Tumor Microenvironment and Nitric Oxide: Concepts and Mechanisms

Current knowledge on the mechanisms underpinning vasculogenic mimicry in triple negative breast cancer and the emerging role of nitric oxide

Vasculogenic mimicry (VM) is the process by which cancer cells form vascular-like channels to support their growth and dissemination. These channels lack endothelial cells and are instead lined by the tumour cells themselves. VM was first reported in uveal melanomas but has since been associated with other aggressive solid tumours, such as triple-negative breast cancer (TNBC). In TNBC patients, VM is associated with tumour aggressiveness, drug resistance, metastatic burden, and poor prognosis. The lack of effective targeted therapies for TNBC has stimulated research on the mechanisms underpinning VM in order to identify novel druggable targets. In recent years, studies have highlighted the role of nitric oxide (NO), the NO synthesis inhibitor, asymmetric dimethylarginine (ADMA), and dimethylarginine dimethylaminohydrolase 1 (DDAH1), the key enzyme responsible for ADMA metabolism, in regulating VM. Specifically, NO inhibition through downregulation of DDAH1 and consequent accumulation of ADMA appears to be a promising strategy to suppress VM in TNBC. This review discusses the current knowledge regarding the molecular pathways underpinning VM in TNBC, anti-VM therapies under investigation, and the emerging role of NO regulation in VM.

Engineered a Gemcitabine Nano-Prodrug Targeting Desmoplastic Pancreatic Tumor with Dual Enhancement of Penetration Dynamics

The desmoplastic nature characterized by dense tissue and poor vascular conditions in pancreatic cancer (PDAC) poses a significant barrier to effective chemotherapy. Targeting the extracellular matrix and reducing desmoplasia in the tumor microenvironment is a rational approach to improve the penetration and efficacy of gemcitabine (GEM) in PDAC. Herein, a small molecular self-assembly nano-prodrug is developed for the "three-in-one" co-delivery of GEM chemotherapeutics, all-trans retinoic acid (ATRA), and nitric oxide (NO) donors, decorated with PDAC-homing targeting peptide. Stimulated by the PDAC microenvironment, the nano-prodrug releases ATRA that quiesces activated pancreatic stellate cells to alleviate stromal desmoplasia. Simultaneously, it generates abundant NO to induce a vasodilatory effect as well as a "nanomotor" effect. This combinational nano-prodrug delivery strategy, with a dual enhancement of drug penetration dynamics, effectively improves the distribution and bioavailability of the co-delivered GEM into the deep and dense pancreatic tumor tissue, which leads to significant amplification of tumor growth inhibition in different PDAC mouse models.

Cumulative effect of photobiomodulation by blue and red light on tumor cells: in vitro study with mammary adenocarcinoma cells - MCF-7

Although the mechanism of action of photobiomodulation (PBM) on tumor cells is already well described in the literature, its cumulative effect is not. The purpose of this study was to evaluate the cumulative effect of photobiomodulation (PBM) with blue (470 nm) and red (658 nm) light at doses of 6 J/cm² and 19 J/cm², respectively, in mammary adenocarcinoma (MCF-7) tumor cells. The study analyzed how single and sequential exposures to these lights modulated cell viability, proliferation, dsDNA release, nitric oxide (NO) production, and reactive oxygen species (ROS). Experimental analyses were carried out to verify cell viability and proliferation, release of dsDNA into the extracellular environment, production of nitric oxide (NO), and formation of reactive oxygen species (ROS). Exposures caused a reduction in cell viability and/or proliferation and there was no increase in mitosis at any of the wavelengths tested. Blue light promoted a reduction in the production of NO and ROS in all analyses. Red light, in a single irradiation at 6 J/cm², was able to promote an increase in NO rates and two cumulative doses at 19 J/cm² increased the formation of ROS. In this study, PBM with blue and red LED, at doses of 6 J/cm² and 19 J/cm² did not cause an increase in cell proliferation but rather reduced the viability and division capacity of breast adenocarcinoma cells.

Nitric oxide-based multi-synergistic nanomedicine: an emerging therapeutic for anticancer

Gas therapy has emerged as a promising approach for treating cancer, with gases like NO, H2S, and CO showing positive effects. Among these, NO is considered a key gas molecule with significant potential in stopping cancer progression. However, due to its high reactivity and short half-life, delivering NO directly to tumors is crucial for enhancing cancer treatment. NO-driven nanomedicines (NONs) have been developed to effectively deliver NO donors to tumors, showing great progress in recent years. This review provides an overview of the latest advancements in NO-based cancer nanotherapeutics. It discusses the types of NO donors used in current research, the mechanisms of action behind NO therapy for cancer, and the different delivery systems for NO donors in nanotherapeutics. It also explores the potential of combining NO donors with other treatments for enhanced cancer therapy. Finally, it examines the future prospects and challenges of using NONs in clinical settings for cancer treatment.

