Role of peroxisome proliferator-activated receptor-gamma and its coactivator DRIP205 in cellular responses to CDDO (RTA-401) in acute myelogenous leukemia

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a member of the nuclear receptor (NR) family of transcription factors with important regulatory roles in cellular growth, differentiation, and apoptosis. Using proteomic analysis, we showed expression of PPARgamma protein in a series of 260 newly diagnosed primary acute myelogenous leukemia (AML) samples. Forced expression of PPARgamma enhanced the sensitivity of myeloid leukemic cells to apoptosis induced by PPARgamma agonists 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) and 15-deoxy-(12,14)-15DPGJ(2), through preferential cleavage of caspase-8. No effects on cell cycle distribution or differentiation were noted, despite prominent induction of p21 in PPARgamma-transfected cells. In turn, antagonizing PPARgamma function by small interfering RNA or pharmacologic PPARgamma inhibitor significantly diminished apoptosis induction by CDDO. Overexpression of coactivator protein DRIP205 resulted in enhanced differentiation induction by CDDO in AML cells through PPARgamma activation. Studies with DRIP205 deletion constructs showed that the NR boxes of DRIP205 are not required for this coactivation. In a phase I clinical trial of CDDO (RTA-401) in leukemia, CDDO induced an increase in PPARgamma mRNA expression in six of nine patient samples; of those, induction of differentiation was documented in four patients and that of p21 in three patients, all expressing DRIP205 protein. In summary, these findings suggest that cellular levels of PPARgamma regulate induction of apoptosis via caspase-8 activation, whereas the coactivator DRIP205 is a determinant of induction of differentiation, in response to PPARgamma agonists in leukemic cells.

Methyl 2-cyano-3,12-dioxooleana-1,9-dien-28-oate decreases specificity protein transcription factors and inhibits pancreatic tumor growth: role of microRNA-27a

The anticancer agent 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) and its methyl ester (CDDO-Me) typically induce a broad spectrum of growth-inhibitory, proapoptotic, and antiangiogenic responses. Treatment of Panc1, Panc28, and L3.6pL pancreatic cancer cells with low micromolar concentrations of CDDO or CDDO-Me resulted in growth inhibition, induction of apoptosis, and down-regulation of cyclin D1, survivin, vascular endothelial growth factor (VEGF), and its receptor (VEGFR2). RNA interference studies indicate that these repressed genes are regulated by specificity protein (Sp) transcription factors Sp1, Sp3, and Sp4, and Western blot analysis of lysates from pancreatic cancer cells treated with CDDO and CDDO-Me shows for the first time that both compounds decreased the expression of Sp1, Sp3, and Sp4. Moreover, CDDO-Me (7.5 mg/kg/day) also inhibited pancreatic human L3.6pL tumor growth and down-regulated Sp1, Sp3, and Sp4 in tumors using an orthotopic pancreatic cancer model. CDDO-Me also induced reactive oxygen species (ROS) and decreased mitochondrial membrane potential (MMP) in Panc1 and L3.6pL cells, and cotreatment with antioxidants (glutathione and dithiothreitol) blocked the formation of ROS, reversed the loss of MMP, and inhibited down-regulation of Sp1, Sp3, and Sp4. Repression of Sp and Sp-dependent genes by CDDO-Me was due to the down-regulation of microRNA-27a and induction of zinc finger and BTB domain containing 10 (ZBTB10), an Sp repressor, and these responses were also reversed by antioxidants. Thus, the anticancer activity of CDDO-Me is due, in part, to activation of ROS, which in turn targets the microRNA-27a:ZBTB10-Sp transcription factor axis. This results in decreased expression of Sp-regulated genes, growth inhibition, induction of apoptosis, and antiangiogenic responses.

Activation of FOXO3a is sufficient to reverse mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor chemoresistance in human cancer

Drug resistance is a central challenge of cancer therapy that ultimately leads to treatment failure. In this study, we characterized a mechanism of drug resistance that arises to AZD6244, an established mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) 1/2 inhibitor currently being evaluated in cancer clinical trials. AZD6244 enhanced the expression of transcription factor FOXO3a, which suppressed cancer cell proliferation. In AZD6244-resistant cancer cells, we observed the impaired nuclear localization of FOXO3a, reduced FOXO3a-mediated transcriptional activity, and decreased the expression of FOXO3a target gene Bim after cell treatment with AZD6244. Resistant cells could be sensitized by phosphoinositide 3-kinase (PI3K)/AKT inhibitors, which are known to enhance FOXO3a nuclear translocation. Our findings define FOXO3a as candidate marker to predict the clinical efficacy of AZD6244. Furthermore, they suggest a mechanism of resistance to MEK inhibitors that may arise in the clinic yet can be overcome by cotreatment with PI3K/AKT inhibitors.

