Cancer stem-like cell behavior in anaplastic thyroid cancer: A challenging dilemma

Epigenetic inhibition of CTCF by HN1 promotes dedifferentiation and stemness of anaplastic thyroid cancer

Anaplastic thyroid cancer (ATC) is one of the deadliest cancers, whose important malignant feature is dedifferentiation. Chromatin remodeling is critical for tumorigenesis and progression, while its roles and regulator in facilitating dedifferentiation of ATC had been poorly understood. In our study, an emerging function of hematological and neurological expressed 1 (HN1) in promoting dedifferentiation of ATC cells was uncovered. HN1 expression was negatively correlated with the thyroid differentiation markers both at mRNA and protein level. Knockdown of HN1 in ATC cells effectively upregulated the thyroid differentiation markers and impeded the sphere formation capacity, accompanying with the loss of cancer stemness. In contrast, overexpression of HN1 drove the gain of stemness and the loss of thyroid differentiation markers. Nude mouse and zebrafish xenograft models showed that inhibition of HN1 in ATC cells effectively hindered tumor growth due to the loss of cancer stemness. Further study showed that HN1 was negatively correlated with CTCF in an independent thyroid-cancer cohort, and inhibition of HN1 enhanced the expression of CTCF in ATC cells. Overexpression of CTCF significantly reversed the dedifferentiation phenotypes of ATC cells, whereas simultaneously inhibiting HN1 and CTCF was unable to recover the level of thyroid differentiation markers. The combination of ATAC-seq and ChIP-seq analysis confirmed that CTCF regulated genes relating with thyroid gland development through influencing their chromatin accessibility. HN1 inhibited the acetylation of H3K27 at the promoter of CTCF by recruiting HDAC2, thereby inhibiting the transcriptional activation of CTCF. These findings demonstrated an essential role of HN1 in regulating the chromatin accessibility of thyroid differentiation genes during ATC dedifferentiation.

Illuminating the role of lncRNAs ROR and MALAT1 in cancer stemness state of anaplastic thyroid cancer: An exploratory study

Background

Anaplastic thyroid cancer (ATC) is one of the most aggressive malignancies in humans that accounts for a considerable rate of cancer-associated mortality. Since conventional therapies are lacking sufficient efficacy, new treatment approaches are required. This goal could be achieved through a better understanding of the molecular pathogenesis of ATC. Thyroid tumorigenesis is initiated by a subpopulation of cells known as cancer stem cells (CSCs) with specific markers such as CD133 that confers to processes such as self-renewal and metastasis. Besides, some long non-coding RNAs (lncRNAs) promote tumorigenesis by mediating the aforementioned processes.

Methods

Here, we designed an exploratory study to investigate the role of lncRNAs ROR and MALAT1 and their related genes in CSC stemness. Using magnetic-activated cell sorting (MACS), the CD133^- and CD133⁺ subpopulations were separated in SW1736 and C643 ATC cell lines. Next, the expression profiles of the CD133 marker, MALAT1, and its associated genes (CCND1, NESTIN, MYBL2, MCL1, IQGAP1), as well as ROR and its related genes (POU5F1, SOX2, NANOG), were explored by qRT-PCR.

Results

We found significant up-regulation of ROR, POU5F1, SOX2, NANOG, CD133, MALAT1, IQGAP1, and MCL1 in CD133⁺ SW1736 cells compared to CD133^- cells. As for CD133⁺ C643 cells, CCND1, IQGAP1, POU5F1, SOX2, NANOG, and NESTIN were significantly up-regulated compared to CD133^- cells.

Conclusions

This study suggests that these lncRNAs in CD133-positive SW1736 and C643 cells might regulate stemness behaviors in ATC.

Inflammatory Components of the Thyroid Cancer Microenvironment: An Avenue for Identification of Novel Biomarkers

