Tiantian Ji

Cell-free Tumor Microparticle Vaccines Stimulate Dendritic Cells via cGAS/STING Signaling

Zhang, Tang, Zhang, and colleagues report that wide-spectrum antitumor immunity from vaccination with tumor microparticles (T-MP) or T-MP–loaded dendritic cells (DC) is mediated by the cGAS/STING DNA-sensing innate immune pathway and production of type I IFN, which promotes DC maturation and tumor-antigen presentation. Tumor antigens and innate signals are vital considerations in developing new therapeutic or prophylactic antitumor vaccines. The role or requirement of intact tumor cells in the development of an effective tumor vaccine remains incompletely understood. This study reveals the mechanism by which tumor cell–derived microparticles (T-MP) can act as a cell-free tumor vaccine. Vaccinations with T-MPs give rise to prophylactic effects against the challenge of various tumor cell types, while T-MP–loaded dendritic cells (DC) also exhibit therapeutic effects in various tumor models. Such antitumor effects of T-MPs are perhaps attributable to their ability to generate immune signaling and to represent tumor antigens. Mechanically, T-MPs effectively transfer DNA fragments to DCs, leading to type I IFN production through the cGAS/STING-mediated DNA-sensing pathway. In turn, type I IFN promotes DC maturation and presentation of tumor antigens to T cells for antitumor immunity. These findings highlight a novel tumor cell-free vaccine strategy with potential clinical applications. Cancer Immunol Res; 3(2); 196–205. ©2014 AACR.

Upregulation of Cytosolic Phosphoenolpyruvate Carboxykinase Is a Critical Metabolic Event in Melanoma Cells That Repopulate Tumors

Although metabolic defects have been investigated extensively in differentiated tumor cells, much less attention has been directed to the metabolic properties of stem-like cells that repopulate tumors [tumor-repopulating cells (TRC)]. Here, we show that melanoma TRCs cultured in three-dimensional soft fibrin gels reprogram glucose metabolism by hijacking the cytosolic enzyme phosphoenolpyruvate carboxykinase (PCK1), a key player in gluconeogenesis. Surprisingly, upregulated PCK1 in TRCs did not mediate gluconeogenesis but promoted glucose side-branch metabolism, including in the serine and glycerol-3-phosphate pathways. Moreover, this retrograde glucose carbon flow strengthened rather than antagonized glycolysis and glucose consumption. Silencing PCK1 or inhibiting its enzymatic activity slowed the growth of TRCs in vitro and impeded tumorigenesis in vivo. Overall, our work unveiled metabolic features of TRCs in melanoma that have implications for targeting a unique aspect of this disease.

Blockade of IDO-kynurenine-AhR metabolic circuitry abrogates IFN-γ-induced immunologic dormancy of tumor-repopulating cells.

Interactions with the immune system may lead tumorigenic cells into dormancy. However, the underlying molecular mechanism is poorly understood. Using a 3D fibrin gel model, we show that IFN-γ induces tumour-repopulating cells (TRCs) to enter dormancy through an indolamine 2,3-dioxygenase 1 (IDO1)-kynurenine (Kyn)-aryl hydrocarbon receptor (AhR)-p27 dependent pathway. Mechanistically, IFN-γ signalling triggers differentiated tumour cell apoptosis via STAT1; however, when IDO1 and AhR are highly expressed as in TRCs, IFN-γ results in IDO1/AhR-dependent p27 induction that prevents STAT1 signalling, thus suppressing the process of cell death and activating the dormancy program. Blocking the IDO/AhR metabolic circuitry not only abrogates IFN-γ-induced dormancy but also results in enhanced repression of tumour growth by IFN-γ-induced apoptosis of TRCs both in vitro and in vivo. These data present a previously unrecognized mechanism of inducing TRC dormancy by IFN-γ, suggesting a potential effective cancer immunotherapeutic modality through the combination of IFN-γ and IDO/AhR inhibitors.

Reversing drug resistance of soft tumor-repopulating cells by tumor cell-derived chemotherapeutic microparticles

Developing novel approaches to reverse the drug resistance of tumor-repopulating cells (TRCs) or stem cell-like cancer cells is an urgent clinical need to improve outcomes of cancer patients. Here we show an innovative approach that reverses drug resistance of TRCs using tumor cell-derived microparticles (T-MPs) containing anti-tumor drugs. TRCs, by virtue of being more deformable than differentiated cancer cells, preferentially take up T-MPs that release anti-tumor drugs after entering cells, which in turn lead to death of TRCs. The underlying mechanisms include interfering with drug efflux and promoting nuclear entry of the drugs. Our findings demonstrate the importance of tumor cell softness in uptake of T-MPs and effectiveness of a novel approach in reversing drug resistance of TRCs with promising clinical applications.

