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Cancer stem cells (CSCs) are responsible for the initiation of primary tumors and for metastasis seeding at distant organs. Therefore, they represent crucial targets for the study and preclinical testing of new antimetastatic approaches. We recently generated a molecularly characterized biobank of colorectal CSCs, isolated from individual patients and cultured in serum-free medium as multicellular spheroids. Here, we describe in detail the generation of a metastatic model of colorectal cancer based on the orthotopic injection of CSCs into the cecum serosa of immunodeficient mice. Such a model represents an excellent experimental system to investigate the cellular and molecular mechanisms involved in colorectal cancer metastasis, to analyze rare premetastatic elements such as circulating and disseminated tumor cells, and for the preclinical testing of new agents with potential antimetastatic activity.

Simple Summary In recent years, colorectal cancer stem cells (cCSCs) have been the object of intense investigation for their promise to disclose new aspects of colorectal cancer cell biology, as well as to devise new treatment strategies for colorectal cancer (CRC). However, accumulating studies on cCSCs by complementary technologies have progressively disclosed their plastic nature, i.e., their capability to acquire different phenotypes and/or functions under different circumstances in response to both intrinsic and extrinsic signals. In this review, we aim to recapitulate how a progressive methodological development has contributed to deepening and remodeling the concept of cCSCs over time, up to the present. Abstract Colorectal cancer (CRC) represents one of the most deadly cancers worldwide. Colorectal cancer stem cells (cCSCs) are the driving units of CRC initiation and development. After the concept of cCSC was first formulated in 2007, a huge bulk of research has contributed to expanding its definition, from a cell subpopulation defined by a fixed phenotype in a plastic entity modulated by complex interactions with the tumor microenvironment, in which cell position and niche-driven signals hold a prominent role. The wide development of cellular and molecular technologies recent years has been a main driver of advancements in cCSCs research. Here, we will give an overview of the parallel role of technological progress and of theoretical evolution in shaping the concept of cCSCs.

Background Circulating tumor cells (CTCs) are responsible for the metastatic dissemination of colorectal cancer (CRC) to the liver, lungs and lymph nodes. CTCs rarity and heterogeneity strongly limit the elucidation of their biological features, as well as preclinical drug sensitivity studies aimed at metastasis prevention. Methods We generated organoids from CTCs isolated from an orthotopic CRC xenograft model. CTCs-derived organoids (CTCDOs) were characterized through proteome profiling, immunohistochemistry, immunofluorescence, flow cytometry, tumor-forming capacity and drug screening assays. The expression of intra- and extracellular markers found in CTCDOs was validated on CTCs isolated from the peripheral blood of CRC patients. Results CTCDOs exhibited a hybrid epithelial-mesenchymal transition (EMT) state and an increased expression of stemness-associated markers including the two homeobox transcription factors Goosecoid and Pancreatic Duodenal Homeobox Gene-1 (PDX1), which were also detected in CTCs from CRC patients. Functionally, CTCDOs showed a higher migratory/invasive ability and a different response to pathway-targeted drugs as compared to xenograft-derived organoids (XDOs). Specifically, CTCDOs were more sensitive than XDOs to drugs affecting the Survivin pathway, which decreased the levels of Survivin and X-Linked Inhibitor of Apoptosis Protein (XIAP) inducing CTCDOs death. Conclusions These results indicate that CTCDOs recapitulate several features of colorectal CTCs and may be used to investigate the features of metastatic CRC cells, to identify new prognostic biomarkers and to devise new potential strategies for metastasis prevention.

Cancer stem cells (CSCs) are tumor subpopulations driving disease development, progression, relapse and therapy resistance, and their targeting ensures tumor eradication. CSCs display heterogeneous replication stress (RS), but the functionality/relevance of the RS response (RSR) centered on the ATR-CHK1 axis is debated. Here, we show that the RSR is efficient in primary CSCs from colorectal cancer (CRC-SCs), and describe unique roles for PARP1 and MRE11/RAD51. First, we demonstrated that PARP1 is upregulated in CRC-SCs resistant to several replication poisons and RSR inhibitors (RSRi). In these cells, PARP1 modulates replication fork speed resulting in low constitutive RS. Second, we showed that MRE11 and RAD51 cooperate in the genoprotection and mitosis execution of PARP1-upregulated CRC-SCs. These roles represent therapeutic vulnerabilities for CSCs. Indeed, PARP1i sensitized CRC-SCs to ATRi/CHK1i, inducing replication catastrophe, and prevented the development of resistance to CHK1i. Also, MRE11i + RAD51i selectively killed PARP1-upregulated CRC-SCs via mitotic catastrophe. These results provide the rationale for biomarker-driven clinical trials in CRC using distinct RSRi combinations.

Biobanking of molecularly characterized colorectal cancer stem cells (CSCs) generated from individual patients and growing as spheroids in defined serum-free media offer a fast, feasible, and multi-level approach for the screening of targeted therapies and drug resistance molecular studies. By combining in vitro and in vivo analyses of cetuximab efficacy with genetic data on an ongoing collection of stem cell-enriched spheroids, we describe the identification and preliminary characterization of microsatellite stable (MSS) CSCs that, despite the presence of the KRAS (G12D) mutation, display epidermal growth factor (EGF)-dependent growth and are strongly inhibited by anti-EGF-receptor (EGFR) treatment. In parallel, we detected an increased resistance to anti-EGFR therapy of microsatellite instable (MSI) CSC lines irrespective of KRAS mutational status. MSI CSC lines carried mutations in genes coding for proteins with a role in RAS and calcium signaling, highlighting the role of a genomically unstable context in determining anti-EGFR resistance. Altogether, these results argue for a multifactorial origin of anti-EGFR resistance that emerges as the effect of multiple events targeting direct and indirect regulators of the EGFR pathway. An improved understanding of key molecular determinants of sensitivity/resistance to EGFR inhibition will be instrumental to optimize the clinical efficacy of anti-EGFR agents, representing a further step towards personalized treatments.

