Impact of chromatin context on Cas9-induced DNA double-strand break repair pathway balance

DNA double-strand break (DSB) repair is mediated by multiple pathways. It is thought that the local chromatin context affects the pathway choice, but the underlying principles are poorly understood. Using a multiplexed reporter assay in combination with Cas9 cutting, we systematically measure the relative activities of three DSB repair pathways as a function of chromatin context in >1,000 genomic locations. This reveals that non-homologous end-joining (NHEJ) is broadly biased toward euchromatin, while the contribution of microhomology-mediated end-joining (MMEJ) is higher in specific heterochromatin contexts. In H3K27me3-marked heterochromatin, inhibition of the H3K27 methyltransferase EZH2 reverts the balance toward NHEJ. Single-stranded template repair (SSTR), often used for precise CRISPR editing, competes with MMEJ and is moderately linked to chromatin context. These results provide insight into the impact of chromatin on DSB repair pathway balance and guidance for the design of Cas9-mediated genome editing experiments.

Correction to: A role for the unfolded protein response stress sensor ERN1 in regulating the response to MEK inhibitors in KRAS mutant colon cancers

An amendment to this paper has been published and can be accessed via the original article.

The RECQL helicase prevents replication fork collapse during replication stress

Most tumors lack the G1/S phase checkpoint and are insensitive to antigrowth signals. Loss of G1/S control can severely perturb DNA replication as revealed by slow replication fork progression and frequent replication fork stalling. Cancer cells may thus rely on specific pathways that mitigate the deleterious consequences of replication stress. To identify vulnerabilities of cells suffering from replication stress, we performed an shRNA-based genetic screen. We report that the RECQL helicase is specifically essential in replication stress conditions and protects stalled replication forks against MRE11-dependent double strand break (DSB) formation. In line with these findings, knockdown of RECQL in different cancer cells increased the level of DNA DSBs. Thus, RECQL plays a critical role in sustaining DNA synthesis under conditions of replication stress and as such may represent a target for cancer therapy.

CDK12 inhibition mediates DNA damage and is synergistic with sorafenib treatment in hepatocellular carcinoma

OBJECTIVES

Hepatocellular carcinoma (HCC) is one of the most frequent malignancies and a major leading cause of cancer-related deaths worldwide. Several therapeutic options like sorafenib and regorafenib provide only modest survival benefit to patients with HCC. This study aims to identify novel druggable candidate genes for patients with HCC.

DESIGN

A non-biased CRISPR (clustered regularly interspaced short palindromic repeats) loss-of-function genetic screen targeting all known human kinases was performed to identify vulnerabilities of HCC cells. Whole-transcriptome sequencing (RNA-Seq) and bioinformatics analyses were performed to explore the mechanisms of the action of a cyclin-dependent kinase 12 (CDK12) inhibitor in HCC cells. Multiple in vitro and in vivo assays were used to study the synergistic effects of the combination of CDK12 inhibition and sorafenib.

RESULTS

We identify CDK12 as critically required for most HCC cell lines. Suppression of CDK12 using short hairpin RNAs (shRNAs) or its inhibition by the covalent small molecule inhibitor THZ531 leads to robust proliferation inhibition. THZ531 preferentially suppresses the expression of DNA repair-related genes and induces strong DNA damage response in HCC cell lines. The combination of THZ531 and sorafenib shows striking synergy by inducing apoptosis or senescence in HCC cells. The synergy between THZ531 and sorafenib may derive from the notion that THZ531 impairs the adaptive responses of HCC cells induced by sorafenib treatment.

CONCLUSION

Our data highlight the potential of CDK12 as a drug target for patients with HCC. The striking synergy of THZ531 and sorafenib suggests a potential combination therapy for this difficult to treat cancer.

