Colorectal cancer stem cells are enriched in xenogeneic tumors following chemotherapy

Drug Delivery Systems Using Surface Markers for Targeting Cancer Stem Cells

The innate abilities of cancer stem cells (CSCs), such as multi-drug resistance, drug efflux, quiescence and ionizing radiation tolerance, protect them from most traditional chemotherapeutics. As a result, this small subpopulation of persistent cells leads to more aggressive and chemoresistant cancers, causing tumour relapse and metastasis. This subpopulation is differentiated from the bulk tumour population through a wide variety of surface markers expressed on the cell surface. Recent developments in nanomedicine and targeting delivery methods have given rise to new possibilities for specifically targeting these markers and preferentially eliminating CSCs. Herein, we first summarize the range of surface markers identifying CSC populations in a variety of cancers; then, we discuss recent attempts to actively target CSCs and their niches using liposomal, nanoparticle, carbon nanotube and viral formulations.

Association of ALDH1A1-NEK-2 axis in cisplatin resistance in ovarian cancer cells

Development of acquired resistance to cisplatin (CDDP) is a major obstacle in the treatment of ovarian cancer patients. According to the cancer stem cell (CSC) hypothesis, the recurrence and chemoresistance are presumed to be linked to cancer stem/progenitor cells. Here, we investigated the CSC-like phenotypes and mechanism of chemoresistance in CDDP resistant ovarian cancer cells. A well-established CDDP sensitive ovarian cancer cell line A2780 and its resistant population A2780-Cp were used. We also developed a supra resistant population (SKOV3-Cp) from a naturally CDDP resistant cell line SKOV3. Both resistant/supra resistant cell lines showed significantly higher self-renewal capability than their parental counterparts. They also showed significant resistance to apoptosis and sub-G1 arrest by CDDP treatment. Stem cell marker ALDH1 positivity rates were higher both in A2780-Cp and SKOV3-Cp cell lines than in their counterparts, quantified by Aldefluor assay kit. Hoechst 33342 dye effluxing side populations were increased up to about five folds in A2780-Cp cells and two folds in SKOV3-Cp cells compared to A2780 and SKOV3 cells, respectively. Among major stemness related genes (POU5F1/OCT4, SOX2, NANOG, NES, BMI1, KLF4 and ALDH1A1), ALDH1A1 and KLF4 were significantly overexpressed in both resistant/supra resistant cells. Silencing ALDH1A1 in A2780 and A2780-Cp cells using siRNA greatly reduced the stem cell population and sensitized cells to CDDP. Moreover, silencing of ALDH1A1 reduced the transcript and protein level of its downstream target NEK-2. We also observed the downregulation of ABC transporters (ABCB1/MDR1, ABCG2 and ABCC1/MRP1) either by ALDH1A1 or NEK-2 silencing and upreguation of ABCB1/MDR1 due to the overexpression of NEK-2. Taken together, the present study suggests that stemness gene ALDH1A1 can be involved in CDDP resistance through the upregulation of NEK-2 in ovarian cancer.

APC mutations in human colon lead to decreased neuroendocrine maturation of ALDH+ stem cells that alters GLP-2 and SST feedback signaling: Clue to a link between WNT and retinoic acid signalling in colon cancer development

APC mutations drive human colorectal cancer (CRC) development. A major contributing factor is colonic stem cell (SC) overpopulation. But, the mechanism has not been fully identified. A possible mechanism is the dysregulation of neuroendocrine cell (NEC) maturation by APC mutations because SCs and NECs both reside together in the colonic crypt SC niche where SCs mature into NECs. So, we hypothesized that sequential inactivation of APC alleles in human colonic crypts leads to progressively delayed maturation of SCs into NECs and overpopulation of SCs. Accordingly, we used quantitative immunohistochemical mapping to measure indices and proportions of SCs and NECs in human colon tissues (normal, adenomatous, malignant), which have different APC-zygosity states. In normal crypts, many cells staining for the colonic SC marker ALDH1 co-stained for chromogranin-A (CGA) and other NEC markers. In contrast, in APC-mutant tissues from familial adenomatous polyposis (FAP) patients, the proportion of ALDH+ SCs progressively increased while NECs markedly decreased. To explain how these cell populations change in FAP tissues, we used mathematical modelling to identify kinetic mechanisms. Computational analyses indicated that APC mutations lead to: 1) decreased maturation of ALDH+ SCs into progenitor NECs (not progenitor NECs into mature NECs); 2) diminished feedback signaling by mature NECs. Biological experiments using human CRC cell lines to test model predictions showed that mature GLP-2R+ and SSTR1+ NECs produce, via their signaling peptides, opposing effects on rates of NEC maturation via feedback regulation of progenitor NECs. However, decrease in this feedback signaling wouldn't explain the delayed maturation because both progenitor and mature NECs are depleted in CRCs. So the mechanism for delayed maturation must explain how APC mutation causes the ALDH+ SCs to remain immature. Given that ALDH is a key component of the retinoic acid (RA) signaling pathway, that other components of the RA pathway are selectively expressed in ALDH+ SCs, and that exogenous RA ligands can induce ALDH+ cancer SCs to mature into NECs, RA signaling must be attenuated in ALDH+ SCs in CRC. Thus, attenuation of RA signaling explains why ALDH+ SCs remain immature in APC mutant tissues. Since APC mutation causes increased WNT signaling in FAP and we found that sequential inactivation of APC in FAP patient tissues leads to progressively delayed maturation of colonic ALDH+ SCs, the hypothesis is developed that human CRC evolves due to an imbalance between WNT and RA signaling.

Expression pattern of ALDH1, E-cadherin, Vimentin and Twist in early and late onset sporadic colorectal cancer

Aim: To evaluate the expression pattern of ALDH1 (aldehyde dehydrogenase 1), E-cadherin, Vimentin and Twist in early and late onset sporadic colorectal cancer (CRC) and to study association of their expression with the occurrence of CRC at a young age. Materials & methods: Immunohistochemistry of ALDH1, E-cadherin, Vimentin and Twist was performed on 103 pretreated CRC biopsy samples. Results: ALDH1 expression was found to have strong correlation with early onset CRC (p < 0.0001). Conclusion: High ALDH1 expression correlates with the early onset of CRC. ALDH1 over-expression correlates with poor overall survival in colon cancer.

Skp2 depletion reduces tumor-initiating properties and promotes apoptosis in synovial sarcoma

Synovial sarcoma (SS) is an aggressive soft-tissue cancer with a poor prognosis and a propensity for local recurrence and distant metastasis. In this study, we investigated whether S phase kinase-associated protein (Skp2) plays an oncogenic role in tumor initiation, progression, and metastasis of SS. Our study revealed that Skp2 is frequently overexpressed in SS specimens and SS18-SSX transgenic mouse tumors, as well as correlated with clinical stages. Next, we identified that genetic depletion of Skp2 reduced mesenchymal and stemness markers, and inhibited the invasive and proliferative capacities of SS cell lines. Furthermore, Skp2 depletion markedly suppressed the growth of SS xenografts tumors. Treatment of SS cell lines with the skp2 inhibitor flavokawain A (FKA) reduced Skp2 expression in a dose-dependent manner and resulted in cell cycle arrest and apoptosis. FKA also suppressed the invasion and tumor-initiating properties in SS, similar to the effects of Skp2 knockdown. In addition, a combination of FKA and conventional chemotherapy showed a synergistic therapeutic efficacy. Taken together, our results suggest that Skp2 plays an essential role in the biology of SS by promoting the mesenchymal state and cancer stemness. Given that chemotherapy resistance is often associated with cancer stemness, strategies of combining Skp2 inhibitors with conventional chemotherapy in SS may be desirable.

