Novel Mechanism Of Chemoresistance Research Articles

The Interaction of Calcium-Sensing Receptor with KIF11 Enhances Cisplatin Resistance in Lung Adenocarcinoma via BRCA1/cyclin B1 pathway.

Cisplatin (DDP) is commonly used in the treatment of non-small cell lung cancer (NSCLC), including lung adenocarcinoma (LUAD), and the primary cause for its clinical inefficacy is chemoresistance. Here, we aimed to investigate a novel mechanism of chemoresistance in LUAD cells, focusing on the calcium-sensing receptor (CaSR). In this study, high CaSR expression was detected in DDP-resistant LUAD cells, and elevated CaSR expression is strongly correlated with poor prognosis in LUAD patients receiving chemotherapy. LUAD cells with high CaSR expression exhibited decreased sensitivity to cisplatin, and the growth of DDP-resistant LUAD cells was inhibited by cisplatin treatment in combination with CaSR suppression, accompanied by changes in BRCA1 and cyclin B1 protein expression both in vitro and in vivo. Additionally, an interaction between CaSR and KIF11 was identified. Importantly, suppressing KIF11 resulted in decreased protein levels of BRCA1 and cyclin B1, enhancing the sensitivity of DDP-resistant LUAD cells to cisplatin with no obvious decrease in CaSR. Here, our findings established the critical role of CaSR in promoting cisplatin resistance in LUAD cells by modulating cyclin B1 and BRCA1 and identified KIF11 as a mediator, highlighting the potential therapeutic value of targeting CaSR to overcome chemoresistance in LUAD.

A hybrid breast cancer/mesenchymal stem cell population enhances chemoresistance and metastasis.

Patients with triple negative breast cancer remain at risk for metastatic disease despite treatment. The acquisition of chemoresistance is a major cause of tumor relapse and death, but the mechanisms are far from understood. We have demonstrated that breast cancer cells (BCCs) can engulf mesenchymal stem/stromal cells (MSCs), leading to enhanced dissemination. Here, we show that clinical samples of primary invasive carcinoma and chemoresistant breast cancer metastasis contain a unique hybrid cancer cell population co-expressing pan-cytokeratin and the MSC marker fibroblast activation protein-alpha. We show that hybrid cells form in primary tumors and that they promote breast cancer metastasis and chemoresistance. Using single cell microfluidics and in vivo models, we found that within the hybrid cell population are polyploid senescent cells that contribute to metastatic dissemination. Our data reveal that WNT5A plays a crucial role in supporting the chemoresistance properties of hybrid cells. Furthermore, we identify that WNT5A mediates hybrid cell formation through a phagocytosis-like mechanism that requires BCC-derived Interleukin 6 and MSC-derived C-C Motif Chemokine Ligand 2. These findings reveal hybrid cell formation as a novel mechanism of chemoresistance and suggest that interrupting this mechanism may be a potential strategy to overcome breast cancer drug resistance.

Stromal cells promote chemoresistance of acute myeloid leukemia cells via activation of the IL-6/STAT3/OXPHOS axis.

BackgroundBone marrow stromal cells (BMSCs) are known to promote chemoresistance in acute myeloid leukemia (AML) cells. However, the molecular basis for BMSC-associated AML chemoresistance remains largely unexplored.MethodsThe mitochondrial oxidative phosphorylation (OXPHOS) levels of AML cells were measured by a Seahorse XFe24 cell metabolic analyzer. The activity of total or mitochondrial signal transducer and transcription activator 3 (STAT3) in AML cells was explored by flow cytometry and Western blotting. Real-time quantitative PCR, Western blotting and enzyme-linked immunosorbent assay (ELISA) were used to analyze expression of interleukin 6 (IL-6) in the human BMSC line HS-5, and IL-6 was knocked out in HS-5 cells by CRISPR/Cas9 system.ResultsIn this study, we observed that co-culturing with BMSCs heightened OXPHOS levels in AML cells, thus promoting chemoresistance in these cells. HS-5 cell-induced upregulation of OXPHOS is dependent on the activation of STAT3, especially on that of mitochondrial serine phosphorylated STAT3 (pS-STAT3) in AML cells. The relationship among pS-STAT3, OXPHOS, and chemosensitivity of AML cells induced by BMSCs was demonstrated by the STAT3 activator and inhibitor, which upregulated and downregulated the levels of mitochondrial pS-STAT3 and OXPHOS, respectively. Intriguingly, AML cells remodeled HS-5 cells to secrete more IL-6, which augmented mitochondrial OXPHOS in AML cells and stimulated their chemoresistance. IL-6 knockout in HS-5 cells impaired the ability of these cells to activate STAT3, to increase OXPHOS, or to promote chemoresistance in AML cells.ConclusionsBMSCs promoted chemoresistance in AML cells via the activation of the IL-6/STAT3/OXPHOS pathway. These findings exhibit a novel mechanism of chemoresistance in AML cells in the bone marrow microenvironment from a metabolic perspective.