Neutrophils Kill Antibody-Opsonized Cancer Cells by Trogoptosis

Destruction of cancer cells by therapeutic antibodies occurs, at least in part, through antibody-dependent cellular cytotoxicity (ADCC), and this can be mediated by various Fc-receptor-expressing immune cells, including neutrophils. However, the mechanism(s) by which neutrophils kill antibody-opsonized cancer cells has not been established. Here, we demonstrate that neutrophils can exert a mode of destruction of cancer cells, which involves antibody-mediated trogocytosis by neutrophils. Intimately associated with this is an active mechanical disruption of the cancer cell plasma membrane, leading to a lytic (i.e., necrotic) type of cancer cell death. Furthermore, this mode of destruction of antibody-opsonized cancer cells by neutrophils is potentiated by CD47-SIRPα checkpoint blockade. Collectively, these findings show that neutrophil ADCC toward cancer cells occurs by a mechanism of cytotoxicity called trogoptosis, which can be further improved by targeting CD47-SIRPα interactions.

High-throughput compound screen reveals mTOR inhibitors as potential therapeutics to reduce (auto)antibody production by human plasma cells

Antibody production by the B cell compartment is a crucial part of the adaptive immune response. Dysregulated antibody production in the form of autoantibodies can cause autoimmune disease. To date, B‐cell depletion with anti‐CD20 antibodies is commonly applied in autoimmunity, but pre‐existing plasma cells are not eliminated in this way. Alternative ways of more selective inhibition of antibody production would add to the treatment of these autoimmune diseases. To explore novel therapeutic targets in signaling pathways essential for plasmablast formation and/or immunoglobulin production, we performed a compound screen of almost 200 protein kinase inhibitors in a robust B‐cell differentiation culture system. This study yielded 35 small cell‐permeable compounds with a reproducible inhibitory effect on B‐cell activation and plasmablast formation, among which was the clinically applied mammalian target of rapamycin (mTOR) inhibitor rapamycin. Two additional compounds targeting the phosphoinositide 3‐kinase‐AKT‐mTOR pathway (BKM120 and WYE‐354) did not affect proliferation and plasmablast formation, but specifically reduced the immunoglobulin production. With this compound screen we successfully applied a method to investigate therapeutic targets for B‐cell differentiation and identified compounds in the phosphoinositide 3‐kinase‐AKT‐mTOR pathway that could specifically inhibit immunoglobulin production only. These drugs may well be explored to be of value in current B‐cell‐depleting treatment regimens in autoimmune disorders.

Inducing and exploiting vulnerabilities for the treatment of liver cancer

Liver cancer remains difficult to treat due to a paucity of drugs that target critical dependencies^1,2 and broad spectrum kinase inhibitors like sorafenib provide only modest benefit to hepatocellular carcinoma (HCC) patients³. Induction of senescence may represent a promising strategy for the treatment of cancer, especially when such pro-senescence therapy is combined with a second drug that selectively eliminates senescent cancer cells (senolysis)^4,5. Through a kinome-focused genetic screen, we report here that pharmacological inhibition of the DNA replication kinase CDC7 induces senescence selectively in TP53 mutant liver cancer cells. A follow-up chemical screen identified the anti-depressant sertraline as an agent that kills HCC cells rendered senescent by CDC7 inhibition. Sertraline supressed mTOR signalling, and selective drugs targeting this pathway were highly effective in causing apoptotic cell death of CDC7 inhibitor-treated HCC cells. Mechanistically, we report that the feedback re-activation of mTOR signalling following its inhibition⁶ is blocked in CDC7-inhibitor treated cells, leading to sustained mTOR inhibition and cell death. Using multiple in vivo liver cancer models, we show that combination of CDC7 and mTOR inhibitors results in dramatic tumour growth inhibition. More generally, our data indicate that exploiting an induced vulnerability could be an effective treatment of liver cancer.

