Mertansine-d3 (DM1-d3) is the deuterium labeled Mertansine (HY-19792). Mertansine (DM1) is a microtubulin inhibitor and is an antibody-conjugatable maytansinoid that is developed to overcome systemic toxicity associated with maytansine and to enhance tumor-specific delivery. Mertansine can be attached to a monoclonal antibody with a linker to create an antibody-drug conjugate (ADC)[1][2].