Retraction Note: Lysyl oxidase is essential for hypoxia-induced metastasis.

A Retraction to this paper has been published and can be accessed via a link at the top of the paper.

Lysyl oxidase is essential for hypoxia-induced metastasis.

Metastasis is a multistep process responsible for most cancer deaths, and it can be influenced by both the immediate microenvironment (cell-cell or cell-matrix interactions) and the extended tumour microenvironment (for example vascularization). Hypoxia (low oxygen) is clinically associated with metastasis and poor patient outcome, although the underlying processes remain unclear. Microarray studies have shown the expression of lysyl oxidase (LOX) to be elevated in hypoxic human tumour cells. Paradoxically, LOX expression is associated with both tumour suppression and tumour progression, and its role in tumorigenesis seems dependent on cellular location, cell type and transformation status. Here we show that LOX expression is regulated by hypoxia-inducible factor (HIF) and is associated with hypoxia in human breast and head and neck tumours. Patients with high LOX-expressing tumours have poor distant metastasis-free and overall survivals. Inhibition of LOX eliminates metastasis in mice with orthotopically grown breast cancer tumours. Mechanistically, secreted LOX is responsible for the invasive properties of hypoxic human cancer cells through focal adhesion kinase activity and cell to matrix adhesion. Furthermore, LOX may be required to create a niche permissive for metastatic growth. Our findings indicate that LOX is essential for hypoxia-induced metastasis and is a good therapeutic target for preventing and treating metastases.

Identification and targeting of a HES1-YAP1-CDKN1C functional interaction in fusion-negative rhabdomyosarcoma.

Rhabdomyosarcoma (RMS), a cancer characterized by features of skeletal muscle, is the most common soft-tissue sarcoma of childhood. With 5-year survival rates among high-risk groups at < 30%, new therapeutics are desperately needed. Previously, using a myoblast-based model of fusion-negative RMS (FN-RMS), we found that expression of the Hippo pathway effector transcriptional coactivator YAP1 (YAP1) permitted senescence bypass and subsequent transformation to malignant cells, mimicking FN-RMS. We also found that YAP1 engages in a positive feedback loop with Notch signaling to promote FN-RMS tumorigenesis. However, we could not identify an immediate downstream impact of this Hippo-Notch relationship. Here, we identify a HES1-YAP1-CDKN1C functional interaction, and show that knockdown of the Notch effector HES1 (Hes family BHLH transcription factor 1) impairs growth of multiple FN-RMS cell lines, with knockdown resulting in decreased YAP1 and increased CDKN1C expression. In silico mining of published proteomic and transcriptomic profiles of human RMS patient-derived xenografts revealed the same pattern of HES1-YAP1-CDKN1C expression. Treatment of FN-RMS cells in vitro with the recently described HES1 small-molecule inhibitor, JI130, limited FN-RMS cell growth. Inhibition of HES1 in vivo via conditional expression of a HES1-directed shRNA or JI130 dosing impaired FN-RMS tumor xenograft growth. Lastly, targeted transcriptomic profiling of FN-RMS xenografts in the context of HES1 suppression identified associations between HES1 and RAS-MAPK signaling. In summary, these in vitro and in vivo preclinical studies support the further investigation of HES1 as a therapeutic target in FN-RMS.

A method to culture human alveolar rhabdomyosarcoma cell lines as rhabdospheres demonstrates an enrichment in stemness and Notch signaling.

The development of three-dimensional cell culture techniques has allowed cancer researchers to study the stemness properties of cancer cells in in vitro culture. However, a method to grow PAX3-FOXO1 fusion-positive rhabdomyosarcoma (FP-RMS), an aggressive soft tissue sarcoma of childhood, has to date not been reported, hampering efforts to identify the dysregulated signaling pathways that underlie FP-RMS stemness. Here, we first examine the expression of canonical stem cell markers in human RMS tumors and cell lines. We then describe a method to grow FP-RMS cell lines as rhabdospheres and demonstrate that these spheres are enriched in expression of canonical stemness factors as well as Notch signaling components. Specifically, FP-RMS rhabdospheres have increased expression of SOX2, POU5F1 (OCT4), and NANOG, and several receptors and transcriptional regulators in the Notch signaling pathway. FP-RMS rhabdospheres also exhibit functional stemness characteristics including multipotency, increased tumorigenicity in vivo, and chemoresistance. This method provides a novel practical tool to support research into FP-RMS stemness and chemoresistance signaling mechanisms.

