Lymphomas and leukemias are in many ways the most metastatic of all cancers. Late-stage hematopoietic cancers can disseminate into diverse non-hematopoietic organs, and the consequences of such dissemination parallel the clinical challenges of treating metastatic solid tumors. Most notably, hematopoietic cancers that invade privileged target sites, like the central nervous system (CNS), are refractory to front-lime chemotherapy. Thus, metastatic progression can be directly coupled with the development of drug resistance. However, surprisingly little research—from our group or others—has been devoted to examining this relationship. Support from the Ludwig Foundation has enabled the development of metastasis research program in our laboratory. Going forward, we see this new initiative as a central focus of our research program.
The major focus of our laboratory has been to identify basic mechanisms of therapeutic resistance—with a particular interest in on understanding the role of the tumor microenvironment on therapeutic response. Funding from the Ludwig Foundation has allowed us to initiate a major effort, including graduate students, post-doctoral fellows and oncologists, to investigate how lymphoid tumor metastasis promotes chemotherapeutic resistance. This work has led to actionable strategies to inhibit tumor survival signaling in metastatic microenvironments, as well as an increased understanding into basic mechanisms of lymphoma and leukemia invasion into non-hematopoietic organs.
Funding from the Ludwig Foundation has led us to examine two basic, yet largely unexplored, questions:
1) Why are sites of tumor dissemination inherently chemoprotective? Using a well-established mouse model of human Burkitt’s lymphoma, we have been able to show that paracrine factors in the tumor microenvironment modulate lymphoma cell survival following the administration of the genotoxic damage. Specifically, prosurvival cytokines, including IL-6 and Timp-1, are released from select tumor-bearing sites in response to radiation or genotoxic chemotherapy, creating “chemo-resistant niches” that promote the persistence of a minimal residual tumor burden. Curiously, the source of cytokine release in this context is vascular endothelial cells—a cell type of central interest in this proposal. Aims 1 and 2 of this proposal focus on the mechanism of cytokine release from endothelial cells and the content and specificity of this paracrine chemoprotective effect.
Surviving tumor cells in these select microenvironments subsequently serve as a reservoir for eventual tumor relapse (Figure 1). Disruption of this chemo-protective cytokine signaling (using either small molecule inhibitors or neutralizing antibodies) or ablation of the protective microenvironment potentiates the action of doxorubicin. Thus, conventional chemotherapies can induce tumor regression while simultaneously eliciting stress responses that protect subsets of tumor cells in distinct anatomical locations from drug action. Notably, we believe that this kind of paracrine pro-survival signaling is intended to protect stem and progenitor cells from organismal stress and is simply coopted by tumor cells in select microenvironments. Thus, a central challenge eradicating residual disease is identifying and inhibiting factors that specifically protect tumor and not normal stem cells in the chemoprotective niche. Importantly, we believe that this type of protection is not specific to hematopoietic disease. Recent data has suggested that paracrine pro-survival signaling might similarly protect metastatic prostate and breast cancers that reside in the bone marrow. Thus, strategies to sensitize disseminated hematopoietic disease to chemotherapy way serve as a template for treating metastatic epithelial disease.
2) Can we sensitize protective metastatic microenvironments to targeted therapies? In addition to identifying microenvironments that can protect tumor cells from conventional chemotherapy, our group has also recently described how specific tumor microenvironments can promote resistance to targeted therapy—including antibody-based therapies. Specifically, we found that infiltration of leukemia cells into the bone marrow “rewires” the tumor microenvironment to block engulfment of antibody-targeted tumor cells. Notably, this inhibition of macrophage-mediated killing could be overcome by combination regimens involving therapeutic antibodies and chemotherapy. For example, the nitrogen mustard cyclophosphamide induces an acute secretory activating phenotype (ASAP), releasing CCL4, IL8, VEGF, and TNFα from treated tumor cells. These factors induce macrophage infiltration and phagocytic activity in the bone marrow (Figure 2). Thus, the acute induction of stress-related cytokines can effectively target cancer cells for removal by the innate immune system. This synergistic chemoimmunotherapeutic regimen represents a potent strategy for using conventional anticancer agents to alter the tumor microenvironment and promote the efficacy of targeted therapeutics. Thus, we can use conventional chemotherapeutics in fundamentally new ways. While high dose cyclophosphamide elicits profound side effects, low dose cyclophosphamide can elicit an immunomodulatory effects that are fundamental to immune-mediated clearance of target cells. Using this approach, we can deconstruct and dose-reduce current chemotherapeutic regimens, yet still target metastatic chemorefractory sites.
