Prox1 Suppresses Proliferation and Drug Resistance of Retinoblastoma Cells via Targeting Notch1

Objective Retinoblastoma(RB)is a prevalent type of eye cancer in youngsters.Prospero homeobox 1(Prox1)is a homeobox transcriptional repressor and downstream target of the proneural gene that is relevant in lymphatic,hepatocyte,pancreatic,heart,lens,retinal,and cancer cells.The goal of this study was to investigate the role of Prox1 in RB cell proliferation and drug resistance,as well as to explore the underlying Notch1 mechanism.Methods Human RB cell lines(SO-RB50 and Y79)and a primary human retinal microvascular endothelial cell line(ACBRI-181)were used in this study.The expression of Prox1 and Notch1 mRNA and protein in RB cells was detected using quantitative real time-polymerase chain reaction(RT-qPCR)and Western blotting.Cell proliferation was assessed after Prox1 overexpression using the Cell Counting Kit-8 and the MTS assay.Drug-resistant cell lines(SO-RB50/vincristine)were generated and treated with Prox1 to investigate the role of Prox1 in drug resistance.We employed pcDNA-Notch1 to overexpress Notch1 to confirm the role of Notch1 in the protective function of Prox1.Finally,a xenograft model was constructed to assess the effect of Prox1 on RB in vivo.Results Prox1 was significantly downregulated in RB cells.Overexpression of Prox1 effectively decreased RB cell growth while increasing the sensitivity of drug-resistant cells to vincristine.Notch1 was involved in Prox1’s regulatory effects.Notch1 was identified as a target gene of Prox1,which was found to be upregulated in RB cells and repressed by increased Prox1 expression.When pcDNA-Notch1 was transfected,the effect of Prox1 overexpression on RB was removed.Furthermore,by downregulating Notch1,Prox1 overexpression slowed tumor development and increased vincristine sensitivity in vivo.Conclusion These data show that Prox1 decreased RB cell proliferation and drug resistance by targeting Notch1,implying that Prox1 could be a potential therapeutic target for RB.

PPP1R14A is Associated with Immunotherapy Resistance in Head and Neck Squamous Cell Carcinoma Identified by Single-Cell and Bulk RNA-Sequencing

Objective To identify nivolumab resistance-related genes in patients with head and neck squamous cell carcinoma(HNSCC)using single-cell and bulk RNA-sequencing data.Methods The single-cell and bulk RNA-sequencing data downloaded from the Gene Expression Omnibus database were analyzed to screen out differentially expressed genes(DEGs)between nivolumab resistant and nivolumab sensitive patients using R software.The Least Absolute Shrinkage Selection Operator(LASSO)regression and Recursive Feature Elimination(RFE)algorithm were performed to identify key genes associated with nivolumab resistance.Functional enrichment of DEGs was analyzed with Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses.The relationships of key genes with immune cell infiltration,differentation trajectory,dynamic gene expression profiles,and ligand-receptor interaction were explored.Results We found 83 DEGs.They were mainly enriched in T-cell differentiation,PD-1 and PD-L1 checkpoint,and T-cell receptor pathways.Among six key genes identified using machine learning algorithms,only PPP1R14A gene was differentially expressed between the nivolumab resistant and nivolumab sensitive groups both before and after immunotherapy(P<0.05).The high PPP1R14A gene expression group had lower immune score(P<0.01),higher expression of immunosuppressive factors(such as PDCD1,CTLA4,and PDCD1LG2)(r>0,P<0.05),lower differentiation of infiltrated immune cells(P<0.05),and a higher degree of interaction between HLA and CD4(P<0.05).Conclusions PPP1R14A gene is closely associated with resistance to nivolumab in HNSCC patients.Therefore,PPP1R14A may be a target to ameliorate nivolumab resistance of HNSCC patients.

