Tumour cells surviving in vivo cisplatin chemotherapy display elevated c-myc expression

Unraveling MYC's Role in Orchestrating Tumor Intrinsic and Tumor Microenvironment Interactions Driving Tumorigenesis and Drug Resistance

The transcription factor MYC plays a pivotal role in regulating various cellular processes and has been implicated in tumorigenesis across multiple cancer types. MYC has emerged as a master regulator governing tumor intrinsic and tumor microenvironment interactions, supporting tumor progression and driving drug resistance. This review paper aims to provide an overview and discussion of the intricate mechanisms through which MYC influences tumorigenesis and therapeutic resistance in cancer. We delve into the signaling pathways and molecular networks orchestrated by MYC in the context of tumor intrinsic characteristics, such as proliferation, replication stress and DNA repair. Furthermore, we explore the impact of MYC on the tumor microenvironment, including immune evasion, angiogenesis and cancer-associated fibroblast remodeling. Understanding MYC's multifaceted role in driving drug resistance and tumor progression is crucial for developing targeted therapies and combination treatments that may effectively combat this devastating disease. Through an analysis of the current literature, this review's goal is to shed light on the complexities of MYC-driven oncogenesis and its potential as a promising therapeutic target.

Evaluate the Prognosis of MYC/TP53 Comutation in Chinese Patients with EGFR-Positive Advanced NSCLC Using Next-Generation Sequencing: A Retrospective Study

Purpose: The purpose of this study was to investigate the effect of MYC and TP53 comutations on the clinical efficacy of EGFR tyrosine kinase inhibitors (TKIs) in Chinese patients with advanced EGFR-positive nonsmall-cell lung cancer (NSCLC). Patients and methods: Tissue samples and information from 65 patients with advanced NSCLC in Northern Jiangsu People's Hospital were collected and analyzed by next-generation sequencing (NGS). Progression-free survival (PFS) and total survival (OS) were the main endpoints, and the objective response rate (ORR) and disease control rate (DCR) were the secondary endpoints. Result: Among 65 patients, 17 had TP53 and MYC wild-type mutations (WT/WT), 36 had TP53 mutant and MYC wild-type mutations (TP53/WT), and 12 had coexisting MYC/TP53 mutations (MYC/TP53). When 12 patients with MYC/TP53 comutation were compared with the other two groups (TP53/WT, WT/WT), mPFS and mOS are significantly lower than those in the other two groups (mPFS: 4.1 months vs 6.0 months, 12.3 months, HR: 0.769, 95% CI: 4.592-7.608, P  =  .047. mOS: 14.6 months vs 24.1 months, 31.5 months, HR: 3.170, 95% CI: 18.786-31.214, P < .001), and the ORR, DCR of patients with MYC/TP53 comutation was lower than that of the other two groups (ORR, 25% vs 44.4%, 70.6%, P  =  .045. DCR, 58.3% vs 72.2%, 82.4%, P  =  .365). Conclusion: Patients with MYC/TP53 comutations with EGFR-positive advanced NSCLC are more likely to develop drug resistance after early treatment with EGFR-TKIs and have a worse clinical outcome.

TOP1 inhibition induces bifurcated JNK/MYC signaling that dictates cancer cell sensitivity

Rationale: Triple-negative breast cancer (TNBC) does not respond to anti-estrogen and anti-HER2 therapies and is commonly treated by chemotherapy. TNBC has a high recurrence rate, particularly within the first 3 years. Thus, there is an urgent clinical need to develop more effective therapies for TNBC. Topoisomerase I (TOP1) inhibitors cause DNA damage, making these drugs desirable for TNBC treatment since DNA repair machinery is defective in this subtype of breast cancer. Among the main molecular subtypes of breast cancer, the TNBC cell lines exhibited the highest TOP1 inhibition sensitivity. However, clinically used TOP1 inhibitors, such as topotecan and irinotecan, have shown limited clinical applications and the reasons remain unclear. Understanding the mechanism of differential responses to TOP1 blockade and identifying the predictive markers for cancer cell sensitivity will help further TOP1-targeted therapy for TNBC treatment and improve the clinical use of TOP1 inhibitors. Methods: Viability assays were used to evaluate breast cancer cell sensitivity to topotecan and other TOP1 inhibitors as well as TOP2 inhibitors. An in vitro-derived topotecan-resistant TNBC cell model and TNBC xenograft models were employed to confirm cancer cell response to TOP1 blockade. RNA-seq was used to identify potential predictive markers for TNBC cell response to TOP1 blockade. Western blotting and qRT-PCR were performed to measure the protein levels and RNA expression. ATAC-seq and luciferase reporter assays were used to examine MYC transcriptional regulations. The effects of MYC and JNK in cancer cell response to TOP1 inhibition were validated via loss-of-function and gain-of-function experiments. Results: We observed two distinct and diverging cancer cell responses - sensitive versus resistant to TOP1 inhibition, which was confirmed by TNBC xenograft mouse models treated by topotecan. TNBC cells exhibited bifurcated temporal patterns of ATR pathway activation upon TOP1 inhibitor treatment. The sensitive TNBC cells showed an "up then down" dynamic pattern of ATR/Chk1 signaling, while the resistant TNBC cells exhibited a "persistently up" profile. On the contrary, opposite temporal patterns of induced expression of MYC, a key regulator and effector of DNA damage, were found in TNBC cells treated by TOP1 inhibitors. Mechanistically, we showed that TOP1-induced JNK signaling upregulated MYC expression. Furthermore, pharmacological inhibition of ATR reversed TNBC cell resistance to topotecan, whereas MYC knockdown and JNK inhibition reduced cancer cell sensitivity. Conclusions: Dynamic temporal profiles of induced ATR/Chk1 and JNK activation as well as MYC expression, may predict cancer cell response to TOP1 inhibitors. JNK activation-mediated constitutive elevation of MYC expression may represent a novel mechanism governing cancer cell sensitivity to TOP1-targeting therapy. Our results may provide implications for identifying TNBC patients who might benefit from the treatment with TOP1 inhibitors.