1,25-dihydroxyvitamin D3 enhances the apoptotic activity of MDM2 antagonist nutlin-3a in acute myeloid leukemia cells expressing wild-type p53

The tumor suppressor p53 is often referred to as "the guardian of the genome" because of its central role in the cellular response to oncogenic stress and prevention of tumor development. Mutations of p53 in acute myeloid leukemia (AML) are rare but resistance to chemotherapy has been reported because of the deregulation of the p53 signaling and differentiation pathways. It is known that the interaction of the vitamin D metabolite 1,25-dihydroxyvitamin D(3) (1,25D) with its functional vitamin D receptor leads to differentiation, G(1) arrest, and increased cell survival in p53-null AML cells. However, there are no reports on the effect of 1,25D in leukemia cells expressing wild-type p53. Here, we examine vitamin D signaling in AML cells MOLM-13 and OCI-AML3 expressing wild-type p53 in the presence and absence of the MDM2 antagonist nutlin-3. We find that 1,25D alone induces monocytic differentiation in these cell lines similar to that seen in p53-null AML cells, suggesting that the presence of wild-type p53 is compatible with activation of vitamin D signaling. Combination of nutlin-3a with 1,25D accelerated programmed cell death, likely because of enhanced nutlin-induced upregulation of the proapoptotic PIG-6 protein and downregulation of antiapoptotic BCL-2, MDMX, human kinase suppressor of Ras 2, and phosphorylated extracellular signal-regulated kinase 2.

Abstract 2314: Epithelial-mesenchymal transition derived cells exhibit multi-lineage differentiation potential similar to mesenchymal stem cells

The epithelial-to-mesenchymal transition (EMT) is an embryonic process that becomes latent in most normal adult tissues. Recently, we have shown that induction of EMT endows stem cell traits to breast epithelial cells. Mesenchymal stem cells (MSC) have the capacity to self-renew and differentiate into multiple tissue lineages. We hypothesized that the activation of EMT by ectopic expression of Twist, Snail or TGF-β in immortalized human mammary epithelial cells (HMEC) will result in the generation of cells with a phenotype and functionality similar to MSC. We found that the EMT-derived cells not only showed similar morphology but also displayed the typical MSC phenotype i.e. CD44+, CD24− and CD45−. Alternatively, MSC expressed EMT inducing genes such as Twist, Snail and FOXC2. Interestingly, CD140b (PDGFR-β), a marker for naive MSC, was exclusively expressed in EMT-derived cells compared to their epithelial counterparts. Moreover, functional analysis revealed that EMT-derived but not the control cells differentiate into Alizarin Red S-positive mature osteoblasts, Oil Red O-positive adipocytes and Alcian Blue-positive chondrocytes similar to MSC. We also observed that EMT-derived but not control cells invade and migrate towards MDA-MB-231 tumor cells in-vitro similar to MSC, displaying the characteristic tropism of MSC for tumor cells as previously reported by us. In-vivo wound homing assays in nude mice revealed that the EMT-derived cells home to wound sites similar to MSC. In conclusion, we demonstrated that the EMT-derived cells are similar to MSC in gene-expression, multi-lineage differentiation, migration towards tumor cells and their ability to home to wounds. These results also suggest that EMT-derived MSC are active participants in cancer growth and invasion.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2314.

Abstract 560: Mesenchymal stem cells promote mammosphere formation in normal and malignant breast cells

Purpose: Normal and malignant breast tissue contains a rare population of cells with the capacity to self-renew, referred to as stem cells, or tumor initiating cells (TIC) in the case of tumors. These cells can be enriched by growth as “mammospheres” in three-dimensional cultures. We tested the hypothesis that mesenchymal stem cells (MSC), which are known to support tumor growth and metastasis, increase mammosphere formation.

Materials and Methods: Normal human mammary epithelial cells (HMEC), and breast cancer cells (MCF-7, SUM149 and IBC3) were grown as mammospheres, plated at low density in serum-free growth factor supplemented suspension cultures. MSC were added as an increasing percentage of total cells plated (0, 2, 5 and 10%). MSC-conditioned media was generated by growing MSC as spheroids for 5 days.

