Indoleamine dioxygenase and tryptophan dioxygenase activities are regulated through control of cell heme allocation by nitric oxide

Discovery and binding mode of small molecule inhibitors of the apo form of human TDO2

Tryptophan-2,3-dioxygenase (TDO2) and indoleamine-2,3-dioxygenase (IDO1) are structurally distinct heme enzymes that catalyze the conversion of L-tryptophan to N-formyl-kynurenine, and play important roles in metabolism, inflammation, and tumor immune surveillance. The enzymes can adopt an inactive, heme-free (apo) state or an active, heme-containing (holo) state, with the balance between them varying dynamically according to biological conditions. Inhibitors of holo-TDO2 are known but, despite several advantages of the heme-free state as a drug target, no inhibitors of apo-TDO2 have been reported. We describe the discovery of the first apo-TDO2 binding inhibitors, to our knowledge, and their inhibition of cellular TDO2 activity at low nanomolar concentrations. The crystal structure of a potent, small molecule inhibitor bound to apo-TDO2 reveals its detailed binding interactions within the large, hydrophobic heme binding pocket of the active site.

Secondary Transcriptomic Analysis of Triple-Negative Breast Cancer Reveals Reliable Universal and Subtype-Specific Mechanistic Markers

Background/Objectives: Breast cancer is diagnosed in 2.3 million women each year and kills 685,000 (~30% of patients) worldwide. The prognosis for many breast cancer subtypes has improved due to treatments targeting the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). In contrast, patients with triple-negative breast cancer (TNBC) tumors, which lack all three commonly targeted membrane markers, more frequently relapse and have lower survival rates due to a lack of tumor-selective TNBC treatments. We aim to investigate TNBC mechanistic markers that could be targeted for treatment. Methods: We performed a secondary TNBC analysis of 196 samples across 10 publicly available bulk RNA-sequencing studies to better understand the molecular mechanism(s) of disease and predict robust mechanistic markers that could be used to improve the mechanistic understanding of and diagnostic capabilities for TNBC. Results: Our analysis identified ~12,500 significant differentially expressed genes (FDR-adjusted p-value < 0.05), including KIF14 and ELMOD3, and two significantly modulated pathways. Additionally, our novel findings include highly accurate mechanistic markers identified using machine learning methods, including CIDEC (97.1% accuracy alone), CD300LG, ASPM, and RGS1 (98.9% combined accuracy), as well as TNBC subtype-differentiating mechanistic markers, including the targets PDE3B, CFD, IFNG, and ADM, which have associated therapeutics that can potentially be repurposed to improve treatment options. We then experimentally and computationally validated a subset of these findings. Conclusions: The results of our analyses can be used to better understand the mechanism(s) of disease and contribute to the development of improved diagnostics and/or treatments for TNBC.

Hypoxia-Targeted Immunotherapy with PD-1 Blockade in Head and Neck Cancer

Intratumoral hypoxia is associated with tumor progression, aggressiveness, and therapeutic resistance in several cancers. Hypoxia causes cancer cells to experience replication stress, thereby activating DNA damage and repair pathways. MutT homologue-1 (MTH1, also known as NUDT1), a member of the Nudix family, maintains the genomic integrity and viability of tumor cells in the hypoxic tumor microenvironment. Although hypoxia is associated with poor prognosis and can cause therapeutic resistance by regulating the microenvironment, it has not been considered a treatable target in cancer. This study aimed to investigate whether hypoxia-induced MTH1 is a useful target for immunotherapy and whether hypoxic conditions influence the antitumor activity of immune cells. Our results showed that MTH1 expression was elevated under hypoxic conditions in head and neck cancer cell lines. Furthermore, we identified a novel MTH1-targeting epitope peptide that can activate peptide-specific CD4+ helper T cells with cytotoxic activity. The proliferation and cytotoxic activity of T cells were maintained under hypoxic conditions, and PD-1 blockade further augmented the cytotoxicity. These results indicate that MTH1-targeted immunotherapy combined with checkpoint blockade can be an effective strategy for the treatment of hypoxic tumors.

