Multiplex polymerase chain reaction in combination with gel electrophoresis-inductively coupled plasma mass spectrometry: A powerful tool for the determination of gene copy number variations and gene expression changes.

During the last few years multiplex real-time or quantitative polymerase chain reaction PCR (qPCR) has become the method of choice for multiplex gene expression changes and gene copy number variations (CNVs) analysis. However, such determinations require the use of different fluorescent labels for the different amplified sequences, which increases significantly the costs of the analysis and limits the applicability of the technique for simultaneous amplification of many targets of interest in a single reaction. In this regard, the use of the coupling between gel electrophoresis (GE) separation with inductively coupled plasma mass spectrometry (ICP-MS) detection allows the label-free determination of multiplex PCR-amplified sequences (amplicons) by monitoring the P present in the DNA backbone. The quantitative dimension is obtained since under optimal and controlled multiplex PCR conditions the peak areas of the separated amplicons are directly proportional to the amount of DNA template in the original sample. Moreover, the calibration of the GE-ICP-MS system with a DNA ladder permits direct estimation of the size (bp) of the PCR products. The suitability of the proposed multiplex strategy has been evaluated addressing two different situations: determination of CNVs and gene expression changes in human ovarian cancer cells. In the first case, the results obtained for the simultaneous quantitation of CNVs of four genes (HER2, CCNE1, GSTM1, ACTB) on DNA obtained from OVCAR-3 cells were in accordance with the literature data, and also with the results obtained by conventional simplex qPCR. In the second case, multiplex gene expression changes of BAX, ERCC1 and CTR1 genes, using ACTB as constitutive gene, on A2780cis respect to A2780 cells, resistant and sensitive to cisplatin, respectively, provided the same information as single reaction reverse transcription (RT)-qPCR.