Mechanisms Underlying Drug Resistance Research Articles

LncRNAs: New players of cancer drug resistance via targeting ABC transporters.

Cancer drug resistance poses a significant obstacle to successful chemotherapy, primarily driven by the activity of ATP-binding cassette (ABC) transporters, which actively efflux chemotherapeutic agents from cancer cells, reducing their intracellular concentrations and therapeutic efficacy. Recent studies have highlighted the pivotal role of long noncoding RNAs (lncRNAs) in regulating this resistance, positioning them as crucial modulators of ABC transporter function. lncRNAs, once considered transcriptional noise, are now recognized for their complex regulatory capabilities at various cellular levels, including chromatin modification, transcription, and post-transcriptional processing. This review synthesizes current research demonstrating how lncRNAs influence cancer drug resistance by modulating the expression and activity of ABC transporters. lncRNAs can act as molecular sponges, sequestering microRNAs that would otherwise downregulate ABC transporter genes. Additionally, they can alter the epigenetic landscape of these genes, affecting their transcriptional activity. Mechanistic insights reveal that lncRNAs contribute to the activity of ABC transporters, thereby altering the efflux of chemotherapeutic drugs and promoting drug resistance. Understanding these interactions provides a new perspective on the molecular basis of chemoresistance, emphasizing the regulatory network of lncRNAs and ABC transporters. This knowledge not only deepens our understanding of the biological mechanisms underlying drug resistance but also suggests novel therapeutic strategies. In conclusion, the intricate interplay between lncRNAs and ABC transporters is crucial for developing innovative solutions to combat cancer drug resistance, underscoring the importance of continued research in this field.

Establishment and characterization of a novel multidrug-resistant pancreatic ductal adenocarcinoma cell line, PDAC-X1

Drug resistance remains a significant challenge in the treatment of pancreatic cancer. The development of drug-resistant cell lines is crucial to understanding the underlying mechanisms of resistance and developing novel drugs to improve clinical outcomes. Here, a novel pancreatic cancer cell line, PDAC-X1, derived from Chinese patients has been established. PDAC-X1 was characterized by the immune phenotype, biology, genetics, molecular characteristics, and tumorigenicity. In vitro analysis revealed that PDAC-X1 cells exhibited epithelial morphology and cell markers (CK7 and CK19), expressed cancer-associated markers (E-cadherin, Vimentin, Ki-67, CEA, CA19-9), and produced pancreatic cancer-like organs in suspension culture. In vivo analysis showed that PDAC-X1 cells maintained tumorigenicity with a 100% tumor formation rate. This cell line exhibited a complex karyotype, dominated by subtriploid karyotypes. In addition, PDAC-X1 cells exhibited intrinsic multidrug resistance to multiple drugs, including gemcitabine, paclitaxel, 5-fluorouracil, and oxaliplatin. In conclusion, the PDAC-X1 cell line has been established and characterized, representing a useful and valuable preclinical model to study the underlying mechanisms of drug resistance and develop novel drug therapeutics to improve patient outcomes.

The Role of Tumor‐Derived Extracellular Vesicles in Drug Resistance in Urologic Cancers

AbstractIn spite of the therapeutic progress achieved in the treatment of urologic tumors, the persistence and intricate nature of tumor resistance significantly impact patient prognoses. Extracellular vesicles (EVs), actively secreted by diverse cell types, assume a crucial role in facilitating intercellular communication. These EVs facilitate the transfer of functional molecules, encompassing RNA, proteins, and lipids, to recipient cells. While these molecules participate in normal physiological processes, they also play a pivotal role in the pathogenesis of various diseases. Notably in the context of cancer, numerous investigations have substantiated the involvement of tumor‐derived EVs in the development of drug resistance. This review comprehensively explores the mechanisms underlying drug resistance in urologic cancers, elucidates the contributions of tumor‐derived EVs to drug resistance in urologic tumors, discusses advancements in targeting EVs to mitigate drug resistance in urologic tumors, and assesses the utility of EVs as biomarkers for drug resistance in urologic tumors.