Inhibition of Ataxia-Telangiectasia Mutated and RAD3-Related (ATR) Overcomes Oxaliplatin Resistance and Promotes Antitumor Immunity in Colorectal Cancer

Although many patients with colorectal cancer initially respond to the chemotherapeutic agent oxaliplatin, acquired resistance to this treatment remains a major challenge to the long-term management of this disease. To identify molecular targets of oxaliplatin resistance in colorectal cancer, we performed an shRNA-based loss-of-function genetic screen using a kinome library. We found that silencing of ataxia-telangiectasia mutated and RAD3-related (ATR), a serine/threonine protein kinase involved in the response to DNA stress, restored oxaliplatin sensitivity in a cellular model of oxaliplatin resistance. Combined application of the ATR inhibitor VE-822 and oxaliplatin resulted in strong synergistic effects in six different colorectal cancer cell lines and their oxaliplatin-resistant subclones, promoted DNA single- and double-strand break formation, growth arrest, and apoptosis. This treatment also increased replicative stress, cytoplasmic DNA, and signals related to immunogenic cell death such as calreticulin exposure and HMGB1 and ATP release. In a syngeneic colorectal cancer mouse model, combined administration of VE-822 and oxaliplatin significantly increased survival by promoting antitumor T-cell responses. Finally, a DNA repair gene signature discriminated sensitive from drug-resistant patients with colorectal cancer. Overall, our results highlight the potential of ATR inhibition combined with oxaliplatin to sensitize cells to chemotherapy as a therapeutic option for patients with colorectal cancer. SIGNIFICANCE: These findings demonstrate that resistance to oxaliplatin in colorectal cancer cells can be overcome with inhibitors of ATR and that combined treatment with both agents exerts synergistic antitumor effects.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/11/2933/F1.large.jpg.

Ezh2 inhibition in Kras-driven lung cancer amplifies inflammation and associated vulnerabilities

Kras-driven non–small-cell-lung cancers (NSCLCs) are a leading cause of death with limited therapeutic options. Serresi et al. show that inhibiting Ezh2 in orthotopic KrasG12D-driven NSCLC unleashes an inflammatory response rewiring tumor progression and amplifying associated vulnerabilities that could be therapeutically exploited.

Kras-driven non–small-cell lung cancers (NSCLCs) are a leading cause of death with limited therapeutic options. Many NSCLCs exhibit high levels of Ezh2, the enzymatic subunit of polycomb repressive complex 2 (PRC2). We tested Ezh2 inhibitors as single agents or before chemotherapy in mice with orthotopic Kras-driven NSCLC grafts, which homogeneously express Ezh2. These tumors display sensitivity to EZH2 inhibition by GSK126 but also amplify an inflammatory program involving signaling through NF-κB and genes residing in PRC2-regulated chromatin. During this process, tumor cells overcome GSK126 antiproliferative effects. We identified oncogenes that may mediate progression through an in vivo RNAi screen aimed at targets of PRC2/NF-κB. An in vitro compound screening linked GSK126-driven inflammation and therapeutic vulnerability in human cells to regulation of RNA synthesis and proteostasis. Interestingly, GSK126-treated NSCLCs in vivo also showed an enhanced response to a combination of nimesulide and bortezomib. Thus, Ezh2 inhibition may restrict cell proliferation and promote defined adaptive responses. Targeting these responses potentially improves outcomes in Kras-driven NSCLCs.

A role for the unfolded protein response stress sensor ERN1 in regulating the response to MEK inhibitors in KRAS mutant colon cancers

Background

Mutations in KRAS are frequent in human cancer, yet effective targeted therapeutics for these cancers are still lacking. Attempts to drug the MEK kinases downstream of KRAS have had limited success in clinical trials. Understanding the specific genomic vulnerabilities of KRAS-driven cancers may uncover novel patient-tailored treatment options.

Methods

We first searched for synthetic lethal (SL) genetic interactions with mutant RAS in yeast with the ultimate aim to identify novel cancer-specific targets for therapy. Our method used selective ploidy ablation, which enables replication of cancer-specific gene expression changes in the yeast gene disruption library. Second, we used a genome-wide CRISPR/Cas9-based genetic screen in KRAS mutant human colon cancer cells to understand the mechanistic connection between the synthetic lethal interaction discovered in yeast and downstream RAS signaling in human cells.

