Decreased Myeloid-derived Suppressor Cells Accumulation Research Articles

5-Fluorouracil Suppresses Colon Tumor through Activating the p53-Fas Pathway to Sensitize Myeloid-Derived Suppressor Cells to FasL+ Cytotoxic T Lymphocyte Cytotoxicity.

Myelosuppression is a major adverse effect of 5-fluorouracil (5-FU) chemotherapy. However, recent findings indicate that 5-FU selectively suppresses myeloid-derived suppressor cells (MDSCs), to enhance antitumor immunity in tumor-bearing mice. 5-FU-mediated myelosuppression may thus have a beneficial effect for cancer patients. The molecular mechanism underlying 5-FU's suppression of MDSCs is currently unknown. We aimed at testing the hypothesis that 5-FU suppresses MDSCs through enhancing MDSC sensitivity to Fas-mediated apoptosis. We observed that, although FasL is highly expressed in T cells, Fas is weakly expressed in myeloid cells in human colon carcinoma, indicating that downregulation of Fas is a mechanism underlying myeloid cell survival and accumulation in human colon cancer. 5-FU treatment upregulated expression of both p53 and Fas, and knocking down p53 diminished 5-FU-induced Fas expression in MDSC-like cells, in vitro. 5-FU treatment also increased MDSC-like cell sensitivity to FasL-induced apoptosis in vitro. Furthermore, we determined that 5-FU therapy increased expression of Fas on MDSCs, suppressed MDSC accumulation, and increased CTL tumor infiltration in colon tumor-bearing mice. In human colorectal cancer patients, 5-FU chemotherapy decreased MDSC accumulation and increased CTL level. Our findings determine that 5-FU chemotherapy activates the p53-Fas pathway, to suppress MDSC accumulation, to increase CTL tumor infiltration.

Inhibition of myeloid-derived suppressive cell function with all-trans retinoic acid enhanced anti-PD-L1 efficacy in cervical cancer

PD-1/PD-L1 inhibitor treatments are relatively inefficacious in advanced cervical cancer patients. The presence of myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment may be one significant barrier to efficacy. It has been shown that all-trans retinoic acid (ATRA) can differentiate MDSCs into mature myeloid cells. However, whether ATRA suppression of MDSCs function could enhance PD-L1 blockade-mediated tumor immunotherapy remains unknown. Here, the frequency of tumor-infiltrating MDSCs in cervical cancer patients was measured. ATRA was used to target MDSCs both in vitro and in tumor-bearing mice. The impact of ATRA on the human cell line HeLa was also investigated. The frequency of MDSCs and T cells was determined by flow cytometry. The expression of immunosuppressive genes was measured with quantitative real time-PCR and infiltration of immune cells was assessed by immunohistochemical examination. We found that tumor-infiltrating PD-L1+ MDSCs were more prevalent in cervical cancer patients. Blockade of PD-L1 expression in MDSCs with anti-PD-L1 antibody cannot relieve the suppressive activity of MDSCs induced by HeLa cells, while ATRA efficiently abrogated the suppressive activity of MDSCs. Furthermore, ATRA had no effect on PD-L1 expression in HeLa cells in vitro. In in vivo treatment, ATRA decreased MDSCs accumulation and increased the frequency of CD8+ T cells in BALB/C mice with U14 cervical tumors. Importantly, a combination treatment of ATRA and anti-PD-L1 antibody further delayed U14 tumor growth and increased the proportion of CD62L−CD8+ T cells, CD62L−CD4+ T cells, CD107a+CD8+ T cells as well as IFN-γ and TNF-α levels in tumors. Our results provide a rationale for the use of ATRA to suppress MDSCs and enhance anti-PD-L1 cancer immunotherapy in cervical cancer.

Autocrine IL6-Mediated Activation of the STAT3-DNMT Axis Silences the TNFα-RIP1 Necroptosis Pathway to Sustain Survival and Accumulation of Myeloid-Derived Suppressor Cells.