Extracellular Vesicle-Based Communication May Contribute to the Co-Evolution of Cancer Stem Cells and Cancer-Associated Fibroblasts in Anti-Cancer Therapy

Analogously to the natural selective forces in ecosystems, therapies impose selective pressure on cancer cells within tumors. Some tumor cells can adapt to this stress and are able to form resistant subpopulations, parallel with enrichment of cancer stem cell properties in the residual tumor masses. However, these therapy-resistant cells are unlikely to be sufficient for the fast tumor repopulation and regrowth by themselves. The dynamic and coordinated plasticity of residual tumor cells is essential both for the conversion of their regulatory network and for the stromal microenvironment to produce cancer supporting signals. In this nursing tissue "niche", cancer-associated fibroblasts are known to play crucial roles in developing therapy resistance and survival of residual stem-like cells. As paracrine messengers, extracellular vesicles carrying a wide range of signaling molecules with oncogenic potential, can support the escape of some tumor cells from their deadly fate. Here, we briefly overview how extracellular vesicle signaling between fibroblasts and cancer cells including cancer progenitor/stem cells may contribute to the progression, therapy resistance and recurrence of malignant tumors.

Mechanisms of cancer stem cell therapy

Cancer stem cells (CSCs) are responsible for carcinogenesis and tumorigenesis and are involved in drug and radiation resistance, metastasis, tumor relapse and initiation. Remarkably, they have other abilities such as inheritance of self-renewal and de-differentiation. Hence, targeting CSCs is considered a potential anti-cancer therapeutic strategy. Recent advances in the identification of biomarkers to recognize CSCs and the development of new techniques to evaluate tumorigenic and carcinogenic roles of CSCs are instrumental to this approach. Elucidation of signaling pathways that regulate CSCs colony progression and drug resistance are critical in establishing effective targeted therapies. CSCs play a central key role in immunomodulation, immune evasion and effector immunity, which alters immune system balancing. These include mTOR, SHH, NOTCH and Wnt/β-catering in cancer progression. In this review article, we discuss the importance of these CSCs pathways in cancer therapy.

Distant Metastasis in Colorectal Cancer Patients-Do We Have New Predicting Clinicopathological and Molecular Biomarkers? A Comprehensive Review

Colorectal cancer (CRC) remains a serious health problem worldwide. Approximately half of patients will develop distant metastasis after CRC resection, usually with very poor prognosis afterwards. Because patient performance after distant metastasis surgery remains very heterogeneous, ranging from death within 2 years to a long-term cure, there is a clinical need for a precise risk stratification of patients to aid pre- and post-operative decisions. Furthermore, around 20% of identified CRC cases are at IV stage disease, known as a metastatic CRC (mCRC). In this review, we overview possible molecular and clinicopathological biomarkers that may provide prognostic and predictive information for patients with distant metastasis. These may comprise sidedness of the tumor, molecular profile and epigenetic characteristics of the primary tumor and arising metastatic CRC, and early markers reflecting cancer cell resistance in mCRC and biomarkers identified from transcriptome. This review discusses current stage in employment of these biomarkers in clinical practice as well as summarizes current experience in identifying predictive biomarkers in mCRC treatment.

Multiple Dynamics in Tumor Microenvironment Under Radiotherapy

The tumor microenvironment (TME) is an evolutionally low-level and embryonically featured tissue comprising heterogenic populations of malignant and stromal cells as well as noncellular components. Under radiotherapy (RT), the major modality for the treatment of malignant diseases [1], TME shows an adaptive response in multiple aspects that affect the efficacy of RT. With the potential clinical benefits, interests in RT combined with immunotherapy (IT) are intensified with a large scale of clinical trials underway for an array of cancer types. A better understanding of the multiple molecular aspects, especially the cross talks of RT-mediated energy reprogramming and immunoregulation in the irradiated TME (ITME), will be necessary for further enhancing the benefit of RT-IT modality. Coming studies should further reveal more mechanistic insights of radiation-induced instant or permanent consequence in tumor and stromal cells. Results from these studies will help to identify critical molecular pathways including cancer stem cell repopulation, metabolic rewiring, and specific communication between radioresistant cancer cells and the infiltrated immune active lymphocytes. In this chapter, we will focus on the following aspects: radiation-repopulated cancer stem cells (CSCs), hypoxia and re-oxygenation, reprogramming metabolism, and radiation-induced immune regulation, in which we summarize the current literature to illustrate an integrated image of the ITME. We hope that the contents in this chapter will be informative for physicians and translational researchers in cancer radiotherapy or immunotherapy.

The Roles of Cancer Stem Cells and Therapy Resistance in Colorectal Carcinoma

Cancer stem cells (CSCs) are the main culprits involved in therapy resistance and disease recurrence in colorectal carcinoma (CRC). Results using cell culture, animal models and tissues from patients with CRC suggest the indispensable roles of colorectal CSCs in therapeutic failure. Conventional therapies target proliferating and mature cancer cells, while CSCs are mostly quiescent and poorly differentiated, thereby they can easily survive chemotherapeutic insults. The aberrant activation of Wnt/β-catenin, Notch, Hedgehog, Hippo/YAP (Yes-associated protein) and phosphatidylinositol 3-kinase/protein kinase B facilitates CSCs with excessive self-renewal and therapy resistance property in CRC. CSCs survive the chemo-radiotherapies by escaping therapy mediated DNA damage via altering the cell cycle checkpoints, increasing DNA damage repair capacity and by an efficient scavenging of reactive oxygen species. Furthermore, dysregulations of miRNAs e.g., miR-21, miR-93, miR-203, miR-215, miR-497 etc., modulate the therapeutic sensitivity of colorectal CSCs by regulating growth and survival signalling. In addition, a reversible quiescent G₀ state and the re-entering cell cycle capacity of colorectal CSCs can accelerate tumour regeneration after treatment. Moreover, switching to favourable metabolic signatures during a therapeutic regimen will add more complexity in therapeutic outcomes against CSCs. Therapeutic strategies targeting these underlying mechanisms of CSCs’ therapy resistance could provide a promising outcome, however, deep understanding and concerted research are necessary to design novel therapies targeting CSCs. To conclude, the understanding of these mechanisms of CSC in CRC could lead to the improved management of patients with CRC.

The local and circulating SOX9 as a potential biomarker for the diagnosis of primary bone cancer

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The SOX9 expression increased in tumor tissues and peripheral blood of malignant and benign bone tumors.

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The protein level of SOX9 is enhanced in malignant bone tumor tissues.

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SOX9 over-expression correlated with tumor severity, grade, invasion feature, poor response to therapy, and recurrence.

Purpose

The status of the local and circulating SOX9, a master regulator of the tumor fate, and its relevance to tumor types, severity, invasion feature, response to therapy, and chemotherapy treatment were surveyed in bone cancer in the current study.

Methods

The SOX9 expression level was evaluated in tissue and peripheral blood mononuclear cells from patients with different types of malignant and benign bone tumors also tumor margin tissues using Real-Time PCR. The protein level of SOX9 was assessed using immunohistochemistry and western blot analysis. Also, the correlations of the SOX9 expression level with the patient’s clinical and pathological features were considered.

Results

The remarkable overexpression of SOX9 was detected in bone tumors compared to tumor margin tissues (P < 0.0001). Malignant bone tumors revealed a higher expression of SOX9 compared to benign tumors (P < 0.0001) while osteosarcoma tumors showed higher expression levels compared to Ewing sarcoma, and chondrosarcoma. Overexpression of SOX9 was observed in high grade, metastatic, recurrent tumors also tumors with poor response to therapy. Besides, the patients under the chemotherapy treatment demonstrated higher levels of SOX9 compared to the rest of malignant tumors (P = 0.02). The simultaneous up-regulation of circulating SOX9 in the patients with bone cancer was observed compared to healthy individuals (P < 0.0001) accompanying with overexpression of SOX9 in malignant tumors compared to benign tumors (P < 0.0001). The circulating SOX9 expression was up-regulated in the patients with malignant bone tumors who receive chemotherapy treatment also patients with high grade, metastatic, recurrent tumors. The protein level of SOX9 was in line with our data on the SOX9 gene expression.

Conclusion

The simultaneous overexpression of local and circulating SOX9 in bone cancer besides its positive correlation with tumor severity, malignancy, size, and chemotherapy may deserve receiving more attention in bone cancer diagnosis and therapy.