Rationale for Tailoring an Alternative Oncology Trial Using a Novel Gallium-Based Nanocomplex: Mechanistic Insights and Preclinical Challenges

Introduction: In the fight against cancer, cisplatin is most widely used as a clinical mainstay for the chemotherapy of various human cancers. Meanwhile, its cytotoxic profile, as well as drug resistance, limits its widespread application. The goal of precision medicine is to tailor an optimized therapeutic program based on the biology of the disease. Recently, nanotechnology has been demonstrated to be promising in this scenario. Objective: The current work provides a rationale for the design of an alternative oncology trial for the treatment of hepatocarcinogenesis using a novel eco-friendly nanocomplex, namely gallic acid-coated gallium nanoparticles. Moreover, the study tests whether the antineoplastic efficacy of gallic acid-coated gallium nanoparticles could be enhanced or not when it is administrated together with cisplatin. Methods: The work comprised a series of both in vitro and in vivo investigations. The in vivo therapeutic efficacy of such treatments, against diethylnitrosamine-induced hepatocarcinogenesis, was strictly evaluated by tracking target genes expressions, iron homeostasis, diverse biomarkers alterations, and lastly, routine paraclinical investigations were also assessed. Results: The in vitro biological evaluation of gallic acid-coated gallium nanoparticles in a HepG-2 cancer cell line established its superior cytotoxicity. Else more, the results of the in vivo experiment highlighted that gallic acid-coated gallium nanoparticles could diminish key hallmarks of cancer by ameliorating most of the investigated parameters. This was well-appreciated with the histopathological findings of the liver architectures of the treated groups. Conclusions: Our findings suggest that novel biogenic Ga-based nanocomplexes may potentially present new hope for the development of alternative liver cancer therapeutics, which should attract further scientific interest.

Standard therapy-resistant small cell lung cancer showing dynamic transition of neuroendocrine fate during the cancer trajectory: A case report

While small cell lung cancer (SCLC) has been treated as a single disease historically, recent studies have suggested that SCLC can be classified into molecular subtypes based on the expression of lineage transcription factors such as achaete-scute homolog 1 (ASCL1), neurogenic differentiation factor 1 (NEUROD1), POU domain class 2 transcription factor 3 (POU2F3) and transcriptional coactivator YAP1 (YAP1). These transcription factor-based subtypes may be specifically targeted in therapy, and recent studies have suggested that the SCLC subtypes represent different stages of dynamic evolution of SCLC rather than independent diseases. Nevertheless, evidence of shift in neuroendocrine differentiation during SCLC evolution has been lacking in the clinical setting. In the present study, a 60-year-old male was diagnosed with extensive SCLC. The tumor responded not to the standard SCLC regimen of carboplatin, etoposide and atezolizumab, but to the non-SCLC regimen of carboplatin, nab-paclitaxel and pembrolizumab. The patient succumbed 5 months after the initial diagnosis and a pathological autopsy was performed. The tumor was originally negative for all four transcription factors, ASCL1, NEUROD1, POU2F3 and YAP1, in the biopsy specimens at diagnosis. Loss of synaptophysin expression and emergence of Myc proto-oncogene protein and YAP1 expression was recorded in the autopsy specimens, suggesting the transition to a decreased neuroendocrine fate during the disease trajectory. This case provides clinical evidence of dynamic transition of neuroendocrine fate during SCLC evolution. In light of SCLC heterogeneity and plasticity, development of precision medicine is required.

The Role of Non-Coding RNAs in the Regulation of the Proto-Oncogene MYC in Different Types of Cancer

Alterations in the expression level of the MYC gene are often found in the cells of various malignant tumors. Overexpressed MYC has been shown to stimulate the main processes of oncogenesis: uncontrolled growth, unlimited cell divisions, avoidance of apoptosis and immune response, changes in cellular metabolism, genomic instability, metastasis, and angiogenesis. Thus, controlling the expression of MYC is considered as an approach for targeted cancer treatment. Since c-Myc is also a crucial regulator of many cellular processes in healthy cells, it is necessary to find ways for selective regulation of MYC expression in tumor cells. Many recent studies have demonstrated that non-coding RNAs play an important role in the regulation of the transcription and translation of this gene and some RNAs directly interact with the c-Myc protein, affecting its stability. In this review, we summarize current data on the regulation of MYC by various non-coding RNAs that can potentially be targeted in specific tumor types.

Cisplatin exposure causes c-Myc-dependent resistance to CDK4/6 inhibition in HPV-negative head and neck squamous cell carcinoma

The loss of p16 is a signature event in Human Papilloma Virus (HPV)-negative head and neck squamous cell carcinoma (HNSCC) that leads to increased Cyclin Dependent Kinase 4/6 (CDK) signaling. Palbociclib, a CDK4/6 inhibitor, is active for the treatment of a subset of HNSCC. In this study, we analyzed patient response data from a phase I clinical trial of palbociclib in HNSCC and observed an association between prior cisplatin exposure and CDK inhibitor resistance. We studied the effects of palbociclib on cisplatin-sensitive and -resistant HNSCC cell lines. We found that while palbociclib is highly effective against chemo-naive HNSCC cell lines and tumor xenografts, prior cisplatin exposure induces intrinsic resistance to palbociclib in vivo, a relationship that was not observed in vitro. Mechanistically, in the course of provoking a DNA damage-resistance phenotype, cisplatin exposure upregulates both c-Myc and cyclin E, and combination treatment with palbociclib and the c-Myc bromodomain inhibitor JQ1 exerts a synergistic anti-growth effect in cisplatin-resistant cells. These data show the benefit of exploiting the inherent resistance mechanisms of HNSCC to overcome cisplatin- and palbociclib resistance through the use of c-Myc inhibition.

