Rational combinations of amrubicin with cisplatin or irinotecan for small-cell lung cancer cells
Authors: Nagio Takigawa, Masami Takeyema, Takuo Shibayama, Atsuhiko Tada, Noriko Kawata, Keisuke Aoe, Masahiro Tabata, Katsuyuki Kiura, Hiroshi Ueoka, Kiyoshi Takahashi
Journal: Cancer Research (2005)

Proc Amer Assoc Cancer Res, Volume 46, 2005

4947 

A combination of irinotecan and cisplatin is one of the standard chemotherapy regimens in the treatment of small-cell lung cancer (SCLC). SN-38 is an active metabolite of irinotecan. We have already established SN-38-resistant subline (SBC-3/SN-38) and cisplatin-resistant subline (SBC-3/CDDP) from a human SCLC cell line, SBC-3. Amrubicin is a totally synthetic 9-aminoanthracyclin and converted to its active form, amrubicinol, that has 10 to 100 times higher activity than amrubicin in inhibiting topoisomerase II. We evaluated the cytotoxicity of amrubicinol for the SCLC cells using AlamarBlue assay. The drug concentration required to inhibit the growth of tumor cells by 50% (IC50) for 96h exposure was used for evaluating cytotoxicity. The interaction of combined drugs was evaluated by median-effect plot analysis and the combination index (CI) values at IC70 and IC90 levels were used for determining synergism (CI 1). The fraction of apoptotic cells was determined using flow cytometry after staining with propidium iodide. The mean IC50 values for the SBC-3 cells were as follows: amrubicinol, 33 nM; amrubicin, 862 nM; SN-38, 4.1 nM; irinotecan, 195 nM; cisplatin, 345 nM; etoposide, 270 nM; and paclitaxel, 0.55 nM. The SBC-3/SN-38 was 34-fold more resistant to SN-38 and the SBC-3/CDDP was 7.2-fold more resistant to cisplatin than the parental SBC-3. However, these resistant sublines retained the sensitivity to amrubicinol (1.8-fold and 1.7-fold, respectively). The mean CI values of simultaneous exposure at IC70 and IC90 for SBC-3 cells were 1.2 and 1.0 to amrubicinol and SN-38, 1.3 and 2.4 to amrubicinol and paclitaxel, 0.82 and 0.35 to amrubicinol and cisplatin, 1.1 and 0.85 to amrubicinol and etoposide, respectively. Thus, amrubicinol and cisplatin showed synergic effect, however, amrubicinol and paclitaxel exerted antagonistic effect. At IC90, the combination of amrubicinol and SN-38 showed additive effect and that of amrubicinol and etoposide displayed synergistic effect. The CI values of the sequential exposure to SN-38 followed by amrubicinol at IC70 and at IC90 were 1.5 and 2.2, respectively and those of the reverse sequence were 1.0 and 1.1, respectively, which suggest the sequential administration of amrubicinol followed by SN-38 is more effective than the reverse sequence. In addition, sequential exposure of the SBC-3 cells to amrubicinol followed by SN-38 produced more apoptotic cells than the reverse sequence. Simultaneous exposure of the SBC-3/SN-38 cells to amrubicinol and cisplatin showed synergistic effect (CI: 0.99 at IC70, 0.89 at IC90) and that of the SBC-3/CDDP cells to amrubicinol and SN-38 displayed synergistic or additive effects (CI: 0.76 at IC70, 1.0 at IC90). These findings indicate that amrubicin, both monotherapy and combinations with cisplatin or irinotecan, is effective against SCLC refractory to irinotecan and cisplatin.