An investigation of heat shock protein 27 and P-glycoprotein mediated multi-drug resistance in breast cancer using liquid chromatography-tandem mass spectrometry-based targeted proteomics

Simultaneous and quantitative monitoring transcription factors in human embryonic stem cell differentiation using mass spectrometry-based targeted proteomics

Human embryonic stem cells (hESCs) can be self-propagated indefinitely in culture while holding the capacity to generate almost all cell types. Although this powerful differentiation ability of hESCs has become a potential source of cell replacement therapies, application of stem cells in clinical practice relies heavily on the exquisite control of their developmental fate. In general, an essential first step in differentiation is to exit the pluripotent state, which is precariously balanced and depends on a variety of factors, mainly centering on the core transcriptional mechanism. To date, much evidence has indicated that transcription factors such as Sox2, Oct4, and Nanog control the self-renewal and pluripotency of hESCs. Their expression displays a restricted spatial-temporal pattern and their small changes in level can significantly affect directed differentiation and the cell type derived. So far, few assays have been developed to monitor this process. Herein, we provided a mass spectrometry (MS)-based approach for simultaneous and quantitative monitoring of these transcription factors, in an attempt to provide insight into their contributions in hESC differentiation.

Investigation of cancer drug resistance mechanisms by phosphoproteomics

Cancer cell mutations can be identified by genomic and transcriptomic techniques. However, they are not sufficient to understand the full complexity of cancer heterogeneity. Analyses of proteins expressed in cancers and their modification profiles show how these mutations could be translated at the functional level. Protein phosphorylation is a major post-translational modification critical for regulating several cellular functions. The covalent addition of phosphate groups to serine, threonine, and tyrosine is catalyzed by protein kinases. Over the past years, kinases were strongly associated with cancer, thus inhibition of protein kinases emanated as novel cancer treatment. However, cancers frequently develop drug resistance. Therefore, a better understanding of drug effects on tumors is urgently needed. In this perspective, phosphoproteomics arose as advanced tool to monitor cancer therapies and to discover novel drugs. This review highlights the role of phosphoproteomics in predicting sensitivity or resistance of cancers towards tyrosine kinase inhibitors and cytotoxic drugs. It also shows the importance of phosphoproteomics in identifying biomarkers that could be applied in clinical diagnostics to predict responses to drugs.

Specific Roles of HSP27 S15 Phosphorylation Augmenting the Nuclear Function of HER2 to Promote Trastuzumab Resistance

Trastuzumab (TZMB) is widely used as first line therapy for breast cancer (BC) patients overexpressing human epidermal growth factor receptor 2 (HER2). Despite its clinical benefits, many patients suffer from primary or secondary resistance to this drug within one year. As diverse molecular mechanisms occur contemporaneously during the resistance development, we focused on elucidating the role of heat shock protein 27 (HSP27) in TZMB-resistance, as this protein simultaneously regulates the function of diverse client molecules that are involved in the resistance mechanism. By extensively utilizing TZMB-refractory breast cancer cell lines transduced with diverse phosphovariants of HSP27, our study newly revealed that specific phosphorylation of HSP27 at S15 promoted its S78 phosphorylation and served as key mediator to promote direct interactions that increase the stability of HER2 and protein kinase B (AKT). This phosphorylation promoted nuclear translocation of HER2, enhancing the distinct nuclear function of HER2 that promoted AKT activation and cyclin D1 expression. Co-administration of TZMB and a functional inhibitor of HSP27, J2, significantly reduced the S15/78 phosphorylation of HSP27, which downregulated HER2 and its downstream signals, sensitizing TZMB-refractory cell, and JIMT1-xenograft mouse models to TZMB. Collectively, p-HSP27^S15 could serve as a valuable predictive marker and also a therapeutic target for TZMB-resistance.