Although accumulation of myeloid-derived suppressor cells (MDSC) is a hallmark of cancer, the underlying mechanism of this accumulation within the tumor microenvironment remains incompletely understood. We report here that TNFα-RIP1-mediated necroptosis regulates accumulation of MDSCs. In tumor-bearing mice, pharmacologic inhibition of DNMT with the DNA methyltransferease inhibitor decitabine (DAC) decreased MDSC accumulation and increased activation of antigen-specific cytotoxic T lymphocytes. DAC-induced decreases in MDSC accumulation correlated with increased expression of the myeloid cell lineage-specific transcription factor IRF8 in MDSCs. However, DAC also suppressed MDSC-like cell accumulation in IRF8-deficient mice, indicating that DNA methylation may regulate MDSC survival through an IRF8-independent mechanism. Instead, DAC decreased MDSC accumulation by increasing cell death via disrupting DNA methylation of RIP1-dependent targets of necroptosis. Genome-wide DNA bisulfite sequencing revealed that the Tnf promoter was hypermethylated in tumor-induced MDSCs in vivo. DAC treatment dramatically increased TNFα levels in MDSC in vitro, and neutralizing TNFα significantly increased MDSC accumulation and tumor growth in tumor-bearing mice in vivo. Recombinant TNFα induced MDSC cell death in a dose- and RIP1-dependent manner. IL6 was abundantly expressed in MDSCs in tumor-bearing mice and patients with human colorectal cancer. In vitro, IL6 treatment of MDSC-like cells activated STAT3, increased expression of DNMT1 and DNMT3b, and enhanced survival. Overall, our findings reveal that MDSCs establish a STAT3-DNMT epigenetic axis, regulated by autocrine IL6, to silence TNFα expression. This results in decreased TNFα-induced and RIP1-dependent necroptosis to sustain survival and accumulation. SIGNIFICANCE: These findings demonstrate that targeting IL6 expression or function represent potentially effective approaches to suppress MDSC survival and accumulation in the tumor microenvironment.

Autocrine IL6 activates the STAT3-DNMT axis to silence the TNFa-RIP1 necroptosis pathway to sustain myeloid-derived suppressor cell survival and accumulation

Abstract Accumulation of myeloid-derived suppressor cells (MDSCs) is a hallmark of cancer. However, the underlying mechanism of MDSC accumulation in the tumor microenvironment (TME) remain incompletely understood. We report that MDSC accumulation is regulated by the TNFα-RIP1-mediated necroptosis. We determined that inhibition of DNMTs with Decitabine (DAC) abolished MDSC accumulation and increased activation of antigen-specific cytotoxic T lymphocytes (CTLs) in tumor-bearing mice. DAC-induced decrease of MDSC accumulation is correlated with increased IRF8 expression in MDSCs. However, DAC also abolished MDSC-like cell accumulation in IRF8 KO mice, indicating that DNA methylation does not regulate MDSC lineage differentiation but mediates MDSC accumulation at post differentiation stage. We determined that DAC decreased MDSC accumulation through increasing cell death and identified RIP1-dependent necroptosis as target of DNA methylation in MDSCs. Genome-wide DNA bisulfite sequencing revealed that the Tnf promoter is hypermethylated in tumor-induced MDSCs in vivo. Consequently, DAC dramatically increased TNFα level in MDSCs and neutralizing TNFα significantly decreased MDSC cell death. Furthermore, recombinant TNFα induced MDSC cell death in a does- and RIP1-dependent manner. IL6 which is expressed in MDSCs in tumor-bearing mice and human colorectal cancer patients. Our data shows that the autocrine IL6 activates the STAT3-DNMT axis to epigenetically silence the TNFα-RIP1 necroptosis pathway to sustain MDSC survival and accumulation in cancer. Targeting the TNFα-RIP1 necroptosis is potentially an effective approach to supress MDSCs to activate tumor-reactive CTLs in the TME.

