Tumor-derived ILT4 induces T cell senescence and suppresses tumor immunity

BACKGROUND

Current immunotherapies including checkpoint blockade therapy have limited success rates in certain types of cancers. Identification of alternative checkpoint molecules for the development of effective strategies for tumor immunotherapy is urgently needed. Immunoglobulin-like transcript 4 (ILT4) is an immunosuppressive molecule expressed in both myeloid innate cells and malignant tumor cells. However, the role of tumor-derived ILT4 in regulating cancer biology and tumor immunity remains unclear.

METHODS

ILT4 expression in tumor cells and patient samples was determined by real-time PCR, flow cytometry, and immunohistochemistry. T cell senescence induced by tumor was evaluated using multiple markers and assays. Moreover, metabolic enzyme and signaling molecule expression and lipid droplets in tumor cells were determined using real-time PCR, western blot and oil red O staining, respectively. Loss-of-function and gain-of-function strategies were used to identify the causative role of ILT4 in tumor-induced T cell senescence. In addition, breast cancer and melanoma mouse tumor models were performed to demonstrate the role of ILT4 as a checkpoint molecule for tumor immunotherapy.

RESULTS

We reported that ILT4 is highly expressed in human tumor cells and tissues, which is negatively associated with clinical outcomes. Furthermore, tumor-derived ILT4/PIR-B (ILT4 ortholog in mouse) is directly involved in induction of cell senescence in naïve/effector T cells mediated by tumor cells in vitro and in vivo. Mechanistically, ILT4/PIR-B increases fatty acid synthesis and lipid accumulation in tumor cells via activation of MAPK ERK1/2 signaling, resulting in promotion of tumor growth and progression, and induction of effector T cell senescence. In addition, blocking tumor-derived PIR-B can reprogram tumor metabolism, prevent senescence development in tumor-specific T cells, and enhance antitumor immunity in both breast cancer and melanoma mouse models.

CONCLUSIONS

These studies identify a novel mechanism responsible for ILT4-mediated immune suppression in the tumor microenvironment, and prove a novel concept of ILT4 as a critical checkpoint molecule for tumor immunotherapy.

Keratinocytes: innate immune cells in atopic dermatitis

The skin is a unique immune organ that constitutes a complex network of physical, chemical and microbiological barriers against external insults. Keratinocytes are the most abundant cell type in the epidermis. These cells form the physical skin barrier and represent the first line of the host defense system by sensing pathogens via innate immune receptors, initiating anti-microbial responses and producing various cytokines, chemokines and anti-microbial peptides, which are important events in immunity. A damaged epidermal barrier in atopic dermatitis allows the penetration of potential allergens and pathogens to activate keratinocytes. Among the dysregulation of immune responses in atopic dermatitis, activated keratinocytes play a role in several biological processes that contribute to the pathogenesis of atopic dermatitis. In this review, we summarize the current understanding of the innate immune functions of keratinocytes in the pathogenesis of atopic dermatitis, with a special emphasis on skin-derived anti-microbial peptides and atopic dermatitis-related cytokines and chemokines in keratinocytes. An improved understanding of the innate immunity mediated by keratinocytes can provide helpful insight into the pathophysiological processes of atopic dermatitis and support new therapeutic efforts.

Senescent T cells within suppressive tumor microenvironments: emerging target for tumor immunotherapy

The functional state of the preexisting T cells in the tumor microenvironment is a key determinant for effective antitumor immunity and immunotherapy. Increasing evidence suggests that immunosenescence is an important state of T cell dysfunction that is distinct from exhaustion, a key strategy used by malignant tumors to evade immune surveillance and sustain the suppressive tumor microenvironment. Here, we discuss the phenotypic and functional characteristics of senescent T cells and their role in human cancers. We also explore the possible mechanisms and signaling pathways responsible for induction of T cell senescence by malignant tumors, and then discuss potential strategies to prevent and/or reverse senescence in tumor-specific T cells. A better understanding of these critical issues should provide novel strategies to enhance cancer immunotherapy.

