All-trans retinoic acid suppresses malignant characteristics of CD133-positive thyroid cancer stem cells and induces apoptosis

Novel Anti-Cancer Stem Cell Compounds: A Comprehensive Review

Cancer stem cells (CSCs) possess a significant ability to renew themselves, which gives them a strong capacity to form tumors and expand to encompass additional body areas. In addition, they possess inherent resistance to chemotherapy and radiation therapies used to treat many forms of cancer. Scientists have focused on investigating the signaling pathways that are highly linked to the ability of CSCs to renew themselves and maintain their stem cell properties. The pathways encompassed are Notch, Wnt/β-catenin, hedgehog, STAT3, NF-κB, PI-3K/Akt/mTOR, sirtuin, ALDH, MDM2, and ROS. Recent studies indicate that directing efforts towards CSC cells is essential in eradicating the overall cancer cell population and reducing the likelihood of tumor metastasis. As our comprehension of the mechanisms that stimulate CSC activity, growth, and resistance to chemotherapy advances, the discovery of therapeutic drugs specifically targeting CSCs, such as small-molecule compounds, holds the potential to revolutionize cancer therapy. This review article examines and analyzes the novel anti-CSC compounds that have demonstrated effective and selective targeting of pathways associated with the renewal and stemness of CSCs. We also discussed their special drug metabolism and absorption mechanisms. CSCs have been the subject of much study in cancer biology. As a possible treatment for malignancies, small-molecule drugs that target CSCs are gaining more and more attention. This article provides a comprehensive review of the current state of key small-molecule compounds, summarizes their recent developments, and anticipates the future discovery of even more potent and targeted compounds, opening up new avenues for cancer treatment.

Potential Role of Nrf2, HER2, and ALDH in Cancer Stem Cells: A Narrative Review

Cancer is one of the main causes of death among humans, second only to cardiovascular diseases. In recent years, numerous studies have been conducted on the pathophysiology of cancer, and it has been established that this disease is developed by a group of stem cells known as cancer stem cells (CSCs). Thus, cancer is considered a stem cell disease; however, there is no comprehensive consensus about the characteristics of these cells. Several different signaling pathways including Notch, Hedgehog, transforming growth factor-β (TGF-β), and WNT/β-catenin pathways cause the self-renewal of CSCs. CSCs change their metabolic pathways in order to access easy energy. Therefore, one of the key objectives of researchers in cancer treatment is to destroy CSCs. Nuclear factor erythroid 2-related factor 2 (Nrf2) plays an essential role in the protection of CSCs from reactive oxygen species (ROS) and chemotherapeutic agents by regulating antioxidants and detoxification enzymes. Human epidermal growth factor receptor 2 (HER2) is a member of the tyrosine kinase receptor family, which contributes to the protection of cancer cells against treatment and implicated in the invasion, epithelial-mesenchymal transition (EMT), and tumorigenesis. Aldehyde dehydrogenases (ALDHs) are highly active in CSCs and protect the cells against damage caused by active aldehydes through the regulation of aldehyde metabolism. On the other hand, ALDHs promote the formation and maintenance of tumor cells and lead to drug resistance in tumors through the activation of various signaling pathways, such as the ALDH1A1/HIF-1α/VEGF axis and Wnt/β-catenin, as well as changing the intracellular pH value. Given the growing body of information in this field, in the present narrative review, we attempted to shed light on the function of Nrf2, HER2, and ALDH in CSCs.

Is beta-carotene consumption associated with thyroid hormone levels?