Ageing microenvironment mediates lymphocyte carcinogenesis and lymphoma drug resistance: From mechanisms to clinical therapy (Review).

Cellular senescence has a complex role in lymphocyte carcinogenesis and drug resistance of lymphomas. Senescent lymphoma cells combine with immunocytes to create an ageing environment that can be reprogrammed with a senescence‑associated secretory phenotype, which gradually promotes therapeutic resistance. Certain signalling pathways, such as the NF‑κB, Wnt and PI3K/AKT/mTOR pathways, regulate the tumour ageing microenvironment and induce the proliferation and progression of lymphoma cells. Therefore, targeting senescence‑related enzymes or their signal transduction pathways may overcome radiotherapy or chemotherapy resistance and enhance the efficacy of relapsed/refractory lymphoma treatments. Mechanisms underlying drug resistance in lymphomas are complex. The ageing microenvironment is a novel factor that contributes to drug resistance in lymphomas. In terms of clinical translation, some senolytics have been used in clinical trials on patients with relapsed or refractory lymphoma. Combining immunotherapy with epigenetic drugs may achieve better therapeutic effects; however, senescent cells exhibit considerable heterogeneity and lymphoma has several subtypes. Extensive research is necessary to achieve the practical application of senolytics in relapsed or refractory lymphomas. This review summarises the mechanisms of senescence‑associated drug resistance in lymphoma, as well as emerging strategies using senolytics, to overcome therapeutic resistance in lymphoma.

Glioblastoma stem cells deliver ABCB4 transcribed by ATF3 via exosomes conferring glioblastoma resistance to temozolomide

Glioblastoma stem cells (GSCs) play a key role in glioblastoma (GBM) resistance to temozolomide (TMZ) chemotherapy. With the increase in research on the tumour microenvironment, exosomes secreted by GSCs have become a new focus in GBM research. However, the molecular mechanism by which GSCs affect drug resistance in GBM cells via exosomes remains unclear. Using bioinformatics analysis, we identified the specific expression of ABCB4 in GSCs. Subsequently, we established GSC cell lines and used ultracentrifugation to extract secreted exosomes. We conducted in vitro and in vivo investigations to validate the promoting effect of ABCB4 and ABCB4-containing exosomes on TMZ resistance. Finally, to identify the transcription factors regulating the transcription of ABCB4, we performed luciferase assays and chromatin immunoprecipitation-quantitative PCR. Our results indicated that ABCB4 is highly expressed in GSCs. Moreover, high expression of ABCB4 promoted the resistance of GSCs to TMZ. Our study found that GSCs can also transmit their highly expressed ABCB4 to differentiated glioma cells (DGCs) through exosomes, leading to high expression of ABCB4 in these cells and promoting their resistance to TMZ. Mechanistic studies have shown that the overexpression of ABCB4 in GSCs is mediated by the transcription factor ATF3. In conclusion, our results indicate that GSCs can confer resistance to TMZ in GBM by transmitting ABCB4, which is transcribed by ATF3, through exosomes. This mechanism may lead to drug resistance and recurrence of GBM. These findings contribute to a deeper understanding of the mechanisms underlying drug resistance in GBM and provide novel insights into its treatment.

WNT3 promotes chemoresistance to 5-Fluorouracil in oral squamous cell carcinoma via activating the canonical β-catenin pathway