A self-assembled pH/enzyme dual-responsive prodrug with PEG deshielding for multidrug-resistant tumor therapy

Multidrug resistance (MDR) is one of the major obstacles for tumor therapy. Intake by receptor-mediated endocytosis enables molecules to bypass ABC transporter efflux, which is the primary mechanism of MDR. Here, we developed a novel pH/enzyme dual-responsive polypeptide prodrug to reverse multidrug resistance. This drug is composed of pH/MMP2-sensitive nanoparticles (MSNPs) self-assembled from mPEG-peptide-DOX. MSNPs can overcome sequential physiological barriers of multidrug resistance by prolonging the circulation time through PEGylation, enhancing tumor accumulation through passive targeting, increasing tumor penetration by enzyme-sensitive PEG deshielding, bypassing ABC transporter efflux by undergoing receptor-mediated endocytosis, and inducing sufficient DOX release from nanoparticles triggered by lysosomal pH. The reversal of MDR by MSNPs was evaluated in MCF-7/ADR cells and nude mice bearing tumors consisting of MCF-7/ADR cells. Both in vitro and in vivo studies showed that the MSNPs can effectively reverse MDR. Thus, MSNPs may constitute a potentially promising strategy for overcoming MDR in clinical applications.

Targeted Proteomics

Targeted proteomics detects proteins of interest with high sensitivity, quantitative accuracy, and reproducibility. In a targeted proteomics assay, surrogate peptides are generated by proteolytic digestion of target proteins and selected reaction monitoring (SRM) assays are developed to quantify these peptides using liquid chromatography-tandem mass spectrometry (LC-MS/MS). In this report, we describe the details of quantitative analysis of target protein in cells and tissue samples.

Quantitative assessment of serum heat shock protein 27 for the diagnosis of epithelial ovarian cancer using targeted proteomics coupled with immunoaffinity enrichment

BACKGROUND

Heat shock protein 27 (HSP27) may take part in the epithelial ovarian cancer (EOC) malignant process because it is elevated in the serum of EOC patients, suggesting that HSP27 may serve as an EOC biomarker to complement the standard serum carbohydrate antigen 125 (CA125) test. Thus, accurate quantification of serum HSP27 would assist the diagnosis of EOC.

METHODS

Liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based targeted proteomics coupled with an immunoaffinity enrichment assay was developed and validated to monitor HSP27 concentrations in serum.

RESULTS

Tryptic peptide 80QLSSGVSEIR89 was selected as a surrogate analyte for quantification, and an immuno-depleted serum extract was used as a surrogate matrix. Immunoaffinity enrichment was effective for protein enrichment and sensitivity enhancement, and the resulting LOQ was 500 pg/ml (>10-fold increase). Then, serum HSP27 concentrations in EOC patients, benign ovarian tumors patients and healthy volunteers were accurately determined to be 4.95 ± 0.37 ng/ml, 2.98 ± 0.16 ng/ml and 2.82 ± 0.15 ng/ml, respectively, suggesting that the EOC samples had significantly higher concentrations of HSP27 than a sample from benign ovarian tumor patients. The experimental values for the samples were compared with those obtained from enzyme-linked immune sorbent assays (ELISAs). The ROC curve analysis showed that the combined area under the curve (AUC) for CA125 and HSP27 was 0.88, which is significantly superior to that of CA125 alone.

CONCLUSIONS

Targeted proteomics coupled with immunoaffinity enrichment may provide more accurate quantification of low-abundant proteins.

Curcumin Reverses 5-Fluorouracil Resistance by Promoting Human Colon Cancer HCT-8/5-FU Cell Apoptosis and Down-regulating Heat Shock Protein 27 and P-Glycoprotein

OBJECTIVE

To investigate the potential mechanisms that curcumin reverses 5-fluorouracil (5-FU) multidrug resistance (MDR).

METHODS

Cell growth and the inhibitory rate of curcumin (2-25 μg/mL) and/or 5-FU (0.05-1000 μg/mL) on human colon cancer HCT-8 and HCT-8/5-FU (5-FU-resistant cell line) were determined using cell counting kit-8 (CCK-8) assay. Apoptosis and cell cycle after 5-FU and/or curcumin treatment were detected by flow cytometry (FCM) and transmission electron microscopy (TEM). The expression of the multidrug resistance related factors p-glycoprotein (P-gp) and heat shock protein 27 (HSP-27) genes and proteins were analyzed by reverse transcription polymerase chain reaction (RT-PCR) and Western blotting (WB), respectively.