Baicalein and Baicalin Promote Melanoma Apoptosis and Senescence via Metabolic Inhibition

Malignant melanoma is one of the most common and dangerous skin cancers with a high rate of death every year. Furthermore, N-RAS and B-RAF mutations in melanoma cells increase the difficulties for clinical treatment in patients. Therefore, development of effective and universal drugs against melanoma is urgently needed. Here we demonstrate that baicalein and baicalin, the active components of the Chinese traditional medicinal plant Scutellaria baicalensis Georgi, can significantly inhibit melanoma cell growth and proliferation, suppress tumor cell colony formation and migration, as well as induce apoptosis and senescence in melanoma cells. The anti-tumor effects mediated by baicalein and baicalin are independent of N-RAS and B-RAF mutation statuses in melanoma cells. Mechanistically, we identify that the suppression of baicalein and baicalin on melanoma cells is due to inhibition of tumor cell glucose uptake and metabolism by affecting the mTOR-HIF-1α signaling pathway. In addition, we demonstrated that baicalein and baicalin can suppress tumorigenesis and tumor growth in vivo in the melanoma model. These studies clearly indicate that baicalein and baicalin can control tumor growth and development metabolically and have great potential as novel and universal drugs for melanoma therapy.

Incidence and Risk Factors of In-Stent Restenosis for Symptomatic Intracranial Atherosclerotic Stenosis: A Systematic Review and Meta-Analysis

BACKGROUND

In-stent restenosis affects long-term outcome in patients with intracranial atherosclerotic stenosis.

PURPOSE

The aim of this meta-analysis was to evaluate the incidence and risk factors of in-stent restenosis.

DATA SOURCES

All literature that reported in-stent restenosis was searched on PubMed, Ovid EMBASE and Ovid MEDLINE data bases.

STUDY SELECTION

Original articles about stents for symptomatic intracranial atherosclerotic stenosis were selected.

DATA ANALYSIS

Meta-analysis was conducted to derive the pooled in-stent restenosis using a random-effects model. Meta-regression was performed to explore the risk factors predisposing to in-stent restenosis.

DATA SYNTHESIS

In total, 51 studies with 5043 patients were included. The pooled incidence rate of in-stent restenosis was 14.8% (95% CI, 11.9%-17.9%). Among the lesions with in-stent restenosis, 28.8% of them led to (95% CI, 22.0%-36.0%) related neurologic symptoms. The series in the United States had a higher in-stent restenosis rate (27.0%; 95% CI, 20.6%-33.9%) compared with those from Asia (13.6%; 95% CI, 10.3%-17.2%) and other regions as a whole (7.6%; 95% CI, 1.1%-18.1%) (P < .01). Multiregression analysis revealed that younger patient age was related to high in-stent restenosis rates (P = .019), and vertebrobasilar junction location (P = .010) and low residual stenosis (P = .018) were 2 independent risk factors for symptomatic in-stent restenosis rate.

LIMITATIONS

The heterogeneity of most outcomes was high.

CONCLUSIONS

Our study showed promising results of in-stent restenosis for symptomatic atherosclerotic stenosis. Studies are needed to further expatiate on the mechanisms by which younger patient age, vertebrobasilar junction location, and low residual stenosis could increase in-stent restenosis and symptomatic in-stent restenosis, respectively.

Human herpesvirus 6A promotes glycolysis in infected T cells by activation of mTOR signaling

Human herpesvirus 6 (HHV-6) is an important immunosuppressive and immunomodulatory virus worldwide. However, whether and how HHV-6 infection influences the metabolic machinery of the host cell to provide the energy and biosynthetic resources for virus propagation remains unknown. In this study, we identified that HHV-6A infection promotes glucose metabolism in infected T cells, resulting in elevated glycolytic activity with an increase of glucose uptake, glucose consumption and lactate secretion. Furthermore, we explored the mechanisms involved in HHV-6A-mediated glycolytic activation in the infected T cells. We found increased expressions of the key glucose transporters and glycolytic enzymes in HHV-6A-infected T cells. In addition, HHV-6A infection dramatically activated AKT-mTORC1 signaling in the infected T cells and pharmacological inhibition of mTORC1 blocked HHV-6A-mediated glycolytic activation. We also found that direct inhibition of glycolysis by 2-Deoxy-D-glucose (2-DG) or inhibition of mTORC1 activity in HHV-6A-infected T cells effectively reduced HHV-6 DNA replication, protein synthesis and virion production. These results not only reveal the mechanism of how HHV-6 infection affects host cell metabolism, but also suggest that targeting the metabolic pathway could be a new avenue for HHV-6 therapy.

