High-sensitivity PCR method for detecting BRAF V600Emutations in metastatic colorectal cancer using LNA/DNA chimeras to block wild-type alleles

The response to epidermal growth factor receptor (EGFR)-targeted therapy in metastatic colorectal cancer (mCRC) is variable because of intra-tumor heterogeneity at the genetic level, and consequently, it is important to develop sensitive and selective assays to predict patient responses to therapy. Low-abundance BRAF V600E mutations are associated with poor response to treatment with EGFR inhibitors. We developed a method for the detection of BRAF V600E mutations in mCRC using real-time wild-type blocking PCR (WTB-PCR), in which a chimera composed of locked nucleic acids and DNA is incorporated to amplify the mutant allele at high efficiency while simultaneously inhibiting the amplification of wild-type alleles. Mixing experiments showed that this method is exquisitely sensitive, with detection of the mutated allele at a mutant/wild-type ratio of 1:10,000. To demonstrate the applicability of this approach for mCRC patients, we assessed the V600E mutations in 50 clinical cases of mCRC by real-time WTB-PCR. The percentage of patients with V600E mutation as determined by WTB-PCR (16 %, 8/50) was higher than by traditional PCR (10 %, 5/50), suggesting an increased sensitivity for WTB-PCR. By calculating the Δ C q for real-time traditional PCR, which amplifies all BRAF alleles, versus WTB-PCR, which selectively amplifies mutant BRAF , we demonstrated that among the V600E-positive mCRC patient samples, the percentage of BRAF DNA with the V600E mutation ranged from 0.05 to 52.32 %. In conclusion, WTB-PCR provides a rapid, simple, and low-cost method to detect trace amounts of mutated BRAF V600E gene.