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PDF - 69K, Effect of siRNA-mediated TAZ knockdown on activation of EMT pathways.

PDF - 70K, Respective contributions of AMPK and Lats1 in mediating the action of C19.

Embryonic signaling pathways, in particular those mediated by Wnt and TGF-β, are known to play key roles in tumor progression through the induction of epithelial–mesenchymal transition (EMT). Their simultaneous targeting could therefore represent a desirable anticancer strategy. On the basis of recent findings that both Wnt and TGF-β–associated pathways are regulated by Hippo signaling in mammalian cells, we reasoned that targeting the latter would be more effective in inhibiting EMT. In a search for such inhibitors, we identified a small molecule (C19) with remarkable inhibitory activity not only against Hippo, but also against Wnt and TGF-β pathways. C19 inhibited cancer cell migration, proliferation, and resistance to doxorubicin in vitro, and exerted strong antitumor activity in a mouse tumor model. Mechanistically, C19 induced GSK3-β–mediated degradation of the Hippo transducer TAZ, through activation of the Hippo kinases Mst/Lats and the tumor suppressor kinase AMPK upstream of the degradation complex. Overall, this study identified C19 as a multi-EMT pathway inhibitor with a unique mechanism of action. The findings that both AMPK and Mst/Lats mediate the antitumor activity of C19 shed light on a potential cross-talk between metabolic and organ size control pathways in regulating cancer progression. By simultaneously targeting these two pathways, C19 may represent a new type of agents to suppress cancer progression and/or its recurrence. Mol Cancer Ther; 13(6); 1457–67. ©2014 AACR.

PDF - 102K, Chemical synthesis of C19.

PDF - 62K, Legends for Supplementary Figures.

PDF - 253K, Effect of degradation refractory TAZ on activity of the Hippo reporter, autophagy and cell migration.

PDF - 86K, Western blot density analysis.

PDF - 218K, Effect of C19 on ligand induced activation of EMT pathways and cell migration.

PDF - 57K, Respective contributions of AMPK and Lats1 in mediating the action of C19.

PDF - 65K, Regulation of C19 activity by TDZD and rapamycin.

A major limitation in aging research is the lack of reliable biomarkers to assess phenotypic changes with age or monitor response to anti-aging interventions. The present study investigates the role of intracellular ferrous iron (Fe2+) as a potential biomarker of senescence. Iron is known to accumulate in various tissues with age and recent studies have demonstrated that its level increases dramatically in senescent cells. The techniques used are however cumbersome and only measure total iron. Also, it is still to be determined whether the damaging form of iron (Fe2+) is elevated in senescent cells. Here we assessed the potential use of a newly discovered Fe2+ reactive probe (SiRhoNox-1) for selective labeling of senescent cells in vitro. For this we have generated and characterized various senescent cell models and subjected them to SiRhoNox-1 labeling. Our results indicate that SiRhoNox-1 selectivity labels live senescent cells and was more specific and faster than current staining such as SA-βGal or a derived fluorescent probe C12FDG. By using SiRhoNox-1, we also showed that intracellular ferrous iron accumulation is secondary to senescence induction and it is not reversed by stress removal. Together these findings suggest that SiRhoNox-1 may serve as a convenient tool to detect senescent cells based on their ferrous iron level.

Macrophages play important roles in recycling iron derived from the clearance of red blood cells (RBCs). They are also a critically important component of host defense, protecting against invading pathogens. However, the effects on macrophage biology of acutely ingesting large numbers of RBCs are not completely understood. To investigate this issue, we used a mouse model of RBC transfusion and clearance, which mimics the clinical setting. In this model, transfusions of refrigerator storage-damaged (ie, “old”) RBCs led to increased erythrophagocytosis by splenic red pulp macrophages (RPMs). This robust erythrophagocytosis induced ferroptosis, an iron-dependent form of cell death, in RPMs. This was accompanied by increases in reactive oxygen species and lipid peroxidation in vivo, which were reduced by treatment in vitro with ferrostatin-1, a ferroptosis inhibitor. Old RBC transfusions also induced RPM-dependent chemokine expression by splenic Ly6C(hi) monocytes, which signaled Ly6C(hi) monocyte migration from bone marrow to spleen, where these cells subsequently differentiated into RPMs. The combination of cell division among remaining splenic RPMs, along with the influx of bone marrow–derived Ly6C(hi) monocytes, suggests that, following RPM depletion induced by robust erythrophagocytosis, there is a coordinated effort to restore homeostasis of the RPM population by local self-maintenance and contributions from circulating monocytes. In conclusion, these findings may be clinically relevant to pathological conditions that can arise as a result of increased erythrophagocytosis, such as transfusion-related immunomodulation and impaired host immunity.

There is a need for a comprehensive anti-cancer strategy that simultaneously targets abnormal proliferation, angiogenesis rates, and development of chemotherapy resistance. We have identified a small molecule, OT-404, that effectively inhibited proliferation and angiogenesis of either chemo-sensitive or resistant human cancer cells and enhanced cancer cell sensitivity to different chemotherapy. In vivo studies of human tumor xenografts in nude mice showed that OT-404, used alone or encapsulated into nanoparticles, inhibited the growth of doxorubicin-resistant breast cancer MCF-7 by more than 80%, and by 95% when combined with doxorubicin. These findings provide evidence for the potential of OT-404 in cancer management. Othera Pharmaceuticals

BACKGROUND. Some countries have limited the maximum allowable storage duration for red cells to 5 weeks before transfusion. In the US, red blood cells can be stored for up to 6 weeks, but randomized trials have not assessed the effects of this final week of storage on clinical outcomes. METHODS. Sixty healthy adult volunteers were randomized to a single standard, autologous, leukoreduced, packed red cell transfusion after 1, 2, 3, 4, 5, or 6 weeks of storage (n = 10 per group). 51-Chromium posttransfusion red cell recovery studies were performed and laboratory parameters measured before and at defined times after transfusion. RESULTS. Extravascular hemolysis after transfusion progressively increased with increasing storage time (P < 0.001 for linear trend in the AUC of serum indirect bilirubin and iron levels). Longer storage duration was associated with decreasing posttransfusion red cell recovery (P = 0.002), decreasing elevations in hematocrit (P = 0.02), and increasing serum ferritin (P < 0.0001). After 6 weeks of refrigerated storage, transfusion was followed by increases in AUC for serum iron (P < 0.01), transferrin saturation (P < 0.001), and nontransferrin-bound iron (P < 0.001) as compared with transfusion after 1 to 5 weeks of storage. CONCLUSIONS. After 6 weeks of refrigerated storage, transfusion of autologous red cells to healthy human volunteers increased extravascular hemolysis, saturated serum transferrin, and produced circulating nontransferrin-bound iron. These outcomes, associated with increased risks of harm, provide evidence that the maximal allowable red cell storage duration should be reduced to the minimum sustainable by the blood supply, with 35 days as an attainable goal. REGISTRATION. ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT02087514","term_id":"NCT02087514"}}NCT02087514. FUNDING. NIH grant HL115557 and UL1 TR000040.

