Serine protease modulation of Dependence Receptors and EMT protein expression

Enzymatic activity of HIV-1 protease defines migration of tumor cells in vitro and enhances their metastatic activity in vivo

Overexpression of aspartic proteases, as cathepsin D, is an independent marker of poor prognosis in breast cancer, correlated with the incidence of clinical metastasis. We aimed to find if HIV-1 aspartic protease (PR) can play a similar role. Murine adenocarcinoma 4T1luc2 cells were transduced with lentivirus encoding inactivated drug-resistant PR, generating subclones PR20.1 and PR20.2. Subclones were assessed for production of reactive oxygen species (ROS), expression of epithelial-mesenchymal transition (EMT) factors, and in vitro migratory activity in the presence or absence of antioxidant N-acetyl cysteine and protease inhibitors. Tumorigenic activity was evaluated by implanting cells into BALB/c mice and following tumor growth by calipering and bioluminescence imaging in vivo, and metastases, by organ imaging ex vivo. Both subclones expressed PR mRNA, and PR20.2, also the protein detected by Western blotting. PR did not induce production of ROS, and had no direct effect on cell migration rate, however, treatment with inhibitors of drug-resistant PR suppressed the migratory activity of both subclones. Furthermore, expression of N-cadherin and Vimentin in PR20.2 cells and their migration were enhanced by antioxidant treatment. Sensitivity of in vitro migration to protease inhibitors and to antioxidant, known to restore PR activity, related the effects to the enzymatic activity of PR. In vivo, PR20.2 cells demonstrated higher tumorigenic and metastatic activity than PR20.1 or parental cells. Thus, HIV-1 protease expressed in breast cancer cells determines their migration in vitro and metastatic activity in vivo. This effect may aggravate clinical course of cancers in people living with HIV-1.

The Complex World of Kynurenic Acid: Reflections on Biological Issues and Therapeutic Strategy

It has been unequivocally established that kynurenic acid has a number of actions in a variety of cells and tissues, raising, in principle, the possibility of targeting its generation, metabolism or sites of action to manipulate those effects to a beneficial therapeutic end. However, many basic aspects of the biology of kynurenic acid remain unclear, potentially leading to some confusion and misinterpretations of data. They include questions of the source, generation, targets, enzyme expression, endogenous concentrations and sites of action. This essay is intended to raise and discuss many of these aspects as a source of reference for more balanced discussion. Those issues are followed by examples of situations in which modulating and correcting kynurenic acid production or activity could bring significant therapeutic benefit, including neurological and psychiatric conditions, inflammatory diseases and cell protection. More information is required to obtain a clear overall view of the pharmacological environment relevant to kynurenic acid, especially with respect to the active concentrations of kynurenine metabolites in vivo and changed levels in disease. The data and ideas presented here should permit a greater confidence in appreciating the sites of action and interaction of kynurenic acid under different local conditions and pathologies, enhancing our understanding of kynurenic acid itself and the many clinical conditions in which manipulating its pharmacology could be of clinical value.

Targeting RGMb interactions: Discovery and preclinical characterization of potent anti-RGMb antibodies blocking multiple ligand bindings

