Lamin A: a putative colonic epithelial stem cell biomarker which identifies colorectal tumours with a more aggressive phenotype

Abnormalities in the expression, distribution and structural organization of A-type lamins are most commonly associated with a spectrum of inherited disorders which predominantly affect mesenchymal lineages, collectively known as laminopathies. However, a new role for lamin A has been discovered in the progression of a common epithelial cancer. CRC (colorectal cancer) patients expressing lamin A/C in their tumour tissue were found to have a 2-fold greater risk of CRC-related mortality compared with patients with lamin A/C-negative tumours. Consequently, lamin A/C is a prognostic biomarker in CRC. In vitro studies suggest that lamin A is an upstream regulator of a pathway linking actin dynamics to loss of cell adhesion, leading to enhanced cell motility and consequently increased invasive potential within a tumour. The finding that lamin A is a putative colonic epithelial stem cell biomarker suggests that the poor outcome associated with lamin A/C-positive tumours may be reflective of a more stem-cell-like phenotype. The present review discusses the link between lamin A expression and tumour progression in one of the commonest causes of cancer-related death in the Western world.

DNA Methylation in Circulating Tumour DNA as a Biomarker for Cancer

Free circulating DNA, which is thought to be derived from the primary tumour, can be detected in the blood of patients with cancer. Detection of genetic and epigenetic alteration in this tumour DNA offers a potential source of development of prognostic and predictive biomarkers for cancer. One such change is DNA methylation of the promotor region of tumour suppressor genes. This causes down regulation of tumour suppressor gene expression, a frequent event in carcinogenesis. Hypermethylation of the promotor region of a number of genes has been detected in many tumour types and more recently these changes have been detected in circulating tumour DNA. This review will summarise the literature detailing DNA methylation in circulating tumour DNA and discuss some of the current controversies and technical challenges facing its use as a potential biomarker for cancer.

Homogeneous Amplification and Mutation Scanning of the p53 Gene Using Fluorescent Melting Curves

Background: In malignancy, gene mutations frequently occur in tumor suppressor genes such as p53 and are sporadically located. We describe a homogeneous method for amplification and mutation scanning, and apply the method to the p53 gene.

Methods: Using a series of overlapping fluorescein-labeled oligonucleotides complementary to a wild-type p53 sequence, we detected somatic mutations in colorectal cancers by aberrant probe:target melting temperatures (Tm). The probes were designed so that fluorescence decreased on target annealing as a result of deoxyguanosine quenching. Probes were walked along the sequence to be scanned, using two to three probes per cuvette and placing overlapping probes in separate reactions. After amplification, the reaction was cooled to anneal probes and then slowly heated (0.1 °C/s) while fluorescence was continuously monitored. Somatic mutations in tumor tissue were detected by changes from a characteristic wild-type melting curve profile using leukocyte DNA.

Results: A complete scanning of the DNA binding domain (exons 5–8) of the p53 gene was completed in a single run (∼30 min) starting from genomic leukocyte DNA. To show proof-of-principle, p53 exons 6–8 from 63 colon cancers were probe-scanned and showed 100% agreement with direct sequencing for detecting alterations from wild-type DNA.

Conclusions: p53 mutation scanning by single-labeled hybridization probes is a homogeneous, rapid, and sensitive method with application in both research and clinical diagnostics.

Chemoprevention of Colorectal Cancer

Goal

After completing this CE program, the participant will understand the basic concepts of chemoprevention and will be able to discuss the currently existing clinical data for the chemoprevention of colorectal cancer.

Objectives

At the completion of this program the participant will be able to: 1. Discuss the complicating factors in performing chemoprevention trials. 2. Describe the dietary modifications to prevent colorectal cancer. 3. Describe the proposed mechanisms of action of agents used in the chemoprevention of colorectal cancer. 4. Discuss, and where appropriate recommend, appropriate agents for use in the chemoprevention of colorectal cancer. 5. Describe the differences between familial adenomatous polyposis (FAP), hereditary nonpolyposis colorectal cancer (HNPCC), and spontaneous adenoma formation.