel-induced tumor apoptosis. J Biol Chem. 2000, 275: 38953-38956. 10.1074/jbc.C000684200.PubMedView ArticleGoogle Scholar
- Mukohara T, Shimada H, Ogasawara N, Wanikawa R, Shimomura M, Nakatsura T, Ishii G, Park JO, Janne PA, Saijo N, Minami H: Sensitivity of breast cancer cell lines to the novel insulin-like growth factor-1 receptor (IGF-1R) inhibitor NVP-AEW541 is dependent on the level of IRS-1 expression. Cancer Lett. 2009, 282: 14-24. 10.1016/j.canlet.2009.02.056.PubMedView ArticleGoogle Scholar
- Ready NE, Lipton A, Zhu Y, Statkevich P, Frank E, Curtis D, Bukowski RM: Phase I study of the farnesyltransferase inhibitor lonafarnib with weekly paclitaxel in patients with solid tumors. Clin Cancer Res. 2007, 13: 576-583. 10.1158/1078-0432.CCR-06-1262.PubMedView ArticleGoogle Scholar
- Khuri FR, Glisson BS, Kim ES, Statkevich P, Thall PF, Meyers ML, Herbst RS, Munden RF, Tendler C, Zhu Y, Bangert S, Thompson E, Lu C, Wang XM, Shin DM, Kies MS, Papadimitrakopoulou V, Fossella FV, Kirschmeier P, Bishop WR, Hong WK: Phase I study of the farnesyltransferase inhibitor lonafarnib with paclitaxel in solid tumors. Clin Cancer Res. 2004, 10: 2968-2976. 10.1158/1078-0432.CCR-03-0412.PubMedView ArticleGoogle Scholar
- Hu L, Hofmann J, Lu Y, Mills GB, Jaffe RB: Inhibition of phosphatidylinositol 3'-kinase increases efficacy of paclitaxel in in vitro and in vivo ovarian cancer models. Cancer Res. 2002, 62: 1087-1092.PubMedGoogle Scholar
- Lu X, Nguyen TA, Moon SH, Darlington Y, Sommer M, Donehower LA: The type 2C phosphatase Wip1: an oncogenic regulator of tumor suppressor and DNA damage response pathways. Cancer Metastasis Rev. 2008, 27: 123-135. 10.1007/s10555-008-9127-x.PubMedPubMed CentralView ArticleGoogle Scholar
- Rauta J, Alarmo EL, Kauraniemi P, Karhu R, Kuukasjarvi T, Kallioniemi A: The serine-threonine protein phosphatase PPM1 D is frequently activated through amplification in aggressive primary breast tumours. Breast Cancer Res Treat. 2006, 95: 257-263. 10.1007/s10549-005-9017-7.PubMedView ArticleGoogle Scholar
- Bulavin DV, Demidov ON, Saito S, Kauraniemi P, Phillips C, Amundson SA, Ambrosino C, Sauter G, Nebreda AR, Anderson CW, Kallioniemi A, Fornace AJ, Appella E: Amplification of PPM1 D in human tumors abrogates p53 tumor-suppressor activity. Nat Genet. 2002, 31: 210-215. 10.1038/ng894.PubMedView ArticleGoogle Scholar
- Belova GI, Demidov ON, Fornace AJ, Bulavin DV: Chemical inhibition of Wip1 phosphatase contributes to suppression of tumorigenesis. Cancer Biol Ther. 2005, 4: 1154-1158. 10.4161/cbt.4.10.2204.PubMedView ArticleGoogle Scholar
- Rayter S, Elliott R, Travers J, Rowlands MG, Richardson TB, Boxall K, Jones K, Linardopoulos S, Workman P, Aherne W, Lord CJ, Ashworth A: A chemical inhibitor of PPM1 D that selectively kills cells overexpressing PPM1D. Oncogene. 2008, 27: 1036-1044. 10.1038/sj.onc.1210729.PubMedView ArticleGoogle Scholar
- Zannetti A, Del Vecchio S, Carriero MV, Fonti R, Franco P, Botti G, D'Aiuto G, Stoppelli MP, Salvatore M: Coordinate up-regulation of Sp1 DNA-binding activity and urokinase receptor expression in breast carcinoma. Cancer Res. 2000, 60: 1546-1551.PubMedGoogle Scholar
