bluuebunny/crossref_metadata_2025_split huggingface dataset:
Abstract 4450: Identification of IGF1R as a responsible factor and a therapeutic target for overcoming acquired and intrinsic resistance to PI3K inhibitors.
Authors: Dan Shingo , Isoyama Sho , Nishimura Yumiko , Nakamura Naoki , Kajiwara Gensei , Tamaki Naomi , Okamura Mutsumi , Yamori Takao 
Published: August 2014

Abstract
The phosphatidylinositol 3-kinase (PI3K) pathway is frequently activated in human cancers. Therefore PI3K is thought to be a promising target for cancer therapy, and many compounds targeting PI3K have been developed and tested in clinical trials. Acquired resistance is a major obstacle for conventional cancer chemotherapy, and also for some of the targeted therapies approved to date. Long-term administration of protein tyrosine kinase inhibitors (TKIs), such as gefitinib and imatinib, gives rise to resistant cancer cells carrying a drug-resistant gatekeeper mutation in the kinase domain of the respective target genes, EGFR and BCR-ABL. As for the PI3K inhibitors (PI3Kis), little is known about their acquired resistance. To address this issue, we established four human cancer cell lines that exhibited resistance to ZSTK474, a PI3Ki we developed previously, after drug exposure for a period of more than 1-year in vitro. None of the PI3Ki-reistant cells, however, contained any mutation in the kinase domain of the PIK3CA gene. Instead, we found that insulin-like growth factor 1 receptor (IGF1R) was overexpressed in all four resistant cells. Furthermore, PI3Ki-naïve cancer cells expressing high levels of IGF1R also exhibited resistance to PI3Kis. Interestingly, IGF1R-TKIs strongly enhanced the efficacy of PI3Ki in these cells. Thus, we propose that IGF1R could serve as a biomarker to predict the inefficacy of PI3K inhibitors, and also could be a target for overcoming acquired and intrinsic resistance in IGF1R-overexpressing cancers.
Citation Format: Shingo Dan, Sho Isoyama, Yumiko Nishimura, Naoki Nakamura, Gensei Kajiwara, Naomi Tamaki, Mutsumi Okamura, Takao Yamori. Identification of IGF1R as a responsible factor and a therapeutic target for overcoming acquired and intrinsic resistance to PI3K inhibitors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4450. doi:10.1158/1538-7445.AM2013-4450
Abstract 4451: Long-term resistance to PI3K/mTOR inhibition requires increased expression of c-myc and YAP.
Authors: Muranen Taru E. , Coloff Jonathan , Selfors Laura , Bui Amy , Mills Gordon B. , Brugge Joan S. 
Published: August 2014

Abstract
We have shown that extracellular matrix (ECM) contact contributes to PI3K/mTOR inhibitor resistance, where drug treatment leads to cytostasis but not cell death in ECM-attached cells. These cells do undergo proliferation arrest and this may reflect the situation in vivo, where PI3K/mTOR inhibitor treatment initially leads to growth arrest of the tumor cells. However this is often followed by re-initiation of proliferation, leading to relapse. In this study we have investigated the underlying molecular mechanisms that mediate long-term resistance to PI3K/mTOR inhibitors by selecting for cancer cells that proliferate after chronic inhibitor exposure in 3D cell cultures. To assess the mechanism of resistance, we performed reverse phase protein and RNA-seq arrays to identify signaling pathways that were altered in proliferating drug resistant cells. The protein arrays revealed up-regulated levels of c-myc and the Hippo pathway effector, YAP, in the resistant cells, and introduction of exogenous c-myc and YAP into drug sensitive cells rendered them resistant. While expression of c-myc alone induced partial resistance, YAP was also required, as knock-down of endogenous YAP resulted in loss of resistance. These data suggest that c-myc alone is not sufficient for generating resistance to PI3K/mTOR inhibitors, but an additional driver is required. Since the Hippo pathway is another major growth-promoting pathway (in addition to mTOR), it is conceivable that YAP compensates for the loss of mTOR signaling, contributing to resistance. Our current efforts are aimed at elucidating the mechanism by which YAP and c-myc mediate drug resistance to PI3K/mTOR inhibitors. Preliminary data suggests that c-myc-dependent glutamine metabolism contributes to drug resistance, as inhibition of glutaminase prevents resistance.
Citation Format: Taru E. Muranen, Jonathan Coloff, Laura Selfors, Amy Bui, Gordon B. Mills, Joan S. Brugge. Long-term resistance to PI3K/mTOR inhibition requires increased expression of c-myc and YAP. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4451. doi:10.1158/1538-7445.AM2013-4451
Abstract 4452: p90RSK mediates resistance to PI3K-pathway inhibitors in breast cancer.
Authors: Serra Violeta , Eichhorn Pieter JA , García-García Celina , Ibrahim Yasir , Prudkin Ludmila , Rodríguez Olga , Marlow Sara , Prat Aleix , Hahn William C. , Baselga José 
Published: August 2014

