In This Issue

IN THIS ISSUE

Outlier Kinase Expression May Identify Therapeutic Targets

• Outlier kinases have the highest ab- • FGFR4 is a frequent outlier kinase • Outlier kinase expression impli- solute and differential expression in HER2-positive cancers that pro- cates PLK2 and MET as drivers in in individual samples. motes cell proliferation. some pancreatic cancers.

Cancers dependent on activat- cancer samples. Unexpectedly, a subset of HER2-positive sam- ing kinase mutations are obvious ples also showed outlier expression of FGFR4, implicating candidates for targeted therapies, FGFR4 as a potential therapeutic target. Indeed, knockdown of but cancers lacking druggable FGFR4 led to decreased cell proliferation in these cell lines, and mutations require alternative combined treatment with the HER2 antibody trastuzumab approaches. Hypothesizing that and an FGFR inhibitor had an additive effect. Extension of cancer cells can become depend- this analysis to pancreatic cancer, a lethal cancer with few known ent on aberrant signaling caused actionable targets, identifi ed multiple sample-specifi c outlier by kinase overexpression, Kothari kinases, including PLK2 and MET. Knockdown or inhibition of and colleagues profiled the these kinases in cells with outlier expression suppressed prolif- expression of every human kinase in cancer cell lines and eration, and the clinically available MET inhibitor cabozantinib patient samples with high-throughput transcriptome sequenc- inhibited the growth of pancreatic cancer cell lines with outlier ing. Candidate therapeutic targets were prioritized by identify- MET expression in vivo. Outlier kinase analysis may therefore ing sample-specifi c “outlier kinases,” those with the highest represent a readily achievable strategy for identifying patient- gene expression levels compared with other kinases and the specifi c cancer vulnerabilities that could be incorporated in the highest differential expression compared with all other sam- development of personalized treatment plans. ■ ples. As proof of principle, outlier expression of ERBB2 (encod- ing HER2) was specifi cally observed in HER2-positive breast See article, p. 280.

NRAS-Mediated Suppression of Apoptosis Enhances Tumorigenesis

• Nras mutation promotes colo- • Mutant NRAS, but not KRAS or • Treatment with a MEK inhibitor se- rectal cancer growth by blocking HRAS, activates noncanonical MAPK lectively triggers apoptosis in Nras- inflammation-induced apoptosis. signaling via RAF-1 and STAT3. mutant tumors in mice.

RAS proteins share signifi cant was mediated specifi cally by signaling through RAF-1 (also sequence homology, but the known as CRAF), suggestive of distinct functions and bind- results of recent studies suggest ing partners for this RAS isoform. Indeed, whereas all RAS that KRAS, HRAS, and NRAS proteins activated canonical ERK and AKT pathways, only may have isoform-specifi c func- mutant NRAS triggered activation of noncanonical MAPK tions. In contrast with KRAS signaling via phosphorylation of STAT3. Mutant NRAS, but mutations that induce intesti- not KRAS or HRAS, formed a complex with RAF-1 and nal hyperplasia, activating NRAS STAT3 within cholesterol-rich membrane microdomains mutations suppress intestinal to directly activate STAT3 and augment its transcriptional epithelial cell apoptosis under activity in both mouse and human NRAS-mutant tumors. stress conditions. However, it is unclear whether the antia- Importantly, pharmacologic inhibition of MAP/ERK kinase poptotic function of mutant NRAS, which is expressed in (MEK) impaired STAT3 activation and induced apoptosis in a small subset of human colorectal cancers, contributes to Nras-mutant tumors. These fi ndings identify a critical role tumorigenesis. Wang and colleagues found that expression of for the antiapoptotic function of mutant NRAS in colorectal mutant NRAS in the intestinal epithelium enhanced colonic tumorigenesis and suggest that patients with NRAS-mutant adenocarcinoma formation under infl ammatory conditions tumors may benefi t from treatment with MEK inhibitors. ■ that stimulate cell death. This effect was associated with inhibition of stress-induced apoptosis by mutant NRAS and See article, p. 294.

MARCH 2013CANCER DISCOVERY | 239

MYCN Amplification Predicts Sensitivity to BET Inhibition

• MYCN amplification is a biomarker • JQ1 downregulates MYCN and • JQ1 prolongs survival in of response to the BET bromodo- MYCN-dependent transcriptional MYCN-amplified neuroblastoma main inhibitor JQ1. programs in neuroblastoma. models.

