Detection of K-ras point mutation by in situ PCR in cell suspensions: comparison of the indirect and direct methods

Detection of gene point mutation in paraffin sections using in situ loop-mediated isothermal amplification

For pathological diagnoses, visualization of genetic status using routine tissue sections is important to determine the relationships between histopathological findings and genetic alterations. Loop-mediated isothermal amplification (LAMP) has been reported to have high levels of specificity and amplification efficiency. An in situ LAMP method was used, along with an amplification refractory mutation system (ARMS) to directly detect a specific point mutation, L858R, which is a mutation of epidermal growth factor receptor (EGFR), useful for the prediction of the effects of the anti-lung cancer drug gefitinib. The investigation was done using two types of cultured cells as well as paraffin-sectioned specimens collected from 26 cases of surgically resected lung cancer. Twelve of the specimens had an L858R mutation and in situ LAMP showed reactions in the nuclei of all cancer cells present in those. Such reactions were also shown on in situ LAMP in three of the remaining 14 cases that were without the L858R mutation. In addition, a few cases showed responses in the nuclei of bronchial epithelium cells located in non-cancerous areas in the vicinity of a positive tumor, which suggested that the mutation had already occurred in the tumorigenic early stage. It is concluded that the present method is useful for pathological and genetic diagnoses.

Non-radioactive detection of K-ras mutations by nested allele specific PCR and oligonucleotide hybridization

The development of methods to detect point mutations has been rapid over the recent years. In human colon tumours, a significant percentage of mutations are found in the K-ras gene. Faster and more sensitive methods for detection of these mutations are important for patient management and treatment. The author has extended the specificity of allele amplification of point mutations by using mismatch oligonucleotide primers in a polymerase chain reaction (PCR). It is shown that in colon tumours, the sensitivity of detecting a mutation is significantly higher when K-ras exon 1 is amplified prior to PCR with allele specific primers (mismatch PCR). It is shown that allele specific oligonucleotide probes which are non-radioactively labelled could be used to detect these point mutations. By utilizing this two-step PCR, K-ras codon 12 mutations were studied in 10 colon carcinoma cell lines and 25 colon tumours. By combining the two-step PCR together with non-radioactively labelled oligonucleotide probes, the detection of point mutations is both accurate and rapid.