The roles of PD‐1/PD‐L1 and its signalling pathway in gastrointestinal tract cancers

Cancer immunotherapy has been increasingly applied in the treatment of advanced malignancies. Consequently, immune checkpoints have become a major concern. As PD‐1 is an important immunomodulatory protein, the blockade of PD‐1 and its ligand PD‐L1 is a promising tumour immunotherapy for human carcinoma. In this review, we first discuss the role of the PD‐1/PD‐L1 interaction in gastrointestinal tract cancers. Targeting PD‐1 and PD‐L1 in immune cells and tumour cells may show remarkable efficiency in gastrointestinal tract cancers. Second, the PD‐1/PD‐L1‐associated signalling pathway involved in cancer immunotherapy in gastrointestinal tract cancers is discussed. Most importantly, this review summarizes the PD‐1/PD‐L1‐targeted immunotherapy combinations with relevant signalling pathways, which may result in a breakthrough for the treatment of gastrointestinal tract cancers, such as gastric cancer, colorectal cancer and liver cancer. Meanwhile, the review provides a deeper insight into the mechanism of checkpoint blockade immunotherapies.     

Acetaminophen-induced differentiation of human breast cancer stem cells and inhibition of tumor xenograft growth in mice

It is now believed that cancer stem cells (CSCs) that are resistant to chemotherapy due to their undifferentiated nature drive tumor growth, metastasis and relapse, so development of drugs that induce differentiation of CSCs should have a profound impact on cancer eradication. In this study, we screened medicines that are already in clinical use for drugs that induce differentiation of CSCs. We used MDA-MB-231, a human breast cancer cell line that contains cancer stem cell-like cells. We found that acetaminophen, an anti-inflammatory, antipyretic and analgesic drug, induces differentiation of MDA-MB-231 cells. Differentiation was assessed by observing alterations in cell shape and expression of differentiated and undifferentiated cell markers, a decrease in cell invasion activity and an increase in susceptibility to anti-tumor drugs. This increased susceptibility seems to involve suppression of expression of multidrug efflux pumps. We also suggest that this induction of differentiation is mediated by inhibition of a Wnt/β-catenin canonical signaling pathway. Treatment of MDA-MB-231 cells with acetaminophen in vitro resulted in the loss of their tumorigenic ability in nude mice. Furthermore, administration of acetaminophen inhibited the growth of tumor xenografts of MDA-MB-231 cells in both the presence and absence of simultaneous administration of doxorubicine, a typical anti-tumor drug for breast cancer. Analysis with various acetaminophen derivatives revealed that o-acetamidophenol has a similar differentiation-inducing activity and a similar inhibitory effect on tumor xenograft growth. These results suggest that acetaminophen may be beneficial for breast cancer chemotherapy by inducing the differentiation of CSCs.     

Targeting IL-8 signalling to inhibit breast cancer stem cell activity

Although survival from breast cancer has improved significantly over the past 20 years, disease recurrence remains a significant clinical problem. The concept of stem-like cells in cancer has been gaining currency over the last decade or so, since evidence for stem cell activity in human leukaemia and solid tumours, including breast cancer, was first published. Evidence indicates that this sub-population of cells, known as cancer stem-like cells (CSCs), is responsible for driving tumour formation and disease progression. In breast cancer, there is good evidence that CSCs are intrinsically resistant to conventional chemo-, radio- and endocrine therapies. By evading the effects of these treatments, CSCs are held culpable for disease recurrence. Hence, in order to improve treatment there is a need to develop CSC-targeted therapies. Interleukin-8 (IL-8), an inflammatory cytokine, is upregulated in breast cancer and associated with poor prognostic factors. Accumulating evidence demonstrates that IL-8, through its receptors CXCR1/2, is an important regulator of breast CSC activity. Inhibiting CXCR1/2 signalling has proved efficacious in pre-clinical models of breast cancer providing a good rationale for targeting CXCR1/2 clinically. Here, we discuss the role of IL-8 in breast CSC regulation and development of novel therapies to target CXCR1/2 signalling in breast cancer.     