Transformation of follicular lymphoma to double-hit lymphoma during adjuvant chemotherapy for concurrent ovarian carcinoma

The frequency of multiple primary malignant neoplasms (MPMN) is increasing due to population aging. Since consensus guidelines for the treatment of MPMN are lacking, treatment strategies are determined by disease status on a per-patient basis. In this report, we describe a case of MPMN with follicular lymphoma (FL) grade 1 that transformed to double-hit lymphoma during adjuvant chemotherapy for concurrent ovarian carcinoma. A 64-year-old woman was diagnosed with MPMN of FL and endometrioid carcinoma by staging laparotomy and lymph node biopsy. She received four cycles of adjuvant chemotherapy (carboplatin and paclitaxel) for endometrioid carcinoma, but during chemotherapy, the FL grade 1 transformed to double-hit lymphoma. We speculate that adjuvant chemotherapy for endometrioid carcinoma may have triggered the transformation of FL in the present case.

Emerging Roles of C-Myc in Cancer Stem Cell-Related Signaling and Resistance to Cancer Chemotherapy: A Potential Therapeutic Target Against Colorectal Cancer

Myc is a nuclear transcription factor that mainly regulates cell growth, cell cycle, metabolism, and survival. Myc family proteins contain c-Myc, n-Myc, and l-Myc. Among them, c-Myc can become a promising therapeutic target molecule in cancer. Cancer stem cells (CSCs) are known to be responsible for the therapeutic resistance. In the previous study, we demonstrated that c-Myc mediates drug resistance of colorectal CSCs using a patient-derived primary three-dimensional (3D) organoid culture. In this review, we mainly focus on the roles of c-Myc-related signaling in the regulation of CSCs, chemotherapy resistance, and colorectal cancer organoids. Finally, we introduce the various types of c-Myc inhibitors and propose the possibility of c-Myc as a therapeutic target against colorectal cancer.

The Influence of Curcumin on the Downregulation of MYC, Insulin and IGF-1 Receptors: A possible Mechanism Underlying the Anti-Growth and Anti-Migration in Chemoresistant Colorectal Cancer Cells

Background and objectives: Mounting evidence shows that curcumin, a bioactive substance originating from turmeric root, has anticancer properties. Additionally, curcumin prevents the migration and metastasis of tumor cells. However, the molecular mechanism involved in the anti-metastatic action of curcumin is not clear. Most studies have suggested that migration inhibition is related to curcumin’s anti-inflammatory properties. Curcumin possesses a regulatory effect on insulin and insulin-like growth factor-1 (IGF-1) receptors and signaling. Insulin signaling is one of the important pathways involved in tumor initiation and progression; therefore, we proposed that the anti-metastatic effect of curcumin may mediate the downregulation of insulin and insulin-like growth factor-1 receptors. Materials and Methods: Viable resistant cells resulting from treating SW480 cells with 5-fluorouracil (5-FU) were subjected to curcumin treatment to analyze the proliferation and migration capacity in comparison to the untreated counterparts. To test the proliferation and migration potential, MTT, colony formation, and wound healing assays were performed. Real-time polymerase chain reaction (RT-PCR) was performed to measure the mRNA expression of insulin-like growth factor-1R (IGF-1R), insulin receptor (IR), and avian myelocytomatosis virus oncogene cellular homolog (MYC). Results: Our findings showed that curcumin significantly decreased insulin and IGF-1 receptors in addition to MYC expression. Additionally, the downregulation of the insulin and insulin-like growth factor-1 receptors was correlated to a greater decrease in the proliferation and migration of chemoresistant colorectal cancer cells. Conclusions: These results suggest the possible therapeutic effectiveness of curcumin in adjuvant therapy in metastatic colorectal cancer.

Genetic instability and recurrent MYC amplification in ALK-translocated NSCLC: a central role of TP53 mutations

The anaplastic lymphoma kinase (ALK) rearrangement defines a distinct molecular subtype of non-small cell lung cancer (NSCLC). Despite the excellent initial efficacy of ALK inhibitors in patients with ALK+ lung cancer, resistance occurs almost inevitably. To date, there is no reliable biomarker allowing the identification of patients at higher risk of relapse. Here, we analysed a subset of 53 ALK+ tumours with and without TP53 mutation and ALK+ NSCLC cell lines by NanoString nCounter technology. We found that the co-occurrence of early TP53 mutations in ALK+ NSCLC can lead to chromosomal instability: 24% of TP53-mutated patients showed amplifications of known cancer genes such as MYC (14%), CCND1 (10%), TERT (5%), BIRC2 (5%), ORAOV1 (5%), and YAP1 (5%). MYC-overexpressing ALK+ TP53-mutated cells had a proliferative advantage compared to wild-type cells. ChIP-Seq data revealed MYC-binding sites within the promoter region of EML4, and MYC overexpression in ALK+ TP53-mutated cells resulted in an upregulation of EML4-ALK, indicating a potential MYC-dependent resistance mechanism in patients with increased MYC copy number. Our study reveals that ALK+ NSCLC represents a more heterogeneous subgroup of tumours than initially thought, and that TP53 mutations in that particular cancer type define a subset of tumours that harbour chromosomal instability, leading to the co-occurrence of pathogenic aberrations. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

miR-137 mediates the functional link between c-Myc and EZH2 that regulates cisplatin resistance in ovarian cancer