PAK4 Is Involved in the Stabilization of PD-L1 and the Resistance to Doxorubicin in Osteosarcoma and Predicts the Survival of Diagnosed Patients

PAK4 and PD-L1 have been suggested as novel therapeutic targets in human cancers. Moreover, PAK4 has been suggested to be a molecule closely related to the immune evasion of cancers. Therefore, this study evaluated the roles of PAK4 and PD-L1 in the progression of osteosarcomas in 32 osteosarcomas and osteosarcoma cells. In human osteosarcomas, immunohistochemical positivity for the expression of PAK4 (overall survival, p = 0.028) and PD-L1 (relapse-free survival, p = 0.002) were independent indicators for the survival of patients in a multivariate analysis. In osteosarcoma cells, the overexpression of PAK4 increased proliferation and invasiveness, while the knockdown of PAK4 suppressed proliferation and invasiveness. The expression of PAK4 was associated with the expression of the molecules related to cell cycle regulation, invasion, and apoptosis. PAK4 was involved in resistance to apoptosis under a treatment regime with doxorubicin for osteosarcoma. In U2OS cells, PAK4 was involved in the stabilization of PD-L1 from ubiquitin-mediated proteasomal degradation and the in vivo infiltration of immune cells such as regulatory T cells and PD1-, CD4-, and CD8-positive cells in mice tumors. In conclusion, this study suggests that PAK4 is involved in the progression of osteosarcoma by promoting proliferation, invasion, and resistance to doxorubicin and stabilized PD-L1 from proteasomal degradation.

Prognostic Role of Clinicopathological Characteristics and Serum Markers in Metastatic Melanoma Patients Treated with BRAF and MEK Inhibitors

Prognostic studies can provide important information about disease biology and improve the use of biomarkers to optimize treatment decisions.

METHODS

A total of 199 patients with advanced melanoma treated with BRAF + MEK inhibitors were included in our single-center retrospective study. We analyzed the risk of progression and death using multivariate Cox proportional hazard models. The predictive effect of prognostic factors on progression-free survival (PFS) was evaluated in ROC analysis.

RESULTS

We found that primary tumor localization, Clark level, pT category, baseline M stage and baseline serum S100B are independent and significant prognostic factors for PFS. The discriminative power of the combination of these factors was excellent for predicting 18 month PFS (AUC 0.822 [95% CI 0.727; 0.916], p < 0.001). Primary tumor localization on the extremities, Clark level V, baseline M1c stage or M1d stage, and elevated baseline serum S100B and LDH levels were independently and significantly associated with unfavorable overall survival (OS).

CONCLUSION

Baseline M stage and serum S100B appear to be independent prognostic factors for both PFS and OS in melanoma patients treated with BRAF + MEK inhibitors. We newly identified significant and independent prognostic effects of primary tumor localization and Clark level on survival that warrant further investigation.

Adverse Events in Anti-PD-1-Treated Adjuvant and First-Line Advanced Melanoma Patients

Introduction: The difference in incidence and severity of anti-PD-1 therapy-related adverse events (irAEs) between adjuvant and advanced treated melanoma patients remains unclear, as no head-to-head studies have compared these groups. Methods: This multi-center cohort study analyzed melanoma patients treated with anti-PD-1 in adjuvant or advanced settings between 2015 and 2021. Comorbidities and ECOG performance status were assessed before treatment, and grade III-IV irAEs were monitored during treatment. Univariate and multivariate regression analyses were conducted to identify factors associated with irAE development. Results: A total of 1465 advanced melanoma patients and 908 resected melanoma patients received anti-PD-1 therapy. Adjuvant-treated patients were younger, with a median age of 63 years compared to 69 years in the advanced group (p < 0.01), and had a better ECOG performance status (p < 0.01). Comorbidities were seen more frequently in advanced melanoma patients than in those receiving adjuvant treatment, 76% versus 68% (p < 0.01). Grade III-IV irAEs occurred in 214 (15%) advanced treated patients and in 119 (13%) adjuvant-treated patients. Multivariate analysis showed an increased risk of severe irAE development with the presence of any comorbidity (adjusted OR 1.22, 95% CI 1.02-1.44) and ECOG status greater than 1 (adjusted OR 2.00, 95% CI 1.20-3.32). Adjuvant therapy was not associated with an increased risk of irAE development compared to advanced treatment (adjusted OR 0.95, 95% CI 0.74-1.21) after correcting for comorbidities and ECOG performance score. Anti-PD-1 therapy was halted due to toxicity (any grade irAE) more often in the adjuvant setting than in the advanced setting, 20% versus 15% (p < 0.01). Conclusions: Higher ECOG performance status and presence of any comorbidity were independently associated with an increased risk of Grade III-IV irAE in adjuvant and advanced treated melanoma patients. Patients treated in the adjuvant setting did not have an increased risk of developing severe irAEs compared to advanced melanoma patients. These findings are of clinical significance in consulting patients for adjuvant anti-PD-1 treatment.