The thyroid hormones play a pivotal role in various physiological processes, including growth, metabolism regulation, and reproduction. While non-modifiable factors are known to impact thyroid function, such as genetics and age, nutritional factors are also important. Diets rich in selenium and iodine are conventionally acknowledged to be beneficial for the production and release of thyroid hormones. Recent studies have suggested a potential link between beta-carotene, a precursor to vitamin A (retinol), and thyroid function. Beta-carotene is known for its antioxidant properties and has been shown to play a role in the prevention of various clinical conditions such as cancer and cardiovascular and neurological diseases. However, its impact on thyroid function is still unclear. Some studies have suggested a positive association between beta-carotene levels and thyroid function, while others have found no significant effect. Conversely, the hormone produced by the thyroid gland, thyroxine, enhances the conversion of beta-carotene to retinol. Furthermore, vitamin A derivatives are being explored as potential therapeutic options for thyroid malignancies. In this review, we highlight the mechanisms through which beta-carotene/retinol and thyroid hormones interact and review the findings of clinical studies examining the association between beta-carotene consumption and thyroid hormone levels. Our review underscores the need for further research to clarify the relationship between beta-carotene and thyroid function.

An update of Nrf2 activators and inhibitors in cancer prevention/promotion

NF-E2-related factor 2 (Nrf2) protein is a basic-region leucine zipper transcription factor that defends against endogenous or exogenous stressors. By inducing several cytoprotective and detoxifying gene expressions, Nrf2 can increase the sensitivity of the cells to oxidants and electrophiles. Transient Nrf2 activation, by its specific activators, has protective roles against carcinogenesis and cancer development. However, permanent activation of Nrf2 promotes various cancer properties, comprising malignant progression, chemo/radio resistance, and poor patient prognosis. Taken together, these findings suggest that reaching an optimal balance between paradoxical functions of Nrf2 in malignancy may render a selective improvement to identify therapeutic strategies in cancer treatment. In this review, we describe lately discovered Nrf2 inducers and inhibitors, and their chemopreventive and/or anticancer activities.

The Nrf2 pathway signifies one of the most significant cell defense procedures against exogenous or endogenous stressors. Certainly, by increasing the expression of several cytoprotective genes, the transcription factor Nrf2 can shelter cells and tissues from multiple sources of damage including electrophilic, xenobiotic, metabolic, and oxidative stress. Notably, the aberrant activation or accumulation of Nrf2, a common event in many tumors, confers a selective advantage to cancer cells and is connected to malignant progression, therapy resistance, and poor prognosis. Therefore, lately, Nrf2 has arisen as a hopeful target in treatment of cancer, and many struggles have been made to detect therapeutic strategies intended at disrupting its pro-oncogenic role. By summarizing the outcomes from past and recent studies, this review provided an overview concerning the Nrf2 pathway and the molecular mechanisms causing Nrf2 hyperactivation in cancer cells. Finally, this paper also described some of the most promising therapeutic approaches that have been successfully employed to counteract Nrf2 activity in tumors, with a particular emphasis on the development of natural compounds and the adoption of drug repurposing strategies.

All-trans-retinoic acid induces RARB-dependent apoptosis via ROS induction and enhances cisplatin sensitivity by NRF2 downregulation in cholangiocarcinoma cells

All-trans-retinoic acid (ATRA) has been clinically used to treat acute promyelocytic leukemia and is being studied to treat other types of cancer; however, the therapeutic role and mechanism of ATRA against cholangiocarcinoma (CCA) remain unclear. The present study investigated the cytotoxic effect and underlying mechanisms of ATRA on CCA cell lines. Cell viability was evaluated by sulforhodamine B assay. Intracellular reactive oxygen species (ROS) levels were assessed by dihydroethidium assay. Apoptosis analysis was performed by flow cytometry. The pathways of apoptotic cell death induction were examined using enzymatic caspase activity assay. Proteins associated with apoptosis were evaluated by western blotting. The effects on gene expression were analyzed by reverse transcription-quantitative PCR analysis. ATRA induced a concentration- and time-dependent toxicity in CCA cells. Furthermore, when the cytotoxicity of ATRA against retinoic acid receptor (RAR)-deficient cells was assessed, it was revealed that ATRA cytotoxicity was RARB-dependent. Following ATRA treatment, there was a significant accumulation of cellular ROS and ATRA-induced ROS generation led to an increase in the expression levels of apoptosis-inducing proteins and intrinsic apoptosis. Pre-treatment with ROS scavengers could diminish the apoptotic effect of ATRA, suggesting that ROS and mitochondria may have an essential role in the induction of apoptosis. Furthermore, following ATRA treatment, an increase in cellular ROS content was associated with suppressing nuclear factor erythroid 2-related factor 2 (NFE2L2 or NRF2) and NRF2-downstream active genes. ATRA also suppressed cisplatin-induced NRF2 expression, suggesting that the enhancement of cisplatin cytotoxicity by ATRA may be associated with the downregulation of NRF2 signaling. In conclusion, the results of the present study demonstrated that ATRA could be repurposed as an alternative drug for CCA therapy.

