Fluoro-edenite fibres induce lung cell apoptosis: an in vivo study

We previously showed that apoptosis in the lungs of sheep exposed to fluoro-edenite fibres is induced via the receptor pathway. The present study was performed to gain further insights into the mechanisms of activation of programmed cell death induced by the fibres. Fluoro-edenite fibres are similar in size and morphology to some amphibolic asbestos fibres. They have been found in benmoreitic lavas, in the local stone quarry, in building materials and in road paving at Biancavilla, a town in eastern Sicily (Italy), where epidemiological surveys revealed a cluster of mortality from pleural mesothelioma. Inhalation of asbestos fibres can cause chronic inflammation and carcinogenesis. Since fluoro-edenite has been shown to activate the apoptotic process, we set out to characterise the expression of apoptosis-regulating proteins in fluoro-edenite-exposed lung disease and sought to determine if apoptosis results from fluoro-edenite exposure. Lung tissue from apparently healthy sheep habitually grazing near Biancavilla was processed for immunohistochemical localisation of bcl-2 and bax. Results showed epithelial and interstitial bax overexpression, especially in cells directly in contact with the fibres, and negative bcl-2 immunoexpression. TUNEL-positive cells were detected in alveoli and connective tissue. The integrity of alveolar epithelium and alveolar apoptosis are critical determinants in the pathways that initiate fibrogenesis in the lung and fibroblastic foci are usually found close to abnormal or denuded alveolar epithelium. Our results are consistent with the hypothesis that apoptosis is an important mechanism for removing cells with irreparable fluoro-edenite-induced genetic changes that predispose them to a neoplastic evolution.     

Behaviour of the new asbestos amphibole fluor-edenite in different lung cell systems

The aim of the present research was to determine whether the recently identified and characterized new fibrous amphibole fluoro-edenite may induce a cytopathic response in cultured cells. The final goal was to gain suggestions on the potentiality of fluoro-edenite to be harmful to human beings. Epidemiological studies, in fact, have shown an excess of developing mesothelioma among residents in Biancavilla, a town in eastern Sicily located in the Etna volcanic area. Therefore, we treated human lung fibroblasts, human lung alveolar epithelial cancer cell line A549 and monocyte-macrophage cell line J774 with fluoro-edenite or crocidolite; the latter used as a highly toxic amphibole asbestos reference. Our results show that fluoro-edenite may induce functional modifications and affects some biochemical parameters in tested cell cultures in a concentration and time dependent manner. However, the observed functional modifications induced by fluoro-edenite are generally less dramatic than those induced by crocidolite and more evident on human lung alveolar epithelial cancer cell line A549 with respect to those obtained on human lung fibroblasts or monocyte-macrophage cell line J774. The sequence of the damage is hypothesised to be as follows: at increasing fluoro-edenite concentrations, and/or treatment times, the increase in reactive oxygen species (ROS) production could trigger significant DNA damage in cell cultures, concomitantly with drop in cell metabolism and increase in lactic dehydrogenase release. In conclusion, according to our data, fluoro-edenite appears as a probable carcinogenic agent, responsible for the high incidence of malignant pleural mesothelioma in Biancavilla.     

Mineral fibre toxicity: expression of retinoblastoma (Rb) and phospho-retinoblastoma (pRb) protein in alveolar epithelial and mesothelial cell lines exposed to fluoro-edenite fibres

Several asbestos-like mineral fibres, including fluoro-edenite, may cause lung cancer and/or other lung diseases. However, biological and molecular mechanisms linked to cancer development after mineral fibre exposure have not been fully investigated. In the present study, human non-malignant mesothelial (MeT-5A) and human bronchoalveolar alveolar epithelial (A549) cell lines were incubated with rising concentrations of fluoro-edenite to evaluate the expression of retinoblastoma (Rb) protein, which has been demonstrated to play an important role in cell cycle control and tumour progression. Intriguingly, these results show that Rb expression was unchanged, while the level of the phosphorylated protein increased significantly in a dose-dependent manner, suggesting an involvement of this regulator protein in the pathogenesis of the lung diseases induced by mineral fibres. In conclusion, fluoro-edenite regulates the expression of phospho-retinoblastoma to trigger a network of signals strictly connected with cell proliferation and neoplastic cell transformation.     

