The acidic tumor microenvironment enhances PD-L1 expression via activation of STAT3 in MDA-MB-231 breast cancer cells

Hallmarks of cancer resistance

This review explores the hallmarks of cancer resistance, including drug efflux mediated by ATP-binding cassette (ABC) transporters, metabolic reprogramming characterized by the Warburg effect, and the dynamic interplay between cancer cells and mitochondria. The role of cancer stem cells (CSCs) in treatment resistance and the regulatory influence of non-coding RNAs, such as long non-coding RNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs), are studied. The chapter emphasizes future directions, encompassing advancements in immunotherapy, strategies to counter adaptive resistance, integration of artificial intelligence for predictive modeling, and the identification of biomarkers for personalized treatment. The comprehensive exploration of these hallmarks provides a foundation for innovative therapeutic approaches, aiming to navigate the complex landscape of cancer resistance and enhance patient outcomes.

A NIR-Fluorochrome for Live Cell Dual Emission and Lifetime Tracking from the First Plasma Membrane Interaction to Subcellular and Extracellular Locales

Molecular probes with the ability to differentiate between subcellular variations in acidity levels remain important for the investigation of dynamic cellular processes and functions. In this context, a series of cyclic peptide and PEG bio-conjugated dual near-infrared emissive BF2-azadipyrromethene fluorophores with maxima emissions at 720 nm (at pH > 6) and 790 nm (at pH < 5) have been developed and their aqueous solution photophysical properties determined. Their inter-converting emissions and fluorescence lifetime characteristics were exploited to track their spatial and temporal progression from first contact with the plasma membrane to subcellular locales to their release within extracellular vesicles. A pH-dependent reversible phenolate/phenol interconversion on the fluorophore controlled the dynamic changes in dual emission responses and corresponding lifetime changes. Live-cell confocal microscopy experiments in the metastatic breast cancer cell line MDA-MB-231 confirmed the usability of the dual emissive properties for imaging over prolonged periods. All three derivatives performed as probes capable of real-time continuous imaging of fundamental cellular processes such as plasma membrane interaction, tracking endocytosis, lysosomal/large acidic vesicle accumulation, and efflux within extracellular vesicles without perturbing cellular function. Furthermore, fluorescence lifetime imaging microscopy provided valuable insights regarding fluorophore progression through intracellular microenvironments over time. Overall, the unique photophysical properties of these fluorophores show excellent potential for their use as information-rich probes.

Evaluation of PDL1 positive cancer cell-specific binding activity of recombinant anti-PDL1 scFv

Programmed cell death-ligand 1 (PDL1) is a transmembrane protein that is characterized as an immune regulatory molecule. We recently developed a recombinant single-chain fragment of variable domain (scFv) against PDL1, which showed high binding efficiency to purified recombinant PDL1 protein. However, at that time, proof-of-concept data for the effect of scFv using PDL1-expressing cells was lacking. In this study, we conducted two kinds of cell-based immunoassays, western blotting and enzyme-linked immunosorbent assay, using anti-PDL1 scFv. The results indicate that scFv can selectively and sensitively detect PDL1 from PDL1 positive human cancer cell lines. Our findings suggest that scFv could be used as a potential PDL1 inhibitor agent and probe for cell-based immunoassays to detect PDL1.

Impact of Acute or Chronic Acidosis and Hypoxia on Gene Expression Patterns in Tumour Cells: Potential Functional Implications