Tumor Microenvironment-Activatable Phototheranostic: Leveraging Nitric Oxide and Weak Acidity as Dual Biomarkers for Ratiometric Fluorescence, Photoacoustic Imaging, and Photothermal Therapy

Tumor microenvironment-responsive phototheranostic agents are highly sought after for their ability to improve diagnostic accuracy and treatment specificity. Here, we introduce a novel single-molecule probe, POZ-NO, which is activated by nitric oxide (NO) and weak acidity, enabling dual-mode imaging and photothermal therapy (PTT) of tumors. In acidic environments with elevated NO levels, POZ-NO exhibits a distinctive ratiometric fluorescence signal shift from the red to near-infrared, accompanied by a 700 nm photoacoustic signal. Additionally, POZ-NO demonstrated potent photothermal effects upon NO and acidity activation, achieving an impressive conversion efficiency of 74.3% under 735 nm laser irradiation. In vivo studies confirm POZ-NO's ability to accurately image tumors through ratiometric fluorescence and photoacoustic modes while selectively treating tumors with PTT.

Photodynamic Therapy and Adaptive Immunity Induced by Reactive Oxygen Species: Recent Reports

Cancer is one of the most significant causes of death worldwide. Despite the rapid development of modern forms of therapy, results are still unsatisfactory. The prognosis is further worsened by the ability of cancer cells to metastasize. Thus, more effective forms of therapy, such as photodynamic therapy, are constantly being developed. The photodynamic therapeutic regimen involves administering a photosensitizer that selectively accumulates in tumor cells or is present in tumor vasculature prior to irradiation with light at a wavelength corresponding to the photosensitizer absorbance, leading to the generation of reactive oxygen species. Reactive oxygen species are responsible for the direct and indirect destruction of cancer cells. Photodynamically induced local inflammation has been shown to have the ability to activate an adaptive immune system response resulting in the destruction of tumor lesions and the creation of an immune memory. This paper focuses on presenting the latest scientific reports on the specific immune response activated by photodynamic therapy. We present newly discovered mechanisms for the induction of the adaptive response by analyzing its various stages, and the possible difficulties in generating it. We also present the results of research over the past 10 years that have focused on improving the immunological efficacy of photodynamic therapy for improved cancer therapy.

Nitric Oxide Prevents Glioblastoma Stem Cells' Expansion and Induces Temozolomide Sensitization

Glioblastoma multiforme (GBM) has high mortality and recurrence rates. Malignancy resilience is ascribed to Glioblastoma Stem Cells (GSCs), which are resistant to Temozolomide (TMZ), the gold standard for GBM post-surgical treatment. However, Nitric Oxide (NO) has demonstrated anti-cancer efficacy in GBM cells, but its potential impact on GSCs remains unexplored. Accordingly, we investigated the effects of NO, both alone and in combination with TMZ, on patient-derived GSCs. Experimentally selected concentrations of diethylenetriamine/NO adduct and TMZ were used through a time course up to 21 days of treatment, to evaluate GSC proliferation and death, functional recovery, and apoptosis. Immunofluorescence and Western blot analyses revealed treatment-induced effects in cell cycle and DNA damage occurrence and repair. Our results showed that NO impairs self-renewal, disrupts cell-cycle progression, and expands the quiescent cells' population. Consistently, NO triggered a significant but tolerated level of DNA damage, but not apoptosis. Interestingly, NO/TMZ cotreatment further inhibited cell cycle progression, augmented G0 cells, induced cell death, but also enhanced DNA damage repair activity. These findings suggest that, although NO administration does not eliminate GSCs, it stunts their proliferation, and makes cells susceptible to TMZ. The resulting cytostatic effect may potentially allow long-term control over the GSCs' subpopulation.

LacNAc modification in bone marrow stromal cells enhances resistance of myelodysplastic syndrome cells to chemotherapeutic drugs

Chemotherapeutic drugs are used routinely for treatment for myelodysplastic syndrome (MDS) patients but are ineffective in a substantial proportion of patients. Abnormal hematopoietic microenvironments, in addition to spontaneous characteristics of malignant clones, contribute to ineffective hematopoiesis. In our study, we found expression of enzyme β1,4-galactosyltransferase 1 (β4GalT1), which regulates N-acetyllactosamine (LacNAc) modification of proteins, is elevated in bone marrow stromal cells (BMSCs) of MDS patients, and also contributes to drug ineffectiveness through a protective effect on malignant cells. Our investigation of the underlying molecular mechanism revealed that β4GalT1-overexpressing BMSCs promoted MDS clone cells resistant to chemotherapeutic drugs and also showed enhanced secretion of cytokine CXCL1 through degradation of tumor protein p53. Chemotherapeutic drug tolerance of myeloid cells was inhibited by application of exogenous LacNAc disaccharide and blocking of CXCL1. Our findings clarify the functional role of β4GalT1-catalyzed LacNAc modification in BMSCs of MDS. Clinical alteration of this process is a potential new strategy that may substantially enhance effectiveness of therapies for MDS and other malignancies, by targeting a niche interaction.

