Cell surface markers of cancer stem cells: diagnostic macromolecules and targets for drug delivery

Control of mammalian gene expression by modulation of polyA signal cleavage at 5' UTR

The ability to control gene expression in mammalian cells is crucial for safe and efficacious gene therapies and for elucidating gene functions. Current gene regulation systems have limitations such as harmful immune responses or low efficiency. We describe the pA regulator, an RNA-based switch that controls mammalian gene expression through modulation of a synthetic polyA signal (PAS) cleavage introduced into the 5' UTR of a transgene. The cleavage is modulated by a 'dual-mechanism'-(1) aptamer clamping to inhibit PAS cleavage and (2) drug-induced alternative splicing that removes the PAS, both activated by drug binding. This RNA-based methodology circumvents the immune responses observed in other systems and achieves a 900-fold induction with an EC50 of 0.5 µg ml-1 tetracycline (Tc), which is well within the FDA-approved dose range. The pA regulator effectively controls the luciferase transgene in live mice and the endogenous CD133 gene in human cells, in a dose-dependent and reversible manner with long-term stability.

Cancer stem cells and strategies for targeted drug delivery

Cancer stem cells (CSCs) are a small proportion of cancer cells with high tumorigenic activity, self-renewal ability, and multilineage differentiation potential. Standard anti-tumor therapies including conventional chemotherapy, radiation therapy, and molecularly targeted therapies are not effective against CSCs, and often lead to enrichment of CSCs that can result in tumor relapse. Therefore, it is hypothesized that targeting CSCs is key to increasing the efficacy of cancer therapies. In this review, CSC properties including CSC markers, their role in tumor growth, invasiveness, metastasis, and drug resistance, as well as CSC microenvironment are discussed. Further, CSC-targeted strategies including the use of targeted drug delivery systems are examined.

Effect of Cinnamic acid and FOLFOX in diminishing side population and downregulating cancer stem cell markers in colon cancer cell line HT-29

PURPOSE

There is a lot of evidence suggesting that a small subset of cancer cells resistant to conventional chemotherapy and radiotherapy and known as cancer stem cells (CSCs) is responsible for promoting metastasis and cancer relapse. Therefore, targeting and eliminating the CSCs could lead to higher survival rates and a better quality of life. In comparison with conventional chemical drugs that may not be effective against CSCs, phytochemicals are strong anti-CSCs agents. The current study examines the effect of 5-fluorouracil plus oxaliplatin (FOLFOX) as a common chemotherapy drug on colorectal cancer as well as the influence of Cinnamic acid (CINN) as a plant-derived phytochemical on colon cancer stem-like cells in HT-29 adenocarcinoma cell line.

METHODS

The anti-proliferative effect of FOLFOX and CINN was determined using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. Flow cytometry analysis was used for the identification of side population (SP), CD44, and CD133 positive cells. The expression of OCT4, NANOG, ABCB1, and ALDH1A was assessed by RT-PCR.

RESULTS

The FOLFOX and CINN decreased cell viability in certain drug concentrations: IC50 = 5,40 μM oxaliplatin +220 μM 5-fluorouracil, and 13,50 mM for CINN. The CSC-associated markers (OCT4, NANOG, ABCB1, and ALDH1A) and the proportion of cancer stem-like cells (SP cells, CD44, and CD133 positive cells) were downregulated following the treatment of HT-29 adenocarcinoma cell line with IC50 concentrations of FOLFOX and CINN.

CONCLUSION

Our data suggests that CINN, a naturally occurring component, could be more effective than FOLFOX treatment in reducing the cancer stem-like cells and expression of CSC markers from HT-29 colon cancer cells. Graphical abstract ᅟ.

Upregulation of stem cell markers ALDH1A1 and OCT4 as potential biomarkers for the early detection of cervical carcinoma

