Bases [5]. Therefore, recognition of the AP site holds great promise for

Bases [5]. Therefore, recognition of the AP site holds great promise for diagnostic and therapeutic applications [6]. Although the AP site can be targeted by non-fluorescent small molecules including binder/insertor heterodimer [5,7?], metalloinsertor [6,10], redox probe [11], nitroxide spin label [12], and DNA base analog [13], fluorescent small molecules have received much attention due to simplicity and cost saving in the detection technologies. In this aspect, some fluorophores were found to be effective such as environment polarity-sensitive naphthalene get CASIN derivative [14] as well as the organic probes possessing hydrogen bond moieties that are complementary to the bases opposite the AP site, including naphthyridine [15,16], pyrazine [17], lumazine [18], pteridine [19,20] and flavin [21] derivatives. However, dueto formation of the static DNA complexes, excited state electron transfer, and the other intricate processes, fluorescence quenching was usually observed [15?1]. More seriously, the presence of the AP site-containing DNA (AP-DNA) did not alter the fluorophores’ emission wavelength. Thus, high background emissions can not be overcome using 25331948 these probes as the AP site binders. We have being focused on seeking new fluorophores exhibiting novel optical properties upon binding to the AP site. A new longwavelength emission band arising from an excited-state intramolecular proton transfer (ESIPT) probe [22], fisetin, one of natural 3-hydroxyflavonols, was observed in the presence of the AP site. Recently, we found that berberine [23], one of natural isoquinoline alkaloids, can selectively bind to the AP site with a sequencedependent manner. Although fluorescence I-BRD9 enhancement was observed for these fluorophores, the alteration in their emission wavelengths upon binding to the AP site was not more than 60 nm. Herein, another alkaloid, sanguinarine (SG), was employed to achieve a much larger emission shift up to 170 nm when binding to the AP site. SG belongs to a benzophenanthridine alkaloid, which is known for its antitumor property and possesses the potential for selective/DNA Abasic Site Binderpreferential elimination of cancer cells [24?8]. Besides its interaction with proteins [29] and amino acids [30], one of the potential antitumor activities of SG is believed to result from its highly specific binding to many types of nucleic acid structures and subsequent modification of the genetic information [31]. SG exhibits a pH-dependent structure equilibrium in aqueous solution between the positively charged iminium (in the pH rang 1.0?.0) and the neutral alkanolamine (in the pH rang 8.5?1.0) forms (Figure 1) [31,32]. The iminium form is unsaturated and completely planar, while the alkanolamine form has a buckled structure. SG can interact with polymorphic nucleic acid structures including DNA (B form [33], Z form, triplex [34], quadruplex [35]) and RNA (for example, poly(A) [36]). It is widely believed that the iminium form is mainly responsible for the DNA binding [37]. In addition, binding-induced fluorescence quenching and a strong GC base pair binding preference were observed [38?41]. In this work, we found that SG exhibits a sequence-dependent AP site binding behavior in the aspect of the enhanced emission for the iminium form that is converted from the alkanolamine form. Thus, targeting the AP site with a larger emission shift can be realized by thorough conversion of the alkanolamine emission band to the iminium emission band. The.Bases [5]. Therefore, recognition of the AP site holds great promise for diagnostic and therapeutic applications [6]. Although the AP site can be targeted by non-fluorescent small molecules including binder/insertor heterodimer [5,7?], metalloinsertor [6,10], redox probe [11], nitroxide spin label [12], and DNA base analog [13], fluorescent small molecules have received much attention due to simplicity and cost saving in the detection technologies. In this aspect, some fluorophores were found to be effective such as environment polarity-sensitive naphthalene derivative [14] as well as the organic probes possessing hydrogen bond moieties that are complementary to the bases opposite the AP site, including naphthyridine [15,16], pyrazine [17], lumazine [18], pteridine [19,20] and flavin [21] derivatives. However, dueto formation of the static DNA complexes, excited state electron transfer, and the other intricate processes, fluorescence quenching was usually observed [15?1]. More seriously, the presence of the AP site-containing DNA (AP-DNA) did not alter the fluorophores’ emission wavelength. Thus, high background emissions can not be overcome using 25331948 these probes as the AP site binders. We have being focused on seeking new fluorophores exhibiting novel optical properties upon binding to the AP site. A new longwavelength emission band arising from an excited-state intramolecular proton transfer (ESIPT) probe [22], fisetin, one of natural 3-hydroxyflavonols, was observed in the presence of the AP site. Recently, we found that berberine [23], one of natural isoquinoline alkaloids, can selectively bind to the AP site with a sequencedependent manner. Although fluorescence enhancement was observed for these fluorophores, the alteration in their emission wavelengths upon binding to the AP site was not more than 60 nm. Herein, another alkaloid, sanguinarine (SG), was employed to achieve a much larger emission shift up to 170 nm when binding to the AP site. SG belongs to a benzophenanthridine alkaloid, which is known for its antitumor property and possesses the potential for selective/DNA Abasic Site Binderpreferential elimination of cancer cells [24?8]. Besides its interaction with proteins [29] and amino acids [30], one of the potential antitumor activities of SG is believed to result from its highly specific binding to many types of nucleic acid structures and subsequent modification of the genetic information [31]. SG exhibits a pH-dependent structure equilibrium in aqueous solution between the positively charged iminium (in the pH rang 1.0?.0) and the neutral alkanolamine (in the pH rang 8.5?1.0) forms (Figure 1) [31,32]. The iminium form is unsaturated and completely planar, while the alkanolamine form has a buckled structure. SG can interact with polymorphic nucleic acid structures including DNA (B form [33], Z form, triplex [34], quadruplex [35]) and RNA (for example, poly(A) [36]). It is widely believed that the iminium form is mainly responsible for the DNA binding [37]. In addition, binding-induced fluorescence quenching and a strong GC base pair binding preference were observed [38?41]. In this work, we found that SG exhibits a sequence-dependent AP site binding behavior in the aspect of the enhanced emission for the iminium form that is converted from the alkanolamine form. Thus, targeting the AP site with a larger emission shift can be realized by thorough conversion of the alkanolamine emission band to the iminium emission band. The.