Leon Raskin

MRE11 deficiency increases sensitivity to poly(ADP-ribose) polymerase inhibition in microsatellite unstable colorectal cancers

Microsatellite instability (MSI) is displayed by approximately 15% of colorectal cancers (CRC). Defective DNA mismatch repair generates mutations at repetitive DNA sequences such as those located in the double strand break (DSB) repair gene MRE11. We assessed the mutational status of MRE11 in a panel of 17 CRC cell lines and 46 primary tumors and found a strong correlation with MSI status in both cell lines and tumors. Therefore, we hypothesized that deficiency in MRE11 may sensitize CRC cells to poly(ADP-ribose) polymerase (PARP-1) inhibition based on the concept of synthetic lethality. We further assessed the activity of the PARP-1 inhibitor, ABT-888, in CRC cell lines and observed preferential cytotoxicity in those MSI cell lines harboring mutations in MRE11 compared with both wild-type cell lines and microsatellite stable (MSS) cell lines. A significant correlation between MRE11 expression levels and cytotoxicity to ABT-888 at 10 μM was observed (R² = 0.915, P < 0.001). Using two experimental approaches, including short hairpin RNA knocking down MRE11 in the wild-type and MSS cell line SW-480 and a second cell line model transfected with mutant MRE11, we experimentally tried to confirm the role of MRE11 in conferring sensitivity to PARP-1 inhibition. Both models led to changes in proliferation in response to ABT-888 at different concentrations, and a drug-response effect was not observed, suggesting a possible contribution of additional genes. We conclude that MSI colorectal tumors deficient in DSB repair secondary to mutation in MRE11 show a higher sensitivity to PARP-1 inhibition. Further clinical investigation of PARP-1 inhibitors is warranted in MSI CRCs.

Copy Number Variations and Clinical Outcome in Atypical Spitz Tumors

Atypical Spitz tumors (ASTs) are rare spitzoid neoplasms of uncertain biological behavior. Our study was designed to characterize genetic abnormalities that may help to differentiate ASTs from melanoma or Spitz nevi. We examined copy number variation in formalin-fixed, paraffin-embedded samples using an Agilent 44k array comparative genomic hybridization platform. Sixteen patients with AST (8 with positive sentinel lymph node biopsy, 1 with distant metastasis), 8 patients with Spitz nevi, and 3 patients with melanoma (2 spitzoid, 1 superficial spreading) were evaluated. Chromosomal aberrations were found in 7 of 16 ASTs, 1 with fatal outcome, 2 spitzoid melanomas, and 1 conventional melanoma. We found no difference in chromosomal instability between AST patients with positive and negative sentinel lymph node biopsies. Our patient with widely metastatic AST lacked the most frequent aberrations in melanoma involving chromosomes 6 and 11q that are loci targeted by fluorescence in situ hybridization (FISH) probes developed to distinguish malignant melanoma from benign melanocytic lesions. The vast majority of chromosomal abnormalities observed in ASTs are not commonly found in melanomas, suggesting that AST may be a distinct clinical entity and raising additional questions regarding their malignant potential, prognosis, and clinical management. The current FISH probes failed to detect 1 spitzoid melanoma, 1 fatal metastatic AST case, and the other chromosomally aberrant ASTs in our series, but detected 1 spitzoid melanoma and 1 conventional melanoma. Thus, a comprehensive, genome-wide approach to chromosomal abnormalities offered greater sensitivity and specificity than current FISH probes in identifying spitzoid lesions of uncertain malignant potential in this series.

Gene Expression Patterns in Mismatch Repair-Deficient Colorectal Cancers Highlight the Potential Therapeutic Role of Inhibitors of the Phosphatidylinositol 3-Kinase-AKT-Mammalian Target of Rapamycin Pathway

Purpose: High-frequency microsatellite-instable (MSI-H) tumors account for ∼15% of colorectal cancers. Therapeutic decisions for colorectal cancer are empirically based and currently do not emphasize molecular subclassification despite an increasing collection of gene expression information. Our objective was to identify low molecular weight compounds with preferential activity against MSI colorectal cancers using combined gene expression data sets. Experimental Design: Three expression/query signatures (discovery data set) characterizing MSI-H colorectal cancer were matched with information derived from changes induced in cell lines by 164 compounds using the systems biology tool “Connectivity Map.” A series of sequential filtering and ranking algorithms were used to select the candidate compounds. Compounds were validated using two additional expression/query signatures (validation data set). Cytotoxic, cell cycle, and apoptosis effects of validated compounds were evaluated in a panel of cell lines. Results: Fourteen of the 164 compounds were validated as targeting MSI-H cell lines using the bioinformatics approach; rapamycin, LY-294002, 17-(allylamino)-17-demethoxygeldanamycin, and trichostatin A were the most robust candidate compounds. In vitro results showed that MSI-H cell lines due to hypermethylation of MLH1 are preferentially targeted by rapamycin (18.3 versus 4.4 μmol/L; P = 0.0824) and LY-294002 (15.02 versus 10.37 μmol/L; P = 0.0385) when compared with microsatellite-stable cells. Preferential activity was also observed in MSH2 and MSH6 mutant cells. Conclusion: Our study shows that the phosphatidylinositol 3-kinase-AKT-mammalian target of rapamycin pathway is of special relevance in mismatch repair-deficient colorectal cancer. In addition, we show that amalgamation of gene expression information across studies provides a robust approach for selection of potential therapies corresponding to specific groups of patients.

