TXNL1-XRCC1 pathway regulates cisplatin-induced cell death and contributes to resistance in human gastric cancer

Cisplatin is a cytotoxic platinum compound that triggers DNA crosslinking induced cell death, and is one of the reference drugs used in the treatment of several types of human cancers including gastric cancer. However, intrinsic or acquired drug resistance to cisplatin is very common, and leading to treatment failure. We have recently shown that reduced expression of base excision repair protein XRCC1 (X-ray repair cross complementing group1) in gastric cancerous tissues correlates with a significant survival benefit from adjuvant first-line platinum-based chemotherapy. In this study, we demonstrated the role of XRCC1 in repair of cisplatin-induced DNA lesions and acquired cisplatin resistance in gastric cancer by using cisplatin-sensitive gastric cancer cell lines BGC823 and the cisplatin-resistant gastric cancer cell lines BGC823/cis-diamminedichloridoplatinum(II) (DDP). Our results indicated that the protein expression of XRCC1 was significantly increased in cisplatin-resistant cells and independently contributed to cisplatin resistance. Irinotecan, another chemotherapeutic agent to induce DNA damaging used to treat patients with advanced gastric cancer that progressed on cisplatin, was found to inhibit the expression of XRCC1 effectively, and leading to an increase in the sensitivity of resistant cells to cisplatin. Our proteomic studies further identified a cofactor of 26S proteasome, the thioredoxin-like protein 1 (TXNL1) that downregulated XRCC1 in BGC823/DDP cells via the ubiquitin-proteasome pathway. In conclusion, the TXNL1-XRCC1 is a novel regulatory pathway that has an independent role in cisplatin resistance, indicating a putative drug target for reversing cisplatin resistance in gastric cancer.     

Inhibition of Autophagy Potentiated the Antitumor Effect of Nedaplatin in Cisplatin-Resistant Nasopharyngeal Carcinoma Cells

Nedaplatin, a cisplatin analog, was developed to reduce the toxicity of cisplatin, whereas it can be cross-resistant with cisplatin in some circumstances. This study aimed to investigate the role of autophagy in nedaplatin induced cell death in cisplatin-resistant nasopharyngeal carcinoma cells. Here, we showed that HNE1/DDP and CNE2/DDP cells were resistant to nedaplatin-induced cell death with reduced apoptotic activity. Nedaplatin treatment resulted in autophagosome accumulation and increased expression of LC3-II, indicating the induction of autophagy by nedaplatin in HNE1/DDP and CNE2/DDP cells. Inhibition of autophagy by Bafilomycin A1 (Baf A1) and 3-Methyladenine (3-MA) remarkably enhanced the antitumor efficacy of nedaplatin in HNE1/DDP and CNE2/DDP cells, suggesting that the resistance to nedaplatin-induced cell death was caused by enhanced autophagy in nedaplatin-resistant NPC cells. Additionally, Baf A1 enhanced reactive oxygen species (ROS) generation and apoptosis induced by nedaplatin in HNE1/DDP cells. Mechanistically, nedaplatin treatment caused activation of ERK1/2 and suppression of Akt/mTOR signaling pathways. While inhibition of ERK1/2 by MEK1/2 inhibitor, U0126, could reduce the expression of LC3-II in nedaplatin-resistant NPC cells. Furthermore, suppression of ROS could inhibit nedaplatin-induced ERK activation in HNE1/DDP cells, indicating that ROS and ERK were involved in nedaplatin-induced autophagy. Together, these findings suggested that autophagy played a cytoprotective role in nedaplatin-induced cytotoxicity of HNE1/DDP and CNE2/DDP cells. Furthermore, our results highlighted a potential approach to restore the sensitivity of cisplatin-resistant nasopharyngeal cancer cells to nedaplatin in combination with autophagy inhibitors.     

RNA interferences targeting the Fanconi anemia/BRCA pathway upstream genes reverse cisplatin resistance in drug-resistant lung cancer cells

Background

Cisplatin is one of the most commonly used chemotherapy agent for lung cancer. The therapeutic efficacy of cisplatin is limited by the development of resistance.In this study, we test the effect of RNA interference (RNAi) targeting Fanconi anemia (FA)/BRCA pathway upstream genes on the sensitivity of cisplatin-sensitive (A549 and SK-MES-1) and -resistant (A549/DDP) lung cancer cells to cisplatin.

