Abstract 5011: Targeting hypoxia-induced immune suppression to overcome immunotherapy resistance in prostate cancer

Immune checkpoint blockade is effective in “hot” tumors like melanoma with pre-existing immune infiltrates; however, “cold” tumors like prostate cancer fail to respond. We found that prostate cancers harbor regions of hypoxia that resist T cell infiltration even in the context of anti-CTLA-4 (cytotoxic T lymphocyte associated protein-4) and anti-PD-1 (programmed cell death protein 1) blockade. These hypoxic zones serve as islands of immune privilege through the recruitment and suppressive polarization of immature myeloid cells into myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAM). We found that targeted hypoxia ablation using TH-302, a hypoxia-activated prodrug, sensitized both transplantable and spontaneous models of prostate cancer to checkpoint blockade, coincident with enhanced T cell infiltration and effector function and loss of MDSC recruitment and suppressive function. Tumors treated with the combination of TH-302 and checkpoint blockade showed a reduced capacity to suppressively polarize new myeloid immigrants, implying a durable reconditioning of the tumor microenvironment (TME) into an immune-infiltrated, pro-inflammatory milieu. T cells infiltrating combination-treated tumors exhibited increased mitochondrial respiration, consistent with creation of a metabolically favorable milieu for T cell function. Based on these findings, we hypothesized that other approaches capable of metabolically rewiring the TME should promote anti-tumor immunity and sensitize checkpoint blockade-resistant tumors to immunotherapy. With this in mind, we performed a longitudinal study comparing a panel of different mitochondrial respiration inhibitors and a glutaminase inhibitor for their efficacy in reducing hypoxia, improving T cell infiltration and decreasing myeloid cell recruitment and suppressive polarization using immunofluorescence staining and confocal microscopy. Our preliminary data suggests that inhibitors targeting mitochondrial respiration, rather than those targeting glutamine metabolism synergize with checkpoint blockade and exhibit the highest efficacy in increasing T cell recruitment. We continue to characterize the dynamics of hypoxia reduction, duration of normalization following drug withdrawal, and impact on the immune microenvironment of these diverse approaches to metabolic reconditioning.

Citation Format: Priyamvada Jayaprakash, Midan Ai, Arthur Liu, Pratha Budhani, Todd Bartkowiak, Jie Sheng, Casey Ager, Courtney Nicholas, Ashvin Jaiswal, Yanqiu Sun, Krishna Shah, Sadhana Balasubramanyam, Nan Li, Guocan Wang, Jing Ning, Anna Zal, Tomasz Zal, Michael Curran. Targeting hypoxia-induced immune suppression to overcome immunotherapy resistance in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5011.

Targeted hypoxia reduction restores T cell infiltration and sensitizes prostate cancer to immunotherapy

Despite the success of immune checkpoint blockade against melanoma, many "cold" tumors like prostate cancer remain unresponsive. We found that hypoxic zones were prevalent across preclinical prostate cancer and resisted T cell infiltration even in the context of CTLA-4 and PD-1 blockade. We demonstrated that the hypoxia-activated prodrug TH-302 reduces or eliminates hypoxia in these tumors. Combination therapy with this hypoxia-prodrug and checkpoint blockade cooperated to cure more than 80% of tumors in the transgenic adenocarcinoma of the mouse prostate-derived (TRAMP-derived) TRAMP-C2 model. Immunofluorescence imaging showed that TH-302 drives an influx of T cells into hypoxic zones, which were expanded by checkpoint blockade. Further, combination therapy reduced myeloid-derived suppressor cell density by more than 50%, and durably reduced the capacity of the tumor to replenish the granulocytic subset. Spontaneous prostate tumors in TRAMP transgenic mice, which completely resist checkpoint blockade, showed minimal adenocarcinoma tumor burden at 36 weeks of age and no evidence of neuroendocrine tumors with combination therapy. Survival of Pb-Cre4, Ptenpc-/-Smad4pc-/- mice with aggressive prostate adenocarcinoma was also significantly extended by this combination of hypoxia-prodrug and checkpoint blockade. Hypoxia disruption and T cell checkpoint blockade may sensitize some of the most therapeutically resistant cancers to immunotherapy.

