Elevated Methionine Flux Drives Pyroptosis Evasion in Persister Cancer Cells.

Induction of cell death represents a primary goal of most anticancer treatments. Despite the efficacy of such approaches, a small population of "persisters" develop evasion strategies to therapy-induced cell death. While previous studies have identified mechanisms of resistance to apoptosis, the mechanisms by which persisters dampen other forms of cell death, such as pyroptosis, remain to be elucidated. Pyroptosis is a form of inflammatory cell death that involves formation of membrane pores, ion gradient imbalance, water inflow, and membrane rupture. Herein, we investigate mechanisms by which cancer persisters resist pyroptosis, survive, then proliferate in the presence of tyrosine kinase inhibitors (TKI). Lung, prostate, and esophageal cancer persister cells remaining after treatments exhibited several hallmarks indicative of pyroptosis resistance. The inflammatory attributes of persisters included chronic activation of inflammasome, STING, and type I interferons. Comprehensive metabolomic characterization uncovered that TKI-induced pyroptotic persisters display high methionine consumption and excessive taurine production. Elevated methionine flux or exogenous taurine preserved plasma membrane integrity via osmolyte-mediated effects. Increased dependency on methionine flux decreased the level of one carbon metabolism intermediate S-(5'-adenosyl)-L-homocysteine, a determinant of cell methylation capacity. The consequent increase in methylation potential induced DNA hypermethylation of genes regulating metal ion balance and intrinsic immune response. This enabled thwarting TKI resistance by using the hypomethylating agent decitabine. In summary, the evolution of resistance to pyroptosis can occur via a stepwise process of physical acclimation and epigenetic changes without existing or recurrent mutations. SIGNIFICANCE: Methionine enables cancer cells to persist by evading pyroptotic osmotic lysis, which leads to genome-wide hypermethylation that allows persisters to gain proliferative advantages.

Macrophage-Derived Cholesterol Contributes to Therapeutic Resistance in Prostate Cancer.

Castration-resistant prostate cancer (CRPC) is a lethal stage of disease in which androgen receptor (AR) signaling is persistent despite androgen deprivation therapy (ADT). Most studies have focused on investigating cell-autonomous alterations in CRPC, while the contributions of the tumor microenvironment are less well understood. Here we sought to determine the role of tumor-associated macrophages in CRPC, based upon their role in cancer progression and therapeutic resistance. In a syngeneic model that reflected the mutational landscape of CRPC, macrophage depletion resulted in a reduced transcriptional signature for steroid and bile acid synthesis, indicating potential perturbation of cholesterol metabolism. As cholesterol is the precursor of the five major types of steroid hormones, we hypothesized that macrophages were regulating androgen biosynthesis within the prostate tumor microenvironment. Macrophage depletion reduced androgen levels within prostate tumors and restricted AR nuclear localization in vitro and in vivo. Macrophages were also cholesterol-rich and were able to transfer cholesterol to tumor cells in vitro. AR nuclear translocation was inhibited by activation of liver X receptor (LXR)-ß, the master regulator of cholesterol homeostasis. Consistent with these data, macrophage depletion extended survival during ADT and the presence of macrophages correlated with therapeutic resistance in patient-derived explants. Taken together, these findings support the therapeutic targeting of macrophages in CRPC. SIGNIFICANCE: These results suggest that macrophage-targeted therapies can be combined with androgen deprivation therapy to treat patients with prostate cancer by limiting cholesterol bioavailability and the production of intratumoral androgens.See related commentary by Al-Janabi and Lewis, p. 5399.

Spatial clustering of CD68+ tumor associated macrophages with tumor cells is associated with worse overall survival in metastatic clear cell renal cell carcinoma.

Immune infiltration is typically quantified using cellular density, not accounting for cellular clustering. Tumor-associated macrophages (TAM) activate oncogenic signaling through paracrine interactions with tumor cells, which may be better reflected by local cellular clustering than global density metrics. Using multiplex immunohistochemistry and digital pathologic analysis we quantified cellular density and cellular clustering for myeloid cell markers in 129 regions of interest from 55 samples from 35 patients with metastatic ccRCC. CD68+ cells were found to be clustered with tumor cells and dispersed from stromal cells, while CD163+ and CD206+ cells were found to be clustered with stromal cells and dispersed from tumor cells. CD68+ density was not associated with OS, while high tumor/CD68+ cell clustering was associated with significantly worse OS. These novel findings would not have been identified if immune infiltrate was assessed using cellular density alone, highlighting the importance of including spatial analysis in studies of immune cell infiltration of tumors. Significance: Increased clustering of CD68+ TAMs and tumor cells was associated with worse overall survival for patients with metastatic ccRCC. This effect would not have been identified if immune infiltrate was assessed using cell density alone, highlighting the importance of including spatial analysis in studies of immune cell infiltration of tumors.