Roles of the tumor microenvironment in the resistance to programmed cell death protein 1 inhibitors in patients with gastric cancer

Despite the continuous developments and advancements in the treatment of gastric cancer(GC),which is one of the most prevalent types of cancer in China,the overall survival is still poor for most patients with advanced GC.In recent years,with the progress in tumor immunology research,attention has shifted toward immunotherapy as a therapeutic approach for GC.Programmed cell death protein 1(PD-1)inhibitors,as novel immunosuppressive medications,have been widely utilized in the treatment of GC.However,many patients are still resistant to PD-1 inhibitors and experience recurrence in the advanced stages of PD-1 immunotherapy.To reduce the occurrence of drug resistance and recurrence in GC patients receiving PD-1 immunotherapy,to maximize the clinical activity of immunosuppressive drugs,and to elicit a lasting immune response,it is essential to research the tumor microenvironment mechanisms leading to PD-1 inhibitor resistance in GC patients.This article reviews the progress in studying the factors influencing the resistance to PD-1 inhibitors in the GC tumor microenvironment,aiming to provide insights and a basis for reducing resistance to PD-1 inhibitors for GC patients in the future.

Research progress on lung cancer stem cells in epidermal growth factor receptor–tyrosine kinase inhibitor targeted therapy resistance in lung adenocarcinoma

Lung cancer is the leading cause of cancer-related deaths globally.In recent years,with the widespread use of genetic testing,epidermal growth factor receptor–tyrosine kinase inhibitor(EGFR-TKI)–targeted drugs have been efficacious to patients with lung adenocarcinoma exhibiting EGFR mutations.However,resistance to treatment is inevitable and eventually leads to tumor progression,recurrence,and reduction in the overall treatment efficacy.Lung cancer stem cells play a crucial role in the development of resistance toward EGFR-TKI–targeted therapy for lung adenocarcinoma.Lung cancer stem cells possess self-renewal,multilineage differentiation,and unlimited proliferation capabilities,which efficiently contribute to tumor formation and ultimately lead to tumor recurrence andmetastasis.In this study,we evaluated the origin,markers,stemness index,relevant classic studies,resistance mechanisms,related signaling pathways,and strategies for reversing lung cancer stem cell resistance to EGFR-TKIs to provide new insights on delaying or reducing resistance and to improve the treatment efficacy of patients with EGFR-mutated lung adenocarcinoma in the future.

Hepatic cancer stem cells and drug resistance: Relevance in targeted therapies for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of most common malignancies in the world. Systemic treatments for HCC, particularly for advanced stages, are limited by the drug resistance phenomenon which ultimately leads to therapy failure. Recent studies have indicated an association between drug resistance and the existence of the cancer stem cells (CSCs) as tumor initiating cells. The CSCs are resistant to conventional chemotherapies and might be related to the mechanisms of the ATP Binding Cassette (ABC) transporters and alterations in the CSCs signaling pathways. Therefore, to contribute to the development of new HCC treatments, further information on the characterization of CSCs, the modulation of the ABC transporters expression and function and the signaling pathway involved in the self renewal, initiation and maintenance of the cancer are required. The combination of transporters modulators/inhibitors with molecular targeted therapies may be a potent strategy to block the tumoral progression. This review summarizes the association of CSCs, drug resistance, ABC transporters activities and changes in signaling pathways as a guide for future molecular therapy for HCC.

Effects of Taxotere on invasive potential and multidrug resistance phenotype in pancreatic carcinoma cell line SUIT-2

INTRODUCTIONDevelopment of drug-resistance to chemotherapyand subsequent metastasis of tumor are primarilyresponsible for treatment failure and the death fromcancer. There have been many previous studies onthe relationship between expression of multidrugresistance (MDR) phenotype P-glycoprotein (P-gp)and the malignant properties of tumors, but theresults are often conflicting[1-8]. The difference intumor types or MDR phenotype induced by specificagents might account for this discrepancy. Taxotere(TXT), a member of the family of taxanes, hasantitumor activity through its effect of promotingthe polymerization of tubulin[9,10].

Multifactorial nature of hepatocellular carcinoma drug resistance: Could plant polyphenols be helpful?

