Coamplification at lower denaturation temperature-PCR increases mutation-detection selectivity of TaqMan-based real-time PCR.

backgroundDNA genotyping with mutation-specific TaqMan(R) probes (Applied Biosystems) is broadly used in detection of single-nucleotide polymorphisms but is less so for somatic mutations because of its limited selectivity for low-level mutations. We recently described coamplification at lower denaturation temperature-PCR (COLD-PCR), a method that amplifies minority alleles selectively from mixtures of wild-type and mutation-containing sequences during the PCR. We demonstrate that combining COLD-PCR with TaqMan technology provides TaqMan genotyping with the selectivity needed to detect low-level somatic mutations.

methodsMinor-groove binder-based or common TaqMan probes were designed to contain a nucleotide that matches the desired mutation approximately in the middle of the probe. The critical denaturation temperature (T(c)) of each amplicon was then experimentally determined. COLD-PCR/TaqMan genotyping was performed in 2 steps: denaturation at the T(c), followed by annealing and extension at a single temperature (fast COLD-PCR). The threshold cycle was used to identify mutations on the basis of serial dilutions of mutant DNA into wild-type DNA and to identify TP53 (tumor protein p53) and EGFR [epidermal growth factor receptor (erythroblastic leukemia viral (v-erb-b) oncogene homolog, avian)] mutations in tumors.

resultsCOLD-PCR/TaqMan genotyping identified G>A mutations within TP53 exon 8 (codon 273 mutation hot spot) and C>T mutations within the EGFR gene (drug-resistance mutation T790M) with a selectivity improvement of 15- to 30-fold over regular PCR/TaqMan genotyping. A second round of COLD-PCR/TaqMan genotyping improved the selectivity by another 15- to 30-fold and enabled detection of 1 mutant in 2000 wild-type alleles. Use of COLD-PCR/TaqMan genotyping allowed quantitative identification of low-level TP53 and T790 mutations in colon tumor samples and in non-small-cell lung cancer cell lines treated with kinase inhibitors.

conclusionsThe major improvement in selectivity provided by COLD-PCR enables the popular TaqMan genotyping method to become a powerful tool for detecting low-level mutations in clinical samples.