thiohydantoins and methyl-thiohydantoin-tryptophan

The enzyme indoleamine 2,3-dioxygenase (IDO) regulates immune responses through the capacity to degrade the essential amino acid tryptophan into kynurenine and other downstream metabolites that suppress effector T-cell function and favour the differentiation of regulatory T cells. Considerable experimental evidence indicates that IDO can be expressed by dendritic cells, by tumour cells or by surrounding stromal cells, either within proximity of the tumour or at distal sites. Recent advances in the biochemistry of IDO and in our understanding of the biological relevance of IDO-mediated tryptophan consumption to the establishment of dominant immune tolerance to cancer will be summarised and discussed. Within the wider context of cancer immunotherapy, this Review also delineates how IDO could be exploited as a molecular target for therapeutic intervention in order to boost anti-cancer immunity.

Topics: Animals; Antigens, CD; Binding Sites; CTLA-4 Antigen; Cyclooxygenase 2; Enzyme Inhibitors; Humans; Immune Tolerance; Indoleamine-Pyrrole 2,3,-Dioxygenase; Indoles; Interferon-gamma; Interleukin-2 Receptor alpha Subunit; Neoplasms; Thiohydantoins

Renal cell carcinoma (RCC) is increasing in incidence, and a complete cure remains elusive. While immune-checkpoint antibodies are promising, interferon-based immunotherapy has been disappointing. Tryptophan metabolism, which produces immunosuppressive metabolites, is enhanced in RCC. Here we show indolamine-2,3-dioxygenase-1 (IDO1) expression, a kynurenine pathway enzyme, is increased not only in tumor cells but also in the microenvironment of human RCC compared to normal kidney tissues. Neither kynurenine metabolites nor IDO inhibitors affected the survival or proliferation of human RCC or murine renal cell adenocarcinoma (RENCA) cells in vitro. However, interferon-gamma (IFNγ) induced high levels of IDO1 in both RCC and RENCA cells, concomitant with enhanced kynurenine levels in conditioned media. Induction of IDO1 by IFNα was weaker than by IFNγ. Neither the IDO1 inhibitor methyl-thiohydantoin-DL-tryptophan (MTH-trp) nor IFNα alone inhibited RENCA tumor growth, however the combination of MTH-trp and IFNα reduced tumor growth compared to IFNα. Thus, the failure of IFNα therapy for human RCC is likely due to its inability to overcome the immunosuppressive environment created by increased IDO1. Based on our data, and given that IDO inhibitors are already in clinical trials for other malignancies, IFNα therapy with an IDO inhibitor should be revisited for RCC.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Carcinoma, Renal Cell; Cell Line, Tumor; Humans; Indoleamine-Pyrrole 2,3,-Dioxygenase; Indoles; Interferon-alpha; Kidney Neoplasms; Mice; Mice, Inbred BALB C; Thiohydantoins; Tryptophan

Indoleamine 2,3-dioxygenase (IDO) is a tryptophan-catabolizing enzyme with immunoregulatory properties in cancer. By focusing on multiple myeloma cells and its microenvironment as potential sources of IDO, we aimed to delineate its influence on myeloma cell growth and survival and examine effector mechanisms.. IDO expression was assessed in myeloma cells and in a coculture system with mesenchymal stromal cells (MSCs), including prior cytokine priming to induce IDO in MSCs. IDO expression was correlated with induction of apoptosis in myeloma cells and coupled with tryptophan depletion as well as rescue using IDO inhibitors.. We report low levels of expression of IDO in myeloma cell lines (MMCLs) and primary myeloma cells (MMCs), despite priming with interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), or hepatocyte growth factor (HGF). In MSCs, however, IDO could be functionally induced by IFN-γ, mediating apoptosis in myeloma cells following coculture. Addition of IDO-specific inhibitors, as well as addition of tryptophan, was shown to abrogate these effects.. IDO is expressed in primary MMCs to a low degree and is unlikely to play a direct major role in vivo in dampening antitumor immunity. However, cytokine stimulation of MSCs specifically induced IDO, which mediated a marked sensitivity of proximal myeloma cells to tryptophan depletion in the microenvironment, suggesting that selective measures to regulate its availability could be a useful strategy to achieve myeloma growth inhibition and apoptosis.