Background5-Fluorouracil (5FU) is a primary chemotherapeutic agent used to treat oral squamous cell carcinoma (OSCC). However, the development of drug resistance has significantly limited its clinical application. Therefore, there is an urgent need to determine the mechanisms underlying drug resistance and identify effective targets. In recent years, the Wingless and Int-1 (WNT) signaling pathway has been increasingly studied in cancer drug resistance; however, the role of WNT3, a ligand of the canonical WNT signaling pathway, in OSCC 5FU-resistance is not clear. This study delved into this potential connection.Methods5FU-resistant cell lines were established by gradually elevating the drug concentration in the culture medium. Differential gene expressions between parental and resistant cells underwent RNA sequencing analysis, which was then substantiated via Real-time quantitative PCR (RT-qPCR) and western blot tests. The influence of the WNT signaling on OSCC chemoresistance was ascertained through WNT3 knockdown or overexpression. The WNT inhibitor methyl 3-benzoate (MSAB) was probed for its capacity to boost 5FU efficacy.ResultsIn this study, the WNT/β-catenin signaling pathway was notably activated in 5FU-resistant OSCC cell lines, which was confirmed through transcriptome sequencing analysis, RT-qPCR, and western blot verification. Additionally, the key ligand responsible for pathway activation, WNT3, was identified. By knocking down WNT3 in resistant cells or overexpressing WNT3 in parental cells, we found that WNT3 promoted 5FU-resistance in OSCC. In addition, the WNT inhibitor MSAB reversed 5FU-resistance in OSCC cells.ConclusionsThese data underscored the activation of the WNT/β-catenin signaling pathway in resistant cells and identified the promoting effect of WNT3 upregulation on 5FU-resistance in oral squamous carcinoma. This may provide a new therapeutic strategy for reversing 5FU-resistance in OSCC cells.

Angelica sinensis polysaccharide combined with cisplatin reverses cisplatin resistance of ovarian cancer by inducing ferroptosis via regulating GPX4

Cisplatin (DDP) resistance poses a significant challenge in the treatment of ovarian cancer. Studies have shown that the combination of certain polysaccharides derived from plants with DDP is an effective approach to overcoming drug resistance in some cancers. Angelica sinensis (Oliv.) Diels has been used for centuries in China to treat gynecological ailments. Numerous studies indicate that Angelica sinensis polysaccharide (ASP), an extract from Angelica sinensis, can inhibit various forms of cancer. However, the impact of ASP on ovarian cancer remains unexplored. Through both in vitro and in vivo experiments, our study revealed the capability of ASP to effectively reversing DDP resistance in cisplatin-resistant ovarian cancer cells, while exhibiting acceptable safety profiles in vivo. To elucidate the mechanism underlying drug resistance reversal, we employed RNA-seq analysis and identified GPX4 as a key gene. Considering the role of GPX4 in ferroptosis, we conducted additional research to explore the effects of combining ASP with DDP on SKOV3/DDP cells. In summary, our findings demonstrate that the combination of ASP and DDP effectively suppresses GPX4 expression in SKOV3/DDP cells, thereby reversing their resistance to DDP.

Rhein exerts anti-multidrug resistance in acute myeloid leukemia via targeting FTO to inhibit AKT/mTOR.

Chemotherapy failure and resistance are the leading causes of mortality in patients with acute myeloid leukemia (AML). However, the role of m6A demethylase FTO and its inhibitor rhein in AML and AML drug resistance is unclear. Therefore, this study aimed to investigate the antileukemic effect of rhein on AML and explore its potential mechanisms underlying drug resistance. Bone marrow fluid was collected to assess FTO expression in AML. The Cell Counting Kit 8 reagent was used to assess cell viability. Migration assays were conducted to assess the cell migration capacity. Flow cytometry was used to determine the apoptotic effects of rhein and western blot analysis was used to detect protein expression. Online SynergyFinder software was used to calculate the drug synergy scores. The in-vivo antileukemic effect of rhein was assessed in an AML xenograft mouse model. We analyzed different types of AML bone marrow specimens to confirm that FTO is overexpressed in AML, particularly in cases of multidrug resistance. Subsequently, we conducted in-vivo and in-vitro investigations to explore the pharmacological activity and mechanism of rhein in AML and AML with multidrug resistance. The findings demonstrated that rhein effectively suppressed the proliferation and migration of AML cells in a time- and dose-dependent manner and induced apoptosis. Rhein targets FTO, inhibits the AKT/mTOR pathway, and exhibits synergistic antitumor effects when combined with azacitidine. This study elucidates the significant role of FTO and its inhibitor rhein in AML and AML with multidrug resistance, providing new insights for overcoming multidrug resistance in AML.

