In vitro analysis of single chain variable fragment-based immunotoxins against Erythropoietin-producing hepatocellular A2 receptor overexpressed in breast cancer cells

Breast cancer is one of the leading causes of cancer deaths worldwide. Thereafter, designing new treatments with higher specificity and efficacy is urgently required. In this regard, targeted immunotherapy using immunotoxins has shown great promise in treating cancer. To target a breast cancer cell, the authors used the antibody fragment against a receptor tyrosine kinase, EphA2, which is overexpressed in many cancers. This fragment was conjugated to a plant toxin, subunit A of ricin, in two different orientations from N to C-terminal (EphA2- C-Ricin and EphA2- N-Ricin). Then, these two immunotoxins were characterized using in vitro cell-based assays. Three different cell lines were treated, MDA-MB-231 (breast cancer) which has a high level of EphA2 expression, MCF-7 (breast cancer) which has a low level of EphA2 expression, and HEK293 (human embryonic kidney) which has a very low level of EphA2 expression. Moreover, binding ability, cytotoxicity, internalization, and apoptosis capacity of these two newly developed immunotoxins were investigated. The flow cytometry using Annexin V- Propidium iodide (PI) method indicated significant induction of apoptosis only in the MDA-MB-231 cells at different concentrations. It was also found that construct I, EphA2- C-Ricin immunotoxin, could bind, internalize, and induce apoptosis better than the EphA2- N-Ricin immunotoxin. In addition, the obtained data suggested that the N or C-terminal orientation conformation is of significant importance.