Ovarian Cancer Stem Cells: Characterization and Role in Tumorigenesis

Spotlight on New Hallmarks of Drug-Resistance towards Personalized Care for Epithelial Ovarian Cancer

Epithelial ovarian cancer (EOC) is the deadliest gynecological malignancy worldwide. Despite the latest advances, a major clinical issue in EOC is the disappointing prognosis related to chemoresistance in almost one-third of cases. Drug resistance relies on heterogeneous cancer stem cells (CSCs), endowed with tumor-initiating potential, leading to relapse. No biomarkers of chemoresistance have been validated yet. Recently, major signaling pathways, micro ribonucleic acids (miRNAs), and circulating tumor cells (CTCs) have been advocated as putative biomarkers and potential therapeutic targets for drug resistance. However, further investigation is mandatory before their routine implementation. In accordance with the increasing rate of therapeutic efforts in EOC, the need for biomarker-driven personalized therapies is growing. This review aims to discuss the emerging hallmarks of drug resistance with an in-depth insight into the underlying molecular mechanisms lacking so far. Finally, a glimpse of novel therapeutic avenues and future challenges will be provided.

The Role of Cancer Stem Cell Markers in Ovarian Cancer

Ovarian cancer is the most lethal gynaecological cancer and the eighth most common female cancer. The early diagnosis of ovarian cancer remains a clinical problem despite the significant development of technology. Nearly 70% of patients with ovarian cancer are diagnosed with stages III-IV metastatic disease. Reliable diagnostic and prognostic biomarkers are currently lacking. Ovarian cancer recurrence and resistance to chemotherapy pose vital problems and translate into poor outcomes. Cancer stem cells appear to be responsible for tumour recurrence resulting from chemotherapeutic resistance. These cells are also crucial for tumour initiation due to the ability to self-renew, differentiate, avoid immune destruction, and promote inflammation and angiogenesis. Studies have confirmed an association between CSC occurrence and resistance to chemotherapy, subsequent metastases, and cancer relapses. Therefore, the elimination of CSCs appears important for overcoming drug resistance and improving prognoses. This review focuses on the expression of selected ovarian CSC markers, including CD133, CD44, CD24, CD117, and aldehyde dehydrogenase 1, which show potential prognostic significance. Some markers expressed on the surface of CSCs correlate with clinical features and can be used for the diagnosis and prognosis of ovarian cancer. However, due to the heterogeneity and plasticity of CSCs, the determination of specific CSC phenotypes is difficult.

Inflammation Control and Tumor Growth Inhibition of Ovarian Cancer by Targeting Adhesion Molecules of E-Selectin

Objective: The aim is to use E-selectin-binding peptide (ESBP) to actively recognize E-selectin, so allowing a drug delivery system to actively recognize the cells and inhibit the tumor growth of ovarian cancer by targeting adhesion molecules of E-selectin. An ovarian-cancer-directed drug delivery system was designed based on the high affinity of E-selectin-binding peptide (ESBP) to E-selectin. The effects and mechanisms of ESBP-bovine serum albumin (BSA) polymerized nanoparticles were investigated. Methods: BSA polymerized nanoparticles (BSANPs) and ESBP-BSANPs-paclitaxel (PTX) were prepared and their characteristics were measured. The in vitro targetability and cytotoxicity of ESBP-BSANPs-PTX were evaluated through in vitro drug uptake and MTT experiments. The mechanisms of ESBP-BSANPs-PTX were investigated via apoptosis, wound healing and immunohistochemistry assays. The in vivo targeting properties and drug effects were observed in a mouse tumor-bearing model. Results: In vitro experiments revealed an increase in the uptake of ESBP-BSANPs-FITC. The cytotoxicity of ESBP-BSANPs-PTX in A2780/CP70, HUVEC, RAW264.7 and ID8 cells was higher than that of PTX alone. ESBP-BSANPs-PTX increased cell apoptosis in a dose-dependent manner and exhibited a greater ability to inhibit cell migration than BSANPs-PTX. In vivo experiments demonstrated the targetability and good effects of ESBP-BSANPs. Conclusions: ESBP-BSANPs-PTX improve PTX targetability, provide tumor-specific and potent therapeutic activities, and show promise for the development of agents in preclinical epithelial ovarian cancer.

CircNFIX stimulates the proliferation, invasion, and stemness properties of ovarian cancer cells by enhancing SH3RF3 mRNA stability via binding LIN28B

We aimed to study the regulatory roles and mechanism of circular nuclear factor IX (circNFIX) in cancer growth and stemness properties of ovarian cancer (OC). CircNFIX and SH3RF3 levels in OC tissues and cells were tested by quantitative real-time PCR. RNase R treatment quantified circNFIX RNA stability. Molecular interaction among circNFIX, LIN28B, and SH3RF3 was predicted by bioinformatics software and validated through RNA immunoprecipitation (RIP) assay. The gain- or loss-experiments of circNFIX on capabilities of metastasis and stemness in vitro were assessed using Cell Counting Kit-8, Transwell, western blot, and sphere-formation assays. CircNFIX and SH3RF3 were markedly elevated in OC tissues and OC cells. Knocking down circNFIX repressed the proliferation, migration, invasion, and stemness properties of A2780 and SKOV3 cells. The RIP assay verified the direct binding relationship between LIN28B, circNFIX, and SH3RF3. Additionally, overexpression of circNFIX elevated the SH3RF3 expression, while this effect was reversed by LIN28B silence. Rescue experiments demonstrated that the overexpression of SH3RF3 reversed the knockdown of circNFIX on OC cells' proliferation, metastasis, and stemness properties. CircNFIX improved the mRNA stability and translation of SH3RF3 via recruiting LIN28B, thus promoting the proliferation, invasion, and stemness properties of OC cells in vitro.

