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

How Reciprocal Interactions Between the Tumor Microenvironment and Ion Transport Proteins Drive Cancer Progression

Solid tumors comprise two major components: the cancer cells and the tumor stroma. The stroma is a mixture of cellular and acellular components including fibroblasts, mesenchymal and cancer stem cells, endothelial cells, immune cells, extracellular matrix, and tumor interstitial fluid. The insufficient tumor perfusion and the highly proliferative state and dysregulated metabolism of the cancer cells collectively create a physicochemical microenvironment characterized by altered nutrient concentrations and varying degrees of hypoxia and acidosis. Furthermore, both cancer and stromal cells secrete numerous growth factors, cytokines, and extracellular matrix proteins which further shape the tumor microenvironment (TME), favoring cancer progression.Transport proteins expressed by cancer and stromal cells localize at the interface between the cells and the TME and are in a reciprocal relationship with it, as both sensors and modulators of TME properties. It has been amply demonstrated how acid-base and nutrient transporters of cancer cells enable their growth, presumably by contributing both to the extracellular acidosis and the exchange of metabolic substrates and waste products between cells and TME. However, the TME also impacts other transport proteins important for cancer progression, such as multidrug resistance proteins. In this review, we summarize current knowledge of the cellular and acellular components of solid tumors and their interrelationship with key ion transport proteins. We focus in particular on acid-base transport proteins with known or proposed roles in cancer development, and we discuss their relevance for novel therapeutic strategies.

Ovarian Cancer Biomarkers: Moving Forward in Early Detection

Ovarian cancer is a silent cancer which rate survival mainly relays in early stage detection. The discovery of reliable ovarian cancer biomarkers plays a crucial role in the disease management and strongly impact in patient's prognosis and survival. Although having many limitations CA125 is a classical ovarian cancer biomarker, but current research using proteomic or metabolomic methodologies struggles to find alternative biomarkers, using non-invasive our relatively non-invasive sources such as urine, serum, plasma, tissue, ascites or exosomes. Metabolism and metabolites are key players in cancer biology and its importance in biomarkers discovery cannot be neglected. In this chapter we overview the state of art and the challenges facing the use and discovery of biomarkers and focus on ovarian cancer early detection.

Dynamic supraparticles for the treatment of age-related diseases

Age-related diseases (ARDs) are arising as a major threat to public health in our fast-aging society. Current development of nanomedicine has sparked much optimism toward ARDs management by improving drug delivery and controlled drug release. However, effective treatments for ARDs, such as cancer and Alzheimer's diseases (AD), are still lacking, due to the complicated pathological features of ARDs including multifactorial pathogenesis, intricate disease microenvironment, and dynamic symptom manifestation. Recently, dynamic supraparticles (DS), which are reversibly self-assembled functional nanoparticles, have provided a novel strategy for combating ARDs. Besides the intrinsic advantages of nanomedicine including multifunctional and multitarget, DS are capable of dynamic structural reconfiguration upon certain stimulation, creating another layer of maneuverability that allows programmed response to the spatiotemporal alterations of ARDs during progression and treatment. In this review, we will overview the challenges faced by ARDs management, and discuss the unique opportunities brought by DS. Then, we will summarize the designed synthesis of DS for ARDs treatment. Finally, we will dissect the therapeutic targets in ARDs that can be exploited by DS, and present the encouraging advances in this field. Hopefully, this review will bridge our knowledge of the design principle of DS and ARDs management, which may inspire the future development of potent theranostic agents to improve the healthcare.

[Metformin inhibits proliferation and functions of regulatory T cells in acidic environment]

OBJECTIVE

To investigate the regulatory effect of metformin on regulatory T cells (Treg) in acidic environment.

METHODS

CD4⁺ CD25⁺ Treg cells were obtained by magnetic bead sorting. Treg and conventional T cells (Tcon) cells were cultured for 24-72 h in pH 7.4 or pH 6.7 medium, and the cell proliferation, apoptosis and Foxp3 expression were detected by flow cytometry. Real-time PCR was used to detect the expression levels of the genes related with glucose metabolism. Thirty-two C57BL/6 male mouse models bearing subcutaneous prostate cancer xenograft derived from RM-1 cells were randomized into 4 equal groups for treatment with PBS, metformin, tumor vaccine, or both metformin and the vaccine. The treatment started on the 4th day following tumor cell injection, and metformin (100 mg/kg) or PBS was administered by intraperitoneal injection on a daily basis; the vaccine was intramuscularly injected every 4 days. The tumor size was continuously monitored, and the mice were euthanized on day 25 after tumor implantation to obtain tumor and blood samples. Flow cytometry was used to detect the changes in CD4⁺, CD8⁺, CD4⁺Foxp3⁺ cell subsets in the tumor tissue and peripheral blood.

RESULTS

Treg cells showed significantly enhanced proliferation (P < 0.05) while the proliferation of Tcon cells was suppressed in acidic medium (P < 0.001). Treg cells cultured in acidic medium showed significantly increased expressions of OXPHOS-related genes pgc1a (P < 0.001) and cox5b (P < 0.01), which did not vary significantly in Tcon cells in acidic medium. Treg cells exhibited significantly decreased apoptosis in acidic medium (P < 0.01) with increased Foxp3⁺ cells (P < 0.001) and intracellular alkaline levels (P < 0.01). Metformin obviously reversed the acid tolerance of Treg cells without producing significant effect on Tcon cells. In the animal experiment, both metformin (P < 0.05) and vaccine (P < 0.01) alone reduced the tumor volume, but their combined treatment more potently reduced the tumor volume (P < 0.001). Metformin alone did not obviously affect CD4⁺ cells or CD8⁺ cells but significantly decreased the percentage of CD4⁺Foxp3⁺ (P < 0.05); the vaccine alone significantly increased CD4⁺ cells and CD8⁺ cells (P < 0.001) and also the percentage of CD4⁺Foxp3⁺ cells (P < 0.05). The combined treatment, while reducing the percentage of CD4⁺Foxp3⁺cells to a level lower than that in the vaccine group (P < 0.01), produced the strongest effect to increase CD4⁺ cells and CD8⁺ cells (P < 0.01).

CONCLUSIONS

Metformin can inhibit the proliferation and function of regulatory T cells in an acidic environment and enhance the effect of tumor vaccine by reducing the proportion of Treg cells in vivo to achieve the anti-tumor effect.

Tumor Microenvironment: A Metabolic Player that Shapes the Immune Response

Immune cells survey and patrol throughout the body and sometimes take residence in niche environments with distinct cellular subtypes and nutrients that may fluctuate from those in which they matured. Rooted in immune cell physiology are metabolic pathways and metabolites that not only deliver substrates and energy for growth and survival, but also instruct effector functions and cell differentiation. Unlike cancer cells, immune cells are not subject to a "Darwinian evolutionary pressure" that would allow them to adapt to developing tumors but are often irrevocably affected to local nutrient deprivation. Thus, immune cells must metabolically adapt to these changing conditions in order to perform their necessary functions. On the other hand, there is now a growing appreciation that metabolic changes occurring in cancer cells can impact on immune cell functionality and contribute to tumor immune evasion, and as such, there is a considerable and growing interest in developing techniques that target metabolism for immunotherapy. In this review, we discuss the metabolic plasticity displayed by innate and adaptive immune cells and highlight how tumor-derived lactate and tumor acidity restrict immunity. To our knowledge, this review outlines the most recent insights on how tumor microenvironment metabolically instructs immune responsiveness.