Previous studies have reported the upregulation of stem cell biomarkers that are associated with tumorigenesis, in particular with cancer infiltration, recurrence and metastasis. Infection by human papilloma virus (HPV) is the main etiopathological factor of cervical carcinogenesis, but the expression of stem cell markers in cervical carcinoma and HPV infection have yet to be investigated so far. A total of 94 cases of fresh cervical tissues, 116 cases of paraffin-embedded cervical specimens and 72 cases of peripheral blood samples were collected from Uighur women who were either diagnosed with cervical squamous cell carcinoma (SCC) or cervical intraepithelial neoplasia (CIN) II-III, or from healthy subjects (negative controls, NC). HPV infection was detected in tissue DNA by polymerase chain reaction (PCR) with a HPV genotyping kit. The mRNA expression levels of aldehyde dehydrogenase 1 family member A1 (ALDH1A1), nanog homeobox (NANOG), POU class 5 homeobox 1 (OCT4), SRY-box 2 (SOX2) and twist family BHLH transcription factor 1 (Twist1) were determined using reverse transcription-quantitative PCR (RT-qPCR). Histological analysis was performed in order to examine the protein expression of ALDH1A1 and OCT4 in paraffin-embedded tissue specimens by immunohistochemical staining and the plasma levels of those two proteins was measured by ELISA. RT-qPCR analysis indicated a significant increase in the mRNA expression of ALDH1A1 and OCT4 in CIN II-III and SCC tissue specimens compared with NC (P<0.05). Although the expression levels of NANOG, SOX2 and Twist1 were significantly higher in SCC compared with NC (P<0.05), no significant difference was revealed in CIN II-III tissues compared with SCC or NC (P>0.05). Subsequent analysis by immunohistochemistry staining confirmed that the upregulation of ALDH1A1 and OCT4 was also significantly increased in SCC and CIN II-III compared with controls at the protein level. Notably, ELISA analysis detected significantly higher levels of ALDH1A1 and OCT4 in the peripheral blood (plasma) of patients with SCC compared with healthy subjects. The upregulation of stem cell markers ALDH1A1 and OCT4 in cervical carcinoma and its precursor lesions, in particular in the peripheral blood, indicates that ALDH1A1 and OCT4 may serve as biomarkers for the early detection of cervical carcinoma or for the monitoring of treatment of patients.

Progress in research of surface markers of liver cancer stem cells

In recent years, cancer stem cell theory, in which a tumor is considered to consist of a handful of tumor stem cells and most common tumor cells, has been put forward by many scientists, which helps researchers to understand cancer from a new perspective. Isolating tumor stem cells is based mainly on their markers and in this way, many kinds of cancer stem cell markers have been confirmed, including live cancer stem cells. Isolating and identifying live cancer stem cells will provide a new hope for curing cancer. This paper mainly discusses seven liver cancer stem cell surface markers and their clinical significance.

Clinicopathological Significance of CD133 and ALDH1 Cancer Stem Cell Marker Expression in Invasive Ductal Breast Carcinoma

BACKGROUND

Biomarkers in breast neoplasms provide invaluable information regarding prognosis and help determining the optimal treatment. We investigated the possible correlation between cancer stem cell (CSC) markers (CD133, and ALDH1) in invasive ductal breast carcinomas with some clinicopathological parameters.

AIM

To assess the correlation between expression of cancer stem cell (CSC) markers (CD133, and ALDH1) and clinicopathological parameters of invasive ductal breast carcinomas.

MATERIALS AND METHODS

Immunohistochemical analysis of CD133 and ALDH1 was performed on a series of 120 modified radical mastectomy (MRM) specimens diagnosed as invasive ductal breast carcinoma.

RESULTS

Expression of both CD133 and ALDH1 was significantly changed and related to tumor size, tumor stage (TNM), and lymph node metastasis. A negative correlation between CD133 and ALDH1 was found.

CONCLUSIONS

Detecting the expression of CD133 and ALDH1 in invasive ductal breast carcinomas may be of help in more accurately predicting the aggressive properties and determining the optimal treatment.

Tumor-Initiating Cells: Emerging Biophysical Methods of Isolation

The discovery and subsequent isolation of tumor-initiating cells (TICs), a small population of highly tumorigenic and drug-resistant cancer cells also called cancer stem cells (CSCs), have revolutionized our understanding of cancer. TICs are isolated using various methodologies, including selection of surface marker expression, ALDH activity, suspension culture, and chemotherapy/drug resistance. These methods have several drawbacks, including their variability, lack of robustness and scalability, and low specificity. Alternative methods of purification take advantage of biophysical properties of TICs including their adhesion and stiffness. This review will provide a brief overview of TIC biology as well as review the most important methods of TIC isolation with a focus on biophysical methods of TIC purification.