FGFR2 Is a Breast Cancer Susceptibility Gene in Jewish and Arab Israeli Populations

Genetic variation in FGFR2 is a newly described risk factor for breast cancer. We estimated the relative risk and contribution of FGFR2 polymorphisms to breast cancer risk in diverse ethnic groups within Jewish and other Middle Eastern populations. We genotyped four FGFR2 single nucleotide polymorphisms (SNP) and tested for association of these SNPs and haplotypes with breast cancer risk in a population-based case-control study of 1,529 women with breast cancer and 1,528 controls. We found significant associations between breast cancer risk and all four studied SNPs in FGFR2 (Ptrend for all SNPs < 0.0001). In ethnicity-specific analysis, all four SNPs were significantly associated with breast cancer risk in Ashkenazi and Sephardi Jews, with a similar but not significant trend in Arabs. Haplotype analysis identified five common haplotypes (>1%). The previously described AAGT risk haplotype was significantly associated with breast cancer risk in Ashkenazi [odds ratio (OR), 1.25; 95% confidence interval (95% CI), 1.07-1.45; P = 0.0059] and Sephardi Jews (OR, 1.46; 95% CI, 1.17-1.80; P = 0.0006) compared with the reference GGAC haplotype. The AAAC haplotype was significantly associated with breast cancer risk in Sephardi Jews (OR, 1.97; 95% CI, 1.16-3.35; P = 0.0125) but not in Ashkenazi Jews (OR, 0.83; 95% CI, 0.41-1.62; P = 0.5613) or in Arabs (OR, 1.31; 95% CI, 0.80-2.14; P = 0.2881). Genetic variation in FGFR2, identified by rs1219648, may account for a substantial fraction of breast cancer in Arab (12%), Ashkenazi (15%), and Sephardi Jewish (22%) populations. The identification of population-specific risk haplotypes in FGFR2 is likely to help identify causal variants for breast cancer. (Cancer Epidemiol Biomarkers Prev 2008;17(5):1060–5)

Genome-wide association study of colorectal cancer identifies six new susceptibility loci

Genetic susceptibility to colorectal cancer is caused by rare pathogenic mutations and common genetic variants that contribute to familial risk. Here we report the results of a two-stage association study with 18,299 cases of colorectal cancer and 19,656 controls, with follow-up of the most statistically significant genetic loci in 4,725 cases and 9,969 controls from two Asian consortia. We describe six new susceptibility loci reaching a genome-wide threshold of P<5.0E-08. These findings provide additional insight into the underlying biological mechanisms of colorectal cancer and demonstrate the scientific value of large consortia-based genetic epidemiology studies.

Transcriptome profiling identifies HMGA2 as a biomarker of melanoma progression and prognosis.

The genetic alterations contributing to melanoma pathogenesis are incompletely defined, and few independent prognostic features have been identified beyond the clinicopathological characteristics of the primary tumor. We used transcriptome profiling of 46 primary melanomas, 12 melanoma metastases, and 16 normal skin (N) samples to find genes associated with melanoma development and progression. Results were confirmed using immunohistochemistry and real-time PCR and replicated in an independent set of 330 melanomas using AQUA analysis of tissue microarray (TMA). Transcriptome profiling revealed that transcription factor HMGA2, previously unrecognized in melanoma pathogenesis, is significantly upregulated in primary melanoma and metastases (P-values=1.2 × 10(-7) and 9 × 10(-5)) compared with N. HMGA2 overexpression is associated with BRAF/NRAS mutations (P=0.0002). Cox proportional hazard regression model and log-rank test showed that HMGA2 is independently associated with disease-free survival (hazard ratio (HR)=6.3, 95% confidence interval (CI)=1.8-22.3, P=0.004), overall survival (OS) (stratified log-rank P=0.008), and distant metastases-free survival (HR=6.4, 95% CI=1.4-29.7, P=0.018) after adjusting for American Joint Committee on Cancer (AJCC) stage and age at diagnosis. Survival analysis in an independent replication TMA of 330 melanomas confirmed the association of HMGA2 expression with OS (P=0.0211). Our study implicates HMGA2 in melanoma progression and demonstrates that HMGA2 overexpression can serve as an independent predictor of survival in melanoma.