The reciprocal regulation between host tissue and immune cells in pancreatic ductal adenocarcinoma: new insights and therapeutic implications

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related death and is one of the most difficult-to-treat cancers. Surgical resection and adjuvant therapy have limited effects on the overall survival of PDAC patients. PDAC exhibits an immunosuppressive microenvironment, the immune response predicts survival, and activation of immune system has the potential to produce an efficacious PDAC therapy. However, chimeric antigen receptor T (CAR-T) cell immunotherapy and immune checkpoint blockade (ICB), which have produced unprecedented clinical benefits in a variety of different cancers, produce promising results in only some highly selected patients with PDAC. This lack of efficacy may be because existing immunotherapies mainly target the interactions between cancer cells and immune cells. However, PDAC is characterized by an abundant tumor stroma that includes a heterogeneous mixture of immune cells, fibroblasts, endothelial cells, neurons and some molecular events. Immune cells engage in extensive and dynamic crosstalk with stromal components in the tumor tissue in addition to tumor cells, which subsequently impacts tumor suppression or promotion to a large extent. Therefore, exploration of the interactions between the stroma and immune cells may offer new therapeutic opportunities for PDAC. In this review, we discuss how infiltrating immune cells influence PDAC development and explore the contributions of complex components to the immune landscape of tumor tissue. The roles of stromal constituents in immune modulation are emphasized. We also predict potential therapeutic strategies to target signals in the immune network in the abundant stromal microenvironment of PDAC.

High-resolution label-free 3D mapping of extracellular pH of single living cells

Dynamic mapping of extracellular pH (pHe) at the single-cell level is critical for understanding the role of H+ in cellular and subcellular processes, with particular importance in cancer. While several pHe sensing techniques have been developed, accessing this information at the single-cell level requires improvement in sensitivity, spatial and temporal resolution. We report on a zwitterionic label-free pH nanoprobe that addresses these long-standing challenges. The probe has a sensitivity > 0.01 units, 2 ms response time, and 50 nm spatial resolution. The platform was integrated into a double-barrel nanoprobe combining pH sensing with feedback-controlled distance dependance via Scanning Ion Conductance Microscopy. This allows for the simultaneous 3D topographical imaging and pHe monitoring of living cancer cells. These classes of nanoprobes were used for real-time high spatiotemporal resolution pHe mapping at the subcellular level and revealed tumour heterogeneity of the peri-cellular environments of melanoma and breast cancer cells.

Intratumoral delivery of M-CSF by calcium crosslinked polymer micelles enhances cancer immunotherapy

Immunotherapy has shown promising results in multiple malignancies. However, there are still significant challenges in cancer immunotherapy including the powerful immunosuppressive tumor microenvironment and adverse off-target side effects. Nanomaterials with defined physico-biochemical properties are versatile drug delivery platforms that may address these key technical challenges faced by cancer immunotherapy. Here, a tumor acidity-responsive biomacromolecule delivery system was designed to intratumorally deliver an immune-activating cytokine, macrophage colony-stimulating factor (M-CSF) and attenuate the acidic microenvironment. This nanoparticle was prepared by introducing CaCO3 as a crosslinker to form an M-CSF-loaded stable micelle (NP/M-CSF/CaCO3). Administration of NP/M-CSF/CaCO3 significantly inhibited tumor growth by enhancing T cell-mediated anti-tumor immune responses and reversing the TAM-mediated immunosuppression. This study provides new avenues for cascade amplification of the antitumor effects by targeting the tumor microenvironment. This approach may also help avoid unwanted complications.

Antitumor and antioxidant effects of Clinacanthus nutans Lindau in 4 T1 tumor-bearing mice

Background

Clinacanthus nutans Lindau (C. nutans) is a species of in Acanthaceae family and primarily used in South East Asian countries. C. nutans is well known as Sabah snake grass in Malaysia, and its leaves have diverse medicinal potential in conventional applications, including cancer treatments. On the basis of literature search, there is less conclusive evidence of the involvement of phytochemical constituents in breast cancer, in particular, animal tumor models. The current study aimed to determine the antitumor and antioxidant activities of C. nutans extract in 4 T1 tumor-bearing mice.

Methods

C. nutans leaves were subjected to methanol extraction and divided into two different concentrations, 200 mg/kg (low-dose) and 1000 mg/kg (high-dose). The antitumor effects of C. nutans extracts were assessed using bone marrow smearing, clonogenic, and splenocyte immunotype analyses. In addition, hematoxylin and eosin, tumor weight and tumor volume profiles also used to indicate apoptosis appearance. Serum cytokine levels were examined using ELISA assay. In addition, nitric oxide assay reflecting antioxidant activity was performed.

Results

From the results obtained, the methanol extract of C. nutans leaves at 200 mg/kg (P < 0.05) and 1000 mg/kg (P < 0.05) showed a significant decrease in nitric oxide (NO) and malondialdehyde (MDA) levels in the blood. On the other hand, C. nutans extract (1000 mg/kg) also showed a significant decrease in the number of mitotic cells, tumor weight, and tumor volume. No inflammatory and adverse reactions related to splenocytes activities were found in all treated groups of mice. Despite its promising results, the concentration of both C. nutans extracts have also reduced the number of colonies formed in the liver and lungs.

Conclusion

In conclusion, C. nutans extracts exert antitumor and antioxidant activities against 4 T1 mouse breast model with no adverse effect and inflammatory response at high dose of 1000 mg/kg, indicating an effective and complementary approach for cancer prevention and treatment.

Novel anti-HER2 peptide-conjugated theranostic nanoliposomes combining NaYF4:Yb,Er nanoparticles for NIR-activated bioimaging and chemo-photodynamic therapy against breast cancer

Herein, we reported the fabrication of novel peptide-conjugated ligand-targeted nanoliposomes (LTLs) for chemo-photodynamic therapy against HER2-positive breast cancer. The LTL core was utilized for encapsulating doxorubicin (DOX) for chemotherapy, and methylene blue (MB) attached NaYF₄:Yb,Er upconversion nanoparticles (UCNPs) for NIR-activated bioimaging and leveraging its visible emission for photoexciting MB for enhanced photodynamic therapy (PDT). The specificity of our LTLs was achieved by conjugating a newly discovered anti-HER2 peptide screened from a phage display peptide library. The high selectivity of the peptide-conjugated LTLs was confirmed by confocal imaging of SKBR-3 (HER2-positive) and MCF-7 (HER2-negative) breast cancer cell lines, illustrating its target-specific nature. The energy transfer from UCNPs to MB was verified, thus enabling the generation of reactive oxygen species upon activation with a 975 nm laser source (0.60 W cm^-2) under 5 min continuous excitation. A significant decline in the cell viability by 95% was observed using chemo-photodynamic combinational therapy, whereas for chemo-drug alone and PDT alone, the cell proliferation declined by 77% and 84%, respectively. Furthermore, we demonstrated an improved uptake of the LTLs inside a 3D model of SKBR-3 tumor spheroids, where the spheroid cell viability was suppressed by 66% after the use of combinational therapy. Thus, our results suggest great prospective use of theranostic LTLs for breast cancer management.

