Lexicon Pharmaceuticals has reported positive, top-line proof-of-concept data from its recently completed phase II study in carcinoid syndrome with LX1032, telotristat etiprate. Carcinoid syndrome is a chronic condition caused by neuroendocrine tumors that usually originate from the gastrointestinal tract. It is characterized by severe diarrhea and flushing episodes with long-term consequences including malnutrition, heart disease, and death. Symptoms of carcinoid syndrome have been linked to excess production of serotonin by metastatic tumor cells. Telotristat etiprate is designed to reduce serotonin production.

The randomized, double-blind, placebo-controlled study was conducted in the United States in 23 patients with carcinoid syndrome who were refractory to currently available therapy. Patients in the study had metastatic carcinoid disease and were experiencing an average of about six bowel movements per day at baseline. Patients received either placebo (n=5) or one of four doses of telotristat etiprate (n=18) daily for 28 days. The primary endpoint of the study was safety and tolerability. Efficacy measures included change in bowel movement frequency, relief of symptoms, and reduction in serotonin synthesis.

Telotristat etiprate was well tolerated, and adverse events in the study were usually mild to moderate with similar frequencies overall between treatment groups and placebo. Five telotristat etiprate patients achieved clinical responses characterized by reductions of at least 30% in the number of bowel movements per day for two weeks or more during the study.

Six telotristat etiprate patients reported adequate relief of carcinoid symptoms at the end of the study. There were nine telotristat etiprate patients with a complete biochemical response defined as a reduction of at least 50% in urinary 5-HIAA, a biomarker of serotonin synthesis. No patients on placebo experienced a clinical response, adequate relief of symptoms, or biochemical response during the study. The difference between telotristat etiprate and placebo in bowel movement frequency ranged between 1.6 and 2.9 bowel movements/day across telotristat etiprate doses, all favoring telotristat etiprate treatment. All eligible patients elected to continue treatment with telotristat etiprate under an extension protocol.

Preliminary data were also reported from a separate, ongoing, open-label, single-arm study of telotristat etiprate in Europe. To date, 5 out of 6 patients with refractory carcinoid syndrome have experienced sustained reductions of at least 30% in bowel movement frequency when treated with telotristat etiprate. Two of these responses were within the first 4 weeks of therapy, while three more occurred between 4 and 8 weeks of treatment under the 12-week protocol.