T-cells produce acidic niches in lymph nodes to suppress their own effector functions.

The acidic pH of tumors profoundly inhibits effector functions of activated CD8 + T-cells. We hypothesize that this is a physiological process in immune regulation, and that it occurs within lymph nodes (LNs), which are likely acidic because of low convective flow and high glucose metabolism. Here we show by in vivo fluorescence and MR imaging, that LN paracortical zones are profoundly acidic. These acidic niches are absent in athymic Nu/Nu and lymphodepleted mice, implicating T-cells in the acidifying process. T-cell glycolysis is inhibited at the low pH observed in LNs. We show that this is due to acid inhibition of monocarboxylate transporters (MCTs), resulting in a negative feedback on glycolytic rate. Importantly, we demonstrate that this acid pH does not hinder initial activation of naïve T-cells by dendritic cells. Thus, we describe an acidic niche within the immune system, and demonstrate its physiological role in regulating T-cell activation.

Correction: Acidity promotes tumour progression by altering macrophage phenotype in prostate cancer.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The Immune Microenvironment and Cancer Metastasis.

The dynamic interplay between neoplastic cells and the immune microenvironment regulates every step of the metastatic process. Immune cells contribute to invasion by secreting a cornucopia of inflammatory factors that promote epithelial-to-mesenchymal transition and remodeling of the stroma. Cancer cells then intravasate to the circulatory system assisted by macrophages and use several pathways to avoid recognition by cytotoxtic lymphocytes and phagocytes. Circulating tumor cells that manage to adhere to the vasculature and encounter premetastic niches are able to use the associated myeloid cells to extravasate into ectopic organs and establish a dormant microscopic colony. If successful at avoiding repetitive immune attack, dormant cells can subsequently grow into overt, clinically detectable metastatic lesions, which ultimately account to most cancer-related deaths. Understanding how disseminated tumor cells evade and corrupt the immune system during the final stages of metastasis will be pivotal in developing new therapeutic modalities that combat metastasis.

Acidity promotes tumour progression by altering macrophage phenotype in prostate cancer.

BACKGROUND: Tumours rapidly ferment glucose to lactic acid even in the presence of oxygen, and coupling high glycolysis with poor perfusion leads to extracellular acidification. We hypothesise that acidity, independent from lactate, can augment the pro-tumour phenotype of macrophages. METHODS: We analysed publicly available data of human prostate cancer for linear correlation between macrophage markers and glycolysis genes. We used zwitterionic buffers to adjust the pH in series of in vitro experiments. We then utilised subcutaneous and transgenic tumour models developed in C57BL/6 mice as well as computer simulations to correlate tumour progression with macrophage infiltration and to delineate role of acidity. RESULTS: Activating macrophages at pH 6.8 in vitro enhanced an IL-4-driven phenotype as measured by gene expression, cytokine profiling, and functional assays. These results were recapitulated in vivo wherein neutralising intratumoural acidity reduced the pro-tumour phenotype of macrophages, while also decreasing tumour incidence and invasion in the TRAMP model of prostate cancer. These results were recapitulated using an in silico mathematical model that simulate macrophage responses to environmental signals. By turning off acid-induced cellular responses, our in silico mathematical modelling shows that acid-resistant macrophages can limit tumour progression. CONCLUSIONS: This study suggests that tumour acidity contributes to prostate carcinogenesis by altering the state of macrophage activation.

Inflammation, ROS, and Mutagenesis.

It has long been hypothesized that reactive oxygen species (ROS) are responsible for the association between chronic inflammatory diseases and increased tumor incidence. In this issue of Cancer Cell, Canli et al. now demonstrate that amplified ROS production specifically by myeloid cells is sufficient to promote intestinal mutagenesis.

Neutralization of Tumor Acidity Improves Antitumor Responses to Immunotherapy.

