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Molecular Cancer Therapeutics

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Molecular Cancer Therapeutics

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract. Except for surgical resection, no effective treatment strategies have been established. Photodynamic therapy (PDT) consists of intravenous administration of a photosensitizer, activated by a specific wavelength of light, which produces reactive oxygen species that directly kill tumor cells. We analyzed the efficacy of PDT using a newly developed photosensitizer, 5,10,15,20-tetrakis [4-[β-d-glucopyranosylthio-2,3,5,6-tetrafluorophenyl]-2,3,[methano[N-methyl] iminomethano] chlorin (H2TFPC-SGlc), for the GIST treatment. Various photosensitizers were administered in vitro to GIST (GIST-T1) and fibroblast (WI-38) cells, followed by irradiation, after which cell death was compared. We additionally established xenograft mouse models with GIST-T1 tumors and examined the accumulation and antitumor effects of these photosensitizers in vivo. In vitro, the expression of the glucose transporters GLUT1, GLUT3, and GLUT4, the cellular uptake of H2TFPC-SGlc, and apoptosis mediated by PDT with H2TFPC-SGlc were significantly higher in GIST-T1 than in WI-38 cells. In vivo, H2TFPC-SGlc accumulation was higher in xenograft tumors of GIST-T1 cells than in the adjacent normal tissue, and tumor growth was significantly suppressed following PDT. PDT with novel H2TFPC-SGlc is potentially useful for clinical applications about the treatment of GIST. Mol Cancer Ther; 13(4); 767–75. ©2014 AACR.

Mutations in fibroblast growth factor receptor 2 (FGFR2) have been recently described as a molecular-specific feature in endometrial carcinomas and the presence of activated FGFR2 mutations is associated with poor prognosis. For that reason, inhibition of FGFR2 could be a therapeutic target in the treatment of endometriod carcinomas. In this work, we investigated the antitumoral activity of dovitinib (a multiple kinase inhibitor) in human endometrial cancer cell (ECC) lines. We found that dovitinib caused cell growth arrest, loss of clonogenic growth, and cell-cycle arrest in FGFR2-mutated ECCs in in vitro and in vivo experiments. Next, we investigated the mechanistic basis of dovitinib effects. We could determine that dovitinib modified expression levels of well-known key cell-cycle regulatory proteins that induce cellular senescence. To further investigate the role of dovitinib, we analyzed its effect on estrogen receptor α (ER-α) expression. Surprisingly, we discovered that dovitinib enhances ER-α expression in FGFR2-mutant ECCs. Because blocking one signaling pathway is often not sufficient to cause total tumor regression and the effectiveness of individual inhibitors is often short-lived, we examined the impact of targeting FGFR2 with dovitinib in combination with a selective ER antagonist, fulvestrant (ICI182.780). Combination of dovitinib plus ICI182.780 resulted in a significantly higher inhibition of cell growth than dovitinib treatment alone. These findings suggest that combinatory therapies using dovitinib plus ICI182.780 treatment can be truly effective in patients with endometrial carcinomas carrying FGFR2 mutations. Mol Cancer Ther; 13(4); 776–87. ©2014 AACR.

Ionophores are hydrophobic organic molecules that disrupt cellular transmembrane potential by permeabilizing membranes to specific ions. Gramicidin A is a channel-forming ionophore that forms a hydrophilic membrane pore that permits the rapid passage of monovalent cations. Previously, we found that gramicidin A induces cellular energy stress and cell death in renal cell carcinoma (RCC) cell lines. RCC is a therapy-resistant cancer that is characterized by constitutive activation of the transcription factor hypoxia-inducible factor (HIF). Here, we demonstrate that gramicidin A inhibits HIF in RCC cells. We found that gramicidin A destabilized HIF-1α and HIF-2α proteins in both normoxic and hypoxic conditions, which in turn diminished HIF transcriptional activity and the expression of various hypoxia-response genes. Mechanistic examination revealed that gramicidin A accelerates O2-dependent downregulation of HIF by upregulating the expression of the von Hippel–Lindau (VHL) tumor suppressor protein, which targets hydroxylated HIF for proteasomal degradation. Furthermore, gramicidin A reduced the growth of human RCC xenograft tumors without causing significant toxicity in mice. Gramicidin A–treated tumors also displayed physiologic and molecular features consistent with the inhibition of HIF-dependent angiogenesis. Taken together, these results demonstrate a new role for gramicidin A as a potent inhibitor of HIF that reduces tumor growth and angiogenesis in VHL-expressing RCC. Mol Cancer Ther; 13(4); 788–99. ©2014 AACR.