Evidence is accumulating that chromatin plays a major role in the control of cellular response to stress. This is best illustrated by the recent findings that chromatin modifying factors of class III histone deacetylases (sirtuins) are capable of protecting cells from oxidative and genotoxic stress. In particular, Sirt1 has been shown to mimic the action of caloric restriction (CR) for the prevention of aging-associated diseases. In the present study, we have investigated the potential role of class I and II histone deacetylases (HDACs) in cellular protection against various stresses including those caused by nutrient deprivation. For this, we utilized a cellular model in which expression of class I and II HDACs was altered as a result of cellular adaptation to Trichostatin A (TSA), a selective inhibitor of these deacetylases. Our results indicated that TSA-resistant cells also developed resistance to H2O2, DNA damaging agents, and to nutrient deprivation. Interestingly, the insulin signaling pathway mediated by Akt was inhibited in the TSA-resistant cells, mirroring the effect of glucose deprivation on this pathway. Since expression of HDAC4 was consistently enhanced in the TSA-resistant cell lines, we suggest that this enzyme may contribute to their anti-stress response. In agreement with this, siRNA-mediated knockdown of HDAC4 in stress resistant cells enhanced their sensitivity to the DNA damaging drug doxorubicin and also to glucose deprivation. Akt phosphorylation was also up-regulated in response to HDC4 knockdown. Together, these findings suggest that cellular conditioning with TSA may represent a useful approach to mimic the effects of calorie restriction.

Thyroid hormone has been recently shown to induce tumor growth and angiogenesis via a plasma-membrane hormone receptor on integrin alphaVbeta3. The receptor is at or near the Arg-Gly-Asp (RGD) recognition site on the integrin that is important to extracellular matrix (ECM) protein and vascular growth factor interactions with the integrin. In the present study, we examined the possibility that tetraiodothyroacetic acid (tetrac), a deaminated, non-agonist thyroid hormone analog that binds to the integrin receptor, may modulate vascular growth factor-induced angiogenesis in the absence of thyroid hormone. Angiogenesis models were studied in which VEGF or FGF2 (1-2 microg/ml) induced tube formation in human dermal microvascular endothelial cells (HDMEC), stimulated new blood vessel branch formation in the chick chorioallantoic membrane (CAM) and induced angiogenesis in the mouse matrigel model. In all models, tetrac (1-10 microM) and at 10 microg in mouse matrigel inhibited the pro-angiogenesis activity of VEGF and FGF2 by more than 50%. RT-PCR revealed that tetrac (1-3 microM) decreased abundance of angiopoietin-2 mRNA, but not angiopoietin-1 mRNA, in VEGF-exposed endothelial cells, suggesting that specific angiogenic pathways are targeted by tetrac. Tetrac is a novel, inexpensive small molecule whose anti-angiogenic activity in the present studies is proposed to reflect inhibition, via the integrin RGD recognition/thyroid hormone receptor site, of crosstalk between plasma-membrane vascular growth factor receptors and integrin alphaVbeta3.

Resistance to cytotoxic agents is a major limitation for their clinical use to treat human cancers. Tumors become resistant to chemotherapy when a subset of cells undergoes molecular changes leading to overexpression of drug transport proteins, alterations in drug-target interactions or reduced ability to commit apoptosis. However, such changes may not be sufficient to explain why both resistant and nonresistant cells survive drug's action in tumors that ultimately become drug resistant. We hypothesized that, in such tumors, a cytoprotective relationship may exist between drug-resistant and neighboring drug-sensitive cells. The present study addresses the possibility that drug-resistant cells secrete in their culture medium factors able to protect sensitive cells from drug toxicity. A survival molecule, midkine, was identified by cDNA array to be expressed only in drug-resistant cells. Midkine-enriched fractions obtained by affinity chromatography exert a significant cytoprotective effect against doxorubicin in the wild-type drug-sensitive cells. Moreover, transfection of these cells with the midkine gene caused a decreased response to doxorubicin. The underlying mechanism of this cytoprotection appeared to imply activation of the Akt pathway and inhibition of drug-induced proliferation arrest as well as apoptotic cell death. These findings provide evidence for the existence of intercellular cytoprotective signals such as the one mediated by midkine, originating from cells with acquired drug resistance to protect neighboring drug-sensitive cells and thus contribute to development of resistance to chemotherapy.

Irreversible proliferation arrest (also called senescence) has emerged recently as a drug-responsive program able to influence the outcome of cancer chemotherapy. Since the drug amounts required for induction of proliferation arrest are much lower than those necessitated for induction of cell death, forcing cancer cells to undergo senescence may represent a less aggressive approach to control tumor progression. However, to achieve a long-standing control of proliferation, the ability of cancer cells to escape senescence and become drug resistant must be inhibited. Therefore, a clear understanding of the mechanisms that govern drug-induced senescence is critical and can lead to discovery of novel approaches to suppress drug resistance. The present review discusses the relevance of senescence in response to chemotherapy and the onset of drug resistance development. Particular emphasis is directed toward the utilization of findings from the field of research on aging, that can be applied to induction of senescence in cancer cells and reversal of their drug resistance phenotype. Proof of principle for this relationship is represented by the identification of inhibitors of aging associated proteases such as the proteasome and cathepsin L as novel and potent cancer drug resistance reversing agents.