Abstract
The PI3K signaling pathway regulates diverse cellular processes including proliferation, survival and metabolism and is aberrantly activated in human cancer. As such, numerous compounds targeting the PI3K pathway are currently being clinically evaluated for the treatment of cancer and they have shown some early indications of efficacy in breast cancer. However, resistance against these agents, both de novo and acquired, may ultimately limit the efficacy of these compounds. Here, we have taken a systematic functional approach to uncover potential mechanisms of resistance to PI3K inhibitors and have identified several genes whose expression promotes survival under conditions of PI3K/mTOR blockade, including the ribosomal S6 kinases RPS6KA2 (RSK3) and RPS6KA6 (RSK4). We demonstrate that overexpression of RSK3 or RSK4 supports proliferation upon PI3K inhibition both in vitro and in vivo, in part through the attenuation of an apoptotic response and upregulation of protein translation. The addition of MEK- or RSK-specific inhibitors can extinguish these resistance phenotypes, both in cells engineered to overexpress RSK and in breast cancer cells that have elevated levels of RSK activity. These observations provide a strong rationale for the combined use of RSK and PI3K pathway inhibitors to elicit favorable responses in breast cancer patients with activated RSK.
Citation Format: Violeta Serra, Pieter JA Eichhorn, Celina García-García, Yasir Ibrahim, Ludmila Prudkin, Olga Rodríguez, Sara Marlow, Aleix Prat, William C. Hahn, José Baselga. p90RSK mediates resistance to PI3K-pathway inhibitors in breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4452. doi:10.1158/1538-7445.AM2013-4452
Abstract 4463: Activation of FGFR signaling as a mechanism of acquired resistance to erlotinib in EGFR-mutant lung cancer associated with an EMT.
Authors: Ye Xiaofen , Yue Peng , Patel Rajesh , Modrusan Zora , Settleman Jeff , Ashkenazi Avi , Yauch Robert L. 
Published: August 2014

Abstract
Treatment of NSCLC patients harboring activating EGFR mutations with EGFR TKIs results in anti-tumor responses to therapy, however patients ultimately progress on therapy due to the acquisition of drug resistance. Known mechanisms of resistance include secondary mutations in the EGFR gene (EGFRT790M) or MET gene amplification, however the underlying mechanism of resistance remains to be elucidated in ∼40-45% of cases. Previous studies provide evidence for an epithelial-to-mesenchymal transition (EMT) in a subset of cases that is not associated with the known mechanisms of resistance. In this study, we identify 2 models of acquired resistance to erlotinib that are associated with an EMT phenotype and a dependence on autocrine FGF-FGFR signaling for resistance. Evidence for FGFR pathway activation in the erlotinib-resistant cell population included an increase in FGF2, FGFR1 and phospho-FRS2. Inhibition of FGFR signaling using a small molecule kinase inhibitor or FGFR1-Fc neutralization of FGFR1 ligands re-sensitized resistant cells to erlotinib. Re-sensitization was accompanied by an inhibition of downstream signaling. In contrast, inhibition of AXL, a kinase that has recently been identified as an EMT-associated driver of erlotinib resistance in some pre-clinical models, failed to re-sensitize erlotinib-resistant cells. Our findings are consistent with autocrine FGFR pathway activation, as FGF ligand neutralization in the absence of an exogenous source of ligand can re-sensitize cells to erlotinib. Finally, FGFR pathway inhibition suppressed the development of resistance to erlotinib in sensitive parental cells. These data indicate that FGFR activation could potentially serve as a mechanism of acquired resistance to erlotinib in cases associated with an EMT and suggest that combined inhibition of EGFR and FGFR signaling could be beneficial in treating such cases.
Citation Format: Xiaofen Ye, Peng Yue, Rajesh Patel, Zora Modrusan, Jeff Settleman, Avi Ashkenazi, Robert L. Yauch. Activation of FGFR signaling as a mechanism of acquired resistance to erlotinib in EGFR-mutant lung cancer associated with an EMT. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4463. doi:10.1158/1538-7445.AM2013-4463
Abstract 4464: Elucidation of crizotinib resistance in NCI-H3122 and strategies to circumvent bypass resistance.
Authors: Lee Nathan V. , Cao Joan , Scheffelin Timothy , Engstrom Lars , Huang Stephen , Lira Maruja , Garza Scott , Yuan Jing , Enyart Blake , Christensen James , Kan Julie 
Published: August 2014