RESULTS

The inhibitory rate of curcumin or 5-FU on HCT-8 and HCT-8/5-FU cells proliferation at exponential phase were in a dosedependent manner, HCT-8 cell line was more sensitive to curcumin or 5-FU when compared the inhibitory rate of HCT-8/5-FU. The 50% inhibitory concentration (IC₅₀) of combination 5-FU and curcumin (4.0 μg/mL) in HCT-8/5-FU was calculated as 179.26 μg/mL, with reversal fold of 1.85. Another IC₅₀ of combination 5-FU and curcumin (5.5 μg/mL) in HCT-8/5-FU was calculated as 89.25 μg/mL, with reversal fold of 3.71. Synergistic effect of 5-FU and curcumin on HCT-8 and HCT-8/5-FU cells were found. The cell cycle analysis performed by FCM showed that HCT-8 and HCT-8/5-FU cells mostly accumulated at G₀/G₁ phase, which suggested a synergistic effect of curcumin and 5-FU to induce apoptosis. FCM analysis found that the percentage of apoptosis of cells treated with curcumin, 5-FU and their combination were significantly increased compared to the control group (P<0.05), and the percentage of apoptosis of the combination groups were slightly higher than other groups (P<0.05). The mRNA levels of P-gp (0.28±0.02) and HSP-27 (0.28±0.09) in HCT-8/5-FU cells treated with combination drugs were lower than cells treated with 5-FU alone (P-gp, 0.48±0.07, P=0.009; HSP-27, 0.57±0.10, P=0.007). The protein levels of P-gp (0.25±0.06) and HSP-27 (0.09±0.02) in HCT-8/5-FU cells treated with combination drugs were decreased when compared to 5-FU alone (P-gp, 0.46±0.02, P=0.005; HSP-27, 0.43±0.01, P=0.000).

CONCLUSIONS

Curcumin can inhibit the proliferation of human colon cancer cells. Curcumin has the ability of reversal effects on the multidrug resistance of human colon cancer cells lines HCT-8/5-FU. Down-regulation of P-gp and HSP-27 may be the mechanism of curcumin reversing the drug resistance of HCT-8/5-FU to 5-FU.

Simultaneous quantification of Cyt c interactions with HSP27 and Bcl-xL using molecularly imprinted polymers (MIPs) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based targeted proteomics

Cytochrome c (Cyt c) plays an important role in cell apoptosis. However, it could be functionally compromised by interaction with anti-apoptosis proteins, known as protein-protein interactions (PPIs). Among the proteins potentially interacting with Cyt c, both HSP27 and Bcl-xL serve as pivotal anti-apoptosis proteins. Because multiple PPIs, especially those involve the same protein, could affect each other, their simultaneous and quantitative detection is highly needed. In this study, a combined approach of molecularly imprinted polymers (MIPs) and LC-MS/MS-based targeted proteomics was developed for simultaneous quantification of Cyt c-HSP27 and Cyt c-Bcl-xL interactions. Surrogate peptides of Cyt c, HSP27 and Bcl-xL were first selected and used for the corresponding proteins quantification in targeted proteomics analysis. For MIPs, epitope approach was employed and a short peptide of Cyt c was selected as template for protein complexes recognition and enrichment. The characteristics of the synthesized MIPs including adsorption capacity, kinetics and efficiency were then evaluated. After validation, this combined assay was applied to quantitative analysis of total Cyt c including Cyt c in mitochondria and cytosol, total HSP27, total Bcl-xL and Cyt c-HSP27 and Cyt c-Bcl-xL protein complexes in breast cells. The result was also compared with that using Co-IP/Western Blotting. SIGNIFICANCE: Protein-protein interactions (PPIs) are essential for many cellular processes and the changes of PPIs are often associated with cellular dysfunction. More importantly, each protein typically has more than one interaction partner and multiple PPIs, especially those involve the same protein, could affect each other. The selectivity of these interactions determines the activities of proteins and further the developmental potential of the cell. Thus, simultaneous and quantitative detection of multiple PPIs is highly needed in biological research and related disciplines. However, it is still challenging to even qualitatively or semi-quantitatively analyze multiple PPIs because of the limitations of current experimental techniques for interaction detection. In this study, molecularly imprinted polymers (MIPs) epitope approach was combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) targeted proteomics for the simultaneous and quantitative detection of Cyt c-HSP27 and Cyt c-Bcl-xL interactions in breast cancer. Given high sensitivity, high selectivity and wide dynamic range of LC-MS/MS, MIPs approach was employed here to separate and enrich protein complexes prior to targeted proteomics analysis.

