Photodynamic Inactivation of Candida albicans with Imidazoacridinones: Influence of Irradiance, Photosensitizer Uptake and Reactive Oxygen Species Generation

Abstract

The increasing applicability of antifungal treatments, the limited range of available drug classes and the emergence of drug resistance in Candida spp. suggest the need for new treatment options. To explore the applicability of C. albicans photoinactivation, we examined nine structurally different imidazoacridinone derivatives as photosensitizing agents. The most effective derivatives showed a >104-fold reduction of viable cell numbers. The fungicidal action of the three most active compounds was compared at different radiant powers(3.5 to 63 mW/cm2), and this analysis indicated that 7 mW/cm2 was the most efficient. The intracellular accumulation of these compounds in fungal cells correlated with the fungicidal activity of all 9 derivatives. The lack of effect of verapamil, an inhibitor targeting Candida ABC efflux pumps, suggests that these imidazoacridinones are not substrates for ABC transporters. Thus, unlike azoles, a major class of antifungals used against Candida, ABC transporter-mediated resistance is unlikely. Electron paramagnetic resonance (EPR)-spin trapping data suggested that the fungicidal light-induced action of these derivatives might depend on the production of superoxide anion. The highest generation rate of superoxide anion was observed for 1330H, 1610H, and 1611. Singlet oxygen production was also detected upon the irradiation of imidazoacridinone derivatives with UV laser light, with a low to moderate yield, depending on the type of compound. Thus, imidazoacridinone derivatives examined in the present study might act via mixed type I/type II photodynamic mechanism. The presented data indicate lack of direct correlation between the structures of studied imidazoacridinones, cell killing ability, and ROS production. However, we showed for the first time that for imidazoacridinones not only intracellular accumulation is necessary prerequisite of lethal photosensitization of C. albicans, but also localization within particular cellular structures. Our findings present IA derivatives as efficient antifungal photosensitizers with a potential to be used in local treatment of Candida infection.

‘Acridines’ as New Horizons in Antifungal Treatment

“…Acridine and acridone derivatives are molecules with fluorescence properties that have also been demonstrated to possess photosensitizing properties [26][27][28]. Studies performed by Taraszkiewicz et al showed that imidazoacridinones ( Figure 3) were efficient photosensitizers in the PDI of C. albicans and significantly inhibited the growth of planktonic cells [27].…”

“…Importantly, no direct correlation between the structures of studied imidazoacridinone derivatives, cell killing ability and ROS production was observed. For the most effective compounds capable of killing fungal cells by PDI, not only intracellular accumulation was necessary, but also localization within particular cellular structures [28].…”

“…There has been substantial work showing that the mode of action of m-AMSA as DNA intercalation Despite the high efficiency of C-1311 as an anticancer compound that intercalates into DNA and inhibits human topoisomerase II [29] (was in phase II clinical trials for the treatment of breast cancer [30]), it was unable to accumulate in C. albicans cells and no antifungal activity was observed [27]. Results of experimental investigations demonstrated that the fungicidal activity, which is light-induced, might depend on the production of superoxide anions [28]. The highest rate of superoxide anion generation was observed for C-1330 (hydrochloride salt), C-1610 (hydrochloride salt) and C-1611 ( Figure 3).…”

“…On the other hand, recent studies performed with verapamil, a known inhibitor targeting Candida ABC transporters, suggested that imidazoacridinones are not substrates for ABC efflux pumps. In contrast to azoles, a major class of antifungal agents used to treat candidiasis, ABC transporter-mediated resistance is unlikely [28].…”

“…- [17] 1,8-dioxoacridine derivatives - [27,28] Acridine conjugates with branched lysine peptides C. albicans A. niger…”