Zoledronic acid overcomes chemoresistance and immunosuppression of malignant mesothelioma

Zoledronic acid enhances tumor growth and metastatic spread in a mouse model of jaw osteosarcoma

OBJECTIVES

Investigation of the therapeutic effect of zoledronic acid (ZA) in a preclinical model of jaw osteosarcoma (JO).

MATERIALS AND METHODS

The effect of 100 μg/kg ZA administered twice a week was assessed in a xenogenic mouse model of JO. The clinical (tumor growth, development of lung metastasis), radiological (bone microarchitecture by micro-CT analysis), and molecular and immunohistochemical (TRAP, RANK/RANKL, VEGF, and CD146) parameters were investigated.

RESULTS

Animals receiving ZA exhibited an increased tumor volume compared with nontreated animals (71.3 ± 14.3 mm3 vs. 51.9 ± 19.9 mm3 at D14, respectively; p = 0.06) as well as increased numbers of lung metastases (mean 4.88 ± 4.45 vs. 0.50 ± 1.07 metastases, respectively; p = 0.02). ZA protected mandibular bone against tumor osteolysis (mean bone volume of 12.81 ± 0.53 mm3 in the ZA group vs. 11.55 ± 1.18 mm3 in the control group; p = 0.01). ZA induced a nonsignificant decrease in mRNA expression of the osteoclastic marker TRAP and an increase in RANK/RANKL bone remodeling markers.

CONCLUSION

The use of bisphosphonates in the therapeutic strategy for JO should be further explored, as should the role of bone resorption in the pathophysiology of the disease.

Role of indoleamine 2, 3-dioxygenase 1 in immunosuppression of breast cancer

Breast cancer (BC) contributes greatly to global cancer incidence and is the main cause of cancer-related deaths among women globally. It is a complex disease characterized by numerous subtypes with distinct clinical manifestations. Immune checkpoint inhibitors (ICIs) are not effective in all patients and have been associated with tumor resistance and immunosuppression. Because amino acid (AA)-catabolizing enzymes have been shown to regulate immunosuppressive effects, this review investigated the immunosuppressive roles of indoleamine 2,3-dioxygenase 1 (IDO1), a tryptophan (Trp)-catabolizing enzyme, which is overexpressed in various metastatic tumors. It promotes immunomodulatory effects by depleting Trp in the regional microenvironment. This leads to a reduction in the number of immunogenic immune cells, such as effector T and natural killer (NK) cells, and an increase in tolerogenic immune cells, such as regulatory T (Treg) cells. The BC tumor microenvironment (TME) establishes a supportive niche where cancer cells can interact with immune cells and neighboring endothelial cells and is thus a feasible target for cancer therapy. In many immunological contexts, IDO1 regulates immune control by causing regional metabolic changes in the TME and tissue environment, which may further affect the maturation of systemic immunological tolerance. In the development of effective treatment targets and approaches, it is essential to understand the immunomodulatory effects exerted by AA-catabolizing enzymes, such as IDO1, on the components of the TME.

Role of exosomes in transferring chemoresistance through modulation of cancer glycolytic cell metabolism

Chemoresistance constitute a major obstacle in cancer treatment, leading to limited options and decreased patient survival. Recent studies have revealed a novel mechanism of chemoresistance acquisition: the transfer of information via exosomes, small vesicles secreted by various cells. Exosomes play a crucial role in intercellular communication by carrying proteins, nucleic acids, and metabolites, influencing cancer cell behavior and response to treatment. One crucial mechanism of resistance is cancer metabolic reprogramming, which involves alterations in the cellular metabolic pathways to support the survival and proliferation of drug-resistant cancer cells. This metabolic reprogramming often includes increased glycolysis, providing cancer cells with the necessary energy and building blocks to evade the effects of chemotherapy. Notably, exosomes have been found to transport glycolytic enzymes, as identified in proteomic profiling, leading to the reprogramming of metabolic pathways, facilitating altered glucose metabolism and increased lactate production. As a result, they profoundly impact the tumor microenvironment, promoting tumor progression, survival, immune evasion, and drug resistance.Understanding the complexities of such exosome-mediated cell-to-cell communication might open new therapeutic avenues and facilitate biomarker development in managing cancers characterized by aggressive glycolytic features. Moreover, given the intricate nature of metabolic abnormalities combining future exosome-based-targeted therapies with existing treatments like chemotherapy, immunotherapy, and targeted therapies holds promise for achieving synergistic effects to overcome resistance and improve cancer treatment outcomes.

Chronic Inflammation, Oxidative Stress and Metabolic Plasticity: Three Players Driving the Pro-Tumorigenic Microenvironment in Malignant Mesothelioma

Malignant pleural mesothelioma (MPM) is a lethal and rare cancer, even if its incidence has continuously increased all over the world. Asbestos exposure leads to the development of mesothelioma through multiple mechanisms, including chronic inflammation, oxidative stress with reactive oxygen species (ROS) generation, and persistent aberrant signaling. Together, these processes, over the years, force normal mesothelial cells' transformation. Chronic inflammation supported by "frustrated" macrophages exposed to asbestos fibers is also boosted by the release of pro-inflammatory cytokines, chemokines, growth factors, damage-associated molecular proteins (DAMPs), and the generation of ROS. In addition, the hypoxic microenvironment influences MPM and immune cells' features, leading to a significant rewiring of metabolism and phenotypic plasticity, thereby supporting tumor aggressiveness and modulating infiltrating immune cell responses. This review provides an overview of the complex tumor-host interactions within the MPM tumor microenvironment at different levels, i.e., soluble factors, metabolic crosstalk, and oxidative stress, and explains how these players supporting tumor transformation and progression may become potential and novel therapeutic targets in MPM.

