Corrigendum: Human Wharton's Jelly stem cell (hWJSC) extracts inhibit ovarian cancer cell lines OVCAR3 and SKOV3 in vitro by inducing cell cycle arrest and apoptosis

[This corrects the article DOI: 10.3389/fonc.2018.00592.].

Cancer Stem Cell Traits in Tumor Spheres Derived from Primary Laryngeal Carcinoma Cell Lines

Objective

Cancer stem cells (CSCs) belong to a subpopulation of undifferentiated cells present within tumors that have the potential to regenerate, differentiate, maintenance of pluripotency, drug resistance, and tumorigenicity when transplanted into an innate host. These can influence the growth and behavior of these tumors and are used to investigate the initiation, progression, and treatment strategies of laryngeal cancer. Research on CSC science and targeted therapies were hinge on their isolation and/or enrichment procedures. The object of the study is to isolate cancer stem cells from primary laryngeal carcinoma (CSCPLC) by tumor spheres enrichment. We checked the properties of self-renewal, stemness, clonogenicity, and chemotherapeutic resistance.

Materials and Methods

We performed tumor sphere formation assay (primary, secondary, and tertiary) chemotherapy resistance by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay were performed to evaluate the CSC cells. Immunofluorescence for stem cell markers (CD133+, CD44+) and gene expression of stem cell markers for CD133+, CD44+, OCT4, SOX2, and NANOG was done using the real-time polymerase chain reaction technique.

Results

We were able to isolated CSC subpopulations from PLC cell lines by the tumor sphere method. These cells exhibited good primary, secondary, and tertiary tumor sphere formation efficiency and also disclosed a resistant index of more than 2. Immunofluorescence for stem cell markers (CD133+ and CD44+) confirms the presence of CSC. There was significantly higher mRNA expression of stem cell markers in CSC enriched subpopulations compared to the parental cell lines.

Conclusion

We conclude that tumor spheres enrichment is an efficient, economical, and reliable approach for the isolation and characterization of CSC from PLC cell lines. These cells demonstrated the properties of self-renewal, stemness, clonogenicity, and chemotherapeutic resistance.

A Reversible Shift of Driver Dependence from EGFR to Notch1 in Non-Small Cell Lung Cancer as a Cause of Resistance to Tyrosine Kinase Inhibitors

Notch1 plays a key role in epithelial-mesenchymal transition (EMT) and in the maintenance of cancer stem cells. In the present study we tested whether high levels of activated Notch1 in oncogene-driven NSCLC can induce a reversible shift of driver dependence from EGFR to Notch1, and thus causing resistance to EGFR inhibitors. Adherent cells (parental) and tumor spheres (TS) from NSCLC H1975 cells and patient-derived CD133-positive cells were tested for EGFR and Notch1 signaling cascade. The Notch1-dependent modulation of EGFR, NCID, Hes1, p53, and Sp1 were then analyzed in parental cells by binding assays with a Notch1 agonist, DLL4. TS were more resistant than parental cells to EGFR inhibitors. A strong upregulation of Notch1 and a concomitant downregulation of EGFR were observed in TS compared to parental cells. Parental cell exposure to DLL4 showed a dose-dependent decrease of EGFR and a simultaneous increase of NCID, Hes1, p53, and Sp1, along with the dislocation of Sp1 from the EGFR promoter. Furthermore, an enhanced interaction between p53 and Sp1 was observed in TS. In NSCLC cells, high levels of active Notch1 can promote a reversible shift of driver dependence from EGFR to Notch1, leading to resistance to EGFR inhibitors.

Immunophenotypic characterization of sphere-forming cells derived from the human renal cell carcinoma cell line 786-O

Cancer stem cells (CSCs) have been found in many different types of malignant tumors. In our previous study, we found that sphere-forming cells (SFCs) from the renal cell carcinoma (RCC) cell line SK-RC-42 are rich in CSCs. However, our previous reports are based on only one human RCC cell line, which makes it difficult to determine whether the findings from this cell line represent the general mechanisms in human RCC. Therefore, in this study, we attempted to evaluate whether the sphere culture method could enrich for CSCs from another human RCC cell line, 786-O, and to characterize their immunological phenotype. We discovered that a small population of 786-O cells was capable of growing as tumor spheres. The SFCs had many properties similar to CSCs, including greater ability to self-renew in vitro and in vivo, higher mRNA expression levels of several 'stemness' genes, stronger tumorigenicity and resistance to chemotherapeutic agents than monolayer adherent cells (MACs). The SFCs expressed low levels of MHC-I, HLA-DR, CD80, CD86, CD152 and CD154. Additionally, the SFCs had lower expression levels of Her2 and hTERT, FasL, Fas, the transcription factor forkhead box protein 3 (FoxP3) and activating natural killer cell receptors than did the MACs. In addition, both 786-O SFCs and MACs were weakly positive for B7-H4 expression, while the expression level of B7-H1 in 786-O SFCs was lower than that in MACs. Furthermore, 786-O SFCs and MACs both expressed substantial and comparable levels of membrane complement regulatory proteins (mCRPs). Finally, we found that 786-O SFCs triggered T cell apoptosis. These findings suggested that tumor spheres from 786-O cells are rich in CSCs. The immunological phenotype of the SFCs described in our study suggests that CSCs might play an important role in tumor immune evasion.