The incidence of thyroid cancer in the United States is on the rise with an appreciably high disease recurrence rate of 20-30%. Anaplastic thyroid cancer (ATC), although rare in occurrence, is an aggressive form of cancer with limited treatment options and bleak cure rates. This chapter uses discussions of in vitro models that are representative of papillary, anaplastic, and follicular thyroid cancer to evaluate the crosstalk between specific cells of the tumor microenvironment (TME), which serves as a highly heterogeneous realm of signaling cascades and metabolism that are associated with tumorigenesis. The cellular constituents of the TME carry out varying characteristic immunomodulatory functions that are discussed throughout this chapter. The aforementioned cell types include cancer-associated fibroblasts (CAFs), endothelial cells (ECs), and cancer stem cells (CSCs), as well as specific immune cells, including natural killer (NK) cells, dendritic cells (DCs), mast cells, T regulatory (Treg) cells, CD8+ T cells, and tumor-associated macrophages (TAMs). TAM-mediated inflammation is associated with a poor prognosis of thyroid cancer, and the molecular basis of the cellular crosstalk between macrophages and thyroid cancer cells with respect to inducing a metastatic phenotype is not yet known. The dynamic nature of the physiological transition to pathological metastatic phenotypes when establishing the TME encompasses a wide range of characteristics that are further explored within this chapter, including the roles of somatic mutations and epigenetic alterations that drive the genetic heterogeneity of cancer cells, allowing for selective advantages that aid in their proliferation. Induction of these proliferating cells is typically accomplished through inflammatory induction, whereby chronic inflammation sets up a constant physiological state of inflammatory cell recruitment. The secretions of these inflammatory cells can alter the genetic makeup of proliferating cells, which can in turn, promote tumor growth.This chapter also presents an in-depth analysis of molecular interactions within the TME, including secretory cytokines and exosomes. Since the exosomal cargo of a cell is a reflection and fingerprint of the originating parental cells, the profiling of exosomal miRNA derived from thyroid cancer cells and macrophages in the TME may serve as an important step in biomarker discovery. Identification of a distinct set of tumor suppressive miRNAs downregulated in ATC-secreted exosomes indicates their role in the regulation of tumor suppressive genes that may increase the metastatic propensity of ATC. Additionally, the high expression of pro-inflammatory cytokines in studies looking at thyroid cancer and activated macrophage conditioned media suggests the existence of an inflammatory TME in thyroid cancer. New findings are suggestive of the presence of a metastatic niche in ATC tissues that is influenced by thyroid tumor microenvironment secretome-induced epithelial to mesenchymal transition (EMT), mediated by a reciprocal interaction between the pro-inflammatory M1 macrophages and the thyroid cancer cells. Thus, targeting the metastatic thyroid carcinoma microenvironment could offer potential therapeutic benefits and should be explored further in preclinical and translational models of human metastatic thyroid cancer.

Alginate-based 3D cell culture technique to evaluate the half-maximal inhibitory concentration: an in vitro model of anticancer drug study for anaplastic thyroid carcinoma

Background

Three-dimensional (3D) cell culture methods are identified for simulating the biological microenvironment and demonstrating more similarity to in vivo circumstances. Anaplastic thyroid carcinoma (ATC) is a lethal endocrine malignancy. Despite different treatment approaches, no improvement in the survival rate of the patients has been shown. In this study, we used the 3D in vitro ATC model to investigate the cytotoxic effect of BI-847325 anticancer drug in two-dimensional (2D)- and 3D- cultured cells.

Methods

Human ATC cell lines, C643 and SW1736, were cultured in one percentage (w/v) sodium alginate. Spheroids were incubated in medium for one week. The reproducibility of the fabrication of alginate beads was evaluated. Encapsulation of the cells in alginate was examined by DAPI (4^′,6-diamidino-2-phenylindole) staining. Survival of alginate-encapsulated cells was evaluated by CFSE (5,6-Carboxyfluorescein N-hydroxysuccinimidyl ester) staining. The population doubling times of C643 and SW1736 cell lines cultured in 2D monolayer as well as in 3D system were calculated. The cytotoxic effect of BI-847325 on 2D- and 3D- cultured cell lines was assessed for 24–72 h by MTT [3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide] assay. Finally, the 3D culture results were compared with the 2D culture method.

Results

The half-maximal inhibitory concentration (IC₅₀) values of BI-847325 were higher in 3D culture compared to 2D culture. The cytotoxicity data indicated that 3D in vitro models were more resistant to chemotherapy agents.

Conclusions

The findings of this study are beneficial for developing in vitro ATC 3D models to analyze the efficacy of different chemotherapy drugs and formulations.

