CD133-positive cells are resistant to TRAIL due to up-regulation of FLIP

Mitochondria in Cancer Stem Cells: From an Innocent Bystander to a Central Player in Therapy Resistance

Cancer continues to rank among the world's leading causes of mortality despite advancements in treatment. Cancer stem cells, which can self-renew, are present in low abundance and contribute significantly to tumor recurrence, tumorigenicity, and drug resistance to various therapies. The drug resistance observed in cancer stem cells is attributed to several factors, such as cellular quiescence, dormancy, elevated aldehyde dehydrogenase activity, apoptosis evasion mechanisms, high expression of drug efflux pumps, protective vascular niche, enhanced DNA damage response, scavenging of reactive oxygen species, hypoxic stability, and stemness-related signaling pathways. Multiple studies have shown that mitochondria play a pivotal role in conferring drug resistance to cancer stem cells, through mitochondrial biogenesis, metabolism, and dynamics. A better understanding of how mitochondria contribute to tumorigenesis, heterogeneity, and drug resistance could lead to the development of innovative cancer treatments.

Prominin-1 deletion results in spermatogenic impairment, sperm morphological defects, and infertility in mice

Purpose

Spermatogenesis is a complex process orchestrated by several essential genes. Prominin-1 (Prom1/PROM1) is a gene that is expressed in the testis but with a poorly understood role in spermatogenesis.

Methods

We used Prom1 knockout (Prom1 KO) mice to assess the role of Prom1 in spermatogenesis. To this end, we performed immunohistochemistry, immunofluorescence, western blotting, β-galactosidase staining, and apoptosis assay. Additionally, we analyzed the morphology of sperm and assessed litter sizes.

Results

We observed that PROM1 is localized to the dividing spermatocytes in seminiferous epithelial cells, sperm, and columnar epithelium in the epididymis. In the Prom1 KO testis, an aberrant increase in apoptotic cells and a decrease in proliferating seminiferous epithelial cells were observed. Cellular FLICE-like inhibitory protein (c-FLIP) and extracellular signal-regulated kinase 1/2 (ERK1/2) expression were also significantly decreased in Prom1 KO testis. In addition, a significantly increased number of epididymal spermatozoa with abnormal morphology and less motility was found in Prom1 KO mice.

Conclusions

PROM1 maintains spermatogenic cell proliferation and survival via c-FLIP expression in the testis. It is also involved in sperm motility and fertilization potential. The mechanism underlying the effect of Prom1 on sperm morphology and motility remains to be identified.

Modulation of Spheroid Forming Capacity and TRAIL Sensitivity by KLF4 and Nanog in Gastric Cancer Cells

The expression of pluripotency factors, and their associations with clinicopathological parameters and drug response have been described in various cancers, including gastric cancer. This study investigated the association of pluripotency factor expression with the clinicopathological characteristics of gastric cancer patients, as well as changes in the expression of these factors upon the stem cell-enriching spheroid culture of gastric cancer cells, regulation of sphere-forming capacity, and response to cisplatin and TRAIL treatments by Nanog and KLF4. Nanog expression was significantly associated with the emergence of a new tumor and a worse prognosis in gastric cancer patients. The expression of the pluripotency factors varied among six gastric cancer cells. KLF4 and Nanog were expressed high in SNU-601, whereas SOX2 was expressed high in SNU-484. The expression of KLF4 and SOX2 was increased upon the spheroid culture of SNU-601 (KLF4/Nanog-high) and SNU-638 (KLF4/Nanog-low). The spheroid culture of them enhanced TRAIL-induced viability reduction, which was accompanied by the upregulation of death receptors, DR4 and DR5. Knockdown and overexpression of Nanog in SNU-601 and SNU-638, respectively, did not affect spheroid-forming capacity, however, its expression was inversely correlated with DR4/DR5 expression and TRAIL sensitivity. In contrast, KLF4 overexpression in SNU-638 increased spheroid formation, susceptibility to cisplatin and TRAIL treatments, and DR4/DR5 expression, while the opposite was found in KLF4-silenced SNU-601. KLF4 is supposed to play a critical role in DR4/DR5 expression and responses to TRAIL and cisplatin, whereas Nanog is only implicated in the former events only. Direct regulation of death receptor expression and TRAIL response by KLF4 and Nanog have not been well documented previously, and the regulatory mechanism behind the process remains to be elucidated.

Impact of Cancer Stem Cells on Therapy Resistance in Gastric Cancer

Gastric cancer (GC) is the fourth leading cause of cancer death worldwide, with an average 5-year survival rate of 32%, being of 6% for patients presenting distant metastasis. Despite the advances made in the treatment of GC, chemoresistance phenomena arise and promote recurrence, dissemination and dismal prognosis. In this context, gastric cancer stem cells (gCSCs), a small subset of cancer cells that exhibit unique characteristics, are decisive in therapy failure. gCSCs develop different protective mechanisms, such as the maintenance in a quiescent state as well as enhanced detoxification procedures and drug efflux activity, that make them insusceptible to current treatments. This, together with their self-renewal capacity and differentiation ability, represents major obstacles for the eradication of this disease. Different gCSC regulators have been described and used to isolate and characterize these cell populations. However, at the moment, no therapeutic strategy has achieved the effective targeting of gCSCs. This review will focus on the properties of cancer stem cells in the context of therapy resistance and will summarize current knowledge regarding the impact of the gCSC regulators that have been associated with GC chemoradioresistance.

Blood Circulating CD133+ Extracellular Vesicles Predict Clinical Outcomes in Patients with Metastatic Colorectal Cancer

Simple Summary

In this study, we explored the prognostic and predictive value of blood circulating EVs expressing selected surface proteins in patients with metastatic colorectal cancer (mCRC). A recently patented flow cytometry protocol was used for the identification and subtyping of blood circulating EVs in a cohort of patients with stage IV colorectal cancer (n = 54) and in a cohort of healthy controls (n = 48). We observed an increased blood concentration of tumor-induced blood circulating EVs in the mCRC cohort as compared to healthy controls. Additionally, we show an intriguing link between circulating CD133+ EVs and poor clinical outcomes in patients with mCRC. This study provides novel insights about the potential impact of EVs as a relevant source of candidate biomarkers in mCRC.