Basal-like breast cancers (BLBC) are poorly differentiated and display aggressive clinical behavior. These tumors become resistant to cytotoxic agents, and tumor relapse has been attributed to the presence of cancer stem cells (CSC). One of the pathways involved in CSC regulation is the Wnt/β-catenin signaling pathway. LRP6, a Wnt ligand receptor, is one of the critical elements of this pathway and could potentially be an excellent therapeutic target. Niclosamide has been shown to inhibit the Wnt/β-catenin signaling pathway by causing degradation of LRP6. TRA-8, a monoclonal antibody specific to TRAIL death receptor 5, is cytotoxic to BLBC cell lines and their CSC-enriched populations. The goal of this study was to examine whether niclosamide is cytotoxic to BLBCs, specifically the CSC population, and if in combination with TRA-8 could produce increased cytotoxicity. Aldehyde dehydrogenase (ALDH) is a known marker of CSCs. By testing BLBC cells for ALDH expression by flow cytometry, we were able to isolate a nonadherent population of cells that have high ALDH expression. Niclosamide showed cytotoxicity against these nonadherent ALDH-expressing cells in addition to adherent cells from four BLBC cell lines: 2LMP, SUM159, HCC1187, and HCC1143. Niclosamide treatment produced reduced levels of LRP6 and β-catenin, which is a downstream Wnt/β-catenin signaling protein. The combination of TRA-8 and niclosamide produced additive cytotoxicity and a reduction in Wnt/β-catenin activity. Niclosamide in combination with TRA-8 suppressed growth of 2LMP orthotopic tumor xenografts. These results suggest that niclosamide or congeners of this agent may be useful for the treatment of BLBC. Mol Cancer Ther; 13(4); 800–11. ©2014 AACR.

The Wnt signaling pathway is required during embryonic development and for the maintenance of homeostasis in adult tissues. However, aberrant activation of the pathway is implicated in a number of human disorders, including cancer of the gastrointestinal tract, breast, liver, melanoma, and hematologic malignancies. In this study, we identified monensin, a polyether ionophore antibiotic, as a potent inhibitor of Wnt signaling. The inhibitory effect of monensin on the Wnt/β-catenin signaling cascade was observed in mammalian cells stimulated with Wnt ligands, glycogen synthase kinase-3 inhibitors, and in cells transfected with β-catenin expression constructs. Furthermore, monensin suppressed the Wnt-dependent tail fin regeneration in zebrafish and Wnt- or β-catenin–induced formation of secondary body axis in Xenopus embryos. In Wnt3a-activated HEK293 cells, monensin blocked the phoshorylation of Wnt coreceptor low-density lipoprotein receptor related protein 6 and promoted its degradation. In human colorectal carcinoma cells displaying deregulated Wnt signaling, monensin reduced the intracellular levels of β-catenin. The reduction attenuated the expression of Wnt signaling target genes such as cyclin D1 and SP5 and decreased the cell proliferation rate. In multiple intestinal neoplasia (Min) mice, daily administration of monensin suppressed progression of the intestinal tumors without any sign of toxicity on normal mucosa. Our data suggest monensin as a prospective anticancer drug for therapy of neoplasia with deregulated Wnt signaling. Mol Cancer Ther; 13(4); 812–22. ©2014 AACR.

