Modulation of microenvironment acidity reverses anergy in human and murine tumor-infiltrating T lymphocytes

Emerging strategies for delivering antiangiogenic therapies to primary and metastatic brain tumors

Five-year survival rates have not increased appreciably for patients with primary and metastatic brain tumors. Nearly 17,000 patients die from primary brain tumors, whereas approximately 200,000 cases are diagnosed with brain metastasis every year in the US alone. At the same time, with improved control of systemic disease, the incidence of brain metastasis is increasing. Thus, novel approaches for improving the treatment outcome for these uniformly fatal diseases are needed urgently. In the review, we summarize the challenges in the treatment of these diseases using antiangiogenic therapies alone or in combination with radio-, chemo- and immuno-therapies. We also discuss the emerging strategies to improve the treatment outcome using both pharmacological approaches to normalize the tumor microenvironment and physical approaches (e.g., focused ultrasound) to modulate the blood-tumor-barrier, along with limitations of each approach. Finally, we offer some new avenues of future research.

The acidic microenvironment as a possible niche of dormant tumor cells

Although surgical excision, chemo-, and radio-therapy are clearly advanced, tumors may relapse due to cells of the so-called "minimal residual disease". Indeed, small clusters of tumor cells persist in host tissues after treatment of the primary tumor elaborating strategies to survive and escape from immunological attacks before their relapse: this variable period of remission is known as "cancer dormancy". Therefore, it is crucial to understand and consider the major concepts addressing dormancy, to identify new targets and disclose potential clinical strategies. Here, we have particularly focused the relationships between tumor microenvironment and cancer dormancy, looking at a re-appreciated aspect of this compartment that is the low extracellular pH. Accumulating evidences indicate that acidity of tumor microenvironment is associated with a poor prognosis of tumor-bearing patients, stimulates a chemo- and radio-therapy resistant phenotype, and suppresses the tumoricidal activity of cytotoxic lymphocytes and natural killer cells, and all these aspects are useful for dormancy. Therefore, this review discusses the possibility that acidity of tumor microenvironment may provide a new, not previously suggested, adequate milieu for "dormancy" of tumor cells.

Prospect for immune checkpoint blockade: dynamic and comprehensive monitorings pave the way

Immune checkpoint blockade, which releases the brake of the immune system to enhance anticancer immune response, stands out in the cancer immunotherapy field due to their remarkable and long-lasting effect. However, the overall response rate for currently approved immune checkpoint inhibitors is only about 10-40%. We have summarized three major components, which are the presence of checkpoints, the immune-activation mechanism and the immune-inhibitory mechanism, containing six factors to describe the cancer-immune interaction dynamically and comprehensively, which shed light on promising biomarkers in immune checkpoint therapy.

LMP1-mediated glycolysis induces myeloid-derived suppressor cell expansion in nasopharyngeal carcinoma

Myeloid-derived suppressor cells (MDSCs) are expanded in tumor microenvironments, including that of Epstein–Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC). The link between MDSC expansion and EBV infection in NPC is unclear. Here, we show that EBV latent membrane protein 1 (LMP1) promotes MDSC expansion in the tumor microenvironment by promoting extra-mitochondrial glycolysis in malignant cells, which is a scenario for immune escape initially suggested by the frequent, concomitant detection of abundant LMP1, glucose transporter 1 (GLUT1) and CD33⁺ MDSCs in tumor sections. The full process has been reconstituted in vitro. LMP1 promotes the expression of multiple glycolytic genes, including GLUT1. This metabolic reprogramming results in increased expression of the Nod-like receptor family protein 3 (NLRP3) inflammasome, COX-2 and P-p65 and, consequently, increased production of IL-1β, IL-6 and GM-CSF. Finally, these changes in the environment of malignant cells result in enhanced NPC-derived MDSC induction. One key step is the physical interaction of LMP1 with GLUT1 to stabilize the GLUT1 protein by blocking its K48-ubiquitination and p62-dependent autolysosomal degradation. This work indicates that LMP1-mediated glycolysis regulates IL-1β, IL-6 and GM-CSF production through the NLRP3 inflammasome, COX-2 and P-p65 signaling pathways to enhance tumor-associated MDSC expansion, which leads to tumor immunosuppression in NPC.

The expression of the Epstein-Barr virus (EBV) oncogenic protein denoted latent membrane protein 1 (LMP1) varies in patients with NPC and is linked to tumorigenesis and tumor immunosuppression, but the molecular mechanism through which LMP1 leads to tumor immune escape remains unknown. Work to date suggests that the expansion of tumor-associated myeloid-derived suppressor cells (MDSCs) is the main cause of tumor immunosuppression such as that found in NPC. Here, we found that tumor LMP1 expression is correlated with glucose transporter 1 (GLUT1) levels, CD33⁺ MDSC number and unfavorable survival in patients with NPC. Based on the results of our in vitro analysis, LMP1 promotes GLUT1-dependent glycolysis in NPC cells, resulting in activation of the Nod-like receptor family protein 3 (NLRP3) inflammasome, COX-2 and P-p65 signaling pathways and subsequently increased IL-1β, IL-6 and GM-CSF production. Importantly, LMP1 interacts with GLUT1 to stabilize the GLUT1 protein by disrupting its K48-linked ubiquitination and autolysosomal degradation in a p62-dependent manner and up-regulating the GLUT1 mRNA and protein levels by inducing p65 activation. Therefore, we determined that GLUT1-dependent glycolysis is required for tumor-induced MDSC differentiation and that this process is associated with LMP1 expression. Based on our findings, LMP1-mediated glycolysis is a key process involved in controlling tumor immunosuppression and directly contributes to oncogenesis.

Fatty Acid Uptake in T Cell Subsets Using a Quantum Dot Fatty Acid Conjugate

Fatty acid (FA) metabolism directly influences the functional capabilities of T cells in tumor microenvironments. Thus, developing tools to interrogate FA-uptake by T cell subsets is important for understanding tumor immunosuppression. Herein, we have generated a novel FA-Qdot 605 dye conjugate with superior sensitivity and flexibility to any of the previously commercially available alternatives. For the first time, we demonstrate that this nanoparticle can be used as a specific measure of fatty acid uptake by T cells both in-vitro and in-vivo. Flow cytometric analysis shows that both the location and activation status of T cells determines their FA uptake. Additionally, CD4+ Foxp3+ regulatory T cells (Tregs) uptake FA at a higher rate than effector T cell subsets, supporting the role of FA metabolism for Treg function. Furthermore, we are able to simultaneously detect glucose and fatty acid uptake directly within the tumor microenvironment. Cumulatively, our results suggest that this novel fluorescent probe is a powerful tool to understand FA utilization within the tumor, thereby providing an unprecedented opportunity to study T cell FA metabolism in-vivo.