Repurposing therapeutics for malignant pleural mesothelioma (MPM) - Updates on clinical translations and future outlook

INTRODUCTION

Malignant pleural mesothelioma (MPM) is a rare malignancy affecting the mesothelial cells in the pleural lining surrounding the lungs. First approved chemotherapy against MPM was a platinum/antifolate (cisplatin/pemetrexed) (2003). Since then, no USFDA approvals have gone through for small molecules as these molecules have not been proven to be therapeutically able in later stages of clinical studies. An alternative to conventional chemotherapy can be utilization of monoclonal antibodies, which are proven to improve patient survival significantly as compared to conventional chemotherapy (Nivolumab + Ipilimumab, 2020).

AREA COVERED

Drug repurposing has been instrumental in drug discovery for rare diseases such as MPM and multiple repositioned small molecule therapies and immunotherapies are currently being tested for its applicability in MPM management. This article summarizes essential breakthroughs along the pre-clinical and clinical developmental stages of small molecules and monoclonal antibodies for MPM management.

EXPERT OPINION

For rare diseases such as malignant pleural mesothelioma, a drug repurposing strategy can be adapted as it eases the financial burden on pharmaceutical companies along with fast-tracking development. With the rise of multiple small molecule repurposed therapies and innovations in localized treatment, MPM therapeutics are bound to be more effective in this decade.

Hypoxia as a driver of resistance to immunotherapy

Hypoxia, a hallmark of solid tumors, determines the selection of invasive and aggressive malignant clones displaying resistance to radiotherapy, conventional chemotherapy or targeted therapy. The recent introduction of immunotherapy, based on immune checkpoint inhibitors (ICPIs) and chimeric antigen receptor (CAR) T-cells, has markedly transformed the prognosis in some tumors but also revealed the existence of intrinsic or acquired drug resistance. In the current review we highlight hypoxia as a culprit of immunotherapy failure. Indeed, multiple metabolic cross talks between tumor and stromal cells determine the prevalence of immunosuppressive populations within the hypoxic tumor microenvironment and confer upon tumor cells resistance to ICPIs and CAR T-cells. Notably, hypoxia-triggered angiogenesis causes immunosuppression, adding another piece to the puzzle of hypoxia-induced immunoresistance. If these factors concurrently contribute to the resistance to immunotherapy, they also unveil an unexpected Achille's heel of hypoxic tumors, providing the basis for innovative combination therapies that may rescue the efficacy of ICPIs and CAR T-cells. Although these treatments reveal both a bright side and a dark side in terms of efficacy and safety in clinical trials, they represent the future solution to enhance the efficacy of immunotherapy against hypoxic and therapy-resistant solid tumors.

Control of adipogenic commitment by a STAT3-VSTM2A axis

White adipose tissue (WAT) is a dynamic organ that plays crucial roles in controlling metabolic homeostasis. During development and periods of energy excess, adipose progenitors are recruited and differentiate into adipocytes to promote lipid storage capability. The identity of adipose progenitors and the signals that promote their recruitment are still incompletely characterized. We have recently identified V-set and transmembrane domain-containing protein 2A (VSTM2A) as a novel protein enriched in preadipocytes that amplifies adipogenic commitment. Despite the emerging role of VSTM2A in promoting adipogenesis, the molecular mechanisms regulating Vstm2a expression in preadipocytes are still unknown. To define the molecular mechanisms controlling Vstm2a expression, we have treated preadipocytes with an array of compounds capable of modulating established regulators of adipogenesis. Here, we report that Vstm2a expression is positively regulated by PI3K/mTOR and cAMP-dependent signaling pathways and repressed by the MAPK pathway and the glucocorticoid receptor. By integrating the impact of all the molecules tested, we identified signal transducer and activator of transcription 3 (STAT3) as a novel downstream transcription factor affecting Vstm2a expression. We show that activation of STAT3 increased Vstm2a expression, whereas its inhibition repressed this process. In mice, we found that STAT3 phosphorylation is elevated in the early phases of WAT development, an effect that strongly associates with Vstm2a expression. Our findings identify STAT3 as a key transcription factor regulating Vstm2a expression in preadipocytes.NEW & NOTEWORTHY cAMP-dependent and PI3K-mTOR signaling pathways promote the expression of Vstm2a. STAT3 is a key transcription factor that controls Vstm2a expression in preadipocytes. STAT3 is activated in the early phases of WAT development, an effect that strongly associates with Vstm2a expression.

Hypoxia, endoplasmic reticulum stress and chemoresistance: dangerous liaisons

Solid tumors often grow in a micro-environment characterized by < 2% O₂ tension. This condition, together with the aberrant activation of specific oncogenic patwhays, increases the amount and activity of the hypoxia-inducible factor-1α (HIF-1α), a transcription factor that controls up to 200 genes involved in neoangiogenesis, metabolic rewiring, invasion and drug resistance. Hypoxia also induces endoplasmic reticulum (ER) stress, a condition that triggers cell death, if cells are irreversibly damaged, or cell survival, if the stress is mild.Hypoxia and chronic ER stress both induce chemoresistance. In this review we discuss the multiple and interconnected circuitries that link hypoxic environment, chronic ER stress and chemoresistance. We suggest that hypoxia and ER stress train and select the cells more adapted to survive in unfavorable conditions, by activating pleiotropic mechanisms including apoptosis inhibition, metabolic rewiring, anti-oxidant defences, drugs efflux. This adaptative process unequivocally expands clones that acquire resistance to chemotherapy.We believe that pharmacological inhibitors of HIF-1α and modulators of ER stress, although characterized by low specificty and anti-cancer efficacy when used as single agents, may be repurposed as chemosensitizers against hypoxic and chemorefractory tumors in the next future.

