Background: Recent development of novel anticancer drugs has shown possible roles of anticancer chemotherapy, improving patients’ quality of life (QOL) and prognosis. On the other hand, long-term treatment with an anticancer drug will result in progressive acquirement of drug-resistance in cancer cell itself. We previously reported No cross-resistance of taxanes to 5-FU and CDDP and cross-resistance between 5-fluoroutacil(5-FU) and cisplatin (CDDP) using wild types of human gastric cancer cell line (Maeda S, Saikawa Y, et al. Anticancer Res 23: 3147-3150, 2003).Methods: We have established CDDP-resistant and 5-FU-resistant gastric cancer cell lines using wild types of human gastric cancer cell lines; TMK-1, MKN-74, and MKN-45 with long-term exposure (several months) with low concentration of each drug (named as TMK-1/D, MKN-74/D, MKN-45/D, TMK-1/FU, MKN-74/FU, MKN-45/FU). IC50s were analyzed to demonstrate resistance to each drug, calculated with each concentration-survival curve with MTT method, and to evaluate cross-resistance or no cross-resistance to the other drugs including docetaxel (DOC) and paclitaxel (PAC). Results:1.The IC50s of CDDP were as follows: TMK-1 2.14±0.46μg/ml, TMK-1/D 10.43±2.20μg/ml, MKN-74 6.69±3.19μg/ml, MKN-74/D 28.53±9.80μg/ml, MKN-45 10.52±0.24μg/ml, MKN-45/D 13.16±4.62μg/ml, as the IC50 ratio of TMK-1/D to TMK-1 was 4.87 fold, and MKN-74/D to MKN-74 was 4.26 fold, while MKN-45/D to MKN-45 was only 1.25 fold. The IC50s of 5-FU were as follows: TMK-1 240.39±14.04μg/ml, TMK-1/FU 1236.84±54.90μg/ml, MKN-74 169.15±26.51μg/ml, MKN-74/FU 1859.23±52.3μg/ml, MKN-45 25.7±7.35μg/ml, MKN-45/FU 1574.50±105.30μg/ml, as the IC50 ratios of TMK-1/FU to TMK-1 , MKN-74/FU to MKN-74, and MKN-45/FU to MKN-45 were 5.03, 10.99, 61.26 fold, respectively. 2.Cross-resistance between 5-FU and CDDP in each resistant cell were confirmed, as the IC50 ratio of CDDP of TMK-1/FU to TMK-1, MKN-74/FU to MKN-74, and MKN-45/FU to MKN-45 was 4.72, 4.87, 2.77 fold, respectively. 3.The IC50s of DOC and PAC in each wild and resistant cell line were calculated. Interestingly, cross-resistance was not confirmed in PAC (0.38-0.48 fold) treatment, but DOC (5.04- 6.43 fold), in CDDP-resistant cell lines. On the other hand, in 5-FU-resistant cell lines, there is no cross-resistance between 5-FU and DOC (0.32-1.04 fold) or between 5-FU and PAC (0.78-2.00 fold).Conclusion: Acquired chemo-resistant cells established demonstrated various kinds of chemo-sensitivity to DOC/PAC, while 5-FU and CDDP have clearly shown cross-resistance even using the resistant cells to each drug.Appropriate drugs like DOC or PAC should be applied after acquired drug resistance to 5-FU or CDDP was suggested, in order to overcome 5-FU or CDDP chemo-resistance, while these results also suggested that even DOC might not be useful in CDDP chemo-resistance cells because of cross-resistance, in some occasion.

99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA