Fig. 2: Mechanisms of action of T-DM1.
From: Mechanisms of resistance to trastuzumab emtansine (T-DM1) in HER2-positive breast cancer
T-DM1 exerts anti-tumour activity via at least three distinct mechanisms. As for trastuzumab, engagement of HER2 receptors by T-DM1 inhibits downstream signalling pathways (via RAS–mitogen-activated protein kinase [MAPK] and phosphatidylinositol 3-kinase [PI3K]–AKT–mammalian target of rapamycin [mTOR]) and ectodomain shedding while also eliciting immune effector cell function (e.g. antibody-dependent cellular cytotoxicity) mediated via Fc receptors. T-DM1–HER2 complexes are also internalised via receptor-mediated endocytosis, after which endocytic vesicles mature through the endosomal pathway for ultimate delivery to lysosomes. Trastuzumab is proteolytically degraded in lysosomes, liberating lysine-MCC-DM1 for active transport into the cytoplasm, where it inhibits tubulin polymerisation resulting in failure of the mitotic spindle and ultimate mitotic catastrophe.