Abstract

Colorectal cancer (CRC) is one of the most incident and lethal malignancies worldwide. Recent treatment advances prolonged survival in patients with metastatic colorectal cancer (mCRC). However, there are still few biomarkers to guide clinical management and treatment selection in mCRC. In this study, we applied an optimized flow cytometry protocol for EV identification, enumeration, and subtyping in blood samples of 54 patients with mCRC and 48 age and sex-matched healthy controls (HCs). The overall survival (OS) and overall response rate (ORR) were evaluated in mCRC patients enrolled and treated with a first line fluoropyrimidine-based regimen. Our findings show that patients with mCRC presented considerably higher blood concentrations of total EVs, as well as CD133+ and EPCAM+ EVs compared to HCs. Overall survival analysis revealed that increased blood concentrations of total EVs and CD133+ EVs before treatment were significantly associated with shorter OS in mCRC patients (p = 0.001; and p = 0.0001, respectively). In addition, we observed a correlation between high blood levels of CD133+ EVs at baseline and reduced ORR to first-line systemic therapy (p = 0.045). These findings may open exciting perspectives into the application of novel blood-based EV biomarkers for improved risk stratification and optimized treatment strategies in mCRC.

Messing Up the Cancer Stem Cell Chemoresistance Mechanisms Supported by Tumor Microenvironment

Despite the recent advances in cancer patient management and in the development of targeted therapies, systemic chemotherapy is currently used as a first-line treatment for many cancer types. After an initial partial response, patients become refractory to standard therapy fostering rapid tumor progression. Compelling evidence highlights that the resistance to chemotherapeutic regimens is a peculiarity of a subpopulation of cancer cells within tumor mass, known as cancer stem cells (CSCs). This cellular compartment is endowed with tumor-initiating and metastasis formation capabilities. CSC chemoresistance is sustained by a plethora of grow factors and cytokines released by neighboring tumor microenvironment (TME), which is mainly composed by adipocytes, cancer-associated fibroblasts (CAFs), immune and endothelial cells. TME strengthens CSC refractoriness to standard and targeted therapies by enhancing survival signaling pathways, DNA repair machinery, expression of drug efflux transporters and anti-apoptotic proteins. In the last years many efforts have been made to understand CSC-TME crosstalk and develop therapeutic strategy halting this interplay. Here, we report the combinatorial approaches, which perturb the interaction network between CSCs and the different component of TME.

Long non-coding RNAs in cancer stem cells

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Long non coding RNAs are involved in the regulation of multiple cellular processes.

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Cancer stemness and escape from immunological anti-cancer mechanisms are important mechanisms of resistance to anti-cancer agents and are pivotal in controlling cancer development and metastases.

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Long non coding RNAs have deep effects on the immune-modulation and on the control of cancer stem cells.

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Several pathways involved in immunological escape and cancer stemness are modulated by long non coding RNAs.

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Targeting long non coding RNAs is a potential new strategy to control tumor development and metastases.

In recent years, it has been evidenced that the human transcriptome includes several types of non-coding RNAs (ncRNAs) that are mainly involved in the regulation of different cellular processes. Among ncRNAs, long-non-coding RNAs (lncRNAs) are defined as longer than 200 nucleotides and have been shown to be involved in several physiological and pathological events, including immune system regulation and cancer. Cancer stem cells (CSCs) are defined as a population of cancer cells that possess characteristics, such as resistance to standard treatments, cancer initiation, ability to undergo epithelial-to-mesenchymal transition, and the ability to invade, spread, and generate metastases. The cancer microenvironment, together with genetic and epigenetic factors, is fundamental for CSC maintenance and tumor growth and progression. Unsurprisingly, lncRNAs have been involved in both CSC biology and cancer progression, prognosis and recurrence. Here we review the most recent literature on IncRNAs involvement in CSC biology and function.

M1 Macrophages Promote TRAIL Expression in Adipose Tissue-Derived Stem Cells, Which Suppresses Colitis-Associated Colon Cancer by Increasing Apoptosis of CD133+ Cancer Stem Cells and Decreasing M2 Macrophage Population

We have previously reported that adipose tissue-derived stem cells (ASCs) cultured at high cell density can induce cancer cell death through the expression of type I interferons and tumor necrosis factor (TNF)-related apoptosis-inducing ligands (TRAIL). Here, we investigated whether TRAIL-expressing ASCs induced by M1 macrophages can alleviate colitis-associated cancer in an azoxymethane (AOM)/dextran sodium sulfate (DSS) animal model. M1 macrophages significantly increased the TRAIL expression in ASCs, which induced the apoptosis of LoVo cells in a TRAIL-dependent manner. However, CD133^knockout LoVo cells, generated using the CRISPR-Cas9 gene-editing system, were resistant to TRAIL. In the AOM/DSS-induced colitis-associated cancer model, the intraperitoneal transplantation of TRAIL-expressing ASCs significantly suppressed colon cancer development. Moreover, immunohistochemical staining revealed a low CD133 expression in tumors from the AOM/DSS + ASCs group when compared with tumors from the untreated group. Additionally, the ASC treatment selectively reduced the number of M2 macrophages in tumoral (45.7 ± 4.2) and non-tumoral mucosa (30.3 ± 1.5) in AOM/DSS + ASCs-treated animals relative to those in the untreated group (tumor 71.7 ± 11.2, non-tumor 94.3 ± 12.5; p < 0.001). Thus, TRAIL-expressing ASCs are promising agents for anti-tumor therapy, particularly to alleviate colon cancer by inducing the apoptosis of CD133⁺ cancer stem cells and decreasing the M2 macrophage population.

Cancer Stem Cells and Targeting Strategies

Chemoresistance is a major problem in cancer therapy as cancer cells develop mechanisms that counteract the effect of chemotherapeutic compounds, leading to relapse and the development of more aggressive cancers that contribute to poor prognosis and survival rates of treated patients. Cancer stem cells (CSCs) play a key role in this event. Apart from their slow proliferative property, CSCs have developed a range of cellular processes that involve drug efflux, drug enzymatic inactivation and other mechanisms. In addition, the microenvironment where CSCs evolve (CSC niche), effectively contributes to their role in cancer initiation, progression and chemoresistance. In the CSC niche, immune cells, mesenchymal stem cells (MSCs), endothelial cells and cancer associated fibroblasts (CAFs) contribute to the maintenance of CSC malignancy via the secretion of factors that promote cancer progression and resistance to chemotherapy. Due to these factors that hinder successful cancer therapies, CSCs are a subject of intense research that aims at better understanding of CSC behaviour and at developing efficient targeting therapies. In this review, we provide an overview of cancer stem cells, their role in cancer initiation, progression and chemoresistance, and discuss the progress that has been made in the development of CSC targeted therapies.