Hypoxia Dictates Metabolic Rewiring of Tumors: Implications for Chemoresistance

Hypoxia is a condition commonly observed in the core of solid tumors. The hypoxia-inducible factors (HIF) act as hypoxia sensors that orchestrate a coordinated response increasing the pro-survival and pro-invasive phenotype of cancer cells, and determine a broad metabolic rewiring. These events favor tumor progression and chemoresistance. The increase in glucose and amino acid uptake, glycolytic flux, and lactate production; the alterations in glutamine metabolism, tricarboxylic acid cycle, and oxidative phosphorylation; the high levels of mitochondrial reactive oxygen species; the modulation of both fatty acid synthesis and oxidation are hallmarks of the metabolic rewiring induced by hypoxia. This review discusses how metabolic-dependent factors (e.g., increased acidification of tumor microenvironment coupled with intracellular alkalinization, and reduced mitochondrial metabolism), and metabolic-independent factors (e.g., increased expression of drug efflux transporters, stemness maintenance, and epithelial-mesenchymal transition) cooperate in determining chemoresistance in hypoxia. Specific metabolic modifiers, however, can reverse the metabolic phenotype of hypoxic tumor areas that are more chemoresistant into the phenotype typical of chemosensitive cells. We propose these metabolic modifiers, able to reverse the hypoxia-induced metabolic rewiring, as potential chemosensitizer agents against hypoxic and refractory tumor cells.

Cholesterol metabolism: At the cross road between cancer cells and immune environment

Mevalonate pathway is a highly conserved pathway that produces isoprenoids and cholesterol, and it is often increased in cancer cells. Cholesterol, upstream metabolites including isoprenoids and cholesterol derivatives such as oxysterols modulate cell proliferation, motility, stemness and drug resistance. Moreover, when produced by cancer cells or immune infiltrating cells, they modulate the activity of immune populations of the tumor microenvironment. In this review, we will focus on the recent findings demonstrating that cholesterol derivatives may regulate tumor immune recognition or immune escape, playing a critical role in the immune surveillance. Since the mevalonate pathway is druggable, a deeper knowledge of the metabolic cross talks existing between the mevalonate pathway of cancer cells and immune cells may help to identify novel agents targeting cholesterol metabolism, able to boost the anti-tumor activity of the immune populations.

Various pathways of zoledronic acid against osteoclasts and bone cancer metastasis: a brief review

Zoledronic acid (ZA) is one of the most important and effective class of anti-resorptive drug available among bisphosphonate (BP), which could effectively reduce the risk of skeletal-related events, and lead to a treatment paradigm for patients with skeletal involvement from advanced cancers. However, the exact molecular mechanisms of its anticancer effects have only recently been identified. In this review, we elaborate the detail mechanisms of ZA through inhibiting osteoclasts and cancer cells, which include the inhibition of differentiation of osteoclasts via suppressing receptor activator of nuclear factor κB ligand (RANKL)/receptor activator of nuclear factor κB (RANK) pathway, non-canonical Wnt/Ca2+/calmodulin dependent protein kinase II (CaMKII) pathway, and preventing of macrophage differentiation into osteoclasts, in addition, induction of apoptosis of osteoclasts through inhibiting farnesyl pyrophosphate synthase (FPPS)-mediated mevalonate pathway, and activation of reactive oxygen species (ROS)-induced pathway. Furthermore, ZA also inhibits cancer cells proliferation, viability, motility, invasion and angiogenesis; induces cancer cell apoptosis; reverts chemoresistance and stimulates immune response; and acts in synergy with other anti-cancer drugs. In addition, some new ways for delivering ZA against cancer is introduced. We hope this review will provide more information in support of future studies of ZA in the treatment of cancers and bone cancer metastasis.

ABCA1/ABCB1 Ratio Determines Chemo- and Immune-Sensitivity in Human Osteosarcoma

The ATP Binding Cassette transporter B1 (ABCB1) induces chemoresistance in osteosarcoma, because it effluxes doxorubicin, reducing the intracellular accumulation, toxicity, and immunogenic cell death induced by the drug. The ATP Binding Cassette transporter A1 (ABCA1) effluxes isopentenyl pyrophosphate (IPP), a strong activator of anti-tumor Vγ9Vδ2 T-cells. Recruiting this population may represent an alternative strategy to rescue doxorubicin efficacy in ABCB1-expressing osteosarcoma. In this work, we analyzed how ABCA1 and ABCB1 are regulated in osteosarcoma, and if increasing the ABCA1-dependent activation of Vγ9Vδ2 T-cells could be an effective strategy against ABCB1-expressing osteosarcoma. We used 2D-cultured doxorubicin-sensitive human U-2OS and Saos-2 cells, their doxorubicin-resistant sublines (U-2OS/DX580 and Saos-2/DX580), and 3D cultures of U-2OS and Saos-2 cells. DX580-sublines and 3D cultures had higher levels of ABCB1 and higher resistance to doxorubicin than parental cells. Surprisingly, they had reduced ABCA1 levels, IPP efflux, and Vγ9Vδ2 T-cell-induced killing. In these chemo-immune-resistant cells, the Ras/Akt/mTOR axis inhibits the ABCA1-transcription induced by Liver X Receptor α (LXRα); Ras/ERK1/2/HIF-1α axis up-regulates ABCB1. Targeting the farnesylation of Ras with self-assembling nanoparticles encapsulating zoledronic acid (NZ) simultaneously inhibited both axes. In humanized mice, NZ reduced the growth of chemo-immune-resistant osteosarcomas, increased intratumor necro-apoptosis, and ABCA1/ABCB1 ratio and Vγ9Vδ2 T-cell infiltration. We suggest that the ABCB1^highABCA1^low phenotype is indicative of chemo-immune-resistance. We propose aminobisphosphonates as new chemo-immune-sensitizing tools against drug-resistant osteosarcomas.

