Shenli Zhang

A comprehensive survey of genomic alterations in gastric cancer reveals systematic patterns of molecular exclusivity and co-occurrence among distinct therapeutic targets

Objective Gastric cancer is a major gastrointestinal malignancy for which targeted therapies are emerging as treatment options. This study sought to identify the most prevalent molecular targets in gastric cancer and to elucidate systematic patterns of exclusivity and co-occurrence among these targets, through comprehensive genomic analysis of a large panel of gastric cancers. Design Using high-resolution single nucleotide polymorphism arrays, copy number alterations were profiled in a panel of 233 gastric cancers (193 primary tumours, 40 cell lines) and 98 primary matched gastric non-malignant samples. For selected alterations, their impact on gene expression and clinical outcome were evaluated. Results 22 recurrent focal alterations (13 amplifications and nine deletions) were identified. These included both known targets (FGFR2, ERBB2) and also novel genes in gastric cancer (KLF5, GATA6). Receptor tyrosine kinase (RTK)/RAS alterations were found to be frequent in gastric cancer. This study also demonstrates, for the first time, that these alterations occur in a mutually exclusive fashion, with KRAS gene amplifications highlighting a clinically relevant but previously underappreciated gastric cancer subgroup. FGFR2-amplified gastric cancers were also shown to be sensitive to dovitinib, an orally bioavailable FGFR/VEGFR targeting agent, potentially representing a subtype-specific therapy for FGFR2-amplified gastric cancers. Conclusion The study demonstrates the existence of five distinct gastric cancer patient subgroups, defined by the signature genomic alterations FGFR2 (9% of tumours), KRAS (9%), EGFR (8%), ERBB2 (7%) and MET (4%). Collectively, these subgroups suggest that at least 37% of gastric cancer patients may be potentially treatable by RTK/RAS directed therapies.

A common BIM deletion polymorphism mediates intrinsic resistance and inferior responses to tyrosine kinase inhibitors in cancer

Tyrosine kinase inhibitors (TKIs) elicit high response rates among individuals with kinase-driven malignancies, including chronic myeloid leukemia (CML) and epidermal growth factor receptor–mutated non–small-cell lung cancer (EGFR NSCLC). However, the extent and duration of these responses are heterogeneous, suggesting the existence of genetic modifiers affecting an individuals response to TKIs. Using paired-end DNA sequencing, we discovered a common intronic deletion polymorphism in the gene encoding BCL2-like 11 (BIM). BIM is a pro-apoptotic member of the B-cell CLL/lymphoma 2 (BCL2) family of proteins, and its upregulation is required for TKIs to induce apoptosis in kinase-driven cancers. The polymorphism switched BIM splicing from exon 4 to exon 3, which resulted in expression of BIM isoforms lacking the pro-apoptotic BCL2-homology domain 3 (BH3). The polymorphism was sufficient to confer intrinsic TKI resistance in CML and EGFR NSCLC cell lines, but this resistance could be overcome with BH3-mimetic drugs. Notably, individuals with CML and EGFR NSCLC harboring the polymorphism experienced significantly inferior responses to TKIs than did individuals without the polymorphism (P = 0.02 for CML and P = 0.027 for EGFR NSCLC). Our results offer an explanation for the heterogeneity of TKI responses across individuals and suggest the possibility of personalizing therapy with BH3 mimetics to overcome BIM-polymorphism–associated TKI resistance.

Exome sequencing identifies distinct mutational patterns in liver fluke–related and non-infection-related bile duct cancers

The impact of different carcinogenic exposures on the specific patterns of somatic mutation in human tumors remains unclear. To address this issue, we profiled 209 cholangiocarcinomas (CCAs) from Asia and Europe, including 108 cases caused by infection with the liver fluke Opisthorchis viverrini and 101 cases caused by non–O. viverrini–related etiologies. Whole-exome sequencing (n = 15) and prevalence screening (n = 194) identified recurrent somatic mutations in BAP1 and ARID1A, neither of which, to our knowledge, has previously been reported to be mutated in CCA. Comparisons between intrahepatic O. viverrini–related and non–O. viverrini–related CCAs demonstrated statistically significant differences in mutation patterns: BAP1, IDH1 and IDH2 were more frequently mutated in non–O. viverrini CCAs, whereas TP53 mutations showed the reciprocal pattern. Functional studies demonstrated tumor suppressive functions for BAP1 and ARID1A, establishing the role of chromatin modulators in CCA pathogenesis. These findings indicate that different causative etiologies may induce distinct somatic alterations, even within the same tumor type.