Risk of Non-Melanoma Cancers in First-Degree Relatives of CDKN2A Mutation Carriers

The purpose of this study was to quantify the risk of cancers other than melanoma among family members of CDKN2A mutation carriers using data from the Genes, Environment and Melanoma study. Relative risks (RRs) of all non-melanoma cancers among first-degree relatives (FDRs) of melanoma patients with CDKN2A mutations (n = 65) and FDRs of melanoma patients without mutations (n = 3537) were calculated as the ratio of estimated event rates (number of cancers/total person-years) in FDRs of carriers vs noncarriers with exact Clopper-Pearson-type tests and 95% confidence intervals (CIs). All statistical tests were two-sided. There were 56 (13.1%) non-melanoma cancers reported among 429 FDRs of mutation carriers and 2199 (9.4%) non-melanoma cancers in 23 452 FDRs of noncarriers. The FDRs of carriers had an increased risk of any cancer other than melanoma (56 cancers among 429 FDRs of carrier probands vs 2199 cancers among 23 452 FDRs of noncarrier probands; RR = 1.5, 95% CI = 1.2 to 2.0, P = .005), gastrointestinal cancer (20 cancers among 429 FDRs of carrier probands vs 506 cancers among 23 452 FDRs of noncarrier probands; RR = 2.4, 95% CI = 1.4 to 3.7, P = .001), and pancreatic cancer (five cancers among 429 FDRs of carrier probands vs 41 cancers among 23 452 FDRs of noncarrier probands; RR = 7.4, 95% CI = 2.3 to 18.7, P = .002). Wilms tumor was reported in two FDRs of carrier probands and three FDRs of noncarrier probands (RR = 40.4, 95% CI = 3.4 to 352.7, P = .005). The lifetime risk of any cancer other than melanoma among CDKN2A mutation carriers was estimated as 59.0% by age 85 years (95% CI = 39.0% to 75.4%) by the kin-cohort method, under the standard assumptions of Mendelian genetics on the genotype distribution of FDRs conditional on proband genotype.

Returning Individual Research Results: Development of a Cancer Genetics Education and Risk Communication Protocol

The obligations of researchers to disclose clinically and/or personally significant individual research results are highly debated, but few empirical studies have addressed this topic. We describe the development of a protocol for returning research results to participants at one site of a multicenter study of the genetic epidemiology of melanoma. Protocol development involved numerous challenges: (1) deciding whether genotype results merited disclosure; (2) achieving an appropriate format for communicating results; (3) developing education materials; (4) deciding whether to retest samples for additional laboratory validation; (5) identifying and notifying selected participants; and (6) assessing the impact of disclosure. Our experience suggests potential obstacles depending on researcher resources and the design of the parent study, but offers a process by which researchers can responsibly return individual study results and evaluate the impact of disclosure.

Blood BDNF Level Is Gender Specific in Severe Depression

Though the role of brain derived neurotrophic factor (BDNF) as a marker for major depressive disorder (MDD) and antidepressant efficacy has been widely studied, the role of BDNF in distinct groups of patients remains unclear. We evaluated the diagnostic value of BDNF as a marker of disease severity measured by HAM-D scores and antidepressants efficacy among MDD patients. Fifty-one patients who met DSM-IV criteria for MDD and were prescribed antidepressants and 38 controls participated in this study. BDNF in serum was measured at baseline, 1st, 2nd and 8th treatment weeks. Depression severity was evaluated using the Hamilton Rating Scale for Depression (HAM-D). BDNF polymorphism rs6265 (val66met) was genotyped. We found a positive correlation between blood BDNF levels and severity of depression only among untreated women with severe MDD (HAM-D>24). Serum BDNF levels were lower in untreated MDD patients compared to control group. Antidepressants increased serum BDNF levels and reduced between-group differences after two weeks of treatment. No correlations were observed between BDNF polymorphism, depression severity, duration of illness, age and BDNF serum levels. Further supporting the role of BDNF in the pathology and treatment of MDD, we suggest that it should not be used as a universal biomarker for diagnosis of MDD in the general population. However, it has diagnostic value for the assessment of disease progression and treatment efficacy in individual patients.

Characterization of two Ashkenazi Jewish founder mutations in MSH6 gene causing Lynch syndrome

Raskin L, Schwenter F, Freytsis M, Tischkowitz M, Wong N, Chong G, Narod SA, Levine DA, Bogomolniy F, Aronson M, Thibodeau SN, Hunt KS, Rennert G, Gallinger S, Gruber SB, Foulkes WD. Characterization of two Ashkenazi Jewish founder mutations in MSH6 gene causing Lynch syndrome.