Abstract
The Anaplastic Lymphoma Kinase (ALK) fusion proteins such as EML4-ALK act as oncogenic drivers in approximately 5-7% of non-small cell lung carcinomas (NSCLC). The rationale for targeting this kinase as a means of treatment has been validated by the clinical efficacy and subsequent approval of the ALK inhibitor, crizotinib (Xalkori ®). The overall response rate of 61% suggests potential intrinsic resistance to crizotinib. In addition, like many tyrosine kinase inhibitors, acquired resistance inevitably leads to treatment refractory cancers. To better understand resistance mechanisms (both intrinsic and acquired), and circumvent resistance to crizotinib, we developed in vitro resistance models through prolonged crizotinib exposure. We isolated resistance clones and characterization identified different resistance mechanisms, including pathway bypass as well as an ALK kinase mutation (G1269A), similar to those that have been reported from refractory patient samples. The majority of the resistance clones escaped crizotinib suppression via pathway bypass. In several resistance clones, simultaneous activation of EGFR and IGF1R receptors limited the efficacy of double combination strategies and required triple combinations. In addition, phospho-proteomic analysis revealed simultaneous activation of different receptor tyrosine kinases, suggesting that combination treatment with inhibitors of downstream mediators such as PI3K and MEK may be effective strategies.
Our resistance models demonstrate the heterogeneity of cancers and reveal the multiplicity of escape mechanisms. Our results provide support for the evaluation of combination therapy with downstream mediator inhibitors as a way to restore as well as enhance sensitivity to crizotinib.
Citation Format: Nathan V. Lee, Joan Cao, Timothy Scheffelin, Lars Engstrom, Stephen Huang, Maruja Lira, Scott Garza, Jing Yuan, Blake Enyart, James Christensen, Julie Kan. Elucidation of crizotinib resistance in NCI-H3122 and strategies to circumvent bypass resistance. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4464. doi:10.1158/1538-7445.AM2013-4464
Abstract 4472: PI3K pathway dependencies in endometrioid endometrial cancer.
Authors: Weigelt Britta , Warne Patricia H. , Lambros Maryou B. , Reis-Filho Jorge S. , Downward Julian 
Published: August 2014

Abstract
Background: Endometrioid endometrial cancers (EECs) frequently harbor coexisting mutations in PI3K pathway genes, including PTEN, PIK3CA, PIK3R1, and KRAS. We sought to determine the genetic determinants of PI3K pathway inhibitor response in EEC cells, and whether PTEN-mutant EEC cells rely on p110β signaling for survival. Methods: Twenty-four human EEC cell lines were characterized for their mutation profile using the Sequenom OncoCarta Panel v1.0 and Sanger sequencing for PTEN, PIK3CA, and PIK3R1 transcripts, and their protein and phospho-protein expression levels of PI3K and MAPK signaling pathway components. The cell line panel was treated with pan-class I PI3K, p110α and p110β isoform-specific, allosteric mTOR, mTOR kinase, dual PI3K/mTOR, MEK and RAF inhibitors, and the correlations between protein expression, gene mutations, and sensitivity to targeted therapeutics determined. RNA interference was employed to assess effects of KRAS silencing on EEC cells. Results: The prevalence of PI3K pathway mutations in the EEC cell line panel studied mirrored that reported for primary EECs. PI3K pathway activation as determined by levels of AKTSer473 phosphorylation was significantly associated with PTEN but not PIK3CA or KRAS mutation status. EEC cell lines harboring PIK3CA and PTEN mutations were selectively sensitive to the pan-class I PI3K inhibitor GDC-0941 and allosteric mTOR inhibitor Temsirolimus, respectively. Subsets of EEC cells with concurrent PIK3CA and/or PTEN and KRAS mutations were sensitive to PI3K pathway inhibition. Only 2/6 KRAS-mutant EEC cell lines showed response to MEK inhibition, and KRAS siRNA silencing did not induce apoptosis in KRAS-mutant EEC cells. EEC cell lines harboring PTEN mutations were resistant to the p110β inhibitors GSK2636771 and AZD6482, and only combination with the p110α selective inhibitor A66 resulted in a decrease in cell viability. Conclusions: Our findings provide evidence to suggest that selective pan-PI3K and mTOR inhibition in EEC cells may be most effective in PIK3CA- and PTEN-mutant cancers, respectively, and that these PI3K inhibitors may even be effective in a subset of EECs concurrently harboring KRAS mutations. Our results further demonstrate that p110β inhibition alone is not sufficient to sensitize PTEN-mutant EEC cells, suggesting that combination with other targeted agents may be required to increase efficacy.
Citation Format: Britta Weigelt, Patricia H. Warne, Maryou B. Lambros, Jorge S. Reis-Filho, Julian Downward. PI3K pathway dependencies in endometrioid endometrial cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4472. doi:10.1158/1538-7445.AM2013-4472
Abstract 4474: Suppression of gefitinib-resistant human lung cancer cells by indolizino[6,7-b]indole derivatives.
Authors: Chen Chi-Wei , Tala Satishkumar , Su Tsann-Long , Lee Te-Chang 
Published: August 2014

