PET Imaging Quantifying 68Ga-PSMA-11 Uptake in Metastatic Colorectal Cancer

At diagnosis, 22% of colorectal cancer (CRC) patients have metastases, and 50% later develop metastasis. Peptide receptor radionuclide therapy (PRRT), such as ¹⁷⁷Lu-PSMA-617, is used to treat metastatic prostate cancer. ¹⁷⁷Lu-PSMA-617 targets prostate-specific membrane antigen (PSMA), a cell-surface protein enriched in prostate cancer and the neovasculature of other solid tumors, including CRC. We performed ⁶⁸Ga-PSMA-11 PET/CT imaging of 10 patients with metastatic CRC to assess metastasis avidity. Eight patients had lesions lacking avidity, and 2 had solitary metastases exhibiting very low avidity. Despite expression of PSMA in CRC neovasculature, none of the patients exhibited tumor avidity sufficient to be considered for ¹⁷⁷Lu-PSMA-617 PRRT.

Abstract 479: BRAF and KRAS mutation define distinct subtypes of the CpG island methylator phenotype in colorectal cancers

BACKGROUND AND AIMS: Colorectal cancer is an epigenetically heterogeneous disease, however the extent and spectrum of the CpG Island Methylator Phenotype (CIMP) is not clear.METHODS: Genome scale methylation and transcript expression were measured using the Illumina HM450 DNA methylation and HT12 V3 expression microarrays in 216 unselected colorectal cancers. Mutations in epigenetic regulators were assessed using CIMP-classified Cancer Genome Atlas exomes.RESULTS: CIMP-High cancers dichotomised into CIMP-H1 and CIMP-H2 based on methylation profile, which was supported by over-representation of BRAF (74%, P<0.0001) or KRAS (55%, P<0.0001) mutation. Congruent with increasing methylation, there was a stepwise increase in patient age from 62 years in the CIMP-Negative subgroup to 75 years in the CIMP-H1 subgroup (P<0.0001). CIMP-H1 were predominantly comprised of consensus molecular subtype 1 (CMS1) cancers (70%) whilst CMS3 was over-represented in the CIMP-H2 subgroup (55%). PRC2-marked loci were subjected to significant gene body methylation in CIMP cancers (P<1.6x10-78). We identified oncogenes susceptible to gene body methylation and Wnt pathway antagonists resistant to gene body methylation. CIMP cluster specific mutations were observed for in chromatin remodeling genes, such as in the SWI/SNF and NuRD complexes, suggesting synthetic lethality.CONCLUSION: There are five clinically and molecularly distinct subgroups of colorectal cancer. We show a striking association between CIMP and age, gender and tumor location and identify an unidentified role for gene body methylation in progression of serrated neoplasia. These data support our recent findings that CIMP is uncommon in young patients and that BRAF mutant polyps in young patients may have limited potential for malignant progression.

Citation Format: Vicki L. Whitehall, Lochlan Fennell, Troy Dumenil, Gunter Hartel, Katia Nones, Catherine Bond, Diane McKeone, Ann-Marie Patch, Stephen Kazakoff, John Pearson, Nicola Waddell, Pratyaksha Wirapati, Paul Lochead, Shuji Ogino, Sabine Tejpar, Barbara Leggett. BRAF and KRAS mutation define distinct subtypes of the CpG island methylator phenotype in colorectal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 479.

Abstract 2076: RNF43 is a frequent mutational target in serrated colorectal neoplasia

BACKGROUND. The Wnt signalling pathway is altered in the majority of colorectal cancers by APC mutation. Cancers arising via the serrated neoplasia pathway are hallmarked by BRAF mutation and microsatellite instability (MSI), but do not commonly mutate APC. RNF43 and ZNRF3 are transmembrane E3 ubiquitin ligases that are localised to intestinal stem cells where they cooperate to suppress Wnt signaling. Mutation of these genes may be an alternate mechanism to bypass the Wnt signal. RNF43 / ZNRF3 double knockout mice develop intestinal neoplasia and germline mutation of RNF43 has been reported in serrated polyposis. We therefore hypothesised that somatic mutation of RNF43 and/or ZNRF3 would be important in the development of serrated colorectal neoplasia.

METHODS. RNF43 and ZNRF3 mutations were assessed in a pilot series of 24 BRAF mutant cancers representing the serrated neoplasia pathway and 10 control BRAF wild type cancers using Agilent V4+UTR whole exome capture followed by sequencing on an Illumina HiSeq 2000. An extended cohort of 80 BRAF mutant cancers (48 MSI, 32 MSS) and 67 BRAF wild type cancers was examined by Sanger sequencing. The frequency of a common hotspot mutation in RNF43 was validated in a second series of 42 BRAF mutant and 22 BRAF wild type colorectal cancers. Transcript expression for RNF43 and ZNRF3 was assayed using Illumina HT-12v4 BeadChip expression arrays in 29 BRAF mutant cancers, 187 BRAF wild type cancers and a subset of 32 matched normal mucosa samples.