Many clinical cases of acquired resistance to the BRAF inhibitor vemurafenib have recently been reported. One of the causes of this acquired resistance is the BRAF downstream kinase point mutation MEK1-C121S. This mutation confers resistance to not only vemurafenib, but also to the allosteric MEK inhibitor selumetinib (AZD6244). Here, we investigated the pharmacologic activities and effectiveness of the novel MEK inhibitor E6201 against BRAF (v-raf murine sarcoma viral oncogene homolog B1)-V600E mutant melanoma harboring the MEK1-C121S mutation. A cell-free assay confirmed that E6201 is an ATP-competitive MEK inhibitor, meaning it has a different binding mode with MEK compared with allosteric MEK inhibitors. E6201 is more effective against BRAF-V600E mutant melanoma compared with BRAF wild-type melanoma based on MEK inhibition. We found that the acquired MEK1-C121S mutation in BRAF-V600E mutant melanoma conferred resistance to both vemurafenib and selumetinib but not E6201. The effectiveness of E6201 in this preclinical study is a result of its binding with MEK1 far from the C121S point mutation so the mutation is unable to influence the MAPK pathway inhibitory activity. These results support further clinical investigation of E6201. Mol Cancer Ther; 13(4); 823–32. ©2014 AACR.

Burkitt lymphoma is a rare malignancy arising from B cells. Current chemotherapeutic regimens achieve excellent overall survival rates in children, but less impressive rates in adults. There are cases with poor outcome caused by toxic effects of the therapy, tumor lysis syndrome, or metastatic spread of lymphomas to the central nervous system. Modulators of reactive oxygen species are currently discussed as potential drugs for the treatment of cancer. The NADPH oxidase 4 inhibitor imipramine-blue might satisfy the aforementioned requirements, and was studied here. We used MTT assay, crystal violet assay, and thymidine 3H-incorporation assay to analyze the effects of imipramine-blue on Burkitt lymphoma (BL2, BL2B95, BL30B95, BL41B95), neuroblastoma (KELLY, SH-SY5Y, SMS-KAN), cervix carcinoma (HeLa), breast cancer (MDA-MB231), angiosarcoma (AS-M), human embryonic kidney (HEK293WT), and nonmalignant (FLP1) cell lines. The effects of imipramine-blue on BL2B95 cells in vivo were investigated in xenografts on the chick chorioallantoic membrane (CAM). We report that imipramine-blue is a potent growth inhibitor for several cancer cell lines in vitro with IC50 values comparable to those of doxorubicin (0.16–7.7 μmol/L). Tumor size of BL2B95 cells inoculated in the CAM was reduced significantly (P < 0.05) after treatment with 10 μmol/L imipramine-blue. Lymphogenic dissemination of BL2B95 and the formation of blood and lymphatic vessels in experimental tumors were not affected. We show that imipramine-blue can be used to decrease the viability of cancer cell lines in vitro and in vivo. Imipramine-blue reduces the size of experimental Burkitt lymphoma significantly but does not affect the dissemination of BL2B95 cells, angiogenesis, and lymphangiogenesis. Mol Cancer Ther; 13(4); 833–41. ©2014 AACR.

Mutations within the catalytic domain of the histone methyltransferase EZH2 have been identified in subsets of patients with non-Hodgkin lymphoma (NHL). These genetic alterations are hypothesized to confer an oncogenic dependency on EZH2 enzymatic activity in these cancers. We have previously reported the discovery of EPZ005678 and EPZ-6438, potent and selective S-adenosyl-methionine-competitive small molecule inhibitors of EZH2. Although both compounds are similar with respect to their mechanism of action and selectivity, EPZ-6438 possesses superior potency and drug-like properties, including good oral bioavailability in animals. Here, we characterize the activity of EPZ-6438 in preclinical models of NHL. EPZ-6438 selectively inhibits intracellular lysine 27 of histone H3 (H3K27) methylation in a concentration- and time-dependent manner in both EZH2 wild-type and mutant lymphoma cells. Inhibition of H3K27 trimethylation (H3K27Me3) leads to selective cell killing of human lymphoma cell lines bearing EZH2 catalytic domain point mutations. Treatment of EZH2-mutant NHL xenograft-bearing mice with EPZ-6438 causes dose-dependent tumor growth inhibition, including complete and sustained tumor regressions with correlative diminution of H3K27Me3 levels in tumors and selected normal tissues. Mice dosed orally with EPZ-6438 for 28 days remained tumor free for up to 63 days after stopping compound treatment in two EZH2-mutant xenograft models. These data confirm the dependency of EZH2-mutant NHL on EZH2 activity and portend the utility of EPZ-6438 as a potential treatment for these genetically defined cancers. Mol Cancer Ther; 13(4); 842–54. ©2014 AACR.