8-Oxoguanine, a common mutagenic DNA lesion, generates G:C > T:A transversions via mispairing with adenine during DNA replication. When operating normally, the MUTYH DNA glycosylase prevents 8-oxoguanine-related mutagenesis by excising the incorporated adenine. Biallelic MUTYH mutations impair this enzymatic function and are associated with colorectal cancer (CRC) in MUTYH-Associated Polyposis (MAP) syndrome. Here, we perform whole-exome sequencing that reveals a modest mutator phenotype in MAP CRCs compared to sporadic CRC stem cell lines or bulk tumours. The excess G:C > T:A transversion mutations in MAP CRCs exhibits a novel mutational signature, termed Signature 36, with a strong sequence dependence. The MUTYH mutational signature reflecting persistent 8-oxoG:A mismatches occurs frequently in the APC, KRAS, PIK3CA, FAT4, TP53, FAT1, AMER1, KDM6A, SMAD4 and SMAD2 genes that are associated with CRC. The occurrence of Signature 36 in other types of human cancer indicates that DNA 8-oxoguanine-related mutations might contribute to the development of cancer in other organs., Graphical Abstract Image 1, Highlights • A modest mutator phenotype in MUTYH-defective colorectal cancer • Novel mutational signature of G>T mutations from persisting 8-oxoguanine:A mispair • This mutational signature is present in oncogenes/tumor suppressor associated with colorectal cancer • The mutational signature allows identifying a role for 8-oxoguanine-related mutations in other types of human cancer. Viel et al. identifies by exome-sequencing a mutational signature in colorectal cancer defective in the MUTYH DNA glycosylase, a DNA repair gene preventing 8-oxoguanine-related mutagenesis. A strong sequence dependence of G > T transversions characterizes this mutational fingerprint and unveils the contribution of persistent 8-oxoG:A mismatches in human cancer.

Background Quiescent/slow cycling cells have been identified in several tumors and correlated with therapy resistance. However, the features of chemoresistant populations and the molecular factors linking quiescence to chemoresistance are largely unknown. Methods A population of chemoresistant quiescent/slow cycling cells was isolated through PKH26 staining (which allows to separate cells on the basis of their proliferation rate) from colorectal cancer (CRC) xenografts and subjected to global gene expression and pathway activation analyses. Factors expressed by the quiescent/slow cycling population were analyzed through lentiviral overexpression approaches for their ability to induce a dormant chemoresistant state both in vitro and in mouse xenografts. The correlation between quiescence-associated factors, CRC consensus molecular subtype and cancer prognosis was analyzed in large patient datasets. Results Untreated colorectal tumors contain a population of quiescent/slow cycling cells with stem cell features (quiescent cancer stem cells, QCSCs) characterized by a predetermined mesenchymal-like chemoresistant phenotype. QCSCs expressed increased levels of ZEB2, a transcription factor involved in stem cell plasticity and epithelial-mesenchymal transition (EMT), and of antiapototic factors pCRAF and pASK1. ZEB2 overexpression upregulated pCRAF/pASK1 levels resulting in increased chemoresistance, enrichment of cells with stemness/EMT traits and proliferative slowdown of tumor xenografts. In parallel, chemotherapy treatment of tumor xenografts induced the prevalence of QCSCs with a stemness/EMT phenotype and activation of the ZEB2/pCRAF/pASK1 axis, resulting in a chemotherapy-unresponsive state. In CRC patients, increased ZEB2 levels correlated with worse relapse-free survival and were strongly associated to the consensus molecular subtype 4 (CMS4) characterized by dismal prognosis, decreased proliferative rates and upregulation of EMT genes. Conclusions These results show that chemotherapy-naive tumors contain a cell population characterized by a coordinated program of chemoresistance, quiescence, stemness and EMT. Such population becomes prevalent upon drug treatment and is responsible for chemotherapy resistance, thus representing a key target for more effective therapeutic approaches.

Fenretinide is a synthetic retinoid characterized by anticancer activity in preclinical models and favorable toxicological profile, but also by a low bioavailability that hindered its clinical efficacy in former clinical trials. We developed a new formulation of fenretinide complexed with 2-hydroxypropyl-beta-cyclodextrin (nanofenretinide) characterized by an increased bioavailability and therapeutic efficacy. Nanofenretinide was active in cell lines derived from multiple solid tumors, in primary spheroid cultures and in xenografts of lung and colorectal cancer, where it inhibited tumor growth independently from the mutational status of tumor cells. A global profiling of pathways activated by nanofenretinide was performed by reverse-phase proteomic arrays and lipid analysis, revealing widespread repression of the mTOR pathway, activation of apoptotic, autophagic and DNA damage signals and massive production of dihydroceramide, a bioactive lipid with pleiotropic effects on several biological processes. In cells that survived nanofenretinide treatment there was a decrease of factors involved in cell cycle progression and an increase in the levels of p16 and phosphorylated p38 MAPK with consequent block in G0 and early G1. The capacity of nanofenretinide to induce cancer cell death and quiescence, together with its elevated bioavailability and broad antitumor activity indicate its potential use in cancer treatment and chemoprevention.