The Rational Development of CD133-Targeting Immunotherapies for Glioblastoma

CD133 marks self-renewing cancer stem cells (CSCs) in a variety of solid tumors, and CD133+ tumor-initiating cells are known markers of chemo- and radio-resistance in multiple aggressive cancers, including glioblastoma (GBM), that may drive intra-tumoral heterogeneity. Here, we report three immunotherapeutic modalities based on a human anti-CD133 antibody fragment that targets a unique epitope present in glycosylated and non-glycosylated CD133 and studied their effects on targeting CD133+ cells in patient-derived models of GBM. We generated an immunoglobulin G (IgG) (RW03-IgG), a dual-antigen T cell engager (DATE), and a CD133-specific chimeric antigen receptor T cell (CAR-T): CART133. All three showed activity against patient-derived CD133+ GBM cells, and CART133 cells demonstrated superior efficacy in patient-derived GBM xenograft models without causing adverse effects on normal CD133+ hematopoietic stem cells in humanized CD34+ mice. Thus, CART133 cells may be a therapeutically tractable strategy to target CD133+ CSCs in human GBM or other treatment-resistant primary cancers.

TCF4 promotes colorectal cancer drug resistance and stemness via regulating ZEB1/ZEB2 expression

The present study aims to investigate the roles of TCF4 and its underlying mechanism in colorectal cancer (CRC). Doxorubicin-resistant DLD-1 (DLD1 DR), TCF4 overexpression, and TCF4 knockdown cell lines were constructed. A flow cytometer was used to analyze frequencies of CD133⁺ cell in the DLD1 and DLD1 DR cells. Quantitative real-time PCR (qPCR) was used to determine the expressions of cancer stem cell (CSC) makers. Stemness of CRC cells were determined using tumorsphere formation assay. The correlation between TCF4 and ZEB1/ZEB2 were determined using public data from The Cancer Genome Atlas (TCGA) datasets. ZEB1/ZEB2 overexpression cell lines were constructed and cell viabilities were then determined using MTT and colony formation assays. TCF4 overexpression promoted proliferation of CRC cell lines and relative expressions of TCF4 were significantly increased in the DLD1 DR cells. TCF4 overexpression promoted CRC cell doxorubicin resistance, whereas TCF4 knockdown significantly decreased doxorubicin resistance. Additionally, TCF4 overexpression also significantly increased frequencies of CSC cells, expressions of CSC markers, and CRC ability to form tumorsphere. Furthermore, TCF4 promoted ZEB1 and ZEB2 expression, leading to CRC proliferation and doxorubicin resistance. TCF4 promoted CRC doxorubicin resistance and stemness by regulating expressions of ZEB1 and ZEB2.

DNA damage response and resistance of cancer stem cells

The cancer stem cell (CSC) model defines tumors as hierarchically organized entities, containing a small population of tumorigenic CSC, or tumour-initiating cells, placed at the apex of this hierarchy. These cells may share common qualities with chemo- and radio-resistant cancer cells and contribute to self-renewal activities resulting in tumour formation, maintenance, growth and metastasis. Yet, it remains obscure what self-defense mechanisms are utilized by these cells against the chemotherapeutic drugs or radiotherapy. Recently, attention has been focused on the pivotal role of the DNA damage response (DDR) in tumorigenesis. In line with this note, an increased DDR that prevents CSC and chemoresistant cells from genotoxic pressure of chemotherapeutic drugs or radiation may be responsible for cancer metastasis. In this review, we focus on the current knowledge concerning the role of DDR in CSC and resistant cancer cells and describe the existing opportunities of re-sensitizing such cells to modulate therapeutic treatment effects.

Repurposing old drugs as new inhibitors of the ubiquitin-proteasome pathway for cancer treatment

The ubiquitin-proteasome system (UPS) plays a central role in the degradation of cellular proteins. Targeting protein degradation has been validated as an effective strategy for cancer therapy since 2003. Several components of the UPS have been validated as potential anticancer targets, including 20S proteasomes, 19S proteasome-associated deubiquitinases (DUBs) and ubiquitin ligases (E3s). 20S proteasome inhibitors (such as bortezomib/BTZ and carfilzomib/CFZ) have been approved by the U.S. Food and Drug Administration (FDA) for the treatment of multiple myeloma (MM) and some other liquid tumors. Although survival of MM patients has been improved by the introduction of BTZ-based therapies, these clinical 20S proteasome inhibitors have several limitations, including emergence of resistance in MM patients, neuro-toxicities, and little efficacy in solid tumors. One of strategies to improve the current status of cancer treatment is to repurpose old drugs with UPS-inhibitory properties as new anticancer agents. Old drug reposition represents an attractive drug discovery approach compared to the traditional de novo drug discovery process which is time-consuming and costly. In this review, we summarize status of repurposed inhibitors of various UPS components, including 20S proteasomes, 19S-associated DUBs, and ubiquitin ligase E3s. The original and new mechanisms of action, molecular targets, and potential anticancer activities of these repurposed UPS inhibitors are reviewed, and their new uses including combinational therapies for cancer treatment are discussed.

Evodiamine Eliminates Colon Cancer Stem Cells via Suppressing Notch and Wnt Signaling

Evodiamine, an alkaloid contained in traditional Asian herbal medicines that have been used for hundreds years, is interesting due to its cytotoxic effects against many cancers. We examined the effect of evodiamine on the cancer stem cell (CSC) population and the bulk cultured cancer cells (BCC) of colon cancers to examine the double targeting effect. We found that three colon cancer cell lines’ BCC and CSC are effectively targeted by evodiamine. Evodiamine was able to suppress BCC proliferation and induce apoptosis of the cells captured in G2/M phase, as previously reported. However, evodiamine did not cause the accumulation of CSCs at a certain stage of the cell cycle, resulting in the elimination of stemness through an unknown mechanism. By analyzing the expression of 84 genes related to CSCs in two colon cancer cell lines’ CSC, as well as performing further informatics analyses, and quantitative RT-PCR analyses of 24 CSC genes, we found that evodiamine suppressed the expression of the genes that control key signaling pathways of CSC, namely, WNT and NOTCH signaling, to lead CSC elimination. These results suggest that evodiamine should be further developed for targeting both BCCs and CSCs in colon cancers.

Ovarian cancer stem cells and targeted therapy

BACKGROUND

Ovarian cancer has the highest ratio of mortality among gynecologic malignancies. Chemotherapy is one of the most common treatment options for ovarian cancer. However, tumor relapse in patients with advanced tumor stage is still a therapeutic challenge for its clinical management.

MAIN BODY

Therefore, it is required to clarify the molecular biology and mechanisms which are involved in chemo resistance to improve the survival rate of ovarian cancer patients. Cancer stem cells (CSCs) are a sub population of tumor cells which are related to drug resistance and tumor relapse.

CONCLUSION

In the present review, we summarized the recent findings about the role of CSCs in tumor relapse and drug resistance among ovarian cancer patients. Moreover, we focused on the targeted and combinational therapeutic methods against the ovarian CSCs.

A Snapshot of The Tumor Microenvironment in Colorectal Cancer: The Liquid Biopsy

The molecular profile of liquid biopsies is emerging as an alternative to tissue biopsies in the clinical management of malignant diseases. In colorectal cancer, significant liquid biopsy-based biomarkers have demonstrated an ability to discriminate between asymptomatic cancer patients and healthy controls. Furthermore, this non-invasive approach appears to provide relevant information regarding the stratification of tumors with different prognoses and the monitoring of treatment responses. This review focuses on the tumor microenvironment components which are detected in blood samples of colorectal cancer patients and might represent potential biomarkers. Exosomes released by tumor and stromal cells play a major role in the modulation of cancer progression in the primary tumor microenvironment and in the formation of an inflammatory pre-metastatic niche. Stromal cells-derived exosomes are involved in driving mechanisms that promote tumor growth, migration, metastasis, and drug resistance, therefore representing substantial signaling mediators in the tumor-stroma interaction. Besides, recent findings of specifically packaged exosome cargo in Cancer-Associated Fibroblasts of colorectal cancer patients identify novel exosomal biomarkers with potential clinical applicability. Furthermore, additional different signals emitted from the tumor microenvironment and also detectable in the blood, such as soluble factors and non-tumoral circulating cells, arise as novel promising biomarkers for cancer diagnosis, prognosis, and treatment response prediction. The therapeutic potential of these factors is still limited, and studies are in their infancy. However, innovative strategies aiming at the inhibition of tumor progression by systemic exosome depletion, exosome-mediated circulating tumor cell capturing, and exosome-drug delivery systems are currently being studied and may provide considerable advantages in the near future.