Abstract 5271: Chemotherapy-induced anastasis as a novel mechanism of therapeutic resistance

Abstract Resistance to chemotherapy and targeted cytotoxic therapy is an important contributor to tumor recurrence and metastatic progression, and remains a major hurdle in the treatment of cancer. Evidence suggests that cancer cells can recover from apoptosis subsequent to activation of caspase 3 (Cas3) through “anastasis”, a recently discovered process which enables recovery of cells from the brink of cell death following transient exposure to a potentially lethal dose of an apoptotic stimulus. Since chemotherapy induces apoptosis and is often delivered at maximum tolerated doses to patients, anastasis is a novel potential survival mechanism used by cancer cells to enable recovery after chemotherapy, thereby facilitating disease recurrence. Here, we investigated the extent to which triple negative breast cancer (TNBC) cells undergo anastasis in response to chemotherapy and identified potential molecular pathways and mechanisms of anastasis used by these cells. Analysis by time-lapse microscopy of human TNBC cells expressing a GFP-tagged Cas3 reporter and exposed to lethal doses of cisplatin or paclitaxel overnight demonstrated the presence of GFP+ cells showing phenotypic hallmarks of apoptosis that recovered with normal morphology. Furthermore, TNBC cells transduced with a novel genetically encoded biosensor that permanently labels cells that survive transient caspase activation, called mammalian CasExpress, were observed to be labeled with GFP following exposure to cisplatin, whereas mock-treated control cells were GFP negative. GFP+ TNBC cells enriched by FACS sorting showed significantly increased levels of resistance to chemotherapeutic agents (P < .05). Analysis by qPCR and Western blot demonstrated that TNBC cells recovering from exposure to cisplatin or paclitaxel significantly increased time-dependent expression of an alternatively spliced short isoform of Cas3 (Cas3s; P < 0.001), which acts an antagonist of full length Cas3 and confers resistance to apoptosis by breast cancer cells, while levels of full length Cas3 were not altered. Recovered cells also expressed significantly increased levels of genes (P < .05) and proteins associated with epithelial mesenchymal plasticity and hypoxic stress, including snail, slug, twist and HIF-1A, and showed increased levels of migration and invasion (P < .05). Finally, post-anastasis cells grown orthotopically as xenografts in vivo showed increased metastatic burden, compared to controls. Collectively, these data suggest that anastasis is a novel mechanism of chemoresistance used by TNBC cells and identify potential molecular pathways and vulnerabilities in anastatic cancer cells that could be targeted to develop new therapeutic strategies to overcome cancer recurrence and metastasis. Citation Format: Jennifer Nagel, Paul C. McDonald, Denise J. Montell, Shoukat Dedhar. Chemotherapy-induced anastasis as a novel mechanism of therapeutic resistance [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5271.