Platinum drugs are used in first-line to treat ovarian cancer, but most of the patients eventually generate resistance after treatment with these drugs. Although both c-Myc and EZH2 have been implicated in regulating cisplatin resistance in ovarian cancer, the interplay between these two regulators is poorly understood. Using RNA sequence analysis (RNA-seq), for the first time we find that miR-137 level is extremely low in cisplatin resistant ovarian cancer cells, correlating with higher levels of c-Myc and EZH2 expression. Further analyses indicate that in resistant cells c-Myc enhances the expression of EZH2 by directly suppressing miR-137 that targets EZH2 mRNA, and increased expression of EZH2 activates cellular survival pathways, resulting in the resistance to cisplatin. Inhibition of c-Myc-miR-137-EZH2 pathway re-sensitizes resistant cells to cisplatin. Both in vivo and in vitro analyses indicate that cisplatin treatment activates c-Myc-miR-137-EZH2 pathway. Importantly, elevated c-Myc-miR-137-EZH2 pathway in resistant cells is sustained by dual oxidase maturation factor 1 (DUOXA1)-mediated production of reactive oxygen species (ROS). Significantly, clinical studies further confirm the activated c-Myc-miR-137-EZH2 pathway in platinum drug-resistant or recurrent ovarian cancer patients. Thus, our studies elucidate a novel role of miR-137 in regulating c-Myc-EZH2 axis that is crucial to the regulation of cisplatin resistance in ovarian cancer.

Non-Coding RNAs and Resistance to Anticancer Drugs in Gastrointestinal Tumors

Non-coding RNAs are important regulators of gene expression and transcription. It is well established that impaired non-coding RNA expression especially the one of long non-coding RNAs and microRNAs is involved in a number of pathological conditions including cancer. Non-coding RNAs are responsible for the development of resistance to anticancer treatments as they regulate drug resistance-related genes, affect intracellular drug concentrations, induce alternative signaling pathways, alter drug efficiency via blocking cell cycle regulation, and DNA damage response. Furthermore, they can prevent therapeutic-induced cell death and promote epithelial-mesenchymal transition (EMT) and elicit non-cell autonomous mechanisms of resistance. In this review, we summarize the role of non-coding RNAs for different mechanisms resulting in drug resistance (e.g., drug transport, drug metabolism, cell cycle regulation, regulation of apoptotic pathways, cancer stem cells, and EMT) in the context of gastrointestinal cancers.

TCRP1 transcriptionally regulated by c-Myc confers cancer chemoresistance in tongue and lung cancer

Previously, we cloned a new gene termed ‘tongue cancer resistance-associated protein 1’ (TCRP1), which modulates tumorigenesis, enhances cisplatin (cDDP) resistance in cancers, and may be a potential target for reversing drug resistance. However, the mechanisms for regulating TCRP1 expression remain unclear. Herein, we combined bioinformatics analysis with luciferase reporter assay and ChIP assay to determine that c-Myc could directly bind to TCRP1 promoter to upregulate its expression. TCRP1 upregulation in multidrug resistant tongue cancer cells (Tca8113/PYM) and cisplatin-resistant A549 lung cancer cells (A549/DDP) was accompanied by c-Myc upregulation, compared to respective parental cells. In tongue and lung cancer cells, siRNA-mediated knockdown of c-Myc led to decrease TCRP1 expression, whereas overexpression c-Myc did the opposite. Moreover, TCRP1 knockdown attenuated chemoresistance resulting from c-Myc overexpression, but TCRP1 overexpression impaired the effect of c-Myc knockdown on chemosensitivity. Additionally, in both human tongue and lung cancer tissues, c-Myc protein expression positively correlated with TCRP1 protein expression and these protein levels were associated with worse prognosis for patients. Combined, these findings suggest that c-Myc could transcriptionally regulate TCRP1 in cell lines and clinical samples and identified the c-Myc-TCRP1 axis as a negative biomarker of prognosis in tongue and lung cancers.

The Dual Roles of MYC in Genomic Instability and Cancer Chemoresistance

Cancer is associated with genomic instability and aging. Genomic instability stimulates tumorigenesis, whereas deregulation of oncogenes accelerates DNA replication and increases genomic instability. It is therefore reasonable to assume a positive feedback loop between genomic instability and oncogenic stress. Consistent with this premise, overexpression of the MYC transcription factor increases the phosphorylation of serine 139 in histone H2AX (member X of the core histone H2A family), which forms so-called γH2AX, the most widely recognized surrogate biomarker of double-stranded DNA breaks (DSBs). Paradoxically, oncogenic MYC can also promote the resistance of cancer cells to chemotherapeutic DNA-damaging agents such as cisplatin, clearly implying an antagonistic role of MYC in genomic instability. In this review, we summarize the underlying mechanisms of the conflicting functions of MYC in genomic instability and discuss when and how the oncoprotein exerts the contradictory roles in induction of DSBs and protection of cancer-cell genomes.

