New perspectives on the medicinal chemistry of the somatostatin receptor agonist SOM230

MEDI 234

Ian Lewis, ian.lewis@novartis.com, Rainer Albert, Janos Pless, Rainer Kneuer, Herbert A. Schmid, Antonio P. Silva, Daniel Hoyer, Gisbert Weckbecker, and Christian Bruns. Global Discovery Chemistry, Novartis Institutes of Biomedical Research, S-507.3.03, CH-4002 Basel, Switzerland
The somatostatin (SRIF, somatotropin release inhibiting factor) field has been a success story in terms of medicinal chemistry and drug discovery offering a variety of therapeutic opportunities, e.g. acromegaly, gastrointestinal neuroendocrine tumors, whole body imaging and radiotherapy. Indeed, a rational medicinal chemistry approach capitalising on structure activity relationships led to the discovery of SOM230, a stable cyclohexapeptide somatostatin analogue which exhibits unique binding to human SRIF receptors (sst1-5). This approach, based on transposing functional groups, in the form of unnatural amino acids, from SRIF-14 into the stable, reduced size cyclohexapeptide template. Further, the hydroxyproline urethane extension of SOM230 has been functionalized with the chelators DTPA and DOTA, which is a necessary prerequisite for the possible development of ligands which could be used for whole body imaging. Uniquely, SOM230 exhibits binding with a 30 to 40 times higher affinity than Sandostatin® to the sst1 and sst5 receptors and exhibits higher efficacy in preclinical models in lowering Growth Hormone, Insulin-Like Growth Factor-1, ACTH and corticosterone than Sandostatin®. Phase III clinical studies are underway to establish the therapeutic potential of SOM230 including novel treatment of Cushing's disease.