Visualizing mitochondrial heme flow through GAPDH in living cells and its regulation by NO

Iron protoporphyrin IX (heme) is a redox-active cofactor that is bound in mammalian cells by GAPDH and allocated by a process influenced by physiologic levels of NO. This impacts the activity of many heme proteins including indoleamine dioxygenase-1 (IDO1), a redox enzyme involved in immune response and tumor growth. To gain further understanding we created a tetra-Cys human GAPDH reporter construct (TC-hGAPDH) which after labeling could indicate its heme binding by fluorescence quenching. When purified or expressed in a human cell line, TC-hGAPDH had properties like native GAPDH and heme binding quenched its fluorescence by 45-65%, allowing it to report on GAPDH binding of mitochondrially-generated heme in live cells in real time. In cells with active mitochondrial heme synthesis, low-level NO exposure increased heme allocation to IDO1 while keeping the TC-hGAPDH heme level constant due to replenishment by mitochondria. When mitochondrial heme synthesis was blocked, low NO caused a near complete transfer of the existing heme in TC-hGAPDH to IDO1 in a process that required IDO1 be able to bind the heme and have an active hsp90 present. Higher NO exposure had the opposite effect and caused IDO1 heme to transfer back to TC-hGAPDH. This demonstrated: (i) flow of mitochondrial heme through GAPDH is tightly coupled to target delivery, (ii) NO up- or down-regulates IDO1 activity by promoting a conserved heme exchange with GAPDH that goes in either direction according to the NO exposure level. The ability to drive a concentration-dependent, reversible protein heme exchange is unprecedented and reveals a new role for NO in biology.

Heme metabolism in nonerythroid cells

Heme is an iron-containing prosthetic group necessary for the function of several proteins termed "hemoproteins." Erythrocytes contain most of the body's heme in the form of hemoglobin and contain high concentrations of free heme. In nonerythroid cells, where cytosolic heme concentrations are 2 to 3 orders of magnitude lower, heme plays an essential and often overlooked role in a variety of cellular processes. Indeed, hemoproteins are found in almost every subcellular compartment and are integral in cellular operations such as oxidative phosphorylation, amino acid metabolism, xenobiotic metabolism, and transcriptional regulation. Growing evidence reveals the participation of heme in dynamic processes such as circadian rhythms, NO signaling, and the modulation of enzyme activity. This dynamic view of heme biology uncovers exciting possibilities as to how hemoproteins may participate in a range of physiologic systems. Here, we discuss how heme is regulated at the level of its synthesis, availability, redox state, transport, and degradation and highlight the implications for cellular function and whole organism physiology.