The present study was undertaken to verify whether induction of senescence could be sufficient to reverse drug resistance and, if so, to determine the underlying mechanism(s). Our findings indicated that cotreatment of drug-resistant neuroblastoma cells with doxorubicin, at sublethal concentrations, in combination with the pan-caspase inhibitor, Q-VD-OPH, elicited a strong reduction of cell viability that occurred in a caspase-independent manner. This was accompanied by the appearance of a senescence phenotype, as evidenced by increased p21/WAF1 expression and senescence-associated β-galactosidase activity. Experiments using specific inhibitors of major cellular proteases other than caspases have shown that inhibition of cathepsin L, but not proteasome or cathepsin B, was responsible for the senescence-initiated reversal of drug resistance. This phenomenon appeared to be general because it was valid for other drugs and drug-resistant cell lines. A nonchemical approach, through cell transfection with cathepsin L small interfering RNA, also strongly reversed drug resistance. Further investigation of the underlying mechanism revealed that cathepsin L inhibition resulted in the alteration of intracellular drug distribution. In addition, in vitro experiments have demonstrated that p21/WAF1 is a substrate for cathepsin L, suggesting that inhibition of this enzyme may result in p21/WAF1 stabilization and its increased accumulation. All together, these findings suggest that cathepsin L inhibition in drug-resistant cells facilitates induction of senescence and reversal of drug resistance. This may represent the basis for a novel function of cathepsin L as a cell survival molecule responsible for initiation of resistance to chemotherapy.

Little is known about the role of the N-linked oligosaccharides in the function of the epidermal growth factor (EGF) receptor (EGF-R). In a human glioma cell line, U373 MG, EGF-Rs contain the bisecting N-linked oligosaccharide sequence recognized by erythroagglutinating phytohemagglutinin lectin from Phaseolus vulgaris (E-PHA). Incubation of E-PHA with cultured U373 MG cells results in inhibition of EGF binding to its receptor and consequently inhibition of EGF-induced autophosphorylation of the receptor. Consistent with the inhibitory effects on the EGF-R, phenotypic events that depend on EGF-R signaling, such as cell spreading and proliferation, were also found to be modified. The effect of this lectin seems to be specific because leukoagglutinating phytohemagglutinin lectin from P. vulgaris (L-PHA), an isolectin of E-PHA, had no effect on EGF-R activity or the biological functions of these cells even though L-PHA was able to bind to the EGF-R. These findings suggest the presence of an important bisecting N-linked oligosaccharide structure in close proximity to the EGF binding site on the receptor. Furthermore, these results suggest the possibility that E-PHA lectin binding may provide an additional approach to blocking EGF-dependent glioma cell growth.

Embryonic signaling pathways, in particular those mediated by Wnt and TGF-β, are known to play key roles in tumor progression through the induction of epithelial–mesenchymal transition (EMT). Their simultaneous targeting could therefore represent a desirable anticancer strategy. On the basis of recent findings that both Wnt and TGF-β–associated pathways are regulated by Hippo signaling in mammalian cells, we reasoned that targeting the latter would be more effective in inhibiting EMT. In a search for such inhibitors, we identified a small molecule (C19) with remarkable inhibitory activity not only against Hippo, but also against Wnt and TGF-β pathways. C19 inhibited cancer cell migration, proliferation, and resistance to doxorubicin in vitro, and exerted strong antitumor activity in a mouse tumor model. Mechanistically, C19 induced GSK3-β–mediated degradation of the Hippo transducer TAZ, through activation of the Hippo kinases Mst/Lats and the tumor suppressor kinase AMPK upstream of the degradation complex. Overall, this study identified C19 as a multi-EMT pathway inhibitor with a unique mechanism of action. The findings that both AMPK and Mst/Lats mediate the antitumor activity of C19 shed light on a potential cross-talk between metabolic and organ size control pathways in regulating cancer progression. By simultaneously targeting these two pathways, C19 may represent a new type of agents to suppress cancer progression and/or its recurrence. Mol Cancer Ther; 13(6); 1457–67. ©2014 AACR.

The induction of p53 expression and stimulation of the Fas/caspase-8 pathway represent major mechanisms by which cytotoxic drugs induce apoptosis, but in neuroblastomas, the caspase-8 gene is often not expressed. Purpose: The aim of this study was to determine whether doxorubicin could induce apoptosis in caspase-8-deficient neuroblastoma cells and to define its mechanism of action. Methods: The caspase-8-deficient human neuroblastoma cell line, SKN-SH, was incubated with doxorubicin and the apoptotic response, as well as expression of apoptotic molecules in the p53/Fas/caspase-8 pathway, were determined. Results: SKN-SH cells incubated with doxorubicin readily underwent apoptosis in a concentration-dependent manner. Western blot analyses with specific antibodies demonstrated that both p53 and Fas ligand were endogenously expressed in SKN-SH cells, but their expression was not stimulated by doxorubicin. Fas receptor was not detected in these cells and caspase-8 was totally absent. Electron microscopic analyses of SKN-SH cells treated with doxorubicin revealed pronounced alterations in mitochondrial structure. This treatment also induced the release of cytochrome c from mitochondria and activated the downstream apoptotic intermediate, caspase-3. Conclusion: These results indicate that the p53/Fas/caspase-8 system does not play a role in mediating the apoptotic action of doxorubicin in the human neuroblastoma cell line SKN-SH. Thus, mitochondria and downstream apoptotic signaling intermediates may be considered as key targets for doxorubicin-induced apoptosis in neuroblastoma tumors having deficiencies in the Fas/caspase-8 system.

The transcription factor Stat3 has been reported to play a key role in protecting cells against apoptosis by up-regulating expression of the anti-apoptotic gene Bcl-xL. This investigation analyzes the relationship between the development of resistance to doxorubicin-mediated apoptosis in neuroblastoma cells (SKN-SH) and activation of the Stat3 signaling pathway. A drug-resistant cell line (SKN-SH/Dox6) was generated by continuous exposure to incremental concentrations of doxorubicin. Specific antibodies were utilized for Western blots and confocal microscopy to determine the nuclear localization of activated Stat3. Doxorubicin-mediated DNA fragmentation was inhibited and caspase-3 activity decreased in SKN-SH/Dox6 cells. Up-regulation of Stat3 phosphorylation and Bcl-xL expression, increased nuclear translocation of phospho-Stat3, and binding to DNA occurred only in resistant SKN-SH/Dox6 cells. The expression of Bcl-xL was inhibited by AG490, an inhibitor of the JAK/Stat3 signaling pathway, suggesting that the regulation of Bcl-xL and Stat3 involved a common mechanism. Activation of Stat3 in SKN-SH/Dox6 cells was contingent upon stimulation evoked by ligands secreted by the drug-resistant cells. Evidence to support this hypothesis was provided by experiments in which doxorubicin-sensitive SKN-SH cells were preincubated with conditioned media obtained from doxorubicin-resistant SKN-SH/Dox6 cells. This treatment increased Stat3 activation. It also rendered SKN-SH cells resistant to doxorubicin as demonstrated by a sharp decrease in doxorubicin-induced DNA degradation and cytotoxic potency. These findings suggest that the resistance of SKN-SH/Dox6 cells to doxorubicin may be mediated by anti-apoptotic factor(s) that are synthesized and secreted by tumor cells in response to cytotoxic agents.

