XL557

XL557 is an investigational, orally bioavailable small molecule agonist of the somatostatin receptor subtype 2 (SSTR2). Developed by Exelixis, it is primarily being investigated for the treatment of neuroendocrine tumors (NET). Somatostatin receptors are widely expressed in NETs, and their activation inhibits hormone secretion and tumor cell proliferation. While traditional somatostatin analogs (SSAs) typically require frequent or long-acting depot injections, XL557 is designed as an oral therapeutic to enhance patient convenience and potentially optimize receptor activation kinetics. As of early 2026, the program is in the discovery and preclinical development stages, with an Investigational New Drug (IND) filing planned for 2026.