Abstract
According to the most prevalent, poor prognosis, and lowest 5 year survival rate, patients with non-small cell lung cancer (NSCLC) are one of the most common issues in global health problem. Although tyrosine receptor inhibitors (TKI), cetuximab, erlotinib, and gefitinib, which target epidermal growth factor receptor (EGFR), are only effective in certain subpopulations, TKI resistance is developed after a median of 10 to 14 months via acquisition of second mutation as well as several other mechanisms. Developing therapeutic agent against TKI resistance is of critical and essential. In this study, we demonstrated that the derivatives of 1,2-bis-hydroxy- indolizino[6,7-b]indiole diols, a novel class of DNA crosslinking agent, effectively kill NSCLC cell lines including PC9 (exon 19 deletion), PC9/gefb4 (exon 19 deletion and resistant to gefitinib), CL100 (exon 19 deletion), and CL97 (exon 19 deletion and T790M). Our results also showed that BO-1922, one of derivatives, was almost equally effective in suppression the growth of various H1299 cell lines which ectopically expressed wild type or a variety of mutant EGFR (such as including L858R, exon 19 deletion, L858R/T790M, and exon 19 deletion/T790M, respectively). The selected derivatives, BO-1922 and BO-1978, were shown to induce DNA double-strand crosslink by modified comet assay and modulate the expression of DNA repair proteins. By aid of flow cytometric assay, we found that exposure of PC9 and PC9/gefb4 cells to BO-1922 resulted in accumulation of cells at the G2/M phase, while BO-1978 causes cell cycle delay at the G1 and S phase. Furthermore, BO-1922 and BO-1978 given at 25 mg/kg significantly suppressed the growth of PC9/gefb4 xenograft tumors. Our present results revealed that BO-1922 and BO-1978 may have potential against NSCLC with EGFR mutations and gefitinib resistance.
Citation Format: Chi-Wei Chen, Satishkumar Tala, Tsann-Long Su, Te-Chang Lee. Suppression of gefitinib-resistant human lung cancer cells by indolizino[6,7-b]indole derivatives. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4474. doi:10.1158/1538-7445.AM2013-4474
Abstract 4480: New approaches to changing an enzyme into a cytotoxic agent: A novel way to stimulate DNA cleavage by topoisomerase II.
Authors: Rogojina Anna , Nitiss Karin C. , Nitiss John L. 
Published: August 2014

