In vitro action of flavonoids in the canine malignant histiocytic cell line DH82

Abstract

Cancer is commonly diagnosed in dogs over the age of 10 and is a leading cause of death due to the lack of effective drugs. Flavonoids possess antioxidant, anti-inflammatory and anticarcinogenic properties and have been studied as chemopreventive agents in human cancer therapy. However, the literature on dogs is sparse. In this study, we analyzed the effect of nine flavonoids on cell viability, DNA damage and topoisomerase IIa/IIb gene expression in a canine tumor cell line (DH82). Apigenin, luteolin, trans-chalcone and 4-methoxychalcone showed the highest degree of cytotoxicity in the absence of considerable DNA damage, whereas genistein exhibited low cytotoxicity but induced a high level of DNA damage. These five flavonoids inhibited topoisomerase IIa and IIb gene expression to variable extents and with variable specificity. Genistein exerted a lower inhibitory effect on the two topoisomerases than luteolin and apigenin. trans-Chalcone and 4-methoxychalcone exerted greater inhibition of topoisomerase IIa expression than topoisomerase IIb. The differences in the effects between genistein and luteolin and apigenin might be explained by the position of ring B, whereas the more specific effect of chalcones on topoisomerase IIa might be due to their open chain structure.

Figure 1

Inhibition of the viability of DH82 cells induced by flavonoids and topoisomerase after 24, 48 and 72 h of treatment. (A) Quercetin; (B) myricetin; (C) fisetin; (D) epigallocatechin gallate (EGCG); (E) genistein; (F) luteolin; (G) apigenin; (H) trans-chalcone; (I) 4-methoxychalcone; (J) etoposide; (L) merbarone. Symbols represent the mean of at least three independent experiments and the error bar indicates the standard deviation. Different letters indicate statistically significant results (p < 0.05).

Figure 2

Chemical structure of flavonoids and topoisomerase inhibitors. (A) General structure of flavonoids; (B) general structure of chalcones; (C) quercetin; (D) myricetin; (E) fisetin; (F) epigallocatechin gallate (EGCG); (G) genistein; (H) luteolin; (I) apigenin; (J) trans-chalcone; (L) 4-methoxychalcone; (M) etoposide; (N) merbarone.

Figure 3

Effect of flavonoids and topoisomerase inhibitors on the expression of topoisomerase IIa and IIb genes. The cells were treated with flavonoids at a concentration of 12.5 µg/mL for 6 h. The concentration of etoposide and merbarone was 2.5 µg/mL. The results are expressed as the mean ± standard error of at least three independent experiments. Different letters indicate statistically significant results (p < 0.1).