Hypoxia is a common feature of solid tumors and is associated with a poor response to anticancer therapies. Hypoxia also induces metabolic changes, such as a switch to glycolysis. This glycolytic switch causes acidification of the tumor microenvironment (TME), thereby attenuating the anticancer immune response. A promising therapeutic strategy to reduce hypoxia and thereby sensitize tumors to irradiation and/or antitumor immune responses is pharmacological inhibition of oxidative phosphorylation (OXPHOS). Several OXPHOS inhibitors (OXPHOSi) have been tested in clinical trials. However, moderate responses and/or substantial toxicity have hampered clinical implementation. OXPHOSi tested in clinical trials inhibit the oxidative metabolism in tumor cells as well as healthy cells. Therefore, new strategies are needed to improve the efficacy of OXPHOSi while minimizing side effects. To enhance the therapeutic window, available OXPHOSi have, for instance, been conjugated to triphenylphosphonium to preferentially target the mitochondria of cancer cells, resulting in increased tumor uptake compared with healthy cells, as cancer cells have a higher mitochondrial membrane potential. However, OXPHOS inhibition also induces reactive oxygen species and subsequent antioxidant responses, which may influence the efficacy of therapies, such as platinum-based chemotherapy and radiotherapy. Here, we review the limitations of the clinically tested OXPHOSi metformin, atovaquone, tamoxifen, BAY 87-2243, and IACS-010759 and the potential of mitochondria-targeted OXPHOSi and their influence on reactive oxygen species production. Furthermore, the effect of the mitochondria-targeting moiety triphenylphosphonium on mitochondria is discussed as it affects mitochondrial bioenergetics.

AbstractObjectivesPD‐1/PD‐L1 immune checkpoint blockade can be an effective treatment for advanced breast cancer patients. However, patients with oestrogen receptor positive (ER+) tumors often display only low lymphocyte infiltration, while a large part of triple negative (TN) breast tumors does not generate an effective immunotherapy response. Therefore, new treatment strategies have to be developed. Here, we investigate Siglec‐7 and Siglec‐9 as novel ITIM‐bearing inhibitory immune checkpoint receptors similar to PD‐1, but expressed on a broader range of immune cells.MethodsWe assessed Siglec‐7 and Siglec‐9 (ligand) expression in TN and ER+ breast cancer tumors and their breast cancer cell line‐induced signalling.ResultsWe report that Siglec‐7 and Siglec‐9 are highly expressed in TN tumors, and to a low extent in ER+ tumors. Siglec‐7 was observed on myeloid cells, T cells, and NK cells and Siglec‐9 preferentially on myeloid cells. Expression of sialoglycans, including Siglec‐7 and Siglec‐9 ligands, was observed in both TN and ER+ breast cancer tissue sections. Expression levels of Siglec‐7 and Siglec‐9 ligands were higher on in vitro cultured TN cell lines than ER+ cell lines. Importantly, by applying chimeric Siglec‐7 reporter cells, we showed the induction of Siglec‐7 signalling by multiple TN cell lines, but only by one ER+ cell line. Moreover, Siglec‐7 signalling is directly related to Siglec‐7 ligand expression levels of breast cancer cell lines.ConclusionThese data imply that immunotherapy targeting Siglec receptors may be particularly interesting for TN breast cancer patients not responding to current treatment strategies with tumors displaying high immune cell infiltration.