BACKGROUND: Chronic transfusion is associated with an increased risk of bone marrow graft rejection. In prior studies with mouse models, minor histocompatibility antigens in red blood cell (RBC) and platelet products were presented in the context of recipient MHC class I to prime recipient cytotoxic T cells; these represent cross presentation and cross priming, respectively. Once primed in the recipient, these T cells may attack allogeneic bone marrow grafts. Thus, understanding the mechanism of transfusion-induced T cell cross priming may lead to new methods to reduce bone marrow graft rejection in chronically transfused patients. Cross presentation is performed by a specialized subset of antigen presenting cells (APCs) - CD11b lo, XCR1+ dendritic cells (XCR DCs). Transfusion of RBCs after prolonged refrigerated storage induces erythrophagocytosis and pro-inflammatory gene expression in the spleen. Fluorescent tracking of transfused RBCs showed that splenic red pulp macrophages (RPMs) ingest the majority of damaged RBCs, but RPMs are weak APCs. Splenic dendritic cells, including XCR DCs, also display increased uptake of stored vs. fresh RBCs. These data suggested that refrigerated storage may increase cross presentation of RBC antigens, thereby enhancing T cell cross priming. AIMS: To compare T cell cross priming after transfusion of fresh and refrigerator-stored RBCs, a mouse model was used with transgenic OVA-carrying RBCs as the antigen source and transgenic naive MHC class I-restricted (H-2Kb) OVA-specific T cells (OT-1) as responders. In parallel, an in-vitro system was established to determine the cellular elements required for cross presentation of RBC antigens. METHODS: Purified CD8 T cells from OT-1 mice were loaded with the cell proliferation tracking dye Cell Trace Far Red (CTFR) and adoptively transferred (4 x 10e6 per mouse) into cohorts of 8-12 week old C57BL/6 GFP+ mice (n=3 per group). The next day mice were transfused with 400 uL of fresh ( RESULTS: Transfusion of both fresh and stored HOD RBCs induced vigorous proliferation and activation of OT-1 cells. After 4 days, no differences were seen in the proliferation and activation profiles of OT-1 cells in mice receiving fresh (78±4% CD44hi, CTFR diluted) vs. stored (79±5%) HOD RBCs. The in-vitro cross presentation assay showed weak to absent OVA-specific OT-1 proliferation with co-cultures including fresh or stored HOD RBCs alone, and fresh or stored HOD RBCs plus Flt3L-DCs. In contrast, cultures including RPMs and Flt3L-DCs showed enhanced OVA-specific OT-1 proliferation with fresh (29±10% CTFR diluted) and stored (25±2%) HOD RBCs. CONCLUSION: Cross priming by fresh RBCs was stronger than expected based on prior studies showing minimal RBC uptake by XCR DCs after fresh GFP + RBC transfusion. Cross priming in this system may be more sensitive due to the high frequency of antigen specific T cells and, thus, is saturated by the small antigen load delivered by fresh transfusion. It is also possible that direct uptake of RBCs by DCs harms the cross-presentation machinery and offsets the effect of increased RBC antigen delivery. Optimal cross-presentation of RBC antigen may require cooperation with cells functionally specialized for metabolizing RBC by-products. Indeed, the in-vitro study shows RPMs promote DC-mediated cross presentation of antigens on fresh and stored RBCs. Thus, RPMs may share ingested RBC antigen with adjacent DCs and increase DC activation by secreting inflammatory cytokines. . Figure Figure. Disclosures No relevant conflicts of interest to declare.

BACKGROUND: Although iron is an essential element in critical metabolic pathways of both pathogenic microorganisms and their hosts it is less essential in certain barrier bacteria, such as Lactobacilli. Dietary iron supplementation increases mortality and affects the microbiome in African children, decreasing the abundance of beneficial Lactobacilli. Furthermore, the method of iron repletion influences the microbiome in patients with inflammatory bowel disease. AIM: To determine whether iron status and different methods of iron supplementation/overload affect the gut microbiome in mice. METHODS: Cohorts of iron-deficient, iron-replete, and iron-overloaded wild-type C57BL/6 female mice (n=5 per group) were generated by dietary manipulation and by injection of iron dextran (0.3mg weekly x 6) or RBC transfusion (0.3mL at 60% hematocrit weekly x 6). The day after the last injection/transfusion, mice were sacrificed and tissues (blood, liver, spleen, and duodenum) and feces, from the cecum and rectum, were collected. Iron levels in tissues and in rectal feces were quantified by a wet ashing procedure. Commercial ELISA kits were used to quantify circulating hepcidin and ferritin levels. DNA from feces was extracted using the Fecal DNA extraction kit (Mo Bio) and sent to the Molecular Research (MRDNA) center for 16S rDNA Illumina platform sequencing and analysis. Statistical analyses were performed using LEfSe database (https://huttenhower.sph.harvard.edu/galaxy/) and GraphPad Prism. RESULTS: Mice fed an iron-deficient diet from weaning developed iron deficiency anemia with decreased intracellular iron stores, as measured by serum ferritin and liver and spleen iron (see Table). Iron dextran injections induced iron overload in mice fed either an iron deficient or iron replete diet. Chronic transfusion induced iron overload in mice fed an iron replete diet, but led to iron repletion without overload in mice fed an iron deficient diet. The iron deficient diet decreased, whereas the iron supplemented diet increased, fecal iron significantly. Although, iron dextran injections and chronic transfusion increased hepcidin levels, they did not significantly affect fecal iron. Analysis of microbiome data showed that fecal iron modulated the relative abundance of different bacteria. The phylum Proteobacteria showed a negative trend with increasing fecal iron associated with decreasing relative abundance (R2 0.5; p CONCLUSIONS: In this study, iron status modified the microbiome in mice. The microbiome was further modulated by different types of iron overload, especially in the class Clostrida. Similar to human studies, increasing fecal iron decreases the abundance in the gut of potentially beneficial lactobacilli. Although there are differences between mouse and human gut microbiomes, this mouse model can be used to study the effects of iron supplementation strategies and iron overload and can provide the foundation for further studies focused on the role of iron in host-pathogen interactions and immune function. Disclosures No relevant conflicts of interest to declare.