Calcium/Calmodulin Dependent Protein Kinase Kinase 2 (CaMKK2) Expressed in the Host Promotes Lymphoma Cells Growth By Controlling Myeloid Derived Suppressor Cells Expansion

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of immunosuppressive cells that generate from myeloid progenitors under pathological conditions including cancers.In response to tumor-derived factors, myeloid progenitors differentiate intoimmature myeloid cells and accumulate as monocyte and granulocyte-MDSC (M- and G-MDSC), and correlate with poor survival in patients. Promoting the differentiation of MDSCs towards mature dendritic cells and macrophage is a potential way to eliminate MDSCs and restore anti-tumor immunity. In this study, we demonstrate that the enzyme Calcium/Calmodulin dependent Kinase Kinase 2 (CaMKK2) as a potential therapeutic target to control the growth of lymphoma by regulating the expansion of MDSCs.CaMKK2 is a crucial kinase in the calcium-signaling cascade. Activated by the Ca2+/CaM complex, CaMKK2 can phosphorylate the down stream targets including CaMKI, CaMKIV, and 5' AMP-activated kinase (AMPK). Beyond central nerve system, CaMKK2 is expressed in hematopoietic stem and progenitors cells, and some hematopoietic mature cells including macrophages and monocytes. In adipogenesis, granulopoiesis, and muscle development, CaMKK2 inhibits the differentiation of progenitors towards mature cells. We reasoned that CaMKK2 might have a similar function in myeloid cells, controlling terminal differentiation of tumor-induced MDSCs.We first confirmedthe expression of CaMKK2 in tumor-induced MDSCs. EG.7-OVA lymphoma cells were injected s.c. in the flank of Camkk2-egfp reporter mice, and MDSCs subsets from the tumors and spleens of the mice were assessed by flow cytometry. We found that Camkk2 promoter was highly active in Ly6Chigh/Ly6Gdim subset (M-MDSC), but low in Ly6Cdim/Ly6Ghigh subset (G-MDSC) and Ly6Cneg/Ly6Gneg/F4/80dim/neg/MHC-IIdim/neg cells. (Figure 1) Camkk2 promoter was not active in lymphocytes as previous reported.To determine the function of CaMKK2 expressed in the host, E.G7 cells with luciferase expression were injected into the flank of wild type (WT) and Camkk2-/- mice, and monitored by tumor size and bioluminescent imaging. (Figure 2 A&B) In WT mice injected with E.G7-OVA cells, tumors were detectable by bioluminescence by day 7, and gradually increased in photon signal during the following two weeks. Although tumors successfully engrafted in Camkk2-/- mice, bioluminescent signal gradually decreased after 21 days and eventually disappeared after 32 days. (Figure 2A) In LyM-Cre+Camkk2loxP mice which Camkk2 is selectively deleted in myeloid cell compartment, when challenged with E.G7-OVA cells, similar E.G7 tumor grow suppression was observed as in the Camkk2-/- global knockout model. (Figure 2C)We next demonstrated that Camkk2 deletion decreased MDSCs accumulation in EG7 bearing mice. In normal conditions, Camkk2-/- mice had comparable CD11b+and Ly6ChighLy6Gdim percentage in the spleenswith WT mice, but slightly higher Ly6Cdim Ly6Ghigh percentage. A significant increase of MDSCs percentage was detected in EG.7-bearing mice compared to tumor-free mice; while in Camkk2-/- mice, the MDSC accumulation in E.G7-OVA spleens and tumors showed a significant decrease in percentage compared to WT ones. (Figure 3 A & B) To evaluate whether the failure of MDSC expansion in tumor-bearing Camkk2-/- mice regulated tumor suppression, MDSCs were isolated from the spleens of WT and Camkk2-/- E.G7-OVA-bearing mice, adoptively transferred into Camkk2-/- mice, and followed by tumor inoculation. As expected, lymphoma cells failed to growth in Camkk2-/- control mice without MDSC injection. However, tumors developed in all Camkk2-/- mice that received either WT or Camkk2-/- MDSCs, with no significant difference. (Figure 3C) These results indicated that restoring the number of MDSC was sufficient to revert the protective effect of Camkk2 deletion on tumor growth. Interestingly, this data also suggested that WT and Camkk2-/- MDSCs have a comparable immunosuppressive activity at single-cell level.In conclusion, our results identifies for the first time CaMKK2 as an important component of molecular machinery that mediates the detrimental effect of lymphoma cells on myeloid development. Of note, our data also pinpoint CaMKK2 as a new pharmacological target to limit the expansion of tumor-induced MDSC. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

The Adaptor Protein CARD9 Protects against Colon Cancer by Restricting Mycobiota-Mediated Expansion of Myeloid-Derived Suppressor Cells