Result

Using small interfering RNA (siRNA), knockdown of FANCF, FANCL, or FANCD2 inhibited function of the FA/BRCA pathway in A549, A549/DDP and SK-MES-1 cells, and potentiated sensitivity of the three cells to cisplatin. The extent of proliferation inhibition induced by cisplatin after knockdown of FANCF and/or FANCL in A549/DDP cells was significantly greater than in A549 and SK-MES-1 cells, suggesting that depletion of FANCF and/or FANCL can reverse resistance of cisplatin-resistant lung cancer cells to cisplatin. Furthermore, knockdown of FANCL resulted in higher cisplatin sensitivity and dramatically elevated apoptosis rates compared with knockdown of FANCF in A549/DDP cells, indicating that FANCL play an important role in the repair of cisplatin-induced DNA damage.

Conclusion

Knockdown of FANCF, FANCL, or FANCD2 by RNAi could synergize the effect of cisplatin on suppressing cell proliferation in cisplatin-resistant lung cancer cells through inhibition of FA/BRCA pathway.     

DNA damage responsive miR-33b-3p promoted lung cancer cells survival and cisplatin resistance by targeting p21WAF1/CIP1

Cisplatin is the most potent and widespread used chemotherapy drug for lung cancer treatment. However, the development of resistance to cisplatin is a major obstacle in clinical therapy. The principal mechanism of cisplatin is the induction of DNA damage, thus the capability of DNA damage response (DDR) is a key factor that influences the cisplatin sensitivity of cancer cells. Recent advances have demonstrated that miRNAs (microRNAs) exerted critical roles in DNA damage response; nonetheless, the association between DNA damage responsive miRNAs and cisplatin resistance and its underlying molecular mechanism still require further investigation. The present study has attempted to identify differentially expressed miRNAs in cisplatin induced DNA damage response in lung cancer cells, and probe into the effects of the misexpressed miRNAs on cisplatin sensitivity. Deep sequencing showed that miR-33b-3p was dramatically down-regulated in cisplatin-induced DNA damage response in A549 cells; and ectopic expression of miR-33b-3p endowed the lung cancer cells with enhanced survival and decreased γH2A.X expression level under cisplatin treatment. Consistently, silencing of miR-33b-3p in the cisplatin-resistant A549/DDP cells evidently sensitized the cells to cisplatin. Furthermore, we identified CDKN1A (p21) as a functional target of miR-33b-3p, a critical regulator of G1/S checkpoint, which potentially mediated the protection effects of miR-33b-3p against cisplatin. In aggregate, our results suggested that miR-33b-3p modulated the cisplatin sensitivity of cancer cells might probably through impairing the DNA damage response. And the knowledge of the drug resistance conferred by miR-33b-3p has great clinical implications for improving the efficacy of chemotherapies for treating lung cancers.     

Exosomal MiR‐500a‐3p promotes cisplatin resistance and stemness via negatively regulating FBXW7 in gastric cancer

Chemoresistance has been a major challenge in advanced gastric cancer (GC) therapy. Exosomal transfer of oncogenic miRNAs implicates important effects in mediating recipient cell chemoresistance by transmitting active molecules. In this study, we found that microRNA‐500a‐3p was highly expressed in cisplatin (DDP) resistant GC cells (MGC803/DDP and MKN45/DDP) and their secreted exosomes than that in the corresponding parental cells. MGC803/DDP‐derived exosomes enhance DDP resistance and stemness properties of MGC803 recipient cells via exosomal delivery of miR‐500a‐3p in vitro and in vivo through targeting FBXW7. However, reintroduction of FBXW7 in MGC803 cells reverses miR‐500a‐3p‐mediated DDP resistance as well as stemness properties. Furthermore, elevated miR‐500a‐3p in the plasma exosomes of GC patients is correlated with DDP resistance and thereby results in poor progression‐free prognosis. Our finding highlights the potential of exosomal miR‐500a‐3p as an potential modality for the prediction and treatment of GC with chemoresistance.     