Relationship of adiponectin, leptin, visfatin and IGF-1 in cow's venous blood and venous cord blood with calf birth weight

The Intrauterine fetal development process is complicated and affected by many regulating factors such as maternal nutritional status, transcription factors and adipokines. Adipokines are kinds of active substances secreted by adipose tissue, including more than 50 kinds of molecules. To explore the correlation between calf birth weights and adipokines including adiponectin, leptin, visfatin, and IGF-1 in cows venous and venous cord blood. Fifty-four healthy multiparous Chinese Holstein cows were used; in which, cows with a calf weight less than 40 kg were included in group A (n=9); those with a calf weight between 40 kg~45 kg were included in group B (n=25) and ≥45 kg were included in group C (n=20), venous blood and cord venous blood was collected. An ELISA kit was used to evaluate the concentration of adiponectin, leptin, visfatin, and IGF-1, correlations between index-index and index-calf birth weight were analysed. In both cows venous and cord venous blood, adiponectin, leptin, visfatin, and IGF-1 levels were significantly correlated with each other (p⟨0.01), and levels of these adipokines in venous blood were significantly higher than cord venous blood (p⟨0.01). Adiponectin, leptin, visfatin, and IGF-1 in venous cord blood were positively correlated with calf birth weights, and significantly correlated with calf birth weights respectively (p⟨0.01). Our study showed that adiponectin, leptin, and IGF-1 were found in venous blood and cord venous blood, and adiponectin, leptin, and IGF-1 in venous and cord venous blood potentially inter-regulated each other; adiponectin, leptin, and IGF-1 in venous blood were not significantly correlated with calf birth weights, while adiponectin, leptin, visfatin, and IGF-1 in venous cord blood were significantly correlated with calf birth weights, respectively.

Exhaustion and senescence: two crucial dysfunctional states of T cells in the tumor microenvironment

The failure of a massive influx of tumor-infiltrating T lymphocytes to eradicate tumor cells in the tumor microenvironment is mainly due to the dysfunction of T cells hyporesponsive to tumors. T-cell exhaustion and senescence induced by malignant tumors are two important dysfunctional states that coexist in cancer patients, hindering effective antitumor immunity and immunotherapy and sustaining the suppressive tumor microenvironment. Although exhausted and senescent T cells share a similar dysfunctional role in antitumor immunity, they are distinctly different in terms of generation, development, and metabolic and molecular regulation during tumor progression. Here, we discuss the unique phenotypic and functional characteristics of these two types of dysfunctional T cells and their roles in tumor development and progression. In addition, we further discuss the potential molecular and metabolic signaling pathways responsible for the control of T-cell exhaustion and senescence in the suppressive tumor microenvironment. Understanding these critical and fundamental features should facilitate rethinking the unresponsiveness to current immunotherapies in clinical patients and lead to further development of novel and effective strategies that target different types of dysfunctional T cells to enhance cancer immunotherapy.

Targeting citrate as a novel therapeutic strategy in cancer treatment

An important feature shared by many cancer cells is drastically altered metabolism that is critical for rapid growth and proliferation. The distinctly reprogrammed metabolism in cancer cells makes it possible to manipulate the levels of metabolites for cancer treatment. Citrate is a key metabolite that bridges many important metabolic pathways. Recent studies indicate that manipulating the level of citrate can impact the behaviors of both cancer and immune cells, resulting in induction of cancer cell apoptosis, boosting immune responses, and enhanced cancer immunotherapy. In this review, we discuss the recent developments in this emerging area of targeting citrate in cancer treatment. Specifically, we summarize the molecular basis of altered citrate metabolism in both tumors and immune cells, explore the seemingly conflicted growth promoting and growth inhibiting roles of citrate in various tumors, discuss the use of citrate in the clinic as a novel biomarker for cancer progression and outcomes, and highlight the new development of combining citrate with other therapeutic strategies in cancer therapy. An improved understanding of complex roles of citrate in the suppressive tumor microenvironment should open new avenues for cancer therapy.