Therapeutic efficacy with durable responses has been demonstrated with several antibody drugs that block key immune checkpoint receptors, including PD-1, PD-L1, and CTLA-4. Despite the success of these drugs, a substantial proportion of patients do not benefit. Targeting multiple inhibitory pathways simultaneously to augment anti-tumor immunity has proven to be a promising approach. The emergence of Repulsive Guidance Molecule b (RGMb), a ligand for PD-L2, as a novel co-inhibitory pathway in T cells, together with its regulation by the gut microbiome, encouraged the discovery and development of fully human anti-RGMb antibodies. Here, we describe phage display-derived monoclonal antibodies (mAbs) 2C11 and 5C10 that bind human RGMb with high affinities of 1.4 nM and 0.72 nM, respectively. Both mAbs 2C11 and 5C10 potently inhibited RGMb interaction with PD-L2. MAb 2C11 effectively inhibited RGMb interaction with bone morphogenetic proteins 2 and 4 (BMP2-4), while leaving RGMb interaction with Neogenin 1 (Neo1) unaffected. Conversely, mAb 5C10 disrupted RGMb interaction with Neo1 while maintaining RGMb binding to BMP2-4. These findings map the 2C11 epitope at the membrane-distal N-terminal region of RGMb, which coincides with both PD-L2- and BMP2-4-binding sites. The PD-L2 binding interface is likely positioned between RGMb's N-terminal BMP-binding and C-terminal Neo1-binding regions. The in vivo activity of mAb 2C11 in combination with anti-PD-1 or anti-PD-L1 was tested in MC38 and B16-OVA cancer models and demonstrated synergistic effects by significantly enhancing anti-tumor responses. These properties make mAb 2C11 a promising candidate for therapeutic use to overcome immune checkpoint inhibitor resistances, warranting further exploration in clinical settings.

Interactions of IDO and the Kynurenine Pathway with Cell Transduction Systems and Metabolism at the Inflammation-Cancer Interface

The mechanisms underlying a relationship between inflammation and cancer are unclear, but much emphasis has been placed on the role of tryptophan metabolism to kynurenine and downstream metabolites, as these make a substantial contribution to the regulation of immune tolerance and susceptibility to cancer. The proposed link is supported by the induction of tryptophan metabolism by indoleamine-2,3-dioxygenase (IDO) or tryptophan-2,3-dioxygenase (TDO), in response to injury, infection or stress. This review will summarize the kynurenine pathway and will then focus on the bi-directional interactions with other transduction pathways and cancer-related factors. The kynurenine pathway can interact with and modify activity in many other transduction systems, potentially generating an extended web of effects other than the direct effects of kynurenine and its metabolites. Conversely, the pharmacological targeting of those other systems could greatly enhance the efficacy of changes in the kynurenine pathway. Indeed, manipulating those interacting pathways could affect inflammatory status and tumor development indirectly via the kynurenine pathway, while pharmacological modulation of the kynurenine pathway could indirectly influence anti-cancer protection. While current efforts are progressing to account for the failure of selective IDO1 inhibitors to inhibit tumor growth and to devise means of circumventing the issue, it is clear that there are wider factors involving the relationship between kynurenines and cancer that merit detailed consideration as alternative drug targets.

Preparation of Nereid oligopeptide and investigation of the mechanism underlying the induction of apoptosis in human lung cancer H1299 cells

In the present study, oligopeptides from Nereid (Perinereis aibuhitensis) were prepared via enzymatic hydrolysis, and the mechanism underlying the induction of apoptosis in H1299 cells was investigated. According to the analysis of the inhibition rate on proliferation, alkaline protease demonstrated the best enzymatic efficiency. The optimal conditions for hydrolysis were as follows: 50°C and pH 10 for 6 h; a material-to-liquid ratio of 1:1 (g/ml); and addition of 400 U/g enzyme. The hydrolysates were purified using ultrafiltration, anion chromatography, gel filtration chromatography, and high-performance liquid chromatography. The Nereid oligopeptide (NOP), with a molecular weight of 841 kDa and an amino acid sequence of glutamine-isoleucine-asparagine-glutamine-histidine-leucine, was obtained. NOP inhibited the proliferation of H1299 cells in a time- and dose-dependent manner. Morphological changes and apoptosis were also induced by NOP in H1299 cells. The western blot analysis revealed that the B-cell lymphoma 2/Bcl-2 associated X (Bcl-2/Bax) ratio was reduced by 24.7% in the NOP treatment group compared with the control group. The relative expression levels of cleaved caspase-9 (cleaved-CASP9) and cleaved caspase-3 (cleaved-CASP3) in the NOP treatment group were 2.55- and 1.71-fold higher than those measured in the control group, respectively. These results suggested that NOP exerts antitumor effects by influencing the proliferation and apoptosis of H1299 cells.

