We have studied clinical and pre-clinical models to investigate neuroendocrine tumour (NET) development and efficacy of novel therapy for NETs. We focused on multiple endocrine neoplasia type 1 (MEN1), an autosomal dominantly inherited condition characterised by the combined occurrence of pancreatic islet and anterior pituitary NETs with parathyroid and adrenocortical tumours. MEN1 is due to MEN1 gene mutations that inactivate Menin, a tumour suppressor. Our clinical studies revealed the unexpected occurrence of >2 cm non-functioning pancreatic NETs in >15% of asymptomatic children with MEN1, leading to updated international guidelines for pancreatic NET screening and detection by 10 years of age in MEN1 patients. Treatment of MEN1-associated foregut carcinoids, pancreatic and pituitary NETs is more difficult than for equivalent tumours in non-MEN1 patients as they are larger, multiple, more aggressive, have a higher prevalence of metastases, and resist chemotherapy or radiotherapy due to low proliferation rates. Therefore, to facilitate development of better and alternative therapies for MEN1-associated NETs, we established a knockout mouse model for MEN1 and novel in vivo methodologies to: evaluate NET proliferation using long-term five-bromo-two-deoxyuridine administration in drinking water; mathematically model NET growth kinetics; and MRI for NET imaging. Our pre-clinical studies revealed that homozygous loss of Men1was embryologically lethal and influenced by genetic modifiers. However, heterozygous (Men1+/−) mice developed pancreatic, pituitary, parathyroid, and adrenocortical tumours with hypercalcaemia, hypophosphataemia and hypercorticosteronaemia. Furthermore, NETs had loss of heterozygosity for Men1 and loss of menin expression, whilst proliferation rates were <2% and followed second-order kinetics. Therefore, we undertook a blinded, randomised-controlled trial of Men1 gene therapy for treating Men1+/− pituitary NETs using a recombinant replication-deficient adenoviral vector expressing wild-type Men1. Treated NETs demonstrated in vivo expression of menin and inhibition of proliferation, without significant adverse effects or increased mortality, and established pre-clinical proof-of-concept for gene replacement therapy in pituitary NETs.
Declaration of funding
This work was supported by the United Kingdom Medical Research Council (grants numbers G9825289, G0501780/76451 and G1000467), the Wellcome Trust (grant number 087332/Z/08/Z), Portuguese Foundation for Science and Technology (grant number BD/12415/2003) and the United Kingdom National Institute of Health Research.