Retinoids as anti-cancer agents and their mechanisms of action

Retinoids (vitamin A) have been reported extensively for anti-cancer properties due to their high receptor-binding affinities and gene regulation abilities. However, the anti-cancer potential of retinoids has not been reviewed in recent years. Thus, this review focused on the anti-cancer effects of retinoids and their synergistic effects with other drugs, together with their mechanisms of action in different types of cancers reported in the past five years. The retinoids were well studied in breast cancer, melanoma, and colorectal cancer. Synthetic retinoids have shown higher selectivity, stronger effectiveness, and lower toxicity than endogenous retinoids. Interestingly, the combination treatment of endogenous retinoids with chemotherapy drugs showed enhanced anti-cancer effects. The mechanisms of action reported for retinoids mainly involved the RAR/RXR signaling pathway. However, limited clinical studies were conducted in recent years. Thus, retinoids which are highly potential anti-cancer agents are worth further study in clinical, especially as a combination therapy with chemotherapy drugs.

The Multifaceted Role of Aldehyde Dehydrogenases in Prostate Cancer Stem Cells

Cancer stem cells (CSCs) are the only tumor cells possessing self-renewal and differentiation properties, making them an engine of tumor progression and a source of tumor regrowth after treatment. Conventional therapies eliminate most non-CSCs, while CSCs often remain radiation and drug resistant, leading to tumor relapse and metastases. Thus, targeting CSCs might be a powerful tool to overcome tumor resistance and increase the efficiency of current cancer treatment strategies. The identification and isolation of the CSC population based on its high aldehyde dehydrogenase activity (ALDH) is widely accepted for prostate cancer (PCa) and many other solid tumors. In PCa, several ALDH genes contribute to the ALDH activity, which can be measured in the enzymatic assay by converting 4, 4-difluoro-4-bora-3a, 4a-diaza-s-indacene (BODIPY) aminoacetaldehyde (BAAA) into the fluorescent product BODIPY-aminoacetate (BAA). Although each ALDH isoform plays an individual role in PCa biology, their mutual functional interplay also contributes to PCa progression. Thus, ALDH proteins are markers and functional regulators of CSC properties, representing an attractive target for cancer treatment. In this review, we discuss the current state of research regarding the role of individual ALDH isoforms in PCa development and progression, their possible therapeutic targeting, and provide an outlook for the future advances in this field.

Expression of cancer stem cell markers in tall cell variant papillary thyroid cancer identifies a molecular profile predictive of recurrence in classic papillary thyroid cancer

BACKGROUND

Tall cell variant of papillary thyroid carcinoma is an aggressive subtype of papillary thyroid carcinoma. We examined expression of cancer stem cell markers in tall cell variant compared with other well-differentiated thyroid cancers.

METHODS

Expression of cancer stem cell markers was examined in 572 thyroid tumors from The Cancer Genome Atlas Thyroid Cancer database and tall cell variant and papillary thyroid carcinoma tumors by immunohistochemistry.