Ganglioside GM3 is a membrane component that has been described to modulate cell growth through inhibition of EGF receptor associated tyrosine kinase. In order to determine if the inhibition of cell growth by this ganglioside is specifically mediated through EGF receptor signaling, the effects of GM3 on key enzymes implicated in EGF signaling were determined and compared to another inhibitor of the EGF receptor kinase. Treatment of A IS cells in culture by GM3 or a tyrosine kinase inhibitor, leflunomide, led to the inhibition of MAP kinase and PI3 kinase activities. There was no detectable effect on phosphotyrosi ne phosphatases. In a cell free system, however, GM3 had no effect on the activity of these signaling intermediates. Leflunomide was able to directly inhibit MAP kinase activity. GM3 and leflunomide were also found to act differently on the expression of the early immediate genes. The expression of c-fos and c-jun was inhibited by both GM3 and leflunomide. The expression of c-myc, however, was only inhibited by leflunomide. These findings suggest that the action of GM3 on cell growth and signaling is specifically mediated by EGF receptor and that this ganglioside does not act directly on the intracellular intermediates of EGF receptor signaling. In addition, soluble small molecule tyrosine kinase inhibitors such as leflunomide can directly affect the activity of MAP kinases and possibly other signaling intermediates. The direct effects of leflunomide on signaling intermediates may explain the differential effects of leflunomide and GM3 on gene expression and cell growth.

The glycosphingolipid patterns were analyzed on two clones derived from a human melanoma cell line and selected for their respectively high and low metastatic ability in immunosuppressed newborn rats. Conversely to the weakly metastatic cells which exhibited a pattern similar to that of the parental cell line, highly metastatic human melanoma cells appeared to be deficient in ganglioside biosynthesis. An accumulation of lactosylceramide was found in the latter cells, with low amounts of GM3 as the only ganglioside detected and a fourfold decreased activity of GM3 synthase (EC 2.4.99.9). After subcutaneous injection of metastatic cells in newborn rats, the cells proliferating in the tumor induced at the injection site re-expressed the four common gangliosides of melanoma: GM3, GM2, GD3 and GD2, whereas the cells growing in the lungs as metastatic nodules were deficient in ganglioside synthesis and showed an accumulation of lactosylceramide. Taken together, our results suggest that the human melanoma cells which are able to escape from the primary tumor and invade the lungs have an impaired ganglioside biosynthesis with a deficient GM3 synthase.

Gangliosides in normal serum are found only in lipoproteins and the relative content of the three major lipoprotein fractions is low density lipoprotein > high density lipoprotein > very low density lipoprotein (LDL > HDL > VLDL). Upon in vitro incubation of labeled gangliosides with human serum, about 15% of the exogenous gangliosides became associated with the albumin fraction and 85% were distributed on the lipoproteins in the order HDL > LDL > VLDL. To compare the relative affinities of serum proteins for gangliosides, the levels of exchange of exogenous gangliosides between preloaded serum proteins were determined. Although albumin had the highest binding capacity for gangliosides, 85% of the albumin-loaded gangliosides were transferred to the total lipoprotein fraction and this exchange was reversible. The transfer rate from albumin to isolated lipoproteins was higher to LDL (90%) and HDL (85%) whereas only 55% of albumin-loaded gangliosides were transferred to VLDL. The study of exchanges of preloaded gangliosides between isolated lipoproteins showed that the extent of transfer of gangliosides from a given lipoprotein fraction onto other lipoproteins was inversely correlated with its endogenous ganglioside content. Moreover, in the absence of albumin from the incubation medium, the final lipoprotein distribution of remaining exogenous gangliosides was similar to the normal distribution of endogenous gangliosides in serum lipoproteins. The formation of unexchangeable complexes between albumin and micellar exogenous gangliosides could be a possible explanation for the observed differences in the distribution of exogenous and endogenous gangliosides in serum proteins.

Increased neovasculature and resistance to chemotherapy are hallmarks of aggressive cancer; therefore, the development of approaches to simultaneously inhibit these two processes is highly desirable. Previous findings from our laboratory have demonstrated that cathepsin L plays a key role in the development of drug resistance in cancer, and that its inhibition reversed this phenomenon. The goal of the present study was to determine whether targeting cathepsin L would inhibit angiogenesis. For this, the effects of a specific cathepsin L inhibitor, Napsul-Ile-Trp-CHO (NSITC), were tested in vitro on endothelial cell proliferation and interaction with the extracellular matrix, and also in vivo, by measuring its effect on angiogenesis in the chick chorioallantoic membrane (CAM) and mouse matrigel models. The results indicated that NSITC readily inhibits the proliferation of endothelial cells by inducing cell cycle arrest at the G(0)/G(1) phase, and suppresses cell adhesion to different substrates. Investigation of the underlying mechanism(s) indicated that NSITC was able to reduce expression of the adhesion molecule alphaVbeta3 integrin, inhibit cathepsin L-mediated degradation of the extracellular matrix, and disrupt secretion of the pro-angiogenic factors fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF). NSITC demonstrated potent efficacy in inhibiting growth factor- and tumor mediated-angiogenesis in the CAM and mouse matrigel models of angiogenesis. The anti-angiogenic effects of NSITC resulted in inhibition of tumor growth in the CAM and in nude mouse xenograft models. Together, these findings provide evidence that cathepsin L plays an important role in angiogenesis and suggest that NSITC represents a potential drug for the treatment of aggressive cancer.

Cancer stem cells are known for their inherent resistance to therapy. Here we investigated whether normal stem cells with acquired resistance to stress can be used to identify novel markers of cancer stem cells. For this, we generated a human embryonic stem cell line resistant to Trichostatin A and analyzed changes in its gene expression. The resistant cells over-expressed various genes associated with tumor aggressiveness, many of which are also expressed in the CD133+ glioma cancer stem cells. These findings suggest that stress-resistant stem cells generated in vitro may be useful for the discovery of novel markers of cancer stem cells.

