Effects of small interfering RNA targeting thymidylate synthase on survival of ACC3 cells from salivary adenoid cystic carcinoma

An ACC cell line (ACC3) was transfected with siRNA targeting the TS gene and inhibition of cell growth and induction of apoptosis-associated molecules were evaluated in vitro. In addition, the in vivo effect of TS siRNA on tumor progression was assessed using a xenograft model.Our results demonstrated that ACC3 cells showed significantly higher TS expression than non-cancer cell lines and the induction of TS siRNA led to inhibition of cell proliferation. The effect was associated with an increase in p53, p21, and active caspase-3 and S-phase accumulation. We also found up-regulation of spermidine/spermine N1-acetyltransferase (SSAT), a polyamine metabolic enzyme. Furthermore, treatment with TS siRNA delivered by atelocollagen showed a significant cytostatic effect through the induction of apoptosis in a xenograft model.TS may be an important therapeutic target and siRNA targeting TS may be of potential therapeutic value in ACC.Adenoid cystic carcinoma (ACC) is one of the most common salivary gland carcinomas and has indolent characteristics and an ultimately fatal outcome. Although ACC is thought to typically grow slowly, late occurrence of locoregional recurrence and distance metastasis is very common because of a propensity for perineural invasion. ACC shows various histological patterns including tubular, cribriform, and solid types. It has been widely accepted that the prognosis for tumors that predominantly comprise solid patterns is worse than that of those with a tubular or cribriform pattern [1]. Several molecules, including p16, p27, and E-cadherin, have been proposed as prognostic markers [2-4], but markers useful as therapeutic targets have not been identified in ACC.Thymidylate synthase (TS), a folate-dependent enzyme, plays a crucial role in DNA biosynthesis. TS catalyzes the transfer of one methyl group from methylenetetrahydrofolate to generate deoxythymidine-5'-monophosphate (dTMP) from 2'-deoxyuridine-5'-monophosphate (dUMP). dTMP is then phosphoryl