Tumours often exhibit pronounced hypoxia and hereby extracellular acidosis due to intensified glycolysis. Since metabolic parameters can modulate gene expression, the aim of the study was to analyse changes in gene expression patterns induced by acute (24 h) acidosis or hypoxia and also in tumour cells adapted to long-term acidosis (5 weeks). Three tumour cell lines (AT1 prostate carcinoma, MCF-7, and MDA-MB-231 breast carcinoma) were exposed to acidosis (pH 6.6) or hypoxia (pO2 1.5 mmHg) for 24 h. For long-term acidosis, AT1 tumour cells were continuously cultured at pH 6.6 for 5 weeks. Gene expression was examined by total RNA-sequencing and the functional significance was assessed by gene set enrichment analysis using the Gene Ontology database. Under short-term acidosis (24 h), AT1 and MCF-7 cells showed comparable changes. 714 genes were acidosis-dependently regulated in AT1 cells (275 up, 439 down), and 221 genes in MCF-7 cells (95 up, 126 down). MDA-MB-231 cells almost did not respond to low pH (13 regulated genes). Hypoxia affected MCF-7 cells the most (1498 regulated genes), whereas fewer genes were regulated in AT1 and MDA-MB-231 cells. Concerning the function of the regulated genes by short-term acidosis, RNA processing, cell cycle regulation, DNA synthesis, and mitochondrial function were negatively affected. Chronic acidosis showed a different picture. In AT1 cells, 1160 genes were differentially expressed (638 up, 522 down) when cells exposed to low pH for 5 weeks. The putatively acidosis-induced changes in functions included tissue structural development, RNA processing, and mitochondrial activity. This study shows that both acute and chronic acidosis of tumour cells lead to altered gene expression and thus affect cell function. Long-term acidosis leads to fundamentally different changes, indicating an adaptation process of the tumour cells.

Acidosis-mediated increase in IFN-γ-induced PD-L1 expression on cancer cells as an immune escape mechanism in solid tumors

Immune checkpoint inhibitors have revolutionized cancer therapy, yet the efficacy of these treatments is often limited by the heterogeneous and hypoxic tumor microenvironment (TME) of solid tumors. In the TME, programmed death-ligand 1 (PD-L1) expression on cancer cells is mainly regulated by Interferon-gamma (IFN-γ), which induces T cell exhaustion and enables tumor immune evasion. In this study, we demonstrate that acidosis, a common characteristic of solid tumors, significantly increases IFN-γ-induced PD-L1 expression on aggressive cancer cells, thus promoting immune escape. Using preclinical models, we found that acidosis enhances the genomic expression and phosphorylation of signal transducer and activator of transcription 1 (STAT1), and the translation of STAT1 mRNA by eukaryotic initiation factor 4F (elF4F), resulting in an increased PD-L1 expression. We observed this effect in murine and human anti-PD-L1-responsive tumor cell lines, but not in anti-PD-L1-nonresponsive tumor cell lines. In vivo studies fully validated our in vitro findings and revealed that neutralizing the acidic extracellular tumor pH by sodium bicarbonate treatment suppresses IFN-γ-induced PD-L1 expression and promotes immune cell infiltration in responsive tumors and thus reduces tumor growth. However, this effect was not observed in anti-PD-L1-nonresponsive tumors. In vivo experiments in tumor-bearing IFN-γ-/- mice validated the dependency on immune cell-derived IFN-γ for acidosis-mediated cancer cell PD-L1 induction and tumor immune escape. Thus, acidosis and IFN-γ-induced elevation of PD-L1 expression on cancer cells represent a previously unknown immune escape mechanism that may serve as a novel biomarker for anti-PD-L1/PD-1 treatment response. These findings have important implications for the development of new strategies to enhance the efficacy of immunotherapy in cancer patients.

How protons pave the way to aggressive cancers

Cancers undergo sequential changes to proton (H+) concentration and sensing that are consequences of the disease and facilitate its further progression. The impact of protonation state on protein activity can arise from alterations to amino acids or their titration. Indeed, many cancer-initiating mutations influence pH balance, regulation or sensing in a manner that enables growth and invasion outside normal constraints as part of oncogenic transformation. These cancer-supporting effects become more prominent when tumours develop an acidic microenvironment owing to metabolic reprogramming and disordered perfusion. The ensuing intracellular and extracellular pH disturbances affect multiple aspects of tumour biology, ranging from proliferation to immune surveillance, and can even facilitate further mutagenesis. As a selection pressure, extracellular acidosis accelerates disease progression by favouring acid-resistant cancer cells, which are typically associated with aggressive phenotypes. Although acid-base disturbances in tumours often occur alongside hypoxia and lactate accumulation, there is now ample evidence for a distinct role of H+-operated responses in key events underpinning cancer. The breadth of these actions presents therapeutic opportunities to change the trajectory of disease.