Signal transducer and activator of transcription 3 inhibition alleviates resistance to BRAF inhibition in anaplastic thyroid cancer

Anaplastic thyroid cancer (ATC) is a rare type of thyroid cancer (TC) with no effective therapeutic strategy. Although surgery, chemotherapy and radiation are all available for ATC treatment, the median survival for ATC patients is less than 6 months. In this study, we aimed to study on resistant mechanisms to B-Raf proto-oncogene serine/threonine kinase (BRAF) inhibitor and identify effective combinational therapy for ATC patients. TC cells were treated with Vemurafenib and cell apoptosis and viability were analyzed by flow cytometry and MTT assay. Monolayer and sphere cells were isolated from ATC cells to detect the mRNA level of stem cell markers and differentiation markers by RT-PCR. Phosphor-STAT3 level in sphere and monolayer cells was tested by Western blotting. The xenotransplantation animal model has established to analyze the anti-tumor effect of Vemurafenib and Stattic combinational therapy. Undifferentiated TC cells were resistant to Vemurafenib treatment. Sphere cells isolated from ATC showed no significant change in cell viability and apoptosis upon Vemurafenib treatment, and expressed a high level of stem cell marker and phosphor-STAT3. STAT3 inhibition enhanced the tumorigenic capacity and increased Vemurafenib sensitivity in ATC cell lines. Stattic significantly enhanced anti-tumor effect of Vemurafenib in mouse model. Our findings demonstrate that the combinational therapy of Vemurafenib and Stattic is an effective therapeutic treatment for ATC patients.

Synthesis and characterization of CD133 targeted aptamer-drug conjugates for precision therapy of anaplastic thyroid cancer

Anaplastic thyroid cancer (ATC) is an undifferentiated and highly aggressive type of thyroid cancer and is extremely resistant to standard therapies such as surgical resection and radioactive iodine therapy. Although targeted therapeutic agents including small molecule drugs and monoclonal antibodies are rapidly developed in recent years, no ATC targeted drugs are available to date; thereby, novel targeted therapies are needed to improve the outcomes of ATC patients. Aptamers are single-stranded DNA (or RNA) molecules that can selectively bind to cancer specific antigens, and aptamer-based targeted therapy has certain advantages over that based on antibodies due to its high binding affinity and low immunogenicity. Here, we identified that CD133, a cancer stem cell marker, was specifically expressed in ATC tumor tissues and cells, implying that CD133 is a potential drug target for ATC therapy. Additionally, we successfully obtained a CD133 targeted aptamer AP-1 by paired cell-based SELEX, which can precisely recognize CD133 antigen in vitro. Furthermore, the truncated AP-1-M aptamer from its precursor AP-1 has shown higher binding affinity for CD133, and specifically accumulated in anaplastic thyroid cancer FRO cell derived tumor in vivo. Conjugation of truncated AP-1-M with doxorubicin could dramatically inhibit CD133 positive FRO cell proliferation, induce cell apoptosis in vitro, and also suppress tumor growth in FRO cell xenograft mice in vivo. Our results clearly demonstrated that the CD133 targeted aptamer AP-1-M conjugated with anticancer drugs has potential to become a promising therapeutic approach against ATC in the near future.

Diallyl trisulphide, a H2 S donor, compromises the stem cell phenotype and restores thyroid-specific gene expression in anaplastic thyroid carcinoma cells by targeting AKT-SOX2 axis

It is widely accepted that anaplastic thyroid carcinoma (ATC), a rare, extremely aggressive malignant, is enriched by cancer stem cells (CSCs), which are closely related to the pathogenesis of ATC. In the present study, we demonstrated that diallyl trisulphide (DATS), a well-known hydrogen sulphide (H₂ S) donor, suppressed sphere formation and restored the expression of iodide-metabolizing genes in human ATC cells, which were associated with H₂ S generation. Two other H₂ S donors, NaHS and GYY4137, could also suppress the self-renewal properties of ATC cells in vitro. Compared with normal thyroid tissues and papillary thyroid carcinomas (PTCs), the elevated expressions of SOX2 and MYC, two cancer stem cell markers, in ATCs were validated in the combined Gene Expression Omnibus (GEO) cohort. DATS decreased the expression of SOX2, which was mediated by H₂ S generation. Furthermore, knockdown of AKT or inhibition of AKT by DATS led to a decrease of SOX2 expression in ATC cells. AKT knockdown phenocopied restoration of thyroid-specific gene expression in ATC cells. Our data suggest that H₂ S donors treatment can compromise the stem cell phenotype and restore thyroid-specific gene expression of ATC cells by targeting AKT-SOX2 pathway, which may serve as a therapeutic strategy to intervene the CSC progression of ATC.

