Kathryn Scott

A global expression-based analysis of the consequences of the t(4;14) translocation in myeloma

Purpose: Our purpose in this report was to define genes and pathways dysregulated as a consequence of the t(4;14) in myeloma, and to gain insight into the downstream functional effects that may explain the different prognosis of this subgroup. Experimental Design: Fibroblast growth factor receptor 3 (FGFR3) overexpression, the presence of immunoglobulin heavy chain-multiple myeloma SET domain (IgH-MMSET) fusion products and the identification of t(4;14) breakpoints were determined in a series of myeloma cases. Differentially expressed genes were identified between cases with (n = 5) and without (n = 24) a t(4;14) by using global gene expression analysis. Results: Cases with a t(4;14) have a distinct expression pattern compared with other cases of myeloma. A total of 127 genes were identified as being differentially expressed including MMSET and cyclin D2, which have been previously reported as being associated with this translocation. Other important functional classes of genes include cell signaling, apoptosis and related genes, oncogenes, chromatin structure, and DNA repair genes. Interestingly, 25% of myeloma cases lacking evidence of this translocation had up-regulation of the MMSET transcript to the same level as cases with a translocation. Conclusions: t(4;14) cases form a distinct subgroup of myeloma cases with a unique gene signature that may account for their poor prognosis. A number of non-t(4;14) cases also express MMSET consistent with this gene playing a role in myeloma pathogenesis.

MLH1 −93G>A promoter polymorphism and risk of mismatch repair deficient colorectal cancer

Rare inherited mutations in the mutL homolog 1 (MLH1) DNA mismatch repair gene can confer an increased susceptibility to colorectal cancer (CRC) with high penetrance where disease frequently develops in the proximal colon. The core promoter of MLH1 contains a common single nucleotide polymorphism (SNP) (−93G>A, dbSNP ID:rs1800734) located in a region essential for maximum transcriptional activity. We used logistic regression analysis to examine the association between this variant and risk of CRC in patients in the United Kingdom. All statistical tests were 2 sided. In an analysis of 1,518 patients with CRC, homozygosity for the MLH1 −93A variant was associated with a significantly increased 3‐fold risk of CRC negative for MLH1 protein by immunohistochemistry (odds ratio (OR): AA vs GG = 3.30, 95% CI 1.46–7.47, n = 1392, p = 0.004, MLH1 negative vs MLH1 positive CRC) and with a 68% excess of proximal CRC (OR: AA vs GG=1.68, 95% confidence interval (CI) 1.00–2.83, n = 1,518, p = 0.05, proximal vs distal CRC). These findings suggest that the MLH1 −93G>A polymorphism defines a low penetrance risk allele for CRC.

Polymorphic MLH1 and risk of cancer after methylating chemotherapy for Hodgkin lymphoma

Background and objective: Methylating agents are effective chemotherapy agents for Hodgkin lymphoma, but are associated with the development of second primary cancers. Cytotoxicity of methylating agents is mediated primarily by the DNA mismatch repair (MMR) system. Loss of MLH1, a major component of DNA MMR, results in tolerance to the cytotoxic effects of methylating agents and persistence of mutagenised cells at high risk of malignant transformation. We hypothesised that a common substitution in the basal promoter of MLH1 (position -93, rs1800734) modifies the risk of cancer after methylating chemotherapy. Methods: 133 patients who developed cancer following chemotherapy and/or radiotherapy (n = 133), 420 patients diagnosed with de novo myeloid leukaemia, 242 patients diagnosed with primary Hodgkin lymphoma, and 1177 healthy controls were genotyped for the MLH1 -93 polymorphism by allelic discrimination polymerase chain reaction (PCR) and restriction fragment length polymorphism assay. Odds ratios and 95% confidence intervals for cancer risk by MLH1 -93 polymorphism status, and stratified by previous exposure to methylating chemotherapy, were calculated using unconditional logistic regression. Results: Carrier frequency of the MLH1 -93 variant was higher in patients who developed therapy related acute myeloid leukaemia (t-AML) (75.0%, n = 12) or breast cancer (53.3%. n = 15) after methylating chemotherapy for Hodgkin lymphoma compared to patients without previous methylating exposure (t-AML, 30.4%, n = 69; breast cancer patients, 27.2%, n = 22). The MLH1 -93 variant allele was also over-represented in t-AML cases when compared to de novo AML cases (36.9%, n = 420) and healthy controls (36.3%, n = 952), and was associated with a significantly increased risk of developing t-AML (odds ratio 5.31, 95% confidence interval 1.40 to 20.15), but only in patients previously treated with a methylating agent. Conclusions: These data support the hypothesis that the common polymorphism at position -93 in the core promoter of MLH1 defines a risk allele for the development of cancer after methylating chemotherapy for Hodgkin lymphoma. However, replication of this finding in larger studies is suggested.

