Cancer stem cells: a target for overcoming therapeutic resistance and relapse

Cancer stem cells(CSCs) are a small subset of cells in cancers that are thought to initiate tumorous transformation and promote metastasis, recurrence, and resistance to treatment. Growing evidence has revealed the existence of CSCs in various types of cancers and suggested that CSCs differentiate into diverse lineage cells that contribute to tumor progression. We may be able to overcome the limitations of cancer treatment with a comprehensive understanding of the biological features and mechanisms underlying therapeutic resistance in CSCs. This review provides an overview of the properties, biomarkers, and mechanisms of resistance shown by CSCs. Recent findings on metabolic features, especially fatty acid metabolism and ferroptosis in CSCs, are highlighted, along with promising targeting strategies. Targeting CSCs is a potential treatment plan to conquer cancer and prevent resistance and relapse in cancer treatment.

Application of nanotechnology in reversing therapeutic resistance and controlling metastasis of colorectal cancer

Colorectal cancer(CRC)is the most common digestive malignancy across the world.Its first-line treatments applied in the routine clinical setting include surgery,chemotherapy,radiotherapy,targeted therapy,and immunotherapy.However,resistance to therapy has been identified as the major clinical challenge that fails the treatment method,leading to recurrence and distant metastasis.An increasing number of studies have been attempting to explore the underlying mechanisms of the resistance of CRC cells to different therapies,which can be summarized into two aspects:(1)The intrinsic characters and adapted alterations of CRC cells before and during treatment that regulate the drug metabolism,drug transport,drug target,and the activation of signaling pathways;and(2)the suppressive features of the tumor microenvironment(TME).To combat the issue of therapeutic resistance,effective strategies are warranted with a focus on the restoration of CRC cells’sensitivity to specific treatments as well as reprogramming impressive TME into stimulatory conditions.To date,nanotechnology seems promising with scope for improvement of drug mobility,treatment efficacy,and reduction of systemic toxicity.The instinctive advantages offered by nanomaterials enable the diversity of loading cargoes to increase drug concentration and targeting specificity,as well as offer a platform for trying the combination of different treatments to eventually prevent tumor recurrence,metastasis,and reversion of therapy resistance.The present review intends to summarize the known mechanisms of CRC resistance to chemotherapy,radiotherapy,immunotherapy,and targeted therapy,as well as the process of metastasis.We have also emphasized the recent application of nanomaterials in combating therapeutic resistance and preventing metastasis either by combining with other treatment approaches or alone.In summary,nanomedicine is an emerging technology with potential for CRC treatment;hence,efforts should be devoted to targeting cancer cells for the restoration of therapeutic sensitivity as well as reprogramming the TME.It is believed that the combined strategy will be beneficial to achieve synergistic outcomes contributing to control and management of CRC in the future.

Role of exosomes in metastasis and therapeutic resistance in esophageal cancer

Esophageal cancer(EC)has a high incidence and mortality rate and is emerging as one of the most common health problems globally.Owing to the lack of sensitive detection methods,uncontrollable rapid metastasis,and pervasive treatment resistance,EC is often diagnosed in advanced stages and is susceptible to local recurrence.Exosomes are important components of intercellular communication and the exosome-mediated crosstalk between the cancer and surrounding cells within the tumor microenvironment plays a crucial role in the metastasis,progression,and therapeutic resistance of EC.Considering the critical role of exosomes in tumor pathogenesis,this review focused on elucidating the impact of exosomes on EC metastasis and therapeutic resistance.Here,we summarized the relevant signaling pathways involved in these processes.In addition,we discussed the potential clinical applications of exosomes for the early diagnosis,prognosis,and treatment of EC.