Targeting oxidative pentose phosphate pathway prevents recurrence in mutant Kras colorectal carcinomas

Recurrent tumors originate from cancer stem cells (CSCs) that survive conventional treatments. CSCs consist of heterogeneous subpopulations that display distinct sensitivity to anticancer drugs. Such a heterogeneity presents a significant challenge in preventing tumor recurrence. In the current study, we observed that quiescent CUB-domain–containing protein 1 (CDCP1)+ CSCs are enriched after chemotherapy in mutant Kirsten rat sarcoma viral oncogene homolog (Kras) colorectal carcinomas (CRCs) and serve as a reservoir for recurrence. Mechanistically, glucose catabolism in CDCP1+ CSCs is routed to the oxidative pentose phosphate pathway (PPP); multiple cycling of carbon backbones in the oxidative PPP potentially maximizes NADPH reduction to counteract chemotherapy-induced reactive oxygen species (ROS) formation, thereby allowing CDCP1+ CSCs to survive chemotherapeutic attack. This is dependent on silent mating type information regulation 2 homolog 5 (Sirt5)-mediated inhibition of the glycolytic enzyme triosephosphate isomerase (TPI) through demalonylation of Lys56. Blocking demalonylation of TPI at Lys56 increases chemosensitivity of CDCP1+ CSCSs and delays recurrence of mutant Kras CRCs in vivo. These findings pinpoint a new therapeutic approach for combating mutant Kras CRCs.

This study shows that CDCP1-positive cancer stem cells represent a critical driving force behind tumor relapse in colorectal tumors that have mutant Kras and reveals a unique role for the oxidative pentose phosphate pathway in this process.

Linking stemness with colorectal cancer initiation, progression, and therapy

The discovery of cancer stem cells caused a paradigm shift in the concepts of origin and development of colorectal cancer. Several unresolved questions remain in this field though. Are colorectal cancer stem cells the cause or an effect of the disease? How do cancer stem cells assist in colorectal tumor dissemination to distant organs? What are the molecular or environmental factors affecting the roles of these cells in colorectal cancer? Through this review, we investigate the key findings until now and attempt to elucidate the origins, physical properties, microenvironmental niches, as well as the molecular signaling network that support the existence, self-renewal, plasticity, quiescence, and the overall maintenance of cancer stem cells in colorectal cancer. Increasing data show that the cancer stem cells play a crucial role not only in the establishment of the primary colorectal tumor but also in the distant spread of the disease. Hence, we will also look at the mechanisms adopted by cancer stem cells to influence the development of metastasis and evade therapeutic targeting and its role in the overall disease prognosis. Finally, we will illustrate the importance of understanding the biology of these cells to develop improved clinical strategies to tackle colorectal cancer.

Expression of CD133 is associated with poor prognosis in stage II colorectal carcinoma

CD133 is currently believed to be one of the best colorectal cancer stem cell markers. This study aimed to evaluate prognostic significance of CD133 expression in colorectal cancer patients.A total of 303 patients with stage I to III colorectal cancer who underwent curative surgical resection from 2003 to 2008 at a single institution were included. CD133 expression was evaluated using immunohistochemical staining, and clinicopathological data were retrospectively reviewed. The patients were dichotomized after scoring CD133 expression (0 to 2+: low CD133 expression vs 3+ to 4+: high CD133 expression) according to the extent of area of CD133 positive tumor cells (<50% vs ≥50%) and pattern of staining (membranous staining of the luminal surface and/or staining of cellular debris in the tumor glands and cytoplasm).The 5-year overall survival (OS) (61.9% vs 80.2%, P = .001) and disease-free survival (64.8% vs 75.8%, P = .026) were poorer in the high CD133 expression group than the low CD133 expression group. In the multivariate analysis for risk factors of OS in the whole population, higher nodal stage (N2 compared to N0: hazard ratio [HR] 3.141; 95% confidence interval [CI] 1.718-5.744, P < .001), perineural invasion (HR 2.262; 95% CI 1.347-3.798, P = .002) and high CD133 expression (HR 1.929; 95% CI 1.221-3.048, P = .005) were independent poor prognostic factors of OS. Subgroup analyses according to each TNM stage revealed that CD133 expression was associated with OS only within the stage II patients (HR 3.167 95% CI 1.221-8.216, P = .018). Furthermore, the stage II patients demonstrating the high CD133 expression showed survival benefit of adjuvant chemotherapy, regardless of high-risk feature positivity (HR 0.201 95% CI 0.054-0.750, P = .017).High CD133 expression is correlated with poor prognosis in colorectal cancer patients after radical resection. The CD133 expression may serve as a more potent and informative biomarker for prognosis than conventional high-risk features in the stage II colorectal cancer patients.

A randomized phase II trial of nab-paclitaxel and gemcitabine with tarextumab or placebo in patients with untreated metastatic pancreatic cancer

Purpose

Notch signaling dysregulation is implicated in the development of pancreatic adenocarcinoma (PDAC). Tarextumab is a fully human IgG2 antibody that inhibits Notch2/3 receptors.

Patients and Methods

Aphase 2, randomized, placebo‐controlled, multicenter trial evaluated the activity of tarextumab in combination with nab‐paclitaxel and gemcitabine in patients with metastatic PDAC. Patients were stratified based on ECOG performance score and Ca 19‐9 level and randomized 1:1 to nab‐paclitaxel, gemcitabine with either tarextumab or placebo. Based on preclinical and phase Ib results suggesting a positive correlation between Notch3 gene expression and tarextumab anti‐tumor activity, patients were also divided into subgroups of low, intermediate, and high Notch3 gene expression. Primary endpoint was overall survival (OS) in all and in patients with the three Notch3 gene expression subgroups (≥25th, ≥50% and ≥75% percentiles); secondary end points included progression‐free survival (PFS), 12‐month OS, overall response rate (ORR), and safety and biomarker investigation.

Results

Median OS was 6.4 months in the tarextumab group vs 7.9 months in the placebo group (HR = 1.34 [95% CI = 0.95, 1.89], P = .0985). No difference observed in OS in the Notch3 gene expression subgroups. PFS in the tarextumab‐treated group (3.7 months) was significantly shorter compared with the placebo group (5.5 months) (hazard ratio was 1.43 [95% CI = 1.01, 2.01]; P = .04). Grade 3 diarrhea and thrombocytopenia were more common in the tarextumab group.

Conclusions

The addition of tarextumab to nab‐paclitaxel and gemcitabine did not improve OS, PFS, or ORR in first‐line metastatic PDAC, and PFS was specifically statistically worse in the tarextumab‐treated patients.

Clinical trial registry no

NCT01647828.

Expression of UPR effector proteins ATF6 and XBP1 reduce colorectal cancer cell proliferation and stemness by activating PERK signaling

The unfolded protein response (UPR) acts through its downstream branches, PERK-eIF2α signaling, IRE1α-XBP1 signaling and ATF6 signaling. In the intestine, activation of the UPR through the kinase PERK results in differentiation of intestinal epithelial stem cells and colon cancer stem cells, whereas deletion of XBP1 results in increased stemness and adenomagenesis. How downstream activation of XBP1 and ATF6 influences intestinal stemness and proliferation remains largely unknown. We generated colorectal cancer cells (LS174T) that harbor doxycycline inducible expression of the active forms of either XBP1(s) or ATF61-373. Activation of either XBP1 or ATF6 resulted in reduced cellular proliferation and reduced expression of markers of intestinal epithelial stemness. Moreover, XBP1 and ATF6 activation reduced global protein synthesis and lowered the threshold for UPR activation. XBP1-mediated loss of stemness and proliferation resulted from crossactivation of PERK-eIF2α signaling and could be rescued by constitutive expression of eIF2α phosphatase GADD34. We thus find that enforced activation of XBP1 and ATF6 results in reduction of stemness and proliferation. We expose a novel interaction between XBP1 and PERK-eIF2α signaling.

