Rituximab is a chimeric monoclonal antibody directed against B-lymphocyte specific antigen CD20, which is used for the treatment of B-cell malignancies. However, the effectiveness of rituximab is limited partly due to treatment resistance. The aim of this study was to develop rituximab-based antibody drug conjugate (ADC) to enhance rituximab activity. In this study, monomethyl auristatin E (MMAE) was covalently conjugated to dithiothreitol -reduced rituximab via a valine-citrulline peptide linker (rituximab-vcMMAE). The conjugates were then characterized by using nonreducing sodium dodecyl sulfate-polyacrylamide electrophoresis (SDS-PAGE) and cell-based enzyme-linked immunosorbent assay (ELISA). The cytotoxic activity of the ADC was evaluated against Raji (human B-cell lymphoma; CD20-positive) and MOLT-4 (T lymphoblast; acute lymphoblastic leukemia; CD20-negative) cell lines. In addition, the colony formation assay was used to identify the propagation ability of ADC-treated cells in vitro. Results from nonreducing SDS-PAGE revealed various species of rituximab-MC-Val-Cit-PABC-MMAE (rituximab-vcMMAE), as compared with unconjugated rituximab. The binding capacity of rituximab-vcMMAE to the CD20-positive cell was similar to that of the parental rituximab. Most importantly, our results revealed that rituximab-vcMMAE was highly potent against the CD20-positive cell line, but not against the CD20-negative cell. At the same time, rituximab-vcMMAE was able to inhibit colony formation in CD20-positive cells. These data indicate that rituximab-vcMMAE may be a highly effective and selective therapy for the treatment of B-cell lymphoma.

Background and objectives: The present study was conducted to detect class 1 integrons and evaluate antibiotic susceptibility patterns among clinical isolates of P. aeruginosa. Methods: Sixty clinical samples from blood, tracheal wounds, burns and urinary tract infections were collected from three general hospitals in Tehran, Iran. Culture of specimens was performed on common bacteriological culture media. Bacteria were identified based on mobility, pigment production, growth at 42 o C, and oxidase and catalase tests. Overall, 21 P. aeruginosa strains were isolated. Antimicrobial susceptibility of was evaluated via the disk diffusion method (Kirby-Bauer) according to the CLSI guidelines. Presence of the intI1, sul1, aadA2 and aadB gene cassettes was investigated using PCR. The collected data were analyzed using SPSS software (version 21). Results: The most effective antimicrobial agents against P. aeruginosa isolates were tetracycline and gentamicin. All P. aeruginosa isolates were multidrug resistant. Moreover, the intI1, sul1, aadA2 and aadB genes were found in 90.5%, 90.5%, 47.6% and 19% of the P. aeruginosa isolates, respectively. Conclusion: The results indicate that the presence of aadB, aadA2 and sul1 gene cassetes may play an important role in the dissemination of antimicrobial resistance determinants.

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