Therapeutic resistance in cancer: microRNA regulation of EGFR signaling networks

Receptor tyrosine kinases(RTKs)such as the epidermal growth factor receptor(EGFR)regulate cellular homeostatic processes.EGFR activates downstream signaling cascades that promote tumor cell survival,proliferation and migration.Dysregulation of EGFR signaling as a consequence of overexpression,amplification and mutation of the EGFR gene occurs frequently in several types of cancers and many become dependent on EGFR signaling to maintain their malignant phenotypes.Consequently,concerted efforts have been mounted to develop therapeutic agents and strategies to effectively inhibit EGFR.However,limited therapeutic benefits to cancer patients have been derived from EGFR-targeted therapies.A well-documented obstacle to improved patient survival is the presence of EGFR-inhibitor resistant tumor cell variants within heterogeneous tumor cell masses.Here,we summarize the mechanisms by which tumors resist EGFR-targeted therapies and highlight the emerging role of microRNAs(miRs)as downstream effector molecules utilized by EGFR to promote tumor initiation,progression and that play a role in resistance to EGFR inhibitors.We also examine evidence supporting the utility of miRs as predictors of response to targeted therapies and novel therapeutic agents to circumvent EGFR-inhibitor resistance mechanisms.

When fats commit crimes: fatty acid metabolism, cancer stemness and therapeutic resistance

The role of fatty acid metabolism,including both anabolic and catabolic reactions in cancer has gained increas-ing attention in recent years.Many studies have shown that aberrant expression of the genes involved in fatty acid synthesis or fatty acid oxidation correlate with malignant phenotypes including metastasis,therapeutic resistance and relapse.Such phenotypes are also strongly associated with the presence of a small percentage of unique cells among the total tumor cell population.This distinct group of cells may have the ability to self-renew and propagate or may be able to develop resistance to cancer therapies independent of genetic alterations.Therefore,these cells are referred to as cancer stem cells/tumor-initiating cells/drug-tolerant persisters,which are often refractory to cancer treatment and difficult to target.Moreover,interconversion between cancer cells and cancer stem cells/tumor-initiating cells/drug-tolerant persisters may occur and makes treatment even more challenging.This review highlights recent findings on the relationship between fatty acid metabolism,cancer stemness and therapeutic resistance and prompts discussion about the potential mechanisms by which fatty acid metabolism regulates the fate of cancer cells and therapeutic resistance.

Nuclear TIGAR mediates an epigenetic and metabolic autoregulatory loop via NRF2 in cancer therapeutic resistance

Metabolic and epigenetic reprogramming play important roles in cancer therapeutic resistance.However,their interplays are poorly understood.We report here that elevated TIGAR(TP53-induced glycolysis and apoptosis regulator),an antioxidant and glucose metabolic regulator and a target of oncogenic histone methyltransferase NSD2(nuclear receptor binding SET domain protein 2),is mainly localized in the nucleus of therapeutic resistant tumor cells where it stimulates NSD2 expression and elevates global H3K36me2 mark.Mechanistically,TIGAR directly interacts with the antioxidant master regulator NRF2 and facilitates chromatin recruitment of NRF2,H3K4me3 methylase MLL1 and elongating Pol-II to stimulate the expression of both new(NSD2)and established(NQO1/2,PRDX1 and GSTM4)targets of NRF2,independent of its enzymatic activity.Nuclear TIGAR confers cancer cell resistance to chemotherapy and hormonal therapy in vitro and in tumors through effective maintenance of redox homeostasis.In addition,nuclear accumulation of TIGAR is positively associated with NSD2 expression in clinical tumors and strongly correlated with poor survival.These findings define a nuclear TIGAR-mediated epigenetic autoregulatory loop in redox rebalance for tumor therapeutic resistance.