New horizons from novel therapies in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a relatively rare, but highly lethal cancer of the pleural mesothelial cells. Its pathoge-nesis is integrally linked to asbestos exposure. In spite of recent developments providing a more detailed understanding of the pathogenesis, the outcomes continue to be poor. To date, trimodality therapy involving surgery coupled with chemotherapy and/or radiotherapy remains the standard of therapy. The development of resistance of the tumor cells to radiation and several che-motherapeutic agents poses even greater challenges in the management of this cancer. Ionizing radiation damages cancer cell DNA and aids in therapeutic response, but it also activates cell survival signaling pathways that helps the tumor cells to overcome radiation-induced cytotoxicity. A careful evaluation of the biology involved in mesothelioma with an emphasis on the workings of pro-survival signaling pathways might offer some guidance for treatment options. This review focuses on the existing treatment options for MPM, novel treatment approaches based on recent studies combining the use of inhibitors which target different pro-survival pathways, and radiotherapy to optimize treatment.

The Immune Microenvironment in Mesothelioma: Mechanisms of Resistance to Immunotherapy

Although mesothelioma is the consequence of a protracted immune response to asbestos fibers and characterized by a clear immune infiltrate, novel immunotherapy approaches show less convincing results as compared to those seen in melanoma and non-small cell lung cancer. The immune suppressive microenvironment in mesothelioma is likely contributing to this therapy resistance. Therefore, it is important to explore the characteristics of the tumor microenvironment for explanations for this recalcitrant behavior. This review describes the stromal, cytokine, metabolic, and cellular milieu of mesothelioma, and attempts to make connection with the outcome of immunotherapy trials.

What sustains the multidrug resistance phenotype beyond ABC efflux transporters? Looking beyond the tip of the iceberg

Identification of multidrug (MDR) efflux transporters that belong to the ATP-Binding Cassette (ABC) superfamily, represented an important breakthrough for understanding cancer multidrug resistance (MDR) and its possible overcoming. However, recent data indicate that drug resistant cells have a complex intracellular physiology that involves constant changes in energetic and oxidative-reductive metabolic pathways, as well as in the molecular circuitries connecting mitochondria, endoplasmic reticulum (ER) and lysosomes. The aim of this review is to discuss the key molecular mechanisms of cellular reprogramming that induce and maintain MDR, beyond the presence of MDR efflux transporters. We specifically highlight how cancer cells characterized by high metabolic plasticity - i.e. cells able to shift the energy metabolism between glycolysis and oxidative phosphorylation, to survive both the normoxic and hypoxic conditions, to modify the cytosolic and mitochondrial oxidative-reductive metabolism, are more prone to adapt to exogenous stressors such as anti-cancer drugs and acquire a MDR phenotype. Similarly, we discuss how changes in mitochondria dynamics and mitophagy rates, changes in proteome stability ensuring non-oncogenic proteostatic mechanisms, changes in ubiquitin/proteasome- and autophagy/lysosome-related pathways, promote the cellular survival under stress conditions, along with the acquisition or maintenance of MDR. After dissecting the complex intracellular crosstalk that takes place during the development of MDR, we suggest that mapping the specific adaptation pathways underlying cell survival in response to stress and targeting these pathways with potent pharmacologic agents may be a new approach to enhance therapeutic efficacy against MDR tumors.

ERK is a Pivotal Player of Chemo-Immune-Resistance in Cancer

The extracellular signal-related kinases (ERKs) act as pleiotropic molecules in tumors, where they activate pro-survival pathways leading to cell proliferation and migration, as well as modulate apoptosis, differentiation, and senescence. Given its central role as sensor of extracellular signals, ERK transduction system is widely exploited by cancer cells subjected to environmental stresses, such as chemotherapy and anti-tumor activity of the host immune system. Aggressive tumors have a tremendous ability to adapt and survive in stressing and unfavorable conditions. The simultaneous resistance to chemotherapy and immune system responses is common, and ERK signaling plays a key role in both types of resistance. In this review, we dissect the main ERK-dependent mechanisms and feedback circuitries that simultaneously determine chemoresistance and immune-resistance/immune-escape in cancer cells. We discuss the pros and cons of targeting ERK signaling to induce chemo-immune-sensitization in refractory tumors.

Potential Diagnostic and Prognostic Role of Microenvironment in Malignant Pleural Mesothelioma

INTRODUCTION

A comprehensive analysis of the immune cell infiltrate collected from pleural fluid and from biopsy specimens of malignant pleural mesothelioma (MPM) may contribute to understanding the immune-evasion mechanisms related to tumor progression, aiding in differential diagnosis and potential prognostic stratification. Until now such approach has not routinely been verified.

METHODS

We enrolled 275 patients with an initial clinical diagnosis of pleural effusion. Specimens of pleural fluids and pleural biopsy samples used for the pathologic diagnosis and the immune phenotype analyses were blindly investigated by multiparametric flow cytometry. The results were analyzed using the Kruskal-Wallis test. The Kaplan-Meier and log-rank tests were used to correlate immune phenotype data with patients' outcome.

