Thymidylate Synthase (TS) is the key enzyme responsible for thymidylate synthesis and DNA replication which is often up-regulated in cancer cells exposed to 5-Fluorouracil (5-FU), a widely used anti-tumor drug. TS is the target enzyme inhibited by 5-FU, thus its over-expression or mutation, commonly detected in gastric and colon cancer cells, is predictive of drug-resistance and poor prognosis. We have performed an immunopharmacological study in order to evaluate the possibility of using a novel 28-mer [TS/PP] peptide containing the amino-acidic sequences of three TS-derived-epitopes with HLA-(*)02.01-binding motifs, to raise a TS-directed CTL-response with anti-tumor activity. An in vitro study was performed by testing the peptide-specificity and the anti-tumor activity of CTL lines generated from human HLA-(*)02.01+ PBMCs, with IL-2 and autologous TS/PP peptide loaded DC. The immunological activity, the toxicity and anti-tumor activity of the TS/PP peptide alone or in combination with 5-FU +/- Gemcitabine were tested an HLA-(*)02.01-trangenic (HHD) mice. Prevention and therapeutic models were performed in mice inoculated with syngenic EL-4/HHD. Results- The CTL lines generated with the TS/PP peptide showed a TS-multi-epitopic specificity and the ability to kill TS+/HLA-A(*)02.01+breast and colon carcinoma cells. The killing ability was significantly greater against target cells previously exposed to sublethal doses of 5-FU able to induce TS-up-regulation. TS/PP vaccination of HHD mice induced a TS-peptide-specific CTL response with no sign of autoimmunity or toxicity. The Antitumor activity was particularly significant when TS/PP was combined with 5-FU and gemcitabine treatment. The results of this study provide a new means of anticancer vaccine and provide the rationale of combining TS-directed cancer vaccines with fluoropyrimidine-based chemotherapy.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]