Abstract ND02: Discovery of BMS-986365, a ligand-directed androgen receptor degrader (AR LDD) with a dual mechanism-of-action and best-in-class potential, for the treatment of advanced prostate cancer

Abstract The androgen receptor (AR) is a key driver of the cellular processes that contribute to the pathology of prostate cancers at most stages, and drugs that inhibit the activity of this receptor or interfere with androgen biosynthesis have become the cornerstone of treatments for prostate cancer. While both types of therapy have had a significant positive impact on disease progression and overall survival, de novo and acquired resistance remains an impediment to a durable clinical response in patients with metastatic castration-resistant prostate cancer (mCRPC). The mechanisms underlying drug resistance are complex and multifactorial, being attributable to AR overexpression, point mutations in the receptor that alter drug pharmacology, and to the upregulation of receptor-associated coregulators, which render AR less dependent on an activating ligand. Regardless, absolute inhibition of AR signaling remains the objective of contemporary approaches to treat prostate cancer. Recently, there has been specific interest in the development of approaches to eliminate AR proteins using drugs that enable targeted degradation of AR in cancer cells.This puts in context the significance of our discovery of BMS-986365 (also known as CC-94676), a heterobifunctional ligand-directed degrader (LDD) that enables the CRL4CRBN E3 ligase-dependent ubiquitination and degradation of AR (DC50 10 to 40 nM, Ymin 7 to 19%). BMS-986365 is a highly potent and selective AR degrader that induces rapid and deep degradation of both wildtype and mutant forms of the receptor residing in either the cytoplasmic or nuclear compartments of the cell. The drug is ~100-fold more potent than enzalutamide (ENZ) at inhibiting androgen-stimulated transcription of AR target genes, and 10 to 120-fold more potent than ENZ at inhibiting AR-dependent proliferation of multiple prostate cancer cell lines in vitro. In animal models of advanced prostate cancer, BMS-986365 demonstrates on-target activity, degrading AR, suppressing AR signaling, and inhibiting tumor growth. Indeed, tumor volume reductions of 63-92% were achieved by BMS-986365 in validated models of advanced CRPC and therapy resistant patient-derived xenografts, including those with acquired resistance to ENZ. Collectively our preclinical data suggest that the AR degrader BMS-986365 is superior to standard-of-care AR antagonists, such as ENZ, in both preclinical and disease-relevant animal models, and support its clinical development for treatment of prostate cancer. BMS-986365 has advanced into clinical studies where it has demonstrated encouraging clinical activity in patients with mCRPC. Citation Format: Shuichan Xu, Surendra Nayak, John D. Norris, Massimo Ammirante, Emyly Rychak, Suzanne E. Wardell, Toshiya Tsuji, Ken Liu, Joseph Meiring, Joseph R. Piccotti, Deepak Dalvie, Debbie Liao, Raju Kandimalla, Nadia Guerrero, Lisa Sapinoso, Jennifer G. Baker, Yeeun Bae, Joshua Baughman, Brandon Toyama, Celia Fontanillo Fontanillo, Stephen Norris, Evan J. Horn, Veronique Plantevin-Krenitsky, Deborah Mortensen, Brian Cathers, Marie Hong Nguyen, Joshua D. Hensen, Lawrence G. Hamann, Donald P. McDonnell, Rama Krishna Narla, Mark Rolfe. Discovery of BMS-986365, a ligand-directed androgen receptor degrader (AR LDD) with a dual mechanism-of-action and best-in-class potential, for the treatment of advanced prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr ND02.