A functional variant in the core promoter of the CD95 cell death receptor gene predicts prognosis in acute promyelocytic leukemia

Up to 15% of acute promyelocytic leukemia (APL) patients fail to achieve or maintain remission. We investigated a common G > A polymorphism at position -1377 (rs2234767) in the core promoter of the CD95 cell death receptor gene in 708 subjects with acute myeloid leukemia, including 231 patients with APL. Compared with the GG genotype, carrier status for the -1377A variant was associated with a significantly worse prognosis in APL patients. Carriers were more likely to fail remission induction (odds ratio = 4.22; 95% confidence interval, 1.41-12.6, P = .01), were more likely to die during the first 8 weeks of remission induction therapy (hazard ratio = 7.26; 95% confidence interval, 2.39-22.9, P = .0005), and had a significantly worse 5-year overall survival (odds ratio = 2.14; 95% confidence interval, 1.10-4.15, P = .03). The -1377A variant destroys a binding site for the SP1 transcriptional regulator and is associated with lower transcriptional activity of the CD95 promoter. Identifying patients at high risk of life-threatening events, such as remission induction failure, is a high priority in APL, especially because such events represent a major cause of death despite the introduction of differentiation therapy.

DNA mismatch repair status affects cellular response to Ara-C and other anti-leukemic nucleoside analogs

DNA mismatch repair status affects cellular response to Ara-C and other anti-leukemic nucleoside analogs

Genetic variation in genes expressed in the germinal center and risk of B cell lymphoma among Caucasians

The germinal center reaction is integral to B-cell maturation, where class switch recombination (CSR) and somatic hypermutation (SHM) are targeted to the immunoglobulin (Ig) locus to facilitate antibody diversity.[1][1] Selection against B cells with auto-reactive or low affinity antigen receptors

Abstract 1962: DNA mismatch repair status modulates cellular response to cytarabine: Implications for treatment of acute myeloid leukemia

The DNA mismatch repair (MMR) pathway is responsible for repair of spontaneous errors arising during DNA replication, thus maintaining the integrity of the genome. DNA MMR is frequently dysregulated in some forms of leukemia. We and others have shown that microsatellite instability, the hallmark of dysfunctional DNA MMR, is present in up to 90% of therapy-related myeloid leukemia, 50% of relapsed myeloid leukemia, but is rarely seen in de novo leukemia. Paradoxically, functional MMR mediates the cytotoxicity of certain chemotherapeutic agents, particularly methylating agents and the nucleoside analogue 6-thioguanine, and dysregulation of the MMR pathway confers tolerance to these agents. In the present study, using cell lines harbouring defects in MMR components, we show that MMR status also modulates response to the nucleoside analogue cytarabine and to other therapeutic nucleoside analogues commonly used in the treatment of leukemia. We have determined gene and protein expression levels of the major MMR components in a panel of 4 psuedo-isogenic cell line pairs, and investigated the ability of cell extracts to bind to defined mismatches in electrophoretic mobility shift assays. The cell lines HL-60R (which demonstrates 200-fold overexpression of MSH3) and MT-1 (which lacks functional MSH6 due to bi-allelic gene mutation) were tolerant to the cytotoxic effects of methylating agents and 6-thioguanine by virtue of loss of MutSα activity. However, two additional cell lines, TK6 MTX R and PreB697 MTX R (which demonstrate approximately 5-fold and 2-fold overexpression of MSH3 respectively), did not demonstrate differential response to the cytotoxic effects of methylating agent or 6-thioguanine, suggesting that relatively modest MMR defects do not significantly perturb the pathway. Consistent with a role for MMR in affecting cellular response to other nucleoside analogues used to treat leukemia, those cell lines with major defects in MMR (HL-60R and MT-1) displayed differential toxicity to the killing effects of cytarabine, clofarabine, cladribine and fludarabine compared to their MMR-proficient parental counterparts. In contrast, those cell lines with modest perturbation of the MMR pathway did not respond differently to their parental counterparts following treatment with these agents. Taken together, these data suggest that cellular MMR status affects response to nucleoside analogues and furthermore, the specific nature of the defect is important in determining the exact response. These findings have implications for the use of nucleoside analogues in the treatment of cancers where MMR dysfunction has been identified to occur with high frequency, such as therapy-related and relapsed acute myeloid leukemia. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1962.