Determinants of response and resistance to CAR T cell therapy

The remarkable success of chimeric antigen receptor (CAR)-engineered T cells in pre-B cell acute lymphoblastic leukemia (ALL) and B cell lymphoma led to the approval of anti-CD19 CAR T cells as the first ever CAR T cell therapy in 2017. However, with the number of CAR T cell-treated patients increasing, observations of tumor escape and resistance to CAR T cell therapy with disease relapse are demonstrating the current limitations of this therapeutic modality. Mechanisms hampering CAR T cell efficiency include limited T cell persistence, caused for example by T cell exhaustion and activation-induced cell death (AICD), as well as therapy-related toxicity. Furthermore, the physical properties, antigen heterogeneity and immunosuppressive capacities of solid tumors have prevented the success of CAR T cells in these entities. Herein we review current obstacles of CAR T cell therapy and propose strategies in order to overcome these hurdles and expand CAR T cell therapy to a broader range of cancer patients.

Pre-treatment serum bicarbonate predicts for primary tumor control after stereotactic body radiation therapy in patients with localized non-small cell lung cancer

BACKGROUND

Tumor aggressiveness and hypoxia are linked to acidosis in the tumor microenvironment (TME). We hypothesized that low pre-treatment serum bicarbonate, potentially correlating with an acidic and hypoxic TME, predicts for poor outcomes after stereotactic body radiation therapy (SBRT) for non-small cell lung cancer (NSCLC).

METHODS

We included patients with localized NSCLC treated to a biologically effective dose (BED) ≥ 100 Gy, with available pre-treatment bicarbonate values within 3 months of treatment. We used receiver operating characteristic analysis to determine the bicarbonate concentration optimally predicting for primary tumor recurrence, and evaluated its association with recurrence and survival. We validated our findings in an independent cohort of patients from three collaborating institutions.

RESULTS

A total of 110 patients and 114 tumors were included in the training cohort, with median follow-up of 15.0 months. Bicarbonate < 26 mEq/L was associated with primary tumor recurrence on univariate (HR = 5.92; 95% CI 1.69-24.88; p = 0.005) and multivariate analysis (HR = 5.48; 95% CI 1.37-25.19; p = 0.020). The validation cohort consisted of 195 patients and 208 tumors with median follow-up of 27.5 months. In the validation cohort, bicarbonate < 26 mEq/L was again associated with primary tumor recurrence on univariate (HR = 3.38; 95% CI 1.27-9.37; p = 0.015) and multivariate analysis (HR = 3.33; 1.18-10.07; p = 0.023).

CONCLUSIONS

Pre-treatment bicarbonate predicts for primary tumor control in NSCLC treated with SBRT and may be useful for risk stratification. These findings should be confirmed prospectively.

Extracellular pH modulating injectable gel for enhancing immune checkpoint inhibitor therapy

Clinical data from diverse cancer types shows that the increased T cell infiltration in tumors correlates with improved patient prognosis. Acidic extracellular pH is a major attribute of the tumor microenvironment (TME) that promotes immune evasion and tumor progression. Therefore, antagonizing tumor acidity can be a powerful approach in cancer immunotherapy. Here, Pluronic F-127 is used as a NaHCO₃ releasing carrier to focally alleviate extracellular tumor acidity. In a mouse tumor model, intratumoral treatment with pH modulating injectable gel (pH_e-MIG) generates immune-favorable TME, as evidenced by the decrease of immune-suppressive cells and increase of tumor infiltrating CD8+T cells. The combination of pH_e-MIG with immune checkpoint inhibitors, anti-PD-1 and anti-TIGIT antibodies, increases intratumoral T cell function, which leads to tumor clearance. Mechanistically, extracellular acidity was shown to upregulate co-inhibitory immune checkpoint receptors and inhibit mTOR signaling pathways in memory CD8+T cells, which impaired effector functions. Furthermore, an acidic pH environment increased the expression and engagement of TIGIT and its ligand CD155, which suggested that the extracellular pH can regulate the suppressive function of TIGIT pathway. Collectively, these findings suggest that pH_e-MIG holds potential as a new TME modulator for effective immune checkpoint inhibitor therapies.

Near-Infrared II Phototherapy Induces Deep Tissue Immunogenic Cell Death and Potentiates Cancer Immunotherapy

The deep and inner beds of solid tumors lack lymphocytic infiltration and are subjected to various immune escape mechanisms. Reversing immunosuppression deep within the tumor is vital in clinical cancer therapy, however it remains a huge challenge. In this work, we have demonstrated the use of a second window near-infrared (NIR(II)) photothermal treatment to trigger more homogeneous and deeper immunogenic cancer cell death in solid tumors, thereby eliciting both innate and adaptive immune responses for tumor control and metastasis prevention. Specifically, photothermal transducers with similar components, structures, and photothermal conversion efficiencies, but different absorptions in red light, NIR(I), and NIR(II) biowindows, were constructed by controlling the self-assembly of gold nanoparticles on fluidic liposomes. In vitro, photothermal treatments induced immunogenic cell death (ICD) that were accompanied by the release of damage-associated molecular patterns (DAMPs) regardless of the wavelength of incident lasers. In vivo, NIR(II) light resulted in a more homogeneous release and distribution of DAMPs in the deeper parts of the tumors. With the induction of ICD, NIR(II) photothermal therapy simultaneously triggered both innate and adaptive immune responses and enabled efficient tumor control with 5/8 of the mice remaining tumor-free in the cancer vaccination assay. Additionally, the NIR(II) photothermal treatment in combination with checkpoint blockade therapy exerted long-term tumor control over both primary and distant tumors. Finally, using systemically administered two-dimensional polypyrrole nanosheets as a NIR(II) transducer, we achieved striking therapeutic effects against whole-body tumor metastasis via a synergistic photothermal-immunological response.

Hyperthermia-Triggered Doxorubicin Release from Polymer-Coated Magnetic Nanorods

In this paper, it is proposed that polymer-coated magnetic nanorods (MNRs) can be used with the advantage of a double objective: first, to serve as magnetic hyperthermia agents, and second, to be used as magnetic vehicles for the antitumor drug doxorubicin (DOX). Two different synthetic methodologies (hydrothermal and co-precipitation) were used to obtain MNRs of maghemite and magnetite. They were coated with poly(ethyleneimine) and poly(sodium 4-styrenesulfonate), and loaded with DOX, using the Layer-by-Layer technique. Evidence of the polymer coating and the drug loading was justified by ATR-FTIR and electrophoretic mobility measurements, and the composition of the coated nanorods was obtained by a thermogravimetric analysis. The nanorods were tested as magnetic hyperthermia agents, and it was found that they provided sufficiently large heating rates to be used as adjuvant therapy against solid tumors. DOX loading and release were determined by UV-visible spectroscopy, and it was found that up to 50% of the loaded drug was released in about 5 h, although the rate of release could be regulated by simultaneous application of hyperthermia, which acts as a sort of external release-trigger. Shape control offers another physical property of the particles as candidates to interact with tumor cells, and particles that are not too elongated can easily find their way through the cell membrane.