Synthesis and antileukemic activities of C1-C10-modified parthenolide analogues

Parthenolide (PTL) is a sesquiterpene lactone natural product with anti-proliferative activity to cancer cells. Selective eradication of leukemic stem cells (LSCs) over healthy hematopoietic stem cells (HSCs) by PTL has been demonstrated in previous studies, which suggests PTL and related molecules may be useful for targeting LSCs. Eradication of LSCs is required for curative therapy. Chemical optimizations of PTL to improve potency and pharmacokinetic parameters have focused largely on the α-methylene-γ-butyrolactone, which is essential for activity. Conversely, we evaluated modifications to the C1-C10 olefin and benchmarked new inhibitors to PTL with respect to inhibitory potency across a panel of cancer cell lines, ability to target drug-resistant acute myeloid leukemia (AML) cells, efficacy for inhibiting clonal growth of AML cells, toxicity to healthy bone marrow cells, and efficiency for promoting intracellular reactive oxygen species (ROS) levels. Cyclopropane 4 was found to possess less toxicity to healthy bone marrow cells, enhanced potency for the induction of cellular ROS, and similar broad-spectrum anti-proliferative activity to cancer cells in comparison to PTL.

Upregulation of circulating cancer stem cell marker, DCLK1 but not Lgr5, in chemoradiotherapy-treated colorectal cancer patients

Cancer stem cell (CSC) markers have attracted considerable attention in tumor diagnostic, prognostic, and therapeutic implications. Detection of cancer stem cells in circulating blood using cancer stem cell markers has received remarkable attention recently. In this study, we aimed to investigate the messenger RNA (mRNA) expression level of Lgr5 and DCLK1 as most proposed colorectal CSC markers in blood circulation also determine the subsequent association to patients' clinical and pathological findings. Peripheral blood mononuclear cells (PBMCs) of 58 patients with colorectal cancer at stage I-IV with 33 out of 58 patients undergoing preoperative chemoradiotherapy (CRT), as well as 58 healthy controls have been isolated and the extracted RNAs were analyzed using real-time PCR. The mRNA expression pattern of CSC markers of patients and controls was compared using ΔΔCt method. The expression level of Lgr5 was significantly higher in colorectal cancer (CRC) patients comparing to healthy group (4.8-fold change, p < 0.001). Also there was a significant increase in expression level of Lgr5 in patients at stages III and IV comparing to stages I and II (p = 0.031) and higher grades (p = 0.039) of CRC. The expression of DCLK1 was also elevated in patients significantly (2.7-fold change, p < 0.001) and the related expression was increased by increasing disease stage (p = 0.025). Combination of DCLK1 and Lgr5 markers was analyzed by logistic regression and proved to be a slightly better marker compared to each marker alone. Interestingly the DCLK1 expression level was significantly higher in patients undergoing preoperative CRT (p = 0.041); however, no association to neoadjuvant CRT was observed for Lgr5. Considering the over-expression of DCLK1 and Lgr5 in circulating blood of CRC patients comparing to controls, our results might emphasize on the presence of CSCs in blood of these patients which might be attributed to their clinical and pathological characteristics and may lead to apply in future clinical implications. Moreover, the higher expression level of DCLK1 in patients undergoing CRT can propose it as a more relevant candidate among CSC markers comparing to Lgr5 for CRC patients.

CD133-targeted paclitaxel delivery inhibits local tumor recurrence in a mouse model of breast cancer

Expression of the membrane protein CD133 marks a subset of cancer cells with drug resistant phenotype and enhanced tumor initiating ability in xenotransplantation assays. Because drug resistance and tumor relapse are significant problems, approaches to eliminate these cells are urgently needed. As a step towards achieving this goal, we developed polymeric nanoparticles targeting CD133 by conjugating an anti-CD133 monoclonal antibody to nanoparticles formulated using poly(D,L lactide-co-glycolide) polymer. Nanoparticles were loaded with paclitaxel, a microtubule-stabilizing anticancer agent, as well as with 6-coumarin, a fluorescent probe. CD133-targeted nanoparticles (CD133NPs) were efficiently internalized by Caco-2 cells, which abundantly express CD133 (>9-fold higher uptake than non-targeted control nanoparticles). The effectiveness of CD133NPs in reducing tumor initiating cell (TIC) fraction was investigated using mammosphere formation and soft-agar colony formation assays. Free paclitaxel treatment was not effective in decreasing the TIC population relative to untreated control, whereas CD133NPs effectively decreased the number of mammospheres and colonies formed. In vivo studies in the MDA-MB-231 xenograft model showed that free paclitaxel was initially effective in inhibiting tumor growth but the tumors rebounded rapidly once the treatment was stopped. Tumor regrowth was significantly lower when paclitaxel was delivered through CD133NPs (tumor volume was 518.6±228 vs. 1370.9±295mm(3) for free paclitaxel at 63days; P<0.05). Our studies thus show that encapsulation of paclitaxel in CD133NPs results in a significant decrease in the TIC population and improved therapeutic efficacy compared to that with free paclitaxel treatment. These results indicate the potential of targeting anticancer therapeutics to CD133+ cells for reducing tumor recurrence.