Quantitative phase imaging of erythrocytes under microfluidic constriction in a high refractive index medium reveals water content changes.

Changes in the deformability of red blood cells can reveal a range of pathologies. For example, cells which have been stored for transfusion are known to exhibit progressively impaired deformability. Thus, this aspect of red blood cells has been characterized previously using a range of techniques. In this paper, we show a novel approach for examining the biophysical response of the cells with quantitative phase imaging. Specifically, optical volume changes are observed as the cells transit restrictive channels of a microfluidic chip in a high refractive index medium. The optical volume changes indicate an increase of cell's internal density, ostensibly due to water displacement. Here, we characterize these changes over time for red blood cells from two subjects. By storage day 29, a significant decrease in the magnitude of optical volume change in response to mechanical stress was witnessed. The exchange of water with the environment due to mechanical stress is seen to modulate with storage time, suggesting a potential means for studying cell storage.

Single-Cell Analysis Reveals Distinct Gene Expression and Heterogeneity in Male and Female Plasmodium falciparum Gametocytes.

Sexual reproduction is an obligate step in the Plasmodium falciparum life cycle, with mature gametocytes being the only form of the parasite capable of human-to-mosquito transmission. Development of male and female gametocytes takes 9 to 12 days, and although more than 300 genes are thought to be specific to gametocytes, only a few have been postulated to be male or female specific. Because these genes are often expressed during late gametocyte stages and for some, male- or female-specific transcript expression is debated, the separation of male and female populations is technically challenging. To overcome these challenges, we have developed an unbiased single-cell approach to determine which transcripts are expressed in male versus female gametocytes. Using microfluidic technology, we isolated single mid- to late-stage gametocytes to compare the expression of 91 genes, including 87 gametocyte-specific genes, in 90 cells. Such analysis identified distinct gene clusters whose expression was associated with male, female, or all gametocytes. In addition, a small number of male gametocytes clustered separately from female gametocytes based on sex-specific expression independent of stage. Many female-enriched genes also exhibited stage-specific expression. RNA fluorescent in situ hybridization of male and female markers validated the mutually exclusive expression pattern of male and female transcripts in gametocytes. These analyses uncovered novel male and female markers that are expressed as early as stage III gametocytogenesis, providing further insight into Plasmodium sex-specific differentiation previously masked in population analyses. Our single-cell approach reveals the most robust markers for sex-specific differentiation in Plasmodium gametocytes. Such single-cell expression assays can be generalized to all eukaryotic pathogens.IMPORTANCE Most human deaths that result from malaria are caused by the eukaryotic parasite Plasmodium falciparum The only form of this parasite that is transmitted to the mosquito is the sexual form, called the gametocyte. The production of mature gametocytes can take up to 2 weeks and results in phenotypically distinct males and females, although what causes this gender-specific differentiation remains largely unknown. Here, we demonstrate the first use of microfluidic technology to capture single gametocytes and determine their temporal sex-specific gene expression in an unbiased manner. We were able to determine male or female identity of single cells based on the upregulation of gender-specific genes as early as mid-stage gametocytes. This analysis has revealed strong markers for male and female gametocyte differentiation that were previously concealed in population analyses. Similar single-cell analyses in eukaryotic pathogens using this method may uncover rare cell types and heterogeneity previously masked in population studies.

The potential role of intrinsic hypoxia markers as prognostic variables in cancer.