Melanoma:Molecular genetics,metastasis,targeted therapies,immunotherapies,and therapeutic resistance

Cutaneous melanoma is a common cancer and cases have steadily increased since the mid 70s.For some patients,early diagnosis and surgical removal of melanomas is lifesaving,while other patients typically turn to molecular targeted therapies and immunotherapies as treatment options.Easy sampling of melanomas allows the scientific community to identify the most prevalent mutations that initiate melanoma such as the BRAF,NRAS,and TERT genes,some of which can be therapeutically targeted.Though initially effective,many tumors acquire resistance to the targeted therapies demonstrating the need to investigate compensatory pathways.Immunotherapies represent an alternative to molecular targeted therapies.However,inter-tumoral immune cell populations dictate initial therapeutic response and even tumors that responded to treatment develop resistance in the long term.As the protocol for combination therapies develop,so will our scientific understanding of the many pathways at play in the progression of melanoma.The future direction of the field may be to find a molecule that connects all of the pathways.Meanwhile,noncoding RNAs have been shown to play important roles in melanoma development and progression.Studying noncoding RNAs may help us to understand how resistance e both primary and acquired e develops;ultimately allow us to harness the true potential of current therapies.This review will cover the basic structure of the skin,the mutations and pathways responsible for transforming melanocytes into melanomas,the process by which melanomas metastasize,targeted therapeutics,and the potential that noncoding RNAs have as a prognostic and treatment tool.

Cancer-associated fibroblasts as accomplices to confer therapeutic resistance in cancer

The “seed and soil” concept has reformed paradigms for cancer treatment in the past decade. Accumulatingevidence indicates that the intimate crosstalk between cancer cells and stromal cells plays a tremendous role intumor progression. Cancer-associated fibroblasts (CAFs), the largest population of stroma cells, influencetherapeutic effects through diverse mechanisms. Herein, we summarize the recent advances in the versatilefunctions of CAFs regarding their heterogeneity, and we mainly discuss the pro-tumorigenic functions of CAFswhich promote tumorigenesis and confer therapeutic resistance to tumors. Targeting CAFs is emerging as one ofthe most appealing strategies in anticancer therapies. The endeavors to target or reprogram the specific subtypesof CAFs provide great cancer treatment opportunities, which may provide a better clinical benefit to cancerpatients.

Pancreatic cancer: genetics, disease progression, therapeutic resistance and treatment strategies

Pancreatic cancer is a deadly disease and the third-highest cause of cancer-related deaths in the United States.It has a very low five-year survival rate(<5%)in the United States as well as in the world(about 9%).The current gemcitabine-based therapy soon becomes ineffective because treatment resistance and surgical resection also provides only selective benefit.Signature mutations in pancreatic cancer confer chemoresistance by deregulating the cell cycle and promoting anti-apoptotic mechanisms.The stroma-rich tumor microenvironment impairs drug delivery and promotes tumor-specific immune escape.All these factors render the current treatment incompetent and prompt an urgent need for new,improved therapy.In this review,we have discussed the genetics of pancreatic cancer and its role in tumor evolution and treatment resistance.We have also evaluated new treatment strategies for pancreatic cancer,like targeted therapy and immunotherapy.

MicroRNA-216a: a potential therapeutic target for drug resistance and recurrent of liver cancer

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Molecular modulation of autophagy: New venture to target resistant cancer stem cells

Autophagy is a highly regulated catabolic process in which superfluous,damaged organelles and other cytoplasmic constituents are delivered to the lysosome for clearance and the generation of macromolecule substrates during basal or stressed conditions.Autophagy is a bimodal process with a context dependent role in the initiation and the development of cancers.For instance,autophagy provides an adaptive response to cancer stem cells to survive metabolic stresses,by influencing disease propagation via modulation of essential signaling pathways or by promoting resistance to chemotherapeutics.Autophagy has been implicated in a cross talk with apoptosis.Understanding the complex interactions provides an opportunity to improve cancer therapy and the clinical outcome for the cancer patients.In this review,we provide a comprehensive view on the current knowledge on autophagy and its role in cancer cells with a particular focus on cancer stem cell homeostasis.