Metabolic Interactions in the Tumor Microenvironment

Tumors are dynamic pseudoorgans that contain numerous cell types interacting to create a unique physiology. Within this network, the malignant cells encounter many challenges and rewire their metabolic properties accordingly. Such changes can be experienced and executed autonomously or through interaction with other cells in the tumor. The focus of this review is on the remodeling of the tumor microenvironment that leads to pathophysiologic interactions that are influenced and shaped by metabolism. They include symbiotic nutrient sharing, nutrient competition, and the role of metabolites as signaling molecules. Examples of such processes abound in normal organismal physiology, and such heterocellular metabolic interactions are repurposed to support tumor metabolism and growth. The importance and ubiquity of these processes are just beginning to be realized, and insights into their role in tumor development and progression are being used to design new drug targets and cancer therapies.

Increased PSA expression on prostate cancer exosomes in in vitro condition and in cancer patients

Prostate specific antigen (PSA) test is the most common, clinically validated test for the diagnosis of prostate cancer (PCa). While neoplastic lesions of the prostate may cause aberrant levels of PSA in the blood, the quantitation of free or complexed PSA poorly discriminates cancer patients from those developing benign lesions, often leading to invasive and unnecessary surgical procedures. Microenvironmental acidity increases exosome release by cancer cells. In this study we evaluated whether acidity, a critical phenotype of malignancy, could influence exosome release and increase the PSA expression in nanovesicles released by PCa cells. To this aim, we exploited Nanoparticle Tracking Analysis (NTA), an immunocapture-based ELISA, and nanoscale flow-cytometry. The results show that microenvironmental acidity induces an increased release of nanovesicles expressing both PSA and the exosome marker CD81. In order to verify whether the changes induced by the local selective pressure of extracellular acidity may correspond to a clinical pathway we used the same approach to evaluate the levels of PSA-expressing exosomes in the plasma of PCa patients and controls, including subjects with benign prostatic hypertrophy (BPH). The results show that only PCa patients have high levels of nanovesicles expressing both CD81 and PSA. This study shows that tumor acidity exerts a selective pressure leading to the release of extracellular vesicles that express both PSA and exosome markers. A comparable scenario was shown in the plasma of prostate cancer patients as compared to both BPH and healthy controls. These results suggest that microenvironmental acidity may represent a key factor which determines qualitatively and quantitatively the release of extracellular vesicles by malignant tumors, including prostate cancer. This condition leads to the spill-over of nanovesicles into the peripheral blood of prostate cancer patients, where the levels of tumor biomarkers expressed by exosomes, such as PSA-exosomes, may represent a novel, non-invasive clinical tool for the screening and early diagnosis of prostate cancer.

Similarities and Distinctions of Cancer and Immune Metabolism in Inflammation and Tumors

It has been appreciated for nearly 100 years that cancer cells are metabolically distinct from resting tissues. More recently understood is that this metabolic phenotype is not unique to cancer cells but instead reflects characteristics of proliferating cells. Similar metabolic transitions also occur in the immune system as cells transition from resting state to stimulated effectors. A key finding in immune metabolism is that the metabolic programs of different cell subsets are distinctly associated with immunological function. Further, interruption of those metabolic pathways can shift immune cell fate to modulate immunity. These studies have identified numerous metabolic similarities between cancer and immune cells but also critical differences that may be exploited and that affect treatment of cancer and immunological diseases.

Fine-Tuning Tumor Endothelial Cells to Selectively Kill Cancer

Tumor endothelial cells regulate several aspects of tumor biology, from delivering oxygen and nutrients to shaping the immune response against a tumor and providing a barrier against tumor cell dissemination. Accordingly, targeting tumor endothelial cells represents an important modality in cancer therapy. Whereas initial anti-angiogenic treatments focused mainly on blocking the formation of new blood vessels in cancer, emerging strategies are specifically influencing certain aspects of tumor endothelial cells. For instance, efforts are generated to normalize tumor blood vessels in order to improve tumor perfusion and ameliorate the outcome of chemo-, radio-, and immunotherapy. In addition, treatment options that enhance the properties of tumor blood vessels that support a host’s anti-tumor immune response are being explored. Hence, upcoming anti-angiogenic strategies will shape some specific aspects of the tumor blood vessels that are no longer limited to abrogating angiogenesis. In this review, we enumerate approaches that target tumor endothelial cells to provide anti-cancer benefits and discuss their therapeutic potential.

Restoring microenvironmental redox and pH homeostasis inhibits neoplastic cell growth and migration: therapeutic efficacy of esomeprazole plus sulfasalazine on 3-MCA-induced sarcoma

Neoplastic cells live in a stressful context and survive thanks to their ability to overcome stress. Thus, tumor cell responses to stress are potential therapeutic targets. We selected two such responses in melanoma and sarcoma cells: the xc- antioxidant system, that opposes oxidative stress, and surface v-ATPases that counteract the low pHi by extruding protons, and targeted them with the xc- blocker sulfasalazine and the proton pump inhibitor esomeprazole. Sulfasalazine inhibited the cystine/cysteine redox cycle and esomeprazole decreased pHi while increasing pHe in tumor cell lines. Although the single treatment with either drug slightly inhibited cell proliferation and motility, the association of sulfasalazine and esomeprazole powerfully decreased sarcoma and melanoma growth and migration. In the 3-methylcholanthrene (3-MCA)-induced sarcoma model, the combined therapy strongly reduced the tumor burden and increased the survival time: notably, 22 % of double-treated mice recovered and survived off therapy. Tumor-associated macrophages (TAM) displaying M2 markers, that abundantly infiltrate sarcoma and melanoma, overexpress xc- and membrane v-ATPases and were drastically decreased in tumors from mice undergone the combined therapy. Thus, the double targeting of tumor cells and macrophages by sulfasalazine and esomeprazole has a double therapeutic effect, as decreasing TAM infiltration deprives tumor cells of a crucial allied. Sulfasalazine and esomeprazole may therefore display unexpected therapeutic values, especially in case of hard-to-treat cancers.