Visualizing Mitochondrial Heme Flow through GAPDH to Targets in Living Cells and its Regulation by NO

Iron protoporphyrin IX (heme) is an essential cofactor that is chaperoned in mammalian cells by GAPDH in a process regulated by NO. To gain further understanding we generated a tetra-Cys human GAPDH reporter construct (TC-hGAPDH) which after being expressed and labeled with fluorescent FlAsH reagent could indicate heme binding by fluorescence quenching. When purified or expressed in HEK293T mammalian cells, FlAsH-labeled TC-hGAPDH displayed physical, catalytic, and heme binding properties like native GAPDH and its heme binding (2 mol per tetramer) quenched its fluorescence by 45-65%. In live HEK293T cells we could visualize TC-hGAPDH binding mitochondrially-generated heme and releasing it to the hemeprotein target IDO1 by monitoring cell fluorescence in real time. In cells with active mitochondrial heme synthesis, a low-level NO exposure increased heme allocation into IDO1 while keeping steady the level of heme-bound TC-hGAPDH. When mitochondrial heme synthesis was blocked at the time of NO exposure, low NO caused cells to reallocate existing heme from TC-hGAPDH to IDO1 by a mechanism requiring IDO1 be present and able to bind heme. Higher NO exposure had an opposite effect and caused cells to reallocate existing heme from IDO1 to TC-hGAPDH. Thus, with TC-hGAPDH we could follow mitochondrial heme as it travelled onto and through GAPDH to a downstream target (IDO1) in living cells, and to learn that NO acted at or downstream from the GAPDH heme complex to promote a heme reallocation in either direction depending on the level of NO exposure.

Association between AHR Expression and Immune Dysregulation in Pancreatic Ductal Adenocarcinoma: Insights from Comprehensive Immune Profiling of Peripheral Blood Mononuclear Cells

Pancreatic cancer, particularly pancreatic ductal adenocarcinoma (PDAC), has an immune suppressive environment that allows tumour cells to evade the immune system. The aryl-hydrocarbon receptor (AHR) is a transcription factor that can be activated by certain exo/endo ligands, including kynurenine (KYN) and other tryptophan metabolites. Once activated, AHR regulates the expression of various genes involved in immune responses and inflammation. Previous studies have shown that AHR activation in PDAC can have both pro-tumorigenic and anti-tumorigenic effects, depending on the context. It can promote tumour growth and immune evasion by suppressing anti-tumour immune responses or induce anti-tumour effects by enhancing immune cell function. In this study involving 30 PDAC patients and 30 healthy individuals, peripheral blood samples were analysed. PDAC patients were categorized into Low (12 patients) and High/Medium (18 patients) AHR groups based on gene expression in peripheral blood mononuclear cells (PBMCs). The Low AHR group showed distinct immune characteristics, including increased levels of immune-suppressive proteins such as PDL1, as well as alterations in lymphocyte and monocyte subtypes. Functional assays demonstrated changes in phagocytosis, nitric oxide production, and the expression of cytokines IL-1, IL-6, and IL-10. These findings indicate that AHR's expression level has a crucial role in immune dysregulation in PDAC and could be a potential target for early diagnostics and personalised therapeutics.

The Preventive Effect of Melatonin on Radiation-Induced Oral Mucositis

Melatonin exerts various physiological effects through melatonin receptors and their ability to scavenge free radicals. Radiotherapy is a common treatment for head and neck tumors, but stomatitis, a side effect affecting irradiated oral mucosa, can impact treatment outcomes. This study investigated the preventive effect of melatonin, a potent free radical scavenger, on radiation-induced oral mucositis. Mice were irradiated with 15 Gy of X-ray radiation to the head and neck, and the oral mucosa was histologically compared between a melatonin-administered group and a control group. The results showed that radiation-induced oral mucositis was suppressed in mice administered melatonin before and after irradiation. It was suggested that the mechanism involved the inhibition of apoptosis and the inhibition of DNA damage. From these findings, we confirmed that melatonin has a protective effect against radiation-induced oral mucositis.

A natural heme deficiency exists in biology that allows nitric oxide to control heme protein functions by regulating cellular heme distribution

A natural heme deficiency that exists in cells outside of the circulation broadly compromises the heme contents and functions of heme proteins in cells and tissues. Recently, we found that the signaling molecule, nitric oxide (NO), can trigger or repress the deployment of intracellular heme in a concentration-dependent hormetic manner. This uncovers a new role for NO and sets the stage for it to shape numerous biological processes by controlling heme deployment and consequent heme protein functions in biology.