Liposomal co-delivery-based quantitative evaluation of chemosensitivity enhancement in breast cancer stem cells by knockdown of GRP78/CLU

Resistance to chemotherapy is a key factor in the inefficacy of various forms of treatments for cancer. In the present study, chemo-resistant proteins, including glucose-regulated protein 78 (GRP78)/clusterin (CLU) targeted 1,2-dioleoyloxy-3-trimethylammoniumpropane (DOTAP) liposomes, were developed as a delivery system for co-delivery of camptothecin (CPT) and GRP78 siRNA/CLU siRNA. Their drug/gene co-deliveries were quantitatively assessed in cancer stem cells (CSC) and MCF-7 cells. DOTAP-CPT/siRNA were prepared via electrostatic interaction on GRP78 siRNA or CLU siRNA. The size and ζ-potential of liposomes and lipoplexes were measured by dynamic light scattering techniques and electrophoretic light scattering spectrophotometry. The lipoplexes formation was tested by using gel electrophoresis. Immunofluorescence analysis showed that the expression level of CLU and GRP78 were significantly elevated in CSC compared to MCF-7 cells. Transfection and drug-delivery efficiency of DOTAP-CPT/siRNA were quantitatively compared with Lipofectamine 2000. Compared to free CPT, DOTAP-CPT-siCLU delivery in CSC and MCF-7 cells increased transfection efficiency and chemo-sensitivity by 4.1- and 5.9-fold, respectively. On the other hand, DOTAP-CPT-siGRP78 delivery increased transfection efficiency and chemo sensitivity by 4.4- and 6.2-fold in CSC and MCF-7 cells, respectively, compared to free CPT. It is significant that 3 ± 1.2-fold increase in transfection efficiency was achieved by lipofectamine. Consequently, an increase in anti-cancer/gene silencing efficacy was quantitatively observed as an effect of DOTAP-CPT/siRNA treatment, which was relatively higher than lipofectamine treatment. Conclusively, our experimental data quantitatively demonstrate that using DOTAP-CPT-siRNA specifically targeting (CSCs) chemo-resistant protein in vitro offers substantial potential for synergistic anti-cancer therapy.

Transferrin receptor-targeted pH-sensitive micellar system for diminution of drug resistance and targetable delivery in multidrug-resistant breast cancer

The emergence of drug resistance is partially associated with overproduction of transferrin receptor (TfR). To overcome multidrug resistance (MDR) and achieve tumor target delivery, we designed a novel biodegradable pH-sensitive micellar system modified with HAIYPRH, a TfR ligand (7pep). First, the polymers poly(l-histidine)-coupled polyethylene glycol-2000 (PHIS-PEG₂₀₀₀) and 7pep-modified 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-polyethylene glycol-2000 (7pep-DSPE-PEG₂₀₀₀) were synthesized, and the mixed micelles were prepared by blending of PHIS-PEG₂₀₀₀ and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-polyethylene glycol-2000 (DSPE-PEG₂₀₀₀) or 7pep-DSPE-PEG₂₀₀₀ (7-pep HD micelles). The micelles exhibited good size uniformity, high encapsulation efficiency, and a low critical micelle concentration. By changing the polymer ratio in the micellar formulation, the pH response range was specially tailored to pH ~6.0. When loaded with antitumor drug doxorubicin (DOX), the micelle showed an acid pH-triggering drug release profile. The cellular uptake and cytotoxicity study demonstrated that 7-pep HD micelles could significantly enhance the intracellular level and antitumor efficacy of DOX in multidrug-resistant cells (MCF-7/Adr), which attributed to the synergistic effect of poly(l-histidine)-triggered endolysosom escape and TfR-mediated endocytosis. Most importantly, the in vivo imaging study confirmed the target-ability of 7-pep HD micelles to MDR tumor. These findings indicated that 7-pep HD micelles would be a promising drug delivery system in the treatment of drug-resistant tumors.