Foxp3 Reprograms T Cell Metabolism to Function in Low-Glucose, High-Lactate Environments

Immune cells function in diverse metabolic environments. Tissues with low glucose and high lactate concentrations, such as the intestinal tract or ischemic tissues, frequently require immune responses to be more pro-tolerant, avoiding unwanted reactions against self-antigens or commensal bacteria. T-regulatory cells (Tregs) maintain peripheral tolerance, but how Tregs function in low-glucose, lactate-rich environments is unknown. We report that the Treg transcription factor Foxp3 reprograms T cell metabolism by suppressing Myc and glycolysis, enhancing oxidative phosphorylation, and increasing nicotinamide adenine dinucleotide oxidation. These adaptations allow Tregs a metabolic advantage in low-glucose, lactate-rich environments; they resist lactate-mediated suppression of T cell function and proliferation. This metabolic phenotype may explain how Tregs promote peripheral immune tolerance during tissue injury but also how cancer cells evade immune destruction in the tumor microenvironment. Understanding Treg metabolism may therefore lead to novel approaches for selective immune modulation in cancer and autoimmune diseases.

Metabolic Cooperation and Competition in the Tumor Microenvironment: Implications for Therapy

The tumor microenvironment (TME) is an ensemble of non-tumor cells comprising fibroblasts, cells of the immune system, and endothelial cells, besides various soluble secretory factors from all cellular components (including tumor cells). The TME forms a pro-tumorigenic cocoon around the tumor cells where reprogramming of the metabolism occurs in tumor and non-tumor cells that underlies the nature of interactions as well as competitions ensuring steady supply of nutrients and anapleoretic molecules for the tumor cells that fuels its growth even under hypoxic conditions. This metabolic reprogramming also plays a significant role in suppressing the immune attack on the tumor cells and in resistance to therapies. Thus, the metabolic cooperation and competition among the different TME components besides the inherent alterations in the tumor cells arising out of genetic as well as epigenetic changes supports growth, metastasis, and therapeutic resistance. This review focuses on the metabolic remodeling achieved through an active cooperation and competition among the three principal components of the TME—the tumor cells, the T cells, and the cancer-associated fibroblasts while discussing about the current strategies that target metabolism of TME components. Further, we will also consider the probable therapeutic opportunities targeting the various metabolic pathways as well as the signaling molecules/transcription factors regulating them for the development of novel treatment strategies for cancer.

Linking tumor glycolysis and immune evasion in cancer: Emerging concepts and therapeutic opportunities

Metabolic reprogramming and immune evasion are two hallmarks of cancer. Metabolic reprogramming is exemplified by cancer's propensity to utilize glucose at an exponential rate which in turn is linked with "aerobic glycolysis", popularly known as the "Warburg effect". Tumor glycolysis is pivotal for the efficient management of cellular bioenergetics and uninterrupted cancer growth. Mounting evidence suggests that tumor glycolysis also plays a key role in instigating immunosuppressive networks that are critical for cancer cells to escape immune surveillance ("immune evasion"). Recent data show that induction of cellular stress or metabolic dysregulation sensitize cancer cells to antitumor immune cells implying that metabolic reprogramming and immune evasion harmonize during cancer progression. However, the molecular link between these two hallmarks of cancer remains obscure. In this review the molecular intricacies of tumor glycolysis that facilitate immune evasion has been discussed in the light of recent research to explore immunotherapeutic potential of targeting cancer metabolism.

Emerging functional roles of nuclear receptors in breast cancer

Nuclear receptors (NRs) have been targets of intensive drug development for decades due to their roles as key regulators of multiple developmental, physiological and disease processes. In breast cancer, expression of the estrogen and progesterone receptor remains clinically important in predicting prognosis and determining therapeutic strategies. More recently, there is growing evidence supporting the involvement of multiple nuclear receptors other than the estrogen and progesterone receptors, in the regulation of various processes important to the initiation and progression of breast cancer. We review new insights into the mechanisms of action of NRs made possible by recent advances in genomic technologies and focus on the emerging functional roles of NRs in breast cancer biology, including their involvement in circadian regulation, metabolic reprogramming and breast cancer migration and metastasis.

Cancer acidity: An ultimate frontier of tumor immune escape and a novel target of immunomodulation

The link between cancer metabolism and immunosuppression, inflammation and immune escape has generated major interest in investigating the effects of low pH on tumor immunity. Indeed, microenvironmental acidity may differentially impact on diverse components of tumor immune surveillance, eventually contributing to immune escape and cancer progression. Although the molecular pathways underlying acidity-related immune dysfunctions are just emerging, initial evidence indicates that antitumor effectors such as T and NK cells tend to lose their function and undergo a state of mostly reversible anergy followed by apoptosis, when exposed to low pH environment. At opposite, immunosuppressive components such as myeloid cells and regulatory T cells are engaged by tumor acidity to sustain tumor growth while blocking antitumor immune responses. Local acidity could also profoundly influence bioactivity and distribution of antibodies, thus potentially interfering with the clinical efficacy of therapeutic antibodies including immune checkpoint inhibitors. Hence tumor acidity is a central regulator of cancer immunity that orchestrates both local and systemic immunosuppression and that may offer a broad panel of therapeutic targets. This review outlines the fundamental pathways of acidity-driven immune dysfunctions and sheds light on the potential strategies that could be envisaged to potentiate immune-mediated tumor control in cancer patients.

Nanomedicine as a potent strategy in melanoma tumor microenvironment

Melanoma originated from melanocytes is the most aggressive type of skin cancer. Despite considerable progresses in clinical treatment with the discovery of BRAF or MEK inhibitors and monoclonal antibodies, the durability of response to treatment is often limited to the development of acquired resistance and systemic toxicity. The limited success of conventional treatment highlights the importance of understanding the role of melanoma tumor microenvironment in tumor developement and drug resistance. Nanoparticles represent a promising strategy for the development of new cancer treatments able to improve the bioavailability of drugs and increase their penetration by targeting specifically tumors cells and/or tumor environment. In this review, we will discuss the main influence of tumor microenvironment in melanoma growth and treatment outcome. Furthermore, third generation loaded nanotechnologies represent an exciting tool for detection, treatment, and escape from possible mechanism of resistance mediated by tumor microenvironment, and will be highlighted in this review.

Aerobic glycolysis and high level of lactate in cancer metabolism and microenvironment

Metabolic abnormalities is a hallmark of cancer. About 100 years ago, Nobel laureate Otto Heinrich Warburg first described high rate of glycolysis in cancer cells. Recently more and more novel opinions about cancer metabolism supplement to this hypothesis, consist of glucose uptake, lactic acid generation and secretion, acidification of the microenvironment and cancer immune evasion. Here we briefly review metabolic pathways generating lactate, and discuss the function of higher lactic acid in cancer microenvironments.