Background An increasing number of anticancer agents has been proposed in recent years with the attempt to overcome treatment-resistant cancer cells and particularly cancer stem cells (CSC), the major culprits for tumour resistance and recurrence. However, a huge obstacle to treatment success is the ineffective delivery of drugs within the tumour environment due to limited solubility, short circulation time or inconsistent stability of compounds that, together with concomitant dose-limiting systemic toxicity, contribute to hamper the achievement of therapeutic drug concentrations. The synthetic retinoid Fenretinide (4-hydroxy (phenyl)retinamide; 4-HPR) formerly emerged as a promising anticancer agent based on pre-clinical and clinical studies. However, a major limitation of fenretinide is traditionally represented by its poor aqueous solubility/bioavailability due to its hydrophobic nature, that undermined the clinical success of previous clinical trials. Methods Here, we developed a novel nano-micellar fenretinide formulation called bionanofenretinide (Bio-nFeR), based on drug encapsulation in an ion-pair stabilized lipid matrix, with the aim to raise fenretinide bioavailability and antitumour efficacy. Results Bio-nFeR displayed marked antitumour activity against lung, colon and melanoma CSC both in vitro and in tumour xenografts, in absence of mice toxicity. Bio-nFeR is suitable for oral administration, reaching therapeutic concentrations within tumours and an unprecedented therapeutic activity in vivo as single agent. Conclusion Altogether, our results indicate Bio-nFeR as a novel anticancer agent with low toxicity and high activity against tumourigenic cells, potentially useful for the treatment of solid tumours of multiple origin. Electronic supplementary material The online version of this article (10.1186/s13046-019-1383-9) contains supplementary material, which is available to authorized users.

Targeted approaches aiming at modulating NHERF1 activity, rather than its overall expression, would be preferred to preserve the normal functions of this versatile protein. We focused our attention on the NHERF1/PDZ1 domain that governs its membrane recruitment/displacement through a transient phosphorylation switch. We herein report the design and synthesis of novel NHERF1 PDZ1 domain inhibitors. These compounds have potential therapeutic value when used in combination with antagonists of β-catenin to augment apoptotic death of colorectal cancer cells refractory to currently available Wnt/β-catenin-targeted agents.

Banks of genetically characterized cancer stem cells (CSCs) isolated from individual patients and grown as spheroids offer an invaluable approach to identify genetic determinants of drug resistance versus sensitivity, and to study new stem cell-directed therapies. Here, we describe our standardized procedure for in vitro drug screening on colorectal CSCs, taking irinotecan as an example.

Banks of genetically characterized cancer stem cells (CSCs) isolated from individual patients and grown as spheroids offer an invaluable approach to identify genetic determinants of drug resistance versus sensitivity, and to study new stem cell-directed therapies. Here, we describe our standardized procedure for in vitro drug screening on colorectal CSCs, taking irinotecan as an example.

ObjectiveCancer stem cells (CSCs) are responsible for tumour formation and spreading, and their targeting is required for tumour eradication. There are limited therapeutic options for advanced colorectal cancer (CRC), particularly for tumours carrying RAS-activating mutations. The aim of this study was to identify novel CSC-targeting strategies.DesignTo discover potential therapeutics to be clinically investigated as single agent, we performed a screening with a panel of FDA-approved or investigational drugs on primary CRC cells enriched for CSCs (CRC-SCs) isolated from 27 patients. Candidate predictive biomarkers of efficacy were identified by integrating genomic, reverse-phase protein microarray (RPPA) and cytogenetic analyses, and validated by immunostainings. DNA replication stress (RS) was increased by employing DNA replication-perturbing or polyploidising agents.ResultsThe drug-library screening led to the identification of LY2606368 as a potent anti-CSC agent acting in vitro and in vivo in tumour cells from a considerable number of patients (∼36%). By inhibiting checkpoint kinase (CHK)1, LY2606368 affected DNA replication in most CRC-SCs, including RAS-mutated ones, forcing them into premature, lethal mitoses. Parallel genomic, RPPA and cytogenetic analyses indicated that CRC-SCs sensitive to LY2606368 displayed signs of ongoing RS response, including the phosphorylation of RPA32 and ataxia telangiectasia mutated serine/threonine kinase (ATM). This was associated with mutation(s) in TP53 and hyperdiploidy, and made these CRC-SCs exquisitely dependent on CHK1 function. Accordingly, experimental increase of RS sensitised resistant CRC-SCs to LY2606368.ConclusionsLY2606368 selectively eliminates replication-stressed, p53-deficient and hyperdiploid CRC-SCs independently of RAS mutational status. These results provide a strong rationale for biomarker-driven clinical trials with LY2606368 in patients with CRC.