MiR-130a and MiR-374a Function as Novel Regulators of Cisplatin Resistance in Human Ovarian Cancer A2780 Cells

Chemoresistance remains a major obstacle to effective treatment in patients with ovarian cancer, and recently increasing evidences suggest that miRNAs are involved in drug-resistance. In this study, we investigated the role of miRNAs in regulating cisplatin resistance in ovarian cancer cell line and analyzed their possible mechanisms. We profiled miRNAs differentially expressed in cisplatin-resistant human ovarian cancer cell line A2780/DDP compared with parental A2780 cells using microarray. Four abnormally expressed miRNAs were selected (miR-146a,-130a, -374a and miR-182) for further studies. Their expression were verified by qRT-PCR. MiRNA mimics or inhibitor were transfected into A2780 and A2780/DDP cells and then drug sensitivity was analyzed by MTS array. RT-PCR and Western blot were carried out to examine the alteration of MDR1, PTEN gene expression. A total of 32 miRNAs were found to be differentially expressed in A2780/DDP cells. Among them, miR-146a was down-regulated and miR-130a,-374a,-182 were upregulated in A2780/DDP cells, which was verified by RT-PCR. MiR-130a and miR-374a mimics decreased the sensitivity of A2780 cells to cisplatin, reversely, their inhibitors could resensitize A2780/DDP cells. Furthermore, overexpression of miR-130a could increase the MDR1 mRNA and P-gp levels in A2780 and A2780/DDP cells, whereas knockdown of miR-130a could inhibit MDR1 gene expression and upregulate the PTEN protein expression .In a conclusion, the deregulation of miR-374a and miR-130a may be involved in the development and regulation of cisplatin resistance in ovarian cancer cells. This role of miR-130a may be achieved by regulating the MDR1 and PTEN gene expression.     

Reversal of cisplatin and multidrug resistance by ribozyme-mediated glutathione suppression

gamma-Glutamylcysteine synthetase (gamma-GCS) is a key enzyme in glutathione (GSH) synthesis, and is thought to play a significant role in intracellular detoxification, especially of anticancer drugs. Increased levels of GSH are commonly found in the drug-resistant human cancer cells. We designed a hammerhead ribozyme against gamma-GCS mRNA (anti-gamma-GCS Rz), which specifically down-regulated gamma-GCS gene expression in the HCT-8 human colon cancer cell line. The aim of this study was to reverse the cisplatin and multidrug resistance for anticancer drugs. The cisplatin-resistant HCT-8 cells (HCT-8DDP cells) overexpressed MRP and MDR1 genes, and showed resistance to not only cisplatin (CDDP), but also doxorubicin (DOX) and etoposide (VP-16). We transfected a vector expressing anti-gamma-GCS Rz into the HCT-8DDP cells (HCT-8DDP/Rz). The anti-gamma-GCS Rz significantly suppressed MRP and MDR, and altered anticancer drug resistance. The HCT-8DDP/Rz cells were more sensitive to CDDP, DOX and VP-16 by 1.8-, 4.9-, and 1.5-fold, respectively, compared to HCT-8DDP cells. The anti-gamma-GCS Rz significantly down-regulated gamma-GCS gene expression as well as MRP/MDR1 expression, and reversed resistance to CDDP, DOX and VP-16. These results suggested that gamma-GCS plays an important role in both cisplatin and multidrug resistance in human cancer cells.     

Small Molecules Identified from a Quantitative Drug Combinational Screen Resensitize Cisplatin's Response in Drug-Resistant Ovarian Cancer Cells

Drug resistance to chemotherapy occurs in many ovarian cancer patients resulting in failure of treatment. Exploration of drug resistance mechanisms and identification of new therapeutics that overcome the drug resistance can improve patient prognosis. Following a quantitative combination screen of 6060 approved drugs and bioactive compounds in a cisplatin-resistant A2780-cis ovarian cancer cell line, 38 active compounds with IC₅₀s under 1 μM suppressed the growth of cisplatin-resistant ovarian cancer cells. Among these confirmed compounds, CUDC-101, OSU-03012, oligomycin A, VE-821, or Torin2 in a combination with cisplatin restored cisplatin's apoptotic response in the A2780-cis cells, while SR-3306, GSK-923295, SNX-5422, AT-13387, and PF-05212384 directly suppressed the growth of A2780-cis cells. One of the mechanisms for overcoming cisplatin resistance in these cells is mediated by the inhibition of epidermal growth factor receptor (EGFR), though not all the EGFR inhibitors are equally active. The increased levels of total EGFR and phosphorylated-EGFR (p-EGFR) in the A2780-cis cells were reduced after the combined treatment of cisplatin with EGFR inhibitors. In addition, a knockdown of EGFR mRNA reduced cisplatin resistance in the A2780-cis cells. Therefore, the top active compounds identified in this work can be studied further as potential treatments for cisplatin-resistant ovarian cancer. The quantitative combinational screening approach is a useful method for identifying effective compounds and drug combinations against drug-resistant cancer cells.     