Targeting androgen receptor-independent pathways in therapy-resistant prostate cancer

Since androgen receptor(AR)signaling is critically required for the development of prostate cancer(PCa),targeting AR axis has been the standard treatment of choice for advanced and metastatic PCa.Unfortunately,although the tumor initially responds to the therapy,treatment resistance eventually develops and the disease will progress.It is therefore imperative to identify the mechanisms of therapeutic resistance and novel molecular targets that are independent of AR signaling.Recent advances in pathology,molecular biology,genetics and genomics research have revealed novel AR-independent pathways that contribute to PCa carcinogenesis and progression.They include neuroendocrine differentiation,cell metabolism,DNA damage repair pathways and immune-mediated mechanisms.The development of novel agents targeting the non-AR mechanisms holds great promise to treat PCa that does not respond to AR-targeted therapies.

CTRR-ncRNA:A Knowledgebase for Cancer Therapy Resistance and Recurrence Associated Non-coding RNAs

Cancer therapy resistance and recurrence(CTRR)are the dominant causes of death in cancer patients.Recent studies have indicated that non-coding RNAs(ncRNAs)can not only reverse the resistance to cancer therapy but also are crucial biomarkers for the evaluation and prediction of CTRR.Herein,we developed CTRR-ncRNA,a knowledgebase of CTRR-associated ncRNAs,aiming to provide an accurate and comprehensive resource for research involving the association between CTRR and ncRNAs.Compared to most of the existing cancer databases,CTRRncRNA is focused on the clinical characterization of cancers,including cancer subtypes,as well as survival outcomes and responses to personalized therapy of cancer patients.Information pertaining to biomarker ncRNAs has also been documented for the development of personalized CTRR prediction.A user-friendly interface and several functional modules have been incorporated into the database.Based on the preliminary analysis of genotype-phenotype relationships,universal ncRNAs have been found to be potential biomarkers for CTRR.The CTRR-ncRNA is a translation-oriented knowledgebase and it provides a valuable resource for mechanistic investigations and explainable artificial intelligence-based modeling.

Cancer stem cells in glioblastoma—molecular signaling and therapeutic targeting

Glioblastomas(GBMs)are highly lethal primary brain tumors.Despite current therapeutic advances in other solid cancers,the treatment of these malignant gliomas remains essentially palliative.GBMs are extremely resistant to conventional radiation and chemotherapies.We and others have demonstrated that a highly tumorigenic subpopulation of cancer cells called GBM stem cells(GSCs)promotes therapeutic resistance.We also found that GSCs stimulate tumor angiogenesis by expressing elevated levels of VEGF and contribute to tumor growth,which has been translated into a useful therapeutic strategy in the treatment of recurrent or progressive GBMs.Furthermore,stem cell-like cancer cells(cancer stem cells)have been shown to promote metastasis.Although GBMs rarely metastasize beyond the central nervous system,these highly infiltrative cancers often invade into normal brain tissues preventing surgical resection,and GSCs display an aggressive invasive phenotype.These studies suggest that targeting GSCs may effectively reduce tumor recurrence and significantly improve GBM treatment.Recent studies indicate that cancer stem cells share core signaling pathways with normal somatic or embryonic stem cells,but also display critical distinctions that provide important clues into useful therapeutic targets.In this review,we summarize the current understanding and advances in glioma stem cell research,and discuss potential targeting strategies for future development of anti-GSC therapies.

Understanding the biology of HER3 receptor as a therapeutic target in human cancer

HER3 belongs to the human epidermal growth factor receptor(HER) family which also includes HER1/EGFR/erb B1,HER2/erb B2,and HER4/erb B4. As a unique member of the HER family,HER3 lacks or has little intrinsic tyrosine kinase activity. It frequently co-expresses and forms heterodimers with other receptor tyrosine kinases(RTKs) in cancer cells to activate oncogenic signaling,especially the PI-3 K/Akt pathway and Src kinase. Elevated expression of HER3 has been observed in a wide variety of human cancers and associates with a worse survival in cancer patients with solid tumors.Studies on the underlying mechanism implicate HER3 expression as a major cause of treatment failure in cancer therapy. Activation of HER3 signaling has also been shown to promote cancer metastasis. These data strongly support the notion that therapeutic inactivation of HER3 and/or its downstream signaling is required to overcome treatment resistance and improve the outcomes of cancer patients.