Jolkinolide B synergistically potentiates the antitumor activity of GPX4 inhibitors via inhibiting TrxR1 in cisplatin-resistant bladder cancer cells

Glutathione peroxidase 4 (GPX4) is a promising anticancer therapeutic target; however, the application of GPX4 inhibitors (GPX4i) is limited owing to intrinsic or acquired drug resistance. Hence, understanding the mechanisms underlying drug resistance and discovering molecules that can overcome drug resistance are crucial. Herein, we demonstrated that GPX4i killed bladder cancer cells by inducing lipid reactive oxygen species-mediated ferroptosis and apoptosis, and cisplatin-resistant bladder cancer cells were also resistant to GPX4i, representing a higher half-maximal inhibitory concentration value than that of parent bladder cancer cells. In addition, thioredoxin reductase 1 (TrxR1) overexpression was responsible for GPX4i resistance in cisplatin-resistant bladder cancer cells, and inhibiting TrxR1 restored the sensitivity of these cells to GPX4i. In vitro and in vivo studies revealed that Jolkinolide B (JB), a natural diterpenoid and previously identified as a TrxR1 inhibitor, potentiated the antiproliferative efficacy of GPX4i (RSL3 and ML162) against cisplatin-resistant bladder cancer cells. Furthermore, GPX4 knockdown and inhibition could augment JB-induced paraptosis and apoptosis. Our results suggest that inhibiting TrxR1 can effectively improve GPX4 inhibition-based anticancer therapy. A combination of JB and GPX4i, which is well-tolerated and has several anticancer mechanisms, may serve as a promising therapy for treating bladder cancer.

The mechanism by which SIRT1 regulates autophagy and EMT in drug-resistant oesophageal cancer cells

Cancer cell resistance presents a significant clinical challenge. The mechanisms underlying drug resistance in cancer cells are intricate and remain incompletely understood. Notably, tumor cell resistance often coincides with the epithelial-mesenchymal transition (EMT).In this study, we observed an elevation in autophagy levels following the development of drug resistance in oesophageal cancer cells. Inhibition of autophagy led to a reduction in drug-resistant cell migration and the inhibition of EMT.Furthermore, we identified an upregulation of SIRT1 expression in drug-resistant oesophageal cancer cells. Subsequent inhibition of SIRT1 expression in drug-resistant cells resulted in the suppression of autophagy levels, migration ability, and the EMT process.Our additional investigations revealed that a SIRT1 inhibitor effectively curbed tumor growth in human oesophageal cancer xenograft model mice (TE-1, TE-1/PTX) without evident toxic effects. This mechanism appears to be associated with the autophagy levels within the tumor tissue.

A Mini-review on Helicobacter pylori with Gastric Cancer and Available Treatments.

Helicobacter pylori (H. pylori) is the most thoroughly researched etiological component for stomach inflammation and malignancies. Even though there are conventional recommendations and treatment regimens for eradicating H. pylori, failure rates continue to climb. Antibiotic resistance contributes significantly to misdiagnoses, false positive results, and clinical failures, all of which raise the chance of infection recurrence. This review aims to explore the molecular mechanisms underlying drug resistance in H. pylori and discuss novel approaches for detecting genotypic resistance. Modulation of drug uptake/ efflux, biofilm, and coccoid development. Newer genome sequencing approaches capable of detecting H. pylori genotypic resistance are presented. Prolonged infection in the stomach causes major problems such as gastric cancer. The review discusses how H. pylori causes stomach cancer, recent biomarkers such as miRNAs, molecular pathways in the development of gastric cancer, and diagnostic methods and clinical trials for the disease. Efforts have been made to summarize the recent advancements made toward early diagnosis and novel therapeutic approaches for H. pylori-induced gastric cancer.

Cellular and Molecular Determinants of Biologic Drugs Resistance and Therapeutic Failure in Inflammatory Bowel Disease.

The advent of biologic drugs has revolutionized the treatment of Inflammatory Bowel Disease, increasing rates of response and mucosal healing in comparison to conventional therapies by allowing the treatment of corticosteroid-refractory cases and reducing corticosteroid-related side effects. However, biologic therapies (anti-TNFα inhibitors, anti-α4β7 integrin and anti-IL12/23) are still burdened by rates of response that hover around 40% (in biologic-naïve patients) or lower (for biologic-experienced patients). Moreover, knowledge of the mechanisms underlying drug resistance or loss of response is still scarce. Several cellular and molecular determinants are implied in therapeutic failure; genetic predispositions, in the form of single nucleotide polymorphisms in the sequence of cytokines or Human Leukocyte Antigen, or an altered expression of cytokines and other molecules involved in the inflammation cascade, play the most important role. Accessory mechanisms include gut microbiota dysregulation. In this narrative review of the current and most recent literature, we shed light on the mentioned determinants of therapeutic failure in order to pave the way for a more personalized approach that could help avoid unnecessary treatments and toxicities.