Tumor cell-derived microparticles polarize M2 tumor-associated macrophages for tumor progression.

ABSTRACT Despite identification of macrophages in tumors (tumor-associated macrophages, TAM) as potential targets for cancer therapy, the origin and function of TAM in the context of malignancy remain poorly characterized. Here, we show that microparticles (MPs), as a by-product, released by tumor cells act as a general mechanism to mediate M2 polarization of TAM. Taking up tumor MPs by macrophages is a very efficient process, which in turn results in the polarization of macrophages into M2 type, not only leading to promoting tumor growth and metastasis but also facilitating cancer stem cell development. Moreover, we demonstrate that the underlying mechanism involves the activation of the cGAS/STING/TBK1/STAT6 pathway by tumor MPs. Finally, in addition to murine tumor MPs, we show that human counterparts also possess consistent effect on human M2 polarization. These findings provide new insights into a critical role of tumor MPs in remodeling of tumor microenvironment and better understanding of the communications between tumors and macrophages.

Downregulation of PCK2 remodels tricarboxylic acid cycle in tumor-repopulating cells of melanoma

For cancer cells to proliferate, a balance must be built between biomass-forming, glucose-metabolized intermediates and ATP production. How intrinsic glucose carbon flow regulates this balance remains unclear. Here we show that mitochondrial phosphoenolpyruvate carboxykinase (PCK2), the hub molecule linking tricarboxylic acid (TCA) cycle, glycolysis and gluconeogenesis by conversion of mitochondrial oxaloacetate (OAA) to phosphoenolpyruvate, regulates glucose carbon flow direction in stem-like cells that repopulate tumors (tumor-repopulating cells (TRCs)). PCK2 downregulation accelerated biosynthesis and transportation of citrate from mitochondria to the cytosol, leading to cytosolic glucose carbon flow via OAA–malate–pyruvate and acetyl-CoA–fatty acid pathways in TRCs. On the other hand, downregulating PCK2 hindered fumarate carbon flows in TCA cycle, leading to attenuated oxidative phosphorylation. In pathological terms, PCK2 overexpression slowed TRC growth in vitro and impeded tumorigenesis in vivo. Overall, our work unveiled unexpected glucose carbon flows of TRCs in melanoma that have implications for targeting metabolic aspects of melanoma.

Circulating tumor microparticles promote lung metastasis by reprogramming inflammatory and mechanical niches via a macrophage-dependent pathway

Lung macrophages are induced by tumor-derived microparticles to drive development of metastasis via mediators that promote immune, inflammatory, and mechanical reprogramming of the microenvironment. Elucidation of this pathway has implications for therapeutic prevention or treatment of lung metastasis. Despite the frequency of lung metastasis and its associated mortality, the mechanisms behind metastatic tumor cell survival and colonization in the lungs remain elusive. Here, we show that tumor cell–released microparticles (T-MPs) from the primary tumor site play a critical role in the metastatic process. The T-MPs remodeled the lung parenchyma via a macrophage-dependent pathway to create an altered inflammatory and mechanical response to tumor cell invasion. Mechanistically, we show that circulating T-MPs readily enter the lung parenchyma where they are taken up by local macrophages and induce CCL2 production. CCL2 recruits CD11b+Ly6Chigh inflammatory monocytes to the lungs where they mature into F4/80+CD11b+Ly6C− macrophages that not only produce IL6 but also trigger fibrin deposition. IL6 and the deposited fibrin facilitate the survival and growth of tumor-repopulating cells in the lungs by providing chemical and mechanical signals, respectively, thus setting the stage for lung metastasis. These data illustrate that T-MPs reprogram the lung microenvironment promoting metastasis. Cancer Immunol Res; 6(9); 1046–56. ©2018 AACR.

Chemotherapeutic tumor microparticles combining low-dose irradiation reprogram tumor-promoting macrophages through a tumor-repopulating cell-curtailing pathway

ABSTRACT Stem cell-like tumor-repopulating cells (TRCs) have a critical role in establishing a tumor immunosuppressive microenvironment. However, means to enhance antitumor immunity by disrupting TRCs are absent. Our previous studies have shown that tumor cell-derived microparticles (T-MPs) preferentially abrogate TRCs by delivering antitumor drugs into nuclei of TRCs. Here, we show that low dose irradiation (LDI) enhances the effect of cisplatin-packaging T-MPs (Cis-MPs) on TRCs, leading to inhibiting tumor growth in different tumor models. This antitumor effect is not due to the direct killing of tumor cells but is T cell-dependent and relies on macrophages for their efficacy. The underlying mechanism is involved in therapeutic reprograming macrophages from tumor-promotion to tumor-inhibition by disrupting TRCs and curtailing their vicious education on macrophages. These findings provide a novel strategy to reset macrophage polarization and confer their function more like M1 than M2 types with highly promising potential clinical applications.