Cancer Res Treat.  2006 Jun;38(3):159-167.

The Synergism between Belotecan and Cisplatin in Gastric Cancer

• Jung JY
• Song SH
• Kim TY
• Park JH
• Jong HS
• Im SA
• Kim TY
• Bang YJ
• Kim NK

Abstract

PURPOSE: We wanted to demonstrate the anti-cancer effect and interaction between belotecan and cisplatin on gastric cancer cell line and we evaluated the mechanisms of this synergistic effect in vitro.
MATERIALS AND METHODS
The growth inhibitory effect of belotocan and cisplatin against several gastric cancer cell lines (SNU-5, SNU-16 and SNU-601) was estimated by tetrazolium dye assay. The effect of a combination treatment was evaluated by the isobologram method. The biochemical mechanisms for the interaction between the drugs were analyzed by measuring the formation of DNA interstrand cross-links (ICLs) and DNA topo-I activity.
RESULTS
Belotecan showed synergism with cisplatin for growth inhibitory effect on the gastric cancer cell lines SNU-5, and SNU-16, but this was subadditive on the SNU-601 cell line. The formation of DNA ICLs in SNU-16 cells by cisplatin was increased by combination with belotecan, but this was not affected in SNU-601 cells. The topo-I inhibition by belotecan was enhanced at high concentrations of cisplatin in SNU-16, but not in SNU-601 cells.
CONCLUSION
Belotecan and cisplatin show various combination effect against gastric cancer cells. The synergism between cisplatin and belotecan could be the result of one of the following mechanisms: the modulating effect of belotecan on the repair of cisplatin-induced DNA adducts and the enhancing effect of cisplatin on the belotecan-induced topo-I inhibitory effect.

Keyword

Belotecan; Cisplatin; Synergism; Stomach neoplasms

MeSH Terms

Cell Line
Cisplatin*
DNA
DNA Adducts
Stomach Neoplasms*
Cisplatin
DNA
DNA Adducts

Figure

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  Fig. 1 Chemical structures of camptothecin and belotecan (CKD602).

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  Fig. 2 IC50 isobologram in the combination of drug A and drug B.

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  Fig. 3 The dose-response cell survival curve of belotecan in combination with cisplatin against SNU-5 (A), SNU-16 (B), and SNU-601 (C). The addition of increasing doses of cisplatin induced marked suppression of cell survival by belotecan for the SNU-5 and SNU-16 cells. Yet for the SNU-601 cells, the cytotoxicity by belotecan was not much enhanced by the addition of cisplatin.

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  Fig. 4 IC50 isobologram of belotecan in combination with cisplatin against SNU-5 (A), SNU-16 (B), and SNU-601 (C). The isobologram of SNU-5 (A) indicates that the combination effect is mainly additive for the combinations of belotecan with cisplatin. All of the data points of SNU-16 fell in the area of supraadditivity. In case of SNU-601 cells, the data points fell in the area of sub-additivity, and even protectivity. These results can be interpreted that the combined effect of belotecan and cisplatin for SNU-5, SNU-16 and SNU-601 cells is additive, synergistic and antagonistic (not protective), respectively.

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  Fig. 5 The effects of belotecan on cisplatin-induced ICL formation in SNU-16 (A) and SNU-601 cells (B). The CI with cisplatin alone was significantly lower than the CIs (p<0.005) with cisplatin and belotecan in SNU-16 cells (A), and the effect of the addition of belotecan shows a dose-response relationship. In case of SNU-601 cells (B), there was no significant difference between the CI with cisplatin alone and that with combination of cisplatin and belotecan. These results represent that belotecan enhances the formation of cisplatin-induced ICL in SNU-16 cells, but not in SNU-601 cells.

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  Fig. 6 The effects of cisplatin (CDDP) on the inhibitory effect of belotecan (CKD) on topo-I in SNU-16 (A) and SNU-601 cells (B). I, Ir, and II were supercoiled, relaxed, and nicked DNA, respectively. Most of the plasmid DNA was in the superhelical form (Fig. 6A, Lane 1; Fig. 6B, Lane 1). The nuclear extract (2 µg/ml) from the SNU-16 and SNU-601 cells relaxed the supercoiled DNA (Fig. 6A, Lane 2; Fig. 7B, Lane 2), whereas belotecan inhibited this relaxation in the SNU-16 and SNU-601 cell lines (Fig. 6A, Lanes 3 and 6; Fig. 6B Lanes 3 and 6). Five and 10 µg/ml cisplatin increased the inhibition of topo-I by belotecan in the SNU-16 cells (Fig. 6A, Lanes 4, 5, 7 and 8), but it showed no effects on the inhibition of topo-I by belotecan in the SNU-601 cells (Fig. 6B, Lanes 4, 5, 7 and 8). Therefore, these results could be interpreted that cisplatin enhanced the topo-I inhibition by belotecan in SNU-16 cells, but not in SNU-601 cells.

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