Induction of IDO1 and Kynurenine by Serine Proteases Subtilisin, Prostate Specific Antigen, CD26 and HtrA: A New Form of Immunosuppression?

Several serine proteases have been linked to autoimmune disorders and tumour initiation although the mechanisms are not fully understood. Activation of the kynurenine pathway enzyme indoleamine-2,3-dioxygenase (IDO1) modulates cellular activity in the brain, tolerogenesis in the immune system and is a major checkpoint in cancer development. We now report that IDO1 mRNA and IDO1 protein expression (generating kynurenine) are induced in human monocyte-derived macrophages by several chymotryptic serine proteases with direct links to tumorigenesis, including Prostate Specific Antigen (PSA), CD26 (Dipeptidyl-peptidase-4, CD26/DPP-4), High Temperature Requirement protein-A (HtrA), and the bacterial virulence factor subtilisin. These proteases also induce expression of the pro-inflammatory cytokine genes IL1B and IL6. Other serine proteases tested: bacterial glu-C endopeptidase and mammalian Pro-protein Convertase Subtilase-Kexin-3 (PCSK3, furin), urokinase plasminogen activator (uPA), cathepsin G or neutrophil elastase, did not induce IDO1, indicating that the reported effects are not a general property of all serine proteases. The results represent a novel mechanism of activating immunosuppressive IDO1 and inducing kynurenine generation which, together with the production of inflammatory cytokines, would contribute to tumour initiation and progression, providing a new target for drug development. In addition, the proteasomal S20 serine protease inhibitor carfilzomib, used in the treatment of myeloma, prevented the induction of IDO1 and cytokine gene expression, potentially contributing to its clinical anti-cancer activity.

Dependence and Guidance Receptors-DCC and Neogenin-In Partial EMT and the Actions of Serine Proteases

The Epithelial-Mesenchymal Transition (EMT) is an important concept in understanding the processes of oncogenesis, especially with respect to the relationship between cell proliferation and metastatic properties such as spontaneous cell motility, chemotaxic migration and tissue invasion. EMT is now recognized as a more complex phenomenon than an all-or-nothing event, in which different components of the EMT may have distinct roles in the physio-pathological regulation of cell function and which may in turn depend on differential interactions with cell constituents and metabolic products. This mini-review summarizes recent work on the induction of cancer properties in parallel with the presence of EMT activities in the presence of serine proteases, with the focus on those tumor suppressors known as "dependence" receptors such as neogenin and Deleted in Colorectal Cancer (DCC). It is concluded that various forms of partial EMT should be given more detailed investigation and consideration as the results could have valuable implications for the development of disease-specific and patient-specific therapies.

Down-regulation of vimentin by triorganotin isothiocyanates-nuclear retinoid X receptor agonists: A proteomic approach

An attempt has been made to delineate the role of natural and synthetic retinoid receptor ligands on vimentin expression in the human triple-negative breast cancer cells. The effects of currently synthesized triorganotin derivatives of the general formula R₃SnX (R is butyl or phenyl, X is isothiocyanate), which are considered RXR ligands, were investigated in the human MDA-MB-231 breast cancer cell line. Studies were evaluated in the presence and absence of all-trans retinoic acid (ATRA), a natural RAR ligand. Vimentin represents the major protein associated with epithelial-mesenchymal transition (EMT), an essential process when the primary tumour transforms into a malignant one. mRNA and proteomic data obtained in this study, based on the PDQuest software protein evaluation and further quantification of proteins by iTRAQ analysis, suggest that vimentin was significantly reduced in the combination of RAR ligand and RXR ligand treatment. Both tested triorganotin compounds showed similarly reduced expression of vimentin, but tributyltin isothiocyanate (TBT-ITC) proved to be more effective than triphenyltin isothiocyanate (TPT-ITC). Furthermore, the effect of natural (9cRA) and synthetic RXR ligands, both chloride and isothiocyanate derivatives, on vimentin expression was compared.