Somatic Mutations in Circulating Cell-Free D-Loop Region of Mitochondrial DNA: A Study from North-East India

ABSTRACT

Head and neck Squamous cell carcinoma (HNSCC) is highly prevalent in Northeast India. The widespread use of tobacco exposure is a known risk factor, makingmitochondrial DNA (mtDNA) more susceptible to damage by oxidative stress incomparison to nuclear DNA. Mitochondrial dysfunction being a hallmark of cancer, thestudy aims to evaluate liquid biopsy involving circulating cell-free mitochondrial DNA(cfmtDNA) as an early diagnostic marker by reducing the dependability over tumor tissuebiopsy specimen. A total of 50 HNSCC cases reported at Cancer Hospital, Guwahati MedicalCollege from January 2018 to August 2018 were included in this study. Cell-free DNA wasisolated using QIAamp Circulating Nucleic Acid Kit. PCR based amplification ofmitochondrial D-loop, followed by direct sequencing. Our result indicated the presence ofsomatic mutations (73(A/G), 93(G/A), 146(T/C) and 207 (G/A)). Polymorphism was alsoobserved in the sequences (263A>G, 275G>A, 318T>C, 16034T>C, 16257C>A and16519T>C) upon comparison with reference sequence. Analysis of c-tract region showedthe presence of an additional cytosine nucleotide at position 309.Identifying somaticmutations in cfmtDNA using liquid biopsy approach will certainly minimize thedependency of clinicians and molecular biologist over the availability of tumor tissuespecimens. The identified somatic variations from our study will help in theimplementation of preventive measure. Therefore, our study provides an early mtDNAdiagnostic marker using liquid biopsy approach.