Current research links aberrant lipogenesis and cholesterogenesis with prostate cancer development and progression. Sterol regulatory element-binding proteins (SREBP; SREBP-1 and SREBP-2) are key transcription factors controlling lipogenesis and cholesterogenesis via the regulation of genes related to fatty acid and cholesterol biosynthesis. Overexpression of SREBPs has been reported to be significantly associated with aggressive pathologic features in human prostate cancer. Our previous results showed that SREBP-1 promoted prostate cancer growth and castration resistance through induction of lipogenesis and androgen receptor (AR) activity. In the present study, we evaluated the anti–prostate tumor activity of a novel SREBP inhibitor, fatostatin. We found that fatostatin suppressed cell proliferation and anchorage-independent colony formation in both androgen-responsive LNCaP and androgen-insensitive C4-2B prostate cancer cells. Fatostatin also reduced in vitro invasion and migration in both the cell lines. Further, fatostatin caused G2–M cell-cycle arrest and induced apoptosis by increasing caspase-3/7 activity and the cleavages of caspase-3 and PARP. The in vivo animal results demonstrated that fatostatin significantly inhibited subcutaneous C4-2B tumor growth and markedly decreased serum prostate-specific antigen (PSA) level compared with the control group. The in vitro and in vivo effects of fatostatin treatment were due to blockade of SREBP-regulated metabolic pathways and the AR signaling network. Our findings identify SREBP inhibition as a potential new therapeutic approach for the treatment of prostate cancer. Mol Cancer Ther; 13(4); 855–66. ©2014 AACR.

The acquisition of apoptosis resistance is a fundamental event in cancer development. Among the mechanisms used by cancer cells to evade apoptosis is the dysregulation of inhibitor of apoptosis (IAP) proteins. The activity of the IAPs is regulated by endogenous IAP antagonists such as SMAC (also termed DIABLO). Antagonism of IAP proteins by SMAC occurs via binding of the N-terminal tetrapeptide (AVPI) of SMAC to selected BIR domains of the IAPs. Small molecule compounds that mimic the AVPI motif of SMAC have been designed to overcome IAP-mediated apoptosis resistance of cancer cells. Here, we report the preclinical characterization of birinapant (TL32711), a bivalent SMAC-mimetic compound currently in clinical trials for the treatment of cancer. Birinapant bound to the BIR3 domains of cIAP1, cIAP2, XIAP, and the BIR domain of ML-IAP in vitro and induced the autoubiquitylation and proteasomal degradation of cIAP1 and cIAP2 in intact cells, which resulted in formation of a RIPK1:caspase-8 complex, caspase-8 activation, and induction of tumor cell death. Birinapant preferentially targeted the TRAF2-associated cIAP1 and cIAP2 with subsequent inhibition of TNF-induced NF-B activation. The activity of a variety of chemotherapeutic cancer drugs was potentiated by birinapant both in a TNF-dependent or TNF-independent manner. Tumor growth in multiple primary patient–derived xenotransplant models was inhibited by birinapant at well-tolerated doses. These results support the therapeutic combination of birinapant with multiple chemotherapies, in particular, those therapies that can induce TNF secretion. Mol Cancer Ther; 13(4); 867–79. ©2014 AACR.

Acute myeloid leukemia (AML) remains a serious unmet medical need. Despite high remission rates with chemotherapy standard-of-care treatment, the disease eventually relapses in a major proportion of patients. Activating Fms-like tyrosine kinase 3 (FLT3) mutations are found in approximately 30% of patients with AML. Targeting FLT3 receptor tyrosine kinase has shown encouraging results in treating FLT3-mutated AML. Responses, however, are not sustained and acquired resistance has been a clinical challenge. Treatment options to overcome resistance are currently the focus of research. We report here the preclinical evaluation of AMG 925, a potent, selective, and bioavailable FLT3/cyclin-dependent kinase 4 (CDK4) dual kinase inhibitor. AMG 925 inhibited AML xenograft tumor growth by 96% to 99% without significant body weight loss. The antitumor activity of AMG 925 correlated with the inhibition of STAT5 and RB phosphorylation, the pharmacodynamic markers for inhibition of FLT3 and CDK4, respectively. In addition, AMG 925 was also found to inhibit FLT3 mutants (e.g., D835Y) that are resistant to the current FLT3 inhibitors (e.g., AC220 and sorafenib). CDK4 is a cyclin D–dependent kinase that plays an essential central role in regulating cell proliferation in response to external growth signals. A critical role of the CDK4–RB pathway in cancer development has been well established. CDK4-specific inhibitors are being developed for treating RB-positive cancer. AMG 925, which combines inhibition of two kinases essential for proliferation and survival of FLT3-mutated AML cells, may improve and prolong clinical responses. Mol Cancer Ther; 13(4); 880–9. ©2014 AACR.