Background Hypoxia is a common feature of many solid tumors and causes radiotherapy and immunotherapy resistance. Pharmacological inhibition of oxidative phosphorylation (OXPHOS) has emerged as a therapeutic strategy to reduce hypoxia. However, the OXPHOS inhibitors tested in clinical trials caused only moderate responses in hypoxia alleviation or trials were terminated due to dose-limiting toxicities. To improve the therapeutic benefit, FDA approved OXPHOS inhibitors (e.g. atovaquone) were conjugated to triphenylphosphonium (TPP+) to preferentially target cancer cell's mitochondria. In this study, we evaluated the hypoxia reducing effects of several mitochondria-targeted OXPHOS inhibitors and compared them to non-mitochondria-targeted OXPHOS inhibitors using newly developed spheroid models for diffusion-limited hypoxia.Methods B16OVA murine melanoma cells and MC38 murine colon cancer cells expressing a HIF-Responsive Element (HRE)-induced Green Fluorescent Protein (GFP) with an oxygen-dependent degradation domain (HRE-eGFP-ODD) were generated to assess diffusion-limited hypoxia dynamics in spheroids. Spheroids were treated with IACS-010759, atovaquone, metformin, tamoxifen or with mitochondria-targeted atovaquone (Mito-ATO), PEGylated mitochondria-targeted atovaquone (Mito-PEG-ATO) or mitochondria-targeted tamoxifen (MitoTam). Hypoxia dynamics were followed and quantified over time using the IncuCyte Zoom Live Cell-Imaging system.Results Hypoxic cores developed in B16OVA.HRE and MC38.HRE spheroids within 24 h hours after seeding. Treatment with IACS-010759, metformin, atovaquone, Mito-PEG-ATO and MitoTam showed a dose-dependent reduction of hypoxia in both B16OVA.HRE and MC38.HRE spheroids. Mito-ATO only alleviated hypoxia in MC38.HRE spheroids while tamoxifen was not able to reduce hypoxia in any of the spheroid models. The mitochondria-targeted OXPHOS inhibitors demonstrated stronger anti-hypoxic effects compared to the non-mito-targeted OXPHOS inhibitors.Conclusions We successfully developed a high-throughput spheroid model in which hypoxia dynamics can be quantified over time. Using this model, we showed that the mitochondria-targeted OXPHOS inhibitors Mito-ATO, Mito-PEG-ATO and MitoTam reduce hypoxia in tumor cells in a dose-dependent manner, potentially sensitizing hypoxic tumor cells for radiotherapy.

Introduction and purpose With a significant global impact, treatment of gastrointestinal (GI) cancers still presents with challenges, despite current multimodality approaches in advanced stages. Clinical trials are expanding for checkpoint inhibition (ICI) combined with radiation therapy (RT). This review intends to offer a comprehensive image of the current data regarding the effectiveness of this association, and to reflect on possible directions to further optimize the results. Results Several early phase studies demonstrated encouraging potential. However, translating preclinical outcomes to clinical settings proves challenging, especially in immunologically "cold" environments. GI cancers exhibit heterogeneity, requiring tailored approaches based on disease stage and patient characteristics. Current results, though promising, lack the power of evidence to influence the general practice. Conclusions Finding biomarkers for identifying or converting resistant cancers is essential for maximizing responses, moreover in this context strategic RT parameters need to be carefully considered. Our review emphasizes the significance of having a thorough grasp of how immunology, tumour biology, and treatment settings interact in order to propose novel research avenues and efficient GI cancer therapy.

Introduction: Tumor hypoxia is a feature of many solid malignancies and is known to cause radio resistance. In recent years it has become clear that hypoxic tumor regions also foster an immunosuppressive phenotype and are involved in immunotherapy resistance. It has been proposed that reducing the tumors’ oxygen consumption will result in an increased oxygen concentration in the tissue and improve radio- and immunotherapy efficacy. The aim of this study is to investigate the metabolic rewiring of cancer cells by pharmacological attenuation of oxidative phosphorylation (OXPHOS) and subsequently reduce tumor hypoxia. Material and methods: The metabolic effects of three OXPHOS inhibitors IACS-010759, atovaquone and metformin were explored by measuring oxygen consumption rate, extra cellular acidification rate, and [18F]FDG uptake in 2D and 3D cell culture. Tumor cell growth in 2D cell culture and hypoxia in 3D cell culture were analyzed by live cell imaging. Tumor hypoxia and [18F]FDG uptake in vivo following treatment with IACS-010759 was determined by immunohistochemistry and ex vivo biodistribution respectively. Results: In vitro experiments show that tumor cell metabolism is heterogeneous between different models. Upon OXPHOS inhibition, metabolism shifts from oxygen consumption through OXPHOS towards glycolysis, indicated by increased acidification and glucose uptake. Inhibition of OXPHOS by IACS-010759 treatment reduced diffusion limited tumor hypoxia in both 3D cell culture and in vivo. Although immune cell presence was lower in hypoxic areas compared with normoxic areas, it is not altered following short term OXPHOS inhibition. Discussion: These results show that inhibition of OXPHOS causes a metabolic shift from OXPHOS towards increased glycolysis in 2D and 3D cell culture. Moreover, inhibition of OXPHOS reduces diffusion limited hypoxia in 3D cell culture and murine tumor models. Reduced hypoxia by OXPHOS inhibition might enhance therapy efficacy in future studies. However, caution is warranted as systemic metabolic rewiring can cause adverse effects.

