OBJECTIVETo study target killing of 5-FU drug-fast cancer cells with thymidylate synthase (TS) and p16 gene promoters inducting TK gene expression.

METHODSTS promoter was inserted to 5' end and p16 promoter inserted to 3' end of TK cDNA sequence, constructing recombinant plasmid of pXJ41. Human rectal cancer cell lines of HR-8348 and normal peripheral blood mononuclear cells (PBMC) were transfected with the recombinant plasmid. Plating efficiency was counted and survival rates of cells were tested with MTT method. And suppression rates of xenograft tumors in nude mice were examined.

RESULTSRecombinant pXJ41 with double promotors and TK gene was transfected into HR-8348, and positive expression of TS and TK was observed. The expression of TK gene was consistent with TS expression. Plating efficiency was 9/300, 92/300 in transfected HR-8348 and contrast cells respectively (t = 33.885, P < 0.01). Cancer cell growth rate reduced markedly in the transfected group. The suppression rate of xenograft tumor growth was 74.5%. With the recombinant pXJ41 to transfect PBMC, p16 expression was positive, but TK and TS expressions were negative. No damnification was observed in PBMC.

CONCLUSIONSTS and p16 double promoters are capable of inducting TK target killing of 5-FU drug-fast cancer cells, thus protecting normal cells and improving safety of gene therapy.