Asbestiform fibers in the Biancavilla site of national interest (Sicily, Italy): review of environmental data via GIS platforms

After the observation of cases of malignant pleural neoplasm in Biancavilla (Catania, Italy), a new asbestiform fiber, named fluoro-edenite (NaCa₂Mg₅(Si₇Al)O₂₂F₂), was found in a stone quarry use for local building industry and in the lung tissue of an 86?years old woman who died from pleural mesothelioma. As a consequence the Italian Ministry of the Environment has included the Biancavilla site in the National Priority List. In this study, a point of view on the results from a large scale environmental monitoring program conducted for the implementation of the site investigation is presented. The obtained dataset from the environmental monitoring program results in more than 3,000 values of concentration of asbestos like fibers and fluoro-edenite fibers in air, water and top soil. These data are spatially and temporally distributed in the Biancavilla site, therefore the development and application of a Geographic Information Systems (GIS) was very useful to review, manage and analyze the obtained data and to give direction to the stakeholders in order to define the required remediation activities. A WebGIS was also developed to provide a rapid GIS access and data management by various control bodies.     

Alteration of activity and survival of osteoblasts obtained from human periodontitis patients: role of TRAIL

Periodontal disease (Pd) is characterized by extensive alveolar bone loss, that occurs as a consequence of the impairment of the normal bone remodelling. Bone remodelling is regulated by the correct balance between osteoclast and osteoblast formation and activity. Alveolar bone loss could be due to an increased bone resorption by osteoclasts or a decreased bone formation by osteoblasts (OBs) or both. Although the role played by osteoclasts in increasing bone resorption in Pd is already known, the behaviour of OBs in this disease is poorly understood. In the present study we hypothesized that activity and survival of OBs, locally present in alveolar bone of Pd patients, are altered. Thus, we studied the activity and survival of OBs obtained from alveolar bone fragments of Pd patients. The results, obtained in OBs from the patients were compared with those from OBs obtained from healthy donors. We demonstrated that OBs from Pd patients weakly express OB phenotype in respect to the control cells. In particular, the alkaline phosphatase activity and the collagen type I production, as well as the formation of mineralized nodules, typical markers of differentiated OBs, were significantly lower in Pd patients. Interestingly, we also demonstrated that OBs from the patients were more sensitive to the apoptotic effect induced by TNF-related apoptosis-inducing ligand (TRAIL). TRAIL, a member of the TNF superfamily, induces apoptosis by interacting with its death receptors, (DR4, DR5). However, its activity can be modulated by two decoy receptors, DcR1 and DcR2. Thus, the sensitiveness of TRAIL induced apoptosis is determined by the ratio of death and decoy receptor. We demonstrated that OBs from Pd patients showed an imbalanced ratio between death and decoy TRAIL receptors due to the down-regulation of DcR2 expression. Furthermore, the levels of TRAIL in the serum of the same patients were significantly higher than those detected in the controls. In conclusion, we show for the first time that the alveolar bone loss in Pd patients could be due to the increased TRAIL-mediated apoptosis of OBs.     

全口义齿修复后造成松软牙槽嵴和／或牙槽嵴粘膜增生的原因初探

目的:研究松软牙槽嵴和/或牙槽嵴粘膜增生形成的原因,探讨预防和治疗措施。方法:对180例戴用全口义齿一年以上的患者进行临床调查研究。研究内容包括缺牙原因,义齿戴用的时间,牙槽嵴粘膜情况,松软牙槽嵴和/或牙槽嵴粘膜增生发生的部位,人工牙的类型等。结果:①180例全口义齿病例中,有松软牙槽嵴者20例,占22％,男:女=6:4,其中下牙槽嵴占60％,上牙槽嵴占,20％,上下牙槽嵴均有者占20％。患牙槽嵴粘膜增生者共8例,占4.4％,最多发生在下舌侧,其次为下唇沟。同时患有松软牙槽嵴和牙槽嵴粘膜增生的有4例,占患牙槽嵴粘膜增生病例的一半。②在患松软牙槽嵴的病例中,人工牙为塑料牙和瓷牙各占50％。缺牙原因为牙周病者共12例,占60％,龋病2例,占10％,龋病-牙周病者8例,占30％。③在患松软牙槽嵴的病例中,下颌牙槽嵴条件均为差,上颌牙槽嵴条件均为中或差。在患增生的粘膜组织的病例中,75％病例义齿固位为中或差,25％义齿固位为较好。结论:发病原因与患者缺牙原因,牙槽嵴部位,牙槽嵴条件,人工牙类型等有关。因此可以认为,牙槽嵴粘膜松软是戴用全口义齿后出现的不可忽视的问题,而牙槽嵴粘膜松软和/或增生的粘膜组织是相辅相成的。所以一副全口义齿不是一劳永逸的,使用一定的时间后需要更换,特别对牙槽嵴条件较差的患者     