RESULTS

Expression of the PROM1 gene, encoding the cancer stem cell marker CD133, was elevated in tall cell variant compared to classic papillary thyroid carcinoma in a large cohort of unmatched samples from The Cancer Genome Atlas Thyroid Cancer database (P < .001). By immunohistochemistry in age and stage matched samples, CD133 protein was confirmed to be significantly increased in tall cell variant versus classic papillary thyroid carcinoma (P = .006). Analyzing all thyroid cancers, high PROM1 expression was associated with worse disease-specific survival. Optimal cutoffs were determined to define a tall cell variant-like cancer stem cell signature characterized by high PROM1, high ALDH1A3, and low CD24 expression. Classic papillary thyroid carcinoma with a tall cell variant-like gene signature had worse recurrence disease-free survival compared to classic papillary thyroid carcinoma with a non-tall cell variant signature (P = .02).

CONCLUSION

Tall cell variant of papillary thyroid carcinoma has increased expression of cancer stem cell markers compared to classic papillary thyroid carcinoma. The tall cell variant-like cancer stem cell gene signature identified a molecular subtype of classic papillary thyroid carcinoma that has a worse recurrence-free survival.

Induction Therapy of Retinoic Acid with a Temozolomide-Loaded Gold Nanoparticle-Associated Ultrasound Effect on Glioblastoma Cancer Stem-Like Colonies

Glioblastoma multiforme (GBM) is the most aggressive glioma. The treatment response is always low, and the condition is typically rapidly fatal. The undifferentiated and self-renewal characteristics of cancer stem cells (CSCs) have been reported, and their potential contribution may cause tumor initiation, recurrence, metastasis, and therapeutic resistance. In particular, glioblastoma stem-like cells exhibit highly invasive properties and drug resistance, serving as a model for the development of novel therapeutic strategies. Induction therapy provides an alternative therapeutic strategy to eliminate the stem cell properties of CSCs and enhance therapeutic sensitivity. The differentiated cells may lose their self-renewal ability, downregulate stem cell-related genes and drug resistance genes, and enhance anticancer drug sensitivity. Therefore, the purpose of this study is to establish a niche for glioblastoma stem-like cell selection as a platform and facilitate the assessment of differentiation therapy on GBM cancer stem-like colonies by retinoic acid (RA) with temozolomide (TMZ)-loaded gold nanoparticles (GNPs) associated with low-intensity ultrasound (LIUS). Herein, a hyaluronic acid-based material system was used to isolate GBM cancer stem-like colonies. Colony formation, size determination, stem cell-related marker expression, and GBM cancer stem-like cell marker expression with the culture period were identified. The effect of TMZ on GBM stem-like colonies on HA-based material systems was also determined, and the results revealed that drug resistance was highly enhanced in GBM colonies compared with that in the control cell population. In addition, GBM colonies also exhibited a significant increase in breast cancer resistance protein expression, which is consistent with the drug resistance effect. Furthermore, several factors, including LIUS, RA, and GNPs, were used to determine the possibility of induction therapy. RA with TMZ-loaded GNP-associated LIUS stimulation exhibited a significant and synergistic effect on the differentiation effect and drug sensitivity enhancement. The GBM cancer stem-like colony system presents an opportunity for the development of new therapeutic strategies, and this study provides an alternative differentiation therapy for malignant tumors.

All-Trans Retinoic Acid Fosters the Multifarious U87MG Cell Line as a Model of Glioblastoma

Glioblastoma multiforme (GBM) is a primary brain cancer of poor prognosis, with existing treatments remaining essentially palliative. Current GBM therapy fails due to rapid reappearance of the heterogeneous neoplasm, with models suggesting that the recurrent growth is from treatment-resistant glioblastoma stem-like cells (GSCs). Whether GSCs depend on survival/proliferative cues from their surrounding microenvironmental niche, particularly surrounding the leading edge after treatment remains unknown. Simulating human GBM in the laboratory relies on representative cell lines and xenograft models for translational medicine. Due to U87MG source discrepancy and differential proliferation responses to retinoic acid treatment, this study highlights the challenges faced by laboratory scientists working with this representative GBM cell line. Investigating the response to all trans-retinoic acid (ATRA) revealed its sequestering of the prominin-1 stem cell marker. ICAM-1 universally present throughout U87MG was enhanced by ATRA, of interest for chemotherapy targeting studies. ATRA triggered diverse expression patterns of long non-coding RNAs PARTICLE and GAS5 in the leading edge and established monolayer growth zone microenvironment. Karyotyping confirmed the female origin of U87MG sourced from Europe. Passaging U87MG revealed the presence of chromosomal anomalies reflective of structural genomic alterations in this glioblastoma cell line. All evidence considered, this study exposes further phenotypic nuances of U87MG which may belie researchers seeking data contributing towards the elusive cure for GBM.