Primary hepatocellular carcinoma （HCC） is a quite frequent tumor which results in high mortality and most often exhibits a poor response to present drug therapies. Clearly, a thorough understanding of the biological bases of this malignancy might suggest new strategies for its treatment. Here we examine the evidences that both ＂pharmacological＂ mechanisms （e.g. drug transporter or detoxification enzyme over-expression） and alterations in other critical factors, including the IAPs （Inhibitory of Apoptosis Proteins）, involved in enhancement of cell survival and proliferation may determine the therapeutic resistance of HCC; we also underline the possible role in the process of the activation of transcription factors, like NF-κB, capable of contemporaneously up-regulating the mechanisms discussed. On this basis, we finally comment on the possible use of natural multi-targeted antitumoral agents like plant polyphenols to achieve sensitization to treatments in HCC.

Anticancer Drug Resistance of HeLa Cells Transfected With Rat Glutathione S-transferase pi Gene

To establish a cytologic expressing system of rat glutathione S-transferase pi (GST-pi) cDNA for detecting the resistance of HeLa cells to anticancer drugs. Methods The assessment was made with various anticancer drugs (adriamycin, mitomycin, cisplatinum and vincristine) that showed different cytotoxicities in transfectant HeLa cells with pSV-GT containing rat GST-pi cDNA (HeLa/pSV-GT) or control pSV-neo (HeLa/pSV-neo). Expression levels of GST-pi mRNA in HeLa/pSV-GT and HeLa/pSV-neo were measured by in situ hybridization using Digoxin-labelled cDNA probe. Results HeLa/pSV-GT expressed significantly high degree of GST-pi mRNA, whereas both HeLa/pSV-neo and HeLa cells had very low expression. Cytotoxicities of HeLa/pSV-GT and HeLa/pSV-neo with 4 anticancer drugs were measured by MTT assay. Drug concentrations for yielding 50% inhibition (IC50) in HeLa/pSV-GT by adriamycin, mitomycin and cisplatinum were 70.13 靏/mL, 10.95 靏/mL and 16.52 靏/mL, respectively. In contrast, IC50 in HeLa/pSV-neo was 10.34 靏/mL, 7.48 靏/mL and 13.70 靏/mL, respectively. The cytotoxicities of vincristine on both HeLa/pSV-GT and HeLa/pSV-neo were not significantly different. Conclusions Our findings suggest that HeLa/pSV-GT containing rat GST-pi cDNA is resistant to some anticancer drugs due to overexpression of GST-pi. Also, HeLa/pSV-GT cell line could serve as a useful cytogenetic model for further research.

Effect of Antisense Oligodeoxynucleotide Directed to NF-κB-RelA on Bcl-x_L mRNA in Extended Drug Resistance Leukemia Cell Line HL- 60/E6

To explore the effect of NF κB on bcl x gene transcription in extended drug resistance leukemia cell line HL 60/E6, drug resistant subline HL 60/E6 was derived by intermittently exposing HL 60 cells to 6 ng/ml epirubicin. Indirect immunofluorescence was used to demonstrate the location of NF κB RelA in HL 60/E6 cells. FCM analysis and RT PCR were used to detect the efficiency of liposome mediated ODN transfection and the change of bcl x L mRNA levels after 5 μmol/L phosphorothioate (PS) derivatized antisense (AS) oligodeoxynucleotide (ODN) directed to RelA was transferred into HL 60/E6 cells. The results showed that RelA remained persistently active and located at the nuclei of HL 60/E6 cells,but in the cytoplasm of HL 60 cells, the efficiency of liposome mediated ODN transfection was significantly higher than that of null ODN ( P <0.01 in 4 h, 6 h, 12 h, 24 h). Exposure of HL 60/E6 cells to 5 μmol/L AS PS ODN directed to RelA led to a maximal 40 % decline of bcl x L mRNA levels within 8 h. The inhibition rate of bcl x L mRNA was (15±1.79) %, (28±2.34) %, (40±3.47) %, (20±1.54) % in 4 h, 6 h, 8 h, 15 h, respectively, but it was less than 15 % in control group. It was concluded that NF κB was involved in regulating bcl x transcription. It was suggested that NF κB was an important factor for drug resistance in leukemia cells.