RESULTS

The cutoffs of intratumor T-regulatory (>1.1%) cells, M2-macrophages (>36%), granulocytic and monocytic myeloid-derived suppressor cells (MDSC; >5.1% and 4.2%, respectively), CD4 molecule-positive (CD4⁺) programmed death 1-positive (PD-1⁺) (>5.2%) and CD8⁺PD-1⁺ (6.4%) cells, CD4⁺ lymphocyte activating 3-positive (LAG-3⁺) (>2.8% ) and CD8⁺LAG-3⁺ (>2.8%) cells, CD4⁺ T cell immunoglobulin and mucin domain 3-positive (TIM-3⁺) (>2.5%), and CD8⁺TIM-3⁺ (>2.6%) cells discriminated MPM from pleuritis with 100% sensitivity and 89% specificity. The presence of intratumor MDSC contributed to the anergy of tumor-infiltrating lymphocytes. The immune phenotype of pleural fluid cells had no prognostic significance. By contrast, the intratumor T-regulatory and MDSC levels significantly correlated with progression-free and overall survival, the PD-1⁺/LAG-3⁺/TIM-3⁺ CD4⁺ tumor-infiltrating lymphocytes correlated with overall survival.

CONCLUSIONS

A clear immune signature of pleural fluids and tissues of MPM patients may contribute to better predict patients' outcome.

Zoledronic acid blocks the interaction between breast cancer cells and regulatory T-cells

BACKGROUND

Zoledronic acid (ZA), a nitrogen-containing bisphosphonate, inhibits osteoclastogenesis. Emerging evidence suggests that ZA has anti-tumor and anti-metastatic properties for breast cancer cells. In a mouse model of ZA-related osteonecrosis of the jaw, ZA administration was found to suppress regulatory T-cells (Tregs) function. Our previous reports also demonstrated ZA acted as an immune modulator to block Tregs. Manipulation of Tregs represents a new strategy for cancer treatment. However, the relationship among ZA, Tregs, and cancer cells remains unclear. In this study, we investigated the effects of ZA on the interaction of breast cancer cells and Tregs.

METHODS

The anti-tumor effect of ZA on triple negative breast cancer cell lines were validated by XTT, wound healing and apoptosis analysis. A flow cytometry-based assay was used to analyze the immunosuppressive effect of Tregs treated with media conditioned by breast cancer cells, and a transwell assay was used to evaluate the chemotactic migration of Tregs. Differential gene expression profile on MDA-MB-231 treated with ZA (25 μM) was analyzed by. microarrays to describe the molecular basis of actions of ZA for possible direct anti-tumor effects. Enzyme-linked immunosorbent assays and quantitative real-time PCR were used to investigate the effect of ZA on the expression of cytokines/factors by breast cancer cells.

RESULTS

ZA was found to inhibit the proliferation and migration of breast cancer cells. Media conditioned by the MDA-MB-231 cells promoted the expansion, chemotactic migration, and immunosuppressive activity of Tregs, and these effects were attenuated in a dose-dependent manner by ZA treatment, and the attenuation was due to reduced expression of selected breast cancer cell factors (CCL2, CCL5, and IDO).

CONCLUSIONS

ZA can significantly affect the interaction between breast cancer cells and Tregs. Our findings indicate that ZA is a potential therapeutic agent that can be used to reduce cancer aggressiveness by abolishing the supportive role of Tregs.

Pyruvate Treatment Restores the Effectiveness of Chemotherapeutic Agents in Human Colon Adenocarcinoma and Pleural Mesothelioma Cells

Emerging evidence supports the idea that a dysfunction in cell metabolism could sustain a resistant phenotype in cancer cells. As the success of chemotherapeutic agents is often questioned by the occurrence of multidrug resistance (MDR), a multiple cross-resistance towards different anti-cancer drugs represent a major obstacle to cancer treatment. The present study has clarified the involvement of the carbon metabolites in a more aggressive tumor colon adenocarcinoma phenotype and in a chemoresistant mesothelioma, and the role of pyruvate treatment in the reversion of the potentially related resistance. For the first time, we have shown that human colon adenocarcinoma cells (HT29) and its chemoresistant counterpart (HT29-dx) displayed different carbon metabolism: HT29-dx cells had a higher glucose consumption compared to HT29 cells, whereas human malignant mesothelioma (HMM) cells showed a lower glucose consumption compared to HT29 cells, accompanied by a lower pyruvate production and, consequently, a higher production of lactate. When treated with pyruvate, both HT29-dx and HMM cells exhibited a re-established accumulation of doxorubicin and a lower survival ability, a decreased activity of multidrug resistance protein 1 (MRP1) and a restored mitochondrial respiratory chain function, improving the effectiveness of the chemotherapeutic agents in these resistant cancer cells.

Checkpoints and beyond - Immunotherapy in colorectal cancer

Immunotherapy is the latest revolution in cancer therapy. It continues to show impressive results in malignancies like melanoma and others. At least so far, effects are modest in colorectal cancer (CRC) and only a subset of patients benefits from already approved checkpoint inhibitors. In this review, we discuss major hurdles of immunotherapy like the immunosuppressive niche and low immunogenicity of CRC next to current achievements of checkpoint inhibitors, interleukin treatment and adoptive cell transfer (dendritic cells/cytokine induced killer cells, tumor infiltrating lymphocytes, chimeric antigen receptor cells, T cell receptor transfer) in pre-clinical models and clinical trials. We intensively examine approaches to overcome low immunogenicity by combination of different therapies and address future strategies of therapy as well as the need of predictive factors in this emerging field of precision medicine.