Mesenchymal Stem Cell Expressing TRAIL as Targeted Therapy against Sensitised Tumour

Tapping into the ability of engineered mesenchymal stem cells (MSCs) to mobilise into the tumour has expanded the scope of cancer treatment. Engineered MSCs expressing tumour necrosis factor (TNF)-related apoptosis inducing ligand (MSC-TRAIL) could serve as a platform for an efficient and targeted form of therapy. However, the presence of cancer stem cells (CSCs) that are resistant to TRAIL and apoptosis may represent a challenge for effective treatment. Nonetheless, with the discovery of small molecular inhibitors that could target CSCs and tumour signalling pathways, a higher efficacy of MSC-TRAIL mediated tumour inhibition can be achieved. This might pave the way for a more effective form of combined therapy, which leads to a better treatment outcome. In this review, we first discuss the tumour-homing capacity of MSCs, its effect in tumour tropism, the different approach behind genetically-engineered MSCs, and the efficacy and safety of each agent delivered by these MSCs. Then, we focus on how sensitisation of CSCs and tumours using small molecular inhibitors can increase the effect of these cells to either TRAIL or MSC-TRAIL mediated inhibition. In the conclusion, we address a few questions and safety concerns regarding the utilization of engineered MSCs for future treatment in patients.

Preferential targeting of cancer stem cells in the radiosensitizing effect of ABT-737 on HNSCC

Head and neck squamous cell carcinomas (HNSCC) are common human malignancies with poor clinical outcomes. The 5-year survival rates for patients with advanced stage HNSCC have not changed appreciably in the past few decades, underscoring a dire need for improved therapeutic options. HNSCC is frequently characterized by overexpression of anti-apoptotic Bcl-2 family members. Increased levels of these anti-apoptotic proteins have been associated with radio- and chemoresistance and poor clinical outcome. The aim of this study was to evaluate combined effects of radiation and ABT-737, a BH3-mimetic molecule, in HNSCC. Although ABT-737, as a single agent, was largely ineffective at promoting HNSCC cell death, we found that combining ABT-737 and radiation induced strong synergistic apoptosis in HNSCC cell lines and delayed tumoral growth in vivo. Moreover, we demonstrated for the first time that ABT-737, alone or in combination with radiation, can efficiently eliminate cancer stem cells (CSCs). Altogether, our results indicate that therapy targeting anti-apoptotic Bcl-2 family members could be a highly effective potential adjuvant to radiotherapy capable of targeting CSCs in HNSCC and therefore overcoming cancer recurrence and metastasis.

Expression of nestin, CD133 and ABCG2 in relation to the clinical outcome in pediatric sarcomas

BACKGROUND

Nestin, CD133 and ABCG2 are recently discussed as putative markers, co-expression of which might determine a cancer stem cell (CSC) phenotype in sarcomas.

OBJECTIVE

Our study is focused on immunohistochemical analysis of nestin, CD133 and ABCG2 expression in rhabdomyosarcoma, Ewing sarcoma and osteosarcoma. Furthermore, we also analyzed the possible correlation of nestin, CD133 and ABCG2 expression levels with the patient outcome to identify potential prognostic values of these three putative CSC markers in the same cohorts.

METHODS

Using immunohistochemistry, expression of nestin, CD133 and ABCG2 was analyzed in 24 rhabdomyosarcoma, 22 Ewing sarcoma and 10 osteosarcoma tissue samples and expression levels of these markers were correlated with clinical outcome.

RESULTS

High nestin levels indicate poor prognosis in patients with Ewing sarcoma (P = 0.001), and high CD133 expression is associated with shorter survival in rhabdomyosarcoma patients (P = 0.002). In contrast, no significant relationship was found between ABCG2 expression and the clinical outcome.

CONCLUSIONS

Our analysis represents the first complex study of these three putative CSCs markers together in three different types of pediatric sarcomas and showed their possible prognostic values in these tumors.

The role of cancer stem cells in tumor heterogeneity and resistance to therapy

Cancer is a heterogenous disease displaying marked inter- and intra-tumoral diversity. The existence of cancer stem cells (CSCs) has been experimentally demonstrated in a number of cancer types as a subpopulation of tumor cells that drives the tumorigenic and metastatic properties of the entire cancer. Thus, eradication of the CSC population is critical for the complete ablation of a tumor. This is, however, confounded by the inherent resistance of CSCs to standard anticancer therapies, eventually leading to the outgrowth of resistant tumor cells and relapse in patients. The cellular mechanisms of therapy resistance in CSCs are ascribed to several factors including a state of quiescence, an enhanced DNA damage response and active repair mechanisms, up-regulated expression of drug efflux transporters, as well as the activation of pro-survival signaling pathways and inactivation of apoptotic signaling. Understanding the mechanisms underlying the acquisition of resistance to therapy may hold the key to targeting the CSC population.

Nanomedicine-Mediated Therapies to Target Breast Cancer Stem Cells

Accumulating evidences have suggested the existence of breast cancer stem cells (BCSCs), which possess the potential of both self-renewal and differentiation. The origin of BCSCs might have relationship to the development of normal mammary stem cells. BCSCs are believed to play a key role in the initiation, recurrence and chemo-/radiotherapy resistances of breast cancer. Therefore, elimination of BCSCs is crucial for breast cancer therapy. However, conventional chemo and radiation therapies cannot eradicate BCSCs effectively. Fortunately, nanotechnology holds great potential for specific and efficient anti-BCSCs treatment. “Smart” nanocarriers can distinguish BCSCs from the other breast cancer cells and selectively deliver therapeutic agents to the BCSCs. Emerging findings suggest that BCSCs in breast cancer could be successfully inhibited and even eradicated by functionalized nanomedicines. In this review, we focus on origin of BCSCs, strategies used to target BCSCs, and summarize the nanotechnology-based delivery systems that have been applied for eliminating BCSCs in breast cancer.

