Base excision repair (BER) is the predominant system correcting simple DNA base lesions formed by oxidation or other DNA damaging agents. Repair of apurinic/apyrimidinic (AP) sites arising in the genome spontaneously or as intermediates of BER is critical owing to their toxic and mutagenic effects. The mammalian apurinic/apyrimidinic endonuclease APE1 (EC 4.2.99.18) is a Mg²⁺-dependent multifunctional protein operating in protection of cells from oxidative stress via its DNA repair, redox, and transcription regulatory activities. The human AP endonuclease APE1, also called Ref-1 is the major and crucial enzyme for the recognition and processing of AP sites in the base excision repair (BER) of DNA[1]. APE1 operates by incising the DNA phosphodiester backbone 5′ to AP sites, generating a nick with 3′-hydroxyl and 5′-deoxyribose phosphate (dRP) termini. Repair of the resulting nick is completed by DNA polymerase and DNA ligase. In addition to its endonuclease activity, APE1 is known to have 3′-phosphodiesterase and 3′-phosphatase activity and 3′ to 5′ exonuclease activity as well as a role in regulating the redox state of several transcription factors[2].