Targeting c-MYC in Platinum-Resistant Ovarian Cancer

The purpose of this study was to investigate the molecular and therapeutic effects of siRNA-mediated c-MYC silencing in cisplatin-resistant ovarian cancer. Statistical analysis of patient's data extracted from The Cancer Genome Atlas (TCGA) portal showed that the disease-free (DFS) and the overall (OS) survival were decreased in ovarian cancer patients with high c-MYC mRNA levels. Furthermore, analysis of a panel of ovarian cancer cell lines showed that c-MYC protein levels were higher in cisplatin-resistant cells when compared with their cisplatin-sensitive counterparts. In vitro cell viability, growth, cell-cycle progression, and apoptosis, as well as in vivo therapeutic effectiveness in murine xenograft models, were also assessed following siRNA-mediated c-MYC silencing in cisplatin-resistant ovarian cancer cells. Significant inhibition of cell growth and viability, cell-cycle arrest, and activation of apoptosis were observed upon siRNA-mediated c-MYC depletion. In addition, single weekly doses of c-MYC-siRNA incorporated into 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG-2000)-based nanoliposomes resulted in significant reduction in tumor growth. These findings identify c-MYC as a potential therapeutic target for ovarian cancers expressing high levels of this oncoprotein.

The c-MYC-ABCB5 axis plays a pivotal role in 5-fluorouracil resistance in human colon cancer cells

c-MYC overexpression is frequently observed in various cancers including colon cancer and regulates many biological activities such as aberrant cell proliferation, apoptosis, genomic instability, immortalization and drug resistance. However, the mechanism by which c-MYC confers drug resistance remains to be fully elucidated. In this study, we found that the c-MYC expression level in primary colorectal cancer tissues correlated with the recurrence rate following 5-fluorouracil (5-FU)-based adjuvant chemotherapy. Supporting this finding, overexpression of exogenous c-MYC increased the survival rate following 5-FU treatment in human colon cancer cells, and knockdown of endogenous c-MYC decreased it. Furthermore, c-MYC knockdown decreased the expression level of ABCB5, which is involved in 5-FU resistance. Using a chromatin immunoprecipitation assay, we found that c-MYC bound to the ABCB5 promoter region. c-MYC inhibitor (10058-F4) treatment inhibited c-MYC binding to the ABCB5 promoter, leading to a decrease in ABCB5 expression level. ABCB5 knockdown decreased the survival rate following 5-FU treatment as expected, and the ABCB5 expression level was increased in 5-FU-resistant human colon cancer cells. Finally, using a human colon cancer xenograft murine model, we found that the combined 5-FU and 10058-F4 treatment significantly decreased tumorigenicity in nude mice compared with 5-FU or 10058-F4 treatment alone. 10058-F4 treatment decreased the ABCB5 expression level in the presence or absence of 5-FU. In contrast, 5-FU treatment alone increased the ABCB5 expression level. Taken together, these results suggest that c-MYC confers resistance to 5-FU through regulating ABCB5 expression in human colon cancer cells.

Inhibition of c-Myc by let-7b mimic reverses mutidrug resistance in gastric cancer cells

Chemotherapy is one of the few effective choices for patients with advanced or recurrent gastric cancer (GC). However, the development of mutidrug resistance (MDR) to cancer chemotherapy is a major obstacle to the effective treatment of advanced GC. Additionally, the mechanism of MDR remains to be determined. In the present study, we tested IC50 of cisplatin (DDP), vincristine (VCR) and 5-fluorouracil (5-FU) in SGC7901, SGC7901/DDP and SGC7901/VCR gastric cancer cells using an MTT assay. The expression of let-7b and c-Myc in these cells was detected by qPCR and western blot analysis. The relationship between let-7b and c-Myc was explored using a luciferase reporter assay. Transfection of let-7b mimic or inhibitor was used to confirm the effect of let-7b on drug sensitivity in chemotherapy via the regulation of c-Myc expression. We found that the expression of let-7b was lower in chemotherapy-resistant SGC7901/DDP and SGC7901/VCR gastric cancer cells than that in chemotherapy-sensitive SGC7901 cells. By contrast, the expression of c-Myc was higher in SGC7901/DDP and SGC7901/VCR cells than that in SGC7901 cells. Furthermore, we confirmed that let-7b suppresses c-Myc gene expression at the mRNA and protein levels in a sequence-specific manner, while transfection of let-7b mimic increases drug sensitivity in chemotherapy-resistant SGC7901/DDP and SGC7901/VCR cells by targeting downregulation of c-Myc. In SGC7901 drug-sensitive cells, however, the sensitivity of chemotherapy was significantly decreased following let-7b inhibitor transfection. The present study results demonstrated that let-7b increases drug sensitivity in chemotherapy‑resistant SGC7901/DDP and SGC7901/VCR gastric cancer cells by targeting the downregulation of c-Myc and that, let-7b mimic reverses MDR by promoting cancer stem cell differentiation controlled by double-negative autoregulatory loops (Lin28/let-7 and Myc/let-7) and a double-positive autoregulatory loop (Lin28/Lin28B/Myc) existing in GC cells, which remains to be confirmed.

Inhibition of c-Myc overcomes cytotoxic drug resistance in acute myeloid leukemia cells by promoting differentiation

Nowadays, drug resistance still represents a major obstacle to successful acute myeloid leukemia (AML) treatment and the underlying mechanism is not fully elucidated. Here, we found that high expression of c-Myc was one of the cytogenetic characteristics in the drug-resistant leukemic cells. c-Myc over-expression in leukemic cells induced resistance to chemotherapeutic drugs, enhanced colony formation capacity and inhibited cell differentiation induced by all-trans retinoic acid (ATRA). Meanwhile, inhibition of c-Myc by shRNA or specific c-Myc inhibitor 10058-F4 rescued the sensitivity to cytotoxic drugs, restrained the colony formation ability and promoted differentiation. RT-PCR and western blotting analysis showed that down-regulation of C/EBPβ contributed to the poor differentiation state of leukemic cells induced by c-Myc over-expression. Importantly, over-expression of C/EBPβ could reverse c-Myc induced drug resistance. In primary AML cells, the c-Myc expression was negatively correlated with C/EBPβ. 10058-F4, displayed anti-proliferative activity and increased cellular differentiation with up-regulation of C/EBPβ in primary AML cells. Thus, our study indicated that c-Myc could be a novel target to overcome drug resistance, providing a new approach in AML therapy.