Role of nanotechnology and gene delivery systems in TRAIL-based therapies

Since its identification as a member of the tumour necrosis factor (TNF) family, TRAIL (TNF-related apoptosis-inducing ligand) has emerged as a new avenue in apoptosis-inducing cancer therapies. Its ability to circumvent the chemoresistance of conventional therapeutics and to interact with cancer stem cells (CSCs) self-renewal pathways, amplified its potential as a cancer apoptotic agent. Many recombinant preparations of this death ligand and monoclonal antibodies targeting its death receptors have been tested in monotherapy and combinational clinical trials. Gene therapy is a new approach for cancer treatment which implies viral or non-viral functional transgene induction of apoptosis in cancer cells or repair of the underlying genetic abnormality on a molecular level. The role of this approach in overcoming the traditional barriers of radiation and chemotherapeutics systemic toxicity, risk of recurrence, and metastasis made it a promising platform for cancer treatment. The recent first Food Drug Administration (FDA) approved oncolytic herpes virus for melanoma treatment brings forth the potency of the cancer gene therapy approach in the future. Many gene delivery systems have been studied for intratumoural TRAIL gene delivery alone or in combination with chemotherapeutic agents to produce synergistic cancer cytotoxicity. However, there still remain many obstacles to be conquered for this different gene delivery systems. Nanomedicine on the other hand offers a new frontier for clinical trials and biomedical research. The FDA approved nanodrugs motivates horizon exploration for other nanoscale designed particles’ implications in gene delivery. In this review we aim to highlight the molecular role of TRAIL in apoptosis and interaction with cancer stem cells (CSCs) self-renewal pathways. Finally, we also aim to discuss the different roles of gene delivery systems, mesenchymal cells, and nanotechnology designs in TRAIL gene delivery.

Cancer Stem Cells: The Potential Targets of Chinese Medicines and Their Active Compounds

The pivotal role of cancer stem cells (CSCs) in the initiation and progression of malignancies has been rigorously validated, and the specific methods for identifying and isolating the CSCs from the parental cancer population have also been rapidly developed in recent years. This review aims to provide an overview of recent research progress of Chinese medicines (CMs) and their active compounds in inhibiting tumor progression by targeting CSCs. A great deal of CMs and their active compounds, such as Antrodia camphorate, berberine, resveratrol, and curcumin have been shown to regress CSCs, in terms of reversing drug resistance, inducing cell death and inhibiting cell proliferation as well as metastasis. Furthermore, one of the active compounds in coptis, berbamine may inhibit tumor progression by modulating microRNAs to regulate CSCs. The underlying molecular mechanisms and related signaling pathways involved in these processes were also discussed and concluded in this paper. Overall, the use of CMs and their active compounds may be a promising therapeutic strategy to eradicate cancer by targeting CSCs. However, further studies are needed to clarify the potential of clinical application of CMs and their active compounds as complementary and alternative therapy in this field.

Modified STAP conditions facilitate bivalent fate decision between pluripotency and apoptosis in Jurkat T-lymphocytes

Low extracellular pH (pHe) is not only the result of cancer metabolism, but a factor of anti-cancer drug efficacy and cancer immunity. In this study, the consequences of acidic stress were evaluated by applying STAP protocol on Jurkat T-lymphocytes (2.0 × 10(6) cells/ml, 25 min in 37 °C). We detected apoptotic process exclusively in pH 3.3 treated cells within 8 h with western blotting (WB). This programmed cell death led to significant drop of cell viability in 72 h measured by MTT assay resulting PI positive population on flow cytometry (FCM) at day 7. Quantified RT-PCR (qRT-PCR) data indicated that all of above mentioned responses are irrelevant to expression of OCT4 gene variants. Interestingly enough, pluripotent cells represented by positive alkaline phosphatase (AP) staining survived acidic stress and consequently proportion of AP positive cells was significantly increased after pH 3.3 treatment (day 7). In general, acidic treatment led to an apoptotic condition for Jurkat T-lymphocytes, which occurred independent of OCT4 induction.

Disruptive environmental chemicals and cellular mechanisms that confer resistance to cell death

Cell death is a process of dying within biological cells that are ceasing to function. This process is essential in regulating organism development, tissue homeostasis, and to eliminate cells in the body that are irreparably damaged. In general, dysfunction in normal cellular death is tightly linked to cancer progression. Specifically, the up-regulation of pro-survival factors, including oncogenic factors and antiapoptotic signaling pathways, and the down-regulation of pro-apoptotic factors, including tumor suppressive factors, confers resistance to cell death in tumor cells, which supports the emergence of a fully immortalized cellular phenotype. This review considers the potential relevance of ubiquitous environmental chemical exposures that have been shown to disrupt key pathways and mechanisms associated with this sort of dysfunction. Specifically, bisphenol A, chlorothalonil, dibutyl phthalate, dichlorvos, lindane, linuron, methoxychlor and oxyfluorfen are discussed as prototypical chemical disruptors; as their effects relate to resistance to cell death, as constituents within environmental mixtures and as potential contributors to environmental carcinogenesis.

Harnessing the apoptotic programs in cancer stem-like cells

Elimination of malignant cells is an unmet challenge for most human cancer types even with therapies targeting specific driver mutations. Therefore, a multi-pronged strategy to alter cancer cell biology on multiple levels is increasingly recognized as essential for cancer cure. One such aspect of cancer cell biology is the relative apoptosis resistance of tumor-initiating cells. Here, we provide an overview of the mechanisms affecting the apoptotic process in tumor cells emphasizing the differences in the tumor-initiating or stem-like cells of cancer. Further, we summarize efforts to exploit these differences to design therapies targeting that important cancer cell population.

