Background: Tumor-associated macrophages (TAM) play an important role in tumor microenvironment. Particularly, M2 macrophages contribute to tumor progression, depending on the expression of NF-κB. Tumor-derived exosomes can modulate tumor microenvironment by transferring miRNAs to immune cells. Epigallocatechin gallate (EGCG) has well known anti-tumor effects; however, no data are available on the influence of EGCG on communication with cancer cells and TAM. Methods: Murine breast cancer cell lines, 4T1, was used for in vivo and ex vivo studies. Exosome was extracted from EGCG-treated 4T1 cells, and the change of miRNAs was screened using microarray. Tumor cells or TAM isolated from murine tumor graft were incubated with exosomes derived from EGCG-treated and/or miR-16 inhibitor-transfected 4T1 cells. Chemokines for monocytes (CSF-1 and CCL-2), cytokines both with high (IL-6 and TGF-β) and low (TNF-α) expression in M2 macrophages, and molecules in NF-κB pathway (IKKα and Iκ-B) were evaluated by RT-qPCR or western blot. Results: EGCG suppressed tumor growth in murine breast cancer model, which was associated with decreased TAM and M2 macrophage infiltration. Expression of chemokine for monocytes (CSF-1 and CCL-2) were low in tumor cells from EGCG-treated mice, and cytokines of TAM was skewed from M2- into M1-like phenotype by EGCG as evidenced by decreased IL-6 and TGF-β and increased TNF-α. Ex vivo incubation of isolated tumor cells with EGCG inhibited the CSF-1 and CCL-2 expression. Ex vivo incubation of TAM with exosomes from EGCG-treated 4T1 cells led to IKKα suppression and concomitant I-κB accumulation; increase of IL-6 and TGF-β; and, decrease of TNF-α. EGCG up-regulated miR-16 in 4T1 cells and in the exosomes. Treatment of tumor cells or TAM with exosomes derived from EGCG-treated and miR-16-knock-downed 4T1 cells restored the above effects on chemokines, cytokines, and NF-κB pathway elicited by EGCG-treated exosomes. Conclusions: Our data demonstrate that EGCG up-regulates miR-16 in tumor cells, which can be transferred to TAM via exosomes and inhibits TAM infiltration and M2 polarization. We suggest a novel mechanism by which EGCG exerts anti-tumor activity via regulation of TAM in tumor microenvironment.

Tumor hypoxia and aerobic glycolysis are well-known resistance factors for anticancer therapies. Here, we demonstrate that tumor-associated macrophages (TAM) enhance tumor hypoxia and aerobic glycolysis in mice subcutaneous tumors and in patients with non–small cell lung cancer (NSCLC). We found a strong correlation between CD68 TAM immunostaining and PET 18fluoro-deoxyglucose (FDG) uptake in 98 matched tumors of patients with NSCLC. We also observed a significant correlation between CD68 and glycolytic gene signatures in 513 patients with NSCLC from The Cancer Genome Atlas database. TAM secreted TNFα to promote tumor cell glycolysis, whereas increased AMP-activated protein kinase and peroxisome proliferator-activated receptor gamma coactivator 1-alpha in TAM facilitated tumor hypoxia. Depletion of TAM by clodronate was sufficient to abrogate aerobic glycolysis and tumor hypoxia, thereby improving tumor response to anticancer therapies. TAM depletion led to a significant increase in programmed death-ligand 1 (PD-L1) expression in aerobic cancer cells as well as T-cell infiltration in tumors, resulting in antitumor efficacy by PD-L1 antibodies, which were otherwise completely ineffective. These data suggest that TAM can significantly alter tumor metabolism, further complicating tumor response to anticancer therapies, including immunotherapy. Significance: These findings show that tumor-associated macrophages can significantly modulate tumor metabolism, hindering the efficacy of anticancer therapies, including anti-PD-L1 immunotherapy.