Mechanisms of Small Heat Shock Proteins

Small heat shock proteins (sHSPs) are ATP-independent chaperones that delay formation of harmful protein aggregates. sHSPs' role in protein homeostasis has been appreciated for decades, but their mechanisms of action remain poorly understood. This gap in understanding is largely a consequence of sHSP properties that make them recalcitrant to detailed study. Multiple stress-associated conditions including pH acidosis, oxidation, and unusual availability of metal ions, as well as reversible stress-induced phosphorylation can modulate sHSP chaperone activity. Investigations of sHSPs reveal that sHSPs can engage in transient or long-lived interactions with client proteins depending on solution conditions and sHSP or client identity. Recent advances in the field highlight both the diversity of function within the sHSP family and the exquisite sensitivity of individual sHSPs to cellular and experimental conditions. Here, we will present and highlight current understanding, recent progress, and future challenges.

The Role of the Lymphocyte Functional Crosstalk and Regulation in the Context of Checkpoint Inhibitor Treatment-Review

During the last decade, the dynamics of the cellular crosstalk have highlighted the significance of the host vs. tumor interaction. This resulted in the development of novel immunotherapeutic strategies in order to modulate/inhibit the mechanisms leading to escape of tumor cells from immune surveillance. Different monoclonal antibodies directed against immune checkpoints, e.g., the T lymphocyte antigen 4 and the programmed cell death protein 1/ programmed cell death ligand 1 have been successfully implemented for the treatment of cancer. Despite their broad activity in many solid and hematologic tumor types, only 20–40% of patients demonstrated a durable treatment response. This might be due to an impaired T cell tumor interaction mediated by immune escape mechanisms of tumor and immune cells as well as alterations in the composition of the tumor microenvironment, peripheral blood, and microbiome. These different factors dynamically regulate different steps of the cancer immune process thereby negatively interfering with the T cell –mediated anti-tumoral immune responses. Therefore, this review will summarize the current knowledge of the different players involved in inhibiting tumor immunogenicity and mounting resistance to checkpoint inhibitors with focus on the role of tumor T cell interaction. A better insight of this process might lead to the development of strategies to revert these inhibitory processes and represent the rational for the design of novel immunotherapies and combinations in order to improve their efficacy.

Complexation of methotrexate via ligand diffusion molecular dynamic simulations under neutral, basic, and acidic conditions

Methotrexate (MTX), an FDA-approved drug employed in the treatment of several types of cancer and autoimmune diseases, is characterized by its poor solubility. Therefore, new strategies have been implemented such as coupling to nanocarriers to increase its solubility. Previous experimental studies have demonstrated complexation of MTX to polyamidoamine of a generation four (PAMAM-G4) dendrimer with a complex stoichiometry of 19/22:1 under neutral conditions, providing important information that can be used to further elucidate the structural and energetic basis of the molecular binding of MTX and PAMAM-G4. In this study, we performed ligand diffusion molecular dynamic simulations (LDMDSs), using 3 μs combined with the molecular mechanics generalized surface area (MMGBSA) approach employing saturating concentrations of MTX to explore the mechanism through which MTX is complexed by PAMAM-G4 at neutral, basic, and acidic conditions. Our results reproduce the reported complex stoichiometry between MTX and PAMAM-G4 in neutral conditions. Binding free energy values suggest a much slower release in neutral and acidic conditions, consistent with the controlled rate of drug release into the bloodstream and when reaching the acidic environment of tumor tissues. Altogether, the methodology employed and the results may be useful in the evaluation of other drugs of pharmaceutical interest.

Hydrogen Ion Dynamics of Cancer and a New Molecular, Biochemical and Metabolic Approach to the Etiopathogenesis and Treatment of Brain Malignancies

The treatment of cancer has been slowly but steadily progressing during the last fifty years. Some tumors with a high mortality in the past are curable nowadays. However, there is one striking exception: glioblastoma multiforme. No real breakthrough has been hitherto achieved with this tumor with ominous prognosis and very short survival. Glioblastomas, being highly glycolytic malignancies are strongly pH-dependent and driven by the sodium hydrogen exchanger 1 (NHE1) and other proton (H⁺) transporters. Therefore, this is one of those pathologies where the lessons recently learnt from the new pH-centered anticancer paradigm may soon bring a promising change to treatment. This contribution will discuss how the pH-centric molecular, biochemical and metabolic perspective may introduce some urgently needed and integral novel treatments. Such a prospective therapeutic approach for malignant brain tumors is developed here, either to be used alone or in combination with more standard therapies.

Immunity, Hypoxia, and Metabolism-the Ménage à Trois of Cancer: Implications for Immunotherapy

It is generally accepted that metabolism is able to shape the immune response. Only recently we are gaining awareness that the metabolic crosstalk between different tumor compartments strongly contributes to the harsh tumor microenvironment (TME) and ultimately impairs immune cell fitness and effector functions. The major aims of this review are to provide an overview on the immune system in cancer; to position oxygen shortage and metabolic competition as the ground of a restrictive TME and as important players in the anti-tumor immune response; to define how immunotherapies affect hypoxia/oxygen delivery and the metabolic landscape of the tumor; and vice versa, how oxygen and metabolites within the TME impinge on the success of immunotherapies. By analyzing preclinical and clinical endeavors, we will discuss how a metabolic characterization of the TME can identify novel targets and signatures that could be exploited in combination with standard immunotherapies and can help to predict the benefit of new and traditional immunotherapeutic drugs.

CD44 Receptor-Specific and Redox-Sensitive Nanophotosensitizers of Hyaluronic Acid-Chlorin e6 Tetramer Having Diselenide Linkages for Photodynamic Treatment of Cancer Cells

For reactive oxygen species (ROS)-sensitive and CD44 receptor-mediated delivery of photosensitizers, chlorin e6 (ce6) tetramer was synthesized using tetra acid (TA) via selenocystamine linkages and then conjugated with hyaluronic acid (HA) (abbreviated as HAseseCe6TA). HAseseCe6TA nanophotosensitizers were fabricated by dialysis procedure. HAseseCe6TA nanophotosensitizers showed spherical morphology with small particle sizes less than 100 nm and monomodal pattern. When H₂O₂ was added, size distribution was changed to multimodal pattern and morphological observation showed disintegration of nanophotosensitizers, indicating that HAseseCe6TA nanophotosensitizers have ROS sensitivity. Furthermore, H₂O₂ addition resulted in acceleration of Ce6 release from HAseseCe6TA nanophotosensitizers. In vitro cell culture study, HAseseCe6TA nanophotosensitizers increase Ce6 uptake ratio, ROS production efficiency, and photodynamic therapy efficacy in both B16F10 cells and CT26 cells. Especially, CD44-receptor blocking of cancer cells by pretreatment of HA showed that fluorescence intensity in B16F10 cells was significantly decreased while fluorescence intensity in CT26 cells was not significantly changed, indicating that HAseseCe6TA nanophotosensitizers can be delivered by CD44 receptor-mediated pathway. In vivo animal tumor xenograft study, HAseseCe6TA nanophotosensitizers was selectively delivered to B16F10 tumor rather than CT26 tumor. These results indicated that HAseseCe6TA nanophotosensitizers have ROS sensitivity and have CD44 receptor-recognition properties.