Protein quantitative trait loci identify novel candidates modulating cellular response to chemotherapy

Annotating and interpreting the results of genome-wide association studies (GWAS) remains challenging. Assigning function to genetic variants as expression quantitative trait loci is an expanding and useful approach, but focuses exclusively on mRNA rather than protein levels. Many variants remain without annotation. To address this problem, we measured the steady state abundance of 441 human signaling and transcription factor proteins from 68 Yoruba HapMap lymphoblastoid cell lines to identify novel relationships between inter-individual protein levels, genetic variants, and sensitivity to chemotherapeutic agents. Proteins were measured using micro-western and reverse phase protein arrays from three independent cell line thaws to permit mixed effect modeling of protein biological replicates. We observed enrichment of protein quantitative trait loci (pQTLs) for cellular sensitivity to two commonly used chemotherapeutics: cisplatin and paclitaxel. We functionally validated the target protein of a genome-wide significant trans-pQTL for its relevance in paclitaxel-induced apoptosis. GWAS overlap results of drug-induced apoptosis and cytotoxicity for paclitaxel and cisplatin revealed unique SNPs associated with the pharmacologic traits (at p<0.001). Interestingly, GWAS SNPs from various regions of the genome implicated the same target protein (p<0.0001) that correlated with drug induced cytotoxicity or apoptosis (p≤0.05). Two genes were functionally validated for association with drug response using siRNA: SMC1A with cisplatin response and ZNF569 with paclitaxel response. This work allows pharmacogenomic discovery to progress from the transcriptome to the proteome and offers potential for identification of new therapeutic targets. This approach, linking targeted proteomic data to variation in pharmacologic response, can be generalized to other studies evaluating genotype-phenotype relationships and provide insight into chemotherapeutic mechanisms.

The central dogma of biology explains that DNA is transcribed to mRNA that is further translated into protein. Many genome-wide studies have implicated genetic variation that influences gene expression and that ultimately affect downstream complex traits including response to drugs. However, because of technical limitations, few studies have evaluated the contribution of genetic variation on protein expression and ensuing effects on downstream phenotypes. To overcome this challenge, we used a novel technology to simultaneously measure the baseline expression of 441 proteins in lymphoblastoid cell lines and compared them with publicly available genetic data. To further illustrate the utility of this approach, we compared protein-level measurements with chemotherapeutic induced apoptosis and cell-growth inhibition data. This study demonstrates the importance of using protein information to understand the functional consequences of genetic variants identified in genome-wide association studies. This protein data set will also have broad utility for understanding the relationship between other genome-wide studies of complex traits.

Amelioration of cisplatin-induced nephrotoxicity in peroxiredoxin I-deficient mice

PURPOSE

Cisplatin is one of the most potent chemotherapeutic agents used to treat cancer. However, cisplatin-induced nephrotoxicity, which is partly caused by oxidative damage, is a serious problem. We previously showed that murine embryonic fibroblasts deficient in Peroxiredoxin I (Prx I), a major Nrf2-linked anti-oxidant enzyme, are susceptible to cisplatin-induced cytotoxicity. In the present study, we examined the role of Prx I against cisplatin-induced renal injury in vivo using Prx I-null mice.

METHODS

Prx I-null mice and wild-type (WT) mice were given an intraperitoneal injection of cisplatin, and tissues were removed and evaluated histopathologically. In addition, gene and protein expression of efflux transporters was analyzed.

RESULTS

In contrast to an in vitro cell study, Prx I-null mice exhibited less cisplatin-induced renal damage than WT mice in histological and blood biochemical analyses. Moreover, Prx I-null mice showed a higher clearance rate of cisplatin than WT mice following intraperitoneal cisplatin injection. Consistent with these results, Prx I-null mice exhibited higher expression of renal efflux transporters Mrp2 and Mrp4 compared with WT mice under both basal and the cisplatin-induced conditions. We suggest the enhanced transcriptional activity of c-Myc in Prx I-null mice may partly contribute the enhanced expression of renal efflux transporters.

CONCLUSION

In summary, the enhanced clearance rate of cisplatin significantly attenuates nephrotoxicity in Prx I-null mice.

Use of ribozymes and antisense oligodeoxynucleotides to investigate mechanisms of drug resistance

Chemotherapy can cure a number of human cancers but resistance (either intrinsic or acquired) remains a significant problem in many patients and in many types of solid tumour. Combination chemotherapy (using drugs with different cellular targets/mechanisms) was introduced in order to kill cells which had developed resistance to a specific drug, and to allow delivery of a greater total dose of anti-cancer chemicals by combining drugs with different side-effects (Pratt et al., 1994). Nearly all anti-cancer drugs kill tumour cells by activating an endogenous bio-chemical pathway for cell suicide, known as programmed cell death or apoptosis.