Topics: Apoptosis; Cell Line, Tumor; Cell Proliferation; Cells, Cultured; Coculture Techniques; Gene Expression Regulation, Neoplastic; Hepatocyte Growth Factor; Humans; Indoleamine-Pyrrole 2,3,-Dioxygenase; Indoles; Interferon-gamma; Mesenchymal Stem Cells; Multiple Myeloma; Reverse Transcriptase Polymerase Chain Reaction; Spectrophotometry, Ultraviolet; Thiohydantoins; Tryptophan; Tumor Cells, Cultured; Tumor Microenvironment; Tumor Necrosis Factor-alpha

The role of the tryptophan-metabolizing enzyme indoleamine 2,3-dioxygenase (IDO) in down-regulating human alloresponses has recently been controversially debated. We here demonstrate that human monocyte-derived dendritic cells (mDCs) can be endowed with sustained IDO competence in vitro by 48-hour activation with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma). IFN-gamma also amplified proinflammatory cytokine secretion during activation. Yet, on reculture after activation cytokine production ceased, whereas IDO enzymatic activity continued. Manipulation of tryptophan metabolism did not affect proinflammatory cytokine release, suggesting that IFN-gamma triggers IDO activity and proinflammatory cytokine release as distinct cellular programs. IDO-competent DCs down-regulated allogeneic T-cell responses, but this IDO-mediated effect was overcome by slightly modifying cell culture conditions. Nevertheless, the CD4(+)CD25(+) T-cell fraction stimulated by IDO-competent DCs displayed substantial suppressor activity. This suppressive activity (1) required allogeneic stimulation for its induction, (2) affected third-party T cells, and (3) was reduced by the IDO inhibitor methyl-thiohydantoin-tryptophan. It became also manifest when DC/T-cell cocultures were initiated with naive (CD4(+)CD25(-)CD45RA(+)) T cells, indicating the differentiation of adaptive regulatory T cells. Together, these findings suggest that IFN-gamma triggered IDO competence in human mDCs constitutes a critical factor for endowing allogeneic T cells with regulatory activity.

Topics: Cell Differentiation; Cells, Cultured; Coculture Techniques; Dendritic Cells; Humans; Indoleamine-Pyrrole 2,3,-Dioxygenase; Indoles; Inflammation Mediators; Interferon-gamma; Lipopolysaccharides; Monocytes; T-Lymphocytes, Regulatory; Thiohydantoins

Immune escape is a crucial feature of cancer progression about which little is known. Elevation of the immunomodulatory enzyme indoleamine 2,3-dioxygenase (IDO) in tumor cells can facilitate immune escape. Not known is how IDO becomes elevated or whether IDO inhibitors will be useful for cancer treatment. Here we show that IDO is under genetic control of Bin1, which is attenuated in many human malignancies. Mouse knockout studies indicate that Bin1 loss elevates the STAT1- and NF-kappaB-dependent expression of IDO, driving escape of oncogenically transformed cells from T cell-dependent antitumor immunity. In MMTV-Neu mice, an established breast cancer model, we show that small-molecule inhibitors of IDO cooperate with cytotoxic agents to elicit regression of established tumors refractory to single-agent therapy. Our findings suggest that Bin1 loss promotes immune escape in cancer by deregulating IDO and that IDO inhibitors may improve responses to cancer chemotherapy.

Topics: Adaptor Proteins, Signal Transducing; Animals; Cell Transformation, Neoplastic; DNA-Binding Proteins; Drug Synergism; Enzyme Inhibitors; Indoleamine-Pyrrole 2,3,-Dioxygenase; Indoles; Interferon-gamma; Mammary Neoplasms, Experimental; Mice; Molecular Sequence Data; Nerve Tissue Proteins; NF-kappa B; Paclitaxel; Rats; STAT1 Transcription Factor; Thiohydantoins; Trans-Activators; Tryptophan Oxygenase; Tumor Escape; Tumor Suppressor Proteins