Revisiting the Role of Exosomes in Colorectal Cancer: Where Are We Now?

Exosomes (Exos) are nano-sized extracellular vesicles constitutively released by both prokaryotic and eukaryotic cells. Their role as inter-cellular messengers involved in both physiological and pathological processes has overwhelmingly come to light in the last decade, and their contribution to cancerogenesis and tumor metastasis is under intensive investigation. Here we review the most recent information concerning Exos in colorectal cancer (CRC) and focus on their effects on tumor microenvironment and the immune system, as well as unravel their role in the formation of the pre-metastatic niche and in drug resistance. Such a recent knowledge on Exos depicts their potential translations into the clinical arena, either as an alternative tool of “liquid biopsy” or novel therapeutic approaches for CRC. However, due to the limited data available from clinical trials, they need further validations before addressing their putative application in oncology.

A phase 1b dose escalation study of ipafricept (OMP54F28) in combination with paclitaxel and carboplatin in patients with recurrent platinum-sensitive ovarian cancer

OBJECTIVES

The WNT pathway is an important oncologic driver of epithelial ovarian cancer (EOC). The first-in-class recombinant fusion protein ipafricept (IPA) blocks Wnt signaling through binding of Wnt ligands. This phase Ib trial was designed to determine the maximum tolerated dose (MTD) and recommended phase 2 dose (RPh2) for IPA in combination with taxane and platinum therapy (C/P).

METHODS

Dose escalation started with a standard 3 + 3 design for IPA/C/P with q3w intravenous IPA on Day 1, in cycles 1 to 6 with C (AUC = 5 mg/ml·min) and P (175 mg/m²). For enhanced bone safety the trial was revised to 6-patient cohorts with a q3w regimen of IPA on Day 1 and C/P on Day 3 (IPA → C/P).

RESULTS

37 patients have been treated; 30 of whom were treated following protocol revision to q3w IPA(D1) → C/P(D3) (2 & 4 mg/kg). IPA-related TEAEs that occurred in ≥15% included: fatigue (40%); nausea (35%); diarrhea and decreased appetite (22%) each; dysgeusia (19%); and vomiting (16.2%). 22% reported ≥1 IPA related TEAE Grade ≥3 the most common of which was neutropenia at 16%. There were no DLTs; the MTD was not reached. The maximum administered dose based on bone safety was 6 mg/kg. The overall response rate (ORR) was 75.7%. Median PFS was 10.3 months (95% CI 8.5-14.2) and OS 33 months (95% CI 23.4-NR).

CONCLUSIONS

IPA is well tolerated in combination with sequential C/P. ORR, PFS and OS are comparable to historical data but bone toxicity at efficacy doses of this particular Wnt inhibitor limit further development in EOC.

Colon cancer stem cells: Potential target for the treatment of colorectal cancer

Despite incessant research, colon cancer still is one of the most common causes of fatalities in both men and women worldwide. Also, nearly 50% of patients with colorectal cancer show tumor recurrence. Recent investigations have highlighted the involvement of colon cancer stem cells (CCSCs) in cancer relapse and chemoresistance. CCSCs deliver a significant protumorigenic niche through persistent overexpression of self-renewal capabilities. Moreover, CSCs cross network with stromal cells, immune infiltrates, and cyotokine-chemokine, which potentiate their aggressive proliferative potential. Targeting CCSCs through small molecule inhibitors, miRNAs, and monoclonal antibodies (mAbs) in in vivo studies has generated compelling evidence for the effectiveness of these various treatments. This review effectively compiles the role of CCSC surface markers and dysregulated and/or upregulated pathways in the pathogenesis of colorectal cancer that can be used to target CCSCs for effective colorectal cancer treatment.

Imatinib inhibits the regrowth of human colon cancer cells after treatment with 5-FU and cooperates with vitamin D analogue PRI-2191 in the downregulation of expression of stemness-related genes in 5-FU refractory cells

Conventional cytotoxic drugs preferentially eliminate differentiated cancer cells but spare relatively more resistant stem-like cancer cells capable to initiate recurrence. Due to cancer cell plasticity, the stem-like phenotype can be also acquired by cancer cells refractory to treatment with cytotoxic drugs. We investigated whether drugs inhibiting receptor tyrosine kinases could be used to target human colon cancer cells initiating cancer regrowth following conventional cytotoxic treatment. The moderately differentiated cell line HT-29 and poorly differentiated cell line HCT-116 were exposed to 5-fluorouracil (5-FU). Cells that resisted the exposure to 5-FU were subsequently treated with imatinib or sunitinib. Both drugs reduced clonogenicity of 5-FU-refractory cells under normoxic and hypoxic culture conditions. The expression of numerous stemness-related genes was upregulated in cancer cells following the exposure to 5-FU, and remained at a high level in 5-FU-refractory cells undergoing renewal under normoxia, but decreased spontaneously under hypoxia. Imatinib downregulated the expression of stemness-related genes in cells undergoing renewal under normoxia. A combination of imatinib with PRI-2191, an analogue of 1,25-dihydroxyvitamin D₃, downregulated stemness-related genes in HCT-116/5-FU cells more efficiently than imatinib alone. A synthetic analogue of 1,25-dihydroxyvitamin D₂ (PRI-1906) abolished the effect of imatinib on gene expression in HCT-116/5-FU cells undergoing renewal under normoxia. Sunitinib promoted shift of phenotype of HT-29/5-FU cells undergoing renewal toward stem-like one. It suggests that the phenotype shift toward stemness induced by sequential sunitinib treatment following 5-FU treatment could increase a risk of cancer recurrence. In contrast to sunitinib, imatinib could be used both to interfere with cancer regrowth after conventional chemotherapy and to downregulate the expression of stemness-related genes in residual colon cancer cells capable to initiate cancer recurrence. The findings suggest that imatinib could also be combined with vitamin D analogue PRI-2191 to prevent recurrence more efficiently than imatinib alone and to compensate for vitamin D deficiency resulting from imatinib treatment.

Immunogenicity of Tumor Initiating Stem Cells: Potential Applications in Novel Anticancer Therapy

Tumor initiating stem cells (TISCs) are a subset of tumor cells, which are implicated in cancer relapse and resistance to chemotherapy. The metabolic programs that drive TISC functions are exquisitely unique and finely-tuned by various oncogene-driven transcription factors to facilitate pro-cancerous adaptive challenges. While this change in TISC metabolic machinery allows for the identification of associated molecular targets with diagnostic and prognostic value, these molecules also have a potential immunological application. Recent studies have shown that these TISC-associated molecules have strong antigenic properties enabling naïve CD8+T lymphocytes to differentiate into cytotoxic effector phenotype with anticancer potential. In spite of the current challenges, a detailed understanding in this direction offers an immense immunotherapeutic opportunity. In this review, we highlight the molecular targets that characterize TISCs, the metabolic landscape of TISCs, potential antitumor immune cell activation, and the opportunities and challenges they present in the development of new cancer therapeutics.

Cancer-on-a-chip for Drug Screening

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The oncology pharmaceutical research spent a shocking amount of money on target validation and drug optimization in preclinical models because many oncology drugs fail during clinical trial phase III. One of the most important reasons for oncology drug failures in clinical trials may due to the poor predictive tool of existing preclinical models. Therefore, in cancer research and personalized medicine field, it is critical to improve the effectiveness of preclinical predictions of the drug response of patients to therapies and to reduce costly failures in clinical trials. Three dimensional (3D) tumor models combine micro-manufacturing technologies mimic critical physiologic parameters present in vivo, including complex multicellular architecture with multicellular arrangement and extracellular matrix deposition, packed 3D structures with cell–cell interactions, such as tight junctions, barriers to mass transport of drugs, nutrients and other factors, which are similar to in vivo tumor tissues. These systems provide a solution to mimic the physiological environment for improving predictive accuracy in oncology drug discovery.