Small-molecule inhibition of sensitivity. In responsive cells, JQ1 treatment induced cell-cycle bromodomain and extra-terminal arrest and increased apoptosis in association with decreased domain (BET) proteins is a prom- expression of MYCN and MYCN target genes caused by JQ1- ising anticancer strategy, par- mediated displacement of the BET family member BRD4 from ticularly in some hematologic the MYCN promoter. These fi ndings were reminiscent of stud- malignancies, but genetic predic- ies in hematologic cancers, in which BET inhibition suppresses tors of BET inhibitor sensitivity MYC expression, and expression analysis indicated that BET that would direct their expanded inhibition with JQ1 leads to changes in expression in a shared clinical use are lacking. Puissant set of genes in neuroblastoma and hematologic malignancies. and colleagues screened 673 Importantly, JQ1 treatment signifi cantly prolonged survival in genetically characterized cancer cell lines to identify those most several independent mouse models of MYCN-amplifi ed neu- sensitive to JQ1, a prototype BET inhibitor that blocks BET roblastoma. These results thus implicate MYCN amplifi cation bromodomain binding to acetylated histones and displaces as a potential biomarker of response to BET inhibitors and BET proteins from chromatin. Notably, neuroblastoma cell provide a strong rationale for the clinical development of BET lines were among the most JQ1-sensitive cell lines, and amplifi - inhibitors in MYCN-amplifi ed neuroblastoma. ■ cation of the MYCN oncogene, a common feature of high-risk neuroblastoma, was the genetic feature most predictive of JQ1 See article, p. 308.

Squamous Cell Carcinomas Are Sensitive to HDAC and BCL-2 Inhibition

• MCL-1 is the dominant antiapop- • Vorinostat induces ABT-737 sensi- • HDAC and BCL-2 inhibitors syner- totic BCL-2 family member in tivity by shuttling BIM from MCL-1 gize to induce squamous cell squamous cell carcinoma. to BCL-2/BCL-XL. carcinoma regression.

Squamous cell carcinoma SCC than leukemia, resulting in a dramatically higher MCL-1/ (SCC) is a common, highly BCL-2 ratio and dependence on MCL-1 for survival. Notably, aggressive cancer that lacks effec- vorinostat induced MCL-1 downregulation and NOXA upregu- tive rational therapies. He and lation in SCC cells, leading to redistribution of the sequestered colleagues evaluated the role proapoptotic protein BIM from MCL-1 to BCL-2/BCL-XL. of antiapoptotic BCL-2 family These effects provide an explanation for vorinostat resistance members in drug resistance and in SCC cells with high BCL-2 expression and suggest that the effect of BCL-2 inhibition vorinostat-induced BIM redistribution might prime SCC cells in SCC cell lines. Although little for sensitivity to ABT-737. Indeed, combined use of vorinostat variation in BCL-XL or MCL-1 and ABT-737 synergized to kill SCC cells in vitro, particularly expression was observed, BCL-2 expression varied greatly and those with MCL-1–stabilizing FBW7 mutations, and induced was inversely correlated with sensitivity to the histone deacety- regression of established SCCs in vivo. Importantly, similar lase (HDAC) inhibitor vorinostat. However, all SCC cell lines MCL-1/BCL-2 ratios and BIM levels were observed in SCC were highly resistant to the BCL-2/BCL-XL inhibitor ABT- clinical samples, providing support for clinical evaluation of 737, unlike leukemia cells, which are killed by this drug at combined HDAC and BCL-2 inhibition in SCC. ■ nanomolar doses. A comparison of BCL-2 levels in SCC and leukemia revealed that BCL-2 expression was much lower in See article, p. 324.

240 | CANCER DISCOVERYMARCH 2013 www.aacrjournals.org

NF1 Inactivation Cooperates with BRAF Mutations in Melanoma

• Nf1 loss enhances melanomagene- • Mutations in Nf1 promote tumor • Nf1 -mutant tumors are resistant to sis by suppressing senescence in growth via increased PI3K/AKT and BRAF inhibitors but sensitive to Braf-mutant melanocytes. RAS/ERK activation. MEK/mTOR inhibition.

