Decreased FANCJ caused by 5FU contributes to the increased sensitivity to oxaliplatin in gastric cancer cells

The function and mechanism of circRNAs in 5-fluorouracil resistance in tumors: Biological mechanisms and future potential

5-Fluorouracil (5-FU) is a well-known chemotherapy drug extensively used in the treatment of breast cancer. It works by inhibiting cancer cell proliferation and inducing cell death through direct incorporation into DNA and RNA via thymidylate synthase (TS). Circular RNAs (circRNAs), a novel family of endogenous non-coding RNAs (ncRNAs) with limited protein-coding potential, contribute to 5-FU resistance. Their identification and targeting are crucial for enhancing chemosensitivity. CircRNAs can regulate tumor formation and invasion by adhering to microRNAs (miRNAs) and interacting with RNA-binding proteins, regulating transcription and translation. MiRNAs can influence enzymes responsible for 5-FU metabolism in cancer cells, affecting their sensitivity or resistance to the drug. In the context of 5-FU resistance, circRNAs can target miRNAs and regulate biological processes such as cell proliferation, cell death, glucose metabolism, hypoxia, epithelial-to-mesenchymal transition (EMT), and drug efflux. This review focuses on the function of circRNAs in 5-FU resistance, discussing the underlying molecular pathways and biological mechanisms. It also presents recent circRNA/miRNA-targeted cancer therapeutic strategies for future clinical application.

5-Fluorouracil (5-FU) resistance and the new strategy to enhance the sensitivity against cancer: Implication of DNA repair inhibition

5-Fluorouracil (5-FU) has been an important anti-cancer drug to date. With an increase in the knowledge of its mechanism of action, various treatment modalities have been developed over the past few decades to increase its anti-cancer activity. But drug resistance has greatly affected the clinical use of 5-FU. Overcoming this chemoresistance is a challenge due to the presence of cancer stem cells like cells, cancer recurrence, metastasis, and angiogenesis. In this review, we have systematically discussed the mechanism of 5-FU resistance and advent strategies to increase the sensitivity of 5-FU therapy including resistance reversal. Special emphasis has been given to the cancer stem cells (CSCs) mediated 5-FU chemoresistance and its reversal process by different approaches including the DNA repair inhibition process.

Inhibitors of the Fanconi anaemia pathway as potential antitumour agents for ovarian cancer

The Fanconi anaemia (FA) pathway is an important mechanism for cellular DNA damage repair, which functions to remove toxic DNA interstrand crosslinks. This is particularly relevant in the context of ovarian and other cancers which rely extensively on interstrand cross-link generating platinum chemotherapy as standard of care treatment. These cancers often respond well to initial treatment, but reoccur with resistant disease and upregulation of DNA damage repair pathways. The FA pathway is therefore of great interest as a target for therapies that aim to improve the efficacy of platinum chemotherapies, and reverse tumour resistance to these. In this review, we discuss recent advances in understanding the mechanism of interstrand cross-link repair by the FA pathway, and the potential of the component parts as targets for therapeutic agents. We then focus on the current state of play of inhibitor development, covering both the characterisation of broad spectrum inhibitors and high throughput screening approaches to identify novel small molecule inhibitors. We also consider synthetic lethality between the FA pathway and other DNA damage repair pathways as a therapeutic approach.

DEAD-Box Protein RNA-Helicase DDX6 Regulates the Expression of HER2 and FGFR2 at the Post-Transcriptional Step in Gastric Cancer Cells