Results

We identify loss of the endoplasmic reticulum (ER) stress sensor IRE1 as synthetic lethal with activated RAS mutants in yeast. In KRAS mutant colorectal cancer cell lines, genetic ablation of the human ortholog of IRE1, ERN1, does not affect growth but sensitizes to MEK inhibition. However, an ERN1 kinase inhibitor failed to show synergy with MEK inhibition, suggesting that a non-kinase function of ERN1 confers MEK inhibitor resistance. To investigate how ERN1 modulates MEK inhibitor responses, we performed genetic screens in ERN1 knockout KRAS mutant colon cancer cells to identify genes whose inactivation confers resistance to MEK inhibition. This genetic screen identified multiple negative regulators of JUN N-terminal kinase (JNK) /JUN signaling. Consistently, compounds targeting JNK/MAPK8 or TAK1/MAP3K7, which relay signals from ERN1 to JUN, display synergy with MEK inhibition.

Conclusions

We identify the ERN1-JNK-JUN pathway as a novel regulator of MEK inhibitor response in KRAS mutant colon cancer. The notion that multiple signaling pathways can activate JUN may explain why KRAS mutant tumor cells are traditionally seen as highly refractory to MEK inhibitor therapy. Our findings emphasize the need for the development of new therapeutics targeting JUN activating kinases, TAK1 and JNK, to sensitize KRAS mutant cancer cells to MEK inhibitors.

Electronic supplementary material

The online version of this article (10.1186/s13073-018-0600-z) contains supplementary material, which is available to authorized users.

High-Throughput Functional Genetic and Compound Screens Identify Targets for Senescence Induction in Cancer

Senescence is a proliferation arrest that can result from a variety of stresses. Cancer cells can also undergo senescence, but the stresses that provoke cancer cells to undergo senescence are unclear. Here, we use both functional genetic and compound screens in cancer cells harboring a reporter that is activated during senescence to find targets that induce senescence. We show that suppression of the SWI/SNF component SMARCB1 induces senescence in melanoma through strong activation of the MAP kinase pathway. From the compound screen, we identified multiple aurora kinase inhibitors as potent inducers of senescence in RAS mutant lung cancer. Senescent melanoma and lung cancer cells acquire sensitivity to the BCL2 family inhibitor ABT263. We propose a one-two punch approach for the treatment of cancer in which a drug is first used to induce senescence in cancer cells and a second drug is then used to kill senescent cancer cells.

Integrative Modeling Identifies Key Determinants of Inhibitor Sensitivity in Breast Cancer Cell Lines

Cancer cell lines differ greatly in their sensitivity to anticancer drugs as a result of different oncogenic drivers and drug resistance mechanisms operating in each cell line. Although many of these mechanisms have been discovered, it remains a challenge to understand how they interact to render an individual cell line sensitive or resistant to a particular drug. To better understand this variability, we profiled a panel of 30 breast cancer cell lines in the absence of drugs for their mutations, copy number aberrations, mRNA, protein expression and protein phosphorylation, and for response to seven different kinase inhibitors. We then constructed a knowledge-based, Bayesian computational model that integrates these data types and estimates the relative contribution of various drug sensitivity mechanisms. The resulting model of regulatory signaling explained the majority of the variability observed in drug response. The model also identified cell lines with an unexplained response, and for these we searched for novel explanatory factors. Among others, we found that 4E-BP1 protein expression, and not just the extent of phosphorylation, was a determinant of mTOR inhibitor sensitivity. We validated this finding experimentally and found that overexpression of 4E-BP1 in cell lines that normally possess low levels of this protein is sufficient to increase mTOR inhibitor sensitivity. Taken together, our work demonstrates that combining experimental characterization with integrative modeling can be used to systematically test and extend our understanding of the variability in anticancer drug response.Significance: By estimating how different oncogenic mutations and drug resistance mechanisms affect the response of cancer cells to kinase inhibitors, we can better understand and ultimately predict response to these anticancer drugs.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/15/4396/F1.large.jpg Cancer Res; 78(15); 4396-410. ©2018 AACR.