Glutamine serves as an important source of energy and building blocks for many tumor cells. The first step in glutamine utilization is its conversion to glutamate by the mitochondrial enzyme glutaminase. CB-839 is a potent, selective, and orally bioavailable inhibitor of both splice variants of glutaminase (KGA and GAC). CB-839 had antiproliferative activity in a triple-negative breast cancer (TNBC) cell line, HCC-1806, that was associated with a marked decrease in glutamine consumption, glutamate production, oxygen consumption, and the steady-state levels of glutathione and several tricarboxylic acid cycle intermediates. In contrast, no antiproliferative activity was observed in an estrogen receptor–positive cell line, T47D, and only modest effects on glutamine consumption and downstream metabolites were observed. Across a panel of breast cancer cell lines, GAC protein expression and glutaminase activity were elevated in the majority of TNBC cell lines relative to receptor positive cells. Furthermore, the TNBC subtype displayed the greatest sensitivity to CB-839 treatment and this sensitivity was correlated with (i) dependence on extracellular glutamine for growth, (ii) intracellular glutamate and glutamine levels, and (iii) GAC (but not KGA) expression, a potential biomarker for sensitivity. CB-839 displayed significant antitumor activity in two xenograft models: as a single agent in a patient-derived TNBC model and in a basal like HER2+ cell line model, JIMT-1, both as a single agent and in combination with paclitaxel. Together, these data provide a strong rationale for the clinical investigation of CB-839 as a targeted therapeutic in patients with TNBC and other glutamine-dependent tumors. Mol Cancer Ther; 13(4); 890–901. ©2014 AACR.

Despite significant advances in biology and medicine, the incidence and mortality due to breast cancer worldwide is still unacceptably high. Thus, there is an urgent need to discover new molecular targets. In this article, we show evidence for a novel target in human breast cancer, the tetraspan protein epithelial membrane protein-2 (EMP2). Using tissue tumor arrays, protein expression of EMP2 was measured and found to be minimal in normal mammary tissue, but it was upregulated in 63% of invasive breast cancer tumors and in 73% of triple-negative tumors tested. To test the hypothesis that EMP2 may be a suitable target for therapy, we constructed a fully human immunoglobulin G1 (IgG1) antibody specific for a conserved domain of human and murine EMP2. Treatment of breast cancer cells with the anti-EMP2 IgG1 significantly inhibited EMP2-mediated signaling, blocked FAK/Src signaling, inhibited invasion, and promoted apoptosis in vitro. In both human xenograft and syngeneic metastatic tumor monotherapy models, anti-EMP2 IgG1 retarded tumor growth without detectable systemic toxicity. This antitumor effect was, in part, attributable to a potent antibody-dependent cell-mediated cytotoxicity response as well as direct cytotoxicity induced by the monoclonal antibody. Together, these results identify EMP2 as a novel therapeutic target for invasive breast cancer. Mol Cancer Ther; 13(4); 902–15. ©2014 AACR.