Genomic Profiles Specific to Patient Ethnicity in Lung Adenocarcinoma

Purpose: East-Asian (EA) patients with non–small-cell lung cancer (NSCLC) are associated with a high proportion of nonsmoking women, epidermal growth factor receptor (EGFR)-activating somatic mutations, and clinical responses to tyrosine kinase inhibitors. We sought to identify novel molecular differences between NSCLCs from EA and Western European (WE) patients. Experimental Design: A total of 226 lung adenocarcinoma samples from EA (n = 90) and WE (n = 136) patients were analyzed for copy number aberrations (CNA) by using a common high-resolution SNP (single nucleotide polymorphism) microarray platform. Univariate and multivariate analyses were carried out to identify CNAs specifically related to smoking history, EGFR mutation status, and ethnicity. Results: The overall genomic profiles of adenocarcinomas from EA and WE patients were highly similar. Univariate analyses revealed several CNAs significantly associated with ethnicity, EGFR mutation, and smoking, but not to gender, and KRAS or p53 mutations. A multivariate model identified four ethnic-specific recurrent CNAs—significantly higher rates of copy number gain were observed on 16p13.13 and 16p13.11 in EA tumors, whereas higher rates of genomic loss on 19p13.3 and 19p13.11 were observed in tumors from WE patients. We identified several potential driver genes in these regions, showing a positive correlation between cis-localized copy number changes and transcriptomic changes. Conclusion: 16p copy number gains (EA) and 19p losses (WE) are ethnic-specific chromosomal aberrations in lung adenocarcinoma. Patient ethnicity should be considered when evaluating future NSCLC therapies targeting genes located on these areas. Clin Cancer Res; 17(11); 3542–50. ©2011 AACR.

Prediction of Clinical Outcome in Multiple Lung Cancer Cohorts by Integrative Genomics: Implications for Chemotherapy Selection

The role of adjuvant chemotherapy in patients with stage IB non-small-cell lung cancer (NSCLC) is controversial. Identifying patient subgroups with the greatest risk of relapse and, consequently, most likely to benefit from adjuvant treatment thus remains an important clinical challenge. Here, we hypothesized that recurrent patterns of genomic amplifications and deletions in lung tumors could be integrated with gene expression information to establish a robust predictor of clinical outcome in stage IB NSCLC. Using high-resolution microarrays, we generated tandem DNA copy number and gene expression profiles for 85 stage IB lung adenocarcinomas/large cell carcinomas. We identified specific copy number alterations linked to relapse-free survival and selected genes within these regions exhibiting copy number-driven expression to construct a novel integrated signature (IS) capable of predicting clinical outcome in this series (P = 0.02). Importantly, the IS also significantly predicted clinical outcome in two other independent stage I NSCLC cohorts (P = 0.003 and P = 0.025), showing its robustness. In contrast, a more conventional molecular predictor based solely on gene expression, while capable of predicting outcome in the initial series, failed to significantly predict outcome in the two independent data sets. Our results suggest that recurrent copy number alterations, when combined with gene expression information, can be successfully used to create robust predictors of clinical outcome in early-stage NSCLC. The utility of the IS in identifying early-stage NSCLC patients as candidates for adjuvant treatment should be further evaluated in a clinical trial.

KRAS and BRAF mutations are rare and related to DNA mismatch repair deficiency in gastric cancer from the East and the West: results from a large international multicentre study.

Background:Inhibitors of the epidermal growth factor (EGFR) signaling pathway have a major role in the treatment of KRAS wild-type colorectal cancer patients. The EGFR pathway has been shown to be activated in gastric cancer (GC). However, published data on KRAS and BRAF mutation status is limited in GC and has not been compared between GC from different geographic regions.Methods:The prevalence of KRAS and BRAF mutations was established in 712 GC: 278 GC from the United Kingdom, 230 GC from Japan and 204 GC from Singapore. The relationship between KRAS/BRAF mutation status, DNA mismatch repair (MMR) status, clinicopathological variables and overall survival was analysed.Results:Overall, 30 (4.2%) GC carried a KRAS mutation. In total, 5.8% of the UK GC, 4% of Japan GC and 1.5% of Singapore GC were KRAS mutant. KRAS mutant GC had fewer lymph node metastases in the UK cohort (P=0.005) and were more frequent in elderly patients in the Japan cohort (P=0.034). KRAS mutations were more frequent in MMR-deficient GC in the UK and the Japanese cohort (P<0.05). A BRAF mutation was only detected in a single Japanese GC.Conclusions:This large multicentre study demonstrated that KRAS mutations and DNA MMR deficiency have a role in a small subgroup of GC irrespective of country of origin, suggesting that this subgroup of GC may have developed along a common pathway. Further studies need to establish whether concomitant mutations or amplifications of other EGFR signalling pathway genes may contribute to the activation of this pathway in GC.