Abstract 3985: GDF15 expression level impacts the canonical pathways of the tumor microenvironment and ovarian tumors with wild-type p53 in response to chemotherapy

Abstract Background The standard treatment for ovarian cancer is surgery, followed by chemotherapy with a platinum agent, such as cisplatin or carboplatin, and a taxane, such as paclitaxel. We previously observed that patients with ovarian cancer that was wild-type for p53 had a lower survival rate than did those with p53 mutations. A better understanding of the molecular changes that occur in epithelial ovarian cancer cells with wild-type p53 in response to cisplatin treatment could reveal a novel mechanism of chemoresistance. Therefore, we might be able to develop novel strategy to overcome chemoresistance. Methods Gene expression profiling was performed on the wild-type p53 ovarian cancer cell line A2780 to identify genes that are highly induced by cisplatin. Growth differentiation factor 15 (GDF15) was identified as being highly induced by cisplatin or carboplatin. This finding was validated in a panel of wild-type and mutant p53 ovarian cancer cell lines. Mouse orthotopic models were used to further investigate the induction of GDF15 by cisplatin in vivo and the effect of GDF15 knockdown (GDF15-KD) on tumor growth and cisplatin response. A novel analysis was performed of RNAseq data generated from tumors formed in cisplatin-treated orthotopic mouse models to understand the tumor and stromal cell signaling changes. Results The induction of GDF15 was demonstrated in vivo, and the serum level of GDF15 after cisplatin treatment was also found to be significantly up-regulated in an A2780 ovarian cancer orthotopic mouse model. More importantly, cisplatin treatment was more effective in shrinking the mouse tumors developed from GDF15-KD A2780 cell line than did control tumors. Histopathological and novel RNAseq analyses of mouse tumors revealed that GDF15-KD tumors had a lower stromal component than did control tumors after cisplatin treatment. GDF15-KD tumors also had a different repertoire of activated and inhibited canonical pathways in their stromal cell and cancer cell components than did control tumors in response to cisplatin treatment. Conclusions GDF15 expression in wild-type p53 ovarian cancer cells can modulate the canonical pathways in the tumor microenvironment in response to cisplatin and may be a mechanism of chemoresistance. Targeting GDF15 signaling could be a novel strategy to enhance the effectiveness of chemotherapy. Citation Format: Daisy I. Izaguirre, Yvonne TM Tsang, Eucharist H. Kun, David M. Gershenson, Kwong-Kwok Wong. GDF15 expression level impacts the canonical pathways of the tumor microenvironment and ovarian tumors with wild-type p53 in response to chemotherapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3985.

Abstract 4751: Overcoming cisplatin resistance of esophageal squamous cell carcinoma by targeting RAC1-regulated Warburg effect

Abstract Esophageal squamous cell carcinoma (ESCC) is a highly aggressive malignancy with poor prognosis. Despite treatment advances, development of chemo-resistance remains a major challenge in treating ESCC patients. Ras-related C3 botulinum toxin substrate 1 (RAC1) is essential in regulating cancer progression. However, its role in chemo-resistance of ESCC and the underlying mechanisms are still unknown. In this study, we found that higher levels of RAC1 expression were associated with poorer disease-free survival (p=0.014) and overall survival (p=0.013) by immunohistochemistry in human ESCC samples (n=106). The over-expression of RAC1 was correlated with enhanced cell proliferation, migration, invasion and chemo-resistance in both KYSE150 and KYSE510 cells, while the knockdown of RAC1 produced the opposite results. The combination of RAC1 inhibitor EHop-016 with cisplatin significantly promoted cell viability reduction, cycle arrest at G2/M phase and apoptosis when compared with the single treatment. To examine the in vivo effects of RAC1 inhibition on chemo-resistance, we performed xenograft implantation studies in immunocompromised mice (n=10 per group). In the combination group, the tumor volume was significantly reduced to 21.4% (p<0.001) as compared to the single treatment groups (cisplatin: 62.7%, RAC1 inhibitor: 58.5%). Mechanistically, the RNA-Seq data indicated that the glycolytic pathway was significantly down-regulated in the EHop-016-treated group (p<0.001, Log2FC=1.86) and the combination group (p<0.001, Log2FC=1.76), as compared to the control group. Moreover, the qRT-PCR and western blot results confirmed that RAC1 inhibitor alone or the combination treatment suppressed Akt/FOXO signaling and resulted in inhibition of key enzymes such as PKM2, LDH-A, ALDOA and HK1 for the Warburg effect. Overall, our study suggests that inhibition of RAC1 overcomes cisplatin resistance in ESCC both in vitro and in vivo, and provides a novel mechanism of chemo-resistance in ESCC. Therefore, targeting RAC1 might be a promising and potent strategy for treating ESCC in clinical practice. Citation Format: Ruijie Zeng, Chunwen Zheng, Jinge Gu, Liu Peng, Haixia Zhang, Pan Feng, Yang Chen, Xiue Xu, Liyan Xu, Enmin Li. Overcoming cisplatin resistance of esophageal squamous cell carcinoma by targeting RAC1-regulated Warburg effect [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4751.

