Definition

A proprietary antibody-drug conjugate (ADC) composed of upinitatug , a proprietary, humanized monoclonal antibody against human sodium-dependent phosphate transport protein 2B (SLC34A2; NaPi2b), site-specifically linked, via a protease cleavable linker, to the proprietary cytotoxic aurastatin derivative auristatin F-HPA (AF-HPA; auristatin F-hydroxypropylamide), with potential antineoplastic activity. Upinitatug rilsodotin is produced via the proprietary dolaflexin ADC conjugation platform, which promotes the conjugation of between 10 and 15 AF-HPA payload molecules to each XMT-1535 antibody. Upon administration of upinitatug rilsodotin, the antibody moiety targets and binds to NaPi2b expressed on tumor cells. Upon binding, internalization by endosomes/lysosomes, and enzymatic cleavage, the AF-HPA binds to tubulin and inhibits microtubule polymerization, which results in G2/M phase arrest and apoptosis of NaPi2b-expressing tumor cells. NaPi2b, a tumor-associated antigen (TAA), is overexpressed on a variety of cancer cells and plays a key role in the transport of inorganic phosphate (Pi) and the maintenance of phosphate homeostasis.