Capsaicin induces mitochondrial dysfunction and apoptosis in anaplastic thyroid carcinoma cells via TRPV1-mediated mitochondrial calcium overload

Anaplastic thyroid cancer (ATC) is a rare malignancy and has a poor prognosis due to its aggressive behavior and resistance to treatments. Calcium (Ca²⁺) serves as a ubiquitous cellular second messenger and influences several tumor behaviors. Therefore, Ca²⁺ modulation is expected to be a novel therapeutic target in cancers. However, whether Ca²⁺ modulation is effective in ATC therapy remains unknown. In this study, we reported that capsaicin (CAP), a transient receptor potential vanilloid type1 (TRPV1) agonist, inhibited the viability of anaplastic thyroid cancer cells. Capsaicin treatment triggered Ca²⁺ influx by TRPV1 activation, resulting in disequilibrium of intracellular calcium homeostasis. The rapidly increased cytosolic Ca²⁺ concentration was mirrored in the mitochondria and caused a severe condition of mitochondrial calcium overload in ATC cells. In addition, the disruption of mitochondrial calcium homeostasis caused by capsaicin led to mitochondrial dysfunction in ATC cells, as evidenced by the production of mitochondrial reactive oxygen species (ROS), depolarization of mitochondrial membrane potential (ΔΨm), and opening of mitochondrial permeability transition pore (mPTP). Next, the resulting release of cyt c into the cytosol triggered apoptosome assembly and subsequent caspase activation and apoptosis. It was worth noting that both TRPV1 antagonist (capsazepine) and calcium chelator (BAPTA) could attenuate aberrant Ca²⁺ homeostasis, mitochondrial dysfunction and apoptosis induced by capsaicin treatment. Thus, our study demonstrated that capsaicin induced mitochondrial calcium overload and apoptosis in ATC cells through a TRPV1-mediated pathway. The better understanding of the anti-cancer mechanisms of calcium modulation provides a potential target for the ATC therapy.

Molecular mechanisms of long non-coding RNAs in anaplastic thyroid cancer: a systematic review

BACKGROUND

anaplastic thyroid cancer (ATC) is one of the most lethal and aggressive cancers. Evidence has shown that the tumorigenesis of ATC is a multistep process involving the accumulation of genetic and epigenetic changes. Several studies have suggested that long non-coding RNAs (lncRNAs) may play an important role in the development and progression of ATC. In this article, we have collected the published reports about the role of lncRNAs in ATC.

METHODS

"Scopus", "Web of Science", "PubMed", "Embase", etc. were systematically searched for articles published since 1990 to 2020 in English language, using the predefined keywords.

RESULTS

961 papers were reviewed and finally 33 papers which fulfilled the inclusion and exclusion criteria were selected. Based on this systematic review, among a lot of evidences on examining the function of lncRNAs in thyroid cancer, there are only a small number of studies about the role of lncRNAs and their molecular mechanisms in the pathogenesis of ATC.

CONCLUSIONS

lncRNAs play a crucial role in regulation of different processes involved in the development and progression of ATC. Currently, just a few lncRNAs have been identified in ATC that may serve as prognosis markers such as GAS5, MIR22HG, and CASC2. Also, because of the dysregulation of Klhl14-AS, HOTAIRM1, and PCA3 during ATC development and progression, they may act as therapeutic targets. However, for most lncRNAs, only a single experiment has evaluated the expression profile in ATC tissues/cells. Therefore, further functional studies and expression profiling is needed to resolve this limitation and identify novel and valid biomarkers.

Anaplastic thyroid cancer: How far can we go?

Globally, thyroid cancer accounts for 2 % of all cancer diagnoses, and can be classified as well-differentiated or undifferentiated. Currently, differentiated thyroid carcinomas have good prognoses, and can be treated with a combination of therapies, including surgical thyroidectomy, radioactive iodine therapy and hormone-based therapy. On the other hand, anaplastic thyroid carcinoma, a subtype of undifferentiated thyroid carcinoma characterized by the loss of thyroid-like phenotype and function, does not respond to either radioactive iodine or hormone therapies. In most cases, anaplastic thyroid carcinomas are diagnosed in later stages of the disease, deeming them inoperable, and showing poor response rates to systemic chemotherapy. Recently, treatment courses using multiple-target agents are being explored and clinical trials have shown very promising results, such as overall survival rates, progression-free survival and tumor shrinkage. This review is focused on thyroid carcinomas, with particular focus on anaplastic thyroid carcinoma, exploring its undifferentiated nature. Special interest will be given to the treatment approaches currently available and respective obstacles or drawbacks. Our purpose is to contribute to understand why this malignancy presents low responsiveness to current treatments, while overviewing novel therapies and clinical trials.