Small-Molecule ONC201/TIC10 Targets Chemotherapy-Resistant Colorectal Cancer Stem-like Cells in an Akt/Foxo3a/TRAIL-Dependent Manner

Self-renewing colorectal cancer stem/progenitor cells (CSC) contribute to tumor maintenance and resistance to therapy. Therapeutic targeting of CSCs could improve treatment response and prolong patient survival. ONC201/TIC10 is a first-in-class antitumor agent that induces TRAIL pathway-mediated cell death in cancer cells without observed toxicity. We have previously described that ONC201/TIC10 exposure leads to transcriptional induction of the TRAIL gene via transcription factor Foxo3a, which is activated by dual inactivation of Akt and ERK. The Akt and ERK pathways serve as important targets in CSCs. Foxo3a is a key mediator of Akt and ERK-mediated CSC regulation. We hypothesized that the potent antitumor effect of ONC201/TIC10 in colorectal cancer involves targeting CSCs and bulk tumor cells. ONC201/TIC10 depletes CD133(+), CD44(+), and Aldefluor(+) cells in vitro and in vivo. TIC10 significantly inhibits colonosphere formation of unsorted and sorted 5-fluorouracil-resistant CSCs. ONC201/TIC10 significantly reduces CSC-initiated xenograft tumor growth in mice and prevents the passage of these tumors. ONC201/TIC10 treatment also decreased xenograft tumor initiation and was superior to 5-fluorouracil treatment. Thus, ONC201/TIC10 inhibits CSC self-renewal in vitro and in vivo. ONC201/TIC10 inhibits Akt and ERK, consequently activating Foxo3a and significantly induces cell surface TRAIL and DR5 expression in both CSCs and non-CSCs. ONC201/TIC10-mediated anti-CSC effect is significantly blocked by the TRAIL sequestering antibody RIK-2. Overexpression of Akt, DR5 knockdown, and Foxo3a knockdown rescues ONC201/TIC10-mediated depletion of CD44(+) cells and colonosphere inhibition. In conclusion, ONC201/TIC10 is a promising agent for colorectal cancer therapy that targets both non-CSCs and CSCs in an Akt-Foxo3a-TRAIL-dependent manner.

Differential characteristics of CD133(+) and CD133 (-) Jurkat cells

T cell acute lymphoblastic leukemia (T-ALL) is a hematological disease including malignancy of T cell precursors. There are some T-ALL patients that are drug-resistant. A major cause of treatment failure in cancers can be associated with the existence of cancer stem cells. The identification of these cell populations helps us to clarify resistance mechanisms and rely on special markers for recognizing cancer stem cells. CD133 is one of the markers that is used for the identification of cancer stem cells. In this study, we evaluated CD133(+) and CD133(-) characteristic cells in Jurkat cells by assay proliferation, invasion, and apoptosis. CD133(+) and CD133(-) Jurkat cells were separated and immediately analyzed for proliferation, invasion, and doxorubicin-induced apoptosis. Proliferation, invasion, and resistance to chemotherapy of CD133(+) Jurkat cells were significantly more than CD133(-) Jurkat cells. Also, our results showed that CD133(+) Jurkat cells expressed ABCG2 gene more than CD133(-) Jurkat cells. In conclusion, CD133 marker could be introduced as a specific marker of cancer stem cells in Jurkat cell line.

Targeting death receptors for TRAIL by agents designed by Mother Nature

Selective killing of cancer cells is one of the major goals of cancer therapy. Although chemotherapeutic agents are being used for cancer treatment, they lack selectivity toward tumor cells. Among the six different death receptors (DRs) identified to date, DR4 and DR5 are selectively expressed on cancer cells. Therefore, unlike chemotherapeutic agents, these receptors can potentially mediate selective killing of tumor cells. In this review we outline various nutraceuticals derived from 'Mother Nature' that can upregulate DRs and thus potentiate apoptosis. These nutraceuticals increase tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of cancer cells through different mechanisms. First, nutraceuticals have been found to induce DRs through the upregulation of various signaling molecules. Second, nutraceuticals can downregulate tumor cell-survival pathways. Third, nutraceuticals alone have been found to activate cell-death pathways. Although both TRAIL and agonistic antibodies against DR4 and DR5 are in clinical trials, combination with nutraceuticals is likely to boost their anticancer potential.

Harnessing of Programmed Necrosis for Fighting against Cancers

Chemotherapy has long been considered as one of useful strategies for cancer treatment. It is primarily based on the apoptosis that can selectively kill cancer cells. However, cancer cells can progressively develop an acquired resistance to apoptotic cell death, rendering refractory to chemo- and radiotherapies. Although the mechanism by which cells attained resistance to drug remains to be clarified, it might be caused by either pumping out of them or interfering with apoptotic signal cascades in response to cancer drugs. In case that cancer cells are defective in some part of apoptotic machinery by repeated exposure to anticancer drugs, alternative cell death mechanistically distinct from apoptosis could be adopted to remove cancer cells refractory to apoptosis-inducing agents. This review will mainly deal with harnessing of necrotic cell death, specifically, programmed necrosis and practical uses. Here, we begin with various defects of apoptotic death machinery in cancer cells, and then provide new perspective on programmed necrosis as an alternative anticancer approach.

Apoptotic death of cancer stem cells for cancer therapy

Cancer stem cells (CSCs) play crucial roles in tumor progression, chemo- and radiotherapy resistance, and recurrence. Recent studies on CSCs have advanced understanding of molecular oncology and development of novel therapeutic strategies. This review article updates the hypothesis and paradigm of CSCs with a focus on major signaling pathways and effectors that regulate CSC apoptosis. Selective CSC apoptotic inducers are introduced and their therapeutic potentials are discussed. These include synthetic and natural compounds, antibodies and recombinant proteins, and oligonucleotides.

MC3 Mucoepidermoid carcinoma cell line enriched cancer stem-like cells following chemotherapy

Mucoepidermoid carcinoma (MEC) is common in human salivary glands. Surgery is the preferred treatment method for MEC and chemotherapy is often administered following surgery as an adjuvant cancer treatment; however, chemotherapy does not completely prevent tumor recurrence. Emerging evidence has indicated the existence of cancer stem-like (CSL)-cells in tumors. CSL-cells are important in the development, invasion and drug resistance of carcinomas. The present study aimed to investigate whether chemotherapy enriched the CSL-cells in the MEC cell line of MC3 using 5-fluorouracil (5-Fu). The MC3 cells were treated with 5-Fu, which enhanced the spherogenesis and vitality of the cells and upregulated the pluripotency gene, octamer-binding transcription factor 4. Side population analysis demonstrated that the proportion of CSL-cells also increased. These findings showed that compared with other types of cancer cells, chemotherapy was unable to effectively kill the CSL-cells resulting in an enriched CSL-cell subpopulation with a higher resistance to chemotherapy, which may have been key the recurrence of MEC.