Nanoscale chromatin profiling of gastric adenocarcinoma reveals cancer-associated cryptic promoters and somatically acquired regulatory elements

Chromatin alterations are fundamental hallmarks of cancer. To study chromatin alterations in primary gastric adenocarcinomas, we perform nanoscale chromatin immunoprecipitation sequencing of multiple histone modifications in five gastric cancers and matched normal tissues. We identify hundreds of somatically altered promoters and predicted enhancers. Many cancer-associated promoters localize to genomic sites lacking previously annotated transcription start sites (cryptic promoters), driving expression of nearby genes involved in gastrointestinal cancer, embryonic development and tissue specification. Cancer-associated promoters overlap with embryonic stem cell regions targeted by polycomb repressive complex 2, exhibiting promoter bivalency and DNA methylation loss. We identify somatically acquired elements exhibiting germline allelic biases and non-coding somatic mutations creating new promoters. Our findings demonstrate the feasibility of profiling chromatin from solid tumours with limited tissue to identify regulatory elements, transcriptional patterns and regulatory genetic variants associated with cancer.

CD44-SLC1A2 Gene Fusions in Gastric Cancer

One partner of a fusion gene found in gastric cancer, CD44-SLC1A2, may contribute to the tumor’s abnormal metabolism. Bad Drivers Steer Scientists Toward New Drug Targets It’s ironic, but cancer cells are notoriously bad at cell division, losing bits and rearranging chunks of the genome in the process. One result of this chaos is the birth of chimeric genes, wherein one gene segment gets erroneously fused to part of another, sometimes forming peculiar hybrid proteins that contribute to the cancer cell phenotype. For example, the fused aberrant BCR-ABL gene drives chronic myelogenous leukemia and has proven to be a vulnerable target for therapy. Gene fusions in solid cancers are not so easy to spot, but have been located in prostate and small cell lung cancers. Now, Tao and her co-workers have documented a fusion gene that forms in a small percentage of gastric tumor cells and may contribute to the development of cancer. The authors analyzed copy number variations of genes in more than 100 primary gastric tumors and 27 established gastric tumor cell lines and pinpointed a common breakpoint in three and one, respectively. The resulting chimeric gene fused most of the coding region of SLC1A2/EAAT2 (which encodes a glutamate transporter) to what is probably the strong transcriptional promoter of its neighboring gene, CD44, likely the result of a chromosome inversion. The fusion gene generated a truncated SLC1A2 protein in the original tumors and in a new group of gastric cancers created by the authors through overexpression of the fusion gene in normal gastric cells. But an abnormal protein that lives in tumor cells can be an innocent bystander. So, the authors asked whether the truncated SLC1A2 contributes to gastric cancer development, and their evidence suggested that the answer is yes. Cells in which shortened SLC1A2 expression was silenced with small interfering RNA were less proficient at dividing and invading soft substrates—hallmarks of cancer cells—and overexpression of the pruned protein enhanced these traits. Consistent with the function of SLC1A2 as a transporter of glutamate, the amino acid—which can act as a growth regulator—existed in higher concentrations in gastric cancer cells and cell lines than in normal cells. And in a final set of incriminating evidence, tumor cells that sported the CD44-SLC1A2 fusion gene had higher amounts of SLC1A2 than did wild-type cells, suggesting that this aberrant protein may trigger a pro-oncogenic phenotype. Most other genes that are fused in cancers encode kinase enzymes or transcriptional regulatory proteins. The implication of an overexpressed metabolism-related gene in some gastric tumors may define a new class of cancer-driving genes, although the protein could also augment other cancer-promoting genetic aberrations. The utility of this fusion gene as a drug target or prognostic tool will require more studies, but this particular mistake made by a dividing cancer cell may act as a GPS that directs researchers down a new therapeutic avenue for gastric cancer. Fusion genes are chimeric genes formed in cancers through genomic aberrations such as translocations, amplifications, and rearrangements. To identify fusion genes in gastric cancer, we analyzed regions of chromosomal imbalance in a cohort of 106 primary gastric cancers and 27 cell lines derived from gastric cancers. Multiple samples exhibited genomic breakpoints in the 5′ region of SLC1A2/EAAT2, a gene encoding a glutamate transporter. Analysis of a breakpoint-positive SNU16 cell line revealed expression of a CD44-SLC1A2 fusion transcript caused by a paracentric chromosomal inversion, which was predicted to produce a truncated but functional SLC1A2 protein. In primary tumors, CD44-SLC1A2 gene fusions were detected in 1 to 2% of gastric cancers, but not in adjacent matched normal gastric tissues. When we specifically silenced CD44-SLC1A2, cellular proliferation, invasion, and anchorage-independent growth were significantly reduced. Conversely, CD44-SLC1A2 overexpression in gastric cells stimulated these pro-oncogenic traits. CD44-SLC1A2 silencing caused significant reductions in intracellular glutamate concentrations and sensitized SNU16 cells to cisplatin, a commonly used chemotherapeutic agent in gastric cancer. We conclude that fusion of the SLC1A2 gene coding region to CD44 regulatory elements likely causes SLC1A2 transcriptional dysregulation, because tumors expressing high SLC1A2 levels also tended to be CD44-SLC1A2–positive. CD44-SLC1A2 may represent a class of gene fusions in cancers that establish a pro-oncogenic metabolic milieu favoring tumor growth and survival.