The human DEAD/H-box RNA helicase DDX6 (RCK/p54) is a protein encoded by the fusion gene from the t(11;14)(q23;q32) chromosomal translocation observed in human B-cell lymphoma cell line RC-K8. DDX6 has a variety of functions such as translation initiation, pre-mRNA splicing, and ribosome assembly. However, details of the regulatory mechanism governing DDX6 and the functions of DDX6 are largely unknown. Previously, we reported that DDX6 is overexpressed in most malignant cell lines and clinical colorectal tumor samples and that DDX6 positively contributes to the pathogenesis of various cancers. In the current study, we aimed at revealing the function of DDX6 in HER2 and FGFR2 related human gastric cancer (GC) by using clinical samples and GC cell lines. DDX6 protein was overexpressed in about 60% of the clinical samples; HER2, in 35%; and FGFR2, in 30%, (n = 20). Interestingly, the DDX6 protein was overexpressed in all HER2-positive samples (n = 7), and in 83% (5 of 6) of the FGFR2-positive samples, which could reflect the contribution of DDX6 to the expression of HER2 and FGFR2. In the GC cell line MKN7, which has HER2 amplification, the knockdown of DDX6 by siR-DDX6 led to the decreased expression of the HER2 protein. On the other hand, the knockdown of HER2 did not influence the DDX6 expression. Similar results were also obtained for the KATO-III and HSC39 cell lines having amplified FGFR2 expression. The increased expression of DDX6 induced a significantly increased expression of the HER2 protein without increasing the mRNA expression. The results of an RNP Immunoprecipitation (RIP)-assay using GC cells indicated that the DDX6 protein acted as an RNA-binding protein for HER2 and FGFR2 mRNAs and positively regulated their post-transcriptional processes. These findings demonstrated that DDX6 was an upstream molecule that positively regulated the expression of HER2 and FGFR2 at the post-transcriptional step in GC cells.

BRIP1 overexpression is correlated with clinical features and survival outcome of luminal breast cancer subtypes

In Oman, breast cancer is most common, representing approximately more than 25% of all cancers in women. Relatively younger populations of patients (25-40 years) present surprisingly with an aggressive phenotype and advanced tumor stages. In this study, we investigated differential gene expressions in Luminal A, Luminal B, triple-negative and Her2+ breast cancer subtypes and compared data to benign tumor samples. We identified a potential candidate gene BRIP1, showing differential expression in the four breast cancer subtypes examined, suggesting that BRIP1 has the profile of a useful diagnostic marker, suitable for targeted therapeutic intervention. RT-qPCR and Western blotting analysis showed higher BRIP1 expression in luminal samples as compared to triple-negative subtype patient's samples. We further screened BRIP1 for eventual mutations/SNPs/deletions by sequencing the entire coding region. Four previously identified polymorphisms were detected, one within the 5'-UTR region (c.141-64G > A) and three in the BRCA-binding domain (c.2755T > C, c.2647G > A and c.3411T > C). Kaplan-Meier analysis revealed that patients with overexpression of BRIP1 displayed a poor survival rate (P < 0.05). BRIP1 has a dual function of an oncogene and a tumor suppressor gene in addition to its role as a potential biomarker to predict survival and prognosis. Data obtained in this study suggest that BRIP1 can plausibly have an oncogenic role in sporadic cancers.

The combination of curcumin and 5-fluorouracil in cancer therapy

5-Fluorouracil (5-FU) alone or in combination with other therapeutic drugs has been widely used for clinical treatment of various cancers. However, 5-FU-based chemotherapy has limited anticancer efficacy in clinic due to multidrug resistance and dose-limiting cytotoxicity. Some molecules and genes in cancer cells, such as nuclear factor kappa B, insulin-like growth factor-1 receptor, epidermal growth factor receptor, cyclooxygenase-2, signal transducer and activator of transcription 3, phosphatase and tensin homolog deleted on chromosome ten and Bcl-2 etc. are related to the chemoresistance and sensitivity of cancer cells to 5-FU. The activation of these molecules and genes expressions in cancer cells will be increased or decreased with long-term exposure of 5-FU. Curcumin has been found to be able to negatively regulate these processes. In order to overcome the problems of 5-FU, curcumin has been used to combine with 5-FU in cancer therapy.

Insights into a Critical Role of the FOXO3a-FOXM1 Axis in DNA Damage Response and Genotoxic Drug Resistance

FOXO3a and FOXM1 are two forkhead transcription factors with antagonistic roles in cancer and DNA damage response. FOXO3a functions like a typical tumour suppressor, whereas FOXM1 is a potent oncogene aberrantly overexpressed in genotoxic resistant cancers. FOXO3a not only represses FOXM1 expression but also its transcriptional output. Recent research has provided novel insights into a central role for FOXO3a and FOXM1 in DNA damage response. The FOXO3a-FOXM1 axis plays a pivotal role in DNA damage repair and the accompanied cellular response through regulating the expression of genes essential for DNA damage sensing, mediating, signalling and repair as well as for senescence, cell cycle and cell death control. In this manner, the FOXO3a-FOXM1 axis also holds the key to cell fate decision in response to genotoxic therapeutic agents and controls the equilibrium between DNA repair and cell termination by cell death or senescence. As a consequence, inhibition of FOXM1 or reactivation of FOXO3a in cancer cells could enhance the efficacy of DNA damaging cancer therapies by decreasing the rate of DNA repair and cell survival while increasing senescence and cell death. Conceptually, targeting FOXO3a and FOXM1 may represent a promising molecular therapeutic option for improving the efficacy and selectivity of DNA damage agents, particularly in genotoxic agent resistant cancer. In addition, FOXO3a, FOXM1 and their downstream transcriptional targets may also be reliable diagnostic biomarkers for predicting outcome, for selecting therapeutic options, and for monitoring treatments in DNA-damaging agent therapy.