Brain tumor-induced neuronal stress orchestrates adaptive immune surveillance through fractalkine

Tissue damage contributes to initiation and modulation of an immune response. Tumor progression generally causes distress to the surrounding tissue. However, how tumor-induced parenchymal damage regulates anti-tumor immune response remains to be understood. We found that tumors that invaded brain parenchyma compressed the surrounding neurons causing increased expression of the neuronal chemokine CX3CL1/fractalkine in the peritumoral margin. Intravital two-photon microscopy revealed perivascular recruitment of monocyte-derived CD11c+ dendritic cells and T cells that interacted and killed individual cancer cells in tumor margins. Immune surveillance of brain tumors became inefficient in mice lacking the receptor for fractalkine, CX3CR1, resulting in more aggressive tumor progression. Our results identify tissue stress and associated chemokine signaling as a potential target to orchestrate anti-tumor immune surveillance in the brain.

Abstract 876: Imaging the interaction of leukemia and bone marrow microenvironment in murine model of ALL

Interactions of leukemia and the bone marrow (BM) microenvironment are known to play a key role in the survival and growth of leukemic cells, and we have shown that HIF-1α stabilization in BM stromal cells facilitates leukemia homing and progression (Chen et al. Blood 2012, 119:4971). Leukemic cells have been shown to hijack the homeostatic mechanisms of normal hematopoietic stem cells (HSCs) and take refuge within the BM niche. This mechanism is pivotal during chemotherapy and contributes to disease relapse. In this study, we aimed to characterize the time-dependent progression of BM hypoxia involving both acute lymphocytic leukemia (ALL) cells and components of the BM niche, using multiphoton intravital microscopy (MP-IVM) . We generated a transplantable, fluorescent leukemia model by retrovirally transducing C57Bl6-Ai14 murine BM cells that express red fluorescing tdTomato with the p190-Bcr/Abl oncogene (KG Harutyunyan et al, Blood 2014 124:2396). The resulting p190-Bcr/Abl tdTomato cells caused rapid development of ALL in non-irradiated C57Bl6 immunocompetent mice, manifested by infiltration of multiple organ and BM sites, followed by death within 14-18 days. We utilized Col2.3-GFPemd transgenic mice as recipients of leukemia to highlight the osteoblastic niche, and visualized vasculature by injection of TRITC-dextran. We showed the dynamic of homing and engraftment of ALL leukemic B cells (LBC) in OB-GFP recipient mice, with homing in the vicinity of blood vessels visualized by MP-IVM, followed by proliferation and leukemia expansion. This was accompanied by invasion of both vascular and osteoblastic components of BM microenvironment. Longitudinal assessment of hypoxia utilizing pimonidazole staining showed progressive development of BM hypoxia starting from Day 10 p.i., paralleling leukemia progression, despite the abundant vascularization of the BM. To assess the integrity of the BM vascular niche during leukemia progression the experimental mice were intravitally injected with low doses of an Alexa-Fluor-647-conjugated VE-cadherin antibody (MG. Poulos et al, Epub 2013 Sep 5) to visualize the number and morphology of the perfused vessels and to analyze the architecture of the hematopoietic compartment. We observed that at late stage of leukemia progression (day 12-14 p.i) BM vessels are disorganized as a result of expansion of leukemic B cells. Ongoing longitudinal imaging experiments will characterize the cellular origin of hypoxic niche cells and the dynamic of vasculature alteration in ALL. In summary, these findings demonstrate rapid development of intra-BM hypoxia that parallels leukemia progression and involves interactions between leukemia cells and BM niche cells, as well as disordered vasculature.