Impact of Age-Related Genetic Differences on the Therapeutic Outcome of Papillary Thyroid Cancer

The incidence of papillary thyroid carcinoma (PTC) has been increasing worldwide. PTC is the most common type of differentiated thyroid cancer and usually shows good prognosis. However, some PTC is driven to advanced stage by epithelial-mesenchymal transition (EMT)-mediated drug resistance, which is particularly noticeable in pediatric patients. There are limited options for systemic treatment, necessitating development of new clinical approaches. Here, we aimed to clarify genetic differences due to age of patients with PTC, and thereby aid in developing novel therapeutics. Patients with biochemically and histologically confirmed PTC were included in this study. PTC cells were acquired from young and older patients showing drug resistance, and were compared via microarray analysis. Cellular proliferation and other properties were determined after treatments with lenvatinib and sorafenib. In vivo, tumor volume and other properties were examined using a mouse xenograft model. Lenvatinib-treated group showed obvious suppression of markers of anti-apoptosis, EMT, and the FGFR signaling pathway, compared with control and Sorafenib-treated group. In the xenograft models, lenvatinib treatment induced significant tumor shrinkage and blocked the proto-oncogene Bcl-2 (B cell lymphoma/leukemia gene-2) and FGFR signaling pathway, along with reduced levels of EMT markers, compared with control and Sorafenib-treated group. Our findings clarify the age-dependent characteristics of pediatric PTC, giving insights into the relationship between young age and poor prognosis. Furthermore, it provides a basis for developing novel therapeutics tailored to the age at diagnosis.

Extensive lymphatic spread of papillary thyroid microcarcinoma is associated with an increase in expression of genes involved in epithelial-mesenchymal transition and cancer stem cell-like properties

Background

Active surveillance is an alternative management for patents with low‐risk papillary thyroid microcarcinoma (PTMC); however, there is an absence of specific molecular markers that predict its progression. We compared gene expression patterns between PTMC with lateral neck‐node metastasis (N1b) and PTMC‐lacking nodal metastasis (N0).

Methods

We performed oligonucleotide microarray analysis in three PTMCs without cervical lymph‐node metastases (N0), and five PTMCs with lateral neck‐node metastasis (N1b) at initial diagnosis, using an Illumina HumanHT‐12 v4.0 Expression BeadChip. Quantitative real‐time PCR (qPCR) and western blot analysis confirmed microarray data. We performed immunohistochemistry (IHC) to confirm protein overexpression in samples from 20 N0 and 24 N1b PTMC patients who underwent thyroidectomy.

Results

Microarray analyses identified 52 probes corresponding to 45 genes. Expression of these genes differed significantly between the two PTMC groups. Forty genes were significantly upregulated and five genes were downregulated in N1b PTMC compared to N0. Four genes related to epithelial‐to‐mesenchymal transition (EMT) and stem cell markers, including ALDH1A3, TM4SF1, PROM1, and CAV1 were significantly upregulated in N1b PTMCs. Real‐time qPCR confirmed this expression and western blot analysis confirmed higher expression of ALDH1A3, TM4SF1, PROM1, and CAV1 in N1b than in N0 PTMCs. IHC indicated overexpression of ALDH1A3 and CAV1 in N1b compared to N0 PTMCs.

Conclusions

Genes related to EMT and thyroid cancer stem cell‐like properties are upregulated in early extensive lymphatic spread of PTMC.

Inhibition of Cancer Stem-Like Phenotype by Curcumin and Deguelin in CAL-62 Anaplastic Thyroid Cancer Cells

Background:

Anaplastic Thyroid Cancer (ATC) is one of the most lethal and aggressive human malignancies. Studies have shown that Cancer Stem-Cell (CSC) phenotype is mainly responsible for ATC aggressiveness. Cytostatic compounds are mostly ineffective because of multidrug resistance mechanisms driven by the CSC phenotype. Taxanes have limited efficacy. Recently, CSC inhibition using plant-derived, less toxic compounds, which have anti-cancer efficacy, has become a novel treatment modality. The aim of the study was to evaluate the anti-cancer activity of two natural compounds (curcumin and deguelin) on ATC cells and their CSC properties. In addition, the efficacies of these compounds were compared with that of docetaxel.

