In vitro sensitivity to platinum-derived drugs is associated with expression of thymidylate synthase and dihydropyrimidine dehydrogenase in human lung cancer

Thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) are critical enzymes in nucleic acid metabolism. Proliferating cell nuclear antigen (PCNA) is a specific protein that is correlated with proliferative activity of cells. The TS gene has a variable number of tandem repeats (VNTR) in its 5'-untranslated region and a single nucleotide polymorphism (SNP) in the VNTR area. We examined the association of in vitro sensitivity to anticancer drugs with TS polymorphism, TS, DPD, and PCNA mRNA expression using human lung cancer tissues. Seventy-eight surgically resected lung cancer tissues were tested for in vitro sensitivity to 5-fluorouracil, cisplatin (CDDP), carboplatin (CBDCA), irinotecan, docetaxel, and gemcitabine by histoculture and MTT assay. The TS polymorphisms were analyzed by PCR and PCR-RFLP. TS, DPD, and PCNA mRNA expression levels were quantified by real-time RT-PCR and normalized relative to beta-actin mRNA expression. The inhibition rates (IRs) of CDDP and CBDCA were significantly correlated with TS/PCNA, the ratio of TS/actin and PCNA/actin, and DPD/PCNA, the ratio of DPD/actin and PCNA/actin. This correlation was further explored by subgroup analyses according to TS VNTR or TS functional type, in which 2R/3G, 3C/3G, or 3G/3G were classified into H-type group and 2R/2R, 2R/3C, or 3C/3C into L-type group. The associations of TS/PCNA and DPD/PCNA with the IRs of CDDP, CBDCA remained significant in the 3R/3R group and H-type group. These results suggest that in vitro sensitivity to platinum-derived drugs, CDDP and CBDCA, is associated with PCNA-normalized mRNA expression of TS and DPD in human lung cancer tissues, as affected by the TS polymorphism. The clinical significance of these pharmacogenomic markers for chemotherapy regimens with platinum-derived drugs should be investigated further for personalized treatment of lung cancer.