Drug repurposing in malignant pleural mesothelioma: a breath of fresh air?

Drug repurposing is the use of known drugs for new indications. Malignant pleural mesothelioma (MPM) is a rare cancer with a poor prognosis. So far, few treatments have been approved in this disease. However, its incidence is expected to increase significantly, particularly in developing countries. Consequently, drug repurposing appears as an attractive strategy for drug development in MPM, since the known pharmacology and safety profile based on previous approvals of repurposed drugs allows for faster time-to-market for patients and lower treatment cost. This is critical in low- and middle-income countries where access to expensive drugs is limited. This review assesses the published preclinical and clinical data about drug repurposing in MPM.In this review, we identified 11 therapeutic classes that could be repositioned in mesothelioma. Most of these treatments have been evaluated in vitro, half have been evaluated in vivo in animal models of MPM and only three (i.e. valproate, thalidomide and zoledronic acid) have been investigated in clinical trials, with limited benefits so far. Efforts could be coordinated to pursue further investigations and test promising drugs identified in preclinical experiments in appropriately designed clinical trials.

Icmt inhibition exerts anti-angiogenic and anti-hyperpermeability activities impeding malignant pleural effusion

Small GTPases are pivotal regulators of several aspects of tumor progression. Their implication in angiogenesis, vascular permeability and tumor-associated inflammatory responses is relevant to the pathobiology of Malignant Pleural Effusion (MPE). Inhibition of isoprenylcysteine carboxylmethyltransferase (Icmt) abrogates small GTPase activation. We therefore hypothesized that cysmethynil, an Icmt inhibitor would limit pleural fluid accumulation in two models, a lung-adenocarcinoma and a mesothelioma-induced MPE. Cysmethynil significantly reduced MPE volume in both models and tumor burden in the adenocarcinoma model. It inhibited pleural vascular permeability and tumor angiogenesis in vivo and reduced endothelial cell proliferation, migration and tube formation in vitro. Cysmethynil also promoted M1 anti-tumor macrophage homing in the pleural space in vivo, and inhibited tumor-induced polarization of macrophages towards a M2 phenotype in vitro. In addition, the inhibitor promoted adenocarcinoma cell apoptosis in vivo. Inhibition of small GTPase might thus represent a valuable strategy for pharmacotherapy of MPE.

Zoledronic acid-encapsulating self-assembling nanoparticles and doxorubicin: a combinatorial approach to overcome simultaneously chemoresistance and immunoresistance in breast tumors

The resistance to chemotherapy and the tumor escape from host immunosurveillance are the main causes of the failure of anthracycline-based regimens in breast cancer, where an effective chemo-immunosensitizing strategy is lacking.

The clinically used aminobisphosphonate zoledronic acid (ZA) reverses chemoresistance and immunoresistance in vitro. Previously we developed a nanoparticle-based zoledronic acid-containing formulation (NZ) that allowed a higher intratumor delivery of the drug compared with free ZA in vivo. We tested its efficacy in combination with doxorubicin in breast tumors refractory to chemotherapy and immune system recognition as a new combinatorial approach to produce chemo- and immunosensitization.

NZ reduced the IC₅₀ of doxorubicin in human and murine chemoresistant breast cancer cells and restored the doxorubicin efficacy against chemo-immunoresistant tumors implanted in immunocompetent mice. By reducing the metabolic flux through the mevalonate pathway, NZ lowered the activity of Ras/ERK1/2/HIF-1α axis and the expression of P-glycoprotein, decreased the glycolysis and the mitochondrial respiratory chain, induced a cytochrome c/caspase 9/caspase 3-dependent apoptosis, thus restoring the direct cytotoxic effects of doxorubicin on tumor cell. Moreover, NZ restored the doxorubicin-induced immunogenic cell death and reversed the tumor-induced immunosuppression due to the production of kynurenine, by inhibiting the STAT3/indoleamine 2,3 dioxygenase axis. These events increased the number of dendritic cells and decreased the number of immunosuppressive T-regulatory cells infiltrating the tumors.

Our work proposes the use of nanoparticle encapsulating zoledronic acid as an effective tool overcoming at the same time chemoresistance and immunoresistance in breast tumors, thanks to the effects exerted on tumor cell and tumor-infiltrating immune cells.

Bromodomain inhibition exerts its therapeutic potential in malignant pleural mesothelioma by promoting immunogenic cell death and changing the tumor immune-environment

Systemic treatment of malignant pleural mesothelioma (MPM) is moderately active for the intrinsic pharmacological resistance of MPM cell and its ability to induce an immune suppressive environment. Here we showed that the expression of bromodomain (BRD) proteins BRD2, BRD4 and BRD9 was significantly higher in human primary MPM cells compared to normal mesothelial cells (HMC). Nanomolar concentrations of bromodomain inhibitors (BBIs) JQ1 or OTX015 impaired patient-derived MPM cell proliferation and induced cell-cycle arrest without affecting apoptosis. Importantly, BBIs primed MPM cells for immunogenic cell death, by increasing extracellular release of ATP and HMGB1, and by promoting membrane exposure of calreticulin and ERp57. Accordingly, BBIs activated dendritic cell (DC)-mediated phagocytosis and expansion of CD8⁺ T-lymphocyte clones endorsed with antitumor cytotoxic activity. BBIs reduced the expression of the immune checkpoint ligand PD-L1 in MPM cells; while both CD8⁺ and CD4⁺ T-lymphocytes co-cultured with JQ1-treated MPM cells decreased PD-1 expression, suggesting a disruption of the immune-suppressive PD-L1/PD-1 axis. Additionally, BBIs reduced the expansion of myeloid-derived suppressor cells (MDSC) induced by MPM cells. Finally, a preclinical model of MPM confirmed that the anti-tumor efficacy of JQ1 was largely due to its ability to restore an immune-active environment, by increasing intra-tumor DC and CD8⁺ T-lymphocytes, and decreasing MDSC. Thereby, we propose that, among novel drugs, BBIs should be investigated for MPM treatment for their combined activity on both tumor cells and surrounding immune-environment.