Similarities and divergences in the metabolism of immune cells in cancer and helminthic infections

Energetic and nutritional requirements play a crucial role in shaping the immune cells that infiltrate tumor and parasite infection sites. The dynamic interaction between immune cells and the microenvironment, whether in the context of tumor or helminth infection, is essential for understanding the mechanisms of immunological polarization and developing strategies to manipulate them in order to promote a functional and efficient immune response that could aid in the treatment of these conditions. In this review, we present an overview of the immune response triggered during tumorigenesis and establishment of helminth infections, highlighting the transition to chronicity in both cases. We discuss the energetic demands of immune cells under normal conditions and in the presence of tumors and helminths. Additionally, we compare the metabolic changes that occur in the tumor microenvironment and the infection site, emphasizing the alterations that are induced to redirect the immune response, thereby promoting the survival of cancer cells or helminths. This emerging discipline provides valuable insights into disease pathogenesis. We also provide examples of novel strategies to enhance immune activity by targeting metabolic pathways that shape immune phenotypes, with the aim of achieving positive outcomes in cancer and helminth infections.

Immunotherapy Enhancement by Targeting Extracellular Tumor pH in Triple-Negative Breast Cancer Mouse Model

Triple-negative breast cancer (TNBC), as one of the most aggressive forms of breast cancer, is characterized by a poor prognosis and a very low rate of disease-free and overall survival. In recent years, immunotherapeutic approaches targeting T cell checkpoint molecules, such as cytotoxic lymphocyte antigen-4 (CTLA-4), programmed death1 (PD-1) or its ligand, programmed death ligand 1 (PD-L1), have shown great potential and have been used to treat various cancers as single therapies or in combination with other modalities. However, despite this remarkable progress, patients with TNBC have shown a low response rate to this approach, commonly developing resistance to immune checkpoint blockade, leading to treatment failure. Extracellular acidosis within the tumor microenvironment (also known as the Warburg effect) is one of the factors preventing immune cells from mounting effective responses and contributing to immunotherapy treatment failure. Therefore, reducing tumor acidity is important for increasing cancer immunotherapy effectiveness and this has yet to be realized in the TNBC environment. In this study, the oral administration of sodium bicarbonate (NaHCO3) enhanced the antitumor effect of anti-PD-L1 antibody treatment, as demonstrated by generated antitumor immunity, tumor growth inhibition and enhanced survival in 4T1-Luc breast cancer model. Here, we show that NaHCO3 increased extracellular pH (pHe) in tumor tissues in vivo, an effect that was accompanied by an increase in T cell infiltration, T cell activation and IFN-γ, IL2 and IL12p40 mRNA expression in tumor tissues, as well as an increase in T cell activation in tumor-draining lymph nodes. Interestingly, these changes were further enhanced in response to combined NaHCO3 + anti-PD-L1 therapy. In addition, the acidic extracellular conditions caused a significant increase in PD-L1 expression in vitro. Taken together, these results indicate that alkalizing therapy holds potential as a new tumor microenvironment immunomodulator and we hypothesize that NaHCO3 can enhance the antitumor effects of anti-PD-L1 breast cancer therapy. The combination of these treatments may have an exceptional impact on future TNBC immunotherapeutic approaches by providing a powerful personalized medicine paradigm. Therefore, our findings have a great translational potential for improving outcomes in TNBC patients.

Let-7a/cMyc/CCAT1/miR-17-5p Circuit Re-sensitizes Atezolizumab Resistance in Triple Negative Breast Cancer through Modulating PD-L1

BACKGROUND

Triple negative breast cancer (TNBC) is an immunogenically hot tumor. The immune checkpoint blockades (ICBs) have been recently emerged as promising therapeutic candidates for several malignancies including TNBC. Yet, the development of innate and/or adaptive resistance by TNBC patients towards ICBs such as programmed death-ligand 1 (PD-L1) inhibitors (e.g. Atezolizumab) shed the light on importance of identifying the underlying mechanisms regulating PD-L1 in TNBC. Recently, it was reported that non-coding RNAs (ncRNAs) perform a fundamental role in regulating PD-L1 expression in TNBC. Hence, this study aims to explore a novel ncRNA axis tuning PD-L1 in TNBC patients and investigate its possible involvement in fighting Atezolizumab resistance.

