A new, therapeutic approach in medullary thyroid cancer treatment:: Inhibition of oncogenic RET signaling by adenoviral vector-mediated expression of a dominant-negative RET mutant

Background. Mutations in the RET proto-oncogene that result in constitutive tyrosine kinase activity are the underlying cause for the development of medullary thyroid cancer (MTC). To investigate an alternative strategy in MTC treatment, we took advantage of a dominant-negative RET (dn-RET) mutant, Ret(51) HSCR32, which inhibits oncogenic signal transduction by retaining the oncogenie RET protein in the endoplasmic reticulum, thereby reducing the amount Of oncogenic RET protein from the cell surface. Methods. We constructed an adenoviral (Ad) vector expressing dn-RET under control of the C-cell specific synthetic calcitonin promoter TSE2. CP1 (AdTSE2. CP1-RET(51)HSCR32) and investigated the effect of dn-RET on cell growth of MTC-derived TT cells. Results. Analysis of the subcellular localization of endogenous oncogenic RET protein showed a significant dominant-negotive effect of Ad vector-delivered dn-RET in TT cells, resulting in a strong inhibition of cell viability. The observed effect is partially dependent on growth inhibition, and possibly opoptosis induction. Conclusions. In the present study, growth of human MTC cells was successfully inhibited by Ad vector-mediated delivery of RET(51)HSCR32, suggesting that inhibition of oncogenic RET receptor tyrosine kinase expression by a dn-RET mutant might be a powerful approach for in vivo therapy of MTC.