Biological effect of auger electron emitting radiopharmaceuticals: a comparison of ¹²⁵I-rituximab and ¹²⁵I-deoxy uridine

Auger electrons (AEs) are very low energy electrons that are emitted by radionuclides that decay by electron capture. One of the well know is ¹²⁵I radionuclide. This energy is deposited under micrometre ranges, resulting in high linear energy transfer (LET) that is potent for causing lethal damage in cancer cells. Thus, AE-emitting radiotherapeutic agents have great potential for treatment of cancer. Rituximab is a FDA approved chimeric, murinehuman, anti CD20 antibody against B lymphocyte binds specifically to CD20 antigen present on B-lymphocyte with high affinity and specificity. Deoxy uridine is a nucleotide base analoguse to target nuclear DNA. Both rituximab and deoxy uridine was labeled with I-125 and its effect was studied on Raji cell lines. Materials - MTT solution, LDH assay kit, Metabolism (MDA) Assay kit, human CERK ELISA kit, SOD1 assay kit and 4-HNE assay kit. Cells are treated with labeled Rituximab and 2 '-deoxyuridine with 48 hours of incubation and effect was studied using various assays. Post treatment cells are tested for viability by MTT assay where lesser viable cells found in (¹²⁵I)-2 '-deoxyuridine in comparison to (¹²⁵I)-Rituximab with mean absorbance 0.557 and 0.689 respectively. Membrane integrity tested using LDH assay in which LDH release in medium obtained 18.28% in (¹²⁵I)-Rituximab and 1.28% in (¹²⁵I)-2 '-deoxyuridine. Absorbance in metabolism assay for detection of oxidative stress found 0.058 in (¹²⁵I)-Rituximab and 0.04 in (¹²⁵I)-2 '- Deoxyuridine. Ceramide kinase which is a cell signaling and apoptotic lipid molecule found higher in (¹²⁵I)-2 '-deoxyuridine with concentration 470 ng/ml than (¹²⁵I)-Rituximab whose concentration is 437 ng/ml. Absorbance of SOD1 assay in (¹²⁵I)-Rituximab and (¹²⁵I)-2 '- Deoxyuridine treated cells was 0.393 and 0.303 respectively. Lesser absorbance of 4-HNE obtained in (¹²⁵I)-Rituximab when compared to (¹²⁵I)-2 '-deoxyuridine with actual absorbance 354 and 0.722 respectively. Biological effects post treatment studied in Raji tumor cell line. Since Rituximab bind to CD20 over expressed in Raji cell and biological effects induced by lipid peroxidation of cell membrane, while deoxyuridine is an analogue of base which is building block of DNA, radiation emitted from Iodine -125 may lead to severe DNA damage and cause cell death mostly by apoptosis. (author)