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his review gives an overview of the innovations, development and limitations of different types of tumor-like construction techniques such as self-assemble spheroid formation, spheroids formation by micro-manufacturing technologies, micro-dissected tumor tissues and tumor organoid. Combination of 3D tumor-like construction and microfluidic techniques to achieve tumor on a chip for in vitro tumor environment modeling and drug screening were all included. Eventually, developmental directions and technical challenges in the research field are also discussed. We believe tumor on chip models have provided better sufficient clinical predictive power and will bridge the gap between proof-of-concept studies and a wider implementation within the oncology drug development for pathophysiological applications.

Augmented CD133 expression in distal margin correlates with poor prognosis in colorectal cancer

Pathological assessment of excised tumour and surgical margins in colorectal cancer (CRC) play crucial role in prognosis after surgery. Molecular assessment of margins could be more sensitive and informative than conventional histopathological analysis. Considering this view, we evaluated the distal surgical margins for expression of cancer stem cell (CSC) markers. Cellular and molecular assessment of normal, tumour and distal margin tissues were performed by flow cytometry, real-time q-PCR and immuno-histochemical analysis for CRC patients after tumour excision. CRC patients were evaluated for expression of CSC markers in their normal, tumour and distal tissues. Flow cytometry assay revealed CD133 and CD44 enriched cells in distal margin and tumour compared to normal colorectal tissues, which was further confirmed by immunohistochemistry. Most importantly, immunohistochemistry also revealed the enrichment of CSC markers expression in pathologically negative distal margins. Patients with distal margin enriched for CD133 expression showed an increased recurrence rate and decreased disease-free survival. This study proposes that although distal margin seems to be tumour free in conventional histopathological analysis, it could harbour cells enriched for CSC markers. Further CD133 could be a promising molecule to be used in molecular pathology for disease prognosis after surgery in CRC patients.

Stem cells in homeostasis and cancer of the gut

The intestinal epithelial lining is one of the most rapidly renewing cell populations in the body. As a result, the gut has been an attractive model to resolve key mechanisms in epithelial homeostasis. In particular the role of intestinal stem cells (ISCs) in the renewal process has been intensely studied. Interestingly, as opposed to the traditional stem cell theory, the ISC is not a static population but displays significant plasticity and in situations of tissue regeneration more differentiated cells can revert back to a stem cell state upon exposure to extracellular signals. Importantly, normal intestinal homeostasis provides important insight into mechanisms that drive colorectal cancer (CRC) development and growth. Specifically, the dynamics of cancer stem cells bear important resemblance to ISC functionality. In this review we present an overview of the current knowledge on ISCs in homeostasis and their role in malignant transformation. Also, we discuss the existence of stem cells in intestinal adenomas and CRC and how these cells contribute to (pre-)malignant growth. Furthermore, we will focus on new paradigms in the field of dynamical cellular hierarchies in CRC and the intimate relationship between tumor cells and their niche.

Nectin-1 Expression in Colorectal Cancer: Is There a Group of Patients with High Risk for Early Disease Recurrence?

BACKGROUND

Despite improvements in therapy of colorectal cancer, some patients will present occurrence of recurrence either locally or distantly. Tumor metastasis constitutes the major cause of cancer-associated morbidity and mortality. Nectin-1 belongs to the family of immunoglobulin-like cell adhesion molecules that contribute to the formation of cell-cell adhesions and regulate a series of cellular activities including cell polarization, differentiation, movement, proliferation, and survival. Expression of Nectin-1 in malignant tumors has been associated with aggressive tumor phenotypes.

OBJECTIVES

The aim of the present study was to assess Nectin-1 expression patterns in colorectal cancer and to investigate its clinical significance.

METHODS

Nectin-1 expression was assessed via immunohistochemistry in surgical specimens of a cohort comprised of 111 patients with primary resectable colorectal cancer. Results were correlated with clinicopathological characteristics and survival data. Progression-free survival was defined as the primary outcome of the present study.

RESULTS

Nectin-1 was strongly expressed in the cytoplasm of colorectal cancer cells. High Nectin-1 expression was associated with advanced stage of disease (p = 0.012) and lymph node metastasis (p = 0.007). Progression-free survival of patients exhibiting high expression of Nectin-1 in the first 36 months after surgery was significantly worse compared to patients with low expression of Nectin-1 (55.7%, 95% CI = 47-70, vs. 82.1%, 95% CI = 69-93, p = 0.014) and independent of other clinicopathological characteristics (HR = 0.389, 95% CI = 0.156-0.972, p = 0.043).

CONCLUSION

Nectin-1 expression in colorectal cancer is associated with a significantly worse 3-year progression-free survival identifying therefore a group of patients with high risk for early disease recurrence.

A Pan-ALDH1A Inhibitor Induces Necroptosis in Ovarian Cancer Stem-like Cells

Ovarian cancer is typified by the development of chemotherapy resistance. Chemotherapy resistance is associated with high aldehyde dehydrogenase (ALDH) enzymatic activity, increased cancer "stemness," and expression of the stem cell marker CD133. As such, ALDH activity has been proposed as a therapeutic target. Although it remains controversial which of the 19 ALDH family members drive chemotherapy resistance, ALDH1A family members have been primarily linked with chemotherapy resistant and stemness. We identified two ALDH1A family selective inhibitors (ALDH1Ai). ALDH1Ai preferentially kills CD133+ ovarian cancer stem-like cells (CSCs). ALDH1Ai induce necroptotic CSC death, mediated, in part, by the induction of mitochondrial uncoupling proteins and reduction in oxidative phosphorylation. ALDH1Ai is highly synergistic with chemotherapy, reducing tumor initiation capacity and increasing tumor eradication in vivo. These studies link ALDH1A with necroptosis and confirm the family as a critical therapeutic target to overcome chemotherapy resistance and improve patient outcomes.

MEK5/ERK5 activation regulates colon cancer stem-like cell properties

Colon cancer has been proposed to be sustained by a small subpopulation of stem-like cells with unique properties allowing them to survive conventional therapies and drive tumor recurrence. Identification of targetable signaling pathways contributing to malignant stem-like cell maintenance may therefore translate into new therapeutic strategies to overcome drug resistance. Here we demonstrated that MEK5/ERK5 signaling activation is associated with stem-like malignant phenotypes. Conversely, using a panel of cell line-derived three-dimensional models, we showed that ERK5 inhibition markedly suppresses the molecular and functional features of colon cancer stem-like cells. Particularly, pharmacological inhibition of ERK5 using XMD8-92 reduced the rate of primary and secondary sphere formation, the expression of pluripotency transcription factors SOX2, NANOG, and OCT4, and the proportion of tumor cells with increased ALDH activity. Notably, this was further associated with increased sensitivity to 5-fluorouracil-based chemotherapy. Mechanistically, ERK5 inhibition resulted in decreased IL-8 expression and NF-κB transcriptional activity, suggesting a possible ERK5/NF-κB/IL-8 signaling axis regulating stem-like cell malignancy. Taken together, our results provide proof of principle that ERK5-targeted inhibition may be a promising therapeutic approach to eliminate drug-resistant cancer stem-like cells and improve colon cancer treatment.

Pretreatment detection of circulating and tissue CD133+ CD44+ cancer stem cells as a prognostic factor affecting the outcomes in Egyptian patients with colorectal cancer

Background and aim

Colorectal cancer is one of the most common malignant tumors worldwide. As CD133 and CD44 are notable markers of cancer stem cells (CSCs) identity, it is thought to be a predictive indicator for colorectal cancer. The aim of this study was to investigate the cell cycle state of CD133⁺ CD44⁺ and CD133⁻ CD44⁻cells, isolated from primary human colorectal tumors, and to assess the clinical impact of CD133⁺ CD44⁺ CSCs on patients’ outcome regarding disease-free survival (DFS) and overall survival (OS).

Materials and methods

Tissue samples were collected from 50 primary colorectal cancer patients. Flow cytometric analysis was performed to isolate tissue CD133⁺ CD44⁺ CSCs and CD133⁻ CD44⁻ tumor cells from primary colorectal cancer tissue to compare the cell cycle of both types of cells. Also circulating CSCs were assessed by flow cytometry.