Study on Effect of Chinese Herbal Medicine for Enhancing Therapeutic Efficacy on Refractory Drug Resistant Leukemia

The so-called multidrug resistance （MDR） of leukemic cells means the cross resistance of leukemic cells against multiple anti-tumor agents with different constitution and acting mechanism, which takes place simultaneous after resistance to a single contacted drug has been produced. Tumor cells with MDR would now show a low sensitivity to anti-tumor agents, making chemotherapy ineffective or of little effect. Moreover, MDR is one of the pathogenetic factors for inducing refractory leukemia.

Long Non-coding RNAs and Their Roles in Non-small-cell Lung Cancer

As a leading cause of cancer deaths worldwide, lung cancer is a collection of diseases with diverse etiologies which can be broadly classified into small-cell lung cancer （SCLC） and non-small-cell lung cancer （NSCLC）. Lung cancer is characterized by genomic and epigenomic alterations; however, mechanisms underlying lung tumorigenesis remain to be elucidated. Long noncoding RNAs （lncRNAs） are a group of non-coding RNAs that consist of ≥ 200 nucleotides but possess low or no protein-coding potential. Accumulating evidence indicates that abnormal expression of lncRNAs is associated with tumorigenesis of various cancers, including lung cancer, through multiple biological mechanisms involving epigenetic, transcriptional, and post-transcriptional alterations. In this review, we highlight the expression and roles of lncRNAs in NSCLC and discuss their potential clinical applications as diagnostic or prognostic biomarkers, as well as therapeutic targets.

Revisiting ovarian cancer microenvironment： a friend or a foe？

Development of ovarian cancer involves the co-evolu- tion of neoplastic cells together with the adjacent microenvironment. Steps of malignant progression including primary tumor outgrowth, therapeutic resis- tance, and distant metastasis are not determined solely by genetic alterations in ovarian cancer cells, but con- siderably shaped by the fitness advantage conferred by benign components in the ovarian stroma. As the dynamic cancer topography varies drastically during disease progression, heterologous cell types within the tumor microenvironment （TME） can actively determine the pathological track of ovarian cancer. Resembling many other solid tumor types, ovarian malignancy is nurtured by a TME whose dark side may have been overlooked, rather than overestimated. Further, har- nessing breakthrough and targeting cures in human ovarian cancer requires insightful understanding of the merits and drawbacks of current treatment modalities, which mainly target transformed cells. Thus, designing novel and precise strategies that both eliminate cancer cells and manipulate the TME is increasingly recognized as a rational avenue to improve therapeutic outcome and prevent disease deterioration of ovarian cancer patients.

DNA damage-induced nuclear factor-kappa B activation and its roles in cancer progression

DNA damage is a vital challenge to cell homeostasis.Cellular responses to DNA damage(DDR)play essential roles in maintaining genomic stability and survival,whose failure could lead to detrimental consequences such as cancer development and aging.Nuclear factor-kappa B(NF-kB)is a family of transcription factors that plays critical roles in cellular stress response.Along with p53,NF-kB modulates transactivation of a large number of genes which participate in various cellular processes involved in DDR.Here the authors summarize the recent progress in understanding DNA damage response and NF-kB signaling pathways.This study particularly focuses on DNA damage-induced NF-kB signaling cascade and its physiological and pathological significance in B cell development and cancer therapeutic resistance.The authors also discuss promising strategies for selectively targeting this genotoxic NF-kB signaling aiming to antagonize acquired resistance and resensitize refractory cancer cells to cytotoxic treatments。