Double deficiency of tetraspanins CD9 and CD81 alters cell motility and protease production of macrophages and causes chronic obstructive pulmonary disease-like phenotype in mice

CD9 and CD81 are closely related tetraspanins that regulate cell motility and signaling by facilitating the organization of multimolecular membrane complexes, including integrins. We show that CD9 and CD81 are down-regulated in smoking-related inflammatory response of a macrophage line, RAW264.7. When functions of CD9 and CD81 were ablated with monoclonal antibody treatment, small interfering RNA transfection, or gene knock-out, macrophages were less motile and produced larger amounts of matrix metalloproteinase (MMP)-2 and MMP-9 than control cells in vitro. In line with this, CD9/CD81 double-knock-out mice spontaneously developed pulmonary emphysema, a major pathological component of chronic obstructive pulmonary disease (COPD). The mutant lung contained an increased number of alveolar macrophages with elevated activities of MMP-2 and MMP-9 and progressively displayed enlarged airspace and disruption of elastic fibers in the alveoli. Secretory cell metaplasia, a finding similar to goblet cell metaplasia in cigarette smokers, was also observed in the epithelium of terminal bronchioles. With aging, the double-knockout mice showed extrapulmonary phenotypes, including weight loss, kyphosis, and osteopenia. These results suggest that the tetraspanins CD9 and CD81 regulate cell motility and protease production of macrophages and that their dysfunction may underlie the progression of COPD.     

Three-dimensional microscopy characterization of death receptor 5 expression by over-activated human primary CD4+ T cells and apoptosis

Activation-induced cell death is a natural process that prevents tissue damages from over-activated immune cells. TNF-Related apoptosis ligand (TRAIL), a TNF family member, induces apoptosis of infected and tumor cells by binding to one of its two death receptors, DR4 or DR5. TRAIL was reported to be secreted by phytohemagglutinin (PHA)-stimulated CD4(+) T cells in microvesicles.We investigate here TRAIL and DR5 regulation by activated primary CD4(+) T cells and its consequence on cell death. We observed that PHA induced CD4(+) T cell apoptosis in a dose-dependent manner. Thus, we investigated molecules involved in PHA-mediated cell death and demonstrated that TRAIL and DR5 were over-expressed on the plasma membrane of PHA-stimulated CD4(+) T cells. Surprisingly, DR5 was constitutively expressed in naive CD4(+) T cells at messenger RNA (mRNA) and protein levels. Thus, using 3 dimensional microscopy and intracellular staining assays, we show that DR5 is constitutively expressed in CD4(+) T cells and is pre-stocked in the cytoplasm. When cells are stimulated by PHA, DR5 is relocalized from cytoplasm to plasma membrane. Small interference RNA (siRNA) and blocking antibody assays demonstrate that TRAIL/DR5 interaction is mainly responsible for PHA-mediated CD4(+) T cell apoptosis. Thus, membrane DR5 expression leading to TRAIL-mediated apoptosis may represent one of the pathways responsible for eradication of over-activated CD4(+) T cells during immune responses.     

Hyperthermia-enhanced TRAIL- and mapatumumab-induced apoptotic death is mediated through mitochondria in human colon cancer cells

Colorectal cancer is the third leading cause of cancer-related mortality in the world; death usually results from uncontrolled metastatic disease. Previously, we developed a novel strategy of TNF-related apoptosis-inducing ligand (Apo2L/TRAIL) in combination with hyperthermia to treat hepatic colorectal metastases. However, previous studies suggest a potential hepatocyte cytotoxicity with TRAIL. Unlike TRAIL, anti-human TRAIL receptor antibody induces apoptosis without hepatocyte toxicity. In this study, we evaluated the anti-tumor efficacy of humanized anti-death receptor 4 (DR4) antibody mapatumumab (Mapa) by comparing it with TRAIL in combination with hyperthermia. TRAIL, which binds to both DR4 and death receptor 5 (DR5), was approximately tenfold more effective than Mapa in inducing apoptosis. However, hyperthermia enhances apoptosis induced by either agent. We observed that the synergistic effect was mediated through elevation of reactive oxygen species, c-Jun N-terminal kinase activation, Bax oligomerization, and translocalization to the mitochondria, loss of mitochondrial membrane potential, release of cytochrome c to cytosol, activation of caspases, and increase in poly(ADP-ribose) polymerase cleavage. We believe that the successful outcome of this study will support the application of Mapa in combination with hyperthermia to colorectal hepatic metastases.     