Efficacy of poly (ADP-ribose) polymerase inhibitor olaparib against head and neck cancer cells: Predictions of drug sensitivity based on PAR–p53–NF-κB interactions

Poly (ADP-ribose) polymerase (PARP) is a key molecule in the DNA damage response (DDR), which is a major target of both chemotherapies and radiotherapies. PARP inhibitors therefore comprise a promising class of anticancer therapeutics. In this study, we evaluated the efficacy of the PARP inhibitor olaparib, and also sought to identify the mechanism and predictive marker associated with olaparib sensitivity in head and neck cancer (HNC) cells. A total of 15 HNC cell lines, including AMC HNC cells, were tested. AMC-HN3 and HN4 exhibited stronger responses to olaparib. Among cisplatin-resistant cell lines, only AMC HN9-cisR cells were significantly suppressed by olaparib. We found that basal poly (ADP-ribose) (PAR) levels, but not PARP-1 levels, correlated with olaparib sensitivity. AMC-HN3 and HN4 cells exhibited higher basal levels of NF-κB that decreased significantly after olaparib treatment. In contrast, apoptotic proteins were intrinsically expressed in AMC-HN9-cisR cells. As interference with p53 expression led to NF-κB reactivation, we concluded that elevated basal PAR and NF-κB levels are predictive of olaparib responsiveness in HNC cells; in addition, olaparib inhibits HNC cells via PAR–p53–NF-κB interactions.     

RING finger protein 38 induces the drug resistance of cisplatin in non-small-cell lung cancer

Cisplatin resistance of non-small-cell lung cancer (NSCLC) needs to be well elucidated. RING finger protein (RNF38) has been proposed as a biomarker of NSCLC poor prognosis. However, its role in drug resistance in NSCLC is poorly understood. RNF38 expression was detected in normal lung epithelial cell and four NSCLC cell lines. RNF38 was stably overexpressed in A549 and H460 cells or silenced in H1975 and cisplatin-resistant A549 cells (A549-CDDP resistant) using lentiviral vectors. RNF38 expression levels were determined using quantitative real-time polymerase chain reaction and western blotting analysis. Cell viability in response to different concentrations of cisplatin was evaluated by Cell Counting Kit-8 assay. RNF38 expression levels were markedly elevated in NSCLC cells and cells harboring high RNF38 were less sensitive to cisplatin. Overexpression of RNF38 reduced, while RNF38 silencing increased the drug sensitivity of cisplatin in NSCLC cells. Cisplatin-resistant cells expressed high RNF38 level. RNF38 silencing promoted cell apoptosis and enhanced the drug sensitivity of cisplatin in cisplatin-resistant NSCLC cells. These findings indicate that RNF38 might induce cisplatin resistance of NSCLC cells via promoting cell apoptosis and RNF38 could be a novel target for rectify cisplatin resistance in NSCLC cases.     

Positive correlation between cellular glutathione and acquired cisplatin resistance in human ovarian cancer cells

While multiple changes are frequently found to be associated with cisplatin resistance in a variety of tumor cell lines, a cause-effect relationship of these alterations with the resistant phenotype has not been established. In order to identify the resistance-relevant determinants, a series of cisplatinresistant sublines with different degrees of resistance to cisplatin was developed in a human ovarian carcinoma cell line (O-129). Three derived resistant cell lines displayed 2.1-fold (O-129/DDP₄, low), 4.1-fold (O-129/DDP₈, moderate) and 6.3-fold (O-129/DDP₁₆, high) resistance, respectively, to cisplatin, compared with the sensitive parental line O-129. While the activity of poly(ADP-ribose) polymerase, an enzyme proposed to be involved in DNA repair, was elevated in all three resistant lines, a significant karyotypic change was observed only in the high-resistance line with the karyotype alteration from near diploidy to heteroploidy. The moderate (4.1-fold) and high (6.3-fold) DDP resistance was associated with a slow proliferation rate in drug-free medium, but cellular glutathione level was highly correlated with DDP sensitivity in all four cell lines. Taken together, the present studies establish that while many changes at cellular level can occur with development of cisplatin resistance, only elevation of intracellular glutathione concentration appears to be related to the resistance phenotype in these human ovarian cancer cells.Abbreviations DDP cisplatin - FBS fetal bovine serum - GSH glutathione - IC₅₀ drug concentration required to result in 50% growth inhibition - PARP poly(ADP-ribose) polymerase     