肿瘤干细胞靶向治疗

多种肿瘤中都存在肿瘤干细胞(cancer stem cell,CSC),这部分细胞具有自我更新能力和分化潜能,是肿瘤生长、增殖和转移的根源。此外,肿瘤干细胞具有正常干细胞的自我保护特性,如有效的DNA修复、高表达多药耐药型膜转运蛋白以及处于相对静止状态及拥有特定的微环境,使其能够逃逸现有的肿瘤治疗手段,导致肿瘤复发。针对这些保护机制,并利用肿瘤干细胞与正常干细胞的之间的差异进行靶向治疗,可能达到根治肿瘤的疗效。     

PI3K/Akt/mTOR pathway dual inhibitor BEZ235 suppresses the stemness of colon cancer stem cells

Colon cancer is one of the most common cancers worldwide with high mortality. A major issue in colon cancer treatment is drug‐resistance and metastasis that have been ascribed to the cancer stem cells. In this study, colon cancer stem cells were isolated through sphere culture and verified with the cancer stem cell markers CD133, CD44, and CD24. It was demonstrated that the PI3K/Akt/mTOR signalling pathway was highly activated in the colon cancer stem cells and that inhibition of the PI3K/Akt/mTOR pathway by the inhibitor BEZ235 suppressed the colon cancer stem cell proliferation with reduced stemness indicated by CD133 and Lgr5 expressions. Treatment with insulin as a known activator of the PI3K/Akt pathway increased CD133 expression and decreased the effects of BEZ235 on colon cancer proliferation and survival. The data presented here collectively suggest that the PI3K/Akt/mTOR pathway underpins the stemness of colon cancer stem cells and BEZ235 is potentially a good drug candidate for treatment of colon cancer drug resistance and metastasis.     

Targeting the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin signaling network in cancer stem cells

Cancer stem cells (CSCs) comprise a subset of hierarchically organized, rare cancer cells with the ability to initiate cancer in xenografts of genetically modified murine models. CSCs are thought to be responsible for tumor onset, self-renewal/maintenance, mutation accumulation, and metastasis. The existence of CSCs could explain the high frequency of neoplasia relapse and resistance to all of currently available therapies, including chemotherapy. The phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway is a key regulator of physiological cell processes which include proliferation, differentiation, apoptosis, motility, metabolism, and autophagy. Nevertheless, aberrantly upregulated PI3K/Akt/mTOR signaling characterizes many types of cancers where it negatively influences prognosis. Several lines of evidence indicate that this signaling system plays a key role also in CSC biology. Of note, CSCs are more sensitive to pathway inhibition with small molecules when compared to healthy stem cells. This observation provides the proof-of-principle that functional differences in signaling transduction pathways between CSCs and healthy stem cells can be identified. Here, we review the evidence which links the signals deriving from the PI3K/Akt/mTOR network with CSC biology, both in hematological and solid tumors. We then highlight how therapeutic targeting of PI3K/Akt/mTOR signaling with small molecule inhibitors could improve cancer patient outcome, by eliminating CSCs.     

Drug resistance and cancer stem cells: the shared but distinct roles of hypoxia‐inducible factors HIF1α and HIF2α

Chemotherapy resistance is a major contributor to poor treatment responses and tumour relapse, the development of which has been strongly linked to the action of cancer stem cells (CSCs). Mounting evidence suggests that CSCs are reliant on low oxygen conditions and hypoxia‐inducible factors 1α and 2α (HIF1α and HIF2α) to maintain their stem cell features. Research in the last decade has begun to clarify the functional differences between the two HIFα subtypes (HIFαs). Here, we review and discuss these differences in relation to CSC‐associated drug resistance. Both HIFαs contribute to CSC survival but play different roles –HIF1α being more responsible for survival functions and HIF2α for stemness traits such as self‐renewal – and are sensitive to different degrees of hypoxia. Failure to account for physiologically relevant oxygen concentrations in many studies may influence the current understanding of the roles of HIFαs. We also discuss how hypoxia and HIFαs contribute to CSC drug resistance via promotion of ABC drug transporters Breast cancer resistance protein (BCRP), MDR1, and MRP1 and through maintenance of quiescence. Additionally, we explore the PI3K/AKT cell survival pathway that may support refractory cancer by promoting CSCs and activating both HIF1α and HIF2α. Accordingly, HIF1α and HIF2α inhibition, potentially via PI3K/AKT inhibitors, could reduce chemotherapy resistance and prevent cancer relapse.     