Tumor hypoxia is related to tumor progression and therapy resistance, which leads to poor patient outcome. It has been suggested that measuring the hypoxic status of a tumor helps to predict patient outcome and to select more targeted treatment. However, current methods using needle electrodes or exogenous markers have limitations due to their invasiveness or necessity for preinjection. Recent studies showed that hypoxia-regulated genes could be alternatively used as endogenous hypoxia markers. This is a review of 15 hypoxia-regulated genes, including hypoxia-inducible factor-1 and its targets, and their correlation with tumor hypoxia and patient outcome from 213 studies. Though most of the studies showed significance of these genes in predicting prognosis, there was no definitive prognostic and hypoxia marker. In conclusion, this review suggests the need for further studies with standardized methods to examine gene expression, as well as the use of multiple gene expressions.

Predicting a local recurrence after breast-conserving therapy by gene expression profiling.

INTRODUCTION: To tailor local treatment in breast cancer patients there is a need for predicting ipsilateral recurrences after breast-conserving therapy. After adequate treatment (excision with free margins and radiotherapy), young age and incompletely excised extensive intraductal component are predictors for local recurrence, but many local recurrences can still not be predicted. Here we have used gene expression profiling by microarray analysis to identify gene expression profiles that can help to predict local recurrence in individual patients. METHODS: By using previously established gene expression profiles with proven value in predicting metastasis-free and overall survival (wound-response signature, 70-gene prognosis profile and hypoxia-induced profile) and training towards an optimal prediction of local recurrences in a training series, we establish a classifier for local recurrence after breast-conserving therapy. RESULTS: Validation of the different gene lists shows that the wound-response signature is able to separate patients with a high (29%) or low (5%) risk of a local recurrence at 10 years (sensitivity 87.5%, specificity 75%). In multivariable analysis the classifier is an independent predictor for local recurrence. CONCLUSION: Our findings indicate that gene expression profiling can identify subgroups of patients at increased risk of developing a local recurrence after breast-conserving therapy.

Automated Detection of P. falciparum Using Machine Learning Algorithms with Quantitative Phase Images of Unstained Cells.

Malaria detection through microscopic examination of stained blood smears is a diagnostic challenge that heavily relies on the expertise of trained microscopists. This paper presents an automated analysis method for detection and staging of red blood cells infected by the malaria parasite Plasmodium falciparum at trophozoite or schizont stage. Unlike previous efforts in this area, this study uses quantitative phase images of unstained cells. Erythrocytes are automatically segmented using thresholds of optical phase and refocused to enable quantitative comparison of phase images. Refocused images are analyzed to extract 23 morphological descriptors based on the phase information. While all individual descriptors are highly statistically different between infected and uninfected cells, each descriptor does not enable separation of populations at a level satisfactory for clinical utility. To improve the diagnostic capacity, we applied various machine learning techniques, including linear discriminant classification (LDC), logistic regression (LR), and k-nearest neighbor classification (NNC), to formulate algorithms that combine all of the calculated physical parameters to distinguish cells more effectively. Results show that LDC provides the highest accuracy of up to 99.7% in detecting schizont stage infected cells compared to uninfected RBCs. NNC showed slightly better accuracy (99.5%) than either LDC (99.0%) or LR (99.1%) for discriminating late trophozoites from uninfected RBCs. However, for early trophozoites, LDC produced the best accuracy of 98%. Discrimination of infection stage was less accurate, producing high specificity (99.8%) but only 45.0%-66.8% sensitivity with early trophozoites most often mistaken for late trophozoite or schizont stage and late trophozoite and schizont stage most often confused for each other. Overall, this methodology points to a significant clinical potential of using quantitative phase imaging to detect and stage malaria infection without staining or expert analysis.

Hemoglobin consumption by P. falciparum in individual erythrocytes imaged via quantitative phase spectroscopy.

Plasmodium falciparum infection causes structural and biochemical changes in red blood cells (RBCs). To quantify these changes, we apply a novel optical technique, quantitative phase spectroscopy (QPS) to characterize individual red blood cells (RBCs) during the intraerythrocytic life cycle of P. falciparum. QPS captures hyperspectral holograms of individual RBCs to measure spectroscopic changes across the visible wavelength range (475-700 nm), providing complex information, i.e. amplitude and phase, about the light field which has interacted with the cell. The complex field provides complimentary information on hemoglobin content and cell mass, which are both found to dramatically change upon infection by P. falciparum. Hb content progressively decreases with parasite life cycle, with an average 72.2% reduction observed for RBCs infected by schizont-stage P. falciparum compared to uninfected cells. Infection also resulted in a 33.1% reduction in RBC's optical volume, a measure of the cells' non-aqueous components. Notably, optical volume is only partially correlated with hemoglobin content, suggesting that changes in other dry mass components such as parasite mass may also be assessed using this technique. The unique ability of QPS to discriminate individual healthy and infected cells using spectroscopic changes indicates that the approach can be used to detect disease.