Quantitation of glutathione S-transferases in rice (Oryza sativa L.) roots exposed to cadmium by liquid chromatography-tandem mass spectrometry using isotope-labeled wing peptides as an internal standard

BACKGROUND

Plant glutathione S-transferases (GSTs, EC 2.5.1.18) are multifunctional enzymes involved in heavy metal cellular detoxification by conjugating the tripeptide (g-Glu-Cys-Gly) glutathione to heavy metals. Previous studies demonstrated that individual rice GSTs were differentially induced by heavy metal exposure at the mRNA transcript level. However, little information is available concerning changes in protein concentration of rice GSTs under heavy metal stress. Because the correlation between changes in protein concentration and gene expression under abiotic stress is poor, direct determination of rice GSTs protein concentrations during cadmium (Cd) exposure is a more effective and reliable approach to explore possible mechanisms of rice Cd translocation and accumulation.

RESULTS

This study established an optimized and advanced liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based targeted proteomics assay for quantification of OsGSTF14 and OsGSTU6 proteins in Cd-stressed rice roots. The tryptic signature peptides were chosen as surrogate analytes and winged peptides containing the isotope-labeled signature peptides were used as the internal standards. The signature peptides exhibited good linearity in the range of 0.6-60 and 0.3-30 nM, respectively. The limit of detection and limit of quantification were 4.5 and 14.5 µg/g for OsGSTF14, respectively, and 2.1 and 7.0 µg/g for OsGSTU6. The spiking recoveries rates at low, medium and high levels were in the range of 72.5-93.4%, with intra- and inter-day precisions of 5.5-9.1 and 4.2-10.2%, respectively.

CONCLUSIONS

The assay successfully quantified the temporal and dose responses of OsGSTF14 and OsGSTU6 proteins in Cd-stressed rice roots, with good accuracy, precision and high-throughput. This assay will have significant application in developing quantification methods of other proteins in Cd-stressed rice, which may provide more insight into the mechanisms of Cd translocation and accumulation in rice.

Knockdown of microRNA-29a Changes the Expression of Heat Shock Proteins in Breast Carcinoma MCF-7 Cells

Breast cancer is the most commonly occurring cancer among women. MicroRNAs as noncoding small RNA molecules play pivotal roles in cancer-related biological processes. Increased levels of microRNA-29a in the serum of breast cancer patients have been reported. Since heat shock proteins (HSPs) play important roles in cell events, the quantitative fluctuations in their cellular levels could be deemed as key indicators of how the exerted treatment alters cell behavior. In this regard, using an antisense small RNA, we attempted to investigate the effects of miR-29a knockdown on the expression of HSPs genes in the MCF-7 breast cancer cell line. MCF-7 cells were cultured in high-glucose Dulbecco’s modified Eagle’s medium with 10% FBS. Studied cells were subdivided into five groups: treated with scramble, anti-miR-29a, anti-miR-29a + Taxol, Taxol, and control. Taxol was added 24 h post-anti-miR transfection and RNA extraction, and cDNA synthesis was done 48 h later. The changes in expression of HSP27, HSP40, HSP60, HSP70, and HSP90 were evaluated by real-time PCR. Our results revealed that inhibitors of microRNA-29a promote apoptosis through upregulation of HSP60 level and downregulation of HSP27, HSP40, HSP70, and HSP90 levels and could be contemplated as a compelling alternative for Taxol employment with similar effects and/or to sensitize cancer cells to chemotherapy with fewer side effects.

A targeted proteomics approach to the quantitative analysis of ERK/Bcl-2-mediated anti-apoptosis and multi-drug resistance in breast cancer

Apoptosis suppression caused by overexpression of anti-apoptotic proteins is a central factor to the acquisition of multi-drug resistance (MDR) in breast cancer. As a highly conserved anti-apoptotic protein, Bcl-2 can initiate an anti-apoptosis response via an ERK1/2-mediated pathway. However, the details therein are still far from completely understood and a quantitative description of the associated proteins in the biological context may provide more insights into this process. Following our previous attempts in the quantitative analysis of MDR mechanisms, liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based targeted proteomics was continually employed here to describe ERK/Bcl-2-mediated anti-apoptosis. A targeted proteomics assay was developed and validated first for the simultaneous quantification of ERK1/2 and Bcl-2. In particular, ERK isoforms (i.e., ERK1 and ERK2) and their differential phosphorylated forms including isobaric ones were distinguished. Using this assay, differential protein levels and site-specific phosphorylation stoichiometry were observed in parental drug-sensitive MCF-7/WT cancer cells and drug-resistant MCF-7/ADR cancer cells and breast tissue samples from two groups of patients who were either suspected or diagnosed to have drug resistance. In addition, quantitative analysis of the time course of both ERK1/2 and Bcl-2 in doxorubicin (DOX)-treated MCF-7/WT cells confirmed these findings. Overall, we propose that targeted proteomics can be used generally to resolve more complex cellular events.