The Great Escape: The Power of Cancer Stem Cells to Evade Programmed Cell Death

Cancer is one of the primary causes of death worldwide. Tumour malignancy is related to tumor heterogeneity, which has been suggested to be due to a small subpopulation of tumor cells named cancer stem cells (CSCs). CSCs exert a key role in metastasis development, tumor recurrence, and also epithelial-mesenchymal transition, apoptotic resistance, self-renewal, tumorigenesis, differentiation, and drug resistance. Several current therapies fail to eradicate tumors due to the ability of CSCs to escape different programmed cell deaths. Thus, developing CSC-selective and programmed death-inducing therapeutic approaches appears to be of primary importance. In this review, we discuss the main programmed cell death occurring in cancer and the promising CSC-targeting agents developed in recent years. Even if the reported studies are encouraging, further investigations are necessary to establish a combination of agents able to eradicate CSCs or inhibit their growth and proliferation.

Targeting Aldehyde Dehydrogenases to Eliminate Cancer Stem Cells in Gynecologic Malignancies

Gynecologic cancers cause over 600,000 deaths annually in women worldwide. The development of chemoresistance after initial rounds of chemotherapy contributes to tumor relapse and death due to gynecologic malignancies. In this regard, cancer stem cells (CSCs), a subpopulation of stem cells with the ability to undergo self-renewal and clonal evolution, play a key role in tumor progression and drug resistance. Aldehyde dehydrogenases (ALDH) are a group of enzymes shown to be robust CSC markers in gynecologic and other malignancies. These enzymes also play functional roles in CSCs, including detoxification of aldehydes, scavenging of reactive oxygen species (ROS), and retinoic acid (RA) signaling, making ALDH an attractive therapeutic target in various clinical scenarios. In this review, we discuss the critical roles of the ALDH in driving stemness in different gynecologic malignancies. We review inhibitors of ALDH, both general and isoform-specific, which have been used to target CSCs in gynecologic cancers. Many of these inhibitors have been shown to be effective in preclinical models of gynecologic malignancies, supporting further development in the clinic. Furthermore, ALDH inhibitors, including 673A and CM037, synergize with chemotherapy to reduce tumor growth. Thus, ALDH-targeted therapies hold promise for improving patient outcomes in gynecologic malignancies.

Targeting the TR4 nuclear receptor-mediated lncTASR/AXL signaling with tretinoin increases the sunitinib sensitivity to better suppress the RCC progression

Renal cell carcinoma (RCC) is one of the most lethal urological tumors. Using sunitinib to improve the survival has become the first-line therapy for metastatic RCC patients. However, the occurrence of sunitinib resistance in the clinical application has curtailed its efficacy. Here we found TR4 nuclear receptor might alter the sunitinib resistance to RCC via altering the TR4/lncTASR/AXL signaling. Mechanism dissection revealed that TR4 could modulate lncTASR (ENST00000600671.1) expression via transcriptional regulation, which might then increase AXL protein expression via enhancing the stability of AXL mRNA to increase the sunitinib resistance in RCC. Human clinical surveys also linked the expression of TR4, lncTASR, and AXL to the RCC survival, and results from multiple RCC cell lines revealed that targeting this newly identified TR4-mediated signaling with small molecules, including tretinoin, metformin, or TR4-shRNAs, all led to increase the sunitinib sensitivity to better suppress the RCC progression, and our preclinical study using the in vivo mouse model further proved tretinoin had a better synergistic effect to increase sunitinib sensitivity to suppress RCC progression. Future successful clinical trials may help in the development of a novel therapy to better suppress the RCC progression.