Results: MSC integrated into mammospheres, resulting in a dose-dependent increase in the number of mammospheres formed. Normal mammary epithelial cells formed 1.6 to 2.4 to 2.7-fold (p< 0.001) more mammospheres in the presence of 2, 5 and 10% MSC. Similarly, the number of MCF-7 derived mammospheres increased 5.9 to 8.5 to14.8-fold (p = ≤ 0.001) in the presence of 2, 5 and 10% MSC. A similar dose-dependent increase in sphere formation was seen for SUM149 cells and inflammatory breast cancer cells in short-term culture derived from pleural effusions. This effect was found to be mediated by secreted factors as MSC-conditioned media also increased sphere formation. SUM149 cells formed 6.4 to 14.2 to 13.7-fold more mammospheres when incubated for 5 days in 5, 25 and 50% MSC conditioned-media (p <0.0001). HMEC derived mammospheres had higher levels of expression of N-cadherin and RhoC and lower levels of expression of E-cadherin and Notch when formed in the presence of MSC conditioned media.

Conclusions: Mesenchymal stem cells increase mammosphere formation of normal breast epithelial cells, established cancer cell lines (MCF-7 and SUM149) and short term primary breast cancer cells (IBC3). This effect is mediated by MSC secreted factors and results in cadherin switching, which may promote breast cancer progression and resistance to therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 560.

Abstract 4536: Simultaneous blockade of MEK and mTOR kinase signaling synergizes pro-apoptotic effects in AML cells, which is further potential by interfering with dimerization of BH3 domains

Simultaneous activation of PI3K/Akt/mTOR and Raf/MEK/ERK signaling pathways is common in acute myeloid leukemia (AML) and is associated with worse prognosis(1). Several small molecule inhibitors targeting mTOR or MEK/ERK signaling are being evaluated in clinical trials in AML, including allosteric mTOR inhibitors (CCI-779, RAD001) and MEK inhibitors (CI-1040, AZD6244 [ARRY-142886]), and demonstrated encouraging pre-clinical results(2-4). However, the efficacy of these agents as single agents is variable in AML(3, 5, 6). The predominant effects of these inhibitors are cytostatic rather than cytotoxic in AML. AZD8055 is a novel mTOR kinase inhibitor, acting against both mTORC1 and mTORC2, and is currently in Phase 1 clinical trials in solid tumors.

In the present study, we investigated the anti-leukemia efficacy of the AZD8055, alone or in combination with AZD6244 in human leukemic cells and in primary AML samples. AZD8055 potently suppressed p-S6K and p-4E-BP1 in AML cells (70-85% inhibition), significantly blocked p-AKT(473) in OCI-AML3 and MOLM13 cells, and inhibited both, p-AKT(473) and p-AKT(308) in PTEN-mutant U937 cells. This resulted in profound inhibition of cell growth at lower IC50s (40-147nM) in all these AML cells. However, AZD8055 did not induce apoptosis in the cells even up to 10μM concentrations. The combination of AZD8055 with AZD6244 triggered synergistic pro-apoptotic responses in U937 (CI = 0.22 ± 0.04) and MOLM13 (CI = 0.66 ± 0.06) cells, but not in OCI/AML3 and KG-1 cells. MEK inhibition resulted in partial blockade of S6K phosphorylation in OCI/AML3 and KG-1 cells, suggesting that S6K activity can also be regulated by MAPK pathways in some AML cell lines. Further analysis demonstrated that sensitive cells (U937 and MOLM13) express lower basal levels of Bcl-2 protein compared to resistant cell lines (OCI/AML3 and KG-1), and showed pronounced upregulation of pro-apoptotic Bim after AZD6244 and AZD8055/AZD6244 combination treatment. Furthermore, interference with dimerization of Bcl2 family proteins by BH3 mimetic ABT-737 dramatically enhanced the pro-apoptotic responses of the combination in resistant cells even when all three agents are used at sub-micromolar concentrations. Depleting Bim levels by siRNA rescued sensitive cells from AZD8055/AZD6244-induced apoptosis, indicating a key role of downstream Bim in cytotoxicity of these agents. In primary AML samples AZD8055/AZD6244 induced apoptosis in an additive fashion, while simultaneous use of ABT-737 significantly increased the pro-apoptotic effects.

In summary, our results indicate that parallel blockade of PI3K/MAPK signaling and manipulation of the mitochondrial Bcl-2 rheostat potently enhances apoptosis induction in AML cells and may provide a viable therapeutic strategy for resistant/refractory AML patients.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4536.