EXPRESSION AND REVERSION OF DRUG RESISTANCE-AND APOPTOSIS-RELATED GENES OF A DDP-RESISTANT LUNG ADENOCARCINOMA CELL LINE

Objective: To investigate the co-expression of drug resistance- and apoptosis-related genes of cisplatin (CDDP)-selected lung adenocarcinoma cell line A 549 DDP for compared to the parental cell line A549, and reverse of drug resistance by antisense s-oligodeoxynucleotides (S-ODNs) of differentially expressed genes. Methods: Sense and antisense S-ODN were transferred into A 549 DDP cells by lipofectin. The expression of drug resistance and apoptosis related genes was examined by RT-PCR, immunocytochemistry and flow cytometry, respectively. Apoptostic cells were identified by DNA electrophoresis and terminal deoxynucleotidyl transferase (TdT)-mediated biotin dUTP nick end-labeling(TUNEL). Drug resistance of tumor cells was detected by a cell viability (MTT) assay. Results: The expression of bcl-2 was positive and that of multidrug resistance-associated protein (MRP) at mRNA and protein level was increased in A 549 DDP compared to A549 cells. MDR1, c-myc and topoisomeras II (TOPO II) were similarly co-expressed in two cell lines. Both cell lines were negative for c-erbB-2 expression. In A 549 DDP cells, the expression of bcl-2 and MRP was significantly inhibited by their respective antisense S-ODNs. Antisense S-ODNs could also decrease significantly drug resistance of A 549 DDP cells to CDDP by promoting cell apoptosis. Conclusion: Both intrinsic and acquired drug resistance were involved in co-expression of multiple MDR-related genes in lung adenocarcinoma. Cooperation of bcl-2 and MRP genes appeared to play an important action to confer the resistance of A 549 DDP cells to CDDP. Their antisense S-ODNs are responsible for the decrease of drug resistance of this cell line by promoting apoptosis.

Liposome-mediated Functional Expression of Multiple Drug Resistance Gene in Human Bone Marrow CD34^+ Cells

Summary: The expression and functional activity of multiple drug resistance (MDR1) gene in human normal bone marrow CD34+ cells was observed. Human normal bone marrow CD34+ cells were enriched with magnetic cell sorting (MACS) system, and then liposome-mediated MDR1 gene was transferred into bone marrow CD34+ cells. Fluorescence-activated cell sorter was used to evaluate the expression and functional activity of P-glycoprotein (P-gp) encoded by MDR1 gene. It was found that the purity of bone marrow CD34+ cells was approximately (91±4.56) % and recovery rate was (72.3±2.36) % by MACS. The expression of P-gp in the transfected CD34+cells was obviously higher than that in non-transfected CD34+ cells. The amount of P-gp in non-transfected CD34+ cells was (11.2±2.2) %, but increased to (23.6±2.34) % 48 h after gene transfection (P<0.0l). The amount of P-gp was gradually decreased to the basic level one week later. The accumulation and extrusion assays showed that the overexpression of P-gp could efflux Rh-123 out of cells and there was low fluorescence within the transfected cells. The functional activity of P-gp could be inhibited by 10 μg/ml verapamil. It was suggested that the transient and highly effective expression and functional activity of P-gp could be obtained by liposome-mediated MRD1 transferring into human normal bone marrow CD34+ cells.

Reversion of Multidrug-Resistance by Proteasome Inhibitor Bortezomib in K562/DNR Cell Line