The adaptor protein CARD9 links detection of fungi by surface receptors to the activation of the NF-κB pathway. Mice deficient in CARD9 exhibit dysbiosis and are more susceptible to colitis. Here we examined the impact of Card9 deficiency in the development of colitis-associated colon cancer (CAC). Treatment of Card9-/- mice with AOM-DSS resulted in increased tumor loads as compared to WT mice and in the accumulation of myeloid-derived suppressor cells (MDSCs) in tumor tissue. The impaired fungicidal functions of Card9-/- macrophages led to increased fungal loads and variation in the overall composition of the intestinal mycobiota, with a notable increase in C.tropicalis. Bone marrow cells incubated with C.tropicalis exhibited MDSC features and suppressive functions. Fluconazole treatment suppressed CAC in Card9-/- mice and was associated with decreased MDSC accumulation. The frequency of MDSCs in tumor tissues of colon cancer patients correlated positively with fungal burden, pointing to the relevance of this regulatory axis in human disease.

Targeting myeloid regulators by paclitaxel-loaded enzymatically degradable nanocups.

Tumor microenvironment is characterized by immunosuppressive mechanisms associated with the accumulation of immune regulatory cells - myeloid-derived suppressor cells (MDSC). Therapeutic depletion of MDSC has been associated with inhibition of tumor growth and therefore represents an attractive approach to cancer immunotherapy. MDSC in cancer are characterized by enhanced enzymatic capacity to generate reactive oxygen and nitrogen species (RONS) which have been shown to effectively degrade carbonaceous materials. We prepared enzymatically openable nitrogen-doped carbon nanotube cups (NCNC) corked with gold nanoparticles and loaded with paclitaxel as a therapeutic cargo. Loading and release of paclitaxel was confirmed through electron microscopy, Raman spectroscopy and LC-MS analysis. Under the assumption that RONS generated by MDSCs can be utilized as a dual targeting and oxidative degradation mechanism for NCNC, here we report that systemic administration of paclitaxel loaded NCNC delivers paclitaxel to circulating and lymphoid tissue MDSC resulting in the inhibition of growth of tumors (B16 melanoma cells inoculated into C57BL/6 mice) in vivo. Tumor growth inhibition was associated with decreased MDSC accumulation quantified by flow cytometry that correlated with bio-distribution of gold-corked NCNC resolved by ICP-MS detection of residual gold in mouse tissue. Thus, we developed a novel immunotherapeutic approach based on unique nanodelivery vehicles, which can be loaded with therapeutic agents that are released specifically in MDSC via NCNC selective enzymatic "opening" affecting change in the tumor microenvironment.

Ceramide activates lysosomal cathepsin B and cathepsin D to attenuate autophagy and induces ER stress to suppress myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are immune suppressive cells that are hallmarks of human cancer. MDSCs inhibit cytotoxic T lymphocytes (CTLs) and NK cell functions to promote tumor immune escape and progression, and therefore are considered key targets in cancer immunotherapy. Recent studies determined a key role of the apoptosis pathways in tumor-induced MDSC homeostasis and it is known that ceramide plays a key role in regulation of mammalian cell apoptosis. In this study, we aimed to determine the efficacy and underlying molecular mechanism of ceramide in suppression of MDSCs. Treatment of tumor-bearing mice with LCL521, a lysosomotropic inhibitor of acid ceramidase, significantly decreased MDSC accumulation in vivo. Using a MDSC-like myeloid cell model, we determined that LCL521 targets lysosomes and increases total cellular C16 ceramide level. Although MDSC-like cells have functional apoptosis pathways, LCL521-induced MDSC death occurs in an apoptosis- and necroptosis-independent mechanism. LCL521 treatment resulted in an increase in the number of autophagic vesicles, heterolysosomes and swollen ERs. Finally, concomitant inhibition of cathepsin B and cathepsin D was required to significantly decrease LCL521-induced cell death. Our observations indicate that LCL521 targets lysosomes to activate cathepsin B and cathepsin D, resulting in interrupted autophagy and ER stress that culminates in MDSC death. Therefore, a ceramidase inhibitor is potentially an effective adjunct therapeutic agent for suppression of MDSCs to enhance the efficacy of CTL-based cancer immunotherapy.