Programmed death-1 receptor (PD-1) and PD-ligand-1 (PD-L1) expression in non-small cell lung cancer and the immune-suppressive effect of anaerobic glycolysis

The microenvironment of a tumor may regulate the anti-tumor immune response. Intratumoral acidosis and hypoxia may suppress lymphocyte proliferation and migration, and this may have important implications in modern immunotherapy. The expression of PD-L1 by cancer cells and of PD-1 by tumor infiltrating lymphocytes (TILs) was assessed in tissue specimens from 98 operable NSCLC patients. Their prognostic role and their association with makers of glycolysis and anaerobic metabolism were assessed. Strong cytoplasmic/membrane PD-L1 expression was noted in 45/98 cases. Intense presence of TILs was noted in 42/98 cases (high TIL-score), and intense presence of PD-1 expressing TILs (high PIL-score) in 17/98 cases. PD-L1 expression was directly correlated with high PIL-score (p = 0.005). A significant inverse relationship was found between lactate dehydrogenase LDH5 expression and PIL-score (p = 0.008). Similarly, low PIL-score was significantly linked with high-hexokinase HXKII and monocarboxylate transporter MCT2 expression (p < 0.04). Cases with both intense TIL-score and PIL-score had significantly better survival (p < 0.05). For patients with high TIL-score or high PIL-score, PD-L1 overexpression defined significantly poorer survival (p = 0.01 and p = 0.03, respectively). In multivariate analysis, stage (p = 0.002, HR 3.33, 95%CI 1.4-4.5) and TIL-score (p = 0.02, HR 2.12, 95%CI 1.1-4.0) were independent predictive variables of death events. Given the low specificity of PD-L1 as a biomarker for anti-PD-1/PD-L1 immunotherapy, a combined assessment of TIL, PD-L1, PD-1, and LDH5 provides a tool for an immunological/metabolic classification of NSCLC tumors, with a different prognosis and different expected response to anti-PD-1/PD-L1 immunotherapy, which should be considered in relevant clinical trials.

Diverse Stakeholders of Tumor Metabolism: An Appraisal of the Emerging Approach of Multifaceted Metabolic Targeting by 3-Bromopyruvate

Malignant cells possess a unique metabolic machinery to endure unobstructed cell survival. It comprises several levels of metabolic networking consisting of 1) upregulated expression of membrane-associated transporter proteins, facilitating unhindered uptake of substrates; 2) upregulated metabolic pathways for efficient substrate utilization; 3) pH and redox homeostasis, conducive for driving metabolism; 4) tumor metabolism-dependent reconstitution of tumor growth promoting the external environment; 5) upregulated expression of receptors and signaling mediators; and 6) distinctive genetic and regulatory makeup to generate and sustain rearranged metabolism. This feat is achieved by a "battery of molecular patrons," which acts in a highly cohesive and mutually coordinated manner to bestow immortality to neoplastic cells. Consequently, it is necessary to develop a multitargeted therapeutic approach to achieve a formidable inhibition of the diverse arrays of tumor metabolism. Among the emerging agents capable of such multifaceted targeting of tumor metabolism, an alkylating agent designated as 3-bromopyruvate (3-BP) has gained immense research focus because of its broad spectrum and specific antineoplastic action. Inhibitory effects of 3-BP are imparted on a variety of metabolic target molecules, including transporters, metabolic enzymes, and several other crucial stakeholders of tumor metabolism. Moreover, 3-BP ushers a reconstitution of the tumor microenvironment, a reversal of tumor acidosis, and recuperative action on vital organs and systems of the tumor-bearing host. Studies have been conducted to identify targets of 3-BP and its derivatives and characterization of target binding for further optimization. This review presents a brief and comprehensive discussion about the current state of knowledge concerning various aspects of tumor metabolism and explores the prospects of 3-BP as a safe and effective antineoplastic agent.

mTOR Senses Intracellular pH through Lysosome Dispersion from RHEB

Acidity, generated in hypoxia or hypermetabolic states, perturbs homeostasis and is a feature of solid tumors. That acid peripherally disperses lysosomes is a three-decade-old observation, yet one little understood or appreciated. However, recent work has recognized the inhibitory impact this spatial redistribution has on mechanistic target of rapamycin complex 1 (mTORC1), a key regulator of metabolism. This finding argues for a paradigm shift in localization of mTORC1 activator Ras homolog enriched in brain (RHEB), a conclusion several others have now independently reached. Thus, mTORC1, known to sense amino acids, mitogens, and energy to restrict biosynthesis to times of adequate resources, also senses pH and, via dampened mTOR-governed synthesis of clock proteins, regulates the circadian clock to achieve concerted responses to metabolic stress. While this may allow cancer to endure metabolic deprivation, immune cell mTOR signaling likewise exhibits pH sensitivity, suggesting that suppression of antitumor immune function by solid tumor acidity may additionally fuel cancers, an obstacle potentially reversible through therapeutic pH manipulation.

The Natural Compound Climacostol as a Prodrug Strategy Based on pH Activation for Efficient Delivery of Cytotoxic Small Agents

We synthesized and characterized MOMO as a new small molecule analog of the cytotoxic natural product climacostol efficiently activated in mild extracellular acidosis. The synthesis of MOMO had a key step in the Wittig olefination for the construction of the carbon-carbon double bond in the alkenyl moiety of climacostol. The possibility of obtaining the target (Z)-alkenyl MOMO derivative in very good yield and without presence of the less active (E)-diastereomer was favored from the methoxymethyl ether (MOM)-protecting group of hydroxyl functions in aromatic ring of climacostol aldehyde intermediate. Of interest, the easy removal of MOM-protecting group in a weakly acidic environment allowed us to obtain a great quantity of climacostol in biologically active (Z)-configuration. Results obtained in free-living ciliates that share the same micro-environment of the climacostol natural producer Climacostomum virens demonstrated that MOMO is well-tolerated in a physiological environment, while its cytotoxicity is rapidly and efficiently triggered at pH 6.3. In addition, the cytostatic vs. cytotoxic effects of acidified-MOMO can be modulated in a dose-dependent manner. In mouse melanoma cells, MOMO displayed a marked pH-sensitivity since its cytotoxic and apoptotic effects become evident only in mild extracellular acidosis. Data also suggested MOMO being preferentially activated in the unique extra-acidic microenvironment that characterizes tumoural cells. Finally, the use of the model organism Drosophila melanogaster fed with an acidic diet supported the efficient activity and oral delivery of MOMO molecule in vivo. MOMO affected oviposition of mating adults and larvae eclosion. Reduced survival of flies was due to lethality during the larval stages while emerging larvae retained their ability to develop into adults. Interestingly, the gut of eclosed larvae exhibited an extended damage (cell death by apoptosis) and the brain tissue was also affected (reduced mitosis), demonstrating that orally activated MOMO efficiently targets different tissues of the developing fly. These results provided a proof-of-concept study on the pH-dependence of MOMO effects. In this respect, MOM-protection emerges as a potential prodrug strategy which deserves to be further investigated for the generation of efficient pH-sensitive small organic molecules as pharmacologically active cytotoxic compounds.

Disturbances in H+ dynamics during environmental carcinogenesis

Despite the improvement of diagnostic methods and anticancer therapeutics, the human population is still facing an increasing incidence of several types of cancers. According to the World Health Organization, this growing trend would be partly linked to our environment, with around 20% of cancers stemming from exposure to environmental contaminants, notably chemicals like polycyclic aromatic hydrocarbons (PAHs). PAHs are widespread pollutants in our environment resulting from incomplete combustion or pyrolysis of organic material, and thus produced by both natural and anthropic sources; notably benzo[a]pyrene (B[a]P), i.e. the prototypical molecule of this family, that can be detected in cigarette smoke, diesel exhaust particles, occupational-related fumes, and grilled food. This molecule is a well-recognized carcinogen belonging to group 1 carcinogens. Indeed, it can target the different steps of the carcinogenic process and all cancer hallmarks. Interestingly, H⁺ dynamics have been described as key parameters for the occurrence of several, if not all, of these hallmarks. However, information regarding the role of such parameters during environmental carcinogenesis is still very scarce. The present review will thus mainly give an overview of the impact of B[a]P on H⁺ dynamics in liver cells, and will show how such alterations might impact different aspects related to the finely-tuned balance between cell death and survival processes, thereby likely favoring environmental carcinogenesis. In total, the main objective of this review is to encourage further research in this poorly explored field of environmental molecular toxicology.