PKM1 is involved in resistance to anti-cancer drugs

Resistance to chemotherapy is a crucial problem in the clinical situation. To overcome this issue, many mechanisms of chemoresistance have been elucidated so far. However, this problem still has not been solved completely. In this study, we investigated the mechanism of chemoresistance from the view of cancer metabolism-related genes, especially focusing on the expression profile of pyruvate kinase muscle (PKM) isoforms, which are rate-limiting enzymes in cancer-specific metabolism (Warburg effect). Herein, we showed that PKM1, which promotes oxidative phosphorylation (OXPHOS), was commonly up-regulated in various chemoresistant cells. To clarify the functions of PKM1 in chemoresistance, we investigated effects of PKM1 expression in DLD-1 parental, 5-FU-resistant and oxaliplatin-resistant DLD-1 cells. The overexpression of PKM1 resulted in resistance of the parental cells to 5-FU and oxaliplatin. Moreover, gene-silencing of PKM1 induced apoptosis in these cells including the resistant cells by causing a decrease in the mitochondrial membrane potential. Furthermore, combination therapy using 5-FU or oxaliplatin with siR-PKM1 was also effective against the resistant cells. Our findings should lead to the development of new agents that can cancel the chemoresistance from the view of cancer energy metabolism.

Influence of PJ34 on the genotoxicity induced by melphalan in human multiple myeloma cells

INTRODUCTION

The aim of this study was to evaluate the potential biological activity of N-(6-oxo-5,6-dihydrophenanthridin-2-yl)-(N,N-dimethylamino)acetamide hydrochloride (PJ34) on the genotoxicity induced by melphalan in human multiple myeloma cells.

MATERIAL AND METHODS

The inhibitory effects of the drugs on the growth of RPMI8226 cells were determined by Cell Counting Kit-8 (CCK-8) assay. The expression of Fanconi anemia/breast cancer (FA/BRCA) pathway related genes was determined by western blot analysis. Cell cycle phase and apoptosis were analyzed by flow cytometry. Coadministration of PJ34 and melphalan had additional effects on cell cycle distribution and enhanced apoptosis of RPMI8226 cells. PJ34 plus melphalan inhibited cell-cycle progression, as evidenced by the increased proportion of cells in the G2/M phase with the decreasing proportion of cells in the G0/1 and S phases.

RESULTS

However, no significant synergistic effect of PJ34 and melphalan on cell proliferation was observed. These effects were accompanied by inhibition of the FA/BRCA pathway by downregulation of Fanconi D2 (FANCD2) protein expression. The results showed that treatment with 60 µmol/l of PJ34 previously to melphalan administration increased cell apoptosis. Pretreatment also caused cell cycle arrest.

CONCLUSIONS

This study suggests that enhancement of melphalan efficacy may be best achieved by the poly(ADP-ribose) polymerase-1 (PARP-1) inhibitor PJ34. The effects of PJ34 are associated with inhibition of the FA/BRCA pathway, increased apoptosis percentage, and G2/M cell cycle arrest. Administration of PJ34 has been shown to protect DNA from damage induced by melphalan. This corroborates the biological activities of PJ34 and points to the need for further studies.

PJ34, a poly(ADP-ribose) polymerase (PARP) inhibitor, reverses melphalan-resistance and inhibits repair of DNA double-strand breaks by targeting the FA/BRCA pathway in multidrug resistant multiple myeloma cell line RPMI8226/R