Interference with SMO increases chemotherapy drug sensitivity of A2780/DDP cells by inhibiting the Hh/Gli signaling pathway

Aberrant activation of the Hedgehog (Hh)/Gli pathway contributes to the tumorigenesis of several human cancers, including ovarian cancers. We investigated the function of SMO on cell growth, drug resistance, and invasive ability in A2780/DDP cells. Moreover, we also tested the levels of the downstream target genes of the Hh/Gli pathway in SMO short hairpin RNA (shRNA) lentivirus-infected A2780/DDP cells. Western blot analysis results revealed that the Hh/Gli pathway was activated in cisplatin-resistant A2780/DDP cells. After infection by SMO shRNA lentivirus, the colony formation rate and invasive rate of cisplatin-resistant A2780/DDP cells were decreased. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed that upon transfection with SMO shRNA, cell growth was decreased and drug sensitivity to cisplatin was upregulated. Moreover, interference with SMO decreased the expression of MMP-2, MMP-9, VEGF, and Snail in cisplatin-resistant cells. Thus, the Hh/Gli signaling pathway was aberrantly activated in A2780/DDP cells. The colony formation rate and invasive rate were decreased in SMO shRNA lentivirus–infected A2780/DDP cells. All results showed that inhibiting Hh/Gli signaling may negatively regulate the proliferation, invasion, and metastasis of cisplatin-resistant A2780/DDP cells, as well as increase the sensitivity of A2780/DDP to the chemotherapeutic drug of cisplatin.     

LncRNA MST1P2/miR‐133b axis affects the chemoresistance of bladder cancer to cisplatin‐based therapy via Sirt1/p53 signaling

Although bladder cancer is commonly chemosensitive to standard first‐line therapy, the acquisition of the resistance to cisplatin (DDP)‐based therapeutic regimens remains a huge challenge. Noncoding RNAs (ncRNAs), including long noncoding RNAs (lncRNAs) and microRNAs, have been reported to play a critical role in cancer resistance to DDP. Here, we attempted to provide a novel mechanism by which the resistance of bladder cancer to DDP treatment could be modulated from the perspective of ncRNA regulation. We demonstrated that lncRNA MST1P2 (lnc‐MST1P2) expression was dramatically upregulated, whereas miR‐133b expression was downregulated in DDP‐resistant bladder cancer cell lines, SW 780/DDP and RT4/DDP. Lnc‐MST1P2 and miR‐133b negatively regulated each other via targeting miR‐133b. Both lnc‐MST1P2 silence and miR‐133b overexpression could resensitize DDP‐resistant bladder cancer cells to DDP treatment. More important, miR‐133b could directly target the Sirt1 3′‐untranslated region to inhibit its expression. Inc‐MST1P2/miR‐133b axis affected the resistance of bladder cancer cells to DDP via Sirt1/p53 signaling. In conclusion, MST1P2 serves as a competing endogenous RNA for miR‐133b to counteract miR‐133b‐induced suppression on Sirt1, therefore enhancing the resistance of bladder cancer cells to DDP. MST1P2/miR‐133b axis affects the resistance of bladder cancer cells to DDP via downstream Sirt1/p53 signaling.     