Role of OCT4 in cancer stem-like cells and chemotherapy resistance

Cancer stem-like cells (CSCs) contribute to the tumorigenicity, progression, and chemoresistance of cancers. It is not known whether CSCs arise from normal stem cells or if they arise from differentiated cancer cells by acquiring self-renewal features. These CSCs share stem cell markers that normal stem cells express. There is a rising interest in octamer-binding transcription factor 4 (OCT4), one of the stem cell factors that are essential in embryogenesis and pluripotency. OCT4 is also overexpressed in CSCs of various cancers. Although the majority of the studies in CSCs reported a positive association between the expression of OCT4 and chemoresistance and an inverse correlation between OCT4 and clinical prognosis, there are studies rebuking these findings, possibly due to the sparsity of stem cells within tumors and the heterogeneity of tumors. In addition, post-translational modification of OCT4 affects its activity and warrants further investigation for its association with chemoresistance and prognosis.

LncRNA PTCSC3 affects drug resistance of anaplastic thyroid cancer through STAT3/INO80 pathway

BACKGROUND

LncRNA PTCSC3 is a tumor suppressor in thyroid cancer, and its role in drug resistance of anaplastic thyroid cancer (ATC) to chemotherapy drug doxorubicin was investigated in this study.

METHODS

Expression of RNA and protein was analyzed by qRT-PCR and western blot, respectively. Flow cytometry was used to analyze the expression rate of CD133⁺ cells. The endogenous expression of related genes was modulated by recombinant plasmids and cell transfection. Combination condition and interaction between PTCSC3 and STAT3 were determined by RIP and RNA pull-down assay, respectively. MTT assay was performed to detect cytotoxicity. Chromatin immunoprecipitation was conducted to identify interactions between STAT3 and DNA promoter of INO80.

RESULTS

LncRNA PTCSC3 was low-expressed in ATC tissues and cells. Over-expressed PTCSC3 inhibited the drug resistance of ATC to doxorubicin. PTCSC3 negatively regulated STAT3, and STAT3 promoted expression of INO80. PTCSC3 regulated INO80 through STAT3. PTCSC3 suppressed stem cells properties and drug resistance of ATC to doxorubicin.

CONCLUSION

LncRNA PTCSC3 inhibits INO80 expression by negatively regulating STAT3, and thereby attenuating drug resistance of ATC to chemotherapy drug doxorubicin.

Extremely Low-Frequency Magnetic Fields and Redox-Responsive Pathways Linked to Cancer Drug Resistance: Insights from Co-Exposure-Based In Vitro Studies

Electrical devices currently used in clinical practice and common household equipments generate extremely low-frequency magnetic fields (ELF-MF) that were classified by the International Agency for Research on Cancer as “possible carcinogenic.” Assuming that ELF-MF plays a role in the carcinogenic process without inducing direct genomic alterations, ELF-MF may be involved in the promotion or progression of cancers. In particular, ELF-MF-induced responses are suspected to activate redox-responsive intracellular signaling or detoxification scavenging systems. In fact, improved protection against oxidative stress and redox-active xenobiotics is thought to provide critical proliferative and survival advantage in tumors. On this basis, an ever-growing research activity worldwide is attempting to establish whether tumor cells may develop multidrug resistance through the activation of essential cytoprotective networks in the presence of ELF fields, and how this might trigger relevant changes in tumor phenotype. This review builds a framework around how the activity of redox-responsive mediators may be controlled by co-exposure to ELF-MF and reactive oxygen species-generating agents in tumor and cancer cells, in order to clarify whether and how such potential molecular targets could help to minimize or neutralize the functional interaction between ELF-MF and malignancies.