Activating BRAF mutations nositide 3-kinase (PI3K)/AKT signaling. Melanomas harboring stimulate a feedback loop that Nf1 mutations were desensitized to the BRAF inhibitor PLX4720 inhibits RAS signaling and induces but retained sensitivity to combined inhibition of MAP/ERK senescence in melanocytes, limit- kinase (MEK) and mTOR, which synergistically blocked ERK ing malignant progression in activity and induced tumor regression. In addition, neurofi bro- the absence of additional genetic min expression was suppressed in relapsed tumors derived from events. Maertens and colleagues patients treated with BRAF inhibitors, further suggesting that investigated whether inactivation NF1 inactivation confers drug resistance. NF1 mutations coop- of the tumor suppressor NF1, erated with activating BRAF mutations in human melanomas, which encodes neurofi bromin, a resulting in activation of KRAS and HRAS; NF1 mutations also negative regulator of RAS signaling, is suffi cient to overcome this co-occurred with inactivating BRAF mutations and were associ- growth barrier and promote BRAF-mutant melanomagenesis. ated with oncogenic NRAS mutations and activation of all 3 In support of this idea, Nf1 ablation counteracted oncogenic RAS isoforms in these cells. These results show that NF1 loss RAF–mediated feedback and rescued RAS activity in vitro. Moreo- cooperates with BRAF mutations to stimulate melanoma growth ver, melanocyte-specifi c Nf1 deletion in the context of activated and suggest alternative combinatorial therapeutic strategies for BRAF prevented oncogene-induced senescence, triggered melano- patients with BRAF/NF1-mutant melanomas. ■ cyte hyperproliferation, and augmented melanoma development via sustained ERK phosphorylation and increased phosphoi- See article, p. 338.

NF1 Loss Mediates Drug Resistance in Melanoma

• An shRNA screen identified NF1 • NF1 -deficient cells remain sensi- • NF1 mutations in human melano- loss as a driver of RAF inhibitor tive to ERK blockade and irrevers- mas contribute to both intrinsic and resistance in melanoma. ible RAF inhibition. acquired drug resistance.

Targeted inhibition of BRAF MAPK signaling. This phenotype was also dependent on and MAP/ERK kinase (MEK) increased CRAF activation, as concomitant downregulation activity suppresses ERK sign- of NF1 and CRAF overcame the drug resistance induced by aling and prolongs survival in NF1 loss and resensitized cells to MEK blockade. Further- patients with BRAFV600E-mutant more, BRAF-mutant melanoma cells harboring NF1 knock- melanomas. However, intrinsic down remained sensitive to treatment with the irreversible and acquired resistance to these RAF inhibitor AZ628, which blocks both BRAF and CRAF, drugs promotes tumor relapse, and the ERK inhibitor VTX-11e. Consistent with this fi nding, underscoring the need to char- BRAFV600E cancer cell lines with inactivating NF1 mutations acterize these resistance mecha- were intrinsically resistant to RAF inhibition but retained nisms and develop combinatorial therapeutic strategies. sensitivity to VTX-11e. In addition, NF1 mutations, includ- Using a genome-scale short hairpin RNA (shRNA) screen, ing 1 nonsense and 3 splice-site mutations, were identifi ed Whittaker and colleagues systematically evaluated poten- in melanomas from patients who developed resistance to tial loss-of-function resistance mechanisms in drug-sensitive vemurafenib. These fi ndings establish NF1 loss as a mediator BRAF-mutant melanoma cells and found that loss of the of both intrinsic and acquired resistance to RAF inhibitors tumor suppressor NF1 conferred resistance to both RAF and and suggest alternative strategies for treatment of patients MEK inhibitors. Suppression of NF1, which encodes for the with BRAF/NF1-mutant melanoma. ■ RAS GTPase-activating protein neurofi bromin, enabled con- tinued cell proliferation in drug-treated cells via sustained See article, p. 350.

Note: In This Issue is written by Cancer Discovery Science Writers. Readers are encouraged to consult the original articles for full details.

MARCH 2013CANCER DISCOVERY | 241

Cancer Discovery 2013;3:239-241.

Updated version Access the most recent version of this article at: http://cancerdiscovery.aacrjournals.org/content/3/3/239

E-mail alerts Sign up to receive free email-alerts related to this article or journal.

Reprints and To order reprints of this article or to subscribe to the journal, contact the AACR Publications Department at Subscriptions [email protected].

Permissions To request permission to re-use all or part of this article, use this link http://cancerdiscovery.aacrjournals.org/content/3/3/239. Click on "Request Permissions" which will take you to the Copyright Clearance Center's (CCC) Rightslink site.