Nanog mediates tobacco smoke‐induced enhancement of renal cancer stem cell properties

Nanog plays an important role in the regulation of cancer stem cells (CSCs) which participate in tumorgenesis and progression. In renal cancer, tobacco smoke (TS) is considered a major risk factor. However, the molecular mechanism by which TS induces the development of renal CSC properties remains largely unknown. In this study, we showed that the level of Nanog was elevated in renal cell carcinoma (RCC) patients with a smoking history, and that Nanog overexpression promoted the traits of CSCs in renal cancer. We further demonstrated that a 8‐week exposure of TS enhanced the formation of renal tumorspheres, increased the population of CD133‐positive cells, and stimulated the expression of Nanog and CSC markers. In addition, TS was found to play a role in accelerating the cell growth transition from G1 to S phase in renal CSCs. Finally, we demonstrated that the TS‐induced effects in renal CSCs could be reversed through the downregulation of Nanog. Our results suggested that Nanog plays a role in mediating TS‐induced renal CSC properties. This study may provide new insights into the molecular mechanism of TS‐related renal tumorigenesis, which can contribute to the future development of therapeutics for renal cancer.     

The prognostic value of combining CD133 and mismatch repair proteins in patients with colorectal cancer

The prognostic value of cancer stem cells (CSCs) is a hot topic in colorectal carcinoma (CRC) research. CD133 has been identified as an important colorectal CSC marker, but its prognostic significance remains controversial. Recently, studies have reported a possible functional link between CSCs and DNA mismatch repair (MMR) system. However, the relationship between CRC stemness and MMR proteins remains little explored, and whether the predictive role of CD133 is affected by MMR proteins is still unknown. The aim of our study is to investigate the influence of MMR proteins on the predictive significance of CD133 in terms of CRC patient survival and to further analyze the correlation between MMR proteins and cancer stemness. In our study, we didn't observe the prognostic value of CD133 in CRC patients. However, we demonstrated that in patients with low expression of MSH6, MSH2, PMS2 and MLH1, especially MSH6, CD133 was an effective prognostic biomarker. Moreover, correlation analysis revealed a positive correlation between MSH6 and CD133 expression. In vitro studies supported our clinical data and showed that the expression of cancer‐associated stemness markers CD133, BMI‐1, OCT‐4 and SOX‐2 was significantly decreased in siRNA‐MSH6/MLH1 CRC cells. Thus, our results demonstrated that MMR proteins might play an important role in modulating the stemness of CRC cells. MMR proteins might be a crucial determinant that can help to accurately identify tumour subclones that may benefit from using the CSC marker CD133 as a prognostic marker.     

Rapid phenotyping of cancer stem cells using multichannel nanosensor arrays

Cancer stem cells (CSCs) contribute to multidrug resistance, tumor recurrence and metastasis, making them prime therapeutic targets. Their ability to differentiate and lose stem cell properties makes them challenging to study. Currently, there is no simple assay that can quickly capture and trace the dynamic phenotypic changes on the CSC surface. Here, we report rapid discrimination of breast CSCs from non-CSCs using a nanoparticle-fluorescent-protein based sensor. This nanosensor was employed to discriminate CSCs from non-CSCs, as well as CSCs that had differentiated in vitro in two breast cancer models. Importantly, the sensor platform could also discriminate CSCs from the bulk population of cells in patient-derived xenografts of human breast cancer. Taken together, the results obtained demonstrate the feasibility of using the nanosensor to phenotype CSCs and monitor their fate. Furthermore, this approach provides a novel area for therapeutic interventions against these challenging targets.     

纳米雄黄对MCF-7乳腺癌干细胞的体外抑制作用

目的 研究纳米雄黄对乳腺癌干细胞的体外抑制作用.方法 以人乳腺癌MCF-7亲本细胞为对象,采用无血清培养法培养获得乳腺癌干细胞.以阿霉素(1 mg/L)为阳性对照,以相同质量浓度的水飞雄黄为参照,采用CCK-8法检测纳米雄黄对MCF-7亲本细胞及干细胞增殖的影响;借助悬浮球形成及分化实验、划痕实验、Transwell侵...     