Mast cells and mast cell-derived IL-13 play an important role in MDSC activation, migration, and accumulation. (TUM4P.925)

Abstract Until recently, the interaction between mast cells (MCs) and CD11b+Gr-1+ myeloid derived suppressor cells (MDSCs) was limited to recruitment of MDSCs to the tumor site. However, we report that MCs are also needed for the activity of MDSCs. Adoptive transfer (AT) of MDSCs failed to promote B16 melanoma colonization in MC deficient mice. MDSCs in these mice also failed to localize to the liver and stayed mainly in peripheral blood. MC sufficient mice accumulated MDSCs in the liver and retained significantly lower levels of MDSCs in circulation after AT. Recently, Ma et al. (Cancer Res. 2013 Jul 1; 73(13);3927-37.) has shown that MC derived IL-13 has been show to promote the growth of pancreatic ductal carcinoma. Given this, we investigated the role that IL-13 plays in the MDSC/MC interaction. Our data shows that IL-13 KO mice crossed to ADAM10Tg mice, which carry a mutation resulting in the over-accumulation of MDSCs, have significantly decreased MDSC accumulation in the naïve state, especially evident in the granulocytic subset. In a model of natural MDSC accumulation (Lewis Lung Carcinoma, i.v.), IL-13 KO mice had reduced tumor colonization to the lungs. They also had reduced MDSC accumulation in the liver and spleen, but increased number in circulation. Taken together, our data indicates that MCs and IL-13, an important MC-derived cytokine, play an important role in MDSC migration and accumulation and represent important drug targets for the control of MDSCs in tumor.

Reductions in Myeloid-Derived Suppressor Cells and Lung Metastases using AZD4547 Treatment of a Metastatic Murine Breast Tumor Model

Background: AZD4547, a small-molecule inhibitor targeting the tyrosine kinase of Fibroblast Growth Factor Receptors (FGFRs), is currently under phase II clinical study for human subjects having breast cancer, while the underlying mechanism remains elusive. The aim of this study is to explore the potential mechanism by which AZD4547 inhibits breast tumor lung metastases at the level of the tumor microenvironment. Methods: First, through in vitro experiments, we investigated the efficacy of the FGFRs inhibitor AZD4547 on 4T1 tumor cells for their proliferation, apoptosis, migration, and invasion. Second, by in vivo animal experiments, we evaluated the effects of AZD4547 on tumor growth and lung metastases in 4T1 tumor-bearing mice. Finally, we examined the impact of AZD4547 on the infiltration of myeloid-derived suppressor cells (MDSCs) in lung, spleens, peripheral blood and tumor. Results: Through this study we found that AZD4547 could efficiently suppress tumor 4T1 cells through restraining their proliferation, blocking migration and invasion, and inducing apoptosis in vitro. In animal model we also demonstrated that AZD4547 was able to inhibit tumor growth and lung metastases, consistent with the decreased MDSCs accumulation in the tumor and lung tissues, respectively. Moreover, the reduced number of MDSCs in peripheral blood and spleens were also observed in the AZD4547-treated mice. Importantly, through the AZD4547 treatment, the CD4⁺ and CD8⁺ T-cells were significantly increased in tumor and spleens. Conclusion: Our studies showed that AZD4547 can inhibit breast cancer cell proliferation, induce its apoptosis and block migration and invasion in vitro and suppress tumor growth and lung metastases by modulating the tumor immunologic microenvironment in vivo.

Deregulation of Apoptotic Factors Bcl-xL and Bax Confers Apoptotic Resistance to Myeloid-derived Suppressor Cells and Contributes to Their Persistence in Cancer