There is still no ideal treatment for multidrug resistant multiple myeloma, looking for drugs which can reverse chemotherapy resistance and enhance curative effects of chemotherapy drugs becomes a problem that needs to be solved urgently. Poly(ADP-ribose) polymerase inhibitors appear to be an important tool for medical therapy of several malignancies. In the present study, we investigated the potential of the PARP-1 inhibitor PJ34, in vitro, to further enhance the efficacy of the traditional chemotherapy drug melphalan in the multidrug-resistant multiple myeloma cell line RPMI8226/R. The effects of different concentrations of PJ34 and melphalan on cell proliferation were determined by the CCK-8 assay. The expressions of FA/BRCA pathway-related factors were detected by western blotting and RT-PCR. The percentage of cell apoptosis was measured with flow cytometry. DNA double-strand break (DSB) repair was quantified by γH2AX immunofluorescence. In addition, DNA damage repair at the level of the individual cell was determined by comet assay. Co-administration of PJ34 and melphalan had synergistic inhibitory effects on the proliferation of RPMI8226/R cells, suggesting more powerful antitumor activities. The apoptosis percentage also was increased more obviously by the treatment of melphalan plus PJ34. The activation of FA/BRCA pathway was inhibited by downregulation of related factors including FANCD2, BRCA2 and Rad51. PJ34 significantly increased the ratio of γH2AX-positive cells and the number of foci/cells. The comet tail rate of cells, tail length, tail moment and Olive tail moment all increased after PJ34 treatment in RPMI8226/R cells. These results indicate that PJ34 combined treatment with melphalan produces synergistic effects and reverses multidrug resistance of RPMI8226/R cells effectively. PJ34 cannot induce DNA damage directly, but it may increase the DNA damage induced by melphalan through inhibiting DNA damage repair. The suppression of FA/BRCA pathway may be the mechanism. Therefore, we suggest that PARP inhibitors may deserve future investigations as tools for medical treatment of multidrug resistant multiple myeloma.

Molecular and cellular functions of the FANCJ DNA helicase defective in cancer and in Fanconi anemia

The FANCJ DNA helicase is mutated in hereditary breast and ovarian cancer as well as the progressive bone marrow failure disorder Fanconi anemia (FA). FANCJ is linked to cancer suppression and DNA double strand break repair through its direct interaction with the hereditary breast cancer associated gene product, BRCA1. FANCJ also operates in the FA pathway of interstrand cross-link repair and contributes to homologous recombination. FANCJ collaborates with a number of DNA metabolizing proteins implicated in DNA damage detection and repair, and plays an important role in cell cycle checkpoint control. In addition to its role in the classical FA pathway, FANCJ is believed to have other functions that are centered on alleviating replication stress. FANCJ resolves G-quadruplex (G4) DNA structures that are known to affect cellular replication and transcription, and potentially play a role in the preservation and functionality of chromosomal structures such as telomeres. Recent studies suggest that FANCJ helps to maintain chromatin structure and preserve epigenetic stability by facilitating smooth progression of the replication fork when it encounters DNA damage or an alternate DNA structure such as a G4. Ongoing studies suggest a prominent but still not well-understood role of FANCJ in transcriptional regulation, chromosomal structure and function, and DNA damage repair to maintain genomic stability. This review will synthesize our current understanding of the molecular and cellular functions of FANCJ that are critical for chromosomal integrity.

FOXM1: an emerging master regulator of DNA damage response and genotoxic agent resistance

FOXM1 is a transcription factor required for a wide spectrum of essential biological functions, including DNA damage repair, cell proliferation, cell cycle progression, cell renewal, cell differentiation and tissue homeostasis. Recent evidence suggests that FOXM1 also has a role in many aspects of the DNA damage response. Accordingly, FOXM1 drives the transcription of genes for DNA damage sensors, mediators, signal transducers and effectors. As a result of these functions, it plays an integral part in maintaining the integrity of the genome and so is key to the propagation of accurate genetic information to the next generation. Preserving the genetic code is a vital means of suppressing cancer and other genetic diseases. Conversely, FOXM1 is also a potent oncogenic factor that is essential for cancer initiation, progression and drug resistance. An enhanced FOXM1 DNA damage repair gene expression network can confer resistance to genotoxic agents. Developing a thorough understanding of the regulation and function of FOXM1 in DNA damage response will improve the diagnosis and treatment of diseases including cancer, neurodegenerative conditions and immunodeficiency disorders. It will also benefit cancer patients with acquired genotoxic agent resistance.

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FOXM1 is a potent oncogenic factor essential for cancer initiation, progression and drug resistance.

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FOXM1 also drives the transcription of genes for DNA damage sensors, mediators, signal transducers and effectors.

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It plays an integral part in maintaining the integrity of the genome.

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An enhanced FOXM1 DNA damage repair gene expression network can confer resistance to genotoxic agents.