RESULTS. RNF43 mutations were detected in whole exome sequencing data in 11/24 BRAF mutant but no BRAF wild type cancers (P<0.01). Three of these 11 cancers also had a ZNRF3 mutation. RNF43 and ZNRF3 mutations were also frequently concordant in a larger series of cancers. RNF43 mutations were associated with MSI (P<0.0001), being identified in 43/48 BRAF mutant / MSI cancers (90%), 6/32 (19%) BRAF mutant / MSS cancers and 6/44 BRAF wild type / MSS cancers (14%). The high frequency of a G7 frameshift mutation at position 659 of RNF43 was similarly present in 25/33 (76%) BRAF mutant MSI cancers but only 1/34 MSS cancers from a second, validation cohort. Transcript levels of RNF43 and ZNRF3 were positively correlated (r2 0.47, P<0.0001) and were significantly lower in BRAF mutant compared to BRAF wild type cancers (P<0.0001).

CONCLUSIONS. RNF43 is a frequent mutational target in serrated neoplasia. The high frequency of both substitution and frameshift mutations support the functional relevance of these alterations. We hypothesise that RNF43 is mutated as an alternative to APC in serrated lesions as a mechanism of bypassing control of the Wnt signal. These data support our current model of serrated neoplasia whereby BRAF is mutated early in serrated polyp development and RNF43 is subsequently mutated to remove constraints on the Wnt signal and allow progression to cancer.

Citation Format: Vicki L. Whitehall, Catherine Bond, Diane McKeone, Jonathan Ellis, Mark Bettington, Sally Pearson, Barbara Leggett. RNF43 is a frequent mutational target in serrated colorectal neoplasia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2076. doi:10.1158/1538-7445.AM2015-2076

Abstract 2422: Microsatellite stable colorectal cancers stratified by the BRAF V600E mutation show distinct patterns of chromosomal instability

The BRAF (V600E) mutation in colorectal cancers that are microsatellite stable (MSS) confers a very poor patient prognosis, whereas BRAF mutant microsatellite-unstable (MSI) colorectal cancers have an excellent prognosis. BRAF wild type cancers are typically MSS and display chromosomal instability (CIN). CIN is associated with a poor prognosis but has not been extensively studied on a genome-wide basis in relation to BRAF mutational status in colorectal cancer.

BRAF mutant/MSS (BRAFmut/MSS) cancers (n=33) and BRAF mutant/MSI (BRAFmut/MSI) cancers (n=30) were compared for presence of copy number aberrations (CNAs) indicative of CIN, with BRAF wild type/MSS (BRAFwt/MSS) cancers (n=18) using Illumina CytoSNP-12 arrays.

BRAFmut/MSS and BRAFwt/MSS cancers showed comparable numbers of CNAs per cancer at 32.8 and 29.8 respectively. However there were distinct differences in patterns of CNA length between MSS cohorts, with BRAFmut/MSS cancers having a significantly greater proportion of focal CNAs compared to BRAFwt/MSS cancers (p<0.0001); whereas whole chromosomal arm CNAs were more common in BRAFwt/MSS cancers (p<0.0001). This related to a reduced average CNA length in BRAFmut/MSS compared to BRAFwt/MSS cancers (20.7Mb vs 33.4Mb; p<0.0001); and a smaller average percentage of CIN affected genomes in BRAFmut/MSS compared to BRAFwt/MSS cancers (23.9% vs 34.9% respectively). BRAFmut/MSI cancers were confirmed to have low CNA rates (5.4 per cancer) and minimal CIN-affected genomes (average of 4.5%) compared to MSS cohorts (p<0.0001). BRAFmut/MSS cancers had more frequent deletion CNAs compared to BRAFwt/MSS cancers on 17q and 6p at loci not typically correlated with colorectal cancer, and more frequent amplification CNAs on 8q and 18q compared to BRAFwt/MSS cancers.

These results indicate that although comparable rates of CIN occur between MSS subgroups, significant differences in their patterns of instability exist as BRAFmut/MSS cancers display a ‘focal pattern’ and BRAFwt/MSS cancers have more a ‘whole arm pattern' of CIN. This and the genomic loci more frequently affected in BRAFmut/MSS cancers may warrant extended studies to ascertain correlations with clinical data.