Therapeutic implications of tumor interstitial acidification

Interstitial acidification is a hallmark of solid tumor tissues resulting from the combination of different factors, including cellular buffering systems, defective tissue perfusion and high rates of cellular metabolism. Besides contributing to tumor pathogenesis and promoting tumor progression, tumor acidosis constitutes an important intrinsic and extrinsic mechanism modulating therapy sensitivity and drug resistance. In fact, pharmacological properties of anticancer drugs can be affected not only by tissue structure and organization but also by the distribution of the interstitial tumor pH. The acidic tumor environment is believed to create a chemical barrier that limits the effects and activity of many anticancer drugs. In this review article we will discuss the general protumorigenic effects of acidosis, the role of tumor acidosis in the modulation of therapeutic efficacy and potential strategies to overcome pH-dependent therapy-resistance.

Antitumor effect of combination of the inhibitors of two new oncotargets: proton pumps and reverse transcriptase

Tumor therapy needs new approaches in order to improve efficacy and reduce toxicity of the current treatments. The acidic microenvironment and the expression of high levels of endogenous non-telomerase reverse transcriptase (RT) are common features of malignant tumor cells. The anti-acidic proton pump inhibitor Lansoprazole (LAN) and the non-nucleoside RT inhibitor Efavirenz (EFV) have shown independent antitumor efficacy. LAN has shown to counteract drug tumor resistance. We tested the hypothesis that combination of LAN and EFV may improve the overall antitumor effects. We thus pretreated human metastatic melanoma cells with LAN and then with EFV, both in 2D and 3D spheroid models. We evaluated the treatment effect by proliferation and cell death/apoptosis assays in classical and in pulse administration experiments. The action of EFV was negatively affected by the tumor microenvironmental acidity, and LAN pretreatment overcame the problem. LAN potentiated the cytotoxicity of EFV to melanoma cells and, when administered during the drug interruption period, prevented the replacement of tumor cell growth.This study supports the implementation of the current therapies with combination of Proton Pumps and Reverse Transcriptase inhibitors.

Proton pump inhibition and cancer therapeutics: A specific tumor targeting or it is a phenomenon secondary to a systemic buffering?

One of the unsolved mysteries in oncology includes the strategies that cancer cells adopt to cope with an adverse microenvironment. However, we knew, from the Warburg's discovery that through their metabolism based on sugar fermentation, cancer cells acidify their microenvironment and this progressive acidification induces a selective pressure, leading to the development of very malignant cells entirely armed to survive in the hostile microenvironment generated by their own metabolism. In the last decades a primordial role for proton exchangers has been supported as a key tumor advantage in facing off the acidic milieu. Proton exchangers do not allow intracellular acidification through a continuous elimination of H+ either outside the cells or within the internal vacuoles. This article wants to comment a translational process through that led to the preclinical demonstration that a class of proton pump inhibitors (PPI) exploited worldwide for peptic ulcer treatment and gastroprotection are indeed powerful chemosensitizers as well. In this process we achieved the clinical proof of concept that PPI may well be included in new anti-cancer strategies with a solid background and rationale.

Acidic pH reduces VEGF-mediated endothelial cell responses by downregulation of VEGFR-2; relevance for anti-angiogenic therapies

Anti-angiogenic treatments targeting the vascular endothelial growth factor or its receptors have shown clinical benefits. However, impact on long-term survival remains limited. Solid tumors display an acidic microenvironment that profoundly influences their biology. Consequences of acidity on endothelial cells and anti-angiogenic therapies remain poorly characterized and hence are the focus of this study. We found that exposing endothelial cells to acidic extracellular pH resulted in reduced cell proliferation and migration. Also, whereas VEGF increased endothelial cell proliferation and survival at pH 7.4, it had no effect at pH 6.4. Furthermore, in acidic conditions, stimulation of endothelial cells with VEGF did not result in activation of downstream signaling pathways such as AKT. At a molecular level, acidity significantly decreased the expression of VEGFR-2 by endothelial cells. Consequently, anti-angiogenic therapies that target VEGFR-2 such as sunitinib and sorafenib failed to block endothelial cell proliferation in acidic conditions. In vivo, neutralizing tumor acidity with sodium bicarbonate increased the percentage of endothelial cells expressing VEGFR-2 in tumor xenografts. Furthermore, combining sodium bicarbonate with sunitinib provided stronger anti-cancer activity than either treatment alone. Histological analysis showed that sunitinib had a stronger anti-angiogenic effect when combined with sodium bicarbonate. Overall, our results show that endothelial cells prosper independently of VEGF in acidic conditions partly as a consequence of decreased VEGFR-2 expression. They further suggest that strategies aiming to raise intratumoral pH can improve the efficacy of anti-VEGF treatments.

Dynamic contrast-enhanced MR imaging in predicting progression of enhancing lesions persisting after standard treatment in glioblastoma patients: a prospective study

OBJECTIVES

To prospectively explore the value of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in predicting the progression of enhancing lesions persisting after standard treatment in patients with surgically resected glioblastoma (GBM).

METHODS

Forty-seven GBM patients, who underwent near-total tumorectomy followed by concurrent chemoradiation therapy (CCRT) with temozolomide (TMZ) between May 2014 and February 2016, were enrolled. Twenty-four patients were finally analyzed for measurable enhancing lesions persisting after standard treatment. DCE-MRI parameters were calculated at enhancing lesions. Mann-Whitney U tests and multivariable stepwise logistic regression were used to compare parameters between progression (n = 16) and non-progression (n = 8) groups.

RESULTS

Mean K^trans and v_e were significantly lower in progression than in non-progression (P = 0.037 and P = 0.037, respectively). The 5th percentile of the cumulative K^trans histogram was also significantly lower in the progression than in non-progression group (P = 0.017). Mean v_e was the only independent predictor of progression (P = 0.007), with a sensitivity of 100%, specificity of 63%, and an overall accuracy of 88% at a cut-off value of 0.873.

CONCLUSIONS

DCE-MRI may help predict the progression of enhancing lesions persisting after the completion of standard treatment in patients with surgically resected GBM, with mean v_e serving as an independent predictor of progression.

KEY POINTS

• Enhancing lesions may persist after standard treatment in GBM patients. • DCE-MRI may help predict the progression of the enhancing lesions. • Mean K ^trans and v _e were lower in progression than in non-progression group. • DCE-MRI may help identify patients requiring close follow-up after standard treatment. • DCE-MRI may help plan treatment strategies for GBM patients.

Acidic tumor microenvironment abrogates the efficacy of mTORC1 inhibitors

Background

Blocking the mechanistic target of rapamycin complex-1 (mTORC1) with chemical inhibitors such as rapamycin has shown limited clinical efficacy in cancer. The tumor microenvironment is characterized by an acidic pH which interferes with cancer therapies. The consequences of acidity on the anti-cancer efficacy of mTORC1 inhibitors have not been characterized and are thus the focus of our study.