Abstract 1794: A comparative microRNA expression analysis in breast cancer and melanoma tissues

Recently studies have revealed that a subset of microRNAs (miRNAs) is aberrantly expressed in the development and progression of a variety of cancers including breast cancer and melanoma. Several miRNAs have been implicated in tumorigenesis and progression of human cancer. However, the underlying mechanisms in different types of cancers remain largely unknown. The aim of the study was to compare the expression profiled of miRNA between breast cancer and melanoma patient’s tissues. Methods: Expression levels of 7 miRNAs (miR-15b, miR-142-3p, miR-142-5p, miR-142a, miR-199a, miR-221, miR-424, ) were determine in 17 cases of breast cancer and 25 melanoma tissue samples. MiRNA isolation from tissue samples were performed using Trizol reagent ( Sigma, USA). RNA quality and quantity were assessed using a BioMate TM 3 Series Spectrophotometers (Thermo, Madison, WI). Synthesis of cDNA with reverse transcriptase was performed by TaqManTM microRNA Reversed Transcription Kits, For analysis of miRNA expression, real-time q-PCR analyses were using TaqMan MicroRNA Assays. All real-time q-RT-PCR were performed on a 7300 real-Time PCR system (Applied Biosystems, USA). MiR-24 was used as the internal control for normalization. The relative miRNA expression levels were calculated using the 2 DΔCt methods. Values were presented as means ± standard deviation (SD). The comparison of miRNA levels in breast cancer and melanoma tissues were performed using Student’s t-test. A p value less than 0.05 was considered statistically significant. The expression of miRNAs in different breast cancer subtypes (infiltrating and Invasive ductal cancer) and melanoma (primary and metastatic) was also performed. Results: Relative miRNA expression levels (miR-15b, miR-142-3p, miR-142-5p, miR-146a, miR-199a, miR-221 and miR-424) were found to be differentially expressed in breast cancer and melanoma tissues. Significantly higher relative miRNA expression levels were detected in melanoma tissues compared with breast cancer tissues in all miRNAs evaluated except for miR-424. Four miRNAs (miR-15b, miR-146a, miR-221, and miR-143-3p) had relative expressions over 1.5 compared with only 1 miRNA (miR-15b) in breast cancer tissue. DΔCt values are plotted following comparison with endogenous levels of miR-24 assessed in each sample. Conclusions: Our study demonstrated that miRNA is not only a potential biomarker, but also a valuable therapeutic target for breast cancer and melanoma.

Citation Format: Yanping Zhang, Guangyong Peng, Eddy C. Hsueh. A comparative microRNA expression analysis in breast cancer and melanoma tissues [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1794.

Reprograming human Treg metabolism via innate TLR signaling for tumor immunotherapy

Regulatory T (Treg) cells induce an immunosuppressive microenvironment that is a major obstacle to successful tumor immunotherapy. Dissecting the regulations between energy metabolism and functionality in human Treg cells will provide insights for developing novel immunotherapies against cancer. We discovered that human naturally occurring Treg (nTreg) and tumor-associated Treg cells exhibit distinct metabolic profiles with predominant dependence on glucose metabolism compared with effector T cells. Activated nTreg and tumor-associated Treg cells depend on accelerated glucose consumption for their cellular senescence induction and suppressive activity in responder T cells during their cross-talk. We further identified that TLR8 signaling selectively inhibits glucose uptake and suppresses metabolic processes of glycolysis in human Treg cells, resulting in reversal of Treg suppressive function and cellular senescence induction. In addition, TLR8 signaling activation downregulates mTORC1-HIF1α signaling in Treg cells that control molecular processes of Treg glucose metabolism and suppressive functions. Our in vivo studies further demonstrated that TLR8 signaling-mediated reprogramming of glucose metabolism and function in human Treg cells can enhance anti-tumor immunity and immunotherapy efficacy in a melanoma adoptive transfer T cell therapy model. These studies identify novel mechanistic links between innate signaling and metabolic regulation of human Treg suppression, and provide a new strategy and concept for tumor immunotherapy.