Cyclophilin B induces chemoresistance by degrading wild-type p53 via interaction with MDM2 in colorectal cancer.

Colorectal cancer (CRC) is one of the leading causes of cancer-related deaths worldwide. Chemoresistance is a major problem for effective therapy in CRC. Here, we investigated the mechanism by which peptidylprolyl isomerase B (PPIB; cyclophilin B, CypB) regulates chemoresistance in CRC. We found that CypB is a novel wild-type p53 (p53WT)-inducible gene but a negative regulator of p53WT in response to oxaliplatin treatment. Overexpression of CypB shortens the half-life of p53WT and inhibits oxaliplatin-induced apoptosis in CRC cells, whereas knockdown of CypB lengthens the half-life of p53WT and stimulates p53WT-dependent apoptosis. CypB interacts directly with MDM2, and enhances MDM2-dependent p53WT ubiquitination and degradation. Furthermore, we firmly validated, using bioinformatics analyses, that overexpression of CypB is associated with poor prognosis in CRC progression and chemoresistance. Hence, we suggest a novel mechanism of chemoresistance caused by overexpressed CypB, which may help to develop new anti-cancer drugs. We also propose that CypB may be utilized as a predictive biomarker in CRC patients. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Dysregulation of the MiR-449b target TGFBI alters the TGF\u03b2 pathway to induce cisplatin resistance in nasopharyngeal carcinoma

Despite the improvement in locoregional control of nasopharyngeal carcinoma (NPC), distant metastasis (DM), and chemoresistance persist as major causes of mortality. This study identified a novel role for miR-449b, an overexpressed gene in a validated four-miRNA signature for NPC DM, leading to chemoresistance via the direct targeting of transforming growth factor beta-induced (TGFBI). In vitro shRNA-mediated downregulation of TGFBI induced phosphorylation of PTEN and AKT, increasing cisplatin resistance. Conversely, the overexpression of TGFBI sensitized the NPC cells to cisplatin. In NPC patients treated with concurrent chemoradiotherapy (CRT), the overall survival (OS) was significantly inversely correlated with miR-449b, and directly correlated with both TGFBI mRNA and protein expression, as assessed by RNA sequencing and immunohistochemistry (IHC). Mechanistically, co-immunoprecipitation demonstrated that TGFBI competes with pro-TGFβ1 for integrin receptor binding. Decreased TGFBI led to increased pro-TGFβ1 activation and TGFβ1 canonical/noncanonical pathway-induced cisplatin resistance. Thus, overexpression of miR-449b decreases TGFBI, thereby altering the balance between TGFBI and pro-TGFβ1, revealing a novel mechanism of chemoresistance in NPC.

Abstract 4505: Activating transcription factor-6α dependent regulation of Rheb-mTOR and Notch signaling contributes to chemoresistance in osteosarcoma

