Antifungal Therapy with Itraconazole Impairs Rituximab′s Anti-Lymphoma Effect by Inhibiting CD20 Recruitment to Lipid Rafts.

Abstract 2735

Poster Board II-711

Patients with hematologic malignancies have a high risk of developing invasive fungal infections. The higher risk is attributed to host defense impairment due to intensive cytotoxic chemotherapies, hematopoetic stem cell transplantation, and immunosuppressive agents. As early treatment initiation in patients with invasive fungal infections has a profound impact on mortality rates, different antifungal treatment strategies like prophylaxis, empirical, pre-emptive and targeted treatment after proven fungal infection have been developed. Azoles are the most broadly used antifungal drugs inhibiting CYP51. They play a pivotal role in the treatment and prophylaxis of systemic and dermal mycoses. Azoles inhibit the sterol 14a-demethylase activity and block sterol biosynthesis, which is lethal in unicellular organisms. However, in mammalian cells, it has been shown that they lower endogenous cholesterol production. As lipid rafts consist of sphingolipids and cholesterol and lipid rafts have been demonstrated to be crucial for rituximab induced cell death, we asked whether rituximab exhibits its full anti-lymphoma effect in the presence of azoles.

We now demonstrate that antifungal treatment with itraconazole impairs rituximab's anti-lymphoma effect both in vitro and in vivo. Using a mouse xenograft model, no tumor growth was observed in mice treated with rituximab. In contrast, in the presence of itraconazole there was tumor growth, indicating that the concentration was sufficient to antagonize rituximab′s anti-lymphoma effect. On the molecular level, CD20 raft recruitment was inhibited in the presence of itraconazole. Furthermore, the translocation of CD20 into lipid rafts has been shown to be crucial for calcium influx and apoptosis. Therefore, we tested the rituximab induced calcium flux in the absence and presence of itraconazole. Indeed, calcium flux was almost completely abolished in the presence of itraconazole. The fact that antibody treatment failure in the presence of itraconazole only affects targeted therapy against raft associated molecules i.e. CD20 and CD52 but not the non raft associated molecule CD33 further supports our proposed mechanism of action. Together, our data suggest that concomitant treatment of itraconazole and rituximab attenuates rituximab's anti-lymphoma effect. As chemotherapy by itself has high response rates in lymphoma, the loss of rituximab mediated cell death in the presence of itraconacole may be missed in our daily routine.