Undo the brake of tumour immune tolerance with antibodies,peptide mimetics and small molecule compounds targeting PD‐1/PD‐L1 checkpoint at different locations for acceleration of cytotoxic immunity to cancer cells

Recent clinical success of immunotherapy that inhibits the negative immune regulatory pathway programmed cell death protein‐1/PD‐1 ligand 1 (PD‐1/PD‐L1) has initiated a new era in the treatment of metastatic cancer. However, greater challenges remain to treat all cancers. The molecular architecture in the immune synapse constituting positive engagements for immune activation and negative checkpoints against immune hyperactivity is regulated dynamically by interaction between proteostasis and tumour microenvironment. This article reviews recent progresses in our understandings of the cellular and molecular mechanisms of the negative checkpoint PD‐1/PD‐L1 behaviours in immune tolerance of tumourigenesis and metastasis. We provide an overview on PD‐L1 gene expression regulation, protein turnover, intra‐ and extracellular trafficking, exosome‐mediated inter‐cellular transport, molecular interface peptide mimetics, inhibitory chemical compounds such as metformin, and antibody dynamics. We summarise PD‐L1 post‐translational modifications including glycosylation, palmitoylation, phosphorylation and ubiquitination, reflecting future research directions and opportunities in identifying tumour‐specific signalling targets, their regulatory molecules and pathways for intervention into various types of cancers.     

Difluorinated-Curcumin (CDF): A Novel Curcumin Analog is a Potent Inhibitor of Colon Cancer Stem-Like Cells

Purpose  

Recurrence of colon cancer, which affects nearly 50% of patients treated by conventional therapeutics, is thought to be due to re-emergence of chemotherapy-resistant cancer stem/stem-like cells (CSCs). Therefore, development of therapeutic strategies for targeted elimination of CSCs would be a novel strategy. The current study examines whether diflourinated-curcumin (CDF), a novel analog of the dietary ingredient of curcumin, in combination with 5-fluorouracil and oxaliplatin (5-FU + Ox), the mainstay of colon cancer chemotherapeutic, would be effective in eliminating colon CSCs.     

Targeting Of miR9/NOTCH1 Interaction Reduces Metastatic Behavior in Triple‐negative Breast Cancer

Many reports have indicated deregulation of a variety of microRNAs (miRNAs) in human cancers. In this study, we appraised miR‐9 correlation with NOTCH1 involved in Notch signaling in metastatic breast cancer. The Notch signaling pathway has been approved to be associated with the development and progression of many human cancers, including breast cancer, but the precise mechanism has remained unknown. To the best of our knowledge, this is the first study that introduces miR‐9 and NOTCH1 correlation as an effective factor in breast cancer. We found that miR‐9 expression was decreased in MDA‐MB‐231 breast cancer cells compared with MCF‐10A normal breast cell line. However, NOTCH1 was upregulated in the metastatic breast cancer cells. Furthermore, luciferase assay revealed a significant inverse correlation between miR‐9 and NOTCH1. Overexpression of Notch signaling via Notch1 intracellular domain in MDA‐MB‐231 cell line was suppressed by lentiviruses expressing miR‐9. Taken together, the results obtained by MTT, flow cytometry, migration, and wound healing assays showed that it is possible to inhibit metastasis and induce pro‐apoptotic state by induction of miR‐9 expression in MDA‐MB‐231 cells but with no effect on cell proliferation. These results shows that miR‐9, by direct targeting of NOTCH1, can reveal a suppressor‐like activity in metastatic breast cancer cells.     

Cancer stem cell-targeted chimeric antigen receptor (CAR)-T cell therapy: Challenges and prospects

Cancer stem cells (CSCs) with their self-renewal ability are accepted as cells which initiate tumors. CSCs are regarded as interesting targets for novel anticancer therapeutic agents because of their association with tumor recurrence and resistance to conventional therapies, including radiotherapy and chemotherapy. Chimeric antigen receptor (CAR)-T cells are engineered T cells which express an artificial receptor specific for tumor associated antigens (TAAs) by which they accurately target and kill cancer cells. In recent years, CAR-T cell therapy has shown more efficiency in cancer treatment, particularly regarding blood cancers. The expression of specific markers such as TAAs on CSCs in varied cancer types makes them as potent tools for CAR-T cell therapy. Here we review the CSC markers that have been previously targeted with CAR-T cells, as well as the CSC markers that may be used as possible targets for CAR-T cell therapy in the future. Furthermore, we will detail the most important obstacles against CAR-T cell therapy and suggest solutions.KEY WORDS: Chimeric antigen receptor T cell, Cancer stem cell, Immunotherapy, Tumor associated antigens, Combination therapy, Off-tumor toxicity, Clinical trial, Tumor immunosuppressive microenvironment