Methods

Cancer cell lines were treated with rapamycin in acidic or physiological conditions and cell proliferation was investigated. The effect of acidity on mTORC1 activity was determined by Western blot. The anticancer efficacy of rapamycin in combination with sodium bicarbonate to increase the intratumoral pH was tested in two different mouse models and compared to rapamycin treatment alone. Histological analysis was performed on tumor samples to evaluate proliferation, apoptosis and necrosis.

Results

Exposing cancer cells to acidic pH in vitro significantly reduced the anti-proliferative effect of rapamycin. At the molecular level, acidity significantly decreased mTORC1 activity, suggesting that cancer cell proliferation is independent of mTORC1 in acidic conditions. In contrast, the activation of mitogen-activated protein kinase (MAPK) or AKT were not affected by acidity, and blocking MAPK or AKT with a chemical inhibitor maintained an anti-proliferative effect at low pH. In tumor mouse models, the use of sodium bicarbonate increased mTORC1 activity in cancer cells and potentiated the anti-cancer efficacy of rapamycin. Combining sodium bicarbonate with rapamycin resulted in increased tumor necrosis, increased cancer cell apoptosis and decreased cancer cell proliferation as compared to single treatment.

Conclusions

Taken together, these results emphasize the inefficacy of mTORC1 inhibitors in acidic conditions. They further highlight the potential of combining sodium bicarbonate with mTORC1 inhibitors to improve their anti-tumoral efficacy.

LDHA-Associated Lactic Acid Production Blunts Tumor Immunosurveillance by T and NK Cells

Elevated lactate dehydrogenase A (LDHA) expression is associated with poor outcome in tumor patients. Here we show that LDHA-associated lactic acid accumulation in melanomas inhibits tumor surveillance by T and NK cells. In immunocompetent C57BL/6 mice, tumors with reduced lactic acid production (Ldha^low) developed significantly slower than control tumors and showed increased infiltration with IFN-γ-producing T and NK cells. However, in Rag2^-/-γc^-/- mice, lacking lymphocytes and NK cells, and in Ifng^-/- mice, Ldha^low and control cells formed tumors at similar rates. Pathophysiological concentrations of lactic acid prevented upregulation of nuclear factor of activated T cells (NFAT) in T and NK cells, resulting in diminished IFN-γ production. Database analyses revealed negative correlations between LDHA expression and T cell activation markers in human melanoma patients. Our results demonstrate that lactic acid is a potent inhibitor of function and survival of T and NK cells leading to tumor immune escape.

Targeting Immune Regulatory Networks to Counteract Immune Suppression in Cancer

The onset of cancer is unavoidably accompanied by suppression of antitumor immunity. This occurs through mechanisms ranging from the progressive accumulation of regulatory immune cells associated with chronic immune stimulation and inflammation, to the expression of immunosuppressive molecules. Some of them are being successfully exploited as therapeutic targets, with impressive clinical results achieved in patients, as in the case of immune checkpoint inhibitors. To limit immune attack, tumor cells exploit specific pathways to render the tumor microenvironment hostile for antitumor effector cells. Local acidification might, in fact, anergize activated T cells and facilitate the accumulation of immune suppressive cells. Moreover, the release of extracellular vesicles by tumor cells can condition distant immune sites contributing to the onset of systemic immune suppression. Understanding which mechanisms may be prevalent in specific cancers or disease stages, and identifying possible strategies to counterbalance would majorly contribute to improving clinical efficacy of cancer immunotherapy. Here, we intend to highlight these mechanisms, how they could be targeted and the tools that might be available in the near future to achieve this goal.

Cancer: fundamentals behind pH targeting and the double-edged approach

The highly regulated pH of cells and the less-regulated pH of the surrounding extracellular matrix (ECM) is the result of a delicate balance between metabolic processes and proton production, proton transportation, chemical buffering, and vascular removal of waste products. Malignant cells show a pronounced increase in metabolic processes where the 10- to 15-fold rise in glucose consumption is only the tip of the iceberg. Aerobic glycolysis (Warburg effect) is one of the hallmarks of cancer metabolism that implies excessive production of protons, which if stayed inside the cells would result in fatal intracellular acidosis (maintaining a strict acid-base balance is essential for the survival of eukaryotic cells). Malignant cells solve this problem by increasing mechanisms of proton transportation which expel the excess acidity. This allows cancer cells to keep a normal intracellular pH, or even overshooting this mechanism permits a slightly alkaline intracellular tendency. The proton excess expelled from malignant cells accumulates in the ECM, where chronic hypoxia and relative lack of enough blood vessels impede adequate proton clearance, thus creating an acidic microenvironment. This microenvironment is quite heterogeneous due to the tumor's metabolic heterogeneity and variable degrees of hypoxia inside the tumor mass. The acidic environment (plus other necessary cellular modifications) stimulates migration and invasion and finally intravasation of malignant cells which eventually may result in metastasis. Targeting tumor pH may go in two directions: 1) increasing extracellular pH which should result in less migration, invasion, and metastasis; and 2) decreasing intracellular pH which may result in acidic stress and apoptosis. Both objectives seem achievable at the present state of the art with repurposed drugs. This hypothesis analyzes the altered pH of tumors and its implications for progression and metastasis and also possible repurposed drug combinations targeting this vulnerable side of cancer development. It also analyzes the double-edged approach, which consists in pharmacologically increasing intracellular proton production and simultaneously decreasing proton extrusion creating intracellular acidity, acid stress, and eventual apoptosis.

Clinical significance of T cell metabolic reprogramming in cancer

Conversion of normal cells to cancer is accompanied with changes in their metabolism. During this conversion, cell metabolism undergoes a shift from oxidative phosphorylation to aerobic glycolysis, also known as Warburg effect, which is a hallmark for cancer cell metabolism. In cancer cells, glycolysis functions in parallel with the TCA cycle and other metabolic pathways to enhance biosynthetic processes and thus support proliferation and growth. Similar metabolic features are observed in T cells during activation but, in contrast to cancer, metabolic transitions in T cells are part of a physiological process. Currently, there is intense interest in understanding the cause and effect relationship between metabolic reprogramming and T cell differentiation. After the recent success of cancer immunotherapy, the crosstalk between immune system and cancer has come to the forefront of clinical and basic research. One of the key goals is to delineate how metabolic alterations of cancer influence metabolism-regulated function and differentiation of tumor resident T cells and how such effects might be altered by immunotherapy. Here, we review the unique metabolic features of cancer, the implications of cancer metabolism on T cell metabolic reprogramming during antigen encounters, and the translational prospective of harnessing metabolism in cancer and T cells for cancer therapy.