Acidosis and cancer: from mechanism to neutralization

The extracellular pH of solid tumors is unequivocally acidic due to a combination of high rates of lactic acid production (a consequence of fermentative glycolytic metabolism) and poor perfusion. This has been documented by us and others in a wide variety of solid tumor models, primarily using magnetic resonance spectroscopic imaging (MRSI). This acidity contributes to tumor progression by inducing genome instability, promoting local invasion and metastases, inhibiting anti-tumor immunity, and conferring resistance to chemo- and radio-therapies. Systemic buffer therapies can neutralize tumor acidity and has been shown to inhibit local invasion and metastasis and improve immune surveillance in a variety of cancer model systems. This review will revisit the causes and consequences of acidosis by summarizing strategies used by cancer cells to adapt to acidosis, and how this acidity associated with carcinogenesis, metastasis, and immune function. Finally, this review will discuss how neutralization of acidity can be used to inhibit carcinogenesis and metastasis and improve anti-cancer immunotherapy.

Resveratrol Action on Lipid Metabolism in Cancer

Cancer diseases have the leading position in human mortality nowadays. The age of oncologic patients is still decreasing, and the entire scientific society is eager for new ways to fight against cancer. One of the most discussed issues is prevention by means of natural substances. Resveratrol is a naturally occurring plant polyphenol with proven antioxidant, anti-inflammatory, and anticancer effects. Tumor cells display specific changes in the metabolism of various lipids. Resveratrol alters lipid metabolism in cancer, thereby affecting storage of energy, cell signaling, proliferation, progression, and invasiveness of cancer cells. At the whole organism level, it contributes to the optimal metabolism extent with respect to the demands of the organism. Thus, resveratrol could be used as a preventive and anticancer agent. In this review, we focus on some of the plethora of lipid pathways and signal molecules which are affected by resveratrol during carcinogenesis.

Stromal-induced mitochondrial re-education: Impact on epithelial-to-mesenchymal transition and cancer aggressiveness

Metabolic reprogramming as well as the flexible utilisation of fuel sources by tumour cells has been considered not only intrinsic to malignant cells but also sustained by resident and/or recruited stromal cells. The complexity of tumour-stroma cross-talk is experienced by neoplastic cells through profound changes in the own metabolic machinery. In such context, mitochondria are dynamic organelles that receive, orchestrate and exchange a multiplicity of stromal cues within the tumour cells to finely regulate key metabolic and signalling pathways, allowing malignant cells to adapt and thrive in an ever-changing environment. In this review, we focus on how tumour mitochondria are coached by stromal metabolic supply and how this re-education sustains tumour malignant traits.

Development of a platform for activatable fluorescent substrates of glucose transporters (GLUTs)

We have developed a platform for activatable fluorescent substrates of glucose transporters (GLUTs). We firstly conjugated fluorescein to glucosamine via an amide or methylene linker at the C-2 position of d-glucosamine, but the resulting compounds, FLG1 and FLG2, showed no uptake into MIN6 cells. So, we changed the fluorophore moiety to a fluorescein analogue, 2-Me TokyoGreen, which is less negatively charged. TokyoGreen-conjugated glucosamines TGG1 and TGG2 were successfully taken up into cells via GLUT. We further derivatized TGG1 and TGG2, and among the synthesized compounds, 2-Me-4-OMe TGG showed weak fluorescence under the acidic conditions of the extracellular environment inside tumors and in gastric cancers, and strong fluorescence at the intracellular physiological pH, under the control of a photoinduced electron transfer (PeT) process. This fluorogenic platform should be useful for developing a range of activatable fluorescent substrates targeting GLUTs, as well as derivatives that would be fluorescently activated by various intracellular enzymes, such as esterases, β-galactosidase and bioreductases.

Nanoenabled Modulation of Acidic Tumor Microenvironment Reverses Anergy of Infiltrating T Cells and Potentiates Anti-PD-1 Therapy

While tumor-infiltrating cytotoxic T lymphocytes play a critical role in controlling tumor development, they are generally impotent in an acidic tumor microenvironment. Systemic treatment to neutralize tumor acidity thus holds promise for the reversal of the anergic state of T cells and the improvement of T cell-associated immunotherapy. Herein, we report a proof-of-concept of RNAi nanoparticle-mediated therapeutic reversion of tumor acidity to restore the antitumor functions of T cells and potentiate the checkpoint blockade therapy. Our strategy utilized an in vivo optimized vesicular cationic lipid-assisted nanoparticle, as opposed to its micellar counterpart, to mediate systematic knockdown of lactate dehydrogenase A (LDHA) in tumor cells. The treatment resulted in the reprogramming of pyruvate metabolism, a reduction of the production of lactate, and the neutralization of the tumor pH. In immunocompetent syngeneic melanoma and breast tumor models, neutralization of tumor acidity increased infiltration with CD8⁺ T and NK cells, decreased the number of immunosuppressive T cells, and thus significantly inhibited the growth of tumors. Furthermore, the restoration of tumoral pH potentiated checkpoint inhibition therapy using the antibody of programmed cell death protein 1 (PD-1). However, in immunodeficient B6/ Rag1 ^-/- and NOG mice, the same treatment failed to control tumor growth, further proving that the attenuation of tumor growth by tumor acidity modulation was attributable to the activation of tumor-infiltrating immune cells.

Acidic Stress Triggers Sodium-Coupled Bicarbonate Transport and Promotes Survival in A375 Human Melanoma Cells

Melanoma cells preserve intracellular pH (pH_i) within a viable range despite an acidic ambient pH that typically falls below pH 7.0. The molecular mechanisms underlying this form of acidic preservation in melanoma remain poorly understood. Previous studies had demonstrated that proton transporters including the monocarboxylate transporter (MCT), the sodium hydrogen exchanger (NHE), and V-Type ATPase mediate acid extrusion to counter intracellular acidification in melanoma cells. In this report, the expression and function of the Sodium-Coupled Bicarbonate Transporter (NCBT) family of base loaders were further characterized in melanoma cell lines. NCBT family members were found to be expressed in three different melanoma cell lines – A375, MeWo, and HS695T – and included the electrogenic sodium-bicarbonate cotransporter isoforms 1 and 2 (NBCe1 and NBCe2), the electroneutral sodium-bicarbonate cotransporter (NBCn1), and the sodium-dependent chloride-bicarbonate exchanger (NDCBE). These transporters facilitated 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS)-dependent pH_i recovery in melanoma cells, in response to intracellular acidification induced by ammonium chloride prepulse. Furthermore, the expression of NCBTs were upregulated via chronic exposure to extracellular acidification. Given the current research interest in the NCBTs as a molecular driver of tumourigenesis, characterising NCBT in melanoma provides impetus for developing novel therapeutic targets for melanoma treatment.