Integrated application of transcriptomics and metabolomics provides insight into the mechanism of Eimeria tenella resistance to maduramycin

Avian coccidiosis, caused by Eimeria parasites, continues to devastate the poultry industry and results in significant economic losses. Ionophore coccidiostats, such as maduramycin and monensin, are widely used for prophylaxis of coccidiosis in poultry. Nevertheless, their efficacy has been challenged by widespread drug resistance. However, the underlying mechanisms have not been revealed. Understanding the targets and resistance mechanisms to anticoccidials is critical to combat this major parasitic disease. In the present study, maduramycin-resistant (MRR) and drug-sensitive (DS) sporozoites of Eimeria tenella were purified for transcriptomic and metabolomic analysis. The transcriptome analysis revealed 5016 differentially expressed genes (DEGs) in MRR compared to DS, and KEGG pathway enrichment analysis indicated that DEGs were involved in spliceosome, carbon metabolism, glycolysis, and biosynthesis of amino acids. In the untargeted metabolomics assay, 297 differentially expressed metabolites (DEMs) were identified in MRR compared to DS, and KEGG pathway enrichment analysis indicated that these DEMs were involved in 10 pathways, including fructose and mannose metabolism, cysteine and methionine metabolism, arginine and proline metabolism, and glutathione metabolism. Targeted metabolomic analysis revealed 14 DEMs in MRR compared to DS, and KEGG pathway analysis indicated that these DEMs were involved in 20 pathways, including fructose and mannose metabolism, glycolysis/gluconeogenesis, and carbon metabolism. Compared to DS, energy homeostasis and amino acid metabolism were differentially regulated in MRR. Our results provide gene and metabolite expression landscapes of E. tenella following maduramycin induction. This study is the first work involving integrated transcriptomic and metabolomic analyses to identify the key pathways to understand the molecular and metabolic mechanisms underlying drug resistance to polyether ionophores in coccidia.

Based on whole-exome sequencing to explore the rule of Herceptin and TKI resistance in breast cancer patients

BackgroundBreast cancer is the second leading cause of cancer-related death in women, and drug resistance during treatment is a major challenge. However, the mechanisms underlying drug resistance are not fully understood. Here we applied whole-exome sequencing (WES) to clarify resistant rules to Herceptin and tyrosine kinase inhibitors (TKIs).MethodsThere are 12 HER2+ breast cancer patients who were done WES. Samples from tumor and surrounding tissues underwent DNA sequencing and analysis. Various experimental and bioinformatics techniques were employed, including genomic capture, mutation analysis (Genome Analysis Toolkit (GATK), etc.), bioinformatics assessments, and drug-gene interaction investigations. Ultimately, the study explored the association of APOB gene expression with breast cancer recurrence rates, immune cell infiltration, and drug response.ResultsThe C > T mutation frequency was highest in the Herceptin-insensitive (HI) and verification groups, codenamed YI, contrasting with the Herceptin-sensitive (HE) group. No microsatellite instability (MSI)-H patients were in the HE group, but both HI and YI groups had 1 each. Significant differences in transition-transversion (TiTv) were observed in the HI and YI groups rather than the HE group. In the TKI- insensitive (TI) group, C > T mutations were highest, differing from the TKI-sensitive (TE) group. TE group included 2 MSI-H patients. Significant differences in TiTv were found in the TI group rather than the TE group. Mutated APOB may resist Herceptin and TKI, increasing immune infiltration. We identified potential drugs targeting it.ConclusionsOur study suggested that a higher percentage of C > T mutations, significant differences in TiTv, and MSI-H status may indicate Herceptin resistance, while a higher percentage of C > T mutations, significant differences in TiTv, and the absence of MSI-H may indicate TKI resistance in breast cancer patients. For patients resistant to both Herceptin and TKI, mutated APOB may play a crucial role in resistance.

