Enhancing gemcitabine uptake by promoting dimerization of ENT1 transporter improves response rates of patients with sarcoma.

Transport of nucleoside chemotherapeutic drugs into tumor cells is primarily accomplished through equilibrative nucleoside transporter 1 (ENT1), which is considered constitutively active. Drugs are redistributed via ENT1 across lipid bilayers via facilitated diffusion. Here we discover that ENT1 is not constitutively active, but rather requires activation of acid sphingomyelinase (ASMase) by gemcitabine, generating ceramide-rich platforms (CRPs) on external plasma membranes of endothelial and tumor cells into which ENT1 inserts, dimerizing therein to functionalize transmembrane gemcitabine transport. Whereas sarcoma cells synthesize minimal ASMase, they take up gemcitabine poorly in vitro and in murine xenografts. A strategy designed to augment gemcitabine-induced ASMase secretion into the extravascular space by ASMase-rich neo-angiogenic cells, which then targets tumor cell plasma membranes, yields "bystander" CRPs on sarcoma cells and ENT1 insertion therein, conferring markedly enhanced gemcitabine uptake and xenograft response. Engaging this biology in a prospective phase II clinical trial in advanced sarcoma yielded robust volumetric changes in evaluated tumors that developed early and were often durable.