Combined radiotherapy and immune checkpoint inhibition is a potential treatment option for head and neck squamous cell carcinoma (HNSCC). Immunocompetent mouse models can help to successfully develop radio- immunotherapy combinations and to increase our understanding of the effects of radiotherapy on the tumor microenvironment for future clinical translation. Therefore, the aim of this study was to develop a homogeneous, reproducible HNSCC model originating from the Mouse Oral Cancer 1 (MOC1) HNSCC cell line, and to explore the radiotherapy-induced changes in its tumor microenvironment, using flow cytometry and PD-L1 microSPECT/CT imaging. In vivo growing tumors originating from the parental MOC1 line were used to generate single cell derived clones. These clones were screened in vitro for their ability to induce programmed cell death ligand 1 (PD-L1) and major histocompatibility complex class I (MHC-I) following IFNγ exposure. Clones with different IFNγ sensitivity were inoculated in C57BL/6 mice and assessed for tumor outgrowth. The composition of the tumor microenvironment of a stably growing (non)irradiated MOC1-derived clone was assessed by immunohistochemistry, flow cytometry and PD-L1 microSPECT/CT. Low in vitro inducibility of MHC-I and PD-L1 by IFNγ was associated with increased tumor outgrowth of MOC1 clones in vivo. Flow cytometry analysis of cells derived from a stable in vivo growing MOC1 clone MOC1.3D5low showed expression of MHC-I and PD-L1 on several cell populations within the tumor. Upon irradiation, MHC-I and PD-L1 increased on leukocytes (CD45.2+) and cancer associated fibroblasts (CD45.2−/EpCAM−/CD90.1+). Furthermore, PD-L1 microSPECT/CT showed increased tumor uptake of radiolabeled PD-L1 antibodies with a heterogeneous spatial distribution of the radio signal, which co-localized with PD-L1+ and CD45.2+ areas. PD-L1 and MHC-I inducibility by IFNγ in vitro is associated with tumor outgrowth of MOC1 clones in vivo. In tumors originating from a stably growing MOC1-derived clone, expression of these immune-related markers was induced by irradiation shown by flow cytometry on several cell populations within the tumor microenvironment such as immune cells and cancer associated fibroblasts. PD-L1 microSPECT/CT showed increased tumor uptake following radiotherapy, and autoradiography showed correlation of uptake with areas that are heavily infiltrated by immune cells. Knowledge of radiotherapy-induced effects on the tumor microenvironment in this model can help optimize timing and dosage for radio- immunotherapy combination strategies in future research.

