Quercetin induces cell apoptosis of myeloma and displays a synergistic effect with dexamethasone in vitro and in vivo xenograft models

Quercetin, a kind of dietary flavonoid, has shown its anticancer activity in many kinds of cancers including hematological malignancies (acute myelogenous leukemia, chronic myelogenous leukemia, chronic lymphocytic leukemia, and MM) in vitro and in vivo. However, its effects on MM need further investigation. In this study, MM cell lines were treated with quercetin alone or in combination with dexamethasone. In order to observe the effects in vivo, a xenograft model of human myeloma was established. Quercetin inhibited proliferation of MM cells (RPMI8226, ARP-1, and MM.1R) by inducing cell cycle arrest in the G2/M phase and apoptosis. Western blot showed that quercetin downregulated c-myc expression and upregulated p21 expression. Quercetin also activated caspase-3, caspase-9, and poly(ADP-ribose)polymerase 1. Caspase inhibitors partially blocked apoptosis induced by quercetin. Furthermore, quercetin combined with dexamethasone significantly increased MM cell apoptosis. In vivo xenograft models, quercetin obviously inhibited tumor growth. Caspase-3 was activated to a greater extent when quercetin was combined with dexamethasone. In conclusion, quercetin alone or in combination with dexamethasone may be an effective therapy for MM.