Accumulating evidence indicates that serum and tissue levels of lectin, galactoside-binding soluble 3 binding protein (LGALS3BP), a secreted glycoprotein, are elevated in human cancers. Recently, we have identified LGALS3BP as a factor capable of stimulating angiogenesis of microvascular endothelial cells in vitro as well as in vivo. However, the potential therapeutic implications of LGALS3BP function blockade have not been explored yet. Here, we tested the ability of an anti-LGALS3BP mouse monoclonal antibody, SP-2, to antagonize LGALS3BP-induced angiogenesis and tumor growth. The antibody was found to inhibit endothelial cell tubulogenesis induced by either conditioned medium of breast cancer and melanoma cells or human recombinant LGALS3BP. In addition, SP-2 inhibited phosphorylation of FAK and its recruitment to membrane sites as well as AKT and ERK phosphorylation promoted by LGALS3BP. When used in vivo, the antibody restrained LGALS3BP-stimulated angiogenesis and growth of tumor xenografts. Furthermore, the combination of SP-2 and low-dose bevacizumab was more effective than either agent alone. Taken together, these results lead to consideration of SP-2 as a promising candidate for LGALS3BP-targeted therapy. Mol Cancer Ther; 13(4); 916–25. ©2014 AACR.

Fighting metastasis is a major challenge in cancer therapy and novel therapeutic targets and drugs are highly appreciated. Resistance of invasive cells to anoikis, a particular type of apoptosis induced by loss of cell–matrix contact, is a major prerequisite for their metastatic spread. Inducing anoikis in metastatic cancer cells is therefore a promising therapeutic approach. The vacuolar-ATPase (V-ATPase), a proton pump located at the membrane of acidic organelles, has recently come to focus as an antimetastatic cancer target. As V-ATPase inhibitors have shown to prevent invasion of tumor cells and are able to induce apoptosis, we proposed that V-ATPase inhibition induces anoikis-related pathways in invasive cancer cells. We used the V-ATPase inhibitor archazolid to investigate the mechanism of anoikis induction in various metastatic cancer cells (T24, MDA-MB-231, 4T1, 5637) in vitro. Anoikis induction by archazolid was characterized by decreased c-FLIP expression and caspase-8 activation as well as reduction of active integrin-β1 and an early increase of the proapoptotic protein BIM. However, we observed that archazolid also induces mechanisms opposing anoikis such as degradation of BIM mediated by extracellular signal-regulated kinase (ERK), Akt and Src kinases at later time points and induction of reactive oxygen species. Still, intravenous injection of archazolid-treated 4T1-Luc2 mouse breast cancer cells resulted in reduced metastasis in mouse lungs. Thus, V-ATPase inhibition is not only an interesting option to reduce cancer metastasis, but also to better understand anoikis resistance and to find choices to fight against it. Mol Cancer Ther; 13(4); 926–37. ©2014 AACR.

Protein phosphatase 2A (PP2A) is a tumor suppressor that regulates many signaling pathways crucial for cell transformation. In fact, decreased activity of PP2A has been reported as a recurrent alteration in many types of cancer. Here, we show that PP2A is frequently inactivated in patients with colorectal cancer, indicating that PP2A represents a potential therapeutic target for this disease. We identified overexpression of the endogenous PP2A inhibitors SET and CIP2A, and downregulation of regulatory PP2A such as PPP2R2A and PPP2R5E, as contributing mechanisms to PP2A inhibition in colorectal cancer. Moreover, we observed that its restoration using FTY720 impairs proliferation and clonogenic potential of colorectal cancer cells, induces caspase-dependent apoptosis, and affects AKT and extracellular signal-regulated kinase-1/2 activation status. Interestingly, treatment with FTY720 showed an additive effect with 5-fluorouracil, SN-38, and oxaliplatin, drugs used in standard chemotherapy in patients with colorectal cancer. These results suggest that PP2A activity is commonly decreased in colorectal cancer cells, and that the use of PP2A activators, such as FTY720, might represent a potential novel therapeutic strategy in colorectal cancer. Mol Cancer Ther; 13(4); 938–47. ©2014 AACR.