Phase I/II study of combination therapy with sorafenib, idarubicin, and cytarabine in younger patients with acute myeloid leukemia

PURPOSE To determine the efficacy and toxicity of the combination of sorafenib, cytarabine, and idarubicin in patients with acute myeloid leukemia (AML) younger than age 65 years. PATIENTS AND METHODS In the phase I part of the study, 10 patients with relapsed AML were treated with escalating doses of sorafenib with chemotherapy to establish the feasibility of the combination. We then treated 51 patients (median age, 53 years; range, 18 to 65 years) who had previously untreated AML with cytarabine at 1.5 g/m(2) by continuous intravenous (IV) infusion daily for 4 days (3 days if > 60 years of age), idarubicin at 12 mg/m(2) IV daily for 3 days, and sorafenib at 400 mg orally twice daily for 7 days. RESULTS Overall, 38 (75%) patients have achieved a complete remission (CR), including 14 (93%) of 15 patients with mutated FMS-like tyrosine kinase-3 (FLT3; the 15th patient had complete remission with incomplete platelet recovery [CRp]) and 24 (66%) of 36 patients with FLT3 wild-type (WT) disease (three additional FLT3-WT patients had CRp). FLT3-mutated patients were more likely to achieve a CR than FLT3-WT patients (P = .033). With a median follow-up of 54 weeks (range, 8 to 87 weeks), the probability of survival at 1 year is 74%. Among the FLT3-mutated patients, 10 have relapsed and five remain in CR with a median follow-up of 62 weeks (range, 10 to 76 weeks). Plasma inhibitory assay demonstrated an on-target effect on FLT3 kinase activity. CONCLUSION Sorafenib can be safely combined with chemotherapy, produces a high CR rate in FLT3-mutated patients, and inhibits FLT3 signaling.

Mesenchymal Stem Cells Overexpressing IFN-β Inhibit Breast Cancer Growth and Metastases through Stat3 Signaling in a Syngeneic Tumor Model

We previously demonstrated that mesenchymal stem/stromal cells (MSC) are recruited to tumors and that IFN-β produced by MSC inhibited tumor growth in xenograft models. Because of a deficient immune system, murine xenograft models cannot fully recapitulate tumor and immune cell interactions during progression. Therefore we investigated the capacity of MSC to migrate to and engraft into primary breast tumor sites and subsequently explore mechanisms of tumor inhibition by MSC-delivered IFN-β in a syngeneic, immunocompetent murine model. Herein we report that 1) systemically administrated MSC migrate to established 4 T1 breast cancer sites and localize among the tumor-stroma border and throughout the tumor mass; 2) high levels of IFN-β secreted by MSC are detectable in the tumor microenvironment but not in circulation; 3) intratumorally produced IFN-β inactivates constitutive phosphorylation of signal transducer activator transcription factor 3 (Stat3), Src, and Akt and down-regulates cMyc and MMP2 expression in 4 T1 cells, and 4) in mice with established breast cancer IFN-β expressing MSC administered systemically resulted in inhibition of primary cancer growth and in dramatic reduction of pulmonary and hepatic metastases. 5) MSC-IFN-β treated, but not control mice, maintained normal levels of splenic mature dendritic (DC), CD8+ T cells and CD4+/Foxp3+ regulatory T-cells (Treg). Our findings suggest that MSC are capable of migrating to tumor sites in an immunocompetent environment, that IFN-β produced by MSC suppresses breast cancer growth through inhibition of Stat3 signaling, and dramatically reduces pulmonary and hepatic metastases.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s12307-010-0041-8) contains supplementary material, which is available to authorized users.

Blockade of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase and murine double minute synergistically induces Apoptosis in acute myeloid leukemia via BH3-only proteins Puma and Bim

Molecular aberrations of the Ras/Raf/mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK and/or Murine double minute (MDM2)/p53 signaling pathways have been reported in 80% and 50% of primary acute myeloid leukemia (AML) samples and confer poor outcome. In this study, antileukemic effects of combined MEK inhibition by AZD6244 and nongenotoxic p53 activation by MDM2 antagonist Nutlin-3a were investigated. Simultaneous blockade of MEK and MDM2 signaling by AZD6244 and Nutlin-3a triggered synergistic proapoptotic responses in AML cell lines [combination index (CI) = 0.06 +/- 0.03 and 0.43 +/- 0.03 in OCI/AML3 and MOLM13 cells, respectively] and in primary AML cells (CI = 0.52 +/- 0.01). Mechanistically, the combination upregulated levels of BH3-only proteins Puma and Bim, in part via transcriptional upregulation of the FOXO3a transcription factor. Suppression of Puma and Bim by short interfering RNA rescued OCI/AML3 cells from AZD/Nutlin-induced apoptosis. These results strongly indicate the therapeutic potential of combined MEK/MDM2 blockade in AML and implicate Puma and Bim as major regulators of AML cell survival.