Cellular turnover in the mammary gland is correlated with systemic levels of progesterone and not 17beta-estradiol during the estrous cycle

Adult mammary tissue has been considered "resting" with minimal morphological change. Here, we reveal the dynamic nature of the nulliparous murine mammary gland. We demonstrate specific changes at the morphological and cellular levels, and uncover their relationship with the murine estrous cycle and physiological levels of steroid hormones. Differences in the numbers of higher-order epithelial branches and alveolar development led to extensive mouse-to-mouse mammary variations. Morphology (assigned grades 0-3) ranged from a complete lack of alveoli to the presence of numerous alveoli emanating from branches. Morphological changes were driven by epithelial proliferation and apoptosis, which differed between ductal versus alveolar structures. Proliferation within alveolar epithelium increased as morphological grade increased. Extensive alveolar apoptosis was restricted to tissue exhibiting grade 3 morphology, and was approximately 14-fold higher than at all other grades. Epithelial proliferation and apoptosis exhibited a positive relationship with serum levels of progesterone, but not with 17beta-estradiol. Compared with other estrous stages, diestrus was unique in that the morphological grade, epithelial proliferation, apoptosis, and progesterone levels all peaked at this stage. The regulated tissue remodeling of the mammary gland was orchestrated with mRNA changes in specific matrix metalloproteinases (MMP-9 and MMP-13) and specific tissue inhibitors of metalloproteinases (TIMP-3 and TIMP-4). We propose that the cyclical turnover of epithelial cells within the adult mammary tissue is a sum of spatial and functional coordination of hormonal and matrix regulatory factors.     

Matrix metalloproteinases and tissue inhibitor of metalloproteinase-2 in fetal rabbit lung

Cell-extracellular matrix interaction and extracellular matrix remodeling are known to be important in fetal lung development. We investigated the localization of matrix metalloproteinases (MMPs) in fetal rabbit lungs. Immunohistochemistry for type IV collagen, MMP-1, MMP-2, MMP-9, membrane type (MT) 1 MMP, and tissue inhibitor of metalloproteinase (TIMP)-2 and in situ hybridization for MMP-9 mRNA were performed. Gelatin zymography and Western blotting for MT1-MMP in lung tissue homogenates were also studied. MMP-1 and MT1-MMP were detected in epithelial cells, and MMP-2 and TIMP-2 were detected in epithelial cells and some mesenchymal cells in each stage. MMP-9 was found in epithelial cells mainly in the late stage. Gelatin zymography revealed that the ratio of active MMP-2 to latent MMP-2 increased dramatically during the course of development. MT1-MMP was detected in tissue homogenates, especially predominant in the late stage. These findings suggest that MMPs and their inhibitors may contribute to the formation of airways and alveoli in fetal lung development and that activated MMP-2 of alveolar epithelial cells may function to provide an extremely wide alveolar surface.     

Loose front teeth: radiological and histological correlation with grooming function in the impala Aepyceros melampus

Casual observations have revealed that the anterior dentition of impala and other antelope is loosely embedded, with the tips of the teeth movable over a distance of 1middot;5 to 2mm. The comb-like anterior dentition of impala Aepyceros melampus is utilized extensively for grooming purposes, and it was hypothesized that the looseness of the teeth might be related to the grooming function. A sample of 12 impala mandibles was obtained from Pilanesberg National Park. Boputhatswana. Six of the incisor canine (IC) complexes were examined macroscopically, radiographically and histologically, while the remaining six were used to determine the alveolar depth relative to total root length, The findings were: (1) wide periodontal ligament spaces, most prominent in the apical region; (2) a loose, highly vascular periodontal ligament; (3) well-developed trans-septal periodontal ligament fibres; and (4) relatively shallow alveoli, with only approximately two-thirds of the roots included within the alveoli. In no case could looseness be ascribed to pathological changes in the periodontal ligament, cementum or alveolar bone. These features suggest that the looseness of the teeth is associated with a see-saw action of the teeth about a fulcrum below the alveolar bone crest. with the maintenance of the closed resting position of the teeth being facilitated by the well-developed trans-septal fibres. It is suggested that the minimal interdental space maintained by this arrangement during grooming assists in the efficient removal of parasites from the pelage by impala.     

