Introducing Novel Molecular-based Method for Quantification of Homologous Recombination Efficiency

Background Homologous recombination (HR) pathway is a DNA double-stranded breaks repair pathway well-known for its high level of accuracy. Low HR pathway efficiency clinically known as homologous recombination deficiency (HRD) was identified in some cancers such as breast and ovarian cancers and studies have reported the sensitivity of HRD cancer cells to DNA repair inhibitors such as Olaparib. However, current techniques including immunofluorescence-based technique are qualitative-based, hence lack sensitivity to determine the functionality of HR pathway. Additionally, some of the techniques including gene expression arrays require expression study of wide range genes involve in HR pathway, which is not cost-effective. The aim of the study is to optimise a PCR-based assay (Norgen’s Homologous Recombination kit) that can be employed to quantitate HR efficiency in cells, which accurately reflects the functional status of HR pathway. Methods and Findings The kit has two test plasmids (dl-1 and dl-2) with partial deletions in the LacZ gene and the plasmids are generated from modification of pUC19. HR-proficient (HeLa and AsPC-1) and HR-deficient (CAPAN-1 cells) cancer cell lines were transfected with the two plasmids to generate functional LacZ gene (i.e. recombinant product). The recombinant product was quantified by real-time PCR. Although recombinant product was generated in all the cell lines, our real-time PCR demonstrated a high quantity of recombinant product in HeLa cell line whilst low quantity in CAPAN-1 and AsPC-1 cell lines. The quantity of recombinant product generated and quantified reflects HR pathway efficiency. Conclusion Overall, the results have provided some evidence that the PCR-based kit can be suitably employed for quantification of HR efficiency provided appropriate transfection method and reagent are used. However, further study is required to confirm HR efficiency status of AsPC-1 cells to ascertain the low HR efficiency detected by the kit in these cells.