Objective：To observe the reversion of multi-drug resistance by proteasome inhibitor bortezomib in K562/DNR cell line and to analyze the possible mechanism of reversion of multidrug-resistance.Methods：MTT method was used to determine the drug resistance of K562/DNR cells and the cellular toxicity of bortezomib.K562/DNR cells were cultured for 12 hours,24 hours and 36 hours with 100 μg/ml DNR only or plus 4 μg/L bortezomib.The expressions of NF-κB,IκB and P-gp of K562/DNR were detected with Western blot method,the activity of NF-κB was tested by ELISA method and the apoptosis rate was observed in each group respectively.Results：The IC50 of DNR on cells of K562/S and K562/DNR groups were 1.16 μg/ml and 50.43 μg/mL,respectively.The drug-resistant fold was 43.47.The IC10 of PS-341 on Cell strain K562/DNR was 4 μg/L.Therefore,4 μg/L was selected as the concentration for PS-341 to reverse drug-resistance in this study.DNR induced down-regulation of IκB expression,up-regulation of NF-κB and P-gp expression.After treatment with PS-341,a proteasome inhibitor,the IκB degradation was inhibited,IκB expression increased,NF-κB and P-gp expression decreased in a time dependent manner.Compared to DNR group,the NF-κB p65 activity of DNR＋PS-341 group was decreased.Compared to corresponding DNR group,DNR induced apoptosis rate increases after addition of PS-341 in a time dependent manner.Conclusion：Proteasome inhibitor bortezomib can convert the leukemia cell drug resistance.The mechanism may be that bortezomib decreases the degradation of IκB and the expression of NF-κB and P-gp,therefore induces the apoptosis of multi-drug resistant cells.

Autophagy and multidrug resistance in cancer

Multidrug resistance(MDR) occurs frequently after long-term chemotherapy, resulting in refractory cancer and tumor recurrence.Therefore, combatting MDR is an important issue. Autophagy, a self-degradative system, universally arises during the treatment of sensitive and MDR cancer. Autophagy can be a double-edged sword for MDR tumors: it participates in the development of MDR and protects cancer cells from chemotherapeutics but can also kill MDR cancer cells in which apoptosis pathways are inactive. Autophagy induced by anticancer drugs could also activate apoptosis signaling pathways in MDR cells, facilitating MDR reversal. Therefore, research on the regulation of autophagy to combat MDR is expanding and is becoming increasingly important. We summarize advanced studies of autophagy in MDR tumors, including the variable role of autophagy in MDR cancer cells.

Taxotere resistance in SUIT Taxotere resistance in pancreatic carcinoma cell line SUIT 2 and its sublines

AIM: To investigate the specific mechanisms of intrinsic and acquired resistance to taxotere (TXT) in pancreatic adenocarcinoma (PAC). METHODS: MTT assay was used to detect the sensitivity of PAC cell line SUIT-2 and its sublines (S-007, S-013, S-020, S-028 and TXT selected SUIT-2 cell line, S2/TXT) to TXT. Mdr1 (P-gp), multidrug resistance associated protein (MRP), lung resistance protein (LRP) and beta-tubulin isotype gene expressions were detected by RT-PCR. The functionality of P-gp and MRP was tested using their specific blocker verapamil (Ver) and indomethacin (IMC), respectively. The transporter activity of P-gp was also confirmed by Rhodamine 123 accumulation assay. RESULTS: S-020 and S2/TXT were found to be significantly resistant to TXT(19 and 9.5-fold to their parental cell line SUIT-2, respectively). RT-PCR demonstrated strong expression of Mdr1 in these two cell lines, but weaker expression or no expression in other cells lines. MRP and LRP expressions were found in most of these cell lines. The TXT-resistance in S2-020 and S2/TXT could be reversed almost completely by Ver, but not by IMC. Flow cytometry showed that Ver increased the accumulation of Rhodamine-123 in these two cell lines. Compared with S-020 and SUIT-2, the levels of beta-tubulin isotype II, III expressions in S-2/TXT were increased remarkably. CONCLUSION: The both intrinsic and acquired TXT-related drug resistance in these PAC cell lines is mainly mediated by P-gp, but had no relationship to MRP and LRP expressions. The increases of beta-tubulin isotype II, III might be collateral changes that occur when the SUIT-2 cells are treated with TXT.