Hepatitis C Virus E2 Envelope Glycoprotein Induces an Immunoregulatory Phenotype in Macrophages

A comprehensive strategy to control hepatitis C virus (HCV) infection needs a vaccine. Our phase I study with recombinant HCV E1/E2 envelope glycoprotein (EnvGPs) as a candidate vaccine did not induce a strong immune response in volunteers. We analyzed the interactions of HCV EnvGPs with human monocyte-derived macrophages as antigen-presenting cells. HCV E2 induced immune regulatory cytokine interleukin (IL)-10 and soluble CD163 (sCD163) protein expression in macrophages from 7 of 9 blood donors tested. Furthermore, HCV E2 enhanced Stat3 and suppressed Stat1 activation, reflecting macrophage polarization toward M2 phenotype. E2-associated macrophage polarization appeared to be dependent of its interaction with CD81 leading endothelial growth factor receptor (EGFR) activation. Additionally, E2 suppressed the expression of C3 complement, similar to HCV-exposed dendritic cells (DCs), implying potential impairment of immune cell priming. Conclusion: Our results suggest that E2 EnvGP may not be an ideal candidate for HCV vaccine development, and discrete domains within E2 may prove to be more capable of elliciting a protective immune response. (Hepatology 2018).

Abstract 2942: Enhanced cytotoxic activity of BRAF, MEK and PI3K inhibition with combination CDK4/6 inhibition in melanoma cells

Introduction: We have previously reported that CDK4/6 inhibition enhanced the anti-proliferation and anti-migration effects of BRAF, MEK and PI3K inhibitors in melanoma cells. (Zhang Y et al, AACR 2017) In this study, we investigated the effect of combination CDK4/6 inhibition and BRAF, MEK and PI3K inhibition on induction of cell cycle arrest and apoptosis in melanoma.

Methods: Five human melanoma cell lines were used. CDK4/6 inhibitor (PD0332991; PD), BRAF inhibitor (PLX4032; PLX), MEK inhibitor (AZD6244; AZD), and PI3K/AKT inhibitor (XL765; XL) were used alone or in combination. Cell apoptosis analysis was performed using the FITC Annexin V Apoptosis Detection Kit. Autophagy was evaluated by immunofluorescence using anti-LC3A/B and NECN-1 antibodies. Lysosomal morphology was evaluated using lysosomal associated membrane protein 1-green fluorescent protein fusion construct. Western blotting was performed for apoptosis markers (PARP and caspase-9) and autophagy markers (LC3A/B and Beclin1) using GAPDH as internal control. Data were presented as means ± SD for triplicate experiments. For comparison between groups, the student's t test was used and p&lt; 0.05 was considered to be statically significant.

Results: Apoptosis was evaluated by Annexin V assay. Various levels of apoptosis were observed with single agent PD, PLX, XL and AZD in all 5 melanoma cell lines. Combination of PD enhanced the apoptosis effects of PLX, XL, and AZD in all 5 melanoma cell lines. Increased LC3 and BECN1 detection and increased density of autophagosomes on immunofluorescence was observed after combining CDK4 inhibition with BRAF, MEK, and PI3K/AKT inhibition. Inhibition of PARP and Beclin-1 expression and increase in caspase-9 expression were observed with combination of PD compared with single agent PLX, XL, and AZD.

Conclusion: CDK4 inhibition enhanced anti-melanoma activity of BRAF , PI3K/AKT and MEK inhibitions through increased induction of early autophagy and caspase-mediated apoptosis. This suggests that inhibition of CDK4/6 plus BRAF , MEK and PI3K/AKT inhibition may help understanding the interplay between autophagy and apoptosis and inform the development of future targeted agents.