Understanding the role of the kynurenine pathway in human breast cancer immunobiology

Breast cancer (BrCa) is the leading cause of cancer related death in women. While current diagnostic modalities provide opportunities for early medical intervention, significant proportions of breast tumours escape treatment and metastasize. Gaining increasing recognition as a factor in tumour metastasis is the local immuno-surveillance environment. Following identification of the role played by the enzyme indoleamine dioxygenase 1 (IDO1) in mediating maternal foetal tolerance, the kynurenine pathway (KP) of tryptophan metabolism has emerged as a key metabolic pathway contributing to immune escape. In inflammatory conditions activation of the KP leads to the production of several immune-modulating metabolites including kynurenine, kynurenic acid, 3-hydroxykynurenine, anthranilic acid, 3-hydroxyanthranilic acid, picolinic acid and quinolinic acid. KP over-activation was first described in BrCa patients in the early 1960s. More evidence has since emerged to suggest that the IDO1 is elevated in advanced BrCa patients and is associated with poor prognosis. Further, IDO1 positive breast tumours have a positive correlation with the density of immune suppressive Foxp3+ T regulatory cells and lymph node metastasis. The analysis of clinical microarray data in invasive BrCa compared to normal tissue showed, using two microarray databank (cBioportal and TCGA), that 86.3% and 91.4% BrCa patients have altered KP enzyme expression respectively. Collectively, these data highlight the key roles played by KP activation in BrCa, particularly in basal BrCa subtypes where expression of most KP enzymes was altered. Accordingly, the use of KP enzyme inhibitors in addition to standard chemotherapy regimens may present a viable therapeutic approach.

Immune modulation of CD4+CD25+ regulatory T cells by zoledronic acid

Background

CD4⁺CD25⁺ regulatory T (Treg) cells suppress tumor immunity by inhibiting immune cells. Manipulation of Treg cells represents a new strategy for cancer treatment. Zoledronic acid (ZA), a nitrogen-containing bisphosphonate, inhibits the expression of receptor activator of nuclear factor kappa-B ligand (RANKL) on osteoblasts to inhibit osteoclastogenesis. In a mouse model of bisphosphonate-related osteonecrosis of the jaw, administration of ZA suppressed Treg-cell activity and activated inflammatory Th17 cells. However, the interaction between ZA and Treg cells remained unclear. This study investigated the immune modulation of Treg cells by ZA.

Methods

Flow cytometry was used to analyze the phenotypic and immunosuppressive characteristics of Treg cells treated with ZA. Chemotactic migration was evaluated using transwell assays. Quantitative real-time PCR (qRT-PCR) was used to investigate the effect of ZA on the expression of suppressive molecules by Treg cells.

Results

Proliferation of isolated Treg cells in culture was inhibited by ZA, although ZA did not induce apoptosis. qRT-PCR and flow cytometry showed that ZA significantly downregulated the expression of CCR4, CTLA4, PD-1 and RANKL on Treg cells. Chemotactic migration and immunosuppressive functions were also significantly attenuated in Treg cells pretreated with ZA, and these effects were dose-dependent. Co-culture with Treg cells significantly increased the migration rate of breast cancer cells, while pretreatment of Treg cells with ZA attenuated this effect.

Conclusions

Our findings demonstrated that ZA acted as an immune modulator by significantly inhibiting the expansion, migration, immunosuppressive function and pro-metastatic ability of Treg cells. Immunomodulation of Treg cells by ZA represents a new strategy for cancer therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-016-0183-7) contains supplementary material, which is available to authorized users.

Self-assembling nanoparticles encapsulating zoledronic acid revert multidrug resistance in cancer cells

The overexpression of ATP binding cassette (ABC) transporters makes tumor cells simultaneously resistant to several cytotoxic drugs. Impairing the energy metabolism of multidrug resistant (MDR) cells is a promising chemosensitizing strategy, but many metabolic modifiers are too toxic in vivo. We previously observed that the aminobisphosphonate zoledronic acid inhibits the activity of hypoxia inducible factor-1α (HIF-1α), a master regulator of cancer cell metabolism. Free zoledronic acid, however, reaches low intratumor concentration. We synthesized nanoparticle formulations of the aminobisphosphonate that allow a higher intratumor delivery of the drug. We investigated whether they are effective metabolic modifiers and chemosensitizing agents against human MDR cancer cells in vitro and in vivo.

At not toxic dosage, nanoparticles carrying zoledronic acid chemosensitized MDR cells to a broad spectrum of cytotoxic drugs, independently of the type of ABC transporters expressed. The nanoparticles inhibited the isoprenoid synthesis and the Ras/ERK1/2-driven activation of HIF-1α, decreased the transcription and activity of glycolytic enzymes, the glucose flux through the glycolysis and tricarboxylic acid cycle, the electron flux through the mitochondrial respiratory chain, the synthesis of ATP. So doing, they lowered the ATP-dependent activity of ABC transporters, increasing the chemotherapy efficacy in vitro and in vivo. These effects were more pronounced in MDR cells than in chemosensitive ones and were due to the inhibition of farnesyl pyrophosphate synthase (FPPS), as demonstrated in FPPS-silenced tumors.