Platelet-derived growth factor BB mediates the tropism of human mesenchymal stem cells for malignant gliomas

OBJECTIVE

Bone marrow-derived human mesenchymal stem cells (hMSCs) are capable of localizing to gliomas after systemic delivery and can be used in glioma therapy. However, the mechanism underlying the tropism of hMSCs for gliomas remains unclear. In vitro studies suggest that platelet-derived growth factor BB (PDGF-BB) may mediate this tropism. However, a causal role of PDGF-BB has not been demonstrated in vivo. Therefore, we tested the hypothesis that PDGF-BB mediates the attraction of hMSCs to gliomas in vitro and in vivo.

METHODS

U87 or LN229 glioma cells were transfected with plasmids encoding human PDGF-B. Stable transfected clones that secreted large amounts of PDFG-BB and clones that produced low levels of PDGF were chosen. In vitro migration of hMSCs toward PDGF-B or conditioned media from high- and low-secreting PDGF-B tumor cells was assessed using Matrigel invasion assays. For in vivo localization studies, hMSCs were tracked by bioluminescence imaging (BLI) after transduction with an adenovirus containing luciferase cDNA. In other studies, hMSCs were labeled with green fluorescent protein (gfp) and analyzed for intratumoral localization by immunohistochemistry.

RESULTS

In vitro invasion assays showed that significantly more hMSCs migrated toward glioma cells engineered to secrete high levels of PDGF-BB compared with low-secreting gliomas. Anti-PDGF-BB-neutralizing antibody abrogated this increase in migration. Pretreatment of hMSCs with inhibitory antibodies against PDGF receptor-beta also reduced hMSC migration. To demonstrate that PDGF-BB mediates the localization of hMSCs in vivo, hMSCs-Ad-Luc were injected into the carotid artery of mice harboring orthotopic 7-day-old U87-PDGF-BB-high secreting or U87-PDGF-BB-low secreting xenografts and analyzed by BLI. Statistically significant increases in hMSCs were seen within PDGF-BB-high xenografts compared with PDGF-BB-low xenografts. To control for PDGF-BB-induced differences in tumor size and vascularity, gfp-labeled hMSCs were injected into the carotid arteries of animals harboring 4-day old PDGF-BB-high secreting xenografts or 7-day old PDGF-BB-low secreting xenografts. At these times tumors had similar size and vessel density. Statistically significant more hMSCs localized to PDGF-BB-high secreting xenografts compared with PDGF-BB-low secreting xenografts. Pretreatment of hMSCs with anti-PDGFR-beta-inhibitory antibodies decreased the localization of hMSCs in this intracranial model.

CONCLUSION

PDGF-BB increases the attraction of hMSCs for gliomas in vitro and in vivo, and this tropism is mediated via PDGF-beta receptors on hMSCs. These findings can be exploited for advancing hMSC treatment.

Direct evidence of mesenchymal stem cell tropism for tumor and wounding microenvironments using in vivo bioluminescent imaging

Multipotent mesenchymal stromal/stem cells (MSC) have shown potential clinical utility. However, previous assessments of MSC behavior in recipients have relied on visual detection in host tissue following sacrifice, failing to monitor in vivo MSC dispersion in a single animal and limiting the number of variables that can be observed concurrently. In this study, we used noninvasive, in vivo bioluminescent imaging to determine conditions under which MSC selectively engraft in sites of inflammation. MSC modified to express firefly luciferase (ffLuc-MSC) were injected into healthy mice or mice bearing inflammatory insults, and MSC localization was followed with bioluminescent imaging. The inflammatory insults investigated included cutaneous needle-stick and surgical incision wounds, as well as xenogeneic and syngeneic tumors. We also compared tumor models in which MSC were i.v. or i.p. delivered. Our results demonstrate that ffLuc-expressing human MSC (hMSC) systemically delivered to nontumor-bearing animals initially reside in the lungs, then egress to the liver and spleen, and decrease in signal over time. However, hMSC in wounded mice engraft and remain detectable only at injured sites. Similarly, in syngeneic and xenogeneic breast carcinoma-bearing mice, bioluminescent detection of systemically delivered MSC revealed persistent, specific colocalization with sites of tumor development. This pattern of tropism was also observed in an ovarian tumor model in which MSC were i.p. injected. In this study, we identified conditions under which MSC tropism and selective engraftment in sites of inflammation can be monitored by bioluminescent imaging over time. Importantly, these consistent findings were independent of tumor type, immunocompetence, and route of MSC delivery.