Colorectal cancer (CRC) therapy mainly relies on the use of conventional chemotherapeutic drugs combined, in a subset of patients, with epidermal growth factor receptor [EGFR]-targeting agents. Although CRC is considered a prototype of a cancer stem cell (CSC)-driven tumor, the effects of both conventional and targeted therapies on the CSC compartment are largely unknown. We have optimized a protocol for colorectal CSC isolation that allowed us to obtain CSC-enriched cultures from primary tumor specimens, with high efficiency. CSC isolation was followed by in vitro and in vivo validation, genetic characterization, and drug sensitivity analysis, thus generating panels of CSC lines with defined patterns of genetic mutations and therapy sensitivity. Colorectal CSC lines were polyclonal and maintained intratumor heterogeneity in terms of somatically acquired mutations and differentiation state. Such CSC-enriched cultures were used to investigate the effects of both conventional and targeted therapies on the CSC compartment in vivo and to generate a proteomic picture of signaling pathways implicated in sensitivity/resistance to anti-EGFR agents. We propose CSC lines as a sound preclinical framework to test the effects of therapies in vitro and in vivo and to identify novel determinants of therapy resistance. Significance Colorectal cancer stem cells (CSCs) have been shown to be responsible for tumor propagation, metastatic dissemination, and relapse. However, molecular pathways present in CSCs, as well as mechanisms of therapy resistance, are mostly unknown. Taking advantage of genetically characterized CSC lines derived from colorectal tumors, this study provides an extensive analysis of CSC response to EGFR-targeted therapy in vivo and an overview of factors implicated in therapy response or resistance. Furthermore, the implementation of a biobank of molecularly annotated CSC lines provides an innovative resource for future investigations in colorectal cancer.

Two large families of retrotransposons, that is, LINE-1 (Long Interspersed Nuclear Elements-1) and endogenous retroviruses, encode reverse transcriptase (RT) proteins in vertebrates. We previously showed that mouse preimplantation embryos are endowed with an endogenous, functional RT activity. Inhibiting that activity by microinjecting antisense oligonucleotides against a highly active LINE-1 family member in mouse oocytes blocked developmental progression between the two- and four-blastomere stages, indicating that LINE-1-encoded RT activity is strictly required at this critical transition in early development. Here we show that incubation of mouse zygotes with 5'-bromodeoxyuridine (BrdU) yields massive incorporation of this nucleoside analogue in newly synthesized DNA; surprisingly, a significant incorporation still occurs in both zygotic pronuclei in the presence of aphidicolin, a specific inhibitor of DNA replication. This aphidicolin-resistant BrdU incorporation is quantitatively abolished when embryos are simultaneously exposed to abacavir, a nucleoside RT inhibitor, indicating its retrotranscription-dependent nature. Moreover, quantitative PCR analysis revealed a burst of new synthesis of LINE-1 copies at the zygote- and two-cell embryo stages. These findings support the conclusion that RT-dependent amplification of LINE-1 retrotransposons is a distinctive feature of early embryonic genomes. Its physiological involvement in preimplantation murine development is discussed.

Stemness was recently depicted as a dynamic condition in normal and tumor cells. We found that the embryonic protein Cripto-1 (CR1) was expressed by normal stem cells at the bottom of colonic crypts and by cancer stem cells (CSCs) in colorectal tumor tissues. CR1-positive populations isolated from patient-derived tumor spheroids exhibited increased clonogenic capacity and expression of stem-cell-related genes. CR1 expression in tumor spheroids was variable over time, being subject to a complex regulation of the intracellular, surface and secreted protein, which was related to changes of the clonogenic capacity at the population level. CR1 silencing induced CSC growth arrest in vitro with a concomitant decrease of Src/Akt signaling, while in vivo it inhibited the growth of CSC-derived tumor xenografts and reduced CSC numbers. Importantly, CR1 silencing in established xenografts through an inducible expression system decreased CSC growth in both primary and metastatic tumors, indicating an essential role of CR1 in the regulation the CSC compartment. These results point to CR1 as a novel and dynamically regulated effector of stem cell functions in colorectal cancer.

32D cells grown for 1 year in interleukin-3 (IL-3) and granulocyte colony-stimulating factor (G-CSF) generated the 32D Ro cell line which retained the parental mast cell phenotype but lost ability to generate erythroid cells in response to erythropoietin (EPO). In order to clarify the mechanisms underlying such restriction, we compared 32D and 32D Ro cells for their capacity to express erythroid-specific transcription factors (Gata1, Gata2, Scl, Nef2, Eklf, and Id) and the capacity of short exposure to 5-azacytidine (5-AzaC) to reactivate erythroid differentiation potential in 32D Ro cells. By Northern analysis, the two cell lines expressed similar levels of all these genes. However, after being treated with 5-AzaC, 32D Ro cells acquired the ability to generate EPO-dependent clones (1 clone/104 cells) which gave rise to EPO-dependent cell lines. All the 10 EPO-responsive cell lines independently isolated from 5-AzaC-treated 32D Ro cells had erythroid morphology and expressed high levels of α- and β-globin. In contrast, none of the IL-3-dependent and granulocyte/macrophage colony-stimulating factor-dependent clones concurrently isolated, as a control, showed erythroid properties. Therefore, 5-AzaC treatment reactivates the potential of the myeloid-restricted 32D Ro cells to generate EPO-responsive erythroid clones suggesting that gene methylation played an important role in the G-CSF-mediated restriction/activation of the differentiation potential of these cells.