Programmed cell death (PD)-1/PD-1 ligand-1 (PD-L1)-targeted therapy has emerged as a promising therapeutic strategy for lung cancer. However, whether EML4-ALK regulates PD-L1 expression in lung cancer remains unknown. A total of 532 pulmonary adenocarcinomas (pADCs), including 58 ALK-translocated tumors, were immunohistochemically evaluated for PD-L1 and PD-1. H23 (EGFR^Wild-typeEML4-ALK⁻PD-L1^Low) and H2228 (EGFR^Wild-typeEML4-ALK⁺PD-L1^High) cells were transfected with EML4-ALK or ALK short interfering RNAs and used to investigate the alterations in PD-L1 expression. PD-L1 expression was detected in 81% of ALK-translocated pADCs; this value was significantly higher than those of pADCs with EGFR mutation, KRAS mutation or lacking ALK, EGFR or KRAS mutation (p <0.005 for all). Moreover, ALK-translocated pADC with PD-L1 expression showed significantly higher numbers of tumor-infiltrating PD-1⁺ cells. ALK knockdown or inhibition (crizotinib treatment) in H2228 cells downregulated PD-L1 expression. Transfection of H23 cells with EML4-ALK enhanced PD-L1 expression, which was compromised by crizotinib treatment. This ALK-dependent upregulation of PD-L1 expression was mediated by STAT3 and hypoxia-inducible factor (HIF)-1α under normoxia and hypoxia. Furthermore, EML4-ALK enhanced HIF-1α expression through increasing transcription and decreasing ubiquitination of HIF-1α. In ALK-translocated pADC tissues, significant positive correlations between PD-L1 and nuclear HIF-1α (p < 0.05) or pSTAT3 expression levels (p<0.005) were observed. Among patients with ALK-translocated pADC, strong PD-L1 expression was significantly associated with shorter progression-free (p = 0.001) and overall survival (p = 0.002) after crizotinib treatment. Collectively, our findings demonstrate that ALK-derived pADCs increase PD-L1 expression via HIF-1α and/or STAT3, thus providing a rationale for PD-1/PD-L1 pathway-targeted therapy in ALK-translocated lung cancer.

Background: Some patients with non-small-cell lung cancer (NSCLC) benefit from immune checkpoint inhibitors (ICIs) despite programmed death-ligand 1 (PD-L1) expression. To address the mechanism of ICI resistance in PD-L1-positive NSCLC, we investigated the role of tumor-cell-intrinsic function of PD-L1 in interleukin (IL)-6-mediated immunosuppression. Methods: Cohorts of NSCLC patients treated with ICI and public datasets were analyzed. PD-L1-overexpressing and PD-L1-knockdown NSCLC cells were submitted to RNA-seq, in vitro analyses, chromatin immunoprecipitation-qPCR, CUT&Tag, and biochemical assays. Human myeloid-derived suppressor cells (MDSCs) sorted from peripheral blood mononuclear cells were co-cultured with NSCLC cells and then assessed for their immunosuppressive activity on T-cells. Mouse Lewis lung carcinoma (LLC) cells with PD-L1 overexpression or knockdown were subcutaneously injected into wild-type or PD-1-knockout C57BL/6 mice in the presence of IL-6 and/or PD-1 blockade. Results: In the ICI cohort with RNA-seq data, the IL-6/Jak/Stat3 pathway was enriched, and IL-6 expression was higher in patients with PD-L1-high NSCLCs who did not respond to ICIs. In another cohort, a higher baseline serum IL-6 level was associated with poor clinical outcomes after ICI therapy. IL-6 expression and the IL-6/Jak/Stat3 pathway were enhanced in PD-L1-high NSCLCs in the ICI cohorts and The Cancer Genome Atlas analysis. IL-6 expression correlated positively with tumor-infiltrating MDSCs in NSCLCs. In NSCLC cells, PD-L1 activated Jak2/Stat3 signaling by binding to and inhibiting protein tyrosine phosphatase 1B. PD-L1 also bound to p-Stat3 in the nucleus, thus promoting the activity of p-Stat3 in the transcription of several cytokines (IL-6, TGF-β, TNF-α, IL-1β) and chemokines. PD-L1-overexpressing NSCLC cells enhanced the migration and immunosuppressive activity of human MDSCs in vitro, mediated by IL-6 and CXCL1. In both wild-type and PD-1-knockout mice, PD-L1-overexpressing LLC tumors were infiltrated by increased MDSCs with high immunosuppressive function, increased Tregs, and decreased granzyme B⁺ or IFNγ⁺ CD8 T-cells. These responses were mediated by IL-6 secreted from PD-L1-overexpressing tumor cells. Combined blockade of PD-1 and IL-6 was effective in tumor control and decreased MDSCs while increasing granzyme B⁺ or IFNγ⁺ CD8 T-cells. Conclusions: The tumor-cell-intrinsic function of PD-L1 drives immunosuppression and tumor progression through the PD-L1/Jak/Stat3/IL-6/MDSC axis. This pathway represents a potential therapeutic target to improve ICI efficacy in PD-L1-high NSCLC.