Localization and variation of TRAIL and its receptors in human placenta during gestation

The localization of TRAIL and its receptors in human placenta was studied under light microscopy using immunohistochemistry method. The variation of TRAIL and its receptors with development was also detected by in situ semi-quantification. The syncytiotrophoblast, cytotrophoblast, stromal cells and the capillary endothelium cells in human placenta all appeared to be TRAIL immunoreactive and the immunoreactive material was distributed on membrane and in cytoplasm with negative nuclei. During whole gestation there was no obvious variation of the staining of TRAIL. Although DR4, DR5, DcR1 and DcR2 can also be detected in the placenta throughout pregnancy, DR4 and DR5 staining increased with development whereas DcR1 and DcR2 staining decreased. Interestingly, at the beginning of the gestation DR4 and DR5 staining distributed on the cytotrophoblast mainly, whereas DcR1 and DcR2 mainly located in the syncytiotrophoblast cells. Collectively, these results suggest that human placenta may not only produce TRAIL but also be a TRAIL target organ, and that TRAIL/TRAILR system could take part in the self-homeostasis of placenta during whole gestation.     

The conformation of the extracellular binding domain of Death Receptor 5 in the presence and absence of the activating ligand TRAIL: a molecular dynamics study

The Death Receptor 5 (DR5), a member of tumor necrosis factor receptor (TNFR) superfamily of receptors, triggers apoptosis (programmed cell death) when stimulated by its tridentate ligand TRAIL. Until recently it was generally assumed that the activation of DR5 resulted from the recruitment of three independent receptor units, leading to the trimerization of intracellular domains. However, there is mounting evidence to suggest that, in the absence of ligand, such cytokine receptors primarily reside as preformed complexes. In this work, molecular dynamics simulations of the TRAIL-DR5 complex, the unbound receptor trimer and individual receptor monomers are compared to gain insight in the mechanism of activation. The results suggest that, in the absence of TRAIL, DR5 has a strong propensity to self-associate and that this is primarily mediated through interactions of the membrane proximal domains. The association of the free receptors leads to a loss of the threefold symmetry found within the receptor-ligand complex. The simulations suggest that the primary role of TRAIL is to induce threefold-symmetry within the DR5 complex and to constrain the receptor to a specific conformation. The implications of this in terms of the mechanism by which the receptor switches from an inactive to an active state are discussed.     

Acid contact in the rodent pulmonary alveolus causes proinflammatory signaling by membrane pore formation

Although gastric acid aspiration causes rapid lung inflammation and acute lung injury, the initiating mechanisms are not known. To determine alveolar epithelial responses to acid, we viewed live alveoli of the isolated lung by fluorescence microscopy, then we microinjected the alveoli with HCl at pH of 1.5. The microinjection caused an immediate but transient formation of molecule-scale pores in the apical alveolar membrane, resulting in loss of cytosolic dye. However, the membrane rapidly resealed. There was no cell damage and no further dye loss despite continuous HCl injection. Concomitantly, reactive oxygen species (ROS) increased in the adjacent perialveolar microvascular endothelium in a Ca(2+)-dependent manner. By contrast, ROS did not increase in wild-type mice in which we gave intra-alveolar injections of polyethylene glycol (PEG)-catalase, in mice overexpressing alveolar catalase, or in mice lacking functional NADPH oxidase (Nox2). Together, our findings indicate the presence of an unusual proinflammatory mechanism in which alveolar contact with acid caused membrane pore formation. The effect, although transient, was nevertheless sufficient to induce Ca(2+) entry and Nox2-dependent H(2)O(2) release from the alveolar epithelium. These responses identify alveolar H(2)O(2) release as the signaling mechanism responsible for lung inflammation induced by acid and suggest that intra-alveolar PEG-catalase might be therapeutic in acid-induced lung injury.     