Cancer immunotherapies, such as immune checkpoint blockade or adoptive T-cell transfer, can lead to durable responses in the clinic, but response rates remain low due to undefined suppression mechanisms. Solid tumors are characterized by a highly acidic microenvironment that might blunt the effectiveness of antitumor immunity. In this study, we directly investigated the effects of tumor acidity on the efficacy of immunotherapy. An acidic pH environment blocked T-cell activation and limited glycolysis in vitro. IFNγ release blocked by acidic pH did not occur at the level of steady-state mRNA, implying that the effect of acidity was posttranslational. Acidification did not affect cytoplasmic pH, suggesting that signals transduced by external acidity were likely mediated by specific acid-sensing receptors, four of which are expressed by T cells. Notably, neutralizing tumor acidity with bicarbonate monotherapy impaired the growth of some cancer types in mice where it was associated with increased T-cell infiltration. Furthermore, combining bicarbonate therapy with anti-CTLA-4, anti-PD1, or adoptive T-cell transfer improved antitumor responses in multiple models, including cures in some subjects. Overall, our findings show how raising intratumoral pH through oral buffers therapy can improve responses to immunotherapy, with the potential for immediate clinical translation.

Agmatine improves renal function in gentamicin-induced nephrotoxicity in rats.

The present study was designed to explore the possible protective effects of agmatine, a known nitric oxide (NO) synthase inhibitor, against gentamicin-induced nephrotoxicity in rats. For this purpose, we quantitatively evaluated gentamicin-induced renal structural and functional alterations using histopathological and biochemical approaches. Furthermore, the effect of agmatine on gentamicin-induced hypersensitivity of urinary bladder rings to acetylcholine (ACh) was evaluated. Twenty-four male Wistar albino rats were randomly divided into 3 groups, namely control, gentamicin (100 mg/kg, i.p.), and gentamicin plus agmatine (40 mg/kg, orally). At the end of the study, all rats were sacrificed and then blood and urine samples and kidneys were taken. Administration of agmatine significantly decreased kidney/body mass ratio, serum creatinine, lactate dehydrogenase (LDH), renal malondialdehyde (MDA), myeloperoxidase (MPO), NO, and tumor necrosis factor-alpha (TNF-α) while it significantly increased creatinine clearance and renal superoxide dismutase (SOD) activity when compared with the gentamicin-treated group. Additionally, agmatine ameliorated tissue morphology as evidenced by histological evaluation and reduced the responses of isolated bladder rings to ACh. Our study indicates that agmatine administration with gentamicin attenuates oxidative-stress associated renal injury by reducing oxygen free radicals and lipid peroxidation, restoring NO level and inhibiting inflammatory mediators such as TNF-α.

Protective effect of allicin against gentamicin-induced nephrotoxicity in rats.

In this study, the modulator effect of allicin on the oxidative nephrotoxicity of gentamicin in the kidneys of rats was investigated by determining indices of lipid peroxidation and the activities of antioxidant enzymes, as well as by histological analyses. Furthermore, the effect of allicin on gentamicin induced hypersensitivity of urinary bladder rings to ACh was estimated. Twenty-four male Wistar albino rats were randomly divided into three groups, control, gentamicin (100mg/kg, i.p.) and gentamicin+allicin (50mg/kg, orally). At the end of the study, all rats were sacrificed and then urine, blood samples and kidneys were taken. Gentamicin administration caused a severe nephrotoxicity as evidenced by an elevated kidney/body weight ratio, serum creatinine, blood urea nitrogen (BUN), serum lactate dehydrogenase (LDH) and proteinuria with a reduction in serum albumin and creatinine clearance as compared with control group. In addition, a significant increase in renal contents of malondialdehyde (MDA), myeloperoxidase (MPO), nitric oxide (NOx) and tumor necrosis factor-alpha (TNF-α) concomitantly with a significant decrease in renal reduced glutathione (GSH) and superoxide dismutase (SOD) activities was detected upon gentamicin injection. Exposure to gentamicin increased the sensitivity of isolated urinary bladder rings to ACh and induced acute renal tubular epithelial cells necrosis. Administration of allicin significantly decreased kidney/body weight ratio, serum creatinine, LDH, renal MDA, MPO, NOx and TNF-α while it significantly increased creatinine clearance, renal GSH content and renal SOD activity when compared to gentamicin-treated group. Additionally, allicin significantly reduced the responses of isolated bladder rings to ACh and ameliorated tissue morphology as evidenced by histological evaluation. Our study indicates that allicin exerted protection against structural and functional damage induced by gentamicin possibly due to its antioxidant, anti-inflammatory and immunomodulatory properties in addition to its ability to retaining nitric oxide level.

Flavocoxid attenuates gentamicin-induced nephrotoxicity in rats.