S-nitrosylation of CSF1 receptor increases the efficacy of CSF1R blockage against prostate cancer

Sustained oxidative stress in castration-resistant prostate cancer (CRPC) cells potentiates the overall tumor microenvironment (TME). Targeting the TME using colony-stimulating factor 1 receptor (CSF1R) inhibition is a promising therapy for CRPC. However, the therapeutic response to sustained CSF1R inhibition (CSF1Ri) is limited as a monotherapy. We hypothesized that one of the underlying causes for the reduced efficacy of CSF1Ri and increased oxidation in CRPC is the upregulation and uncoupling of endothelial nitric oxide synthase (NOS3). Here we show that in high-grade PCa human specimens, NOS3 abundance positively correlates with CSF1-CSF1R signaling and remains uncoupled. The uncoupling diminishes NOS3 generation of sufficient nitric oxide (NO) required for S-nitrosylation of CSF1R at specific cysteine sites (Cys 224, Cys 278, and Cys 830). Exogenous S-nitrosothiol administration (with S-nitrosoglutathione (GSNO)) induces S-nitrosylation of CSF1R and rescues the excess oxidation in tumor regions, in turn suppressing the tumor-promoting cytokines which are ineffectively suppressed by CSF1R blockade. Together these results suggest that NO administration could act as an effective combinatorial partner with CSF1R blockade against CRPC. In this context, we further show that exogenous NO treatment with GSNOR successfully augments the anti-tumor ability of CSF1Ri to effectively reduce the overall tumor burden, decreases the intratumoral percentage of anti-inflammatory macrophages, myeloid-derived progenitor cells and increases the percentage of pro-inflammatory macrophages, cytotoxic T lymphocytes, and effector T cells, respectively. Together, these findings support the concept that the NO-CSF1Ri combination has the potential to act as a therapeutic agent that restores control over TME, which in turn could improve the outcomes of PCa patients.

Therapeutic cancer vaccines: From biological mechanisms and engineering to ongoing clinical trials

Therapeutic vaccines are currently at the forefront of medical innovation. Various endeavors have been made to develop more consolidated approaches to producing nucleic acid-based vaccines, both DNA and mRNA vaccines. These innovations have continued to propel therapeutic platforms forward, especially for mRNA vaccines, after the successes that drove emergency FDA approval of two mRNA vaccines against SARS-CoV-2. These vaccines use modified mRNAs and lipid nanoparticles to improve stability, antigen translation, and delivery by evading innate immune activation. Simple alterations of mRNA structure- such as non-replicating, modified, or self-amplifying mRNAs- can provide flexibility for future vaccine development. For protein vaccines, the use of long synthetic peptides of tumor antigens instead of short peptides has further enhanced antigen delivery success and peptide stability. Efforts to identify and target neoantigens instead of antigens shared between tumor cells and normal cells have also improved protein-based vaccines. Other approaches use inactivated patient-derived tumor cells to elicit immune responses, or purified tumor antigens are given to patient-derived dendritic cells that are activated in vitro prior to reinjection. This review will discuss recent developments in therapeutic cancer vaccines such as, mode of action and engineering new types of anticancer vaccines, in order to summarize the latest preclinical and clinical data for further discussion of ongoing clinical endeavors in the field.

Antitumor and antiangiogenic effects of Tonantzitlolone B, an uncommon diterpene from Stillingia loranthacea

Natural products have played a pivotal role for the discovery of anticancer drugs. Tonantzitlolones are flexibilan-type diterpenes rare in nature; therefore, few reports have shown antiviral and cytotoxic activities. This study aimed to investigate the in vivo antitumor action of Tonantzitlolone B (TNZ-B) and its toxicity. Toxicity was evaluated in mice (acute and micronucleus assays). Antitumor activity of TNZ-B (1.5 or 3 mg/kg intraperitoneally - i.p.) was assessed in Ehrlich ascites carcinoma model. Angiogenesis and reactive oxygen species (ROS) and nitric oxide (NO) production were also investigated, in addition to toxicological effects after 7-day treatment. The LD50 (lethal dose 50%) was estimated at around 25 mg/kg (i.p.), and no genotoxicity was recorded. TNZ-B reduced the Ehrlich tumor's volume and total viable cancer cell count (p < 0.001 for both). Additionally, TNZ-B reduced peritumoral microvessel density (p < 0.01), suggesting antiangiogenic action. Moreover, a decrease was observed on ROS (p < 0.05) and nitric oxide (p < 0.001) levels. No significant clinical findings were observed in the analysis of biochemical, hematological, and histological (liver and kidney) parameters. In conclusion, TNZ-B exerts antitumor and antiangiogenic effects by reducing ROS and NO levels and has weak in vivo dose-repeated toxicity. These data contribute to elucidate the antitumor action of TNZ-B and point the way for further studies with this natural compound as an anticancer drug.