A Synthetic Lethal Screen Identifies DNA Repair Pathways that Sensitize Cancer Cells to Combined ATR Inhibition and Cisplatin Treatments

The DNA damage response kinase ATR may be a useful cancer therapeutic target. ATR inhibition synergizes with loss of ERCC1, ATM, XRCC1 and DNA damaging chemotherapy agents. Clinical trials have begun using ATR inhibitors in combination with cisplatin. Here we report the first synthetic lethality screen with a combination treatment of an ATR inhibitor (ATRi) and cisplatin. Combination treatment with ATRi/cisplatin is synthetically lethal with loss of the TLS polymerase ζ and 53BP1. Other DNA repair pathways including homologous recombination and mismatch repair do not exhibit synthetic lethal interactions with ATRi/cisplatin, even though loss of some of these repair pathways sensitizes cells to cisplatin as a single-agent. We also report that ATRi strongly synergizes with PARP inhibition, even in homologous recombination-proficient backgrounds. Lastly, ATR inhibitors were able to resensitize cisplatin-resistant cell lines to cisplatin. These data provide a comprehensive analysis of DNA repair pathways that exhibit synthetic lethality with ATR inhibitors when combined with cisplatin chemotherapy, and will help guide patient selection strategies as ATR inhibitors progress into the cancer clinic.     

Dihydroartemisinin potentiates the anticancer effect of cisplatin via mTOR inhibition in cisplatin-resistant ovarian cancer cells: involvement of apoptosis and autophagy

Dihydroartemisinin (DHA) exhibits anticancer activity in tumor cells but its mechanism of action is unclear. Cisplatin (DDP) is currently the best known chemotherapeutic available for ovarian cancer. However, tumors return de novo with acquired resistance over time. Mammalian target of rapamycin (mTOR) is an important kinase that regulates cell apoptosis and autophagy, and its dysregulation has been observed in chemoresistant human cancers. Here, we show that compared with control ovarian cancer cells (SKOV3), mTOR phosphorylation was abnormally activated in cisplatin-resistant ovarian cancer cells (SKOV3/DDP) following cisplatin monotherapy. Treatment with cisplatin combined with DHA could enhance cisplatin-induced proliferation inhibition in SKOV3/DDP cells. This mechanism is at least partially due to DHA deactivation of mTOR kinase and promotion of apoptosis. Although autophagy was also induced by DHA, the reduced cell death was not found by suppressing autophagic flux by Bafilomycin A1 (BAF). Taken together, we conclude that inhibition of cisplatin-induced mTOR activation is one of the main mechanisms by which DHA dramatically promotes its anticancer effect in cisplatin-resistant ovarian cancer cells.     

Poly(ADP-ribose) polymerase-1 activity facilitates the dissociation of nuclear proteins from platinum-modified DNA

The affinity of the poly(ADP-ribose) polymerase-1 (PARP-1) for platinum-damaged DNA was first discovered during photo-cross-linking experiments using the photoactive compound Pt-BP6 [J. Am. Chem. Soc.2004, 126, 6536-6537], an analogue of the anticancer drug cis-diamminedichloroplatinum(II), cisplatin. Although PARP inhibitors sensitize cancer cells to cisplatin, there are conflicting reports in the literature about their efficacy. In order to improve our understanding of the mechanism by which PARP inhibition might potentiate the cell-killing ability of cisplatin, and to shed light on the source of the discrepancy among different laboratories, we have in the present study probed the influence of three PARP inhibitors in four types of cancer cells, cervical (HeLa), testicular (NTera2), pancreatic (BxPC3), and osteosarcoma (U2OS), on the results of Pt-BP6 photo-cross-linking experiments and cytotoxicity assays. We find that the activity of PARP proteins following exposure to platinum-modified DNA results in the dissociation of DNA-bound proteins. PARP inhibitors were able to sensitize some, but not all, of the cell lines to cisplatin. This cell line-dependence and the potential consequences of PARP-initiated protein removal from platinum-DNA lesions are discussed. Control experiments revealed that NTera2 cells are especially sensitive to PARP inhibition.     

miRNA 17 Family Regulates Cisplatin-Resistant and Metastasis by Targeting TGFbetaR2 in NSCLC

MicroRNAs (miRNAs) have been proven to play crucial roles in cancer, including tumor chemotherapy resistance and metastasis of non-small-cell lung cancer (NSCLC). TGFβ signal pathway abnormality is widely found in cancer and correlates with tumor proliferation, apoptosis and metastasis. Here, miR-17, 20a, 20b were detected down-regulated in A549/DDP cells (cisplatin resistance) compared with A549 cells (cisplatin sensitive). Over-expression of miR-17, 20a, 20b can not only decrease cisplatin-resistant but also reduce migration by inhibiting epithelial-to-mesenchymal transition (EMT) in A549/DDP cells. These functions of miR-17, 20a, 20b may be caused at least in part via inhibition of TGFβ signal pathway, as miR-17, 20a, 20b are shown to directly target and repress TGF-beta receptor 2 (TGFβR2) which is an important component of TGFβ signal pathway. Consequently, our study suggests that miRNA 17 family (including miR-17, 20a, 20b) can act as TGFβR2 suppressor for reversing cisplatin-resistant and suppressing metastasis in NSCLC.     