Highly sensitive electron paramagnetic resonance nanoradicals for quantitative intracellular tumor oxymetric images

Purpose: Tumor oxygenation is a critical parameter influencing the efficacy of cancer therapy. Low levels of oxygen in solid tumor have been recognized as an indicator of malignant progression and metastasis, as well as poor response to chemo- and radiation therapy. Being able to measure oxygenation for an individual's tumor would provide doctors with a valuable way of identifying optimal treatments for patients. Methods: Electron paramagnetic resonance imaging (EPRI) in combination with an oxygen-measuring paramagnetic probe was performed to measure tumor oxygenation in vivo. Triarylmethyl (trityl) radical exhibits high specificity, sensitivity, and resolution for quantitative measurement of O₂ concentration. However, its in vivo applications in previous studies have been limited by the required high dosage, its short half-life, and poor intracellular permeability. To address these limitations, we developed high-capacity nanoformulated radicals that employed fluorescein isothiocyanate-labeled mesoporous silica nanoparticles (FMSNs) as trityl radical carriers. The high surface area nanostructure and easy surface modification of physiochemical properties of FMSNs enable efficient targeted delivery of highly concentrated, nonself-quenched trityl radicals, protected from environmental degradation and dilution. Results: We successfully designed and synthesized a tumor-targeted nanoplatform as a carrier for trityl. In addition, the nanoformulated trityl does not affect oxygen-sensing capacity by a self-relaxation or broadening effect. The FMSN-trityl exhibited high sensitivity/response to oxygen in the partial oxygen pressure range from 0 to 155 mmHg. Furthermore, MSN-trityl displayed outstanding intracellular oxygen mapping in both in vitro and in vivo animal studies. Conclusion: The highly sensitive nanoformulated trityl spin probe can profile intracellular oxygen distributions of tumor in a real-time and quantitative manner using in vivo EPRI.

Acidification of Tumor at Stromal Boundaries Drives Transcriptome Alterations Associated with Aggressive Phenotypes

Acidosis is a fundamental feature of the tumor microenvironment, which directly regulates tumor cell invasion by affecting immune cell function, clonal cell evolution, and drug resistance. Despite the important association of tumor microenvironment acidosis with tumor cell invasion, relatively little is known regarding which areas within a tumor are acidic and how acidosis influences gene expression to promote invasion. Here, we injected a labeled pH-responsive peptide to mark acidic regions within tumors. Surprisingly, acidic regions were not restricted to hypoxic areas and overlapped with highly proliferative, invasive regions at the tumor-stroma interface, which were marked by increased expression of matrix metalloproteinases and degradation of the basement membrane. RNA-seq analysis of cells exposed to low pH conditions revealed a general rewiring of the transcriptome that involved RNA splicing and enriched for targets of RNA binding proteins with specificity for AU-rich motifs. Alternative splicing of Mena and CD44, which play important isoform-specific roles in metastasis and drug resistance, respectively, was sensitive to histone acetylation status. Strikingly, this program of alternative splicing was reversed in vitro and in vivo through neutralization experiments that mitigated acidic conditions. These findings highlight a previously underappreciated role for localized acidification of tumor microenvironment in the expression of an alternative splicing-dependent tumor invasion program. SIGNIFICANCE: This study expands our understanding of acidosis within the tumor microenvironment and indicates that acidosis induces potentially therapeutically actionable changes to alternative splicing.

The role of extracellular vesicles from different origin in the microenvironment of head and neck cancers

The proliferation and metastasis ability of tumors are mediate by the "mutual dialogue" between cells in the tumor microenvironment (TME). Extracellular vesicles (EVs), mainly exosomes and microvesicles, play an important role in achieving intercellular substance transport and information transfer in the TME. Initially considered "garbage dumpsters" and later referred to as "signal boxes", EVs carry "cargo" (proteins, lipids, or nucleic acids) that can redirect the function of a recipient cell. Currently, the molecular mechanisms and clinical applications of EVs in head and neck cancers (HNCs) are still at an early stage and need to be further investigate. In this review, we provide insight into the TME of HNCs, classifying and summarizing EVs derived from different cell types and illuminating their complex signaling networks involved in mediating tumor proliferation, invasion and metastasis, vascular angiogenesis and cancer drug resistance. In addition, we highlight the application of EVs in HNCs, underlining the special pathological and physiological environment of HNCs. The application of tumor heterogeneous EVs in saliva and circulating blood diagnostics will provide a new perspective for the early screening, real-time monitoring and prognostic risk assessment of HNCs. Given the concept of precise and individual therapy, nanostructured EVs are equipped with superior characteristics of biocompatibility, low immunogenicity, loadability and modification ability, making these molecules one of the new strategies for HNCs treatment.

Metabolic alterations and the potential for targeting metabolic pathways in the treatment of multiple myeloma

Metabolism is defined as the collection of complex biochemical processes that living cells use to generate energy and maintain their growth and survival. Metabolism encompasses the synthesis and breakdown of glucose, fatty acids, and amino acids; the generation of energy (ATP); and oxidative phosphorylation. In cancer cells, metabolism can be commandeered to promote tumor growth and cellular proliferation. These alterations in metabolism have emerged as an additional hallmark of various cancers. In this review we focus on metabolic alterations in multiple myeloma (MM) - a malignancy of plasma cells - including derangements in glycolysis, gluconeogenesis, the tricarboxylic acid cycle, oxidative phosphorylation, and fatty acid/amino acid synthesis and degradation. Particular focus is given to metabolic alterations that contribute to myeloma cell growth, proliferation and drug resistance. Finally, novel approaches that target metabolic pathways for the treatment of MM are discussed.

Sculpting tumor microenvironment with immune system: from immunometabolism to immunoediting

Cancer immunotherapy unleashing the power of host immunity on eliminating cancer cells represents a critical advance in cancer treatment; however, effective anti-tumor responses are largely dampened by the immunosuppressive tumor microenvironment (TME). Emerging studies have revealed that physiological features in the TME, including glucose deprivation, hypoxia and low pH, established by the metabolically dysregulated cancer cells restrict anti-tumor immunity by impeding the metabolic fitness of tumor-infiltrating cytotoxic CD8⁺ T cells and natural killer (NK) cells. Furthermore, infiltrating immunomodulatory cells with different metabolic preferences also facilitate the establishment of the immunosuppressive TME. Therefore, deciphering the metabolic cross-talk between immune cells and cancer cells in the TME and elucidating the impact of this process during tumorigenesis are needed to harness anti-tumor immunity more effectively. Herein, we summarize the immunosuppressive features of TME and how these features impair anti-tumor immunity. Moreover, we postulate how immune cells may be involved in shaping the metabolic features of cancer cells and discuss how we might improve the anti-tumor functions of tumor-specific T cells by rewiring their metabolic regulations.

Mechano- and pH-sensing convergence on Ca2+-mobilising proteins - A recipe for cancer?

Alterations in the (bio)chemical and physical microenvironment of cells accompany and often promote disease formation and progression. This is particularly well established for solid cancers, which are typically stiffer than the healthy tissue in which they arise, and often display profound acidification of their interstitial fluid. Cell surface receptors can sense changes in the mechanical and (bio)chemical properties of the surrounding extracellular matrix and fluid, and signalling through these receptors is thought to play a key role in disease development and advancement. This review will look at ion channels and G protein coupled receptors that are activated by mechanical cues and extracellular acidosis, and stimulation of which results in increases in intracellular Ca²⁺ concentrations. Cellular Ca²⁺ levels are dysregulated in cancer as well as cancer-associated cells, and mechano- and proton-sensing proteins likely contribute to these aberrant intracellular Ca²⁺ signals, making them attractive targets for therapeutic intervention.