Human Wharton's Jelly Stem Cell (hWJSC) Extracts Inhibit Ovarian Cancer Cell Lines OVCAR3 and SKOV3 in vitro by Inducing Cell Cycle Arrest and Apoptosis

Ovarian cancer is a highly lethal and the second highest in mortality among gynecological cancers. Stem cells either naïve or engineered are reported to inhibit various human cancers in both in-vitro and in-vivo. Herein we report the cancer inhibitory properties of human Wharton's jelly stem cell (hWJSC) extracts, namely its conditioned medium (hWJSC-CM) and cell lysate (hWJSC-CL) against two ovarian cancer cell lines (OVCAR3 and SKOV3) in-vitro. Cell metabolic activity assay of OVCAR3 and SKOV3 cells treated with hWJSC-CM (12.5, 25, 50, 75, 100%) and hWJSC-CL (5, 10, 15, 30, and 50 μg/ml) demonstrated concentration dependent inhibition at 24-72 h. Morphological analysis of OVCAR3 and SKOV3 cells treated with hWJSC-CM (50, 75, 100%) and hWJSC-CL (15, 30, and 50 μg/ml) for 24-72 h showed cell shrinkage, membrane damage/blebbings and cell death. Cell cycle assay demonstrated an increase in the sub-G1 and G2M phases of cell cycle following treatment with hWJSC-CM (50, 75, 100%) and hWJSC-CL (10, 15, and 30 μg/ml) at 48 h. Both OVCAR3 and SKOV3 cells demonstrated mild positive expression of activated caspase 3 following treatment with hWJSC-CM (50%) and hWJSC-CL (15 μg/ml) for 24 h. Cell migration of OVCAR3 and SKOV3 cells were inhibited following treatment with hWJSC-CM (50%) and hWJSC-CL (15 μg/ml) for 48 h. Tumor spheres (TS) of OVCAR3 and SKOV3 treated with hWJSC-CM (50, 75, 100%) and hWJSC-CL (10, 15, 30 μg/ml) for 48 h showed altered surface changes including vacuolations and reduction in size of TS. TS of OVCAR3 and SKOV3 also showed the presence of few ovarian cancer stem cells (CSCs) in minimal numbers following treatment with hWJSC-CM (50%) or hWJSC-CL (15 μg/ml) for 48 h. Real-time gene expression analysis of OVCAR3 and SKOV3 treated with hWJSC-CM (50%) or hWJSC-CL (15 μg/ml) for 48 h demonstrated decreased expression of cell cycle regulatory genes (cyclin A2, Cyclin E1), prostaglandin receptor signaling genes (EP2, EP4) and the pro-inflmmatory genes (IL-6, TNF-α) compared to untreated controls. The results indicate that hWJSC-CM and hWJSC-CL inhibit ovarian cancer cells at mild to moderate levels by inducing cellular changes, cell cycle arrest, apoptosis, decreasing the expression of CSC markers and related genes regulation. Therefore, the stem cell factors in hWJSCs extracts can be useful in cancer management.

Peptide nucleic acids targeting mitochondria enhances sensitivity of lung cancer cells to chemotherapy

Acquired resistance to chemotherapy is a major limitation for the successful treatment of lung cancer. Previously, we and others showed that formation of tumor spheres is associated with chemotherapy resistance in lung cancer cells, but the underlying mechanisms remained largely unknown. In the current study, we show that mitochondrial activity is significantly higher in A549 tumor spheres versus monolayer cells, establishing mitochondria as a putative target for antitumor therapy. To this end, we designed a peptide nucleic acids (PNAs) coupled with triphenylphosphonium (TPP) to target the displacement loop (D-loop) regulatory region of mitochondrial DNA (PNA-mito). Treatment with PNA-mito significantly disrupted mitochondrial gene expression, inhibited membrane potential and mitochondria fusion, resulting in proliferation inhibition and cell death. Consistently, in mouse xenograft models, PNA-mito could efficiently inhibit mitochondrial gene expression and block tumor growth. Treatment with a low dose of PNA-mito could significantly enhance the chemotoxicity of cisplatin (CDDP) in drug-resistant A549 tumor spheres. These results establish mitochondria-targeting PNAs as a novel strategy to enhance the accumulative therapeutic outcome of lung cancer.