Hurdles in selection process of nanodelivery systems for multidrug-resistant cancer

PURPOSE

Most of the nanomedicines for treatment of multidrug-resistant cancer do not reach Phase III trials and many are terminated or withdrawn or are in an indeterminate state since long without any study results being presented. Extensive perusal of nanomedicine development research revealed that one of the critical aspects influencing clinical outcomes and which requires diligent scrutiny is selection process of nanodelivery system.

METHODS

Research papers and articles published on development of nanodelivery systems for treatment of multidrug-resistant cancer were analyzed. Observations and conclusions noted by these researchers which might shed some light on poor clinical performance of nanocarriers were collated and summarized under observation section. Further research articles were studied to find possible solutions which may be applied to these particular problems for resolving them. The inferences of these findings were composed in Result section.

RESULT

Plausible solutions for the observed obstacles were noted as examples of novel formulations that can yield the following: better in vivo imaging, precise targeting and dosing of a specific site and specific cell type in a particular cancer, modulation of tumor surroundings, intonation of systemic effects and high reproducibility.

CONCLUSION

The angle of approach to the development of best nanosystem for a specific type of tumor needs to be spun around. Some of these changes can be brought about by individual scientists, some need to be established by collated efforts of scientists globally and some await advent of better technologies. Regardless of the stratagem, it can be said decisively that the schematics of development phase need rethinking.

Mass Spectrometry-Based Protein Quantification

Quantification of individual proteins and even entire proteomes is an important theme in proteomics research. Quantitative proteomics is an approach to obtain quantitative information about proteins in a sample. Compared to qualitative or semi-quantitative proteomics, this approach can provide more insight into the effects of a specific stimulus, such as a change in the expression level of a protein and its posttranslational modifications, or to a panel of proposed biomarkers in a given disease state. Proteomics methodologies, along with a variety of bioinformatics approaches, are a major tool in quantitative proteomics. As the theory and technological aspects underlying the proteomics methodologies will be extensively described in Chap. 20 , and protein identification as a prerequisite of quantification has been discussed in Chap. 17 , we will focus on the quantitative proteomics bioinformatics algorithms and software tools in this chapter. Our goal is to provide researchers and newcomers a rational framework to select suitable bioinformatics tools for data analysis, interpretation, and integration in protein quantification. Before doing so, a brief overview of quantitative proteomics is provided.

Quantification of microRNA by DNA-Peptide Probe and Liquid Chromatography-Tandem Mass Spectrometry-Based Quasi-Targeted Proteomics

The distorted and unique expression of microRNAs (miRNAs) in cancer makes them an attractive source of biomarkers. However, one of prerequisites for the application of miRNAs in clinical practice is to accurately profile their expression. Currently available assays normally require pre-enrichment, amplification, and labeling steps, and most of them are semiquantitative. In this study, we converted the signal of target miR-21 into reporter peptide by a DNA-peptide probe and the reporter peptide was ultimately quantified using LC-MS/MS-based targeted proteomics. Specifically, substrate peptide GDKAVLGVDPFR containing reporter peptide AVLGVDPFR and tryptic cleavage site (lysine at position 3) was first designed, followed by the conjugation with DNA sequence that was complementary to miR-21. The newly formed DNA-peptide probe was then hybridized with miR-21, which was biotinylated and attached to streptavidin agarose in advance. After trypsin digestion, the reporter peptide was released and monitored by a targeted proteomics assay. The obtained limit of quantification (LOQ) was 1 pM, and the detection dynamic range spanned ∼5 orders of magnitude. Using this assay, the developed quasi-targeted proteomics approach was applied to determine miR-21 level in breast cells and tissue samples. Finally, qRT-PCR was also performed for a comparison. This report grafted the strategy of targeted proteomics into miRNA quantification.