ARID1A mutation sensitizes most ovarian clear cell carcinomas to BET inhibitors

Current treatment for advanced stage ovarian clear cell cancer is severely hampered by a lack of effective systemic therapy options, leading to a poor outlook for these patients. Sequencing studies revealed that ARID1A is mutated in over 50% of ovarian clear cell carcinomas. To search for a rational approach to target ovarian clear cell cancers with ARID1A mutations, we performed kinome-centered lethality screens in a large panel of ovarian clear cell carcinoma cell lines. Using the largest OCCC cell line panel established to date, we show here that BRD2 inhibition is predominantly lethal in ARID1A mutated ovarian clear cell cancer cells. Importantly, small molecule inhibitors of the BET (bromodomain and extra terminal domain) family of proteins, to which BRD2 belongs, specifically inhibit proliferation of ARID1A mutated cell lines, both in vitro and in ovarian clear cell cancer xenografts and patient-derived xenograft models. BET inhibitors cause a reduction in the expression of multiple SWI/SNF members including ARID1B, providing a potential explanation for the observed lethal interaction with ARID1A loss. Our data indicate that BET inhibition may represent a novel treatment strategy for a subset of ARID1A mutated ovarian clear cell carcinomas.

PIM Kinases Are a Potential Prognostic Biomarker and Therapeutic Target in Neuroblastoma

The majority of high-risk neuroblastoma patients are refractory to, or relapse on, current treatment regimens, resulting in 5-year survival rates of less than 50%. This emphasizes the urgent need to identify novel therapeutic targets. Here, we report that high PIM kinase expression is correlated with poor overall survival. Treatment of neuroblastoma cell lines with the pan-PIM inhibitors AZD1208 or PIM-447 suppressed proliferation through inhibition of mTOR signaling. In a panel of neuroblastoma cell lines, we observed a marked binary response to PIM inhibition, suggesting that specific genetic lesions control responses to PIM inhibition. Using a genome-wide CRISPR-Cas9 genetic screen, we identified NF1 loss as the major resistance mechanism to PIM kinase inhibitors. Treatment with AZD1208 impaired the growth of NF1 wild-type xenografts, while NF1 knockout cells were insensitive. Thus, our data indicate that PIM inhibition may be a novel targeted therapy in NF1 wild-type neuroblastoma. Mol Cancer Ther; 17(4); 849-57. ©2018 AACR.

Intrinsic resistance to PIM kinase inhibition in AML through p38α-mediated feedback activation of mTOR signaling

Although conventional therapies for acute myeloid leukemia (AML) and diffuse large B-cell lymphoma (DLBCL) are effective in inducing remission, many patients relapse upon treatment. Hence, there is an urgent need for novel therapies. PIM kinases are often overexpressed in AML and DLBCL and are therefore an attractive therapeutic target. However, in vitro experiments have demonstrated that intrinsic resistance to PIM inhibition is common. It is therefore likely that only a minority of patients will benefit from single agent PIM inhibitor treatment. In this study, we performed an shRNA-based genetic screen to identify kinases whose suppression is synergistic with PIM inhibition. Here, we report that suppression of p38α (MAPK14) is synthetic lethal with the PIM kinase inhibitor AZD1208. PIM inhibition elevates reactive oxygen species (ROS) levels, which subsequently activates p38α and downstream AKT/mTOR signaling. We found that p38α inhibitors sensitize hematological tumor cell lines to AZD1208 treatment in vitro and in vivo. These results were validated in ex vivo patient-derived AML cells. Our findings provide mechanistic and translational evidence supporting the rationale to test a combination of p38α and PIM inhibitors in clinical trials for AML and DLBCL.