Effect of Modified Alkaline Supplementation on Syngenic Melanoma Growth in CB57/BL Mice

Tumor extracellular acidity is a hallmark of malignant cancers. Thus, in this study we evaluated the effects of the oral administration of a commercially available water alkalizer (Basenpulver®) (BP) on tumor growth in a syngenic melanoma mouse model. The alkalizer was administered daily by oral gavage starting one week after tumor implantation in CB57/BL mice. Tumors were calipered and their acidity measured by in vivo MRI guided 31P MRS. Furthermore, urine pH was monitored for potential metabolic alkalosis. BP administration significantly reduced melanoma growth in mice; the optimal dose in terms of tolerability and efficacy was 8 g/l (p< 0.05). The in vivo results were supported by in vitro experiments, wherein BP-treated human and murine melanoma cell cultures exhibited a dose-dependent inhibition of tumor cell growth. This investigation provides the first proof of concept that systemic buffering can improve tumor control by itself and that this approach may represent a new strategy in prevention and/or treatment of cancers.

Monodispersed calcium carbonate nanoparticles modulate local pH and inhibit tumor growth in vivo

The acidic extracellular environment of tumors potentiates their aggressiveness and metastasis, but few methods exist to selectively modulate the extracellular pH (pHe) environment of tumors. Transient flushing of biological systems with alkaline fluids or proton pump inhibitors is impractical and nonselective. Here we report a nanoparticles-based strategy to intentionally modulate the pHe in tumors. Biochemical simulations indicate that the dissolution of calcium carbonate nanoparticles (nano-CaCO3) in vivo increases pH asymptotically to 7.4. We developed two independent facile methods to synthesize monodisperse non-doped vaterite nano-CaCO3 with distinct size range between 20 and 300 nm. Using murine models of cancer, we demonstrate that the selective accumulation of nano-CaCO3 in tumors increases tumor pH over time. The associated induction of tumor growth stasis is putatively interpreted as a pHe increase. This study establishes an approach to prepare nano-CaCO3 over a wide particle size range, a formulation that stabilizes the nanomaterials in aqueous solutions, and a pH-sensitive nano-platform capable of modulating the acidic environment of cancer for potential therapeutic benefits.

Acidic tumor microenvironment in human melanoma

One characteristic of solid tumors such as malignant melanoma is the acidification of the tumor microenvironment. The deregulation of cancer cell metabolism is considered a main cause of extracellular acidosis. Here, cancer cells utilize aerobic glycolysis instead of oxidative phosphorylation even under normoxic conditions, as originally described by Otto Warburg. These metabolic alterations cause enhanced acid production, especially of lactate and carbon dioxide (CO2 ). The extensive production of acidic metabolites and the enhanced acid export to the extracellular space cause a consistent acidification of the tumor microenvironment, thus promoting the formation of an acid-resistant tumor cell population with increased invasive and metastatic potential. As melanoma is one of the deadliest and most metastatic forms of cancer, understanding the effects of this extracellular acidosis on human melanoma cells with distinct metastatic properties is important. The aim of this review was to summarize recent studies of the acidification of the tumor microenvironment, focusing on the specific effects of the acidic milieu on melanoma cells and to give a short overview of therapeutic approaches.

Suppressive effects of tumor cell-derived 5'-deoxy-5'-methylthioadenosine on human T cells

The immunosuppressive tumor microenvironment represents one of the main obstacles for immunotherapy of cancer. The tumor milieu is among others shaped by tumor metabolites such as 5'-deoxy-5'-methylthioadenosine (MTA). Increased intratumoral MTA levels result from a lack of the MTA-catabolizing enzyme methylthioadenosine phosphorylase (MTAP) in tumor cells and are found in various tumor entities. Here, we demonstrate that MTA suppresses proliferation, activation, differentiation, and effector function of antigen-specific T cells without eliciting cell death. Conversely, if MTA is added to highly activated T cells, MTA exerts cytotoxic effects on T cells. We identified the Akt pathway, a critical signal pathway for T cell activation, as a target of MTA, while, for example, p38 remained unaffected. Next, we provide evidence that MTA exerts its immunosuppressive effects by interfering with protein methylation in T cells. To confirm the relevance of the suppressive effects of exogenously added MTA on human T cells, we used an MTAP-deficient tumor cell-line that was stably transfected with the MTAP-coding sequence. We observed that T cells stimulated with MTAP-transfected tumor cells revealed a higher proliferative capacity compared to T cells stimulated with Mock-transfected cells. In conclusion, our findings reveal a novel immune evasion strategy of human tumor cells that could be of interest for therapeutic targeting.

Metformin is also effective on lactic acidosis-exposed melanoma cells switched to oxidative phosphorylation

Low extracellular pH promotes in melanoma cells a malignant phenotype characterized by an epithelial-to-mesenchymal transition (EMT) program, endowed with mesenchymal markers, high invasiveness and pro-metastatic property. Here, we demonstrate that melanoma cells exposed to an acidic extracellular microenvironment, 6.7±0.1, shift to an oxidative phosphorylation (Oxphos) metabolism. Metformin, a biguanide commonly used for type 2 diabetes, inhibited the most relevant features of acid-induced phenotype, including EMT and Oxphos. When we tested effects of lactic acidosis, to verify whether sodium lactate might have additional effects on acidic melanoma cells, we found that EMT and Oxphos also characterized lactic acid-treated cells. An increased level of motility was the only gained property of lactic acidic-exposed melanoma cells. Metformin treatment inhibited both EMT markers and Oxphos and, when its concentration raised to 10 mM, it induced a striking inhibition of proliferation and colony formation of acidic melanoma cells, both grown in protons enriched medium or lactic acidosis. Thus, our study provides the first evidence that metformin may target either proton or lactic acidosis-exposed melanoma cells inhibiting EMT and Oxphox metabolism. These findings disclose a new potential rationale of metformin addition to advanced melanoma therapy, e.g. targeting acidic cell subpopulation.

Mitochondrial pyruvate carrier function and cancer metabolism

Metabolic reprogramming in cancer supports the increased biosynthesis required for unchecked proliferation. Increased glucose utilization is a defining feature of many cancers that is accompanied by altered pyruvate partitioning and mitochondrial metabolism. Cancer cells also require mitochondrial tricarboxylic acid cycle activity and electron transport chain function for biosynthetic competency and proliferation. Recent evidence demonstrates that mitochondrial pyruvate carrier (MPC) function is abnormal in some cancers and that increasing MPC activity may decrease cancer proliferation. Here we examine recent findings on MPC function and cancer metabolism. Special emphasis is placed on the compartmentalization of pyruvate metabolism and the alternative routes of metabolism that maintain the cellular biosynthetic pools required for unrestrained proliferation in cancer.