STAT3 mediates resistance of CD44^+CD24^(-/low) breast cancer stem cells to tamoxifen in vitro

We sought to determine whether STAT3 mediated tamoxifen resistance of breast cancer stem cells in vitro.The capacities for mammosphere formation and STAT3 expression of CD44＋CD24-/low MCF-7 and MCF-7 were observed.The CD44＋CD24-/low subpopulation ratio and its sensitivity to adriamycin were analyzed in MCF-7 and TAM resistant（TAM-R） cells.Cell cycle,apoptosis,STAT3 and phospho-STAT3 changes were observed af-ter treatment with tamoxifen.Small interference RNA-mediated knockdown of STAT3 in TAM-R cells was also performed.CD44＋CD24-/low MCF-7 showed higher capacities for mammosphere formation and STAT3 expression than total MCF-7.The CD44＋CD24-/low subpopulation was also upregulated in TAM-R cells with less sensitivity to adriamycin than MCF-7.Cell cycle changes,anti-apoptotic effects and STAT3 changes were also found.Mean-while,the knock-down of STAT3 in TAM-R resulted in an increase in sensitivity to tamoxifen.It is concluded that STAT3 plays an essential role in breast cancer stem cells,which correlated with tamoxifen resistance.

The challenge of drug resistance in pancreatic ductal adenocarcinoma:a current overview

Pancreatic ductal adenocarcinoma(PDAC)has one of the highest mortality rates among all cancer types.Its delayed diagnosis precludes curative resection,thus most of the current therapies against PDAC are based on chemo-and radiotherapy.Unfortunately,these strategies are insufficient to improve its poor prognosis.Despite the advances made in chemotherapy(e.g.nab-paclitaxel and gemcitabine),many patients with PDAC are unable to benefit from them due to the rapid development of drug resistance.Currently,more than 165 genes have been found to be implicated in drug resistance of pancreatic tumors,including different integrins,mucins,NF-κB,RAS and CXCR4.Moreover,drug resistance in PDAC is thought to be mediated by the modulation of miRNAs(e.g.miRNA-21,miRNA-145 and miRNA-155),which regulate genes that participate in cell proliferation,invasion and metastasis.Finally,cancer stem cells are intimately related to drug resistance in PDAC due to their ability to overexpress ABC genes-involved in drug transport-,and enzymes such as aldehyde dehydrogenases-implicated in cellular drug metabolism-and poly(ADP-ribose)polymerases-involved in drug-induced DNA damage repair.Understanding the mechanisms involved in drug resistance will contribute to the development of efficient therapeutic strategies and to improve the prognosis of patients with PDAC.

Curcumin Prevents Induced Drug Resistance:A Novel Function?

Objective：We supposed that it will be a promising strategy to ＂prevent＂ multidrug resistance （MDR） instead of ＂reversing＂ it.This study was designed to investigate the potency of curcumin to prevent the acquired drug resistance induced by adriamycin （ADM） in native K562 cells.Methods：K562 cells were pretreated with curcumin or 0.5% DMSO for 24 h and then were co-incubated with ADM.P-glycoprotein （P-gp） and mdr1 mRNA levels were analyzed separately by flow cytometry and quantitative real-time RT-PCR.The intracellular Rh-123 accumulation was also detected by flow cytometer.Finally,we performed a MTT assay to determine the ADM-induced cytotoxicity with or without pretreatment of curcumin.Results：P-gp and mdr1 mRNA expressions were elevated in the ADM alone group.While in the curcumin pretreated groups,the induced P-gp and mdr1 mRNA levels gradually decreased with increasing curcumin concentrations,and the Rh-123 accumulation level was almost recovered close to the control group＇s.Finally,the MTT colorimetric assay verified the enhanced effect of curcumin on ADM-induced cytotoxicity.Conclusion：Our present study suggested that curcumin exhibits the novel ability to prevent the up-regulation of P-gp and its mRNA induced by ADM.The prevention capacity is also functionally associated with the elevated intracellular drug accumulation and parallel enhanced ADM cytotoxicity.We revealed a novel function of curcumin as a potential drug resistance preventor.