Amurensin G enhances the susceptibility to tumor necrosis factor-related apoptosis-inducing ligand-mediated cytotoxicity of cancer stem-like cells of HCT-15 cells

Cancer stem cells (CSCs) are resistant to radiotherapy and chemotherapy and play a significant role in cancer recurrence. Design of better treatment strategies that can eliminate or otherwise control CSC populations in tumors is necessary. In this study, the sensitivity to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced cytotoxicity and the effect of amurensin G, a novel sirtuin 1 (SIRT1) inhibitor, were examined using the CSC-enriched fraction of HCT-15 human colon cancer cells. Cancer stem cell-enriched HCT-15 colony cells were paradoxically less sensitive to doxorubicin, and more sensitive to TRAIL-induced cytotoxicity, than their parental cells. Also, CD44(+) HCT-15 cells were more susceptible to TRAIL-mediated cytotoxicity than CD44(-) HCT-15 cells, possibly due to increased levels of death receptors DR4 and DR5 as well as c-Myc, and decreased levels of c-FLIPL /S in CD44(+) cells compared with CD44(-) HCT-15 cells. The combination effect of amurensin G on TRAIL-mediated cytotoxicity was much more apparent in CD44(+) cells than in CD44(-) HCT-15 cells, and this was associated with more prominent downregulation of c-FLIP(L/S) in CD44(+) cells than in CD44(-) HCT-15 cells. These results indicate that HCT-15 colony or CD44(+) cells, which may have CSC properties, are more sensitive to TRAIL than parental or CD44(-) HCT-15 cells. Amurensin G may be effective in eliminating colon CSCs and be applicable to potentiate the sensitivity of colon CSCs to TRAIL.

Immunocapture of CD133-positive cells from human cancer cell lines by using monodisperse magnetic poly(glycidyl methacrylate) microspheres containing amino groups

Magnetic poly(glycidyl methacrylate)-based macroporous microspheres with an average particle size of 4.2μm were prepared using a modified multi-step swelling polymerization method and by introducing amino functionality on their surfaces. Antibody molecules were oxidized on their carbohydrate moieties and bound to the amino-containing magnetic microspheres via a site-directed procedure. CD133-positive cells could be effectively captured from human cancer cell lines (HepG2, HCT116, MCF7, and IMR-32) by using magnetic microspheres conjugated to an anti-human CD133 antibody. After further culture, the immunocaptured CD133-expressing cells from IMR-32 proliferated and gradually detached from the magnetic microspheres. Flow-cytometric analysis confirmed the enrichment of CD133-expressing cells by using the antibody-bound magnetic microspheres. Such microspheres suitable for immunocapture are very promising for cancer diagnosis because the CD133-expressing cells in cancer cell lines have been suggested to be cancer stem cells.

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.

CD133/prominin-1-mediated autophagy and glucose uptake beneficial for hepatoma cell survival

CD133/Prominin-1 is a pentaspan transmembrane protein that has been frequently used as a biomarker for cancer stem cells, although its biological function is unclear. The aim of our study was to explore the intrinsic functions of CD133 membrane protein in hepatoma cells during autophagy, apoptosis, tumorigenesis and cell survival through expression or downregulation of CD133. In this study, CD133 was found to be dynamically released from plasma membrane into cytoplasm in both of complete medium(CM) and low glucose medium (LGM), and LGM promoted this translocation. Expression of CD133 enhanced autophagic activity in LGM, while silencing CD133 attenuated this activity in HCC LM3 and Huh-7 cells, suggesting that CD133 is associated with autophagy. Immunofluorescence and time-lapsed confocal techniques confirmed that CD133 was associated with autophagy marker, microtubule-associated protein light chain3 (LC3) and lysosome marker during the glucose starvation. We further found that Huh-7 cells with stable expression of shCD133 (Huh-7sh133) impaired the ability of cell proliferation and formation of xenograft tumors in the NOD/SCID mice. Although loss of CD133 did not affect the rates of glucose uptake in Huh-7con and Huh-7sh133 cells under the CM, Huh-7sh133 cells obviously died fast than Huh-7con cells in the LGM and decreased the rate of glucose uptake and ATP production. Furthermore, targeting CD133 by CD133mAb resulted in cell death in HepG2 cells, especially in the LGM, via inhibition of autophagic activity and increase of apoptosis. The results demonstrated that CD133 is involved in cell survival through regulation of autophagy and glucose uptake, which may be necessary for cancer stem cells to survive in tumor microenvironment.

Therapeutic strategies targeting cancer stem cells

Increasing studies have demonstrated a small proportion of cancer stem cells (CSCs) exist in the cancer cell population. CSCs have powerful self-renewal capacity and tumor-initiating ability and are resistant to chemotherapy and radiation. Conventional anticancer therapies kill the rapidly proliferating bulk cancer cells but spare the relatively quiescent CSCs, which cause cancer recurrence. So it is necessary to develop therapeutic strategies acting specifically on CSCs. In recent years, studies have shown that therapeutic agents such as metformin, salinomycin, DECA-14, rapamycin, oncostatin M (OSM), some natural compounds, oncolytic viruses, microRNAs, cell signaling pathway inhibitors, TNF-related apoptosis inducing ligand (TRAIL), interferon (IFN), telomerase inhibitors, all-trans retinoic acid (ATRA) and monoclonal antibodies can suppress the self-renewal of CSCs in vitro and in vivo. A combination of these agents and conventional chemotherapy drugs can significantly inhibit tumor growth, metastasis and recurrence. These strategies targeting CSCs may bring new hopes to cancer therapy.

Ionizing radiation induces stemness in cancer cells

The cancer stem cell (CSC) model posits the presence of a small number of CSCs in the heterogeneous cancer cell population that are ultimately responsible for tumor initiation, as well as cancer recurrence and metastasis. CSCs have been isolated from a variety of human cancers and are able to generate a hierarchical and heterogeneous cancer cell population. CSCs are also resistant to conventional chemo- and radio-therapies. Here we report that ionizing radiation can induce stem cell-like properties in heterogeneous cancer cells. Exposure of non-stem cancer cells to ionizing radiation enhanced spherogenesis, and this was accompanied by upregulation of the pluripotency genes Sox2 and Oct3/4. Knockdown of Sox2 or Oct3/4 inhibited radiation–induced spherogenesis and increased cellular sensitivity to radiation. These data demonstrate that ionizing radiation can activate stemness pathways in heterogeneous cancer cells, resulting in the enrichment of a CSC subpopulation with higher resistance to radiotherapy.