Pharmacological Modulation of Proton Channel Hv1 in Cancer Therapy: Future Perspectives

The pharmacological modulation of the immunosuppressive tumor microenvironment has emerged as a relevant component for cancer therapy. Several approaches aiming to deplete innate and adaptive suppressive populations, to circumvent the impairment in antigen presentation, and to ultimately increase the frequency of activated tumor-specific T cells are currently being explored. In this review, we address the potentiality of targeting the voltage-gated proton channel, Hv1, as a novel strategy to modulate the tumor microenvironment. The function of Hv1 in immune cells such as macrophages, neutrophils, dendritic cells, and T cells has been associated with the maintenance of NADPH oxidase activity and the generation of reactive oxygen species, which are required for the host defense against pathogens. We discuss evidence suggesting that the Hv1 proton channel could also be important for the function of these cells within the tumor microenvironment. Furthermore, as summarized here, tumor cells express Hv1 as a primary mechanism to extrude the increased amount of protons generated metabolically, thus maintaining physiologic values for the intracellular pH. Therefore, because this channel might be relevant for both tumor cells and immune cells supporting tumor growth, the pharmacological inhibition of Hv1 could be an innovative approach for cancer therapy. With that focus, we analyzed the available compounds that inhibit Hv1, highlighted the need to develop better drugs suitable for patients, and commented on the future perspectives of targeting Hv1 in the context of cancer therapy.

Modified STAP conditions facilitate bivalent fate decision between pluripotency and apoptosis in Jurkat T-lymphocytes

Low extracellular pH (pHe) is not only the result of cancer metabolism, but a factor of anti-cancer drug efficacy and cancer immunity. In this study, the consequences of acidic stress were evaluated by applying STAP protocol on Jurkat T-lymphocytes (2.0 × 10(6) cells/ml, 25 min in 37 °C). We detected apoptotic process exclusively in pH 3.3 treated cells within 8 h with western blotting (WB). This programmed cell death led to significant drop of cell viability in 72 h measured by MTT assay resulting PI positive population on flow cytometry (FCM) at day 7. Quantified RT-PCR (qRT-PCR) data indicated that all of above mentioned responses are irrelevant to expression of OCT4 gene variants. Interestingly enough, pluripotent cells represented by positive alkaline phosphatase (AP) staining survived acidic stress and consequently proportion of AP positive cells was significantly increased after pH 3.3 treatment (day 7). In general, acidic treatment led to an apoptotic condition for Jurkat T-lymphocytes, which occurred independent of OCT4 induction.

Proton pump inhibitors induce a caspase-independent antitumor effect against human multiple myeloma

Multiple Myeloma (MM) is the second most common hematological malignancy and is responsive to a limited number of drugs. Unfortunately, to date, despite the introduction of novel drugs, no relevant increase in survival rates has been obtained. Proton pump inhibitors (PPIs) have been shown to have significant antitumor action as single agents as well as in combination with chemotherapy. This study investigates the potential anti-tumor effectiveness of two PPIs, Lansoprazole and Omeprazole, against human MM cells. We found that Lansoprazole exerts straightforward efficacy against myeloma cells, even at suboptimal concentrations (50 µM), while Omeprazole has limited cytotoxic action. The Lansoprazole anti-MM effect was mostly mediated by a caspase-independent apoptotic-like cytotoxicity, with only a secondary anti-proliferative action. This study provides clear evidence supporting the use of Lansoprazole in the strive against MM with an efficacy proven much higher than current therapeutical approaches and without reported side effects. It is however conceivable that, consistent with the results obtained in other human tumors, Lansoprazole may well be combined with existing anti-myeloma therapies with the aim to improve the low level of efficacy of the current strategies.

Lactate Contribution to the Tumor Microenvironment: Mechanisms, Effects on Immune Cells and Therapeutic Relevance

Malignant transformation of cells leads to enhanced glucose uptake and the conversion of a larger fraction of pyruvate into lactate, even under normoxic conditions; this phenomenon of aerobic glycolysis is largely known as the Warburg effect. This metabolic reprograming serves to generate biosynthetic precursors, thus facilitating the survival of rapidly proliferating malignant cells. Extracellular lactate directs the metabolic reprograming of tumor cells, thereby serving as an additional selective pressure. Besides tumor cells, stromal cells are another source of lactate production in the tumor microenvironment, whose role in both tumor growth and the antitumor immune response is the subject of intense research. In this review, we provide an integral perspective of the relationship between lactate and the overall tumor microenvironment, from lactate structure to metabolic pathways for its synthesis, receptors, signaling pathways, lactate-producing cells, lactate-responding cells, and how all contribute to the tumor outcome. We discuss the role of lactate as an immunosuppressor molecule that contributes to tumor evasion and we explore the possibility of targeting lactate metabolism for cancer treatment, as well as of using lactate as a prognostic biomarker.

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.

CAR T-cell immunotherapy: The path from the by-road to the freeway?

Chimeric antigen receptors are genetically encoded artificial fusion molecules that can re-program the specificity of peripheral blood polyclonal T-cells against a selected cell surface target. Unparallelled clinical efficacy has recently been demonstrated using this approach to treat patients with refractory B-cell malignancy. However, the approach is technically challenging and can elicit severe toxicity in patients. Moreover, solid tumours have largely proven refractory to this approach. In this review, we describe the important structural features of CARs and how this may influence function. Emerging clinical experience is summarized in both solid tumours and haematological malignancies. Finally, we consider the particular challenges imposed by solid tumours to the successful development of CAR T-cell immunotherapy, together with a number of innovative strategies that have been developed in an effort to reverse the balance in favour of therapeutic benefit.

Evidence-based support for the use of proton pump inhibitors in cancer therapy

‘We can only cure what we can understand first’, said Otto H. Warburg, the 1931 Nobel laureate for his discovery on tumor metabolism. Unfortunately, we still don’t know too much the mechanisms underlying of cancer development and progression. One of the unsolved mystery includes the strategies that cancer cells adopt to cope with an adverse microenvironment. However, we knew, from the Warburg’s discovery, that through their metabolism based on sugar fermentation, cancer cells acidify their microenvironment and this progressive acidification induces a selective pressure, leading to development of very malignant cells entirely armed to survive in the hostile microenvironment generated by their own metabolism. One of the most mechanism to survive to the acidic tumor microenvironment are proton exchangers not allowing intracellular acidification through a continuous elimination of H⁺ either outside the cells or within the internal vacuoles. This article wants to comment a translational process through which from the preclinical demonstration that a class of proton pump inhibitors (PPI) exploited worldwide for peptic ulcer treatment and gastroprotection are indeed chemosensitizers as well, we have got to the clinical proof of concept that PPI may well be included in new anti-cancer strategies, and with a solid background and rationale.