Our work proposes nanoparticle formulations of zoledronic acid as the first not toxic metabolic modifiers, effective against MDR tumors.

Cancer-associated fibroblast suppresses killing activity of natural killer cells through downregulation of poliovirus receptor (PVR/CD155), a ligand of activating NK receptor

Cancer-associated fibroblasts (CAFs) play an important role in cancer expansion and progression in tumor microenvironment (TME), via both direct and indirect interactions. Natural killer (NK) cells play a crucial role in anticancer immunity. We investigated the inhibitory effects of CAFs on NK cell activity. CAFs were isolated from endometrial cancer tissue, while normal endometrial fibroblasts (NEFs) were obtained from normal endometrium with no pathological abnormality. NK cells were obtained from allogenic healthy volunteers. CAFs or NEFs were co-cultured at an NK/fibroblast ratio of 1:1 with or without inserted membrane. For NK cell activity, K562 cells were cultured as target cells. NK cell-killing activity was determined by calculating the ratio of PI-positive K562 cells in the presence of NK cells co-cultured with fibroblasts versus NK cells alone. To examine whether NK cell activity was suppressed by IDO pathway, we inhibited IDO activity using the IDO inhibitor 1-MT. We demonstrated that CAFs derived from endometrial cancer induced greater suppression of the killing activity of allogenic NK cells compared with normal endometrial fibroblasts (NEFs). The suppression of NK cell activity by CAFs was inhibited when a membrane was inserted between the CAFs and NK cells, but not by 1-MT, an inhibitor of IDO. We focused on receptor-ligand interactions between CAFs and NK cell and found that cell-surface poliovirus receptor (PVR/CD155), a ligand of activating NK receptor DNAM-1, was downregulated in the CAFs compared with NEFs. To confirm whether PVR downregulation results in the decrease of NK cell-killing activity, PVR expression in NEFs was knocked down using siRNA against PVR (PVRsi). NK cell activity was suppressed by co-culture with PVR-knockdown NEFs, to a similar extent than CAF-induced suppression. CAFs showed increased suppression of NK cell-killing activity compared with NEFs, due to decreased PVR cell surface expression, a ligand of an NK activating receptor. This study demonstrated a novel mechanism of suppression of NK cell activity by CAFs in the TME.

Cancer-associated fibroblast suppresses killing activity of natural killer cells through downregulation of poliovirus receptor (PVR/CD155), a ligand of activating NK receptor

Cancer-associated fibroblasts (CAFs) play an important role in cancer expansion and progression in tumor microenvironment (TME), via both direct and indirect interactions. Natural killer (NK) cells play a crucial role in anticancer immunity. We investigated the inhibitory effects of CAFs on NK cell activity. CAFs were isolated from endometrial cancer tissue, while normal endometrial fibroblasts (NEFs) were obtained from normal endometrium with no pathological abnormality. NK cells were obtained from allogenic healthy volunteers. CAFs or NEFs were co-cultured at an NK/fibroblast ratio of 1:1 with or without inserted membrane. For NK cell activity, K562 cells were cultured as target cells. NK cell-killing activity was determined by calculating the ratio of PI-positive K562 cells in the presence of NK cells co-cultured with fibroblasts versus NK cells alone. To examine whether NK cell activity was suppressed by IDO pathway, we inhibited IDO activity using the IDO inhibitor 1-MT. We demonstrated that CAFs derived from endometrial cancer induced greater suppression of the killing activity of allogenic NK cells compared with normal endometrial fibroblasts (NEFs). The suppression of NK cell activity by CAFs was inhibited when a membrane was inserted between the CAFs and NK cells, but not by 1-MT, an inhibitor of IDO. We focused on receptor-ligand interactions between CAFs and NK cell and found that cell-surface poliovirus receptor (PVR/CD155), a ligand of activating NK receptor DNAM-1, was downregulated in the CAFs compared with NEFs. To confirm whether PVR downregulation results in the decrease of NK cell-killing activity, PVR expression in NEFs was knocked down using siRNA against PVR (PVRsi). NK cell activity was suppressed by co-culture with PVR-knockdown NEFs, to a similar extent than CAF-induced suppression. CAFs showed increased suppression of NK cell-killing activity compared with NEFs, due to decreased PVR cell surface expression, a ligand of an NK activating receptor. This study demonstrated a novel mechanism of suppression of NK cell activity by CAFs in the TME.

Trial Watch: Immunotherapy plus radiation therapy for oncological indications

Malignant cells succumbing to some forms of radiation therapy are particularly immunogenic and hence can initiate a therapeutically relevant adaptive immune response. This reflects the intrinsic antigenicity of malignant cells (which often synthesize a high number of potentially reactive neo-antigens) coupled with the ability of radiation therapy to boost the adjuvanticity of cell death as it stimulates the release of endogenous adjuvants from dying cells. Thus, radiation therapy has been intensively investigated for its capacity to improve the therapeutic profile of several anticancer immunotherapies, including (but not limited to) checkpoint blockers, anticancer vaccines, oncolytic viruses, Toll-like receptor (TLR) agonists, cytokines, and several small molecules with immunostimulatory effects. Here, we summarize recent preclinical and clinical advances in this field of investigation.