Cathepsin L is a lysosomal enzyme thought to play a key role in malignant transformation. Recent work from our laboratory has demonstrated that this enzyme may also regulate cancer cell resistance to chemotherapy. The present study was undertaken to define the relevance of targeting cathepsin L in the suppression of drug resistance in vitro and in vivo and also to understand the mechanism(s) of its action. In vitro experiments indicated that cancer cell adaptation to increased amounts of doxorubicin over time was prevented in the presence of a cathepsin L inhibitor, suggesting that inhibition of this enzyme not only reverses but also prevents the development of drug resistance. The combination of the cathepsin L inhibitor with doxorubicin also strongly suppressed the proliferation of drug-resistant tumors in nude mice. An investigation of the underlying mechanism(s) led to the finding that the active form of this enzyme shuttles between the cytoplasm and nucleus. As a result, its inhibition stabilizes and enhances the availability of cytoplasmic and nuclear protein drug targets including estrogen receptor-α, Bcr-Abl, topoisomerase-IIα, histone deacetylase 1, and the androgen receptor. In support of this, the cellular response to doxorubicin, tamoxifen, imatinib, trichostatin A, and flutamide increased in the presence of the cathepsin L inhibitor. Together, these findings provided evidence for the potential role of cathepsin L as a target to suppress cancer resistance to chemotherapy and uncovered a novel mechanism by which protease inhibition-mediated drug target stabilization may enhance cellular visibility and, thus, susceptibility to anticancer agents.

The present investigation was undertaken to measure the relative abilities of pro-death versus pro-survival proteases in degrading each other and to determine how this might influence cellular susceptibility to death. For this, we first carried out in vitro experiments in which recombinant pro-death proteases (caspase-3 or cathepsin D) were incubated with the pro-survival protease (cathepsin L) in their respective optimal conditions and determined the effects of these reactions on enzyme integrity and activity. The results indicated that cathepsin L was able to degrade cathepsin D, which in turn cleaves caspase-3, however the later enzyme was unable to degrade any of the cathepsins. The consequences of this proteolytic sequence on cellular ability to undergo apoptosis or other types of cell death were studied in cells subjected to treatment with a specific inhibitor of cathepsin L or the corresponding siRNA. Both treatments resulted in suppression of cellular proliferation and the induction of a cell death with no detectable caspase-3 activation or DNA fragmentation, however, it was associated with increased accumulation of cathepsin D, cellular vaculolization, expression of the mannose-6-phosphate receptor, and the autophagy marker LC3-II, all of which are believed to be associated with autophagy. Genetic manipulations leading either to the gain or loss of cathepsin D expression implicated this enzyme as a key player in the switch from apoptosis to autophagy. Overall, these findings suggest that a hierarchy between pro-survival and pro-death proteases may have important consequences on cell fate.

Previous studies from our laboratory have demonstrated that thyroid hormones play a key role in cancer progression. In addition, a deaminated form, tetraiodothyroacetic acid (tetrac), that antagonizes the proliferative action of these hormones was found to possess anti-cancer functions through its ability to inhibit cellular proliferation and angiogenesis. The present study was undertaken to investigate whether tetrac could also suppress the development of drug resistance, known as a causative factor of disease relapse. Tetrac was shown to enhance cellular response in vitro to doxorubicin, etoposide, cisplatin, and trichostatin A in resistant tumor cell lines derived from neuroblastoma, osteosarcoma, and breast cancer. The mechanism of action of tetrac did not involve expression of classical drug resistance genes. However, radiolabeled doxorubicin uptake in cells was enhanced by tetrac, suggesting that one or more export mechanisms for chemotherapeutic agents are inhibited. Tetrac was also found to enhance cellular susceptibility to senescence and apoptosis, suggesting that the agent may target multiple drug resistance mechanisms. Tetrac has previously been shown to inhibit tumor cell proliferation in vitro. In vivo studies reported here revealed that tetrac in a pulsed-dose regimen was effective in suppressing the growth of a doxorubicin-resistant human breast tumor in the nude mouse. In this paradigm, doxorubicin-sensitivity was not restored, indicating that (1) the in vitro restoration of drug sensitivity by tetrac may not correlate with in vivo resistance phenomena and (2) tetrac is an effective chemotherapeutic agent in doxorubicin-resistant cells.

Irreversible growth arrest (also called senescence) has emerged recently as a tumor suppressor mechanism and a key determinant of cancer chemotherapy outcome. Previous work from our laboratory suggested that the cellular ability to undergo or to escape senescence dictates its fate to become drug-sensitive or drug-resistant, respectively. In the present study, we made the hypothesis that longevity genes, by virtue of their ability to inhibit senescence, may contribute to the onset of drug resistance. We report that expression of the longevity gene sirt1 increased both at the RNA and protein levels in all the five drug-resistant cell lines tested when compared with their drug-sensitive counterparts. In addition, biopsies from cancer patients treated with chemotherapeutic agents also expressed high levels of this molecule. These changes were specific for sirt1 because the expression of other members of its family was not affected. More importantly, small interfering RNA–mediated down-regulation of sirt1 significantly reversed the resistance phenotype and reduced expression of the multidrug resistance molecule P-glycoprotein. This was further confirmed by ectopic overexpression of sirt1, which induced expression of P-glycoprotein and rendered cells resistant to doxorubicin. Collectively, these findings uncovered a novel function for the longevity gene sirt1 as a potential target for diagnosis and/or treatment of cancer resistance to chemotherapy. They also describe a proof of principle that signaling pathways implicated in longevity may share similarities with those leading to development of drug resistance in cancer.

It is well established that growth factors and their receptors are overexpressed in brain tumors and play a key role in tumor cell proliferation. Glycoconjugate molecules expressed at the plasma membrane of mammalian cells have been also reported to be associated with tumor progression. Growth factor receptors and glycoconjugate molecules are able to interact with each other and this interaction usually results in modulation of growth factor receptor mediated signaling and the biological function of the cell. This review addresses the expression of both growth factor receptors and glycoconjugates molecules in the brain and brain tumors. The mechanism by which these two entities interact with each other and the consequences of their interaction on the biological function of tumor cell are also discussed. Glycoconjugate molecules seems to act more specifically on growth factor receptor signaling pathways than most of tyrosine kinase inhibitors. The use of glycoconjugates or their derivatives may represent a new approach to modulate the proliferative behavior of tumors that overexpress growth factor receptors such as brain tumors.