Lung cancer is the most common cause of cancer-related mortality worldwide, urging the discovery of novel molecular targets and therapeutic strategies. Stem cells have been recently isolated from non-small cell lung cancer (NSCLC), thus allowing the investigation of molecular pathways specifically active in the tumorigenic population. We have found that Bcl-XL is constantly expressed by lung cancer stem cells (LCSCs) and has a prominent role in regulating LCSC survival. Whereas chemotherapeutic agents were scarcely effective against LCSC, the small molecule Bcl-2/Bcl-XL inhibitor ABT-737, but not the selective Bcl-2 inhibitor ABT-199, induced LCSC death at nanomolar concentrations. Differently from gemcitabine, which preferentially eliminated proliferating LCSC, ABT-737 had an increased cytotoxic activity in vitro towards quiescent/slow-proliferating LCSC, which expressed high levels of Bcl-XL. In vivo, ABT-737 as a single agent was able to inhibit the growth of LCSC-derived xenografts and to reduce cancer stem cell content in treated tumors. Altogether, these results indicate that quiescent/slow-proliferating LCSC strongly depend on Bcl-XL for their survival and indicate Bcl-XL inhibition as a potential therapeutic avenue in NSCLC.

H-IL-6 is a hybrid protein constructed to contain IL-6 and its soluble receptor linked by a flexible peptide chain. Here we show that H-IL-6 strongly enhances proliferation of human CD34(+)cells in serum-free liquid culture, and that the majority of the cells generated belong to the erythroid lineage, being positive for the marker Glycophorin A. Conversely, H-IL-6 does not increase the number of myeloid, CD13-positive cells. Comparable effects are observed on progenitors from cord blood and adult peripheral blood. Therefore, H-IL-6 triggers an erythroid-inducing signal in haematopoietic progenitor cells, independently from erythropoietin (EPO).

The Sendai virus fuses with host cell membranes in a pH-independent manner through an unknown mechanism. Here we report that mild trypsin pre-treatments of Sendai virions, for example 15 min at 4°C, give Sendai virions the ability to fuse at a rate up to 10-fold higher than control. By using human erythrocytes as host cell membranes, viral fusion was assessed by hemolysis as well as fluorescence dequenching of octadecyl rhodamine B chloride. The mild protease treatment strikingly shortens the lag time taken by the virus to start the fusion process. Similar data were obtained on reconstituted Sendai virus envelope. Among proteases, tested as fusion enhancer, trypsin is more effective than either endoproteinase Lys-C, chymotrypsin, or endoproteinase Arg-C. After removal of trypsin from treated virions the fusion rate enhancement remains for hours at room temperature. The lack of protease specificity, together with the impossibility to detect any new N-terminal products, suggests that only a small percentage of viral envelope components are cleaved, still a large enough number to set the envelope in a ready-to-fuse state.

Tumor-initiating cells are responsible for tumor maintenance and relapse in solid and hematologic cancers. Although tumor-initiating cells were initially believed to be mainly quiescent, rapidly proliferating tumorigenic cells were found in breast cancer. In colon cancer, the proliferative activity of the tumorigenic population has not been defined, although it represents an essential parameter for the development of more effective therapeutic strategies. Here, we show that tumorigenic colon cancer cells can be found in a rapidly proliferating state in vitro and in vivo, both in human tumors and mouse xenografts. Inhibitors of polo-like kinase1 (Plk1), a mitotic kinase essential for cell proliferation, demonstrated maximal efficiency over other targeted compounds and chemotherapeutic agents in inducing death of colon cancer-initiating cells in vitro. In vivo, Plk1 inhibitors killed CD133+ colon cancer cells leading to complete growth arrest of colon cancer stem cell-derived xenografts, whereas chemotherapeutic agents only slowed tumor progression. While chemotherapy treatment increased CD133+ cell proliferation, treatment with Plk1 inhibitors eliminated all proliferating tumor-initiating cells. Quiescent CD133+ cells that survived the treatment with Plk1 inhibitors could be killed by subsequent Plk1 inhibition when they exited from quiescence. Altogether, these results provide a new insight into the proliferative status of colon tumor-initiating cells both in basal conditions and in response to therapy and indicate Plk1 inhibitors as potentially useful in the treatment of colorectal cancer.

Two large families of retrotransposons, that is, LINE-1 (Long Interspersed Nuclear Elements-1) and endogenous retroviruses, encode reverse transcriptase (RT) proteins in vertebrates. We previously showed that mouse preimplantation embryos are endowed with an endogenous, functional RT activity. Inhibiting that activity by microinjecting antisense oligonucleotides against a highly active LINE-1 family member in mouse oocytes blocked developmental progression between the two- and four-blastomere stages, indicating that LINE-1-encoded RT activity is strictly required at this critical transition in early development. Here we show that incubation of mouse zygotes with 5'-bromodeoxyuridine (BrdU) yields massive incorporation of this nucleoside analogue in newly synthesized DNA; surprisingly, a significant incorporation still occurs in both zygotic pronuclei in the presence of aphidicolin, a specific inhibitor of DNA replication. This aphidicolin-resistant BrdU incorporation is quantitatively abolished when embryos are simultaneously exposed to abacavir, a nucleoside RT inhibitor, indicating its retrotranscription-dependent nature. Moreover, quantitative PCR analysis revealed a burst of new synthesis of LINE-1 copies at the zygote- and two-cell embryo stages. These findings support the conclusion that RT-dependent amplification of LINE-1 retrotransposons is a distinctive feature of early embryonic genomes. Its physiological involvement in preimplantation murine development is discussed.

Human cancer stem cells represent promising tools for new approaches to pathway-targeted drug discovery and preclinical screening. Because of their distinctive capability to recapitulate the development of the original tumors in vivo, the study of human cancer stem cells (CSCs) largely relies on models of xenograft transplantation into immunodeficient mice. In this frame, immunity and microenvironment-related issues need careful consideration. Here we shortly revise present knowledge on xenograft-related aspects of human CSCs studies.