Citation Format: Yanping Zhang, Guangyong Peng, Eddy C. Hsueh. Enhanced cytotoxic activity of BRAF, MEK and PI3K inhibition with combination CDK4/6 inhibition in melanoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2942.

Molecular control of Treg-induced effector T cell DNA damage and senescence for tumor immunotherapy

Regulatory T cells (Treg) have a critical function for the tumor immunosuppressive microenvironments. Defining the suppressive mechanisms utilized by Treg cells is critical for the development of effective strategies to treat human cancers. However, the molecular processes that occur in responder T cells that are suppressed by Treg cells remain largely unknown. We discovered that both naturally occurring Treg and tumor-derived Treg cells induce responder naïve/effector T cell senescence with potent suppressive activity. We further identified that initiation of DNA damage is critical and the main cause for the induction of responder T cell senescence and dysfunction mediated by human Treg cells. In addition, Treg-induced effector T cell DNA damage and senescence is due to the glucose competition between Treg and responder effector T cells. Furthermore, MAPK ERK1/2 and p38 signaling functionally cooperate with the transcription factors STAT1/STAT3 to control the molecular process of responder T cell senescence induced by human Treg cells. Senescent T cells have unique phenotypes, transcriptional profiles, gene regulation signatures, and active functions, distinct from that of exhausted and anergic T cells. Importantly, our in vivo studies suggest that human Treg-induced T cell senescence can be prevented via the inhibition of DNA damage response and/or STAT signaling in T-cell adoptive transfer mouse models. These studies identify novel molecular mechanisms of human Treg suppression and provide an emerging concept that targeting Treg-induced effector T cell senescence is a new checkpoint for immunotherapy against cancer and other diseases associated with Treg cells.

SALL1 functions as a tumor suppressor in breast cancer by regulating cancer cell senescence and metastasis through the NuRD complex

Background

SALL1 is a multi-zinc finger transcription factor that regulates organogenesis and stem cell development, but the role of SALL1 in tumor biology and tumorigenesis remains largely unknown.

Methods

We analyzed SALL1 expression levels in human and murine breast cancer cells as well as cancer tissues from different types of breast cancer patients. Using both in vitro co-culture system and in vivo breast tumor models, we investigated how SALL1 expression in breast cancer cells affects tumor cell growth and proliferation, metastasis, and cell fate. Using the gain-of function and loss-of-function strategies, we dissected the molecular mechanism responsible for SALL1 tumor suppressor functions.

Results

We demonstrated that SALL1 functions as a tumor suppressor in breast cancer, which is significantly down-regulated in the basal like breast cancer and in estrogen receptor (ER), progesterone receptor (PR) and epidermal growth factor receptor 2 (HER2) triple negative breast cancer patients. SALL1 expression in human and murine breast cancer cells inhibited cancer cell growth and proliferation, metastasis, and promoted cell cycle arrest. Knockdown of SALL1 in breast cancer cells promoted cancer cell growth, proliferation, and colony formation. Our studies revealed that tumor suppression was mediated by recruitment of the Nucleosome Remodeling and Deacetylase (NuRD) complex by SALL1, which promoted cancer cell senescence. We further demonstrated that the mechanism of inhibition of breast cancer cell growth and invasion by SALL1-NuRD depends on the p38 MAPK, ERK1/2, and mTOR signaling pathways.

Conclusion

Our studies indicate that the developmental control gene SALL1 plays a critical role in tumor suppression by recruiting the NuRD complex and thereby inducing cell senescence in breast cancer cells.

Electronic supplementary material

The online version of this article (10.1186/s12943-018-0824-y) contains supplementary material, which is available to authorized users.