Results

Higher percentage of tissue CD133⁺ CD44⁺ CSCs isolated from colorectal cancer patients was found in G0/G1 phase. However, tissue CD133⁻ CD44⁻ tumor cells were predominantly found in the S phase; there were significant negative correlations between tissue CD133⁺ CD44⁺ CSCs and DFS and OS (r=−0.470, P<0.001, respectively and r=−0.487, P<0.001, respectively), also significant negative correlations between tissue CSCs and DFS and OS (r=−0.548, P<0.001, respectively and r=−0.497, P<0.001, respectively). Only the pathological grade (P<0.004) and T stage (P<0.004) had a significant effect on circulating CSC counts.

Conclusion

Tissue CD133⁺ CD44⁺ CSCs were more quiescent than tissue CD133⁻ CD44⁻ tumor cells and both circulating CSCs and tissue CSCs were considered independent negative prognostic factors on OS and DFS.

Biophysical Phenotyping and Modulation of ALDH+ Inflammatory Breast Cancer Stem-Like Cells

Cancer stem-like cells (CSCs) have been shown to initiate tumorigenesis and cancer metastasis in many cancer types. Although identification of CSCs through specific marker expression helps define the CSC compartment, it does not directly provide information on how or why this cancer cell subpopulation is more metastatic or tumorigenic. In this study, the functional and biophysical characteristics of aggressive and lethal inflammatory breast cancer (IBC) CSCs at the single-cell level are comprehensively profiled using multiple microengineered tools. Distinct functional (cell migration, growth, adhesion, invasion and self-renewal) and biophysical (cell deformability, adhesion strength and contractility) properties of ALDH+ SUM149 IBC CSCs are found as compared to their ALDH- non-CSC counterpart, providing biophysical insights into why CSCs has an enhanced propensity to metastasize. It is further shown that the cellular biophysical phenotype can predict and determine IBC cells' tumorigenic ability. SUM149 and SUM159 IBC cells selected and modulated through biophysical attributes-adhesion and stiffness-show characteristics of CSCs in vitro and enhance tumorigenicity in in vivo murine models of primary tumor growth. Overall, the multiparametric cellular biophysical phenotyping and modulation of IBC CSCs yields a new understanding of IBC's metastatic properties and how they might develop and be targeted for therapeutic interventions.

Aldehyde Dehydrogenases: Not Just Markers, but Functional Regulators of Stem Cells

Aldehyde dehydrogenase (ALDH) is a superfamily of enzymes that detoxify a variety of endogenous and exogenous aldehydes and are required for the biosynthesis of retinoic acid (RA) and other molecular regulators of cellular function. Over the past decade, high ALDH activity has been increasingly used as a selectable marker for normal cell populations enriched in stem and progenitor cells, as well as for cell populations from cancer tissues enriched in tumor-initiating stem-like cells. Mounting evidence suggests that ALDH not only may be used as a marker for stem cells but also may well regulate cellular functions related to self-renewal, expansion, differentiation, and resistance to drugs and radiation. ALDH exerts its functional actions partly through RA biosynthesis, as all-trans RA reverses the functional effects of pharmacological inhibition or genetic suppression of ALDH activity in many cell types in vitro. There is substantial evidence to suggest that the role of ALDH as a stem cell marker comes down to the specific isoform(s) expressed in a particular tissue. Much emphasis has been placed on the ALDH1A1 and ALDH1A3 members of the ALDH1 family of cytosolic enzymes required for RA biosynthesis. ALDH1A1 and ALDH1A3 regulate cellular function in both normal stem cells and tumor-initiating stem-like cells, promoting tumor growth and resistance to drugs and radiation. An improved understanding of the molecular mechanisms by which ALDH regulates cellular function will likely open new avenues in many fields, especially in tissue regeneration and oncology.

Heterogeneity of Colon Cancer Stem Cells

Colorectal cancer (CRC) remains the fourth leading cause of cancer death worldwide. Cancer stem cells (CSCs) have attracted a great deal of interest because of their potential clinical implications in a range of cancers, including CRC. CSCs were initially considered to be cell populations with well-defined phenotypic and molecular characteristics. However, accumulating evidence suggests that CSCs represent a phenotypically and functionally heterogeneous population. Recent studies also demonstrate colorectal CSCs to be dynamic rather than static populations that are continuously altered by various extrinsic factors in addition to intrinsic cellular factors such as genetic and epigenetic alterations. Thus, CSCs do not represent a fixed target population any longer, and their heterogeneous and dynamic nature present a serious problem in establishing specific therapeutic strategies. This chapter summarizes past and current literature related to CSC population heterogeneity and dynamics in CRC tissues, including evidence of the presence of distinct CSC subpopulations and signaling pathways and intra- and extra-tumoral factors involved in the regulation of CSCs in cancer tissues.

Therapeutic targeting of lipid synthesis metabolism for selective elimination of cancer stem cells

Cancer stem cells (CSCs) are believed to have an essential role in tumor resistance and metastasis; however, no therapeutic strategy for the selective elimination of CSCs has been established. Recently, several studies have shown that the metabolic regulation for ATP synthesis and biological building block generation in CSCs are different from that in bulk cancer cells and rather similar to that in normal tissue stem cells. To take advantage of this difference for CSC elimination therapy, many studies have tested the effect of blocking these metabolism. Two specific processes for lipid biosynthesis, i.e., fatty acid unsaturation and cholesterol biosynthesis, have been shown to be very effective and selective for CSC targets. In this review, lipid metabolism specific to CSCs are summarized. In addition, how monounsaturated fatty acid and cholesterol synthesis may contribute to CSC maintenance are discussed. Specifically, the molecular mechanism required for lipid synthesis and essential for stem cell biology is highlighted. The limit and preview of the lipid metabolism targeting for CSCs are also discussed.

Cancer stem cells as a therapeutic target in bladder cancer

Bladder cancer is one of the most prevalent genitourinary cancers responsible for about 150,000 deaths per year worldwide. Currently, several treatments, such as endoscopic and open surgery, appended by local or systemic immunotherapy, chemotherapy, and radiotherapy are used to treat this malignancy. However, the differences in treatment outcome among patients suffering from bladder cancer are considered as one of the important challenges. In recent years, cancer stem cells, representing a population of undifferentiated cells with stem-cell like properties, have been eyed as a major culprit for the high recurrence rate in superficial papillary bladder cancer. Cancer stem cells have been reported to be resistant to conventional treatments, such as chemotherapy, radiation, and immunotherapy, which induce selective pressure on tumoral populations resulting in selection and growth of the resistant cells. Therefore, targeting the therapeutic aspects of cancer stem cells in bladder cancer may be promising. In this study, we briefly discuss the biology of bladder cancer and then address the possible relationship between molecular biology of bladder cancer and cancer stem cells. Subsequently, the mechanisms of resistance applied by cancer stem cells against the conventional therapeutic tools, especially chemotherapy, are discussed. Moreover, by emphasizing the biomarkers described for cancer stem cells in bladder cancer, we have provided, described, and proposed targets on cancer stem cells for therapeutic interventions and, finally, reviewed some immunotargeting strategies against bladder cancer stem cells.

Tumidulin, a Lichen Secondary Metabolite, Decreases the Stemness Potential of Colorectal Cancer Cells

Lichens produce various unique chemicals that are used in the pharmaceutical industry. To screen for novel lichen secondary metabolites that inhibit the stemness potential of colorectal cancer cells, we tested acetone extracts of 11 lichen samples collected in Chile. Tumidulin, isolated from Niebla sp., reduced spheroid formation in CSC221, DLD1, and HT29 cells. In addition, mRNA expressions and protein levels of cancer stem markers aldehyde dehydrogenase-1 (ALDH1), cluster of differentiation 133 (CD133), CD44, Lgr5, and Musashi-1 were reduced after tumidulin treatment. Tumidulin decreased the transcriptional activity of the glioma-associated oncogene homolog zinc finger protein (Gli) promoter in reporter assays, and western blotting confirmed decreased Gli1, Gli2, and Smoothened (SMO) protein levels. Moreover, the tumidulin activity was not observed in the presence of Gli and SMO inhibitors. Together, these results demonstrate for the first time that tumidulin is a potent inhibitor of colorectal cancer cell stemness.