Mechanisms of Anti-PD Therapy Resistance in Digestive System Neoplasms.

Digestive system neoplasms are highly heterogeneous and exhibit complex resistance mechanisms that render anti-programmed cell death protein (PD) therapies poorly effective. The tumor microenvironment (TME) plays a pivotal role in tumor development, apart from supplying energy for tumor proliferation and impeding the body's anti-tumor immune response, the TME actively facilitates tumor progression and immune escape via diverse pathways, which include the modulation of heritable gene expression alterations and the intricate interplay with the gut microbiota. In this review, we aim to elucidate the mechanisms underlying drug resistance in digestive tumors, focusing on immune-mediated resistance, microbial crosstalk, metabolism, and epigenetics. We will highlight the unique characteristics of each digestive tumor and emphasize the significance of the tumor immune microenvironment (TIME). Furthermore, we will discuss the current therapeutic strategies that hold promise for combination with cancer immune normalization therapies. This review aims to provide a thorough understanding of the resistance mechanisms in digestive tumors and offer insights into potential therapeutic interventions.

Prediction of miRNA‑mRNA network regulating the migration ability of cytarabine‑resistant HL60 cells.

Cytarabine is an important medicine for acute myeloid leukemia (AML) treatment, however, drug resistance hinders the treatment of AML. Although microRNA (miRNA or miR) alteration is one of the well-recognized mechanisms underlying drug resistance in AML, few studies have investigated the role and function of miRNAs in the development of cytarabine resistance. In the present study, total RNA was isolated from parental HL60 and cytarabine-resistant HL60 (R-HL60) cells. Subsequently, miRNAs and mRNAs were detected using small RNA sequencing and gene expression array, respectively. Differentially expressed mRNAs (DEMs) and differentially expressed genes (DEGs) with more than two-fold changes between HL60 and R-HL60 cells were screened out. Negatively associated miRNA-mRNA pairs were selected as candidate miRNA-mRNA target pairs according to the miRDB, Targetscan or miRTar databases. Functional enrichment analysis of DEGs included in the candidate miRNA-mRNA pairs was performed. The results indicated that 10 DEGs (CCL2, SOX9, SLC8A1, ICAM1, CXCL10, SIPR2, FGFR1, OVOL2, MITF and CARD10) were simultaneously involved in seven Gene Ontology pathways related to the regulation of migration ability, namely the 'regulation of cell migration', 'regulation of locomotion', 'regulation of cellular component movement', 'cell migration', 'locomotion', 'cell motility', and 'localization of cell'. DEMs predicted to negatively regulate the aforementioned 10 DEGs were paired with DEGs into 16 candidate miRNA-mRNA pairs related to the regulation of migration ability. In addition, migration assays revealed that the migration ability of R-HL60 cells was greater than that of HL60 cells. These findings provide a new perspective for the treatment of cytarabine-resistant AML and advance our understanding of altered migration ability underlying cytarabine resistance development, specifically related to miRNAs.

Integrin α6β4 Confers Doxorubicin Resistance in Cancer Cells by Suppressing Caspase-3-Mediated Apoptosis: Involvement of N-Glycans on β4 Integrin Subunit.