Cribriform morular thyroid carcinoma: a case report with pathological, immunohistochemical, and molecular findings suggesting an origin from follicular cells (or their endodermal precursors)

Cribriform morular thyroid carcinoma (CMTC) is a rare malignant thyroid tumor with a peculiar growth pattern secondary to permanent activation of the WNT/β-catenin pathway. CMTC may be associated with familial adenomatous polyposis or sporadic; it shares morphological features with papillary thyroid carcinoma (PTC) and was considered a variant of PTC in the 2017 WHO classification of tumors of endocrine organs. The new 5th edition of the WHO classification of endocrine and neuroendocrine tumors considered CMTC an independent thyroid neoplasm of uncertain histogenesis. A thymic/ultimobranchial pouch-related differentiation in CMTC has been recently postulated. We, however, have used the pathological and immunohistochemical features of this case of CMTC with 2 novel oncogenic somatic variants (c.3428_3429insA, p.(Tyr1143Ter) and c.3565del, p. (Ser1189Hisfs*76) of the APC gene to propose an origin from follicular cells (or their endodermal precursors). As usual in CMTC, the morular component of this tumor was positive for CDX2. Given the fact that WNT/β-catenin signaling, through CDX2, activates large intestine and small intestine gene expression, we postulate that in CMTC, the tumor cells have their terminal differentiation blocked, thus showing a peculiar primitive endodermal (intestinal-like) phenotype negative for sodium-iodide symporter, thyroperoxidase, and thyroglobulin. Establishing the histogenesis of CMTC is very relevant for the development of appropriate therapies of redifferentiation, particularly in patients where the tumor cannot be controlled by surgery.

P-Element-Induced Wimpy Testis Proteins and P-Element-Induced Wimpy Testis-Interacting RNAs Expression in Ovarian Cancer Stem Cells

Background: P-element-induced wimpy testis (PIWI)-interacting RNAs (piRNAs) are a type of noncoding RNA and are predominantly expressed in germline cells. piRNAs function as gene regulators and potential biomarkers for the development of a number of malignancies. The biological importance of piRNAs in ovarian cancer is still unknown. In this study, we investigated the expression of piRNAs in ovarian cancer stem cells and compared it with that in adherent cells. Methods: To assess changes in the expression levels of PIWIL1/HIWI, PIWIL2/HILI, PIWIL3, and PIWIL4/HIWI2, we used quantitative reverse-transcription polymerase chain reaction (RT-qPCR) analysis. Changes in piRNA expression levels in ovarian cancer stem cells were analyzed using Arraystar piRNA microarray screening. Gene Ontology (GO) enrichment analysis was conducted to determine the potential functions of piRNAs. Results: Using microarray analysis, we identified a cohort of differentially expressed piRNAs. Fifteen piRNAs, including DQ570763 and DQ597396, were downregulated, and 58 piRNAs were upregulated when compared with those in adherent A2780 and SKOV3 cells (p > 0.05, >2.0, respectively). GO functions of the downregulated piRNAs (DQ570763 and DQ570797) suggest that their roles are commonly associated with the Golgi apparatus. In addition, A2780-SP and SKOV3-SP cells had higher PIWIL3 and PIWIL4 mRNA levels than adherent cells (A2780 and SKOV3). Moreover, we determined, using receiver operating characteristic plot, that the expression level of PIWIL4 was lower in responders than in nonresponders after treatment with platins in patients with ovarian cancer. Finally, in ovarian cancer, PIWIL4 expression was associated with somatic mutations of dynein axonemal heavy chain 2, signal induced proliferation associated 1 like 2, YTH N6-methyladenosine RNA-binding protein 1, TBC1 domain family member 8, and LPS responsive Beige-like anchor protein. Conclusion: Our study showed that PIWI proteins and piRNAs are potential diagnostic and prognostic biomarkers for ovarian cancer.