- Black AR, Black JD, Azizkhan-Clifford J: Sp1 and kruppel-like factor family of transcription factors in cell growth regulation and cancer. J Cell Physiol. 2001, 188: 143-160. 10.1002/jcp.1111.PubMedView ArticleGoogle Scholar
- Miller DM, Polansky DA, Thomas SD, Ray R, Campbell VW, Sanchez J, Koller CA: Mithramycin selectively inhibits transcription of G-C containing DNA. Am J Med Sci. 1987, 294: 388-394. 10.1097/00000441-198711000-00015.PubMedView ArticleGoogle Scholar
- Tan AR, Alexe G, Reiss M: Transforming growth factor-beta signaling: emerging stem cell target in metastatic breast cancer?. Breast Cancer Res Treat. 2009, 115: 453-495. 10.1007/s10549-008-0184-1.PubMedPubMed CentralView ArticleGoogle Scholar
- Muraoka-Cook RS, Shin I, Yi JY, Easterly E, Barcellos-Hoff MH, Yingling JM, Zent R, Arteaga CL: Activated type I TGFbeta receptor kinase enhances the survival of mammary epithelial cells and accelerates tumor progression. Oncogene. 2006, 25: 3408-3423. 10.1038/sj.onc.1208964.PubMedView ArticleGoogle Scholar
- Melisi D, Ishiyama S, Sclabas GM, Fleming JB, Xia Q, Tortora G, Abbruzzese JL, Chiao PJ: LY2109761, a novel transforming growth factor beta receptor type I and type II dual inhibitor, as a therapeutic approach to suppressing pancreatic cancer metastasis. Mol Cancer Ther. 2008, 7: 829-840. 10.1158/1535-7163.MCT-07-0337.PubMedPubMed CentralView ArticleGoogle Scholar
- Fransvea E, Angelotti U, Antonaci S, Giannelli G: Blocking transforming growth factor-beta up-regulates E-cadherin and reduces migration and invasion of hepatocellular carcinoma cells. Hepatology. 2008, 47: 1557-1566. 10.1002/hep.22201.PubMedView ArticleGoogle Scholar
- Liedtke C, Mazouni C, Hess KR, Andre F, Tordai A, Mejia JA, Symmans WF, Gonzalez-Angulo AM, Hennessy B, Green M, Cristofanilli M, Hortobagyi GN, Pusztai L: Response to neoadjuvant therapy and long-term survival in patients with triple-negative breast cancer. J Clin Oncol. 2008, 26: 1275-1281. 10.1200/JCO.2007.14.4147.PubMedView ArticleGoogle Scholar
- Dent R, Trudeau M, Pritchard KI, Hanna WM, Kahn HK, Sawka CA, Lickley LA, Rawlinson E, Sun P, Narod SA: Triple-negative breast cancer: clinical features and patterns of recurrence. Clin Cancer Res. 2007, 13: 4429-4434. 10.1158/1078-0432.CCR-06-3045.PubMedView ArticleGoogle Scholar
- Anders CK, Carey LA: Biology, metastatic patterns, and treatment of patients with triple-negative breast cancer. Clin Breast Cancer. 2009, 9 (Suppl 2): S73-81. 10.3816/CBC.2009.s.008.PubMedPubMed CentralView ArticleGoogle Scholar
- Parssinen J, Alarmo EL, Karhu R, Kallioniemi A: PPM1 D silencing by RNA interference inhibits proliferation and induces apoptosis in breast cancer cell lines with wild-type p53. Cancer Genet Cytogenet. 2008, 182: 33-39. 10.1016/j.cancergencyto.2007.12.013.PubMedView ArticleGoogle Scholar
- Parisi F, Wirapati P, Naef F: Identifying synergistic regulation involving c-Myc and sp1 in human tissues. Nucleic Acids Res. 2007, 35: 1098-1107. 10.1093/nar/gkl1157.PubMedPubMed CentralView ArticleGoogle Scholar
- Wang LG, Ferrari AC: Mithramycin targets Sp1 and the androgen receptor transcription level: potential therapeutic role in advanced prostate cancer. Translational Oncogenomics. 2007, 2006: 19-31.Google Scholar