Mesenchymal stromal cells (MSCs) represent a bone marrow (BM) population, classically defined by five functional properties: extensive proliferation, ability to differentiate into osteoblasts, chondrocytes, adipocytes, and stromal cells-supporting hematopoiesis. However, research progress in this area has been hampered by lack of suitable markers and standardized procedures for MSC isolation. We have isolated a CD146(+) multipotent MSC population from 20 human BM donors displaying the phenotype of self-renewing osteoprogenitors; an extensive 12-week proliferation; and the ability to differentiate in osteoblasts, chondrocytes, adipocytes, and stromal cells supporting hematopoiesis. Furthermore, the CD146(+) MSCs secrete a complex combination of growth factors (GFs) controlling hematopoietic stem cells (HSCs) function, while providing a >2-log increase in the long-term culture (LTC) colony output in 8-week LTC over conventional assays. The hematopoietic stromal function exhibited by the MSCs was further characterized by manipulating LTCs with the chemical inhibitors Imatinib or SU-5416, targeting two GF receptors (GFRs), KIT or VEGFR2/1, respectively. Both treatments similarly impaired LTC colony output, indicating key roles for these two GF/GFR interactions to support LTC-initiating cell activity. CD146(+) MSCs may thus represent a tool to explore the MSC-HSC cross-talk in an in vitro surrogate model for HSC "niches," and for regenerative therapy studies. In addition, the MSC microRNA (miRNA) expression profile was analyzed by microarrays in both basic conditions and chondrogenic differentiation. Our analysis revealed that several miRNAs are modulated during chondrogenesis, and many of their putative targets are genes involved in chondrogenic differentiation.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been reported to exhibit therapeutic activity in cancer. However, many tumors remain resistant to treatment with TRAIL. Therefore, small molecules that potentiate the cytotoxic effects of TRAIL could be used for combinatorial therapy. Here we found that the ionophore antibiotic salinomycin acts in synergism with TRAIL, enhancing TRAIL-induced apoptosis in glioma cells. Treatment with low doses of salinomycin in combination with TRAIL augmented the activation of caspase-3 and increased TRAIL-R2 cell surface expression. TRAIL-R2 upmodulation was required for mediating the stimulatory effect of salinomycin on TRAIL-mediated apoptosis, since it was abrogated by siRNA-mediated TRAIL-R2 knockdown. Salinomycin in synergism with TRAIL exerts a marked anti-tumor effect in nude mice xenografted with human glioblastoma cells. Our results suggest that the combination of TRAIL and salinomycin may be a useful tool to overcome TRAIL resistance in glioma cells and may represent a potential drug for treatment of these tumors. Importantly, salinomycin+TRAIL were able to induce cell death of well-defined glioblastoma stem-like lines.

In order to assess the potential role of IL-6 in rheumatoid arthritis (RA), we have compared IL-6 deficient (IL-6 ko) mice and their wild-type (wt) counterpart for the capacity to develop methylated bovine serum albumin (mBSA)-induced arthritis. Our data show that IL-6 ko mice are not susceptible to antigen-induced arthritis (AIA). In fact, IL-6 ko mice treated by a standard protocol of immunization with mBSA did not develop joint swelling following intra-articular mBSA injection, nor revealed the characteristic joint lesions by histological examination. Conversely, wt mice treated according to the same protocol developed arthritis about 9 days after intra-articular injection, as detected by knee joint swelling and histological confirmation. We observed that the proliferative response of splenocytes to mBSA was impaired in ko mice following arthritis induction, as compared to the strong response observed in wt mice. Furthermore, anti-mBSA IgG levels were lower in ko mice as compared to wt mice. Finally, we show that sensitivity to AIA can be reconstituted in ko mice by subcutaneous injections of recombinant human IL-6 (rhIL-6). In addition, co-administration of IL-6 with mBSA by intra-articular injection into the joint was only partially effective in conferring sensitivity to AIA, suggesting the importance of a systemic effct for IL-6, but also that an additional role for this cytokine can be envisaged in the local inflammatory reaction during establishment of AIA.

We have measured the number of progenitor cells circulating in fetal (17-32 weeks of gestation), perinatal (36 weeks of gestation), and adult (30-50 years old) blood. The progenitor cells at each ontogenetic stage were also characterized in terms both of the minimal combinations of growth factors they required to form maximal numbers of colonies in vitro and of their self-replication potential, as measured by the number of secondary and tertiary progenitor cells each could generate. The number of progenitor cells circulating in fetal and perinatal blood can be measured by directly plating the unfractionated blood. In this assay, fetal blood contains half the number of progenitor cells detected in perinatal blood (18.0 +/- 16.4 versus 40.88 +/- 0.63, p0.01), and the number of progenitor cells in adult blood is below the level of detection of the assay (1/8 microliter of blood). To compare the number of progenitor cells in all three stages of human development, progenitor cell counts were performed on blood mononuclear cells enriched by density separation. In this case, the light density cell fractions from fetal and neonatal blood contained the same number of progenitor cells (300/10(5) cells), numbers that were 10-fold higher than those observed with adult blood (30/10(5) cells). Circulating fetal-neonatal erythroid and multipotential progenitor cells were found to differ from their adult counterparts in terms of their response to growth factors and their self-renewal ability. In fact, the number of cytokines required to observe maximal colony formation increased with the ontogenetic stage of the cells. No differences were found in the frequency of primary colonies containing progenitor cells or in the mean number of secondary progenitor cells per primary colony in cultures of fetal, neonatal, or adult blood. Differences between the three ontogenetic stages, however, were found with respect to the number of sequential replatings that were possible. In fact, although both secondary granulocyte-macrophage (GM) and mixed-cell colonies derived from fetal cells gave rise to tertiary colonies, only perinatal secondary mixed-cell colonies grew in tertiary cultures, and no growth was observed in tertiary cultures of adult cells. These results suggest that the greater amplification of progenitor cells observed in liquid culture of fetal/neonatal versus adult blood is due both to a higher proliferative capacity of neonatal progenitor cells (up to two replatings versus one) and to a higher frequency in these samples of mixed-cell colony-forming cells (CFC) (37.7 +/- 7.3 versus 2.0 +/- 0.7/10(5) light density cells, respectively). Because of the high numbers of progenitor cells circulating in the fetus, as well as their high proliferative capacity, it is predicted that if blood could be harvested directly in utero, fetal blood would be as good a source of stem cells for transplantation as perinatal placental/cord blood. Circulating fetal stem cells would, therefore, represent an ideal target for gene therapy and in utero autologous transplantation.

