Immunotoxin WPD101a as a Potential Drug Candidate for Targeted Therapy in Muscle Invasive Bladder Cancer Expressing IL-13Rα2—In Vitro Study

The failure of therapy in muscle invasive bladder cancer (MIBC) is primarily attributed to tumor heterogeneity and therapy resistance. We propose a novel approach targeting interleukin-13 receptor subunit alpha 2 (IL-13Rα2), which is expressed on bladder cancer (BC) cells but absent in normal urothelial cells. We investigated the therapeutic effects of WPD101a immunotoxin (IL-13-DT390) on IL-13Rα2-expressing BC cells in relation to BC cell phenotype and functional characteristics in vitro using both 2-dimensional (2D) and 3-dimensional (3D) models. Cell phenotype and IL-13Rα2 expression were assessed using flow cytometry, immunofluorescence, and Western blot analysis. The biological effects of WPD101a were evaluated by measuring cell viability and proliferation using the MTT, sulforhodamine B (SRB), CellTiter-Glo and Live/Dead assays. Apoptosis was assessed using Annexin V/propidium iodide (PI) staining, and quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis of CASP genes expression. We found that the reference BC cell lines TCC-SUP, JMSU-1 and UM-UC-3 express IL-13Rα2 at various level in contrast to RT-4, HCV-29 and 5637 cells. Cells expressing IL-13Rα2 were sensitive to WPD101a at lower concentrations in the 2D model (0.1 ng/mL) compared to the 3D model (1.0 ng/mL). IL-13Rα2-negative cells remain resistant to the immunotoxin. WPD101a induces apoptosis in BC cells expressing IL-13Rα2 as confirmed by the presence of apoptotic cells, increase the proportion of cells in the subG1 phase, and by the effector CASP3, CASP7, and initiator CASP8, CASP9 genes expression. This study confirmed receptor-dependent cytotoxic effects of WPD101a and the ability and specificity to inhibit growth and apoptosis induction in MIBC cells expressing IL-13Rα2.