Low dose of 131I-F(ab')2-Rituximab and 131I-Rituximab induces G1arrest and apoptosis in Raji cells (Burkitt’s lymphoma)

Abstract

Radiolabeled fragmented F(ab')₂ antibodies had shown better therapeutic efficacy than radiolabeled intact antibodies in treating cancers.  In this study, we investigated the differences and similarities on the mechanism and extent of cell death in Raji cells (Burkitt’s lymphoma) in response to 370 kBq of ¹³¹I-F(ab')₂-Rituximab and ¹³¹I-Rituximab up to 72 h. F(ab')₂ of Rituximab was prepared and characterized by SE-HPLC and SDS-PAGE. Fragmented and intact Rituximab were radioiodinated by Chloramine-T method. Toxicity and mechanism of cell death in Raji cells in response to ¹³¹I-F(ab')₂-Rituximab and ¹³¹I-Rituximab were studied by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), LDH (lactate dehydrogenase), trypan blue exclusion, viability, apoptotic, caspase assays and cell cycle analysis. The cytotoxicity assays showed slow death of Raji cells up to 24 h in response to both ¹³¹I-F(ab')₂-Rituximab and ¹³¹I-Rituximab. Cell cycle analysis at 30 h showed G1 arrest in Raji cells which led to its slow cell death up to 24 h. Elucidative assays to identify the molecular mechanism of death of G1arrested Raji cells showed apoptotic cell death at 40 h after treatment, which was validated by demonstrating caspase activation in arrested Raji cells. Toxicity studies and mechanism of cell death in Raji cells demonstrated comparable results when treated with equivalent doses (370 kBq) of radiolabeled antibodies indicating ¹³¹I-F(ab')₂-Rituximab as a potential radioimmunotherapeutic agent for patients with Non-Hodgkin’s lymphoma.