Telotristat ethyl: proof of principle and the first oral agent in the management of well-differentiated metastatic neuroendocrine tumor and carcinoid syndrome diarrhea

INTRODUCTION

Metastatic neuroendocrine tumors (NETs) are associated with carcinoid syndrome that is typically characterized by diarrhea, cutaneous flushing and bronchospasm. Treatment with somatostatin analogues (SSA) improves the symptom burden but a significant proportion of patients stop responding to SSA therapy eventually. Novel agents with the potential to effectively control the symptoms are urgently needed.

METHODS

This article reviews an in-depth analysis of the phase I-III clinical trials determining the clinical rationale for the use of tryptophan hydroxylase inhibitor, telotristat ethyl in patients with well-differentiated metastatic NETs and uncontrolled carcinoid syndrome.

DISCUSSION

Telotristat ethyl has already been approved for the treatment of inadequately controlled carcinoid syndrome symptoms in metastatic NET patients on SSA therapy. Results from multiple phase I-III clinical studies of telotristat ethyl therapy have reported a significant decrease in the daily bowel movement frequency, increase in quality of life and the subsequent decrease in annual health costs related to carcinoid syndrome symptoms in NET patients.

FUTURE DIRECTIONS

The associated decrease in urinary 5-hydroxyindoleacetic acid (u5-HIAA) provides evidence that telotristat ethyl effectively decreases serotonin production, and therefore, offers a rationale to investigate this agent to mitigate serotonin-mediated complications in this patient population, especially cardiac valvular disease or mesenteric fibrosis.

Management Options for Advanced Low or Intermediate Grade Gastroenteropancreatic Neuroendocrine Tumors: Review of Recent Literature

Our understanding of the biology, genetics, and natural history of neuroendocrine tumors (NETs) of the gastrointestinal tract and pancreas has improved considerably in the last several decades and the spectrum of available therapeutic options is rapidly expanding. The management of patients with metastatic low or intermediate grade NETs has been revolutionized by the development of new treatment strategies such as molecular targeting therapies with everolimus and sunitinib, somatostatin analogs, tryptophan hydroxylase inhibitors, and peptide receptor radionuclide therapy that can be used alone or as a multimodal approach with or without surgery. To further define and clarify the utility, appropriateness, and the sequence of the growing list of available therapies for this patient population will require more high level evidence; however, data from well-designed randomized phase III clinical trials is rapidly accumulating that will further stimulate development of new management strategies. It is therefore important to thoroughly review emerging evidence and report major findings in frequent updates, which will expand our knowledge and contribute to a better understanding, characterization, and management of advanced NETs.

Telotristat Ethyl: First Global Approval

Telotristat ethyl (Xermelo™) is a peripheral tryptophan hydroxylase (TPH) inhibitor that was developed by Lexicon Pharmaceuticals, Inc. for the treatment of carcinoid syndrome. Many neuroendocrine tumours secrete serotonin (5-HT) into the blood stream, resulting in a number of symptoms, notably diarrhoea. Telotristat ethyl inhibits TPH, thereby reducing the production of 5-HT. In February 2017, telotristat ethyl was approved in the USA for the treatment of carcinoid syndrome diarrhoea in combination with somatostatin analog (SSA) therapy in adults inadequately controlled by SSA therapy. This article summarizes the milestones in the development of telotristat ethyl leading to this first global approval.