Glycyrrhizin as a Nitric Oxide Regulator in Cancer Chemotherapy

Simple Summary

Glycyrrhizin (GL) has anti-cancer, anti-inflammatory, anti-viral, and anti-oxidant activity. In particular, GL reduces multidrug resistance (MDR) in cancer cells, which is a major obstacle to chemotherapy. Nitric oxide (NO) also plays an important role in MDR, and GL affects NO concentration in the tumor microenvironment. However, the effects of GL and NO interaction on MDR have not been reviewed. Here, we review the role of GL as an NO regulator in cancer cells and its subsequent anti-MDR effect and posit that GL is a promising MDR inhibitor for cancer chemotherapy.

Abstract

Chemotherapy is used widely for cancer treatment; however, the evolution of multidrug resistance (MDR) in many patients limits the therapeutic benefits of chemotherapy. It is important to overcome MDR for enhanced chemotherapy. ATP-dependent efflux of drugs out of cells is the main mechanism of MDR. Recent studies have suggested that nitric oxide (NO) can be used to overcome MDR by inhibiting the ATPase function of ATP-dependent pumps. Several attempts have been made to deliver NO to the tumor microenvironment (TME), however there are limitations in delivery. Glycyrrhizin (GL), an active compound of licorice, has been reported to both reduce the MDR effect by inhibiting ATP-dependent pumps and function as a regulator of NO production in the TME. In this review, we describe the potential role of GL as an NO regulator and MDR inhibitor that efficiently reduces the MDR effect in cancer chemotherapy.

CAM-DR: Mechanisms, Roles and Clinical Application in Tumors

Despite the continuous improvement of various therapeutic techniques, the overall prognosis of tumors has been significantly improved, but malignant tumors in the middle and advanced stages still cannot be completely cured. It is now evident that cell adhesion-mediated resistance (CAM-DR) limits the success of cancer therapies and is a great obstacle to overcome in the clinic. The interactions between tumor cells and extracellular matrix (ECM) molecules or adjacent cells may play a significant role in initiating the intracellular signaling pathways that are associated with cell proliferation, survival upon binding to their ligands. Recent studies illustrate that these adhesion-related factors may contribute to the survival of cancer cells after chemotherapeutic therapy, advantageous to resistant cells to proliferate and develop multiple mechanisms of drug resistance. In this review, we focus on the molecular basis of these interactions and the main signal transduction pathways that are involved in the enhancement of the cancer cells’ survival. Furthermore, therapies targeting interactions between cancer cells and their environment to enhance drug response or prevent the emergence of drug resistance will also be discussed.

Optimizing NK Cell-Based Immunotherapy in Myeloid Leukemia: Abrogating an Immunosuppressive Microenvironment

Natural killer (NK) cells are prominent cytotoxic and cytokine-producing components of the innate immune system representing crucial effector cells in cancer immunotherapy. Presently, various NK cell-based immunotherapies have contributed to the substantial improvement in the reconstitution of NK cells against advanced-staged and high-risk AML. Various NK cell sources, including haploidentical NK cells, adaptive NK cells, umbilical cord blood NK cells, stem cell-derived NK cells, chimeric antigen receptor NK cells, cytokine-induced memory-like NK cells, and NK cell lines have been identified. Devising innovative approaches to improve the generation of therapeutic NK cells from the aforementioned sources is likely to enhance NK cell expansion and activation, stimulate ex vivo and in vivo persistence of NK cells and improve conventional treatment response of myeloid leukemia. The tumor-promoting properties of the tumor microenvironment and downmodulation of NK cellular metabolic activity in solid tumors and hematological malignancies constitute a significant impediment in enhancing the anti-tumor effects of NK cells. In this review, we discuss the current NK cell sources, highlight ongoing interventions in enhancing NK cell function, and outline novel strategies to circumvent immunosuppressive factors in the tumor microenvironment to improve the efficacy of NK cell-based immunotherapy and expand their future success in treating myeloid leukemia.