Citation Format: Karine G. Harutyunyan, Saradhi Mallampati, Anna Zal, Mateusz Rytelewski, Michael C. Gutkin, Jason M. Butler, Tomasz Zal, Marina Konopleva. Imaging the interaction of leukemia and bone marrow microenvironment in murine model of ALL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 876. doi:10.1158/1538-7445.AM2017-876

Abstract PL07-01: Altered metabolism in leukemic microenvironment

Interactions of leukemia cells and their bone marrow (BM) microenvironment are known to play a key role in the survival and growth of leukemic cells. It has been postulated that specific niches provide a sanctuary where subpopulations of leukemic cells evade chemotherapy-induced death and acquire a drug-resistant phenotype. Understanding the cellular and molecular biology of the leukemia stem cell (LSC) niche and of microenvironment/leukemia interactions may provide new targets that allow destruction of LSCs without adversely affecting normal stem cell self-renewal. Key emerging therapeutic targets include chemokine receptors such as CXCR4 and hypoxia-related proteins, as well as the metabolic abnormalities of the leukemia-associated stroma. We have recently reported that CXCR4 inhibition causes leukemia cell dislodgement from CXCL12-producing marrow niches, reduced proliferation and induction of differentiation of AML cells in an in vivo model of AML, translating into pronounced anti-leukemia effects. Studies in murine leukemia models using the hypoxia probe pimonidazole demonstrated extensive areas of hypoxia within leukemic, but not healthy normal, bone marrow. Time-course analysis of bone marrow spaces within calvaria and femurs by multiphoton intravital microscopy (MP-IVM) demonstrated lodging of p190-Bcr/Abl tdTomato cells in close proximity to blood vessels, followed by accumulation of leukemia cells localized within the sinusoidal and marrow spaces resulting in the demise of the animals within 3 weeks. In this model, pimonidazole detected hypoxic areas despite abundant vascular supply in the marrow cavities. In vivo magnetic resonance imaging with hyperpolarized pyruvate showed higher pyruvate-lactate conversion (high glycolytic flux) in leukemic marrows. These findings were supported by significant pimonidazole uptake by the diseased bone marrow in patients with acute leukemia, causing stabilization of HIF-1α in 55% (76/138) of primary AML patients and of its target CA9. Paradoxically, AML cells become highly dependent on mitochondrial oxidative phosphorylation (OXPHOS) for their survival, and inhibition of OXPHOS with the novel small molecule complex I inhibitor IACS-10759 inhibits oxygen consumption, eliminates hypoxia in vivo and inhibits AML growth. These findings suggest that altered tumor metabolism underlies the hypoxia observed in leukemias. We postulate that the altered tumor microenvironment within the hypoxic niche cells will influence leukemia development and response to therapy. Hence, targeting key metabolic alterations should be considered in the armamentarium of anti-AML therapies. IACS-10759 is presently completing IND enabling safety/toxicity studies with first in human studies targeting relapsed/refractory AML planned for 2016.

Citation Format: Marina Y. Konopleva, Tomasz Zal, Niki M. Zacharias Millward, Byoung-Sik Cho, Karine Harutyunyan, Anna Zal, Hong Mu, Sergej Konoplev, Juliana Benito, Juliana Velez, Carlos Bueso-Ramso, Jennifer Molina, Pratip K. Bhattacharya, Maria Emilia Di Francesco, Joseph Marszalek, Michael Andreeff. Altered metabolism in leukemic microenvironment. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr PL07-01.

Abstract 5088: Glioblastoma stem cell-secreted exosomes can induce a tumor supportive M2 response

INTRODUCTION: Tumor-released exosomes have pleiotropic functions in promoting autocrine signaling to distant cells. Elucidating the mechanistic modulation of the immune system by these exosomes provides insights into potential biomarkers for detection, recurrence and response and identifies potential new therapeutic targets.

METHODS: Exosomes were isolated from human glioblastoma stem cells (GSCs) and fibroblasts (control) using differential centrifugation and characterized by nanosight technology, electron microscopy, and western blotting. Fluorescent-labeled exosomes were co-cultured with human immune cells. Confocal microscopy was used to determine the preferential uptake in various immune populations and to evaluate the intracellular trafficking. The cell-secreted exosome content was characterized by mass spectrometry and nanostring technology. The phenotypic and functional skewing of the monocyte lineage was analyzed given its propensity to take up exosomes.