Immunotherapy for small cell lung cancer: mechanisms of resistance

INTRODUCTION

Small cell lung cancer (SCLC) is a highly malignant disease with a dismal prognosis that is currently being tested for theclinical activity of checkpoint inhibitors. SCLC is associated with smoking and exhibits a high mutational burden. However, low expression of PD-L1 and MHC antigens, as well low levels of immune cell infiltration and rapid tumor progress seems to limit the efficacy of anticancer immunity. Nevertheless, long-term survival was reported from studies using anti-PD-1/PD-L1 and CTLA-4 agents.

AREAS COVERED

Data of clinical trials of checkpoint inhibitors in SCLC show lower success rates compared to NSCLC. The mechanisms of resistance to immunotherapy are discussed for their relevance to SCLC patients.

EXPERT OPINION

Although some factors, such as a high mutation rate, favor immunotherapy for SCLC patients, downregulation of MHC class I, low expression of PD-L1, poor tumor infiltration by effector T cells, presence of myeloid-derived suppressor cells as well as regulatory T lymphocytes counteract the immune system activation by checkpoint inhibitors. Furthermore, this tumor develops avascular regions which have immunosuppressive effects and restrict access of lymphocytes and antibodies. In conclusion, immunotherapy in SCLC is effective in highly selected patients with good performance status and special and unknown preconditions contributing to long-lasting responses.

An Ultrasensitive Silicon Photonic Ion Sensor Enabled by 2D Plasmonic Molybdenum Oxide

Silicon photonics has demonstrated great potential in ultrasensitive biochemical sensing. However, it is challenging for such sensors to detect small ions which are also of great importance in many biochemical processes. A silicon photonic ion sensor enabled by an ionic dopant-driven plasmonic material is introduced here. The sensor consists of a microring resonator (MRR) coupled with a 2D restacked layer of near-infrared plasmonic molybdenum oxide. When the 2D plasmonic layer interacts with ions from the environment, a strong change in the refractive index results in a shift in the MRR resonance wavelength and simultaneously the alteration of plasmonic absorption leads to the modulation of MRR transmission power, hence generating dual sensing outputs which is unique to other optical ion sensors. Proof-of-concept via a pH sensing model is demonstrated, showing up to 7 orders improvement in sensitivity per unit area across the range from 1 to 13 compared to those of other optical pH sensors. This platform offers the unique potential for ultrasensitive and robust measurement of changes in ionic environment, generating new modalities for on-chip chemical sensors in the micro/nanoscale.

Brain Tumor Microenvironment and Host State: Implications for Immunotherapy

Glioblastoma (GBM) is a highly lethal brain tumor with poor responses to immunotherapies that have been successful in more immunogenic cancers with less immunosuppressive tumor microenvironments (TME). The GBM TME is uniquely challenging to treat due to tumor cell-extrinsic components that are native to the brain, as well as tumor-intrinsic mechanisms that aid in immune evasion. Lowering the barrier of immunosuppression by targeting the genetically stable tumor stroma presents opportunities to treat the tumor in a way that circumvents the complications of targeting a constantly mutating tumor with tumor antigen-directed therapies. Tumor-associated monocytes, macrophages, and microglia are a stromal element of particular interest. Macrophages and monocytes compose the bulk of infiltrating immune cells and are considered to have protumor and immunosuppressive effects. Targeting these cells or other stromal elements is expected to convert what is considered the "cold" TME of GBM to a more "hot" TME phenotype. This conversion could increase the effectiveness of what have become conventional frontline immunotherapies in GBM-creating opportunities for better treatment through combination therapy.

Neutrophil Degranulation, Plasticity, and Cancer Metastasis

Neutrophils are the first responders to inflammation and infection. Recently, an elevated neutrophil-to-lymphocyte ratio has generally become a prognostic indicator of poor overall survival in cancer. Accordingly, heterogeneous ill-defined neutrophil-like populations have been increasingly recognized as important players in cancer development. In addition, neutrophil granule proteins released upon cell activation have been associated with tumor progression; this differential granule mobilization may allow neutrophils - and possibly associated cancer cells - to leave the bloodstream and enter inflamed/infected tissues. This review discusses and proposes how granule mobilization may facilitate neutrophil-mediated transport of cancer cells into different tissues as well as leading to different cellular phenotypes that underlie remarkable neutrophil plasticity. This concept might inform novel neutrophil-centered approaches to putative cancer therapies.

pH as a potential therapeutic target to improve temozolomide antitumor efficacy : A mechanistic modeling study

Despite intensive treatments including temozolomide (TMZ) administration, glioblastoma patient prognosis remains dismal and innovative therapeutic strategies are urgently needed. A systems pharmacology approach was undertaken to investigate TMZ pharmacokinetics-pharmacodynamics (PK-PD) incorporating the effect of local pH, tumor spatial configuration and micro-environment. A hybrid mathematical framework was designed coupling ordinary differential equations describing the intracellular reactions, with a spatial cellular automaton to individualize the cells. A differential drug impact on tumor and healthy cells at constant extracellular pH was computationally demonstrated as TMZ-induced DNA damage was larger in tumor cells as compared to normal cells due to less acidic intracellular pH in cancer cells. Optimality of TMZ efficacy defined as maximum difference between damage in tumor and healthy cells was reached for extracellular pH between 6.8 and 7.5. Next, TMZ PK-PD in a solid tumor was demonstrated to highly depend on its spatial configuration as spread cancer cells or fragmented tumors presented higher TMZ-induced damage as compared to compact tumor spheroid. Simulations highlighted that smaller tumors were less acidic than bigger ones allowing for faster TMZ activation and their closer distance to blood capillaries allowed for better drug penetration. For model parameters corresponding to U87 glioma cells, inter-cell variability in TMZ uptake play no role regarding the mean drug-induced damage in the whole cell population whereas this quantity was increased by inter-cell variability in TMZ efflux which was thus a disadvantage in terms of drug resistance. Overall, this study revealed pH as a new potential target to significantly improve TMZ antitumor efficacy.

Anticancer drug discovery using multicellular tumor spheroid models

INTRODUCTION

Despite the increasing financial outlay on cancer research and drug discovery, many advanced cancers remain incurable. One possible strategy for increasing the approval rate of new anticancer drugs for use in clinical practice could be represented by three-dimensional (3D) tumor models on which to perform in vitro drug screening. There is a general consensus among the scientific community that 3D tumor models more closely recapitulate the complexity of tumor tissue architecture and biology than bi-dimensional cell cultures. In a 3D context, cells are connected to each other through tissue junctions and show proliferative and metabolic gradients that resemble the intricate milieu of organs and tumors. Areas covered: The present review focuses on available techniques for generating tumor spheroids and discusses current and future applications in the field of drug discovery. The article is based on literature obtained from PubMed. Expert opinion: Given the relative simplicity of spheroid models with respect to clinical tumors, we must be careful not to overestimate the reliability of their drug-response prediction capacity. The next challenge is to combine our knowledge of co-culture methodologies with high-content imaging and advanced microfluidic technologies to improve the readout and biomimetic potential of spheroid-based models.