Poly(ADP-Ribose) Polymerase Inhibition Sensitizes Colorectal Cancer-Initiating Cells to Chemotherapy

Colorectal cancer (CRC) remains a leading killer in the U.S. with resistance to treatment as the largest hurdle to cure. Colorectal cancer-initiating cells (CICs) are a self-renewing tumor population that contribute to tumor relapse. Here, we report that patient-derived CICs display relative chemoresistance compared with differentiated progeny. In contrast, conventional cell lines failed model therapeutic resistance. CICs preferentially repaired chemotherapy-induced DNA breaks, prompting us to interrogate DNA damage pathways against which pharmacologic inhibitors have been developed. We found that CICs critically depended on the key single-strand break repair mediator, poly(ADP-ribose) polymerase (PARP), to survive treatment with standard-of-care chemotherapy. Small molecule PARP inhibitors (PARPi) sensitized CICs to chemotherapy and reduced chemotherapy-treated CIC viability, self-renewal, and DNA damage repair. Although PARPi monotherapy failed to kill CICs, combined PARPi therapy with chemotherapy attenuated tumor growth in vivo. Clinical significance of PARPi for CRC patients was supported by elevated PARP levels in colorectal tumors compared with normal colon, with further increases in metastases. Collectively, our results suggest that PARP inhibition serves as a point of fragility for CICs by augmenting therapeutic efficacy of chemotherapy. Stem Cells 2019;37:42-53.

Curcumin in combination with anti-cancer drugs: A nanomedicine review

A huge surge of research is being conducted on combination therapy with anticancer compounds formulated in the form of nanoparticles (NPs). Numerous advantages like dose minimalization and synergism, reversal of multi drug resistance (MDRs), enhanced efficacy have emerged with nanoencapsulation of chemotherapeutic agents with chemo-sensitizing agent like curcumin. Within last couple of years various nano-sized formulations have been designed and tested both in vitro with cell lines for different types of cancers and in vivo with cancer types and drug resistance models. Despite the combinatorial models being advanced, translation to human trials has not been as smooth as one would have hoped, with as few as twenty ongoing clinical trials with curcumin combination, with less than 1/10th being nano-particulate formulations. Mass production of nano-formulation based on their physico-chemical and pharmacokinetics deficits poses as major hurdle up the ladder. Combination of these nano-sized dosage with poorly bioavailable drugs, unspecific target binding ability and naturally unstable curcumin further complicates the formulation aspects. Emphasis is now therefore being laid on altering natural forms of curcumin and usage of formulations like prodrug or coating of curcumin to overcome stability issues and focus more on enhancing the pharmaceutical and therapeutic ability of the nano-composites. Current studies and futuristic outlook in this direction are discussed in the review, which can serve as the basis for upcoming research which could boost commercial translational of improved nano-sized curcumin combination chemotherapy.

Efficiency of All-Trans Retinoic Acid on Gastric Cancer: A Narrative Literature Review

Gastric cancer (GC) is the third leading cause of cancer-related death worldwide with a five-year survival rate of around 25%, and 4% when diagnosed at a metastatic stage. Cancer stem cells (CSC) have recently been characterized as being responsible for resistance to radio/chemotherapies and metastasis formation, opening up perspectives for new targeted therapies. Those CSCs express biomarkers such as cluster of differentiation 44 (CD44) and display high aldehyde dehydrogenase activity that converts vitamin A-derived retinal into retinoic acids. All-trans retinoic acid (ATRA), which has pro-differentiating properties, has revolutionized the prognosis of acute promyelotic leukemia by increasing its remission rate from 15% to 85%. Recent studies have started to show that ATRA also has an anti-tumoral role on solid cancers such as GC. The purpose of this review is therefore to summarize the work that evaluated the effects of ATRA in GC and to evaluate whether its anti-cancerous action involves gastric CSCs targeting. It has been demonstrated that ATRA can block the cell cycle, enhance apoptosis, and decrease gastric CSCs properties in GC cell lines, tumorspheres, and patient-derived xenograft mice models. Therefore, retinoids and new synthetic retinoids seem to be a promising step forward in targeted therapy of gastric CSC in combination with existing chemotherapies. Future studies should probably focus on these points.

Cancer stem cell populations in lymphoma in dogs and impact of cytotoxic chemotherapy

Cancer relapse following chemotherapy has been attributed in part to the presence of cancer stem cells (CSC), which drive tumour growth and metastasis and are highly resistant to the effects of cytotoxic chemotherapy. As a result, treatment with cytotoxic chemotherapy selects for drug-resistant CSC populations that eventually drive tumour recurrence. Little is known currently regarding the role of CSC in dogs with lymphoma, nor the impact of chemotherapy on CSC populations. Therefore, we prospectively quantitated CSC populations in dogs with B-cell (BCL) and T-cell lymphoma (TCL), using tumour aspirates and flow cytometric analysis with a panel of CSC markers. In addition, in vitro studies were carried out to determine the impact of chemotherapy resistance on the stem cell phenotype and stem cell properties of lymphoma cells. We found that the percentages of tumour cells expressing CSC markers were significantly increased in dogs with BCL, compared with B cells from normal lymph nodes. Similar findings were observed in dogs with TCL. In vitro studies revealed that lymphoma cells selected for resistance to CHOP chemotherapy had significantly upregulated expression of CSC markers, formed spheroids in culture more readily, and expressed significantly greater aldehyde dehydrogenase activity compared with chemotherapy-sensitive tumour cells. Similar results were observed in tumour samples dogs with relapsed BCL. These findings suggest that cytotoxic chemotherapy can lead to a relative enrichment of tumour cells with CSC properties, which may be associated with lymphoma recurrence.

Therapy-induced enrichment of cancer stem-like cells in solid human tumors: Where do we stand?

The development of local recurrence and metastatic disease, most probably attributable to the intrinsic or acquired resistance of tumor cells to standard therapy, still constitute the major clinical problem preventing the cure of cancer patients. Despite progress in the research of new therapeutic targets and compounds, resistant cells displaying stem-like properties seem to play a leading role in therapeutic failures and to be the culprit cells responsible for associated tumor recurrence. A whole new plethora of research studies suggest that drug-tolerant cancer stem cells may be induced by conventional cancer chemotherapeutics such as doxorubicin, cisplatinum and ionizing radiation. This phenotypic plasticity and transition from a differentiated to stem-like cell state associates with the activation of diverse stem cell self-renewal (e.g. Notch, Hedgehog, Wnt), drug efflux (e.g. ABC transporters) and survival-related pathways (e.g. TGF-β, ERK, AKT), which may confer resistance and treatment failures in solid tumors. Therefore, combined therapeutic strategies aiming to simultaneously target drug-sensitive tumor cells and their capacity of phenotypic switching may lead to survival benefits and meaningful disease remissions. This knowledge can be applicable to the clinic and contribute to better therapeutic outcomes and prevent tumor recurrence.

Structure-Based Optimization of a Novel Class of Aldehyde Dehydrogenase 1A (ALDH1A) Subfamily-Selective Inhibitors as Potential Adjuncts to Ovarian Cancer Chemotherapy

Aldehyde dehydrogenase (ALDH) activity is commonly used as a marker to identify cancer stem-like cells. The three ALDH1A isoforms have all been individually implicated in cancer stem-like cells and in chemoresistance; however, which isoform is preferentially expressed varies between cell lines. We sought to explore the structural determinants of ALDH1A isoform selectivity in a series of small-molecule inhibitors in support of research into the role of ALDH1A in cancer stem cells. An SAR campaign guided by a cocrystal structure of the HTS hit CM39 (7) with ALDH1A1 afforded first-in-class inhibitors of the ALDH1A subfamily with excellent selectivity over the homologous ALDH2 isoform. We also discovered the first reported modestly selective single isoform 1A2 and 1A3 inhibitors. Two compounds, 13g and 13h, depleted the CD133⁺ putative cancer stem cell pool, synergized with cisplatin, and achieved efficacious concentrations in vivo following IP administration. Compound 13h additionally synergized with cisplatin in a patient-derived ovarian cancer spheroid model.