Whole-Genome Sequencing of Asian Lung Cancers: Second-Hand Smoke Unlikely to Be Responsible for Higher Incidence of Lung Cancer among Asian Never-Smokers

Asian nonsmoking populations have a higher incidence of lung cancer compared with their European counterparts. There is a long-standing hypothesis that the increase of lung cancer in Asian never-smokers is due to environmental factors such as second-hand smoke. We analyzed whole-genome sequencing of 30 Asian lung cancers. Unsupervised clustering of mutational signatures separated the patients into two categories of either all the never-smokers or all the smokers or ex-smokers. In addition, nearly one third of the ex-smokers and smokers classified with the never-smoker-like cluster. The somatic variant profiles of Asian lung cancers were similar to that of European origin with G.C>T.A being predominant in smokers. We found EGFR and TP53 to be the most frequently mutated genes with mutations in 50% and 27% of individuals, respectively. Among the 16 never-smokers, 69% had an EGFR mutation compared with 29% of 14 smokers/ex-smokers. Asian never-smokers had lung cancer signatures distinct from the smoker signature and their mutation profiles were similar to European never-smokers. The profiles of Asian and European smokers are also similar. Taken together, these results suggested that the same mutational mechanisms underlie the etiology for both ethnic groups. Thus, the high incidence of lung cancer in Asian never-smokers seems unlikely to be due to second-hand smoke or other carcinogens that cause oxidative DNA damage, implying that routine EGFR testing is warranted in the Asian population regardless of smoking status.

Mutational landscapes of tongue carcinoma reveal recurrent mutations in genes of therapeutic and prognostic relevance

BackgroundCarcinoma of the oral tongue (OTSCC) is the most common malignancy of the oral cavity, characterized by frequent recurrence and poor survival. The last three decades has witnessed a change in the OTSCC epidemiological profile, with increasing incidence in younger patients, females and never-smokers. Here, we sought to characterize the OTSCC genomic landscape and to determine factors that may delineate the genetic basis of this disease, inform prognosis and identify targets for therapeutic intervention.MethodsSeventy-eight cases were subjected to whole-exome (n = 18) and targeted deep sequencing (n = 60).ResultsWhile the most common mutation was in TP53, the OTSCC genetic landscape differed from previously described cohorts of patients with head and neck tumors: OTSCCs demonstrated frequent mutations in DST and RNF213, while alterations in CDKN2A and NOTCH1 were significantly less frequent. Despite a lack of previously reported NOTCH1 mutations, integrated analysis showed enrichments of alterations affecting Notch signaling in OTSCC. Importantly, these Notch pathway alterations were prognostic on multivariate analyses. A high proportion of OTSCCs also presented with alterations in drug targetable and chromatin remodeling genes. Patients harboring mutations in actionable pathways were more likely to succumb from recurrent disease compared with those who did not, suggesting that the former should be considered for treatment with targeted compounds in future trials.ConclusionsOur study defines the Asian OTSCC mutational landscape, highlighting the key role of Notch signaling in oral tongue tumorigenesis. We also observed somatic mutations in multiple therapeutically relevant genes, which may represent candidate drug targets in this highly lethal tumor type.