Methods:

Besides control, five treatment groups were formed. ATC cells (CAL-62) were treated with curcumin, deguelin, docetaxel, and their combinations (curcumin+docetaxel, deguelin+docetaxel) at previously determined IC50 doses. Stemness was analyzed by quantitative estimation of sphere formation in matrigel, expression of several cell surface markers (CD133, CD90, Nanog, and OCT3/4) using flow cytometry, and quantification of the hypoxic status [Oxidative Stress Index (OSI) and Superoxide Dismutase (SOD) activity]. The anti-cancer efficacies of these compounds and their combinations were evaluated by determining the alterations in the cell cycle, apoptosis, and tumoral cell migration.

Results:

Both the natural compounds (particularly curcumin) significantly suppressed the spheroid formation and cellular motility in matrigel as well as suppressed the accumulation of cells in the G0/1 phase, in which the maximum CSC activity is observed. The compounds did not suppress the expression of CSC markers, but twothirds of the cells expressed CD90. Deguelin was found to be particularly effective in inducing apoptosis similar to docetaxel at IC50 concentrations. Curcumin reduced the OSI and deguelin enhanced the SOD activity, even in docetaxel pre-treated cells.

Conclusion:

A large proportion of anaplastic tumors might consist of heterogeneous CSC population. Curcumin and deguelin have anti-cancer and several anti-stem cell activities against ATC cells. These natural compounds are capable of altering the aggressive behavior of ATC cells through the inhibition of the CSC phenotype. As a novel therapeutic target, CD90 should be investigated in other ATC cell lines and in vivo models.

Targeting the SUMO pathway as a novel treatment for anaplastic thyroid cancer

Cancer stem cells (CSCs) are expanded in anaplastic thyroid cancer (ATC) and standard treatment approaches have failed to improve survival, suggesting a need to specifically target the CSC population. Recent studies in breast and colorectal cancer demonstrated that inhibition of the SUMO pathway repressed CD44 and cleared the CSC population, mediated through SUMO-unconjugated TFAP2A. We sought to evaluate effects of inhibiting the SUMO pathway in ATC. ATC cell lines and primary ATC tumor samples were evaluated. The SUMO pathway was inhibited by knockdown of PIAS1 and use of SUMO inhibitors anacardic acid and PYR-41. The expression of TFAP2A in primary ATC was examined by immunohistochemistry. All ATC cell lines expressed TFAP2A but only 8505C expressed SUMO-conjugated TFAP2A. In 8505C only, inhibition of the SUMO pathway by knockdown of PIAS1 or treatment with SUMO inhibitors repressed expression of CD44 with a concomitant loss of SUMO-conjugated TFAP2A. The effect of SUMO inhibition on CD44 expression was dependent upon TFAP2A. Treatment with SUMO inhibitors resulted in a statistically improved tumor-free survival in mice harboring 8505C xenografts. An examination of primary ATC tissue determined that TFAP2A was expressed in 4 of 11 tumors surveyed. We conclude that inhibition of the SUMO pathway repressed the CSC population, delaying the outgrowth of tumor xenografts in ATC. The effect of SUMO inhibition was dependent upon expression of SUMO-conjugated TFAP2A, which may serve as a molecular marker for therapeutic effects of SUMO inhibitors. The findings provide pre-clinical evidence for development of SUMO inhibitors for the treatment of ATC.

7SK small nuclear RNA transcription level down-regulates in human tumors and stem cells

The small nuclear noncoding RNA (snRNA) 7SK is a highly conserved noncoding RNA of 331 nucleotides in animals, which is present in a nuclear ribonucleoprotein complex with proteins such as methylphosphate capping enzyme (MePCE), hexamethylene bisacetamide-inducible proteins 1 and 2 (HEXIM1 and HEXIM2) and La-related protein 7 (Larp7). Regulating the activity of the positive transcription elongation factor b (P-TEFb) is the key function of 7SK noncoding RNA. Recently, we have shown that 7SK snRNA over-expression reduces human embryonic kidney 293T cell line viability. Here, we attempt to monitor the expression level of 7SK snRNA in different human cell lines and cancer tissues. Examination of 7SK transcription either in cell lines or in different malignant tissues including blood (CML), breast and colon showed that 7SK expression significantly down-regulated in cancer. Similar to human cancer tissues and cell lines, 7SK transcriptional level decreased in stem cells in comparison with differentiated cell types. In this regard, over-expression of 7SK snRNA might be a powerful tool for blocking cancer progression by controlling the activity of P-TEFb.