Wnt antagonist as therapeutic targets in ovarian cancer

Ovarian cancer is a fatal malignancy in women with a low survival rate that demands new therapeutic paradigms. Cancer cells acquire various exclusive alterations to proliferate, invade, metastasize, and escape cell death, acting independently of growth-inducing or growth-inhibiting signals. The nature of cellular signaling in tumorigenesis is interwoven. Wnt signaling is an evolutionarily conserved signaling cascade that has been shown to regulate ovarian cancer pathogenesis. The molecular mechanism of Wnt signaling underlying the development of ovarian cancer, drug resistance, and relapse is not completely understood. Extracellularly secreted Wnt signaling inhibitors are crucial regulators of ovarian cancer tumorigenesis and malignant properties of cancer stem cells. Wnt inhibitors arbitrated modifications affecting Wnt pathway proteins on the cell membranes, in the cytoplasm, and in the nucleus have been shown to span essential contributions in the initiation, progression, and chemoresistance of ovarian cancer. Although many extrinsic inhibitors developed targeting the downstream components of the Wnt signaling pathway, investigating the molecular mechanisms of endogenous secreted inhibitors might substantiate prognostic or therapeutic biomarkers development. Given the importance of Wnt signaling in ovarian cancer, more systematic studies combined with clinical studies are requisite to probe the precise mechanistic interactions of Wnt antagonists in ovarian cancer. This review outlines the latest progress on the Wnt antagonists and ovarian cancer-specific regulators such as micro-RNAs, small molecules, and drugs regulating these Wnt antagonists in ovarian tumourigenesis.

Cancer Stem Cells in Ovarian Cancer-A Source of Tumor Success and a Challenging Target for Novel Therapies

Ovarian cancer is the most lethal neoplasm of the female genital organs. Despite indisputable progress in the treatment of ovarian cancer, the problems of chemo-resistance and recurrent disease are the main obstacles for successful therapy. One of the main reasons for this is the presence of a specific cell population of cancer stem cells. The aim of this review is to show the most contemporary knowledge concerning the biology of ovarian cancer stem cells (OCSCs) and their impact on chemo-resistance and prognosis in ovarian cancer patients, as well as to present the treatment options targeted exclusively on the OCSCs. The review presents data concerning the role of cancer stem cells in general and then concentrates on OCSCs. The surface and intracellular OCSCs markers and their meaning both for cancer biology and clinical prognosis, signaling pathways specifically activated in OCSCs, the genetic and epigenetic regulation of OCSCs function including the recent studies on the non-coding RNA regulation, cooperation between OCSCs and the tumor microenvironment (ovarian cancer niche) including very specific environment such as ascites fluid, the role of shear stress, autophagy and metabolic changes for the function of OCSCs, and finally mechanisms of OCSCs escape from immune surveillance, are described and discussed extensively. The possibilities of anti-OCSCs therapy both in experimental settings and in clinical trials are presented, including the recent II phase clinical trials and immunotherapy. OCSCs are a unique population of cancer cells showing a great plasticity, self-renewal potential and resistance against anti-cancer treatment. They are responsible for the progression and recurrence of the tumor. Several completed and ongoing clinical trials have tested different anti-OCSCs drugs which, however, have shown unsatisfactory efficacy in most cases. We propose a novel approach to ovarian cancer diagnosis and therapy.

[Targeted killing of CD133+ lung cancer stem cells using paclitaxel-loaded PLGA-PEG nanoparticles with CD133 aptamers]

OBJECTIVE

To construct a polylactic acid-glycolic acid-polyethylene glycol (PLGA-PEG) nanocarrier (N-Pac-CD133) coupled with a CD133 nucleic acid aptamer carrying paclitaxel for eliminating lung cancer stem cells (CSCs).

METHODS

Paclitaxel-loaded N-Pac-CD133 was prepared using the emulsion/solvent evaporation method and characterized. CD133⁺ lung CSCs were separated by magnetic bead separation and identified for their biological behaviors and gene expression profile. The efficiency of paclitaxel-loaded N-Pac-CD133 for targeted killing of lung cancer cells was assessed in vitro. SCID mice were inoculated with A549 cells and received injections of normal saline, empty nanocarrier linked with CD133 aptamer (N-CD133), paclitaxel, paclitaxel-loaded nanocarrier (N-Pac) or paclitaxel-loaded N-Pac-CD133 (n=8, 5 mg/kg paclitaxel) on days 10, 15 and 20, and the tumor weight and body weight of the mice were measured on day 40.

RESULTS

Paclitaxel-loaded N-Pac-CD133 showed a particle size of about 100 nm with a high encapsulation efficiency (>80%) and drug loading rate (>8%), and was capable of sustained drug release within 48 h. The CD133⁺ cell population in lung cancer cells showed the characteristic features of lung CSCs, including faster growth rate (30 days, P=0.001) and high expressions of tumor stem cell markers OV6(P < 0.001), CD133 (P=0.001), OCT3/4 (P=0.002), EpCAM (P=0.04), NANOG (P=0.005) and CD44 (P=0.02). Compared with N-Pac and free paclitaxel, paclitaxel-loaded N-Pac-CD133 showed significantly enhanced targeting ability and cytotoxicity against lung CSCs in vitro (P < 0.001) and significantly reduced the formation of tumor spheres (P < 0.001). In the tumor-bearing mice, paclitaxel-loaded N-Pac-CD133 showed the strongest effects in reducing the tumor mass among all the treatments (P < 0.001).

CONCLUSION

CD133 aptamer can promote targeted delivery of paclitaxel to allow targeted killing of CD133⁺ lung CSCs. N-Pac-CD133 loaded with paclitaxel may provide an effective treatment for lung cancer by targeting the lung cancer stem cells.