In this study, a primitive progenitor cell, the blast-cell colony- forming cell (BC-CFC), which is thought by some to be equivalent to the hematopoietic stem cell (HSC), those cells capable of long-term marrow repopulation, has been isolated from normal murine marrow. The cell separation method we employed has, as its final step, the purification of marrow cells based on their ability to take up (bright) or exclude (dull) the mitochondrial dye, Rhodamine (Rho)-123. Rho-bright and Rho- dull cells are enriched for multipotential progenitor cells or for HSC, respectively. It was found that Rho-bright cells contain more BC-CFC than Rho-dull cells (310 +/- 50 v 120 +/- 40 per 10(5) purified cells, respectively). However, the BC-CFC that copurified with the Rho-bright and the Rho-dull cells were different in terms of replating efficiency and response to interleukin-3 (IL-3) and stem cell factor (SCF). In fact, on replating, the blast-cell colonies cultured from the Rho-dull population give rise to many more secondary colonies and had a greater replating efficiency than those obtained from Rho-bright cells (replating efficiency: 29.0 +/- 6.3 v 19.5 +/- 3.7, respectively, P < .01). Furthermore, while the same numbers of blast-cell colonies were detected in culture of Rho-bright cells stimulated with IL-3 alone or in combination with SCF, blast-cell colonies were generated in cultures of Rho-dull cells only in the presence of both IL-3 and SCF. After 5 days in suspension culture stimulated with IL-3 and SCF, Rho-dull cells generated BC-CFC whose replating potential was similar to the replating potential of BC-CFC contained in the Rho-bright population. These results indicate that BC-CFC contained in the Rho-bright and -dull populations are qualitatively different. Because the Rho-dull population contains HSC, the results indicate that few, if any, BC-CFC are HSC.

A Hut-78 celi clone (F12) harboring a non-producer human immunodeficiency virus (HIV-1) variant shows complete resistance to HIV-1 or HIV-2 superinfection. The F12-HIV provirus produces an altered HIV-1 protein pattern and cannot generate even immature viral particles. We demonstrated that HeLa CD4+ cells transfected with the F12-HIV genome resist HIV superinfection through a CD4-independent mechanism. As F12-HIV appears to be a useful system to induce anti-HIV intracellular immunization, we constructed various retroviral vectors containing the F12-HIV genome, modified by elimination of the F12 3’ LTR and part of its nef gene, inserted “antisense” with respect to the Moloney murine leukemia virus 5’ LTR. Here we show that recombinant retroviral particles carrying the N2/F12-HIV nef-(as) construct can stably transduce both CEMss human cells and primary human peripheral blood lymphocytes, inducing the expression of the F12-HIV genome. These results could open the way to an anti-AIDS gene therapy strategy based on F12-HIV-induced intracellular immunization.

We have studied the frequency of colony forming cells (CFC) in fetal and neonatal blood in comparison with adult blood and marrow. Fetal/neonatal blood contains at least as many CFC as adult marrow and higher numbers of the more primitive CFC--those CFC giving rise to colonies composed of erythroid and myeloid cells. CD34+ cord blood cells (selected either by sorting, panning or affinity chromatography) proliferate in culture over time and generate more CFC (from pre-CFC) and differentiated cells in response to Steel factor plus different hematopoietic growth factors. Steel factor is unable to stimulate cell growth by itself under serum-deprived conditions and requires the synergistic action of erythropoietin (Epo), granulocyte colony stimulating factor (G-CSF) or interleukin 3 (IL-3). In the presence of Epo or G-CSF, CFC and differentiated cells are generated for 15 days and are mainly erythroid or granulocytic, respectively. In contrast, Steel factor plus IL-3 generates multilineage CFC and differentiated cells for more than one month. When the conditions for these long-term suspension cultures were optimized (37 degrees C, regular refeeding with fresh growth factors and media without changing the flask), CFC and differentiated cells were generated for more than two months. At this time, CFC were no longer detectable and all cells had a mast cell phenotype. These cells have been maintained and propagated for more than eight months in the presence of IL-3 and Steel factor and may represent a useful tool to study human mast cell differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of the expression of the erythropoietin (Epo) receptor (EpoR) gene is under the control of transcriptional regulatory factor GATA-1. GATA-1 is expressed widely among the nonerythroid, factor-dependent subclones of the interleukin 3-dependent mouse cell line 32D. Consequently, to determine whether GATA-1 and EpoR gene expression are linked even in nonerythroid cells, we have studied the correlation of GATA-1 expression with expression and function of EpoR in these cell lines. EpoR mRNA (by RNase protection analysis) and EpoR protein (by specific antibody immunoprecipitation of metabolically labeled EpoR protein) were detectable not only in 32D and 32D Epo (an Epo-dependent subclone) but also in 32D GM, a subclone dependent for growth on granulocyte/macrophage colony-stimulating factor. EpoR mRNA also was detectable by PCR in 32D G, a subclone dependent for growth on granulocyte colony-stimulating factor. However, only 32D Epo cells bound 125I-labeled Epo and expressed EpoR protein on the cell surface, as determined by immunoprecipitation of surface-labeled proteins. These results indicate that, in these factor-dependent cell lines, the major regulatory step determining the erythroid-specific response to Epo is the efficiency of EpoR protein translocation to the cell surface. Mechanisms that could affect lineage-specific translocation are the presence of a chaperone protein, erythroid-specific editing of EpoR mRNA, or altered processing of the EpoR protein to the cell surface. In this model, lineage-restricted responses to growth factors such as Epo are determined not by expression of the genes for growth factor receptors but, rather, by appropriate processing of the receptor protein.