RESULTS: GSC-secreted exosomes were homogenous in morphology, ranged from 50-120 nm in size, and expressed CD63 and CD9 surface molecules. The GSCs-produced exosomes were preferentially absorbed by CD14+ monocytes (precursors to macrophages) and Gr-1+ derived myeloid cells isolated from healthy volunteers and/or glioblastoma patients. When activated, CD4+ and CD8+ T cells, but not NK cells could also uptake exosomes. Longitudinal kinetic studies established that the highest uptake of PKH67-labeled GCS-secreted exosomes occurred at 48 hours after exposure. Confocal microscopy revealed that monocytes could only internalize GSC-released exosomes but not fibroblast-secreted exosomes. The exposure to GSC-secreted exosomes induced a phenotypic change in monocytes and prevented them from undergoing apoptosis. Studies of M1/M2 macrophage markers by flow cytometry revealed that GSCs-secreted exosomes, but not the fibroblast-secreted exosomes, increased expression of CD80, CD163, CD206 and decreased expression of MHC class II. This profile was similar to myeloid suppressor cells and macrophages that were obtained directly ex vivo from glioblastomas (n = 17). The GSC-secreted exosomes were preferentially enriched relative to fibroblast-secreted exosomes in transcriptional regulators that induced the M2 phenotype.

CONCLUSIONS: Monocytes demonstrate preferential uptake of GSC-secreted exosomes which then induces a glioma-supportive M2 phenotype - similar to the phenotype observed in myeloid cells and macrophages isolated from human glioblastomas. This data indicates that the GSC-secreted exosomes can be a contributing factor in the M2 skewing within the tumor microenvironment.

Citation Format: Konrad Gabrusiewicz, Yuuri Hashimoto, Jun Wei, Maiti Sourindra, John Yu, Shinji Yamashita, Anna Zal, Tomasz Zal, Laurence Cooper, Amy B. Heimberger. Glioblastoma stem cell-secreted exosomes can induce a tumor supportive M2 response. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5088. doi:10.1158/1538-7445.AM2015-5088

Organ specificity of cancer metastasis depends on the adaptive immune surveillance and the neuronal chemokine fractalkine (TUM10P.1030)

The phenomenon of organ specificity in cancer metastasis has been traditionally interpreted in terms of the “seed and soil” hypothesis. However, the role of the adaptive immune system in this phenomenon is largely unknown and controversial. We found that MCA-fibrosarcoma cancer cells formed lethal tumors in the lungs, but not in the brain thereby representing a model of organ-specificity of cancer metastasis. Using this model, we assessed the role of the adaptive immune system. In immune competent multi-color fluorescent reporter mice, longitudinal intravital imaging via cranial windows revealed initial engraftment and growth of MCA cancer cells that was followed by tumor regression in concordance with T cell infiltration. However, MCA cancer cells formed lethal tumors in the brains of Rag1-KO mice indicating a key role for the adaptive immune system in the organ specificity of MCA cancer cell metastasis. In contrast, T cells were recruited to pulmonary MCA lesions but were ineffective in tumor rejection in that organ. Interestingly, T cell recruitment to MCA micrometastases in the brain was dramatically impeded in mice lacking the receptor for the neuronal chemokine fractalkine, and MCA tumors progressed in the brains of those mice. Our results reveal a role for brain-specific adaptive immunity to cancer metastasis and implicate fractalkine in regulating this process thereby broadening the “seed and soil” concept.

B cells solicit their own help from T cells

We have made use of T cell receptor (TCR)-transgenic mice with CD4+ T cells expressing a receptor specific for the self-antigen C5 (fifth component of complement) to study the role of different antigen-presenting cells in the determination of CD4+ T cell effector type. Contact of T cells from C5 TCR-transgenic mice with C5 protein or C5 peptide in vivo or in vitro induces biased T helper cell (Th) 1 type responses resulting in exclusive production of high levels of interferon gamma and interleukin (IL) 2. Transgenic mice, in contrast to nontransgenic littermates, do not generate an antibody response to C5. We show in this paper that B cell presentation in vitro induces a switch to the Th2 subset indicated by production of IL-4, and targetting C5 to B cells in vivo results in the generation of C5-specific antibodies.