Regulation of apoptosis pathways in cancer stem cells

Cancer stem cell are considered to represent a population within the bulk tumor that share many similarities to normal stem cells as far as their capacities to self-renew, differentiate, proliferate and to reconstitute the entire tumor upon serial transplantation are concerned. Since cancer stem cells have been shown to be critical for maintaining tumor growth and have been implicated in treatment resistance and tumor progression, they constitute relevant targets for therapeutic intervention. Indeed, it has been postulated that eradication of cancer stem cells will be pivotal in order to achieve long-term relapse-free survival. However, one of the hallmarks of cancer stem cells is their high resistance to undergo cell death including apoptosis in response to environmental cues or cytotoxic stimuli. Since activation of apoptosis programs in tumor cells underlies the antitumor activity of most currently used cancer therapeutics, it will be critical to develop strategies to overcome the intrinsic resistance to apoptosis of cancer stem cells. Thus, a better understanding of the molecular mechanisms that are responsible for the ability of cancer stem cells to evade apoptosis will likely open new avenues to target this critical pool of cells within the tumor in order to develop more efficient treatment options for patients suffering from cancer.

The potential role of CD133 in immune surveillance and apoptosis: a mitochondrial connection?

SIGNIFICANCE

Recent research has shown that tumors contain a small subpopulation of stem-like cells that are more resistant to therapy and that are likely to produce second-line tumors.

RECENT ADVANCES

Cancer stem-like cells (CSCs) have been characterized by a variety of markers, including, for a number of types of cancer, high expression of the plasma membrane protein CD133, which is also indicative of the increase of stemness of cultured cancer cells growing as spheres.

CRITICAL ISSUES

While the function of this protein has not yet been clearly defined, it may have a role in the stem-like phenotype of CSCs that cause (re-)initiation of tumors as well as their propagation. We hypothesize that CD133 selects for CSC survival against not only immunosurveillance mechanisms but also stress-induced apoptosis.

FUTURE DIRECTIONS

High level of expression of CD133 may be a useful marker of more aggressive tumors that are recalcitrant toward established therapies. Compelling preliminary data indicate that drugs targeting mitochondria may be utilized as a novel, efficient cancer therapeutic modality.

Suppression of apoptosis inhibitor c-FLIP selectively eliminates breast cancer stem cell activity in response to the anti-cancer agent, TRAIL

INTRODUCTION

It is postulated that breast cancer stem cells (bCSCs) mediate disease recurrence and drive formation of distant metastases - the principal cause of mortality in breast cancer patients. Therapeutic targeting of bCSCs, however, is hampered by their heterogeneity and resistance to existing therapeutics. In order to identify strategies to selectively remove bCSCs from breast cancers, irrespective of their clinical subtype, we sought an apoptosis mechanism that would target bCSCs yet would not kill normal cells. Suppression of the apoptosis inhibitor cellular FLICE-Like Inhibitory Protein (c-FLIP) partially sensitizes breast cancer cells to the anti-cancer agent Tumour Necrosis Factor-Related Apoptosis Inducing Ligand (TRAIL). Here we demonstrate in breast cancer cell lines that bCSCs are exquisitely sensitive to the de-repression of this pro-apoptotic pathway, resulting in a dramatic reduction in experimental metastases and the loss of bCSC self-renewal.

METHODS

Suppression c-FLIP was performed by siRNA (FLIPi) in four breast cancer cell lines and by conditional gene-knockout in murine mammary glands. Sensitivity of these cells to TRAIL was determined by complementary cell apoptosis assays, including a novel heterotypic cell assay, while tumour-initiating potential of cancer stem cell subpopulations was determined by mammosphere cultures, aldefluor assay and in vivo transplantation.

RESULTS

Genetic suppression of c-FLIP resulted in the partial sensitization of TRAIL-resistant cancer lines to the pro-apoptotic effects of TRAIL, irrespective of their cellular phenotype, yet normal mammary epithelial cells remained refractory to killing. While 10% to 30% of the cancer cell populations remained viable after TRAIL/FLIPi treatment, subsequent mammosphere and aldefluor assays demonstrated that this pro-apoptotic stimulus selectively targeted the functional bCSC pool, eliminating stem cell renewal. This culminated in an 80% reduction in primary tumours and a 98% reduction in metastases following transplantation. The recurrence of residual tumour initiating capacity was consistent with the observation that post-treated adherent cultures re-acquired bCSC-like properties in vitro. Importantly however this recurrent bCSC activity was attenuated following repeated TRAIL/FLIPi treatment.

CONCLUSIONS

We describe an apoptotic mechanism that selectively and repeatedly removes bCSC activity from breast cancer cell lines and suggest that a combined TRAIL/FLIPi therapy could prevent metastatic disease progression in a broad range of breast cancer subtypes.

Haematopoietic stem cell differentiation promotes the release of prominin-1/CD133-containing membrane vesicles--a role of the endocytic-exocytic pathway

The differentiation of stem cells is a fundamental process in cell biology and understanding its mechanism might open a new avenue for therapeutic strategies. Using an ex vivo co-culture system consisting of human primary haematopoietic stem and progenitor cells growing on multipotent mesenchymal stromal cells as a feeder cell layer, we describe here the exosome-mediated release of small membrane vesicles containing the stem and cancer stem cell marker prominin-1 (CD133) during haematopoietic cell differentiation. Surprisingly, this contrasts with the budding mechanism underlying the release of this cholesterol-binding protein from plasma membrane protrusions of neural progenitors. Nevertheless, in both progenitor cell types, protein–lipid assemblies might be the essential structural determinant in the release process of prominin-1. Collectively, these data support the concept that prominin-1-containing lipid rafts may host key determinants necessary to maintain stem cell properties and their quantitative reduction or loss may result in cellular differentiation.

