Antiprimer quenching-based real-time PCR and its application to the analysis of clinical cancer samples

Background: Nucleic acid amplification plays an increasingly important role in genetic analysis of clinical samples, medical diagnostics, and drug discovery. We present a novel quantitative PCR technology that combines the advantages of existing methods and allows versatile and flexible nucleic acid target quantification in clinical samples of widely different origin and quality. Methods: We modified one of the 2 PCR primers by use of an oligonucleotide "tail" fluorescently labeled at the 5′ end. An oligonucleotide complementary to this tail, carrying a 3′ quenching molecule (antiprimer), was included in the reaction along with 2 primers. After primer extension, the reaction temperature was lowered such that the antiprimer hybridizes and quenches the fluorescence of the free primer but not the fluorescence of the double-stranded PCR product. The latter provides real-time fluorescent product quantification. This antiprimer-based quantitative real-time PCR method (aQRT-PCR) was used to amplify and quantify minute amounts of input DNA for genes important to cancer. Results: Simplex and multiplex aQRT-PCR demonstrated linear correlation (r² >0.995) down to a DNA input equivalent to 20 cells. Multiplex aQRT-PCR reliably identified the HER-2 gene in microdissected breast cancer samples; in formalin-fixed, paraffin-embedded specimens; and in plasma circulating DNA from cancer patients. Adaptation to multiplex single-nucleotide polymorphism detection via allele-specific aQRT-PCR allowed correct identification of apolipoprotein B polymorphisms in 51 of 51 human specimens. Conclusion: The simplicity, versatility, reliability, and low cost of aQRT-PCR make it suitable for genetic analysis of clinical specimens.