Abstract The standard treatment for patients with newly diagnosed osteosarcoma (OS) consists of surgery in combination with multi-agent chemotherapy. However, the optimal treatment strategy for patients with refractory and/or metastatic disease is yet to be defined and continues to be a persistent challenge in osteosarcoma treatment. The high degree of genetic aberrations and tumor heterogeneity has impeded the identification and testing of new and effective therapeutic targets. Therefore, finding and characterizing cellular mechanisms, which contribute to OS chemoresistance could be one promising strategy for designing therapies that can change the outlook for patients with this disease. Due to the well-known role of unfolded protein response (UPR) in promoting chemoresistance in solid tumors our objective here is to examine how this promotes chemoresistance in patients with OS. Using in silico pathway analysis of gene expression datasets from patients with OS we found that protein processing in the ER was one of the pathways that was significantly enriched in OS tumors compared to normal tissue. We then examined whether the UPR sensors ATF6α, PERK and IRE-1α were also activated in OS cells in vitro. Using western blotting, qPCR and immunofluorescence we confirmed that all three UPR pathways were activated in human OS cell lines. However we found that only ATF6α activation significantly enhanced chemoresistance to cisplatin, irinotecan and combinatorial treatment with cisplatin and the mTOR inhibitor rapamycin. This occurred via inhibition of Bax activation, suppression of RHEB-mTOR and NOTCH signaling. Our findings highlight a novel mechanism of chemo-resistance in OS. Furthermore, retrospective analysis of banked OS patient samples for ATF6α expression followed by a preliminary multivariate analysis using Cox regression model showed that high levels of nuclear ATF6α, was an independent prognostic indicator while also taking into account the presence of metastases and tumor site. Moreover, we found that while 50% patients with high nuclear ATF6α levels had a poor histologic response to treatment only 32% patients with low nuclear ATF6α expression suggesting that ATF6α activation could be associated with resistance to chemotherapy and poor outcome for OS patients. Our findings emphasize a role for ATF6α as the nexus of a versatile signaling network that regulates pathways that are crucial for the pathogenesis and therapy resistance of osteosarcoma. Hence therapeutic targeting of the ATF6α pathway holds promise as an innovative and effective treatment strategy for OS. Citation Format: Suma Yarapureddy, Pooja Hingorani, Saravana Kumar, Omar Asad, Jazmine Abril, Veena Sharath, Paul Dickman, Aparna C. Sertil. Activating transcription factor-6α dependent regulation of Rheb-mTOR and Notch signaling contributes to chemoresistance in osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4505. doi:10.1158/1538-7445.AM2017-4505

MiR-140-5p attenuates chemotherapeutic drug-induced cell death by regulating autophagy through inositol 1,4,5-trisphosphate kinase 2 (IP3k2) in human osteosarcoma cells.

Acquisition of drug-resistant phenotypes is often associated with chemotherapy in osteosarcoma. A number of studies have demonstrated a critical role for autophagy in osteosarcoma development, therapy and drug resistance. However, the molecular mechanisms underlying the autophagy-mediated chemotherapy resistance of osteosarcoma cells remain largely unknown. In the present study, we determined the autophagy and microRNA-140 (miR-140-5p, miRBase ID: MIMAT0000431) expression induced by chemotherapeutic drugs in osteosarcoma cells. Then we determined the promotory role of miR-140-5p to the chemotherapy-induced autophagy. Our results demonstrated that miR-140-5p expression was highly induced during chemotherapy of osteosarcoma cells, and this was accompanied by up-regulated autophagy. The increased miR-140-5p expression levels up-regulated anticancer drug-induced autophagy in osteosarcoma cells and ameliorated the anticancer drug-induced cell proliferation and viability decrease. Importantly, miR-140-5p regulates this context-specific autophagy through its target, inositol 1,4,5-trisphosphate kinase 2 (IP3k2). Therefore, the results of the present study demonstrated that miR-140-5p mediated drug-resistance in osteosarcoma cells by inducing autophagy. The present study provides evidence of miRNA regulation of autophagy through modulation of IP3 signalling. The present study recognized a novel mechanism of chemoresistance in osteosarcoma cancers.

DCTPP1 attenuates the sensitivity of human gastric cancer cells to 5-fluorouracil by up-regulating MDR1 expression epigenetically.