Bim protein degradation contributes to cisplatin resistance

Cisplatin is the first-line chemotherapy for the treatment of several cancers. However, the development of cisplatin resistance represents a major clinical problem, and the mechanisms of acquired resistance are not fully understood. Here we show that degradation of the Bcl-2 homology 3-only proapoptotic protein Bim plays an important role in cisplatin resistance in ovarian cancer. Specifically, we show that treatment of ovarian cancer cells with cisplatin caused Bim phosphorylation and subsequent degradation and that its degradation is associated with cisplatin resistance. We also show that cisplatin treatment caused the activation of ERK, which correlated with Bim phosphorylation and degradation. By inhibiting ERK phosphorylation with the MEK inhibitor and knocking down ERK expression with siRNA, we show that Bim phosphorylation and degradation were blocked, which suggests that Bim is phosphorylated by ERK and that such phosphorylation is responsible for cisplatin-induced Bim degradation. We show that ERK was activated in cisplatin-resistant OV433 cells as compared with their counterpart parental OV433 cells. We also show that Bim was phosphorylated and degraded in cisplatin-resistant OV433 cells but not in the parental OV433 cells. Importantly, we show that inhibition of Bim degradation by the proteasome inhibitor MG132 sensitized resistant OV433 cells to cisplatin-induced death. Taken together, our data indicate that degradation of Bim via ERK-mediated phosphorylation can lead to cisplatin resistance. Therefore, these findings suggest that cisplatin resistance can be overcome by the combination of cisplatin and the proteasome inhibitors in ovarian cancer cells.     

The induction of ferroptosis by impairing STAT3/Nrf2/GPx4 signaling enhances the sensitivity of osteosarcoma cells to cisplatin

Recent studies have indicated that promoting ferroptosis is a promising approach to attenuate drug resistance of cancer cells. Hence, this study aimed to induce ferroptosis in osteosarcoma cells, thereby increasing the sensitivity to cisplatin. Osteosarcoma cells MG63 and Saos‐2 were incubated with increasing doses of cisplatin to generate cisplatin‐resistant strains, MG63/DDP and Saos‐2/DDP. 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) and flow cytometry assays were performed to evaluate cell proliferation and cell death, respectively. Malondialdehyde (MDA), reactive oxygen species (ROS), and lipid oxidation in cells were measured to evaluate the degree of cell ferroptosis. MG63/DDP and Saos‐2/DDP cells showed increased viability and decreased death rate compared with MG63 and Saos‐2 cells, respectively, upon cisplatin treatment. Western blotting analysis indicated that protein levels of p‐STAT3 (Ser727), nuclear factor erythroid 2‐related factor 2 (Nrf2), and glutathione peroxidase 4 (GPx4) in drug‐resistant strains increased significantly in response to cisplatin. Co‐treatment with cisplatin and agonists of ferroptosis, Erastin, and RSL3, remarkably increased MDA, ROS, lipid oxidation, and sensitivity to cisplatin, in MG63/DDP and Saos‐2/DDP cells. Similar results were observed by co‐treatment of cells with cisplatin and a STAT3 inhibitor. The reduction of protein levels of p‐STAT3 (Ser727), Nrf2, and GPx4 in MG63/DDP and Saos‐2/DDP cells resulted in increased ferroptosis and sensitivity to cisplatin. These results indicate that cisplatin‐resistant osteosarcoma cells inhibited ferroptosis after exposure to low doses of cisplatin. However, ferroptosis agonists and STAT3 inhibitor reactivated ferroptosis in the cells and consequently increased sensitivity to cisplatin. This study demonstrates a new approach to attenuate resistance of osteosarcoma to cisplatin in vitro .