RESUMO
Formalin-fixed paraffin-embedded (FFPE) tissue specimens have been a staple of research, providing precious resources for molecular and genomic studies. However, the biggest challenge is the extraction of high-quality DNA from FFPE tissues, given that the integrity of DNA is critically affected by formalin fixation. Formaldehyde induces crosslinks in DNA that renders single or double-stranded DNA breaks. Such breaks cause extensive fragmentation that directly influences the quality of DNA purified and the number of templates available for PCR amplification. Thus, protocol for DNA purification from FFPE tissues must effectively extract highly fragmented DNA and reverse cross-linking caused by formalin fixation. DNA extraction methods available in the literature were selected and modified at different stages to optimize a protocol that extracts DNA of sufficient quality and fragment size to be detectable by PCR. Archived FFPE tissues belonged to patients with triple negative breast cancer (TNBC) and benign breast disease were used for the protocol optimization. The best optimized protocol was then used to amplify Exon 4 region of Proviral integration site for Moloney murine leukemia virus1 (Pim1) kinase gene to analyze any probable somatic mutations both in TNBCs and benign breast diseases. Of the 12 different protocols developed, best quality DNA in terms of fragment size and purity was obtained when Tween20 lysis buffer was used for both deparaffinization and overnight digestion along with high salt precipitation. Optimized protocol was then validated by extracting DNAs from 10 TNBCs and 5 benign breast disease specimens with consistent purity and fragment size. PCR amplification and subsequent Sanger's sequencing revealed the presence of mutations in the Exon 4 region of Pim1 kinase. Deparaffinization and overnight digestion in Tween20 lysis buffer along with high salt precipitation yielded the best quality PCR amplifiable DNA for mutational analysis.