Apoptosis in leukemias: regulation and therapeutic targeting

Nearly 25 years after the seminal publication of John Foxton Kerr that first described apoptosis, the process of regulated cell death, our understanding of this basic physiological phenomenon is far from complete [39]. From cardiovascular disease to cancer, apoptosis has assumed a central role with broad ranging therapeutic implications that depend on a complete understanding of this process, yet have also identified an incredibly complex regulatory system that is critical for development and is at the core of many diseases, challenging scientist and clinicians to step into its molecular realm and modulate its circuitry for therapeutic purposes. This chapter will review our understanding of the molecular circuitry that controls apoptosis in leukemia and the pharmacological manipulations of this pathway that may yield therapeutic benefit.

Pharmacologic inhibition of fatty acid oxidation sensitizes human leukemia cells to apoptosis induction

The traditional view is that cancer cells predominately produce ATP by glycolysis, rather than by oxidation of energy-providing substrates. Mitochondrial uncoupling--the continuing reduction of oxygen without ATP synthesis--has recently been shown in leukemia cells to circumvent the ability of oxygen to inhibit glycolysis, and may promote the metabolic preference for glycolysis by shifting from pyruvate oxidation to fatty acid oxidation (FAO). Here we have demonstrated that pharmacologic inhibition of FAO with etomoxir or ranolazine inhibited proliferation and sensitized human leukemia cells--cultured alone or on bone marrow stromal cells--to apoptosis induction by ABT-737, a molecule that releases proapoptotic Bcl-2 proteins such as Bak from antiapoptotic family members. Likewise, treatment with the fatty acid synthase/lipolysis inhibitor orlistat also sensitized leukemia cells to ABT-737, which supports the notion that fatty acids promote cell survival. Mechanistically, we generated evidence suggesting that FAO regulates the activity of Bak-dependent mitochondrial permeability transition. Importantly, etomoxir decreased the number of quiescent leukemia progenitor cells in approximately 50% of primary human acute myeloid leukemia samples and, when combined with either ABT-737 or cytosine arabinoside, provided substantial therapeutic benefit in a murine model of leukemia. The results support the concept of FAO inhibitors as a therapeutic strategy in hematological malignancies.

Selective depletion of a minor subpopulation of B-chronic lymphocytic leukemia cells is followed by a delayed but progressive loss of bulk tumor cells and disease regression

Cancer precursor/progenitor cells may initiate and sustain the growth of tumors, but evidence for their existence in human disease is indirect, relying on their in vitro properties and animal models. More directly, specific elimination of these rare cells from cancer patients should produce a delayed but progressive disappearance of differentiated malignant progeny. Here, we describe selective eradication of a putative precursor population in a patient with B-cell chronic lymphocytic leukemia, followed 6 months later by a progressive loss of mature tumor cells without further treatment. This outcome supports the presence of a rare population of precursor/progenitor cells in human malignancies, and suggests benefit from their removal.

Human bone marrow-derived mesenchymal stem cells for intravascular delivery of oncolytic adenovirus Delta24-RGD to human gliomas

Delta24-RGD is an infectivity-augmented, conditionally replicative oncolytic adenovirus with significant antiglioma effects. Although intratumoral delivery of Delta24-RGD may be effective, intravascular delivery would improve successful application in humans. Due to their tumor tropic properties, we hypothesized that human mesenchymal stem cells (hMSC) could be harnessed as intravascular delivery vehicles of Delta24-RGD to human gliomas. To assess cellular events, green fluorescent protein-labeled hMSCs carrying Delta24-RGD (hMSC-Delta24) were injected into the carotid artery of mice harboring orthotopic U87MG or U251-V121 xenografts and brain sections were analyzed by immunofluorescence for green fluorescent protein and viral proteins (E1A and hexon) at increasing times. hMSC-Delta24 selectively localized to glioma xenografts and released Delta24-RGD, which subsequently infected glioma cells. To determine efficacy, mice were implanted with luciferase- labeled glioma xenografts, treated with hMSC-Delta24 or controls, and imaged weekly by bioluminescence imaging. Analysis of tumor size by bioluminescence imaging showed inhibition of glioma growth and eradication of tumors in hMSC-Delta24-treated animals compared with controls (P < 0.0001). There was an increase in median survival from 42 days in controls to 75.5 days in hMSC-Delta24-treated animals (P < 0.0001) and an increase in survival beyond 80 days from 0% to 37.5%, respectively. We conclude that intra-arterially delivered hMSC-Delta24 selectively localize to human gliomas and are capable of delivering and releasing Delta24-RGD into the tumor, resulting in improved survival and tumor eradication in subsets of mice.