Background and purpose Radiotherapy (RT) is an integral treatment part for patients with head and neck squamous cell carcinoma (HNSCC), but radioresistance remains a major issue. Here, we use MitoTam, a mitochondrially targeted analogue of tamoxifen, which we aim to stimulate ferroptotic cell death with, and sensitize radioresistant cells to RT. Materials and methods We assessed viability, reactive oxygen species (ROS) production, disruption of mitochondrial membrane potential, and lipid peroxidation in radiosensitive (UT-SCC-40) and radioresistant (UT-SCC-5) HNSCC cells following MitoTam treatment. To assess ferroptosis specificity, we used the ferroptosis inhibitor ferrostatin-1 (fer-1). Also, total antioxidant capacity and sensitivity to tert-butyl hydroperoxide were evaluated to assess ROS-responses. 53BP1 staining was used to assess radiosensitivity after MitoTam treatment. Results Our data revealed increased ROS, cell death, disruption of mitochondrial membrane potential, and lipid peroxidation following MitoTam treatment in both cell lines. Adverse effects of MitoTam on cell death, membrane potential and lipid peroxidation were prevented by fer-1, indicating induction of ferroptosis. Radioresistant HNSCC cells were less sensitive to the effects of MitoTam due to intrinsic higher antioxidant capacity. MitoTam treatment prior to RT led to superadditive residual DNA damage expressed by 53BP1 foci compared to RT or MitoTam alone. Conclusion MitoTam induced ferroptosis in HNSCC cells, which could be used to overcome the elevated antioxidant capacity of radioresistant cells and sensitize such cells to RT. Treatment with MitoTam followed by RT could therefore present a promising effective therapy of radioresistant cancers.Statement of significance.Radiotherapy is applied in the treatment of a majority of cancer patients. Radioresistance due to elevated antioxidant levels can be overcome by promoting ferroptotic cell death combining ROS-inducing drug MitoTam with radiotherapy.

Background and purpose: Radiotherapy (RT) is a mainstay component of treatment for patients with head and neck squamous cell carcinoma (HNSCC), but responses vary. As RT relies upon oxidative damage, antioxidant expression in response to RT-induced reactive oxygen species (ROS) could compromise treatment response. We aimed to examine local and systemic antioxidant responses to increased RT-induced ROS in relation to treatment success. Materials and methods: Nuclear factor erythroid 2-related factor 2 (NRF2), the main antioxidant transcription factor, was immunofluorescently stained in FaDu cells and in tumor biopsies of patients with oral cavity/ oropharynx HNSCC before and after five fractions of RT. Besides, total antioxidant capacity (TAC) was analyzed in HNSCC tumor cells in vitro and in serum of HNSCC patients before, during, and after RT. Results: Data revealed an increase in NRF2 expression and TAC in head and neck cancer cells in vitro over the course of 5 daily fractions of 2 Gy. In accordance, also in patients' tumors NRF2 expression increased, which was associated with increased serum TAC during RT. Increasing serum TAC was related to impaired local tumor control. Conclusion: Radiation induced NRF2 expression and upregulated TAC, which may compromise the effect of RTinduced ROS. Changes in serum TAC during RT could serve as a novel predictor of treatment outcome in HNSCC patients. Medical Ethics Review Committee (CMO) approval - CMO number: 2007/104.

Context Some patients with classic congenital adrenal hyperplasia (CAH) survive without glucocorticoid treatment. Increased precursor concentrations in these patients might lead to higher free (biological active) cortisol concentrations by influencing cortisol-protein binding. In 21-hydroxylase deficiency (21OHD), the most common CAH form, accumulated 21-deoxycortisol (21DF) may further increase glucocorticoid activity. Both mechanisms could explain the low occurrence of symptoms in some patients with untreated classic CAH. Objective Develop and validate a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for free cortisol and free 21DF to quantify these steroids in patients with untreated classic CAH before and after Synacthen administration, and compare these concentrations to concentrations measured in patients with nonclassic CAH (NCCAH), other forms of adrenal insufficiency (AI), and controls. Methods An LC-MS/MS method to measure free cortisol and free 21DF was developed and validated. Total and free serum concentrations of both cortisol and 21DF were measured in patients with untreated classic CAH (n = 29), NCCAH (n = 5), AI (n = 3), and controls (n = 11) before and 60 minutes after stimulation with Synacthen. Results Unstimulated total cortisol concentrations of patients with untreated classic CAH (median 109 nmol/L) were lower than in patients with untreated NCCAH (249 nmol/L, P = .010) and controls (202 nmol/L, P = .016), but free cortisol concentrations were similar. Basal free 21DF concentrations were high in patients with 21OHD (median 5.32 nmol/L) and undetectable in patients with AI and controls (<0.19 nmol/L). After Synacthen administration, free 21DF concentrations increased in patients with 21OHD, while free cortisol concentrations did not change. Conclusion Free cortisol concentrations in patients with classic CAH were similar to those in controls and patients with NCCAH, indicating comparable cortisol availability. Additionally, patients with 21OHD produce high concentrations of 21DF, possibly explaining the low occurrence of symptoms in some patients with classic 21OHD. Free cortisol and 21DF levels should be considered in evaluating adrenal insufficiency in patients with CAH.