A paclitaxel-loaded recombinant polypeptide nanoparticle outperforms Abraxane in multiple murine cancer models.

Packaging clinically relevant hydrophobic drugs into a self-assembled nanoparticle can improve their aqueous solubility, plasma half-life, tumour-specific uptake and therapeutic potential. To this end, here we conjugated paclitaxel (PTX) to recombinant chimeric polypeptides (CPs) that spontaneously self-assemble into ∼60 nm near-monodisperse nanoparticles that increased the systemic exposure of PTX by sevenfold compared with free drug and twofold compared with the Food and Drug Administration-approved taxane nanoformulation (Abraxane). The tumour uptake of the CP-PTX nanoparticle was fivefold greater than free drug and twofold greater than Abraxane. In a murine cancer model of human triple-negative breast cancer and prostate cancer, CP-PTX induced near-complete tumour regression after a single dose in both tumour models, whereas at the same dose, no mice treated with Abraxane survived for >80 days (breast) and 60 days (prostate), respectively. These results show that a molecularly engineered nanoparticle with precisely engineered design features outperforms Abraxane, the current gold standard for PTX delivery.

Secreted Frizzled-Related Protein 3 (SFRP3) Is Required for Tumorigenesis of PAX3-FOXO1-Positive Alveolar Rhabdomyosarcoma.

PURPOSE: Rhabdomyosarcoma (RMS) is a soft tissue sarcoma associated with the skeletal muscle lineage. Of the two predominant subtypes, known as embryonal (eRMS) and alveolar (aRMS), aRMS has the poorer prognosis, with a five-year survival rate of <50%. The majority of aRMS tumors express the fusion protein PAX3-FOXO1. As PAX3-FOXO1 has proven chemically intractable, this study aims to identify targetable proteins that are downstream from or cooperate with PAX3-FOXO1 to support tumorigenesis. EXPERIMENTAL DESIGN: Microarray analysis of the transcriptomes of human skeletal muscle myoblasts expressing PAX3-FOXO1 revealed alteration of several Wnt pathway gene members, including secreted frizzled related protein 3 (SFRP3), a secreted Wnt pathway inhibitor. Loss-of-function using shRNAs against SFRP3 was used to interrogate the role of SFRP3 in human aRMS cell lines in vitro and conditional murine xenograft systems in vivo. The combination of SFRP3 genetic suppression and the chemotherapeutic agent vincristine was also examined. RESULTS: In vitro, suppression of SFRP3 inhibited aRMS cell growth, reduced proliferation accompanied by a G1 arrest and induction of p21, and induced apoptosis. In vivo, doxycycline-inducible suppression of SFRP3 reduced aRMS tumor growth and weight by more than three-fold, in addition to increasing myogenic differentiation and ß-catenin signaling. The combination of SFRP3 suppression and vincristine was more effective at reducing aRMS cell growth in vitro than either treatment alone, and ablated tumorigenesis in vivo. CONCLUSIONS: SFRP3 is necessary for the growth of human aRMS cells both in vitro and in vivo and is a promising new target for investigation in aRMS.

Modulation of PICALM Levels Perturbs Cellular Cholesterol Homeostasis.