Reduction of nontarget infection and systemic toxicity by targeted delivery of conditionally replicating viruses transported in mesenchymal stem cells

The fiber-modified adenoviral vector Delta-24-RGD (D24RGD) offers vast therapeutic potential. Direct injection of D24RGD has been used to successfully target ovarian tumors in mice. However, systemic toxicity, especially in the liver, profoundly limits the efficacy of direct viral vector delivery. Mesenchymal stem cells (MSC) have the ability to function as a vector for targeted gene therapy because of their preferential engraftment into solid tumors and participation in tumor stroma formation. We show that MSC-guided delivery of D24RGD is specific and efficient and reduces the overall systemic toxicity in mice to negligible levels compared with D24RGD alone. In our model, we found efficient targeted delivery of MSC-D24RGD to both breast and ovarian cell lines. Furthermore, immunohistochemical staining for adenoviral hexon protein confirmed negligible levels of systemic toxicity in mice that were administered MSC-D24RGD compared with those that were administered D24RGD. These data suggest that delivery of D24RGD through MSC not only increases the targeted delivery efficiency, but also reduces the systemic exposure of the virus, thereby reducing overall systemic toxicity to the host and ultimately enhancing its value as an anti-tumor therapeutic candidate.

[BeO-OSL detectors for dose measurements in cell cultures]

AIM

The absorbed dose is an important parameter in experiments involving irradiation of cells in vitro with unsealed radionuclides. Typically, this is estimated with a model calculation, although the results thus obtained cannot be verified. Generally used real-time measurement methods are not applicable in this setting. A new detector material with in vitro suitability is the subject of this work.

METHODS

Optically-stimulated luminescence (OSL) dosimeters based on beryllium oxide (BeO) were used for dose measurement in cell cultures exposed to unsealed radionuclides. Their qualitative properties (e. g. energy-dependent count rate sensitivity, fading, contamination by radioactive liquids) were determined and compared to the results of a Monte Carlo simulation (using AMOS software). OSL dosimeters were tested in common cell culture setups with a known geometry.

RESULTS

Dose reproducibility of the OSL dosimeters was +/-1.5%. Fading at room temperature was 0.07% per day. Dose loss (optically-stimulated deletion) under ambient lighting conditions was 0.5% per minute. The Monte Carlo simulation for the relative sensitivity at different beta energies provided corresponding results to those obtained with the OSL dosimeters. Dose profile measurements using a 6 well plate and 14 ml PP tube showed that the geometry of the cell culture vessel has a marked influence on dose distribution with 188Re.

CONCLUSION

A new dosimeter system was calibrated with beta-emitters of different energy. It turned out as suitable for measuring dose in liquids. The dose profile measurements obtained are suitably precise to be used as a check against theoretical dose calculations.

Triptolide induces cell death independent of cellular responses to imatinib in blast crisis chronic myelogenous leukemia cells including quiescent CD34+ primitive progenitor cells

The advent of Bcr-Abl tyrosine kinase inhibitors (TKI) has revolutionized the treatment of chronic myelogenous leukemia (CML). However, resistance evolves due to BCR-ABL mutations and other mechanisms. Furthermore, patients with blast crisis CML are less responsive and quiescent CML stem cells are insensitive to these inhibitors. We found that triptolide, a diterpenoid, at nanomolar concentrations, promoted equally significant death of KBM5 cells, a cell line derived from a Bcr-Abl-bearing blast crisis CML patient and KBM5STI571 cells, an imatinib-resistant KBM5 subline bearing the T315I mutation. Similarly, Ba/F3 cells harboring mutated BCR-ABL were as sensitive as Ba/F3Bcr-Abl(p210wt) cells to triptolide. Importantly, triptolide induced apoptosis in primary samples from blast crisis CML patients, who showed resistance to Bcr-Abl TKIs in vivo, with less toxicity to normal cells. Triptolide decreased X-linked inhibitor of apoptosis protein, Mcl-1, and Bcr-Abl protein levels in K562, KBM5, and KBM5STI571 cells and in cells from blast crisis CML patients. It sensitized KBM5, but not KBM5STI571, cells to imatinib. More importantly, triptolide also induced death of quiescent CD34(+) CML progenitor cells, a major problem in the therapy of CML with TKIs. Collectively, these results suggest that triptolide potently induces blast crisis CML cell death independent of the cellular responses to Bcr-Abl TKIs, suggesting that triptolide could eradicate residual quiescent CML progenitor cells in TKI-treated patients and benefit TKI-resistant blast crisis CML patients.