Glioblastoma is the most common malignant brain tumor in adults and characterized by a poor prognosis. Glioma cells expressing O6-methylguanine DNA methyltransferase (MGMT) exhibit a higher level of resistance toward alkylating agents, including the standard of care chemotherapeutic agent temozolomide. Here, we demonstrate that long-term glioma cell lines (LTL) as well as glioma-initiating cell lines (GIC) express receptors for the immune modulatory cytokine IFN-β and respond to IFN-β with induction of STAT-3 phosphorylation. Exposure to IFN-β induces a minor loss of viability, but strongly interferes with sphere formation in GIC cultures. Furthermore, IFN-β sensitizes LTL and GIC to temozolomide and irradiation. RNA interference confirmed that both IFN-β receptors, R1 and R2, are required for IFN-β–mediated sensitization, but that sensitization is independent of MGMT or TP53. Most GIC lines are highly temozolomide-resistant, mediated by MGMT expression, but nevertheless susceptible to IFN-β sensitization. Gene expression profiling following IFN-β treatment revealed strong upregulation of IFN-β–associated genes, including a proapoptotic gene cluster, but did not alter stemness-associated expression signatures. Caspase activity and inhibition studies revealed the proapoptotic genes to mediate glioma cell sensitization to exogenous death ligands by IFN-β, but not to temozolomide or irradiation, indicating distinct pathways of death sensitization mediated by IFN-β. Thus, IFN-β is a potential adjunct to glioblastoma treatment that may target the GIC population. IFN-β operates independently of MGMT-mediated resistance, classical apoptosis-regulatory networks, and stemness-associated gene clusters. Mol Cancer Ther; 13(4); 948–61. ©2014 AACR.

Bone marrow mesenchymal stromal cells (BMMSC) have antitumorigenic activities. Here, we hypothesized that circulating BMMSC are incorporated into tumors and protect tumor cells from therapy-induced apoptosis. Adherent cells harvested from murine bone marrow and expressing phenotypic and functional characteristics of BMMSC were tested for their antitumor activity against murine 4T1 mammary adenocarcinoma and LL/2 Lewis lung carcinoma cells. BMMSC but not NIH3T3 or murine skin fibroblasts stimulated the expansion of 4T1 cells in three-dimensional (3D) cocultures, and conditioned medium (CM) from these cells increased the viability of 4T1 and LL/2 cells in two-dimensional (2D) cultures. 4T1 cells exposed to BMMSC CM exhibited a 2-fold reduction in apoptosis under low serum concentrations (0.5% to 1%). Furthermore, exposure of 4T1 and LL/2 cells to BMMSC CM increased their viability in the presence of paclitaxel or doxorubicin at therapeutic concentrations. This effect was accompanied by reductions in caspase-3 activity and Annexin V expression. When coinjected with 4T1 cells in the mammary fat pad of mice subsequently treated with doxorubicin, BMMSC (and not fibroblasts) also inhibited drug-induced apoptosis in tumor cells by 44%. We demonstrated that BMMSC were attracted by 4T1 and LL/2 cells but not by NIH3T3 cells in vitro and that when injected intravenously in 4T1 tumor-bearing mice, these cells (and not NIH3T3) were specifically detected in tumors within 12 to 18 days in which they preferentially localized at the invasive front. Overall, our data identify BMMSC as an important mediator of tumor cell survival and treatment resistance in primary tumors. Mol Cancer Ther; 13(4); 962–75. ©2014 AACR.

Studies have shown the prognostic significance of disseminated tumor cells (DTC) in bone marrow of patients with colorectal cancer. However, the molecular characteristics of DTCs, including their miRNA expression profiles, remain mostly unknown. In this study, we analyzed the miRNA expression of DTCs in bone marrow. EpCAM+ bone marrow cells were collected using immunomagnetic beads after exclusion of CD14+ and CD45+ cells, then subjected to miRNA microarray analysis. Cluster analysis (7 colorectal cancer patients with liver metastasis and 12 colorectal cancer patients without liver metastasis) indicated that miR-340 and miR-542-3p expressions were significantly decreased in EpCAM+ bone marrow cells of patients with liver metastasis (P = 0.019 and 0.037, respectively). We demonstrated that pre-miR-340 administration inhibited growth of colon cancer cells and suppressed c-Met expression in vitro. In clinical samples of colorectal cancer, miR-340 was expressed at significantly lower levels in tumor tissues compared with normal mucosa. Survival analysis in 136 patients with colorectal cancer indicated that low miR-340 expression was correlated with shorter 5-year disease-free survival (P = 0.023) and poor 5-year overall survival (P = 0.046). It was of note that the colorectal cancer group with low miR-340 and high c-Met expression had the worst prognosis. We further demonstrated that systemic pre-miR-340 administration suppressed growth of pre-established HCT116 tumors in animal therapeutic models. These findings indicate that miR-340 may be useful as a novel prognostic factor and as a therapeutic tool against colorectal cancer. Our data suggest that miR-340 in bone marrow may play an important role in regulating the metastasis cascade of colorectal cancer. Mol Cancer Ther; 13(4); 976–85. ©2014 AACR.