Drug resistance is a major obstacle to successful cancer treatment. Therefore, it is essential to understand the molecular mechanisms underlying drug resistance to develop successful therapeutic strategies. α6β4 integrin confers resistance to apoptosis and regulates the survival of cancer cells; however, it remains unclear whether α6β4 integrin is directly involved in chemoresistance. Here, we show that α6β4 integrin promotes doxorubicin resistance by decreasing caspase-3-mediated apoptosis. We found that the overexpression of α6β4 integrin by the β4 integrin gene rendered MDA-MB435S and Panc-1 cells more resistant to doxorubicin than control cells. The acquired resistance to doxorubicin by α6β4 integrin expression was abolished by the deletion of the cytoplasmic signal domain in β4 integrin. Similar results were found in MDA-MB435S and Panc-1 cells when N-glycan-defective β4 integrin mutants were overexpressed or bisecting GlcNAc residues were increased on β4 integrin by the co-expression of N-acetylglucosaminyltransferase III with β4 integrin. The abrogation of α6β4 integrin-mediated resistance to doxorubicin was accompanied by reduced cell viability and an increased caspase-3 activation. Taken together, our results clearly suggest that α6β4 integrin signaling plays a key role in the doxorubicin resistance of cancer cells, and N-glycans on β4 integrin are involved in the regulation of cancer cells.

Adaptive DNA amplification of synthetic gene circuit opens a way to overcome cancer chemoresistance.

Drug resistance continues to impede the success of cancer treatments, creating a need for experimental model systems that are broad, yet simple, to allow the identification of mechanisms and novel countermeasures applicable to many cancer types. To address these needs, we investigated a set of engineered mammalian cell lines with synthetic gene circuits integrated into their genome that evolved resistance to Puromycin. We identified DNA amplification as the mechanism underlying drug resistance in 4 out of 6 replicate populations. Triplex-forming oligonucleotide (TFO) treatment combined with Puromycin could efficiently suppress the growth of cell populations with DNA amplification. Similar observations in human cancer cell lines suggest that TFOs could be broadly applicable to mitigate drug resistance, one of the major difficulties in treating cancer.

DDDR-30. IDENTIFICATION OF DRIVERS OF RESISTANCE IN BRAFV600E PEDIATRIC HIGH-GRADE GLIOMA AND NOVEL THERAPEUTIC TARGETS

Abstract The BRAFV600E mutation has recently been discovered as a driver mutation in a subset of pediatric high-grade gliomas (pHGG), with tumors driven by this mutation responding to targeted BRAF and MEK inhibitors. Unfortunately, resistance inevitability develops, resulting in disease progression. There is currently limited understanding of the mechanisms underlying drug resistance in BRAFV600E pHGG, and no effective counter-therapies exist. This study aimed to identify driver pathways of resistance in BRAFV600E pHGG and subsequently novel therapeutic targets. BRAF inhibitor-resistant, MEK inhibitor-resistant and BRAF+MEK inhibitor-resistant BRAFV600E pHGG cultures were derived through chronic exposure of a BRAFV600E patient-derived culture to vemurafenib (BRAF inhibitor), trametinib (MEK inhibitor) or a combination of both drugs, respectively. Cytotoxicity assays confirmed resistance. All resistant cell lines spontaneously changed from a spheroid phenotype to adherent growth, indicating changes in tumor characteristics. RNAseq identified > 1500 genes of interest, with subsequent Gene Set Enrichment Analysis identifying key pathways as novel drivers of resistance, the top-ranked gene sets being neural development and plasma membrane/cell adhesion. Approximately 45% of gene sets were enriched across all drug-resistant lines, indicating overlapping resistance mechanisms. Interrogation of the receptor tyrosine kinase (RTK) gene sets identified potent upregulation of several RTKs. Notably, overexpression of the RTK, EGFR, was confirmed through RNAseq and western blot as a potential key mediator of the acquired resistance. Combined treatment with vemurafenib and the EGFR inhibitor, dacomitinib, resulted in synergistic activity against both vemurafenib-resistant BRAFV600E pHGG cells and matched parental cells, providing a viable therapeutic option for drug-resistant BRAFV600E pHGG. Overall, novel drivers of resistance have been identified in BRAFV600E pHGG. EGFR overexpression was pinpointed as a key mediator and dual BRAF/EGFR inhibition displayed promising efficacy as a therapeutic option. Future studies will continue to elucidate the mechanisms of resistance using multi-omic approaches and the in vivo efficacy of dual BRAF/EGFR inhibition.