METHODS

In-silico screening was executed to identify ncRNAs that could potentially target PD-L1. Screening of PD-L1 and the nominated ncRNAs (miR-17-5p, let-7a and CCAT1 lncRNA) was performed in BC patients and cell lines. Ectopic expression and/or knockdown of respective ncRNAs were performed in MDA-MB-231. Cellular viability, migration and clonogenic capacities were evaluated using MTT, scratch assay and colony-forming assay, respectively.

RESULTS

PD-L1 was upregulated in BC patients, especially in TNBC patients. PD-L1 is positively associated with lymph node metastasis and high Ki-67 in recruited BC patients. Let-7a and miR-17-5p were nominated as potential regulators of PD-L1. Ectopic expression of let-7a and miR-17-5p caused a noticeable reduction in PD-L1 levels in TNBC cells. In order to investigate the whole ceRNA circuit regulating PD-L1 in TNBC, intensive bioinformatic studies were performed. The lncRNA, Colon Cancer-associated transcript 1 (CCAT1), was reported to target PD-L1 regulating miRNAs. Results showed that CCAT1 is an upregulated oncogenic lncRNA in TNBC patients and cell lines. CCAT1 siRNAs induced a noticeable reduction in PD-L1 levels and a marked increase in miR-17-5p level, building up a novel regulatory axis CCAT1/miR-17-5p/PD-L1 in TNBC cells that was tuned by the let-7a/c-Myc engine. On the functional level, co-treatment of CCAT-1 siRNAs and let-7a mimics efficiently relieved Atezolizumab resistance in MDA-MB-231 cells.

CONCLUSION

The present study revealed a novel PD-L1 regulatory axis via targeting let-7a/c-Myc/CCAT/miR-17-5p. Additionally, it sheds the light on the potential combinational role of CCAT-1 siRNAs and Let-7a mimics in relieving Atezolizumab resistance in TNBC patients.

Pharmacological anti-tumor effects of natural Chamaecyparis obtusa (siebold & zucc.) endl. Leaf extracts on breast cancer

ETHNOPHARMACOLOGICAL RELEVANCE

Chamaecyparis obtusa (C. obtusa, cypress species) is a plant that grows mainly in the temperate Northern Hemisphere and has long been used as a traditional anti-inflammatory treatment in East Asia. C. obtusa contains phytoncides, flavonoids, and terpenes, which have excellent anti-cancer effects and have been reported to prevent the progression of various cancers. However, the detailed mechanisms underlying the anti-cancer effects of C. obtusa extracts are unknown.

AIM OF THE STUDY

We sought to confirm the anti-cancer effects of C. obtusa leaf extracts and to reveal the mechanism of action, with the possibility of its application in the treatment or prevention of cancer.

MATERIAL &METHODS

The cytotoxicity of C. obtusa leaf extracts was confirmed using an MTT assay. Intracellular changes in protein levels were measured by immunoblotting, and mRNA levels were measured with qRT-PCR. Wound healing assay and transwell migration assay were used to evaluate the metastatic potential of breast cancer cells. The extract-induced apoptosis was observed using IncuCyte Annexin V Red staining analysis. A syngeneic breast cancer mouse model was established by injecting 4T1-Luc mouse breast cancer cells into the fat pad of female BALB/c mice, and the extract was administered orally. Luciferin solution was injected intraperitoneally to assess primary tumor development and metastasis by bioluminescence.