Efficient Molecular Imprinting Strategy for Quantitative Targeted Proteomics of Human Transferrin Receptor in Depleted Human Serum

Soluble transferrin receptor (sTfR) in serum has been suggested as a marker for breast cancer diagnosis, monitoring and treatment. However, sTfR levels in some situations could be far below the limit of quantification (LOQ) of most assays. Thus, an efficient sample pretreatment strategy is required. In this study, molecularly imprinted polymers (MIPs) were developed and coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based targeted proteomics for sTfR measurement. The key to this effort was that the same surrogate peptide of sTfR (VEYHFLSPYVSPK, VK13) was employed in both the enrichment by MIPs and the quantification by targeted proteomics. Specifically, three peptide templates with different lengths were evaluated for the synthesis of MIPs, and the imprinting conditions were optimized. The characteristics of MIPs, including the adsorption capacity, adsorption kinetics, and binding selectivity, were also investigated. As a result, a ∼12-fold enhancement of sensitivity was achieved using MIPs. An LOQ of 200 ng·mL(-1) was obtained. The intra- and interday precision were <10.7 and 7.8%, respectively. The accuracy was 7.5% at the lower limit of quantification (LLOQ) and <8.4% for the other QC levels. After validation, the assay was applied to determine the sTfR levels in breast cancer patients (n = 20) and healthy volunteers (n = 20) using the standard addition method. The corresponding levels of sTfR were 1.59 ± 0.36 μg·mL(-1) (range: 0.96-2.34 μg·mL(-1)) in the volunteers and 1.82 ± 0.42 μg·mL(-1) (range: 0.95-2.47 μg·mL(-1)) in the patients. This study is among the first to combine MIPs and LC-MS/MS targeted proteomics for protein quantification at the peptide level.

Quantitative assessment of human serum transferrin receptor in breast cancer patients pre- and post-chemotherapy using peptide immunoaffinity enrichment coupled with targeted proteomics

BACKGROUND

sTfR, a soluble form of transferrin receptor in serum, has been suggested as an indicator of bone marrow failure in breast cancer patients receiving chemotherapy. However, intensive chemotherapy could also cause a reduction of sTfR to a level below the LOQ of most assays.

METHODS

An advanced liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based targeted proteomics assay coupled with peptide immunoaffinity enrichment (SISCAPA) was developed and validated for monitoring sTfR.

RESULTS

Tryptic peptide 681VEYHFLSPYVSPK693 was selected as a surrogate analyte for quantification. High-abundant proteins were first removed from serum, followed by SISCAPA that was effective in surrogate peptide enrichment and sensitivity enhancement. The resulting LOQ can achieve 100ng/ml (~10-fold increase). Then, sTfR levels in breast cancer patients pre- and post-chemotherapy, and healthy volunteers were accurately quantified as 1.77±0.53μg/ml, 0.98±0.26μg/ml and 1.66±0.50μg/ml, respectively, using a standard addition method. While there was no evidence for a difference between patients and healthy volunteers, differential levels of sTfR pre- and post-chemotherapy were obtained. Comparison between SISCAPA-targeted proteomics and ELISA indicated that the former approach provided a lower value of sTfR.

CONCLUSIONS

SISCAPA-targeted proteomics may allow the quantification of low-abundant proteins in a more accurate manner.

Heat shock protein 27 phosphorylation state is associated with cancer progression

Understanding the mechanisms that control stress-induced survival is critical to explain how tumors frequently resist to treatment and to improve current anti-cancer therapies. Cancer cells are able to cope with stress and escape drug toxicity by regulating heat shock proteins (Hsps) expression and function. Hsp27 (HSPB1), a member of the small Hsp family, represents one of the key players of many signaling pathways contributing to tumorigenicity, treatment resistance, and apoptosis inhibition. Hsp27 is overexpressed in many types of cancer and its functions are regulated by post-translational modifications, such as phosphorylation. Protein phosphorylation is the most widespread signaling mechanism in eukaryotic cells, and it is involved in all fundamental cellular processes. Aberrant phosphorylation of Hsp27 has been associated with cancer but the molecular mechanisms by which it is implicated in cancer development and progression remain undefined. This mini-review focuses on the role of phosphorylation in Hsp27 functions in cancer cells and its potential usefulness as therapeutic target in cancer.