MCC 2011 - Slide 6
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1. Kras and BRAF mutations are important for determining treatment with cetuximab and differentiating Lynch syndrome from sporadic colorectal cancers with microsatellite instability. 2. CpG island methylation phenotype (CIMP) refers to gene silencing through methylation of CpG islands. 3. Rare epimutations can cause multiple cancers through methylation-induced silencing of genes like MLH1.
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MCC 2011 - Slide 6
- 1. ESO-ESSO Masterclass in colorectal cancer surgery Genetic and epigenetic analysis of sporadic colon cancer-Decision & treatment Professor Sir John Burn MD FRCP FRCPCH FRCOG FMedSci Institute of Human Genetics, Newcastle University, UK Institute of Human Genetics Newcastle University Centre for Life, Newcastle UK
- 3. December 11 th 2008;359:2567-2578 CAPP2: 1009 Lynch syndrome recruits Gail Barker Anne-Marie Gerdes Julie Coaker Lynn Reed John Mathers Tim Bishop 600mg aspirin for up to 4 yrs had no effect
- 4. CAPP2: Per protocol analysis (primary endpoint CRC after 2 years treatment) significantly fewer colorectal cancers [submitted] HR 0.45 (0.22-0.93) p = 0.03 IRR 0.41 (0.20-0.84) p= 0.01
- 5. CAPP2 per protocol analysis All Lynch syndrome cancers HR 0.48 (0.28-0.83)p= 0.008 IRR 0.44 (0.26-0.75)p=0.002
- 6. Toronto outline 100 CRC InSiGHT meeting 2005 15 MSI-H 85 MSS 2 HNPCC 13 sporadic 1 MLH1 1 MSH2 1 FAP 1 MAP
- 7. Normal epithelium Adenoma Carcinoma Metastases APC, K-ras 12p, DCC 18q, p53 17p, …….. 85 % 15 % CIN MSI FAP HNPCC hMLH1, hMSH2, TGF-ß RII, Bax, TCF4, ACVRII, Caspase 5 ………. The Genomic Pathogenesis of Colorectal Cancer
- 8. Molecular Classification of Colorectal Cancer Jass, Histopathology 2007, 50, 113–130 FAP Less responsive To 5FU? Gallinger group Ribic CM et al NEJM 2003 ;349:247-57,
- 9. Colorectal Cancer Genetics & 5-FU Ribic CM NEJM 2003 MSS MSI Hazard Ratio 0.69 (0.50-0.94) p=0.02 2.17 (0.84-5.55) p=0.10 Courtesy Steve Gallinger
- 12. SEQUENOM TM MALDI TOF MASS SPECTROMETER Matrix Assisted Laser Desorption/Ionisation Time of Flight mass spectrometry Laser Flight path Detector Time of flight Sequenom chip
- 14. T G G A C C G T T C A A C - ve - ve - ve - ve - ve - ve - ve Polymerase - ve - ve - ve - ve - ve - ve - ve C
- 15. % resistance change A C T G A C T Time = ACTACT
- 18. Cytosine methylation at CpG islands CpG m CpG N N HO NH 2 1 2 3 4 5 6 CH 3 5-methylcytosine cytosine Normal biallelic expression Biallelic methylation – eg cancer cells N N HO NH 2 1 2 3 4 5 6 TF TF
- 19. A C A T C A C G T G A TT A C A Sodium bisulphite (NaHS0 3) conversion of genomic DNA Genomic DNA Treatment with sodium bisulphite Unmethylated sequence Methylated sequence A T A T T A C G T G A TT A T A A T A T T A T G T G A TT A T A
- 23. Dr Magnus von Knebel Doeberitz
- 25. ELISA reactivity reveals immune response to Neopeptides in Lynch syndrome patients with Previous cancer and in MMR mutation carriers patients healthy controls mutation carriers
- 26. Distribution of FSP-specific responses in patients and controls Schwitalle et al., Gastroenterology 2008
- 27. T-cells infiltrating MSI-H CRC recognize MSI-induced FSP Exemplary results derived from a MSI-H CRC-patient Schwitalle et al. Gastroenterology 2008
- 28. Truncating mutations in ß2m are more common with tumour progression but absent from mets Kloor et al Int J Cancer 2007 UICC IV, M1: No truncating mutation in CRC with metastasis ß2m mutation frequency is signif. lower in M1 vs M0 MSI CRC ?Intact ß2m needed for metastasis formation in MSI-H CRC UICC III 9/22 (40.9%) UICC IV 2/26 (7.7%) p=0.01 Only silent mutations or single AA exchanges, w/o functional loss of ß2m
- 30. Aspirin inhibits IL-4 making cancer stem cells more vulnerable to chemotherapy
Editor's Notes
- December 11 th Gail, our manager, was retiring and our statistician had gone on maternity leave All the money was gone but Anne Marie had come as a visiting fellow so I asked her to plot out the cancers covering the whole period as we now had data up to 10 years since commencement. I jokingly predicted that the lines would separate at 4 yeasr just after our last analysis
- Per protocol analysis showing proportion who developed CRC We decided to use tablet counts. 2 per day for 2 years equals 1460 tabs We rounded down to 1400 (blind to the data) to allow for those who missed some tablets Note there are few cases at 10 years out so confidence limits expand Note also that the aspirin placebo group who dropped out early are the same as the aspirin treated groups suggesting they may have dropped into self medication IRR is equivalent to HR using Poisson to allow for multiple primary events eg a person gets endometrial cancer at 3 years and crc at 6 years
- THIS GRAPH ANALYSES ALL Lynch syndrome cancers rather than just colorectal Note again that the early finish placebo aspirin group are tracking with the main treatment line.