Abstract
Topoisomerase poisons are important anti-cancer drugs, and include agents such as etoposide and doxorubicin that target eukaryotic topoisomerase II. Most topoisomerase II poisons act as interstitial inhibitors. This mode of inhibition depends on the coordination of the enzyme and DNA substrate to form a drug binding site. While recent structural studies have localized topoisomerase II poisons to the drug/DNA interface, our understanding of the mechanism of enzyme inhibition remains incomplete. We have combined genetic, biochemical, and structural approaches to identify regions of topoisomerase II that are important for drug action and identified sites near the active site tyrosine that contribute to drug sensitivity. Interestingly, we also identified amino acids near the C-terminal dimerization domain that also control DNA cleavage. Mutations in the C-terminal dimerization domain exhibit several unique characteristics. Importantly, we identified two mutants in the dimerization domain of yeast Top2 that could not be viably expressed in yeast mutants defective in double strand break repair. Expression of these mutants in repair proficient strains led to elevated rates of homologous recombination, suggesting that these mutant proteins are able to generate DNA damage even in the absence of topoisomerase II targeting agents. We purified the mutant proteins and demonstrated that they possess elevated levels of drug independent DNA cleavage, compared to wild type proteins. Elevated cleavage was only seen in the presence of ATP, indicating that the mutant proteins are likely defective in DNA religation at a specific step in the catalytic cycle, and that the C-terminal dimerization and DNA religation occurs by a coordinated process. Finally, we have also shown that homologous mutations in human topoisomerase II alpha generate effects similar to those described for the yeast protein. Taken together, these results suggest that it may be possible to identify potent allosteric inhibitors of topoisomerase II directed against the C-terminal catalytic domain of the protein. These hypothetical inhibitors may have unique therapeutic potential, especially because they represent an approach for isoform specific topoisomerase poisons.
Citation Format: Anna Rogojina, Karin C. Nitiss, John L. Nitiss. New approaches to changing an enzyme into a cytotoxic agent: A novel way to stimulate DNA cleavage by topoisomerase II. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4480. doi:10.1158/1538-7445.AM2013-4480
Abstract 4490: Triapine sensitizes chemoresistant ovarian cancer cells to platinum therapy.
Authors: Ratner Elena S. , Whicker Margaret , Lin Z. Ping , Sartorelli Alan C. 
Published: August 2014

Abstract
Objectives:
Epithelial ovarian cancer (EOC) is the second most common female pelvic reproductive organ cancer in the United States, and carries the highest mortality in this category in the Western world. The progression free survival and overall survival depend greatly on tumor sensitivity to a platinum chemotherapy. Once platinum resistance is encountered, response rates of only 6-30% are achieved. Triapine, a novel small-molecule drug developed in our laboratory, potently inhibits the activity of ribonucleotide reductase involved in the key step of DNA synthesis and replication. Given that triapine caused profound disruption of dNTP levels and S phase progression, we examined the effects of triapine on the repair of replication-associated DSBs and on the sensitivity of platinum resistant EOC to DNA damaging and platinum therapy.
Methods:
Cell sensitivity to varying ratios of treating drug combinations (triapine/6-thio-guanine alone, triapine/6-thioguanine with cisplatin, carboplatin, doxorubicin, or paclitaxel) was carried out by clonogenic survival assays using multiple EOC cells lines (A2780, CP70, CAOV-3, IGROV-1, BG-1, PEO1, PEO4, SKOV-3). Colonies were stained and counted to determine % survival. DNA replication was determined by EdU incorporation into DNA using flow cytometry and confocal microscopy.
Results:
Treatment with triapine leads to synergistic sensitization of BRCA wild-type EOC cells to platinum drugs. The degree of sensitization by triapine is more pronounced toward the lower concentrations of platinum drugs, at which DNA replication is still ongoing. Platinum drugs induce DNA double strand breaks (DSBs) and Rad51 foci in BRCA wild type EOC cells. Triapine attenuates formation of Rad51 foci, a marker of DSB repair, in these cells. For EOC cells that are highly platinum resistant, combination of triapine and 6-thioguanine is required to achieve significant sensitization to platinum drugs.
Conclusions:
Platinum drugs induce replication-associated DSBs and Rad51-dependent repair in BRCA wild-type EOC cells. Triapine inhibits Rad51-dependent repair of DSBs and therefore sensitizes BRCA wild-type EOC cells to platinum drugs. The mechanism by which 6-thioguanine enhances the effects of triapine is currently being investigated. Our findings indicate for the first time that triapine and 6-thioguanine can be used in combination with platinum agents to target BRCA wild-type and platinum-resistant EOC.
Citation Format: Elena S. Ratner, Margaret Whicker, Z. Ping Lin, Alan C. Sartorelli. Triapine sensitizes chemoresistant ovarian cancer cells to platinum therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4490. doi:10.1158/1538-7445.AM2013-4490