Targeting multiple signal pathways by chemopreventive agents for cancer prevention and therapy

In recent years, growing interest has been focused on the field of cancer prevention. Cancer prevention by chemopreventive agents offers significant promise for reducing the incidence and mortality of cancer. Chemopreventive agents may exert their effects either by blocking or metabolizing carcinogens or by inhibiting tumor cell growth. Another important benefit of chemopreventive agents is their nontoxic nature. Therefore, chemopreventive agents have recently been used for cancer treatment in combination with chemotherapeutics or radiotherapy, uncovering a novel strategy for cancer therapy. This strategy opens a new avenue from cancer prevention to cancer treatment. In vitro and in vivo studies have demonstrated that chemopreventive agents could enhance the antitumor activity of chemotherapeutics, improving the treatment outcome. Growing evidence has shown that chemopreventive agents potentiate the efficacy of chemotherapy and radiotherapy through the regulation of multiple signaling pathways, including Akt, NF-kappaB, c-Myc, cyclooxygenase-2, apoptosis, and others, suggesting a multitargeted nature of chemopreventive agents. However, further in-depth mechanistic studies, in vivo animal experiments, and clinical trials are needed to investigate the effects of chemopreventive agents in combination treatment of cancer with conventional cancer therapies. More potent natural and synthetic chemopreventive agents are also needed to improve the efficacy of mechanism-based and targeted therapeutic strategies against cancer, which are likely to make a significant impact on saving lives. Here, we have briefly reviewed the role of chemopreventive agents in cancer prevention, but most importantly, we have reviewed how they could be useful for cancer therapy in combination with conventional therapies.

Increased tumor localization and reduced immune response to adenoviral vector formulated with the liposome DDAB/DOPE

We aimed to increase the efficiency of adenoviral vectors by limiting adenoviral spread from the target site and reducing unwanted host immune responses to the vector. We complexed adenoviral vectors with DDAB-DOPE liposomes to form adenovirus-liposomal (AL) complexes. AL complexes were delivered by intratumoral injection in an immunocompetent subcutaneous rat tumor model and the immunogenicity of the AL complexes and the expression efficiency in the tumor and other organs was examined. Animals treated with the AL complexes had significantly lower levels of beta-galactosidase expression in systemic tissues compared to animals treated with the naked adenovirus (NA) (P<0.05). The tumor to non-tumor ratio of beta-galactosidase marker expression was significantly higher for the AL complex treated animals. NA induced significantly higher titers of adenoviral-specific antibodies compared to the AL complexes (P<0.05). The AL complexes provided protection (immunoshielding) to the adenovirus from neutralizing antibody. Forty-seven percent more beta-galactosidase expression was detected following intratumoral injection with AL complexes compared to the NA in animals pre-immunized with adenovirus.

CONCLUSIONS

Complexing of adenovirus with liposomes provides a simple method to enhance tumor localization of the vector, decrease the immunogenicity of adenovirus, and provide protection of the virus from pre-existing neutralizing antibodies.

Expression of the p14ARF tumor suppressor predicts survival in acute myeloid leukemia

Cell cycle aberrations are associated with therapy outcome in many types of cancer. We analyzed mRNA expression levels of 18 cell cycle-related genes in bone marrow samples from 78 acute myeloid leukemia (AML) patients and six controls using high-throughput quantitative RT-PCR. Samples of AML patients contained significantly increased mRNA expression levels of the mdm2 and c-myc oncogenes. Also, the average expression levels of p14ARF and p16INK4A were higher in patient samples compared to controls. Leukemic blasts and control bone marrow samples did not differ significantly in the expression levels of proliferation-associated genes such as cyclin A2 and pcna. When single genes were analyzed for prognostic significance in Kaplan-Meier and Cox regression analyses, a low p14ARF level emerged as a strong and independent predictor for poor survival (P=0.04 and 0.029). Subsequently, p14ARF mRNA levels were analyzed in a second, independent patient population (n=57). Again, low p14ARF levels were associated with a worse outcome. Finally, immunohistochemistry analysis of AML tissue arrays confirmed the widespread expression of c-myc and p14ARF in AML on the protein level. Taken together, the expression of the p53 regulators mdm2 and p14ARF are altered in AML, and low p14ARF levels indicate a poor prognosis.

Pre-treatment with a non-therapeutic dose of cisplatin increases solid tumour response to liposomal-p53 gene therapy- An in vivo study

Successful liposomal-mediated gene therapy is often limited by poor transfection efficiencies. One method previously shown to increase the efficiency of liposomal gene delivery is through the administration of a non-therapeutic dose of the chemotherapeutic drug cisplatin prior to lipofection. The currents study aims to utilise this method to deliver lipoplexes containing the p53 tumour suppressor gene with the aim of increasing therapeutic effect of the p53 gene on a solid tumour in vivo. Rats, implanted with solid salivary adenocarcinomas, were pre-treated with a low dose of cisplatin seven days prior to liposomal mediated p53 treatment. Following treatment with p53, tumour growth, p53 expression and levels of apoptosis were examined and compared to animals treated with p53 without cisplatin pre-treatment and a saline control. Tumours that had been pre-treated with cisplatin prior to p53-lipofection were significantly smaller than both the saline control and the non-cisplatin treated tumours. Saline treated tumours increased in size by an average of 164% over a 96-hour period compared to 64% and 101% for the cisplatin and non-cisplatin p53-liposome treated tumours. The cisplatin pre-treated tumours resulted in significantly higher levels of apoptosis surrounding the treatment site and exhibited prolonged p53 expression when compared to the non-cisplatin pre-treated tumours. The results suggest that the use of cisplatin to pre-sensitise tumours to lipofection has significant benefits when used in conjunction with p53.

