Quercetin induces apoptosis and autophagy in primary effusion lymphoma cells by inhibiting PI3K/AKT/mTOR and STAT3 signaling pathways.

Quercetin, a bioflavonoid contained in several vegetables daily consumed, has been studied for long time for its antiinflammatory and anticancer properties. Quercetin interacts with multiple cancer-related pathways such as PI3K/AKT, Wnt/β-catenin and STAT3. These pathways are hyperactivated in primary effusion lymphoma (PEL), an aggressive B cell lymphoma whose pathogenesis is strictly linked to the oncogenic virus Kaposis' Sarcoma-associated Herpesvirus (KSHV). In this study, we found that quercetin inhibited PI3K/AKT/mTOR and STAT3 pathways in PEL cells, and as a consequence, it down-regulated the expression of the prosurvival cellular proteins such as c-FLIP, cyclin D1 and cMyc. It also reduced the release of IL-6 and IL-10 cytokines, leading to PEL cell death. Moreover, quercetin induced a prosurvival autophagy in these cells and increased the cytotoxic effect of bortezomib, a proteasomal inhibitor, against them. Interestingly, quercetin decreased also the expression of latent and lytic KSHV proteins involved in PEL tumorigenesis and up-regulated the surface expression of HLA-DR and calreticulin, rendering the dying cells more likely detectable by the immune system. The results obtained in this study indicate that quercetin, which does not exert any cytotoxicity against normal B cells, may represent a good candidate for the treatment of this aggressive B cell lymphoma, especially in combination with autophagy inhibitors or with bortezomib.