Remodeling Components of the Tumor Microenvironment to Enhance Cancer Therapy

Solid tumor pathophysiology is characterized by an abnormal microenvironment that guides tumor progression and poses barriers to the efficacy of cancer therapies. Most common among tumor types are abnormalities in the structure of the tumor vasculature and stroma. Remodeling the tumor microenvironment with the aim to normalize any aberrant properties has the potential to improve therapy. In this review, we discuss structural abnormalities of the tumor microenvironment and summarize the therapeutic strategies that have been developed to normalize tumors as well as their potential to enhance therapy. Finally, we present different in vitro models that have been developed to analyze and better understand the effects of the tumor microenvironment on cancer cell behavior.

Proton pump inhibitors for the treatment of cancer in companion animals

The treatment of cancer presents a clinical challenge both in human and veterinary medicine. Chemotherapy protocols require the use of toxic drugs that are not always specific, do not selectively target cancerous cells thus resulting in many side effects. A recent therapeutic approach takes advantage of the altered acidity of the tumour microenvironment by using proton pump inhibitors (PPIs) to block the hydrogen transport out of the cell. The alteration of the extracellular pH kills tumour cells, reverses drug resistance, and reduces cancer metastasis. Human clinical trials have prompted to consider this as a viable and safe option for the treatment of cancer in companion animals. Preliminary animal studies suggest that the same positive outcome could be achievable. The purpose of this review is to support investigations into the use of PPIs for cancer treatment cancer in companion animals by considering the evidence available in both human and veterinary medicine.

Intermittent high dose proton pump inhibitor enhances the antitumor effects of chemotherapy in metastatic breast cancer

BACKGROUND

Acidity is a hallmark of malignant tumor, representing a very efficient mechanism of chemoresistance. Proton pump inhibitors (PPI) at high dosage have been shown to sensitize chemoresistant human tumor cells and tumors to cytotoxic molecules. The aim of this pilot study was to investigate the efficacy of PPI in improving the clinical outcome of docetaxel + cisplatin regimen in patients with metastatic breast cancer (MBC).

METHODS

Patients enrolled were randomly assigned to three arms: Arm A, docetaxel 75 mg/m(2) followed by cisplatin 75 mg/m(2) on d4, repeated every 21 days with a maximum of 6 cycles; Arm B, the same chemotherapy preceded by three days esomeprazole (ESOM) 80 mg p.o. bid, beginning on d1 repeated weekly. Weekly intermittent administration of ESOM (3 days on 4 days off) was maintained up to maximum 66 weeks; Arm C, the same as Arm B with the only difference being dose of ESOM at 100 mg p.o. bid. The primary endpoint was response rate.

RESULTS

Ninety-four patients were randomly assigned and underwent at least one injection of chemotherapy. Response rates for arm A, B and C were 46.9, 71.0, and 64.5 %, respectively. Median TTP for arm A (n = 32), B (n = 31), C (n = 31) were 8.7, 9.4, and 9.7 months, respectively. A significant difference was observed between patients who had taken PPI and who not with ORR (67.7 % vs. 46.9 %, p = 0.049) and median TTP (9.7 months vs. 8.7 months, p = 0.045) [corrected]. Exploratory analysis showed that among 15 patients with triple negative breast cancer (TNBC), this difference was bigger with median TTP of 10.7 and 5.8 months, respectively (p = 0.011). PPI combination showed a marked effect on OS as well, while with a borderline significance (29.9 vs. 19.2 months, p = 0.090). No additional toxicity was observed with PPI.

CONCLUSIONS

The results of this pilot clinical trial showed that intermittent high dose PPI enhance the antitumor effects of chemotherapy in MBC patients without evidence of additional toxicity, which requires urgent validation in a multicenter, randomized, phase III trial.

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NCT01069081 .

Microenvironment acidity as a major determinant of tumor chemoresistance: Proton pump inhibitors (PPIs) as a novel therapeutic approach

Despite the major progresses in biomedical research and the development of novel therapeutics and treatment strategies, cancer is still among the dominant causes of death worldwide. One of the crucial challenges in the clinical management of cancer is primary (intrinsic) and secondary (acquired) resistance to both conventional and targeted chemotherapeutics. Multiple mechanisms have been identifiedthat underlie intrinsic and acquired chemoresistance: these include impaired drug uptake, increased drug efflux, deletion of receptors, altered drug metabolism, quantitative and qualitative alterations in drug targets, increased DNA damage repair and various mechanisms of anti-apoptosis. The fast efflux of anticancer drugs mediated by multidrug efflux pumps and the partial or complete reversibility of chemoresistance combined with the absence of genetic mutations suggests a multifactorial process. However, a growing body of recent evidence suggests that chemoresistance is often triggered by the highly acidic microenvironment of tumors. The vast majority of drugs, including conventional chemotherapeutics and more recent biological agents, are weak bases that are quickly protonated and neutralized in acidic environments, such as the extracellular microenvironment and the acidic organelles of tumor cells. It is therefore essential to develop new strategies to overcome the entrapment and neutralization of weak base drugs. One such strategy is the use of proton pump inhibitors which can enhance tumor chemosensitivity by increasing the pH of the tumor microenvironment. Recent clinical trials in animals with spontaneous tumors have indicated that patient alkalization is capable of reversing acquired chemoresistance in a large percentage of tumors that are refractory to chemotherapy. Of particular interest was the benefit of alkalization for patients undergoing metronomic regimens which are becoming more widely used in veterinary medicine. Overall, these results provide substantial new evidence that altering the acidic tumor microenvironment is an effective, well tolerated and low cost strategy for the overcoming of anticancer drug resistance.

Cancer cell metabolism as new targets for novel designed therapies

Metabolic processes are altered in cancer cells, which obtain advantages from this metabolic reprogramming in terms of energy production and synthesis of biomolecules that sustain their uncontrolled proliferation. Due to the conceptual progresses in the last decade, metabolic reprogramming was recently included as one of the new hallmarks of cancer. The advent of high-throughput technologies to amass an abundance of omic data, together with the development of new computational methods that allow the integration and analysis of omic data by using genome-scale reconstructions of human metabolism, have increased and accelerated the discovery and development of anticancer drugs and tumor-specific metabolic biomarkers. Here we review and discuss the latest advances in the context of metabolic reprogramming and the future in cancer research.