Radiation therapy depletes extrachromosomally amplified drug resistance genes and oncogenes from tumor cells via micronuclear capture of episomes and double minute chromosomes

PURPOSE

To determine if clinically relevant doses of ionizing radiation are capable of inducing extrachromosomal DNA loss in transformed human cell lines.

MATERIALS AND METHODS

The multidrug-resistant (MDR) human epidermoid KB-C1 cell line and the human neuroendocrine colon carcinoma line COLO320, which contain extrachromosomally amplified MDR1 drug resistance genes and MYCC oncogenes, were irradiated with 2 Gy fractions up to a total dose of 28 Gy. To track the fate of extrachromosomally amplified genes, cells surviving radiation therapy and unirradiated control cells were analyzed by fluorescent in situ hybridization of chromosomes using MDR1 and MYCC-specific cosmid DNA probes. In addition, total DNA and protein isolated from irradiated and control cells was subjected to Southern and Western blotting procedures, respectively, to determine amplified gene copy number and protein expression levels. Dose-response assays to follow loss of function of the MDR1 gene from KB-C1 cells were also performed.

RESULTS

A significant reduction in extrachromosomal DNA, amplified gene copy number, and expression was detected in surviving cells after relatively low doses of radiation. Entrapment of extrachromosomal DNA into micronuclei was a consistent feature of irradiated cells.

CONCLUSIONS

Clinically relevant doses of radiation can deplete extrachromosomal DNA in viable human malignant cells and alter their phenotype. Depletion of extrachromosomally amplified genes from tumor cells occurs via entrapment in radiation-induced micronuclei.

C-myc amplification in breast cancer: a meta-analysis of its occurrence and prognostic relevance

Data from basic research suggests that amplification of the proto-oncogene c-myc is important in breast cancer pathogenesis, but its frequency of amplification and prognostic relevance in human studies have been inconsistent. In an effort to clarify the clinical significance of c-myc amplification in breast cancer, we conducted a comprehensive literature search and a meta-analysis in which 29 studies were evaluated. The weighted average frequency of c-myc amplification in breast tumours was 15.7% (95% CI = 12.5-18.8%), although estimates in individual studies exhibited significant heterogeneity, P<0.0001. C-myc amplification exhibited significant but weak associations with tumour grade (RR = 1.61), lymph-node metastasis (RR = 1.24), negative progesterone receptor status (RR = 1.27), and postmenopausal status (RR = 0.82). Amplification was significantly associated with risk of relapse and death, with pooled estimates RR = 2.05 (95% CI = 1.51-2.78) and RR = 1.74 (95% CI = 1.27-2.39), respectively. This effect did not appear to be merely a surrogate for other prognostic factors. These results suggest that c-myc amplification is relatively common in breast cancer and may provide independent prognostic information. More rigorous studies with consistent methodology are required to validate this association, and to investigate its potential as a molecular predictor of specific therapy response.

Lipoplexes and tumours. A review

The need for genotherapy to refocus its attention on to laboratory evaluation of better methods rather than proceeding to the clinic with semi-apt tools for genetic transfer has been highlighted in clinical study reports documented to date. Quintessential for tumour genotherapy is the ability to target abnormal cells, hence reducing exposure of normal cells to genetic material whilst maximizing gene dosage to tumour cells. This becomes increasingly important as genotherapy establishes itself in the clinic alongside the older modes of treatment. This review has discussed the applicability of lipoplexes for genotherapy of solid tumours. Lipoplexes have been used extensively for gene transfer into cells, such as cancerous cells, deficient for a certain gene product. While cationic liposomes have many advantages over other forms of delivery mechanisms, several problems hinder their use in-vivo. A closer examination of the physical limitations of current lipoplex preparations, the development and testing of novel formulations, combined with more attention to the cellular processes of cell membrane breaching and nuclear entry, may enhance gene delivery. Essential for tumour genotherapy is the ability to target these lipoplexes into tumour sites whilst reducing gene dosage to other normal tissues. Development of a better lipofection agent may indeed require a collaboration of the fields of physiology, cell biology, molecular biology, biochemistry, chemistry and membrane physics.

Cisplatin resistance is associated with reduced interferon-gamma-sensitivity and increased HER-2 expression in cultured ovarian carcinoma cells

In ovarian carcinoma cells, the combination of interferon-gamma (IFN-gamma) and cisplatin (cDDP) has been reported to result in a synergistic amplification of antiproliferative activity. To assess whether IFN-gamma may also prevent the occurrence of cisplatin resistance, the human ovarian carcinoma cell line HTB-77 was treated repeatedly in an intermittent fashion with either cisplatin alone (HTB-77cDDP) or cisplatin plus IFN-gamma (HTB-77cDDP + IFN). After 8 months of treatment, both new lines (HTB-77cDDP or HTB-77cDDP + IFN) were found to be three times more resistant to cisplatin than the wild-type cells (HTB-77wt). IFN-gamma could not prevent the development of cisplatin resistance. Interestingly, both HTB-77cDDP and HTB-77cDDP + IFN cells were also less IFN-gamma sensitive than the parental line. Both cisplatin-resistant lines expressed p185HER-2 and HER-2 mRNA at a higher concentration than the HTB-77wt cells. IFN-gamma was in all three HTB-77 cell lines able to suppress the HER-2 message and its encoded protein. The expression of IFN-gamma-induced antigens, namely CA-125 and class II antigens of the major histocompatibility complex (HLA-DR), was markedly augmented by IFN-gamma in all three lines, whereby the most prominent effect was seen in HTB-77cDDP and HTB-77cDDP + IFN.