- Chandriani S, Frengen E, Cowling VH, Pendergrass SA, Perou CM, Whitfield ML, Cole MD: A core MYC gene expression signature is prominent in basal-like breast cancer but only partially overlaps the core serum response. PLoS One. 2009, 4: e6693-10.1371/journal.pone.0006693.PubMedPubMed CentralView ArticleGoogle Scholar
- Alles MC, Gardiner-Garden M, Nott DJ, Wang Y, Foekens JA, Sutherland RL, Musgrove EA, Ormandy CJ: Meta-analysis and gene set enrichment relative to er status reveal elevated activity of MYC and E2F in the "basal" breast cancer subgroup. PLoS One. 2009, 4: e4710-10.1371/journal.pone.0004710.PubMedPubMed CentralView ArticleGoogle Scholar
- Maor S, Yosepovich A, Papa MZ, Yarden RI, Mayer D, Friedman E, Werner H: Elevated insulin-like growth factor-I receptor (IGF-IR) levels in primary breast tumors associated with BRCA1 mutations. Cancer Lett. 2007, 257: 236-243. 10.1016/j.canlet.2007.07.019.PubMedView ArticleGoogle Scholar
- Wang L, Guan X, Zhang J, Jia Z, Wei D, Li Q, Yao J, Xie K: Targeted inhibition of Sp1-mediated transcription for antiangiogenic therapy of metastatic human gastric cancer in orthotopic nude mouse models. Int J Oncol. 2008, 33: 161-167.PubMedGoogle Scholar
- Shin I, Bakin AV, Rodeck U, Brunet A, Arteaga CL: Transforming growth factor beta enhances epithelial cell survival via Akt-dependent regulation of FKHRL1. Mol Biol Cell. 2001, 12: 3328-3339.PubMedPubMed CentralView ArticleGoogle Scholar
- Ohmori T, Yang JL, Price JO, Arteaga CL: Blockade of tumor cell transforming growth factor-betas enhances cell cycle progression and sensitizes human breast carcinoma cells to cytotoxic chemotherapy. Exp Cell Res. 1998, 245: 350-359. 10.1006/excr.1998.4261.PubMedView ArticleGoogle Scholar
- Biswas S, Guix M, Rinehart C, Dugger TC, Chytil A, Moses HL, Freeman ML, Arteaga CL: Inhibition of TGF-beta with neutralizing antibodies prevents radiation-induced acceleration of metastatic cancer progression. J Clin Invest. 2007, 117: 1305-1313. 10.1172/JCI30740.PubMedPubMed CentralView ArticleGoogle Scholar
- Teicher BA, Holden SA, Ara G, Chen G: Transforming growth factor-beta in in vivo resistance. Cancer Chemother Pharmacol. 1996, 37: 601-609. 10.1007/s002800050435.PubMedView ArticleGoogle Scholar
- Ahmed AA, Mills AD, Ibrahim AE, Temple J, Blenkiron C, Vias M, Massie CE, Iyer NG, McGeoch A, Crawford R, Nicke B, Downward J, Swanton C, Bell SD, Earl HM, Laskey RA, Caldas C, Brenton JD: The extracellular matrix protein TGFBI induces microtubule stabilization and sensitizes ovarian cancers to paclitaxel. Cancer Cell. 2007, 12: 514-527. 10.1016/j.ccr.2007.11.014.PubMedPubMed CentralView ArticleGoogle Scholar
- Dong C, Li Z, Alvarez R, Feng XH, Goldschmidt-Clermont PJ: Microtubule binding to Smads may regulate TGF beta activity. Mol Cell. 2000, 5: 27-34. 10.1016/S1097-2765(00)80400-1.PubMedView ArticleGoogle Scholar
- Yang EY, Moses HL: Transforming growth factor beta 1-induced changes in cell migration, proliferation, and angiogenesis in the chicken chorioallantoic membrane. J Cell Biol. 1990, 111: 731-741. 10.1083/jcb.111.2.731.PubMedView ArticleGoogle Scholar
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