Incubation of trifluoperazine, a local anaesthetic, at concentrations higher than the cmc with Sendai virus particles produces the selective solubilization of the haemagglutinin neuraminidase (HN) and matrix (M) proteins. This phenomenon involves aggregation of the Sendai virions and therefore the separation of HN and M from the rest of the particle can be performed by bench centrifugation. The supernatant contains the HN and M proteins and HN, once inserted into liposomes, elicits its own biological activities. Therefore, the method seems suitable for purifying large amounts of HN.

Recent findings have shown that the expression of the seven trans-membrane G-protein–coupled CXCR4 (the receptor for the stromal cell-derived factor [SDF]-1 chemokine) is necessary for the entry of T-lymphotropic human immunodeficiency virus (HIV) strains, acting as a coreceptor of the CD4 molecule. In the human system, the role of CXCR4 in HIV infection has been determined through env-mediated cell fusion assays and confirmed by blocking viral entry in CD4+/CXCR4+ cells by SDF-1 pretreatment. We observed that the human megakaryoblastic CD4+ UT-7 cell line fails to express CXCR4 RNA and is fully resistant to HIV entry. Transfection of an expression vector containing the CXCR4 c-DNA rendered UT-7 cells readily infectable by different T-lymphotropic syncytium-inducing HIV-1 and HIV-2 isolates. Interestingly, HIV-1 infection of CXCR4 expressing UT-7 cells (named UT-7/fus) induces the formation of polynucleated cells through a process highly reminiscent of megakaryocytic differentiation and maturation. On the contrary, no morphologic changes were observed in HIV-2–infected UT-7/fus cells. These findings further strengthen the role of CXCR4 as a molecule necessary for the replication of T-lymphotropic HIV-1 and HIV-2 isolates and provide a useful model to study the functional role of CD4 coreceptors in HIV infection.

We have developed a quick and simple method to purify the water soluble fragment of Sendai virus neuraminidase (cHN). We used the trifluoperazine (TFP) as detergent because of its ability to selectively solubilize the HN (Baiocchi et al., (1988) FEBS Lett. 238, 171-174). Here we describe conditions by which trypsin produces the cHN from the TFP treated virions. The cHN is further purified by size exclusion chromatography and it fully retains the neuraminidase activity and the allosteric inhibitory site as described in (Dallocchio et al., (1991) Biochem. Int. 25, 663-668). Both circular dichroism (CD) spectra, analyzed by deconvolution methods and secondary structure prediction were used to assess the secondary structure of cHN.

Trypsin solubilized hemagglutinin-neuraminidase of Sendai virus (cHN) displays michaelian kinetics, with native fetuin as substrate, at 37 degrees C. Vmax and Km values are only marginally altered, as compared to intact viral neuraminidase. At lower temperatures, cHN follows non-michaelian kinetics, with marked substrate inhibition at 4 degrees C. With denaturated fetuin, michaelian kinetics are observed in all conditions, while asialo fetuin was an uncompetitive inhibitor of cHN, with native fetuin or sialyl lactose as substrates. These results can be explained assuming that the protein moiety of fetuin acts as an allosteric inhibitor of cHN.

We have previously reported the origin of a class of skeletal myogenic cells from explants of dorsal aorta. This finding disagrees with the known origin of all skeletal muscle from somites and has therefore led us to investigate the in vivo origin of these cells and, moreover, whether their fate is restricted to skeletal muscle, as observed in vitro under the experimental conditions used. To address these issues, we grafted quail or mouse embryonic aorta into host chick embryos. Donor cells, initially incorporated into the host vessels, were later integrated into mesodermal tissues, including blood, cartilage, bone, smooth, skeletal and cardiac muscle. When expanded on a feeder layer of embryonic fibroblasts, the clonal progeny of a single cell from the mouse dorsal aorta acquired unlimited lifespan, expressed hemo-angioblastic markers (CD34, Flk1 and Kit) at both early and late passages, and maintained multipotency in culture or when transplanted into a chick embryo. We conclude that these newly identified vessel-associated stem cells, the meso-angioblasts, participate in postembryonic development of the mesoderm, and we speculate that postnatal mesodermal stem cells may be derived from a vascular developmental origin.