RESULTS

C. obtusa leaf extracts were extracted with boiling water, 70% EtOH, and 99% EtOH. Among the extracts, the 99% EtOH extract of C. obtusa leaf (CO99EL) most clearly inhibited the tyrosine phosphorylation of Signal Transducer and Activator of Transcription 3 (pY-STAT3) in MDA-MB-231 breast cancer cells at a concentration of 25 and 50 μg/mL. In addition, CO99EL strongly inhibited not only endogenous pY-STAT3 levels but also IL-6-induced STAT3 activation in various types of cancer cells, including breast cancer. CO99EL inhibited metastatic potential by downregulating the expression of N-cadherin, fibronectin, TWIST, MMP2, and MMP9 in MDA-MB-231 breast cancer cells. CO99EL also induced apoptotic cell death by increasing cleaved caspase-3 and decreasing anti-apoptotic proteins Bcl-2 and Bcl-xL. In an in vivo syngeneic breast cancer mouse model, 100 mg/kg CO99EL suppressed tumor growth and induced apoptosis of cancer cells. Moreover, CO99EL significantly inhibited lung metastasis from primary breast cancer.

CONCLUSIONS

Our study demonstrated that 100 mg/kg CO99EL has potent anti-tumor effects against breast cancer, thus suggesting that 100 mg/kg CO99EL has potential applications in the treatment and prevention of breast cancer.

Combined therapeutic effect of YHO-1701 with PD-1 blockade is dependent on natural killer cell activity in syngeneic mouse models

The signal transducer and activator of transcription 3 (STAT3) signaling pathway is a key mediator of cancer cell proliferation, survival, and invasion. We discovered YHO-1701 as a small molecule inhibitor of STAT3 dimerization and demonstrated its potent anti-tumor activity using xenograft mouse models as monotherapy and combination therapy with molecular targeted drugs. STAT3 is also associated with cancer immune tolerance; therefore, we used the female CT26 syngeneic mouse model to examine the effect of combining YHO-1701 administration with PD-1/PD-L1 blockade. Pretreatment of the mice with YHO-1701 before starting anti-PD-1 antibody administration resulted in a significant therapeutic effect. In addition, the effect of monotherapy and combination treatment with YHO-1701 was significantly abolished by depleting natural killer (NK) cell activity. YHO-1701 was also found to restore the activity of mouse NK cells under inhibitory conditions in vitro. Furthermore, this combination therapy significantly inhibited tumor growth in an immunotherapy-resistant model of murine CMS5a fibrosarcoma. These results suggest that the combination of YHO-1701 with PD-1/PD-L1 blockade might be a new candidate for cancer immunotherapy involving the enhancement of NK cell activity in the tumor microenvironment.

Permeation enhancers loaded bilosomes for improved intestinal absorption and cytotoxic activity of doxorubicin

The clinical utility of doxorubicin is compromised due to dose related toxic side effects and limited oral bioavailability with no oral formulation being marketed. Enhancement of intestinal absorption and magnification of cytotoxicity can overcome these limitations. Accordingly, the objective was to probe penetration enhancers, bilosomes and their combinations for enhanced intestinal absorption and improved cytotoxicity of doxorubicin. Piperine and dipyridamole were tested as enhancers alone or encapsulated in bilosomes comprising Span60, cholesterol and bile salts. Bilosomes were nanosized spherical vesicles with negative zeta potential and were able to entrap doxorubicin with efficiency ranging from 45.3 % to 53 %. Intestinal absorption studies utilized in-situ rabbit intestinal perfusion which revealed site dependent doxorubicin absorption correlating with regional distribution of efflux transporters. Co-perfusion with the enhancer increased intestinal absorption with further augmentation after bilosomal encapsulation. The latter increased the % fraction absorbed by 4.5-6 and 1.8-2.5-fold from jejuno-ileum and colon, respectively, depending on bilosomes composition. Additionally, doxorubicin cytotoxicity against breast cancer cells (MCF-7) was significantly improved after bilosomal encapsulation and the recorded doxorubicin IC₅₀ value was reduced from 13.3 μM to 0.1 μM for the best formulation. The study introduced bilosomes encapsulating absorption enhancers as promising carriers for enhanced cytotoxicity and oral absorption of doxorubicin.