Overall this investigation has identified that differing patterns of genomic instability exist between the two MSS colorectal subgroups and provides further evidence of the biological distinctions of the aggressive BRAFmut/MSS cancers.

Citation Format: Catherine E. Bond, Derek J. Nancarrow, Leesa F. Wockner, Leanne Wallace, Grant W. Montgomery, Barbara A. Leggett, Vicki LJ Whitehall. Microsatellite stable colorectal cancers stratified by the BRAF V600E mutation show distinct patterns of chromosomal instability. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2422. doi:10.1158/1538-7445.AM2014-2422

Hyperplastic polyposis syndrome is associated with cigarette smoking, which may be a modifiable risk factor

OBJECTIVES

Hyperplastic polyposis syndrome (HPS) confers an increased risk of colorectal cancer and is difficult to manage clinically. Because both polyps and resultant cancers display the CpG island methylator phenotype and mutation of the BRAF oncogene, and because sporadic cancers with these characteristics are associated with cigarette smoking, we hypothesized that cigarette smoking may predispose to the development of HPS.

METHODS

This was a case-control study with two independent control series conducted at a tertiary hospital in Brisbane, Queensland, Australia. Cases comprised patients with HPS (n=32) recruited through the database of the Queensland Familial Bowel Registry, who satisfied the World Health Organization international classification for HPS. Cases were compared with colonoscopy controls (n=298) defined as consecutive patients undergoing colonoscopy for clinical indications, who were free from polyps. We also compared cases with a second set of population controls (n=645) selected at random from a population register serving the catchment area for cases. This was an observational study, and all participants completed a questionnaire to obtain a comprehensive smoking history.

RESULTS

The prevalence rate of current smoking was 47% in HPS patients, 17% in colonoscopy controls, and 12% in population controls. HPS patients were significantly more likely to be current smokers than were either colonoscopy controls (odds ratio (OR)=8.3, 95% confidence interval (CI): 3.0-22.9) or population controls (OR=12.7, 95% CI: 4.9-33.1).

CONCLUSIONS

Cigarette smoking is strongly associated with HPS, thus suggesting that smoking exposure may increase the expression of this condition. Further studies should examine the possible benefits of quitting smoking in HPS patients.

Analysis of the association between CIMP and BRAF in colorectal cancer by DNA methylation profiling

A CpG island methylator phenotype (CIMP) is displayed by a distinct subset of colorectal cancers with a high frequency of DNA hypermethylation in a specific group of CpG islands. Recent studies have shown that an activating mutation of BRAF (BRAF^V600E) is tightly associated with CIMP, raising the question of whether BRAF^V600E plays a causal role in the development of CIMP or whether CIMP provides a favorable environment for the acquisition of BRAF^V600E. We employed Illumina GoldenGate DNA methylation technology, which interrogates 1,505 CpG sites in 807 different genes, to further study this association. We first examined whether expression of BRAF^V600E causes DNA hypermethylation by stably expressing BRAF^V600E in the CIMP-negative, BRAF wild-type COLO 320DM colorectal cancer cell line. We determined 100 CIMP-associated CpG sites and examined changes in DNA methylation in eight stably transfected clones over multiple passages. We found that BRAF^V600E is not sufficient to induce CIMP in our system. Secondly, considering the alternative possibility, we identified genes whose DNA hypermethylation was closely linked to BRAF^V600E and CIMP in 235 primary colorectal tumors. Interestingly, genes that showed the most significant link include those that mediate various signaling pathways implicated in colorectal tumorigenesis, such as BMP3 and BMP6 (BMP signaling), EPHA3, KIT, and FLT1 (receptor tyrosine kinases) and SMO (Hedgehog signaling). Furthermore, we identified CIMP-dependent DNA hypermethylation of IGFBP7, which has been shown to mediate BRAF^V600E-induced cellular senescence and apoptosis. Promoter DNA hypermethylation of IGFBP7 was associated with silencing of the gene. CIMP-specific inactivation of BRAF^V600E-induced senescence and apoptosis pathways by IGFBP7 DNA hypermethylation might create a favorable context for the acquisition of BRAF^V600E in CIMP+ colorectal cancer. Our data will be useful for future investigations toward understanding CIMP in colorectal cancer and gaining insights into the role of aberrant DNA hypermethylation in colorectal tumorigenesis.

A human, double-blind, placebo-controlled, crossover trial of prebiotic, probiotic, and synbiotic supplementation: effects on luminal, inflammatory, epigenetic, and epithelial biomarkers of colorectal cancer

BACKGROUND

Diet is an important factor in colorectal carcinogenesis; thus, dietary supplements may have a role in colorectal cancer prevention.