- Mismatch repair – corrects bases which are not paired according to the Watson-Crick base pairing A-T and C-G.
- CIMP-negative, chromosomal instability, mainly MSS, origin in adenomas (may be sporadic, FAP-associated or MUTYH (formerly MYH) polyposis associated 108) (57%). CIMP-low, KRAS mutation, MGMT methylation, chromosomal instability, MSS or MSI-L, origin in adenomas or serrated polyps (20%). CIMP-high, methylation of MLH1, BRAF mutation, chromosomally stable, MSI-H, origin in serrated polyps, known generally as sporadic MSI-H (12%). CIMP-high, partial methylation of MLH1, BRAF mutation, chromosomally stable, MSS or MSI-L, origin in serrated polyps (8%). Lynch syndrome, CIMP-negative, BRAF mutation negative, chromosomally stable, MSI-H, origin in adenomas (3%) (familial MSI-H CRC) .
- Mismatch repair – corrects bases which are not paired according to the Watson-Crick base pairing A-T and C-G.
- The first case of what we now term a constitutional epimutation to be identified in humans was reported by Richard Kolodner’s group in 2002 in the mismatch repair gene, MLH1, in a patient diagnosed with Lynch syndrome. Constitutional epimutations of MLH1 are characterised by soma-wide monoallelic methylation of the MLH1 promoter, that is methylation of a single allele. We know this because some epimutation carriers are heterozygous for the common G/A SNP in the MLH1 promoter, and through methylation-sequencing of individual alleles, the methylation is shown to be associated with just one genetic allele. Because this methylation is present in normal somatic tissues, epimutation carriers are typically identified by the detection of methylation in their peripheral blood DNA. The effect of the epimutation is to cause transcriptional silencing of the methylated allele, and once again we know this by tracing the activity of SNPs that are present within the expressed part of the gene. In cases that are heterozygous for an exonic SNP, analysis of their RNA has shown that only one allele is detected in their mRNA, due to loss of transcriptional activity from the other allele. Finally, MLH1 epimutations occur in the context of a normal gene sequence – there are no genetic mutations identified in the gene or its vicinity.
- Patient YT, represents the youngest affected case reported to date, but his profile is otherwise typical of other cases with a constitutional MLH1 epimutation. YT was 18 years old when he presented with cancer of the ascending colon, but had no family history of LS. The tumour demonstrated microsatellite instability and immunohistochemical loss of MLH1 and PMS2, but no germline mutation was identified within MLH1 and no evidence for structural alterations of MLH1 or MSH2 was identified by MLPA. Methylation testing revealed hemiallelic soma-wide methylation of the MLH1 promoter, as shown in these epigrams. Approximately half of his alleles were hypermethylated, as seen by the black dots, whilst the other half were unmethylated as indicated by the white dots.
- A small number of families in whom the affected members have loss of the MSH2 protein in their tumours, have now been identified with deletions of the EPCAM gene located immediately upstream of MLH1, which give rise to a somatic epimutation of MSH2. In these cases, there is mosaic methylation of the MSH2 promoter, which is predominant in epithelial tissues. Although MSH2 itself in intact, this epigenetic error is caused by a linked deletion of the final exons of EPCAM. These abolish the transcription termination signal and cause elongation of transcription into MSH2 to produce fusion transcripts, ultimately leading to MSH2 methylation. Since this type of epimutation is associated with a cis-acting genetic defect, it demonstrates dominant inheritance, and has been found in large Lynch syndrome kindreds.