An autocrine/paracrine circuit of growth differentiation factor (GDF) 15 has a role for maintenance of breast cancer stem-like cells

Cancer stem cells are thought to be responsible for tumor growth, recurrence, and resistance to conventional cancer therapy. However, it is still unclear how they are maintained in tumor tissues. Here, we show that the growth differentiation factor 15 (GDF15), a member of the TGFβ family, may maintain cancer stem-like cells in breast cancer tissues by inducing its own expression in an autocrine/paracrine manner. We found that GDF15, but not TGFβ, increased tumor sphere formation in several breast cancer cell lines and patient-derived primary breast cancer cells. As expected, TGFβ strongly stimulated the phosphorylation of Smad2. GDF15 also stimulated the phosphorylation of Smad2, but the GDF15-induced tumor sphere forming efficiency was not significantly affected by treatment with SB431542, an inhibitor of the TGFβ signaling. Although TGFβ transiently activated ERK1/2, GDF15 induced prolonged activation of ERK1/2. Treatment with U0126, an inhibitor of the MEK-ERK1/2 signaling, greatly inhibited the GDF15-induced tumor sphere formation. Moreover, cytokine array experiments revealed that GDF15, but not TGFβ, is able to induce its own expression; furthermore, it appears to form an autocrine/paracrine circuit to continuously produce GDF15. In addition, we found heterogeneous expression levels of GDF15 among cancer cells and in human breast cancer tissues using immunohistochemistry. This may reflect a heterogeneous cancer cell population, including cancer stem-like cells and other cancer cells. Our findings suggest that GDF15 induces tumor sphere formation through GDF15-ERK1/2-GDF15 circuits, leading to maintenance of GDF15^high cancer stem-like cells. Targeting GDF15 to break these circuits should contribute to the eradication of tumors.

Critical role of Wnt/β-catenin signaling in driving epithelial ovarian cancer platinum resistance

Resistance to platinum-based chemotherapy is the major barrier to treating epithelial ovarian cancer. To improve patient outcomes, it is critical to identify the underlying mechanisms that promote platinum resistance. Emerging evidence supports the concept that platinum-based therapies are able to eliminate the bulk of differentiated cancer cells, but are unable to eliminate cancer initiating cells (CIC). To date, the relevant pathways that regulate ovarian CICs remain elusive. Several correlative studies have shown that Wnt/β-catenin pathway activation is associated with poor outcomes in patients with high-grade serous ovarian cancer (HGSOC). However, the functional relevance of these findings remain to be delineated. We have uncovered that Wnt/β-catenin pathway activation is a critical driver of HGSOC chemotherapy resistance, and targeted inhibition of this pathway, which eliminates CICs, represents a novel and effective treatment for chemoresistant HGSOC. Here we show that Wnt/β-catenin signaling is activated in ovarian CICs, and targeted inhibition of β-catenin potently sensitized cells to cisplatin and decreased CIC tumor sphere formation. Furthermore, the Wnt/β-catenin specific inhibitor iCG-001 potently sensitized cells to cisplatin and decreased stem-cell frequency in platinum resistant cells. Taken together, our data is the first report providing evidence that the Wnt/β-catenin signaling pathway maintains stem-like properties and drug resistance of primary HGSOC PDX derived platinum resistant models, and therapeutic targeting of this pathway with iCG-001/PRI-724, which has been shown to be well tolerated in Phase I trials, may be an effective treatment option.

Resistance of papillary thyroid cancer stem cells to chemotherapy

Thyroid carcinoma is the most common endocrine neoplasm, with the highest mortality rate of all the endocrine cancers. Among the endocrine malignancies, ~80% are papillary thyroid carcinomas (PTCs). In the initiation and progression of this tumor, genetic alterations in the mitogen-associated protein kinase pathway, including RAS point mutations, RET/PTC oncogene rearrangements and BRAF point mutations, play an important role, particularly in deciding targeted therapy. In the present study, a small population of thyroid tumor cells, known as tumor spheres, were isolated and characterized from PTC surgical samples. These spheres can be expanded indefinitely in vitro and give rise to differentiated adherent cells when cultivated in differentiative conditions. The present study showed by reverse transcription-polymerase chain reaction and flow cytometric analysis that the undifferentiated PTC cells exhibited a characteristic antigen expression profile of adult progenitor/stem cells. The cells were more resistant to chemotherapeutics, including bortezomib, taxol, cisplatin, etoposide, doxorubicin and vincristine, than differentiated PTC cells and the majority possessed a quiescent status, as revealed by the various cell cycle characteristics and anti-apoptotic protein expression. Such advances in cancer thyroid stem cell biology may provide relevant information for future targeted therapies.

Current and potential use of MAINTRAC method for cancer diagnosis and prediction of metastasis

Cells shed from solid malignant tumors into the circulation are considered to be the origin of metastases. In spite of a wealth of research on the pathway of metastasis formation, it is still not clear when and how metastases develop, nor is there a consensus on the number and the nature of circulating tumor cells present in individual patients and their relationship to the formation of metastases. We have developed a method to detect a maximum of unselected non-hematological, epithelial cells in the blood, assuming that in cancer patients the majority of these cells are derived from the tumor. Assessment of the number of these cells longitudinally during the course of disease and therapy allows the response to different treatments to be monitored. Due to the viability of the cells, additional analyses such as expression profiles and determination of their sensitivity to drugs can be performed.