OBJECTIVE

The objective was to establish the relative luminal, epithelial, and epigenetic consequences of prebiotic, probiotic, and synbiotic dietary supplementation in humans.

DESIGN

This was a randomized, double-blind, placebo-controlled, 4-wk crossover trial of resistant starch and Bifidobacterium lactis, either alone or as a combined synbiotic preparation, in 20 human volunteers. Rectal biopsy, feces, and serum samples were collected. The rectal mucosal endpoints were DNA methylation at 16 CpG island loci and LINE-1, epithelial proliferation (Ki67 immunohistochemistry), and crypt cellularity. The fecal endpoints were short-chain fatty acid concentrations, pH, ammonia, and microbiological profiles (by denaturing gradient gel electrophoresis and sequencing). Serum endpoints were a panel of cytokines and high-sensitivity C-reactive protein.

RESULTS

Seventeen subjects completed the entire study. The synbiotic intervention fostered a significantly different fecal stream bacterial community than did either the prebiotic (P = 0.032) or the probiotic (P = 0.001) intervention alone, in part because of a greater proportion of patients harboring fecal Lachnospiraceae spp. These changes developed in the absence of any significant differences in fecal chemistry. There were no differences in epithelial kinetics.

CONCLUSIONS

This synbiotic supplementation with B. lactis and resistant starch, in the doses used, induced unique changes in fecal microflora but did not significantly alter any other fecal, serum, or epithelial variables. This trial was registered in the Australian New Zealand Clinical Trials Registry at www.anzctr.org.au as ACTRN012606000115538.

Methylation of O-6-methylguanine DNA methyltransferase characterizes a subset of colorectal cancer with low-level DNA microsatellite instability

The significance of low-level DNA microsatellite instability (MSI-L) is not well understood. K-ras mutation is associated with MSI-L colorectal cancer and with the silencing of the DNA repair gene O-6-methylguanine DNA methyltransferase (MGMT) by methylation of its promoter region. MGMT methylation was studied in sporadic colorectal cancers stratified as DNA microsatellite instability-high (n = 23), MSI-L (n = 44), and microsatellite-stable (n = 23). Methylation-specific PCR was used to detect MGMT-promoter hypermethylation in 3 of 23 (13%) microsatellite instability-high, in 28 of 44 (64%) MSI-L, and in 6 of 23 (26%) microsatellite-stable cancers (P = 0.0001). K-ras was mutated in 20 of 29 (69%) methylated MSI-L cancers and in 2 of 15 (13%) unmethylated MSI-L cancers (P = 0.001), indicating a relationship between MGMT-methylation and mutation of K-ras. Loss of nuclear expression of MGMT was demonstrated immunohistochemically in 23 of 31 (74%) cancers with methylated MGMT and in 10 of 49 (20%) cancers with nonmethylated MGMT (P < 0.0001). Loss of expression of MGMT was also demonstrated in 9 of 31 serrated polyps. Silencing of MGMT may predispose to mutation by overwhelming the DNA mismatch repair system and occurs with greatest frequency in MSI-L colorectal cancers.

p73 is up-regulated in a subset of hepatocellular carcinomas

Loss of heterozygosity (LOH) at 1p36 occurs in a number of solid tumors including hepatocellular carcinoma (HCC). Recently, a novel gene, p73, has been identified at 1p36.33. p73 is structurally and functionally related to p53 located at 17p13.1, which is a target for inactivation in HCCs. p73 produces at least two splicing variants, p73alpha and beta, and a polymorphism in exon 2 results in two alleles, GC or AT. Initially, only the AT allele and p73alpha transcripts were identified in malignant cell lines, suggesting a role for these in the malignant phenotype. The aims of this study were to determine the extent of LOH at 1p36 and 17p13.1 in HCCs from Australia and South Africa, and to identify patterns of p73 mRNA and p73 and p53 protein expression. LOH at 1p36 was found in 8 of 25 Australian and 6 of 10 South African cases. p73 mRNA expression occurred in 8 HCCs, but not in nonmalignant liver tissue. Two of these 8 HCCs had LOH of 1p36. Both alpha and beta transcripts were observed in GC/GC homozygotes and GC/AT heterozygotes. No p73 protein expression was observed by immunohistochemistry in nonmalignant liver tissue or in HCC. p53 inactivation appeared to be associated with up-regulation of p73 expression, suggesting a compensatory role for p73 in this situation. The LOH at 1p36 implies a liver-specific tumor suppressor gene is in this region. However, the up-regulation of p73 mRNA suggests p73 is not the target of this loss.