Gastric cancer (GC) is among the most malignant cancers with high incidence and poor prognoses worldwide as well as in China. dCTP pyrophosphatase 1 (DCTPP1) is overexpressed in GC with a poor prognosis. Given chemotherapeutic drugs share similar structures with pyrimidine nucleotides, the role of DCTPP1 in affecting the drug sensitivity in GC remains unclear and is worthy of investigation. In the present study, we reported that DCTPP1-knockdown GC cell line BGC-823 exhibited more sensitivity to 5-fluorouracil (5-FU), demonstrated by the retardation of cell proliferation, the increase in cell apoptosis, cell cycle arrest at S phase and more DNA damages. Multidrug resistance 1 (MDR1) expression was unexpectedly down-regulated in DCTPP1-knockdown BGC-823 cells together with more intracellular 5-FU accumulation. This was in large achieved by the elevated methylation in promoter region of MDR1 gene. The intracellular 5-methyl-dCTP level increased in DCTPP1-knockdown BGC-823 cells as well. More significantly, the strong correlation of DCTPP1 and MDR1 expression was detectable in clinical GC samples. Our results thus imply a novel mechanism of chemoresistance mediated by the overexpression of DCTPP1 in GC. It is achieved partially through decreasing the concentration of intracellular 5-methyl-dCTP, which in turn results in promoter hypomethylation and hyper-expression of drug resistant gene MDR1. Our study suggests DCTPP1 as a potential indicative biomarker for the predication of chemoresistance in GC.

MiR-155 mediates drug resistance in osteosarcoma cells via inducing autophagy.

Frequent acquisition of drug resistance is often associated with the chemotherapy of malignant tumors, including osteosarcoma. A number of studies have demonstrated a critical role for autophagy in osteosarcoma development, therapy and drug resistance. However, the molecular mechanisms underlying the autophagy-mediated chemotherapy resistance of osteosarcoma cells remain largely unknown. In the present study, we determined the autophagy and microRNA-155 (miR-155) expression induced by chemotherapeutic drugs in osteosarcoma cells. Then we determined the promotory role of miR-155 to the chemotherapy-induced autophagy. Our results demonstrated that microRNA-155 (miR-155) expression was highly induced during chemotherapy of osteosarcoma cells, and this was accompanied by upregulated autophagy. The increased miR-155 expression levels upregulated anticancer drug-induced autophagy in osteosarcoma cells and ameliorated the anticancer drug-induced cell proliferation and viability decrease. Therefore, the results of the present study demonstrated that miR-155 mediated drug-resistance in osteosarcoma cells by inducing autophagy. The present study recognized a novel mechanism of chemoresistance in osteosarcoma cancers.

Abstract 705: Interfering with mesenchymal stem cell-induced chemoresistance via COX-1 and thromboxane synthase inhibition

Abstract Background: Environment-mediated resistance to chemotherapy is emerging as a cause of treatment failure. We showed that mesenchymal stem cells (MSCs) induce resistance to a broad spectrum of chemotherapies. Upon platinum stimulation, two unique polyunsaturated fatty acids (PIFAs), 12-oxo-5,8,10-heptadecatrienoic acid (KHT(n-6)) and hexadeca-4,7,10,13-tetraenoic acid (16:4(n-3)) are produced by MSCs, which, via a paracrine mechanism, induce chemoresistance in tumors. Aim: Here, we aim to prevent MSC-induced chemoresistance by blocking PIFA production. Method: Various mouse models were established in which recruitment of MSCs to tumors was mimicked by iv administration of MSCs. Furthermore, cultured MSCs were treated with various drugs in order to block their chemo-protective capacity. Conditioned media were subsequently analyzed in vivo. Results: Conditioned medium of platinum-stimulated, cultured MSCs induced chemoresistance in tumor-bearing mice. However, the capacity to secrete the chemo-protective PIFAs was only retained by mesenchymal cells with multi-lineage differentiation potential: MSCs and mouse embryonic fibroblasts (MEFs). More differentiated progeny from the mesenchymal lineage including 3T3 Fibroblasts, pre-adipocytes (3T3-L1), differentiated adipocytes, pre-osteoblasts (MC3T3) and differentiated osteoblasts were not capable of PIFA production upon platinum stimulation. Furthermore, this cytoprotective response was specific for multipotent cells from the mesenchymal lineage, since administration of hematopoietic stem cells did not influence the tumor response to chemotherapy. One of the identified PIFAs, KHT(n-6), is known to be a by-product of thromboxane A2 synthesis, which is a downstream product of the cyclooxygenase (COX)-1 and thromboxane synthase (TxS) pathway. Interestingly, conditioned media from MSCs pre-treated with SC-560, a highly selective COX-1 inhibitor, indomethacin, a relatively selective COX-1 inhibitor or one of two specific TxS inhibitors (ozagrel and furegrelate) did not induce chemoresistance in vivo. Of note, selective COX-2 inhibition in MSC by celecoxib did not affect their capacity to induce chemoresistance, suggestive of a specific COX-1/TxS-dependent PIFA production. When mice were treated with either indomethacin or ozagrel as single agents no anti-tumor effect was observed. However, combining these drugs with cisplatin in vivo had an additive anti-tumor effect compared to cisplatin alone. Conclusion: We show a novel mechanism of chemoresistance mediated by PIFA released from early, multipotent cells of the mesenchymal lineage. The production of these PIFAs is dependent on COX-1 and TxS, and blocking these enzymes enhanced the antitumor effects of cisplatin in vivo, making these enzymes drugable targets to prevent PIFA-induced chemoresistance. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 705. doi:10.1158/1538-7445.AM2011-705

