Radioimmunotherapy of B-cell lymphoma: In vitro investigations of 177Lu-rituximab on raji cells

Abstract

Background: Rituximab is a chimeric monoclonal antibody, approved by the US Food and Drug Administration for the immunotherapy of non-Hodgkin's lymphoma (NHL).177Lu-labeled rituximab has been identified as a potential agent for the radioimmunotherapy of NHL and is presently under clinical investigations. The objective of the present study is to estimate the magnitude of apoptotic cell death and cell-cycle phase arrest. Materials and Methods: Characterization of177Lu-rituximab was performed by using instant thin-layer chromatography as well as by high-performance liquid chromatography. About 37 MBq (1 mCi) of177Lu-rituximab was incubated with Raji cells up to 48 h at 37°C in a humidified atmosphere of 5% CO2. Simultaneously, an equivalent amount of rituximab present in 37 MBq (1 mCi) of177Lu-rituximab complex was used as a vehicle control. All cell samples (treated, vehicle control, and control cells) were harvested post 24 and 48 h of incubation to perform different assays such as lactate dehydrogenase, XTT, cell viability by flowcytometer, apoptosis, and cell cycle analysis. Results: The studies revealed that177Lu-rituximab induced higher cell death and apoptosis compared to unlabeled rituximab. Similarly, an increase in cell population in G1-phase of cell cycle was observed, upon treatment of Raji cells with177Lu-rituximab complex for 24 h, while an increase in G2/M phase population was observed at 48 h of incubation. Conclusions: The present studies demonstrate that177Lu-rituximab is more effective in inducing apoptotic cell death and cell cycle-phase arrest compared to its unlabeled counterpart, indicating177Lu-rituximab may have better potential in the therapy of B-cell lymphoma.