Abstract 3380: Synthetic lethal interaction between ARID1A mutation and BET bromodomain inhibition in ovarian clear cell carcinoma

Introduction:

Current treatment for advanced stage ovarian clear cell cancer is severely hampered by a lack of effective systemic therapy options, leading to a poor outlook for these patients. Given that ARID1A is inactivated by mutation in over 50% of ovarian clear cell carcinomas, we pursued an ARID1A synthetic lethal screening strategy to identify druggable targets in OCCC.

Experimental procedures:

We performed synthetic lethal kinome short hairpin (shRNA) screens in a large panel (n=14) of OCCC cell lines having different ARID1A mutation status. Hit validation was performed with isogenic ARID1A ko cell line pairs and in (patient-derived) xenograft mouse models.

Summary of the data:

We show here that BRD2 inhibition is synthetic lethal with ARID1A mutation in ovarian clear cell cancer cells. Importantly, inhibiting the BET family of proteins, to which BRD2 belongs, with small molecules specifically inhibits proliferation of ARID1A mutated cell lines both in vitro and in ovarian clear cell cancer xenografts and patient-derived xenograft models. We demonstrate that ARID1A loss leads to upregulation of the WNT ligand WNT10B, possibly causing a WNT dependency in the ARID1A mutant lines. BET inhibitors cause a reduction in WNT10B expression and WNT target genes such as MYC, JUN and WISP1, providing a potential explanation for the observed synthetic lethal interaction with ARID1A loss.

Conclusions:

Our study uncovered a new synthetic lethal interaction between ARID1A mutation and BET bromodomain inhibition, suggesting a new treatment strategy for ARID1A mutant ovarian clear cell carcinomas.

Citation Format: Katrien Berns, Joseph J. Caumanns, E Marielle Hijmans, Annemiek Gennissen, Bastiaan Evers, Bea A. Wisman, Gert Jan Meersema, Cor Lieftink, Roderick L. Beijersbergen, Hiroaki Itamochi, Ate G. van der Zee, Steven de Jong, René Bernards. Synthetic lethal interaction between ARID1A mutation and BET bromodomain inhibition in ovarian clear cell carcinoma [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 3380. doi:10.1158/1538-7445.AM2017-3380

Synthetic Lethality in Cancer Therapeutics

Treatment with targeted drugs has primarily focused on the genes and pathways that are mutated in cancer, which severely limits the repertoire of drug targets. Synthetic lethality exploits the notion that the presence of a mutation in a cancer gene is often associated with a new vulnerability that can be targeted therapeutically, thus greatly expanding the arsenal of potential drug targets. Here we discuss both the experimental and the computational biology tools that can be used to identify synthetic lethal interactions. We also discuss strategies for using synthetic lethality to discover new drug targets and in the rational design of more potent drug combinations. We review the progress made and future opportunities offered by synthetic lethal approaches to treating cancer more effectively.

A Functional Genetic Screen Identifies the Phosphoinositide 3-kinase Pathway as a Determinant of Resistance to Fibroblast Growth Factor Receptor Inhibitors in FGFR Mutant Urothelial Cell Carcinoma

Activating mutations and translocations of the FGFR3 gene are commonly seen in urothelial cell carcinoma (UCC) of the bladder and urinary tract. Several fibroblast growth factor receptor (FGFR) inhibitors are currently in clinical development and response rates appear promising for advanced UCC. A common problem with targeted therapeutics is intrinsic or acquired resistance of the cancer cells. To find potential drug targets that can act synergistically with FGFR inhibition, we performed a synthetic lethality screen for the FGFR inhibitor AZD4547 using a short hairpin RNA library targeting the human kinome in the UCC cell line RT112 (FGFR3-TACC3 translocation). We identified multiple members of the phosphoinositide 3-kinase (PI3K) pathway and found that inhibition of PIK3CA acts synergistically with FGFR inhibitors. The PI3K inhibitor BKM120 acted synergistically with inhibition of FGFR in multiple UCC and lung cancer cell lines having FGFR mutations. Consistently, we observed an elevated PI3K-protein kinase B pathway activity resulting from epidermal growth factor receptor or Erb-B2 receptor tyrosine kinase 3 reactivation caused by FGFR inhibition as the underlying molecular mechanism of the synergy. Our data show that feedback pathways activated by FGFR inhibition converge on the PI3K pathway. These findings provide a strong rationale to test FGFR inhibitors in combination with PI3K inhibitors in cancers harboring genetic activation of FGFR genes.