Our preliminary studies, initiated through the support of the Ludwig Foundation, have identified an unexpected mechanism by which metastatic disease persists following chemotherapy. Specifically, DNA double-strand break-promoting chemotherapy induces the release of pro-survival factors, including IL-6 and Timp-1, from tumor-adjacent cells—most likely vascular endothelial cells. This, in turn, results in the protection of proximal tumor cells. In the future, we propose to: a) use both germ line and tissue-specific knock-out mice to explore the relevance of endothelial cytokine release to the survival of B cell malignancies, as well as proximal stem and progenitor cells and b) identify the signaling pathways linking the DNA damage response in endothelial cells and cytokine release into the tumor microenvironment.
Additionally, we propose to study the specific relevance of other secreted cytokines and chemokines, present in the tumor microenvironment, on chemotherapeutic response. Specifically, we will examine whether these paracrine factors are broadly chemoprotective or show drug-specific effects. We also propose to assess the impact of direct IL-6 and Timp-1 inhibition on the treatment of metastatic disease in vivo.
Publications arising from this work
Zhao B, Pritchard JR, Lauffenburger DA, Hemann MT. Addressing genetic tumor heterogeneity through computationally predictive combination therapy. Cancer Discov. (2014) 4(2):166-74. NIHMSID: 547867
Pallasch C, Leskov I, Braun C, Vorholt D, Drake A, Soto-Feliciano Y, Bent E, Schwamb J, Iliopoulou B, Kutsch N, van Rooijen N, Frenzel L, Wendtner C, Heukamp L, Kreuzer K, Hallek M, Chen J, Hemann M. Sensitizing Protective Tumor Microenvironments to Antibody-Mediated Therapy. Cell. (2014) 156(3):590-602. NIHMSID: 554332
Leskov I, Pallasch CP, Drake A, Iliopoulou BP, Souza A, Shen CH, Schweighofer CD, Abruzzo L, Frenzel LP, Wendtner CM, Hemann MT, Chen J. Rapid generation of human B-cell lymphomas via combined expression of Myc and Bcl2 and their use as a preclinical model for biological therapies. Oncogene. (2013) 32(8):1066-72. NIHMSID: 558730
Pritchard JR, Bruno PM, Gilbert LA, Capron KL, Lauffenburger DA, Hemann MT. Defining principles of combination drug mechanisms of action. Proc Natl Acad Sci U S A. (2013) 110(2):E170-9. PMCID: PMC3545813
Gilbert LA, Hemann MT. Context-specific roles for paracrine IL-6 in lymphomagenesis. Genes & Dev. (2012) 26(15):1758-68. PMCID: PMC3418592
Pritchard JR, Gilbert LA, Meacham CE, Ricks JL, Jiang H, Lauffenburger DA, Hemann MT. (2011). Bcl-2 family genetic profiling reveals microenvironment-specific determinants of chemotherapeutic response. Cancer Res., 71(17), 5850-5858. PMCID: PMC3165087
Gilbert LA, Hemann MT. (2011). Chemotherapeutic resistance: surviving stressful situations. Cancer Res., 71(15), 5062-5066. PMCID: PMC3148403
Gilbert LA, Hemann MT. (2010) DNA damage-mediated induction of a chemoresistant niche. Cell, 143(3), 355-366. PMCID: PMC2972353