Targeting apoptosis pathways in cancer stem cells

There is a significant void in cancer biology with regard to the elucidation of the mechanisms that underlie tumor formation and progression. Recently, the existence of a hierarchy within cancer cell populations has been demonstrated experimentally for several tumor types. The identification of a tumor cell subset that is capable of self-renewal and, concurrently, generation into more differentiated progeny has engendered new perspectives toward selective targeting of tumors. Although the identification of the so-called "cancer stem cells" (CSCs) is a leap in the study of cancer ontogenesis, therapeutic targeting of such cells is plagued by significant difficulties. CSCs are able to evade the control mechanisms that regulate cell survival and proliferation. Apoptosis is one of the most critical and well-studied mechanisms, governing tissue development and homeostasis through a complex network of molecules that mediate death and survival signals. Escape from such a finely tuned death program is a prerequisite for any tumor-initiating cell. Thus, many compounds have been developed to target cancer cells and induce apoptosis directly or indirectly. Several TRAIL receptor agonists are in Phase I or II trials, and IAP inhibitors are undergoing clinical examination to exploit their ability to enhance ionizing radiation- and chemotherapy-induced apoptosis. Further, the EGF-R/Akt pro-survival signaling axis is one of the most frequently explored sources of targets for indirect apoptosis induction, as evidenced by the significant amount of molecules designed to target this pathway and have been approved by the FDA or are under clinical evaluation. Despite the promise of these magic bullets, the absence of reliable clinical models has considerably diminished the therapeutic potential of targeted therapies considerably. A more systematic molecular characterization of the tumor-initiating cell population in many tumors will allow us to refine the stimuli that force CSCs to die, thus accelerating the development of more effective treatment for cancer.

Musashi1 regulates breast tumor cell proliferation and is a prognostic indicator of poor survival

Background

Musashi1 (Msi1) is a conserved RNA-binding protein that regulates the Notch and Wnt pathways, and serves as a stem cell marker in the breast and other tissues. It is unknown how Msi1 relates to other breast cancer markers, whether it denotes tumor initiating cells (TICs), and how it affects gene expression and tumor cell survival in breast cancer cells.

Results

Msi1 expression was analyzed in 20 breast cancer cell lines and in 140 primary breast tumors by western blotting and immunohistochemistry, respectively. Lentivirus RNA interference was used to reduce Msi1 expression in breast cancer cell lines MCF-7 and T47D grown as spheroid cultures and to assess stem cell gene expression and the growth of these cell lines as xenografts. In normal human breast tissue, Msi1 was expressed in 10.6% of myoepithelum and 1.2% of ductal epithelium in the terminal ductal lobular unit (TDLU), whereas, less than 0.05% of ductal epithelium and myoepithelium in large ducts outside the TDLU expressed Msi1. Msi1 was expressed in 55% of the breast cancer cell lines and correlated with ErbB2 expression in 50% of the cell lines. Msi1 was expressed in 68% of primary tumors and in 100% of lymph node metastases, and correlated with 5 year survival. Msi1 was enriched in CD133⁺ MCF-7 and T47D cells and in spheroid cultures of these cells, and Msi1 'knockdown' (KD) with a lentivirus-expressed shRNA decreased the number and size of spheroid colonies. Msi1 KD reduced Notch1, c-Myc, ErbB2 and pERK1/2 expression, and increased p21^CIP1 expression, which is consistent with known Msi1 target mRNAs. Msi1 KD also reduced the expression of the somatic and embryonic stem cell markers, CD133, Bmi1, Sox2, Nanog and Oct4. Xenografts of MCF-7 and T47D Msi1 KD cells resulted in a marked reduction of tumor growth, reduced Msi1 and Notch1 expression and increased p21^CIP1 expression.

Conclusion

Msi1 is a negative prognostic indicator of breast cancer patient survival, and is indicative of tumor cells with stem cell-like characteristics. Msi1 KD reduces tumor cell survival and tumor xenograft growth, suggesting that it may represent a novel target for drug discovery.

Stem-cell-like glioma cells are resistant to TRAIL/Apo2L and exhibit down-regulation of caspase-8 by promoter methylation

Tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL/Apo2L) is a promising cancer drug. However, many tumours are resistant to TRAIL-based therapies. Glioma cells with stem cell features (SCG), such as CD133 expression and neurosphere formation, have been recently identified to be more resistant to cytotoxic drugs than glioma cells lacking stem-cell-like features (NSCGs). Here we report that SCGs are completely resistant to 100-2,000 ng/ml TRAIL, whereas NSCGs revealed a moderate sensitivity to TRAIL. We found that SCGs exhibited only low levels of caspase-8 mRNA and protein, known to be indispensable for TRAIL-induced apoptosis. In addition, we detected hypermethylation of CASP8 promoter in SCGs, whereas NSCGs exhibited a non-methylated CASP8 promoter. Reexpression of caspase-8 by 5-Aza-2'-deoxycytidine was not sufficient to restore TRAIL sensitivity in SCGs cells, suggesting that additional factors cause TRAIL resistance in SCGs. Our data suggest that therapy with TRAIL, either as monotherapy or in combination with demethylating agents, is not effective in treating glioblastoma because SCGs are not targeted by such treatment.

Expectation of success following noncontingent punishment in introverts and extraverts

Recent findings indicate that extraverts are more likely than introverts to continue responding in the face of punishment and frustrating nonreward (Newman & Kosson, 1984; Tiggemann, Winefield, & Brebner, 1982). The current study investigates whether extraverts' expectations for success are, similarly, resistant to interruption and alteration. To test this hypothesis, 50 introverted and 50 extraverted male undergraduates were exposed to pretreatment with either a 50% level of noncontingent reward or a 50% level of noncontingent punishment. As predicted, there were significant Group X Pretreatment interactions on all dependent measures. In comparison to those introverts who received the punishment pretreatment, extraverts exposed to the same pretreatment placed larger wagers on their ability to succeed, and reported higher levels of perceived control. In addition, relative to their estimates for the pretreatment task, extraverts exposed to noncontingent punishment increased their expectation for success, whereas introverts exposed to noncontingent punishment decreased their performance expectations. No differences were observed between the two groups following pretreatment with noncontingent reward. The results suggest that extraverts are characterized by a distinctive reaction to punishment involving response facilitation as opposed to response inhibition.