The heterogeneous delivery of drugs in tumors is an established process contributing to variability in treatment outcome. Despite the general acceptance of variable delivery, the study of the underlying causes is challenging, given the complex tumor microenvironment including intra- and intertumor heterogeneity. The difficulty in studying this distribution is even more significant for small-molecule drugs where radiolabeled compounds or mass spectrometry detection lack the spatial and temporal resolution required to quantify the kinetics of drug distribution in vivo. In this work, we take advantage of the synthesis of fluorescent drug conjugates that retain their target binding but are designed with different physiochemical and thus pharmacokinetic properties. Using these probes, we followed the drug distribution in cell culture and tumor xenografts with temporal resolution of seconds and subcellular spatial resolution. These measurements, including in vivo permeability of small-molecule drugs, can be used directly in predictive pharmacokinetic models for the design of therapeutics and companion imaging agents as demonstrated by a finite element model. Mol Cancer Ther; 13(4); 986–95. ©2014 AACR.

Malignant gliomas are associated with high mortality due to infiltrative growth, recurrence, and malignant progression. Even with the most efficient therapy combinations, median survival of the glioblastoma multiforme (grade 4) patients is less than 15 months. Therefore, new treatment approaches are urgently needed. We describe here identification of a novel homing peptide that recognizes tumor vessels and invasive tumor satellites in glioblastomas. We demonstrate successful brain tumor imaging using radiolabeled peptide in whole-body SPECT/CT imaging. Peptide-targeted delivery of chemotherapeutics prolonged the lifespan of mice bearing invasive brain tumors and significantly reduced the number of tumor satellites compared with the free drug. Moreover, we identified mammary-derived growth inhibitor (MDGI/H-FABP/FABP3) as the interacting partner for our peptide on brain tumor tissue. MDGI was expressed in human brain tumor specimens in a grade-dependent manner and its expression positively correlated with the histologic grade of the tumor, suggesting MDGI as a novel marker for malignant gliomas. Mol Cancer Ther; 13(4); 996–1007. ©2014 AACR.

The effect of activation and overexpression of the nuclear receptor PPAR-β/ in human MDA-MB-231 (estrogen receptor–negative; ER) and MCF7 (estrogen-receptor-positive; ER+) breast cancer cell lines was examined. Target gene induction by ligand activation of PPAR-β/ was increased by overexpression of PPAR-β/ compared with controls. Overexpression of PPAR-β/ caused a decrease in cell proliferation in MCF7 and MDA-MB-231 cells compared with controls, whereas ligand activation of PPAR-β/ further inhibited proliferation of MCF7 but not MDA-MB-231 cells. Overexpression and/or ligand activation of PPAR-β/ in MDA-MB-231 or MCF7 cells had no effect on experimental apoptosis. Decreased clonogenicity was observed in both MDA-MB-231 and MCF7 overexpressing PPAR-β/ in response to ligand activation of PPAR-β/ as compared with controls. Ectopic xenografts developed from MDA-MB-231 and MCF7 cells overexpressing PPAR-β/ were significantly smaller, and ligand activation of PPAR-β/ caused an even greater reduction in tumor volume as compared with controls. Interestingly, the decrease in MDA-MB-231 tumor size after overexpressing PPAR-β/ and ligand activation of PPAR-β/ correlated with increased necrosis. These data show that ligand activation and/or overexpression of PPAR-β/ in two human breast cancer cell lines inhibits relative breast cancer tumorigenicity and provide further support for the development of ligands for PPAR-β/ to specifically inhibit breast carcinogenesis. These new cell-based models will be invaluable tools for delineating the role of PPAR-β/ in breast cancer and evaluating the effects of PPAR-β/ agonists. Mol Cancer Ther; 13(4); 1008–17. ©2014 AACR.