Gentamicin is a widely used antibiotic against serious and life-threatening infections; however, its usefulness is limited by the development of nephrotoxicity. The present study was designed to determine whether flavocoxid has a protective effect against gentamicin-induced nephrotoxicity in rats. For this purpose, we quantitatively evaluated gentamicin-induced renal structural and functional alterations using histopathological and biochemical approaches. Furthermore, the effect of flavocoxid on gentamicin induced hypersensitivity of urinary bladder rings to acetylcholine (ACh) was determined. Twenty-four male Wistar albino rats were randomly divided into three groups, namely control, gentamicin (100 mg/kg, i.p.) and gentamicin plus flavocoxid (20 mg/kg, orally). At the end of the study, all rats were sacrificed and then blood, urine samples and kidneys were collected for further analysis. Gentamicin administration caused a severe nephrotoxicity which was evidenced by an elevated renal somatic index (RSI), serum creatinine, blood urea nitrogen, serum lactate dehydrogenase, and protein in urine with a concomitant reduction in serum albumin and normalized creatinine clearance value as compared with the controls. Moreover, a significant increase in renal contents of malondialdehyde, myeloperoxidase, and tumor necrosis factor-alpha with a significant decrease in renal reduced glutathione and superoxide dismutase activities was detected upon gentamicin administration together with increasing the sensitivity of isolated urinary bladder rings to ACh. Exposure to gentamicin induced necrosis of renal tubular epithelial cells. Flavocoxid protected kidney tissue against the oxidative damage and the nephrotoxic effect caused by gentamicin treatment. In addition, flavocoxid significantly reduced the responses of isolated bladder rings to ACh. The results from our study indicate that flavocoxid supplement attenuates gentamicin-induced renal injury via the amelioration of oxidative stress and inflammation of renal tubular cells.

Angiogenesis inhibitors in cancer therapy: mechanistic perspective on classification and treatment rationales.

Angiogenesis, a process of new blood vessel formation, is a prerequisite for tumour growth to supply the proliferating tumour with oxygen and nutrients. The angiogenic process may contribute to tumour progression, invasion and metastasis, and is generally accepted as an indicator of tumour prognosis. Therefore, targeting tumour angiogenesis has become of high clinical relevance. The current review aimed to highlight mechanistic details of anti-angiogenic therapies and how they relate to classification and treatment rationales. Angiogenesis inhibitors are classified into either direct inhibitors that target endothelial cells in the growing vasculature or indirect inhibitors that prevent the expression or block the activity of angiogenesis inducers. The latter class extends to include targeted therapy against oncogenes, conventional chemotherapeutic agents and drugs targeting other cells of the tumour micro-environment. Angiogenesis inhibitors may be used as either monotherapy or in combination with other anticancer drugs. In this context, many preclinical and clinical studies revealed higher therapeutic effectiveness of the combined treatments compared with individual treatments. The proper understanding of synergistic treatment modalities of angiogenesis inhibitors as well as their wide range of cellular targets could provide effective tools for future therapies of many types of cancer.

Celecoxib, a selective cyclooxygenase-2 inhibitor, attenuates renal injury in a rat model of Cisplatin-induced nephrotoxicity.

BACKGROUND: Cisplatin is an effective chemotherapeutic agent successfully used in the treatment of a wide range of tumors. Nevertheless, nephrotoxicity has restricted its clinical use. Recent studies have strongly suggested that inflammatory mechanisms may play an important role in the pathogenesis of cisplatin nephrotoxicity. Celecoxib, a selective cyclooxygenase-2 inhibitor used as anti-inflammatory, may therefore have a protective effect on cisplatin-induced renal injury. METHODS: In the present study, rats were injected intraperitoneally with a single dose of cisplatin (7 mg/kg) and/or celecoxib (30 mg/kg) for 5 days. RESULTS: Nephrotoxicity manifested biochemically by elevations in serum creatinine, blood urea nitrogen, and proteinuria, and an increase in kidney weight as a percentage of total body weight. In addition, a marked decrease in serum albumin was observed. Lipid peroxidation in the kidney was monitored by measuring the malondialdehyde level and glutathione content, which were increased and depleted, respectively. Administration of celecoxib with cisplatin attenuated cisplatin-induced changes in kidney function parameters and oxidative stress markers. Histopathological examination of the kidney confirmed these results. CONCLUSION: In conclusion, this study indicates that celecoxib may be a promising drug for clinical use as a nephroprotectant against cisplatin-induced nephrotoxicity.