TLR-mediated metabolic reprogramming in the tumor microenvironment: potential novel strategies for cancer immunotherapy

Cellular energy metabolism not only promotes tumor cell growth and metastasis but also directs immune cell survival, proliferation and the ability to perform specific and functional immune responses within the tumor microenvironment. A better understanding of the molecular regulation of metabolism in different cell components in the tumor-suppressive microenvironment is critical for the development of effective strategies for human cancer treatments. Toll-like receptors (TLRs) have recently been recognized as critical factors involved in tumor pathogenesis, regulating both tumor cells and tumor-infiltrating innate and adaptive immune cells. However, little is known about the molecular crosstalk between TLR signaling and tumor or/and immune cell metabolism, although there is abundant expression of TLRs in these cells. In this review, we explore the functional role of TLR signaling in reprogramming cell metabolism in the tumor microenvironment. In particular, we discuss how malignant tumors regulate metabolism to support their growth and survival, summarize more recently identified metabolic profiles of different immune cell subsets and TLR-mediated regulation of cellular metabolism in both tumor and immune cells, and further explore potential strategies targeting cell metabolism for TLR-based cancer therapy. An improved understanding of these issues should open new avenues for the development of novel strategies via TLR-mediated metabolic reprogramming of the tumor microenvironment for cancer immunotherapy.

Abstract PD8-11: APOBEC3 contributes to mutational load in breast cancer

Breast cancer results in large part from the accumulation of multiple mutations in premalignant cells, which provide a molecular basis for genetic diversity. This genetic diversity in premalignant cells allows selection for increased proliferation and survival and ultimately leads to invasion, metastasis, and therapeutic resistance. Recent genome-wide sequencing data showed that APOBEC3B (A3B) contributes to mutational load in breast cancer. A3B, a DNA cytosine deaminase, is overexpressed in more than 50% of breast tumors and more than 75% of breast cancer cell lines. Its overexpression and aberrant activation lead to unexpected clusters of mutations in the majority of breast cancers. This phenomenon of clustered mutations, termed kataegis (shower in Greek) forms a unique mutation signature in breast cancer. On the basis of the finding that A3B is a key molecular determinant of the mutator phenotype in breast cancer, the goal of our research is to utilize informatics tools to systematically characterize genetic alterations of APOBEC3 family proteins in breast cancer genomic data and define the molecular impact of altered APOBEC3 family proteins on mutability and anti-tumor immunity.

Our data showed that the mutation rate and copy number amplification/deletion of APOBEC3 genes are low. The levels of APOBEC3A (A3A) and A3B are highly correlated and are highest in Basal subtype and lowest in Luminal A tumors, in concordance with the proliferation of subtypes. Additionally, A3A and A3B are significantly correlated with total mutational load as well as with TP53 mutation, and with somatic copy number alterations (SCNA), especially focal SCNA. Among APOBEC3 genes, A3B is significantly associated DNA replication, DNA damage repair, cell cycle and proteasome signatures, and shows predictive and prognostic capacity in ER-positive patients. Interestingly, A3G expression is strongly associated with immune response signature genes in all breast tumors. Consequently, A3G is highly associated with tumor-infiltrating lymphocytes in breast and several other disease types.

In summary, our data demonstrate distinct expression pattern of APOBEC3 genes in different breast cancer subpopulations. Overexpression of different APOBEC3 family members leads to distinct molecular consequences. These data provide new molecular insights into pathophysiological functions of APOBEC3 genes in breast cancer and provide therapeutic opportunities for the breast cancer patients whose tumors have altered APOBEC3 expression levels and potentially are driven by APOBEC3 genes. Importantly, APOBEC3G is associated with evidence of immune activation that may signal responsiveness to immune checkpoint inhibitors.

Citation Format: Zhao W, Peng Y, Mills GB, Peng G. APOBEC3 contributes to mutational load in breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD8-11.