Objective Classic androgens such as dehydroepiandrosterone, androstenedione, and testosterone are generally measured for diagnosis and treatment monitoring in children and adolescents with hyperandrogenism, as can occur in congenital adrenal hyperplasia, premature pubarche, or polycystic ovarian syndrome. However, adrenally-derived 11-oxygenated androgens also contribute to the androgen pool and should therefore be considered in clinical management. Nevertheless, paediatric reference intervals are lacking. Therefore, we developed a serum assay to establish reference intervals for four 11-oxygenated androgens in addition to four classic androgens.Design Reference interval study for serum 11-oxygenated androgens in children.Methods We developed and validated a sensitive liquid chromatography-tandem mass spectrometry assay and quantified eight serum androgens, including four 11-oxygenated androgens, in serum of 256 healthy children (aged 0-17 years old). An age-dependency for all androgens was observed, and therefore we divided the cohort based on age (prepubertal [n = 133; 94 boys, 39 girls] and pubertal [n = 123; 52 boys, 71 girls]) to compute reference intervals (2.5th-97.5th percentiles).Results In the prepubertal group, there was no significant sex-difference for any of the measured androgens. In the pubertal group, androstenedione, testosterone, and dihydrotestosterone showed a significant difference between boys and girls. In contrast, adrenal androgens dehydroepiandrosterone, 11-hydroxyandrostenedione, 11-ketoandrostenedione, 11-hydroxytestosterone, and 11-ketotestosterone did not.Conclusions We developed and validated an assay for 11-oxygenated androgens, in addition to four classic androgens and established reference intervals. This enables a comprehensive evaluation of serum androgen status in children with clinical symptoms of hyperandrogenism.

IntroductionCongenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency (21OHD) or 11-hydroxylase deficiency (11OHD) is characterized by underproduction of cortisol and overproduction of adrenal androgens. These androgens lead to a variable degree of virilization of the female external genitalia in 46,XX individuals. Especially in developing countries, diagnosis is often delayed and 46,XX patients might be assigned as males. This study aims to describe the clinical and biochemical characteristics of a unique cohort of untreated male-reared 46,XX classic CAH patients from Indonesia and discusses treatment challenges.MethodsNine untreated classic CAH patients with 46,XX genotype and 21OHD (n=6) or 11OHD (n=3), aged 3-46 years old, were included. Biometrical parameters, clinical characteristics, and biochemical measurements including glucocorticoids, renin, androgens, and the pituitary-gonadal axis were evaluated.ResultsAll patients had low early morning serum cortisol concentrations (median 89 nmol/L) without significant increase after ACTH stimulation. Three patients with salt wasting 21OHD reported one or more periods with seizures and/or vomiting in their past until the age of 6, but not thereafter. The remaining patients reported no severe illness or hospitalization episodes, despite their decreased capacity to produce cortisol. In the 21OHD patients, plasma renin levels were elevated compared to the reference range, and in 11OHD patients renin levels were in the low-normal range. All adult patients had serum testosterone concentrations within the normal male reference range. In 21OHD patients, serum 11-oxygenated androgens comprised 41-60% of the total serum androgen concentrations. Glucocorticoid treatment was offered to all patients, but they refused after counseling as this would reduce their endogenous androgen production and they did not report complaints of their low cortisol levels.DiscussionWe describe a unique cohort of untreated classic 46,XX male CAH patients without overt clinical signs of cortisol deficiency despite their cortisol underproduction and incapacity to increase cortisol levels after ACTH stimulation. The described adolescent and adult patients produce androgen levels within or above the normal male reference range. Glucocorticoid treatment will lower these adrenal androgen concentrations. Therefore, in 46,XX CAH patients reared as males an individual treatment approach with careful counseling and clear instructions is needed.