Myeloid-derived suppressor cells (MDSCs) are heterogeneous immature myeloid cells that accumulate in response to tumor progression. Compelling data from mouse models and human cancer patients showed that tumor-induced inflammatory mediators induce MDSC differentiation. However, the mechanisms underlying MDSC persistence is largely unknown. Here, we demonstrated that tumor-induced MDSCs exhibit significantly decreased spontaneous apoptosis as compared with myeloid cells with the same phenotypes from tumor-free mice. Consistent with the decreased apoptosis, cell surface Fas receptor decreased significantly in tumor-induced MDSCs. Screening for changes of key apoptosis mediators downstream the Fas receptor revealed that expression levels of IRF8 and Bax are diminished, whereas expression of Bcl-xL is increased in tumor-induced MDSCs. We further determined that IRF8 binds directly to Bax and Bcl-x promoter in primary myeloid cells in vivo, and IRF8-deficient MDSC-like cells also exhibit increased Bcl-xL and decreased Bax expression. Analysis of CD69 and CD25 levels revealed that cytotoxic T lymphocytes (CTLs) are partially activated in tumor-bearing hosts. Strikingly, FasL but not perforin and granzymes were selectively activated in CTLs in the tumor-bearing host. ABT-737 significantly increased the sensitivity of MDSCs to Fas-mediated apoptosis in vitro. More importantly, ABT-737 therapy increased MDSC spontaneous apoptosis and decreased MDSC accumulation in tumor-bearing mice. Our data thus determined that MDSCs use down-regulation of IRF8 to alter Bax and Bcl-xL expression to deregulate the Fas-mediated apoptosis pathway to evade elimination by host CTLs. Therefore, targeting Bcl-xL is potentially effective in suppression of MDSC persistence in cancer therapy.

Adiponectin deficiency suppresses lymphoma growth in mice by modulating NK cells, CD8 T cells and myeloid-derived suppressor cells (P2141)

Abstract We previously found that adiponectin (APN) suppresses IL-2-induced natural killer (NK) cell activation by down-regulating IFN-γ-inducible tumor necrosis factor-related apoptosis-inducing ligand and Fas ligand expression. Even though APN’s anti-tumor function has been reported in several solid tumors, with few controversial results, no lymphoma studies have been conducted. In this study, we assessed APN’s role in the function of immune cells, including NK cells, cytotoxic T-lymphocytes (CTL), and myeloid-derived suppressor cells (MDSC), using EL4 and B16F10-bearing C57BL/6J based APN-knockout (APNKO) mice. We observed attenuated EL4 growth in APNKO mice. Increased numbers of splenic NK cells were found under naive conditions and splenic CTLs under EL4-challenged conditions. Splenic NK cells in APNKO mice showed enhanced cytotoxicity, with and without IL-2 stimulation. In addition, decreased MDSC accumulation was found in EL4-bearing APNKO mice. Enforced MHC class I (MHC I) expression in B16F10 led to attenuated growth in APNKO mice. Thus, our results suggest that EL4 regression in APNKO mice is due to not only enhanced anti-tumor immune system but also to high level expression of MHC I.

Abstract 1547: Tumor-derived macrophage Migration Inhibitory Factor and interleukin-6 cooperated in hypoxic accumulation of CD11b+Gr-1+ myeloid cells.

Abstract Recently, myeloid derived suppressor cells (MDSCs) have gained much attention due to their role in tumor immunity suppression as well as promotion of angiogenesis, tumor cell invasion, and metastases. However, the mechanisms that regulate MDSCs recruitment have not been well clarified. Here, we demonstrated that hypoxic tumor microenvironment stimulate the recruitment of MDSCs through increased production of macrophage migration inhibitory factor (MIF) and interleukin-6 (IL-6) by head and neck squamous cell carcinoma (HNSCC) cells. Knock-down (KD) of HIF-1/2α in HNSCC cells decreased MIF level but did not inhibit the MDSCs migration, because HIF-1/2α KD increased NF-κB activity which further enhanced IL-6 secretion. In vivo administration of neutralizing IL-6 antibody and inhibitors against MIF and NF-κB decreased MDSCs accumulation, accompanied by reduced micro-vessel density (MVD), lymphatic vessel density (LVD), and xenograft tumor growth. The supplementation of MDSCs increased MVD, LVD, and xenograft tumor growth. In conclusion, hypoxic HNSCC cells may stimulate the accumulation of MDSCs through secreting MIF and IL-6. This process is mediated by interactions between NF-κB and HIF-1/2α. Strategies targeting hypoxic tumor microenvironment may represent attractive approaches to HNSCC therapy. [G Zhu and Y Tang contributed equally to this paper.] Citation Format: Guiquan Zhu, Yaling Tang, Ling Li, Xinhua Liang. Tumor-derived macrophage Migration Inhibitory Factor and interleukin-6 cooperated in hypoxic accumulation of CD11b+Gr-1+ myeloid cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1547. doi:10.1158/1538-7445.AM2013-1547