Baicalin induces cellular senescence in human colon cancer cells via upregulation of DEPP and the activation of Ras/Raf/MEK/ERK signaling

Baicalin is a natural flavonoid glycoside which has potent anti-tumor and antioxidant activity in cancer cells. In the present study, we found that baicalin treatment significantly induced senescence in colon cancer cells. Furthermore, baicalin upregulated the expression of decidual protein induced by progesterone (DEPP) in HCT116 colon cancer cells, which accompanied with the activation of Ras/Raf/MEK/ERK and p16^INK4A/Rb signaling pathways. Meanwhile, these phenomena also appeared under the anti-oxidation effect exerted by baicalin. In addition, ectopic expression of DEPP in HCT116 cells significantly induced the activity of senescence-associated β-galactosidase (SA-β-Gal) in tumor cells regulated by Ras/Raf/MEK/ERK signaling pathway. Knockdown of DEPP by RNA interference efficiently counteracted the baicalin-mediated growth inhibition, senescence and cell cycle arrest in cancer cells. Importantly, in a xenograft mouse model of human colon cancer, we further confirmed that baicalin treatment dramatically inhibited tumor growth, which was due to the induction of tumor cellular senescence via the upregulation of DEPP and the activation of Ras/Raf/MEK/ERK signaling in vivo. In addition to baicalin treatment, we found that the hypoxia-response protein DEPP functions as a positive regulator involving the regulations of Ras/Raf/MEK/ERK signaling pathway and inhibition of human colon cancer by other anti-oxidative drugs, such as curcumin and sulforaphane, resulting in tumor cellular senescence. These results collectively suggest that baicalin upregulates the expression of DEPP and activates its downstream Ras/Raf/MEK/ERK and p16^INK4A/Rb pathways by acting as an antioxidant, leading to senescence in colon cancer cells.

Baicalein and baicalin inhibit colon cancer using two distinct fashions of apoptosis and senescence

Baicalein and baicalin are active components of the Scutellaria baicalensis Georgi and both have broad anti-tumor activity. However, how and whether baicalein and baicalin inhibit colon cancer is unclear. Here we demonstrate that baicalein and baicalin can significantly inhibit human colon cancer cell growth and proliferation. Furthermore, both can induce cell cycle arrest, and suppress cancer cell colony formation and migration. The suppressive effects are mechanistically due to the induction of colon cancer cell apoptosis and senescence mediated by baicalein and baicalin, respectively. Furthermore, we revealed that baicalin-induced senescence in tumor cells is due to its inhibition of telomerase reverse transcriptase expression in tumor cells, and that MAPK ERK and p38 signaling pathways are causatively involved in the regulation of colon cancer cell apoptosis and senescence mediated by baicalein and baicalin. In addition, our in vivo studies using human colon cancer cells in humanized mouse xenograft models, further demonstrated that baicalein and baicalin can induce tumor cell apoptosis and senescence, resulting in inhibition of tumorigenesis and growth of colon cancer in vivo. These data clearly suggest that baicalein and baicalin have potent anti-cancer effects against human colon cancer and could be potential novel and effective target drugs for cancer therapy.

Immunomodulatory role of bitter melon extract in inhibition of head and neck squamous cell carcinoma growth

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer and leading cause of cancer related mortality worldwide. Despite the advancement in treatment procedures the overall survival rate of patients has not considerably enhanced in the past few decades. Therefore, new strategies to achieve a favorable response for the improvement in the prognosis of HNSCC are urgently needed. In this study, we examined the role of bitter melon extract (BME) in HNSCC tumor microenvironment. Mouse head and neck cancer (SCCVII) cells were subcutaneously injected into the flanks of syngeneic mice. We observed that oral gavage of BME significantly inhibits the tumor growth in mice as compared to control group. Further study suggested that BME inhibits cell proliferation as evident from low expression of proliferating cell nuclear antigen (PCNA) and c-Myc in the tumors of BME fed mice as compared to that of control group. We next investigated the role of BME as an immunomodulator in HNSCC model. Forkhead box protein P3+ (FoxP3+) T cells suppress tumor immunity. Our data suggested that BME treatment decreases the infiltrating regulatory T (Treg) cells by inhibiting FoxP3+ populations in the tumors and in spleens. Additionally, BME treatment reduces Th17 cell population in the tumor. However, BME treatment did not alter Th1 and Th2 cell populations. Together, our findings offer a new insight into how bitter melon extract inhibits head and neck tumor growth by modulating cell proliferation and Treg populations, with implications for how to control tumor-infiltrating lymphocytes and tumor progression.