Regulatory role of the transforming growth factor-β signaling pathway in the drug resistance of gastrointestinal cancers

Gastrointestinal(GI)cancer,including esophageal,gastric,and colorectal cancer,is one of the most prevalent types of malignant carcinoma and the leading cause of cancer-related deaths.Despite significant advances in therapeutic strategies for GI cancers in recent decades,drug resistance with various mechanisms remains the prevailing cause of therapy failure in GI cancers.Accumulating evidence has demonstrated that the transforming growth factor(TGF)-βsignaling pathway has crucial,complex roles in many cellular functions related to drug resistance.This review summarizes current knowledge regarding the role of the TGF-βsignaling pathway in the resistance of GI cancers to conventional chemotherapy,targeted therapy,immunotherapy,and traditional medicine.Various processes,including epithelial-mesenchymal transition,cancer stem cell development,tumor microenvironment alteration,and microRNA biogenesis,are proposed as the main mechanisms of TGF-β-mediated drug resistance in GI cancers.Several studies have already indicated the benefit of combining antitumor drugs with agents that suppress the TGF-βsignaling pathway,but this approach needs to be verified in additional clinical studies.Moreover,the identification of potential biological markers that can be used to predict the response to TGF-βsignaling pathway inhibitors during anticancer treatments will have important clinical implications in the future.

Expression of Histone H2AX Phosphorylation and Its Potential to Modulate Adriamycin Resistance in K562/A02 Cell Line

DNA repair processes play a role in the development of drug resistance which represents a huge obstacle to leukemia chemotherapy. Histone H2AX phosphorylation （ser139） （γH2AX） occurs rapidly at the onset of DNA double strand break （DSB） and is critical to the regulation of DSB repair. If DNA repair is successful, cells exposed to anti-neoplastic drugs will keep entering the cycle and develop resistance to the drugs. In this study, we investigated whether γH2AX can be used as an indicator of tumor chemosensitivity and a potential target for enhancing chemotherapy. K562 and multi-drug resistant cell line K562/A02 were exposed to adriamycin （ADR） and γH2AX formed. Flow cytometry revealed that percentage of cells expressing γH2AX was increased in a dose-dependent manner and the percentage of K562/A02 cells was lower than that of K562 cells when treated with the same concentration of ADR. In order to test the potential of γH2AX to reverse drug resistance, K562/A02 cells were treated with PI3K inhibitor LY294002. It was found that LY249002 decreased ADR-induced γH2AX expression and increased the sensitivity of K562/A02 cells to ADR. Additionally, the single-cell gel electrophoresis assay and the Western blotting showed that LY249002 enhanced DSBs and decreased the expression of repair factor BRCA1. These results illustrate chemosensitivity can partly be measured by detecting γH2AX and drug resistance can be reversed by inhibiting γH2AX.

Smart drug delivery systems to overcome drug resistance in cancer immunotherapy

Cancer immunotherapy,a therapeutic approach that inhibits tumors by activating or strengthening anti-tumor immunity,is currently an important clinical strategy for cancer treatment;however,tumors can develop drug resistance to immune surveillance,resulting in poor response rates and low therapeutic efficacy.In addition,changes in genes and signaling pathways in tumor cells prevent susceptibility to immunotherapeutic agents.Furthermore,tumors create an immunosuppressive microenvironment via immunosuppressive cells and secrete molecules that hinder immune cell and immune modulator infiltration or induce immune cell malfunction.To address these challenges,smart drug delivery systems(SDDSs)have been developed to overcome tumor cell resistance to immunomodulators,restore or boost immune cell activity,and magnify immune responses.To combat resistance to small molecules and monoclonal antibodies,SDDSs are used to co-deliver numerous therapeutic agents to tumor cells or immunosuppressive cells,thus increasing the drug concentration at the target site and improving efficacy.Herein,we discuss how SDDSs overcome drug resistance during cancer immunotherapy,with a focus on recent SDDS advances in thwarting drug resistance in immunotherapy by combining immunogenic cell death with immunotherapy and reversing the tumor immunosuppressive microenvironment.SDDSs that modulate the interferon signaling pathway and improve the efficacy of cell therapies are also presented.Finally,we discuss potential future SDDS perspectives in overcoming drug resistance in cancer immunotherapy.We believe that this review will contribute to the rational design of SDDSs and development of novel techniques to overcome immunotherapy resistance.