Activation of the JNK pathway promotes phosphorylation and degradation of BimEL--a novel mechanism of chemoresistance in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemias (T-ALLs) are highly malignant tumors with 20% of patients continues to fail therapy, in part due to chemoresistance of T-ALL cells via largely unknown mechanisms. Here, we showed that lack of Bcl-2-interacting mediator of cell death (Bim)(EL) protein expression, a BH3-only member of the Bcl-2 family proteins, conferred resistance of a T-ALL cell line, Sup-T1, to etoposide-induced apoptosis. Overexpression of Bim(EL) significantly restored its sensitivity to etoposide-induced caspase activation and poly(ADP-ribose) polymerase cleavage. Surprisingly, we found that constitutive activation of the c-Jun N-terminal kinase (JNK) pathway in Sup-T1 cells promoted phosphorylation and degradation of Bim(EL) via the proteosome. Blocking with a proteosome inhibitor yielded an elevated level of Bim(EL) and accumulation of Bim(EL) species phosphorylated at Ser(69). Pretreatment of Sup-T1 cells with a specific JNK inhibitor, SP600125, also increased the Bim(EL) level and resensitized the cells to etoposide-induced apoptosis. Together, our findings suggest that the JNK activation status may correlate with the Bim(EL) level and in turn can control the sensitivity of T-ALL cells to chemotherapeutic agents.

Plasma membrane sequestration of apoptotic protease-activating factor-1 in human B-lymphoma cells: a novel mechanism of chemoresistance

AbstractBurkitt lymphoma (BL) is a highly aggressive B-cell neoplasm harboring chromosomal rearrangements of the c-myc oncogene. BL cells frequently resist apoptosis induction by chemotherapeutic agents; however, the mechanism of unresponsiveness has not been elucidated. Here, we show that cytochrome c fails to stimulate apoptosome formation and caspase activation in cytosolic extracts of human BL-derived cell lines, due to insufficient levels of apoptotic protease-activating factor-1 (Apaf-1). Enforced expression of Apaf-1 increased its concentration in the cytosolic compartment, restored cytochrome c-dependent caspase activation, and rendered the prototypic Raji BL cell line sensitive to etoposide- and staurosporine-induced apoptosis. Surprisingly, in nontransfected BL cells, the bulk of Apaf-1 was found to associate with discrete domains in the plasma membrane. Disruption of lipid raft domains or the actin cytoskeleton of Raji cells liberated Apaf-1 and restored sensitivity to cytochrome c–dependent apoptosis, indicating that constitutive Apaf-1 retained its ability to promote caspase activation. Moreover, disruption of lipid rafts sensitized BL cells to apoptosis induced by etoposide. Together, our findings suggest that ectopic (noncytosolic) localization of Apaf-1 may constitute a novel mechanism of chemoresistance in B lymphoma.