The (in) auspicious role of mesenchymal stromal cells in cancer: be it friend or foe

Recent progress in the research of mesenchymal stromal cells/multipotent stromal cells (MSC) has revealed numerous beneficial innate characteristics, suggesting potential value in an array of cellular therapies. MSC are easily isolated from bone marrow (BM), fat and other tissues, and are readily propagated in vitro. Transplanted/injected MSC have been shown to migrate to a variety of organs and tissues; however, sites of inflammation and pathology elicit enhanced MSC homing for tissue remodeling and repair. Tumors utilize many of the same inflammatory mediators uncovered in wound healing and likewise provide a site for preferential MSC homing. Although incorporation into the tumor microenvironment is apparent, the role of recruited MSC in the tumor microenvironment remains unclear. Some published studies have shown enhancement of tumor growth and development, perhaps through immunomodulatory and pro-angiogenic properties, while others have shown no apparent effect or have demonstrated inhibition of tumor growth and extended survival. This controversy remains at the forefront as clinical applications of MSC commence in anti-tumor therapies as well as as adjuncts to stem cell transplantation and in ameliorating graft-versus-host disease. Careful analysis of past studies and thoughtful design of future experiments will help to resolve the discrepancies in the field and lead to clinical utility of MSC in disease treatment. This review highlights the current theories of the role of MSC in tumors and explores current controversies.

Phase I/II trial of AEG35156 X-linked inhibitor of apoptosis protein antisense oligonucleotide combined with idarubicin and cytarabine in patients with relapsed or primary refractory acute myeloid leukemia

PURPOSE

X-linked inhibitor of apoptosis protein (XIAP) is an inhibitor of caspases 3 and 9 which are overexpressed in acute myeloid leukemia (AML) and may contribute to chemoresistance. We report on a phase I/II trial of the XIAP antisense oligonucleotide AEG35156 in combination with reinduction chemotherapy.

PATIENTS AND METHODS

Twenty-four patients with rapidly relapsed or refractory AML were treated with escalating doses of AEG35156 (12 to 250 mg/m(2)) as an intravenous solution over 2 hours and 32 patients were treated with the highest planned dose of 350 mg/m(2) in combination with idarubicin and high-dose cytarabine reinduction chemotherapy. Correlative studies were conducted to determine the effects of AEG35156 on levels of XIAP mRNA.

RESULTS

Knockdown of XIAP mRNA during treatment increased with the dose of the antisense. All patients who received 350 mg/m(2) of AEG35156 had higher than 30% target knockdown with a median maximal knockdown of 90% (range, 48% to 100%). The overall response rate was higher among the patients receiving the highest dose of AEG35156. In this group, 15 (47%) of 32 patients achieved complete response (CR)/CR with incomplete platelet count recovery (CRp) compared with only one (4%) of 24 receiving 12 to 250 mg/m(2) AEG35156. Among the patients receiving 350 mg/m(2) of AEG35156 in combination with chemotherapy, 10 (91%) of 11 who were refractory to a single induction chemotherapy regimen achieved CR/CRp after reinduction with AEG35156 and chemotherapy. AEG35156 was well tolerated save for two cases of peripheral neuropathy in patients receiving multiple doses of AEG35156.

CONCLUSION

At the highest dose tested, AEG35156 knocks down its target and appears very effective when combined with chemotherapy in patients with AML refractory to a single induction regimen.

Tetra-O-methyl nordihydroguaiaretic acid inhibits growth and induces death of leukemia cells independent of Cdc2 and survivin

Tetra-O-methyl nordihydroguaiaretic acid (M4N) was shown to induce G2 arrest and suppress human xenograft tumor growth by inhibiting Cdc2 and survivin. We examined the effect of M4N on leukemia and found that M4N inhibited growth and induced cell death in leukemic cell lines and blasts from AML patients. However, no significant changes in Cdc2 and survivin levels and G2 arrest were observed. Cell death and growth inhibition were dependent neither on XIAP, Bcl-2, and Bcl-X(L) levels nor on caspase-8. M4N did not promote cell differentiation in HL-60 cells. Interestingly, significant inhibition of AKT phosphorylation was observed in M4N treated OCI-AML3 cells. Collectively, our data showed that M4N inhibited cell growth and induced cell death in both leukemic cell lines and AML patient sample via a mechanism not mediated by Cdc2 and survivin inhibition and suggested that the extrinsic and the mitochondrial apoptotic pathways are not essential.