Celastrol, a Triterpene, Enhances TRAIL-induced Apoptosis through the Down-regulation of Cell Survival Proteins and Up-regulation of Death Receptors

Whether celastrol, a triterpene from traditional Chinese medicine, can modulate the anticancer effects of TRAIL, the cytokine that is currently in clinical trial, was investigated. As indicated by assays that measure plasma membrane integrity, phosphatidylserine exposure, mitochondrial activity, and activation of caspase-8, caspase-9, and caspase-3, celastrol potentiated the TRAIL-induced apoptosis in human breast cancer cells, and converted TRAIL-resistant cells to TRAIL-sensitive cells. When examined for its mechanism, we found that the triterpene down-regulated the expression of cell survival proteins including cFLIP, IAP-1, Bcl-2, Bcl-xL, survivin, and XIAP and up-regulated Bax expression. In addition, we found that celastrol induced the cell surface expression of both the TRAIL receptors DR4 and DR5. This increase in receptors was noted in a wide variety of cancer cells including breast, lung, colorectal, prostate, esophageal, and pancreatic cancer cells, and myeloid and leukemia cells. Gene silencing of the death receptor abolished the effect of celastrol on TRAIL-induced apoptosis. Induction of the death receptor by the triterpenoid was found to be p53-independent but required the induction of CAAT/enhancer-binding protein homologous protein (CHOP), inasmuch as gene silencing of CHOP abolished the induction of DR5 expression by celastrol and associated enhancement of TRAIL-induced apoptosis. We found that celastrol also induced reactive oxygen species (ROS) generation, and ROS sequestration inhibited celastrol-induced expression of CHOP and DR5, and consequent sensitization to TRAIL. Overall, our results demonstrate that celastrol can potentiate the apoptotic effects of TRAIL through down-regulation of cell survival proteins and up-regulation of death receptors via the ROS-mediated up-regulation of CHOP pathway.     

Contribution of epigenetic silencing of tumor necrosis factor-related apoptosis inducing ligand receptor 1 (DR4) to TRAIL resistance and ovarian cancer

Dysregulation of apoptosis may support tumorigenesis by allowing cells to live beyond their normally intended life span. The various receptors for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) are located on chromosome 8p21.2, a region frequently deleted in ovarian cancer. Lack of expression of TRAIL receptor 1 (death receptor 4, DR4) correlates with resistance to TRAIL-induced apoptosis in ovarian cancer cells. Reconstitution of DR4 in the TRAIL-resistant A2780 ovarian cancer cell line was investigated with the demethylating agent 5-aza-2'-deoxycytidine and transient gene transfer. Regulation of other genes in the TRAIL pathway by 5-aza-2'-deoxycytidine was assessed in DNA GeneChip experiments. Primary ovarian cancers were analyzed by methylation-specific PCR and immunohistochemical analysis of a tissue microarray. Regulation of DR4 expression by demethylation or transient transfection is of functional relevance for TRAIL resistance in an ovarian cancer cell line. Hypermethylation of the DR4 promoter could be found in 10 of 36 (27.7%) DNAs isolated from ovarian cancer tissue. In an independent set of 68 ovarian cancer cases, a complete loss or down-regulation of DR4 protein expression was observed 10.3% and 8.8% patients, respectively. A significant (P = 0.019) majority of these patients was below 50 years of age. Our findings show a functional relevance of the level of DR4 expression in ovarian cancer and suggest a substantial contribution of DR4 hypermethylation and consequent loss of DR4 expression to ovarian cancer pathogenesis, particularly in premenopausal patients.     

Genetically Modified DR5-Specific TRAIL Variant DR5-B Revealed Dual Antitumor and Protumoral Effect in Colon Cancer Xenografts and an Improved Pharmacokinetic Profile

Despite the weak clinical efficacy of TRAIL death receptor agonists, a search is under way for new agents that more efficiently activate apoptotic signaling. We previously created a TRAIL DR5-selective variant DR5-B without affinity for the DR4, DcR1, DcR2, and OPG receptors and increased proapoptotic activity in tumor cells. Here we showed that DR5-B significantly inhibited tumor growth in HCT116 and Caco-2 but not in HT-29 xenografts. The antitumor activity of DR5-B was 2.5 times higher in HCT116 xenografts compared to TRAIL. DR5-B at a dose of 2 or 10 mg/kg/d for 10 days inhibited tumor growth in HCT116 xenografts by 26% or 50% respectively, and increased animal survival. Unexpectedly, DR5-B at a higher dose (25 mg/kg/d) inhibited tumor growth only during the first 8 days of drug exposure, while at the end of the monitoring, no effect or even slight stimulation of tumor growth was observed. The pharmacokinetic parameters of DR5-B were comparable to those of TRAIL, except that the half-life was 3.5 times higher. Thus, enhancing TRAIL selectivity to DR5 may increase both antitumor and proliferative activities depending on the concentration and administration regimens.