PICALM (Phosphatidyl Inositol Clathrin Assembly Lymphoid Myeloid protein) is a ubiquitously expressed protein that plays a role in clathrin-mediated endocytosis. PICALM also affects the internalization and trafficking of SNAREs and modulates macroautophagy. Chromosomal translocations that result in the fusion of PICALM to heterologous proteins cause leukemias, and genome-wide association studies have linked PICALM Single Nucleotide Polymorphisms (SNPs) to Alzheimer's disease. To obtain insight into the biological role of PICALM, we performed gene expression studies of PICALM-deficient and PICALM-expressing cells. Pathway analysis demonstrated that PICALM expression influences the expression of genes that encode proteins involved in cholesterol biosynthesis and lipoprotein uptake. Gas Chromatography-Mass Spectrometry (GC-MS) studies indicated that loss of PICALM increases cellular cholesterol pool size. Isotopic labeling studies revealed that loss of PICALM alters increased net scavenging of cholesterol. Flow cytometry analyses confirmed that internalization of the LDL receptor is enhanced in PICALM-deficient cells as a result of higher levels of LDLR expression. These findings suggest that PICALM is required for cellular cholesterol homeostasis and point to a novel mechanism by which PICALM alterations may contribute to disease.

Alveolar rhabdomyosarcoma-associated PAX3-FOXO1 promotes tumorigenesis via Hippo pathway suppression.

Alveolar rhabdomyosarcoma (aRMS) is an aggressive sarcoma of skeletal muscle characterized by expression of the paired box 3-forkhead box protein O1 (PAX3-FOXO1) fusion oncogene. Despite its discovery nearly two decades ago, the mechanisms by which PAX3-FOXO1 drives tumor development are not well characterized. Previously, we reported that PAX3-FOXO1 supports aRMS initiation by enabling bypass of cellular senescence checkpoints. We have now found that this bypass occurs in part through PAX3-FOXO1-mediated upregulation of RASSF4, a Ras-association domain family (RASSF) member. RASSF4 expression was upregulated in PAX3-FOXO1-positive aRMS cell lines and tumors. Enhanced RASSF4 expression promoted cell cycle progression, senescence evasion, and tumorigenesis through inhibition of the Hippo pathway tumor suppressor MST1. We also found that the downstream Hippo pathway target Yes-associated protein 1 (YAP), which is ordinarily restrained by Hippo signaling, was upregulated in RMS tumors. These data suggest that Hippo pathway dysfunction promotes RMS. This work provides evidence for Hippo pathway suppression in aRMS and demonstrates a progrowth role for RASSF4. Additionally, we identify a mechanism used by PAX3-FOXO1 to inhibit MST1 signaling and promote tumorigenesis in aRMS.

Combining biological gene expression signatures in predicting outcome in breast cancer: An alternative to supervised classification.

INTRODUCTION: Gene expression profiling has been extensively used to predict outcome in breast cancer patients. We have previously reported on biological hypothesis-driven analysis of gene expression profiling data and we wished to extend this approach through the combinations of various gene signatures to improve the prediction of outcome in breast cancer. METHODS: We have used gene expression data (25.000 gene probes) from a previously published study of tumours from 295 early stage breast cancer patients from the Netherlands Cancer Institute using updated follow-up. Tumours were assigned to three prognostic groups using the previously reported Wound-response and hypoxia-response signatures, and the outcome in each of these subgroups was evaluated. RESULTS: We have assigned invasive breast carcinomas from 295 stages I and II breast cancer patients to three groups based on gene expression profiles subdivided by the wound-response signature (WS) and hypoxia-response signature (HS). These three groups are (1) quiescent WS/non-hypoxic HS; (2) activated WS/non-hypoxic HS or quiescent WS/hypoxic tumours and (3) activated WS/hypoxic HS. The overall survival at 15 years for patients with tumours in groups 1, 2 and 3 are 79%, 59% and 27%, respectively. In multivariate analysis, this signature is not only independent of clinical and pathological risk factors; it is also the strongest predictor of outcome. Compared to a previously identified 70-gene prognosis profile, obtained with supervised classification, the combination of signatures performs roughly equally well and might have additional value in the ER-negative subgroup. In the subgroup of lymph node positive patients, the combination signature outperforms the 70-gene signature in multivariate analysis. In addition, in multivariate analysis, the WS/HS combination is a stronger predictor of outcome compared to the recently reported invasiveness gene signature combined with the WS. CONCLUSION: A combination of biological gene expression signatures can be used to identify a powerful and independent predictor for outcome in breast cancer patients.