The inhibition of apoptosis is generally believed to be a major determinant of resistance to chemotherapy. However, recent findings have shown that caspase inhibitors do not protect cancer cells from death by cytotoxic agents, but may switch drug-induced apoptosis to an alternative 'default death'. The primary goals of this study were to determine the major characteristics of the 'default death' and the mechanism by which this switch is activated. For this purpose, we first investigated putative cell death modes induced by doxorubicin. Molecular markers associated with these death modes were utilized to identify the default death resulting from the inhibition of apoptosis. Our findings demonstrated that doxorubicin induced at least three distinct types of cell death, senescence, apoptosis and a type of necrosis, which were concentration dependent. Specific molecular markers such as p21/WAF1, activated caspase-3 and activated Akt were associated with these death modes. The pan-caspase inhibitor (Q-VD-OPH) greatly reduced doxorubicin-induced caspase-3 activation but did not protect cells against drug toxicity. The combination of doxorubicin and Q-VD-OPH caused an increased expression of p21/WAF1 and senescence -associated -beta-galactosidase activity, but did not alter Akt activation. Collectively, these findings suggest that the inhibition of apoptosis may lead to an increased expression of cell cycle inhibitors and cellular senescence.

The present study aims to verify the hypothesis that tumor cells with acquired resistance to chemotherapy may secrete survival factors and thus, participate in the protection of drug-sensitive cells against drug toxicity. A human neuroblastoma cell line, SK-N-SH, and its doxorubicin resistant derivative, RDOX6, have been used. Conditioned medium from RDOX6 cells attenuated the cytotoxic response of SK-N-SH cells to doxorubicin. This protective effect was associated with activation of the Akt survival pathway and inhibition of caspase-3. These data indicate that secretion, by drug-resistant cells, of factors that activate anti-apoptotic pathways in drug-sensitive cells, may constitute a novel mechanism of drug resistance.

Gangliosides expressed by tumor cells constitute potential targets for immunotherapy. A major limitation of protocols aiming to immunize patients against tumor gangliosides is the weak immunogenicity of these molecules. We have previously shown that exogenous gangliosides are essentially bound to serum lipoproteins. In this study we have analyzed the influence of human serum lipoproteins on the immunogenicity of purified human ganglioside 9-O-acetyl-GD3 in BALB/c mice. Although expressed at very low levels in mice, this ganglioside was not immunogenic when administered in the form of micelles. However 9-O-acetyl-GD3 adsorbed onto Very Low Density Lipoproteins (VLDL) was strongly and reproducibly immunogenic, inducing both an IgM and an IgG response, with higher titers than those obtained with total serum. The IgM antibody response appeared after a single injection whereas the IgG response was observed after 3 weeks but was stronger and more durable. The antibody response to 9-O-acetyl-GD3 bound to other serum fractions was weak or absent. The addition of recombinant interleukin 2 (IL-2) enhanced weak antibody responses to 9-O-acetyl-GD3 thereby facilitating responses to ganglioside in micelles and in protein-free Very Low Density Particles. Using in vitro assays, we demonstrated that VLDL-bound ganglioside 14C-GM3 was more sensitive to the effect of neuraminidase than gangliosides bound to other lipoprotein fractions, suggesting greater accessibility of VLDL-bound gangliosides. These results indicate that VLDL-bound gangliosides are the most immunologically active fraction of serum gangliosides. VLDL or similar particles and recombinant IL-2 may be useful adjuvants for immunization with gangliosides.

Glycosyltransferase gene transfection into cell lines has been an approach used successfully to elucidate the functional role of cell surface glycoconjugates. We have transfected the rat CMP-NeuAc:Galbeta1,4GlcNAc alpha2,6-sialyltransferase (EC 2.4.99.1) gene into a human, tumorigenic, glioma cell line, U373 MG. This transfection led to a marked inhibition of invasivity, alterations in adhesivity to fibronectin and collagen matrices, and inappropriately sialylated alpha3beta1 integrin. Adhesion-mediated protein tyrosine phosphorylation was reduced in the transfectants despite increased expression of focal adhesion kinase, p125fak. Furthermore, the transfectants showed a distinct cell morphology, an increased number of focal adhesion sites, and different sensitivity to cytochalasin D treatment than control U373 MG cells. These results suggest that inappropriate sialylation of cell surface glycoconjugates, such as integrins, can change focal adhesion as well as adhesion-mediated signal transduction and block glioma cell invasivity in vitro.

N-linked oligosaccharides appear to be important for the function of the epidermal growth factor (EGF) receptor. In a previous study (Rebbaa, A., Yamamoto, H., Moskal, J. R., and Bremer, E. G. (1996) J. Neurochem. 67, 2265-2272), we showed that binding of the erythroagglutinating phytohemagglutin lectin from Phaseolus vulgaris to the bisecting structures on the EGF receptor from U373 MG glioma cells blocked EGF binding and receptor autophosphorylation. In this study we examined the consequences of overexpression of the bisecting structure on the EGF receptor by gene transfection of U373 MG cells with the N-acetylglucosaminyltransferase III (GnT-III). This modification leads to a significant decrease in EGF binding and EGF receptor autophosphorylation. In addition, the cellular response to EGF was found to be altered. Proliferation of U373 MG cells in serum-free medium is inhibited by EGF. In contrast, proliferation of the GnT-III-transfected cells was stimulated by EGF. These data demonstrate that changes in EGF receptor glycosylation by GnT-III transfection reduces the number of the active receptors in U373 MG cells and that this change results in change in the cellular response to EGF.

The optimal conditions were examined for selective re-N-acetylation with14C or3H acetic anhydride of de-N-acetylated aminosugar-containing glycosphingolipids. Re-N-acetylation, which is nearly quantitative within 10 minutes in methanol, occurs selectively up to a maximal 100% yield when using a molar ratio of 5 mol of acetic anhydride per mole of aminosugar present in the glycosphingolipid. Above this molar ratio, it was observed some O-acytylation of carbohydrates which could be removed by mild alkali treatment. The method allows the choice of14C- or3H-labeling of glycosphingolipids with a final specific radioactivity which depends solely on the one of acetic anhydride. The binding of specific antibodies to glycosphingolipids, which was abolished upon de-N-acetylation, was again detectable after re-N-acetylation with radioactive acetic anhydride, suggesting that the native structures were recovered. This procedure of radiolabeling offers safety, rapidity and broad applicability to alkali-stable aminosugar-containing glycosphingolipids.