Integrated in vivo genetic and pharmacologic screening identifies co-inhibition of EGRF and ROCK as a potential treatment regimen for triple-negative breast cancer

Breast cancer is the second most common cause of cancer-related deaths worldwide among women. Despite several therapeutic options, 15% of breast cancer patients succumb to the disease owing to tumor relapse and acquired therapy resistance. Particularly in triple-negative breast cancer (TNBC), developing effective treatments remains challenging owing to the lack of a common vulnerability that can be exploited by targeted approaches. We have previously shown that tumor cells have different requirements for growth in vivo than in vitro. Therefore, to discover novel drug targets for TNBC, we performed parallel in vivo and in vitro genetic shRNA dropout screens. We identified several potential drug targets that were required for tumor growth in vivo to a greater extent than in vitro. By combining pharmacologic inhibitors acting on a subset of these candidates, we identified a synergistic interaction between EGFR and ROCK inhibitors. This combination effectively reduced TNBC cell growth by inducing cell cycle arrest. These results illustrate the power of in vivo genetic screens and warrant further validation of EGFR and ROCK as combined pharmacologic targets for breast cancer.

Pooled shRNA Screening in Mammalian Cells as a Functional Genomic Discovery Platform

Functional genomic screens using shRNA technology are a great tool in biomedical research. As more labs gain access to the necessary reagents and technology to perform such screens, some may lack in-depth knowledge on the difficulties often encountered. With this protocol, we aim to point out the most important caveats of performing shRNA based screens and provide a streamlined workflow that can be easily adapted to meet the specific needs of any particular screening project.

Abstract B2-37: Understanding the variability in drug response in a panel of breast cancer cell lines using computational models

Cancer cell lines differ widely in their sensitivity to anticancer drugs. While many oncogenic drivers and drug resistance mechanisms have been discovered, it is generally unclear how these mechanisms interact in each cell line to make the cell line sensitive or resistant to a particular drug.

We set out to explain this variability in drug sensitivity in a panel of 30 breast cancer cell lines. We characterized these cell lines at the DNA, RNA and protein level, and accurately measured the proliferation under treatment with various different kinase inhibitors. We then constructed computational models encompassing several of the important driver pathways and sensitivity mechanisms, and tested how well these models describe the available data. After selecting the well-fitting models, we could use these models to estimate the relative contribution of each of the interacting mechanisms to the proliferation of the cells under drug treatment. For example, the models indicated that FGF2 autocrine signaling contributes to fast proliferation in some cell lines; that SGK1 expression provides a bypass for Akt signaling in some cell lines; or that the expression level of 4E-BP1 is a key determinant of mTOR-inhibitor sensitivity on top of other genetic alterations in the PI3K-pathway. Additionally, we could use these models to thoroughly analyze which parts of the data cannot be explained. This greatly narrows down which follow-up studies are necessary to advance our understanding of drug response.

These results show that knowledge-based computational models can be used to systematically study drug response in cell line panels. Such systematic, quantitative understanding of drug response will be useful in working towards precision medicine for individual cancer patients.

Citation Format: Bram Thijssen, Katarzyna Jastrzebski, Roderick L. Beijersbergen, Lodewyk FA Wessels. Understanding the variability in drug response in a panel of breast cancer cell lines using computational models. [abstract]. In: Proceedings of the AACR Special Conference on Computational and Systems Biology of Cancer; Feb 8-11 2015; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(22 Suppl 2):Abstract nr B2-37.