Loncastuximab tesirine

Human CD19 antigen is a membrane glycoprotein in the immunoglobulin superfamily expressed in the various stages of B-cell development; it is detected in most malignancies of B-cell origin. Additionally, CD19 has rapid internalization kinetics and does not shed into the general circulation, rendering it a useful therapeutic target for antibody-drug conjugates (ADCs) in the treatment of B-cell malignancies.

Loncastuximab tesirine is an antibody-drug conjugate designed to target human CD19. It is a humanized monoclonal antibody and conjugated to SG3199, a pyrrolobenzodiazepine (PBD) dimer cytotoxin by a protease enzyme cleavable valine-alanine linker. The monoclonal IgG1 kappa antibody component binds to CD19, a transmembrane protein located on B-cell surfaces. The small molecule component, SG3199, functions as a PBD dimer and alkylating agent. Following binding to CD19, loncastuximab tesirine becomes internalized into the cell and subsequently proteolytic cleavage releases the SG3199 component. SG3199 binds to the DNA minor groove, forming cytotoxic DNA interstrand crosslinks, leading to B-cell cell death.