We have analyzed the immunomodulatory effect of human melanoma gangliosides bound to serum lipoprotein fractions on normal human immune-competent cells in vitro. Total melanoma gangliosides in micelles inhibited proliferation of peripheral blood mononuclear cells stimulated by various mitogens, modulated lymphocyte surface molecules CD2, CD3, CD4, CD5 and CD8 and inhibited the production of interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha (TNF alpha) and IL-6 by stimulated adherent cells. Most of these effects were abrogated in the presence of serum. Purified serum lipoprotein fractions were tested for their ability to allow or inhibit the immunomodulatory effects of gangliosides. Melanoma gangliosides bound to very-low-density lipoproteins (VLDL) were shown to be as potent modulators of the immune response in vitro as when they were presented to cells in the form of micelles. Gangliosides bound to low-density lipoproteins were less active and gangliosides bound to high-density lipoproteins or the lipoprotein-free fraction had no immunomodulatory effects. Given the fact that gangliosides are predominantly bound to lipoproteins in serum, we conclude that lipoproteins are important determinants of the immunomodulating potential of tumor gangliosides, and that the immunomodulatory effects of melanoma gangliosides observed in vitro may also occur in vivo.

Serum kinetics and organ distribution of [14C]-sialic acid-GM3 and [3H]-sphingosine-GM1, administered as an intravenous bolus, were analysed in Wistar rats. [3H]-GM1 and [14C]-GM3 had serum half-lives of 1.4 hours and 1.8 hours, respectively. Three hours after injection 75% of the GM1- and 38% of the GM3-associated label were present in the liver. Smaller yet significant amounts of label were present in the central nervous system, kidneys and lung. In vitro studies showed that [14C]-GM3 and [3H]-GM1 incubated with serum were predominantly bound to the High Density Lipoprotein and the Low Density Lipoprotein fractions. These results suggest a rapid serum clearance of exogenous gangliosides by the liver in rats.

14597 Background: Increased proinflammatory, proangiogenesis, and proliferative activities are among the major features of cancer. Thus, a comprehensive anti-tumor strategy would be to target these...

Thyroid hormone has been recently shown to induce tumor growth and angiogenesis. These angiogenesis modulating activities are initiated at endothelial cell plasma membrane receptor via the integrin αVβ3, at or near the Arg-Gly-Asp (RGD) recognition site on the integrin. In the present study, we have investigated the effect of tetraiodothyroacetic acid (tetrac), a deaminated thyroid hormone analog that inhibits thyroid hormone-binding to the cell surface integrin, on angiogenesis and cancer cell resistance to doxorubicin both in vitro and in vivo. Two angiogenesis models were studied in which vascular endothelial growth factor, VEGF165 or basic fibroblast growth factor, FGF2 (1–2 μg/ml) or thyroid hormone, thyroxin (L-T4 or T3) were used either to induce tube formation in the human dermal micro-vascular endothelial cells (HDMEC), or to stimulate new blood vessel branch formation in the chick chorioallantoic membrane (CAM) models. In both models, Tetrac (0.1–10 μM) inhibited the pro-angiogenesis activity of VEGF, FGF2, L-T4 or T3 by more than 50% at 1.0 uM RT-PCR revealed that tetrac (1–3 μM) decreased abundance of angiopoietin-2 mRNA but did not affect the mRNA levels of angiopoietin-1, in VEGF-exposed endothelial cells, suggesting that specific angiogenic pathways are targeted by this compound. Additionally, microarray was used to examine changes in expression of Matrix Metalloproteinases (MMP) and Tissue Inhibitor of Metalloproteinases (TIMP) following VEGF treatment with and without tetrac. HDMEC cells treated with VEGF exhibited 3–5-fold increase in MMP-15 and MMP-19 expression and tetrac (3μM), inhibited expression of MMP-15 and MMP-19 by 3–9-fold, respectively. Expression of TIMP-3 was increased 5.4-fold following VEGF and tetrac treatment when compared to treatment with VEGF alone. This finding suggests that part of the mechanism by which tetrac inhibits VEGF-stimulated angiogenesis involves inhibition of certain MMPs and increase in TIMP expression. Investigation of the anti-proliferative function of tetrac was carried out using the αVβ3 expressing breast cancer cells MC7 and their drug resistant counterparts. Interestingly, proliferation of both cell lines was inhibited similarly by tetrac suggesting that this analog may circumvent drug resistance. In fact, tetrac was able to reverse resistance to doxorubicin in vitro and to suppress growth of doxorubicin resistant tumors in nude mice. Inhibition of the drug transporter p-glycoprotein was found to play a key role in mediating the action of tetrac. Taken together, findings presented in this study provide evidence that the anticancer function of tetrac can be attributed to its anti-angiogenic and drug resistance reversal activities.

The development of resistance to chemotherapy represents an adaptive biological response by tumor cells that leads to treatment failure and patient relapse. During the course of their evolution (intrinsic resistance) or in response to chemotherapy (acquired resistance), tumor cells may undergo genetic alterations to possess a drug resistant phenotype. Dysregulation of membrane transport proteins and cellular enzymes, as well as altered susceptibility to commit to apoptosis are among the mechanisms that contribute to the genesis of acquired drug resistance. Recently, the development of approaches to prevent and/or to reverse this phenomenon has attracted special interest and a number of drug candidates have been identified. Despite strong effects observed for these candidates in vitro, however, most of them fail in vivo. In the present study, we have identified a novel small molecule inhibitor of dual NF-κB and oxidative stress pathways, OT-304, as a potential candidate to reverse drug resistance. Initial investigations indicate that this compound effectively inhibits proliferation of doxorubicin-sensitive and doxorubicin-resistant cells to the same extent, suggesting that it is capable of bypassing the development of drug resistance. Additional experiments reveal that OT-304 enhances cancer cell sensitivity to doxorubicin and to etoposide, particularly in cells characterized by the over-expression of the drug transporter P-glycoprotein. These findings suggest that either the expression/and or the function of P-glycoprotein could be affected by OT-304. In vivo studies using tumor xenografts in nude mice showed that OT-304 is also capable of preventing the growth of drug resistant cancer cells. This later finding further confirms the role of OT-304 as a drug resistance-reversing agent and warrants further pre-clinical and clinical investigation to determine its efficacy in treating aggressive tumors.