Amrubicin, a novel 9-aminoanthracycline, enhances the antitumor activity of chemotherapeutic agents against human cancer cells in vitro and in vivo

Abstract

Amrubicin, a completely synthetic 9-aminoanthracycline derivative, is an active agent in the treatment of untreated extensive disease-small-cell lung cancer and advanced non-small-cell lung cancer. Amrubicin administered intravenously at 25 mg/kg substantially prevented the growth of five of six human lung cancer xenografts established in athymic nude mice, confirming that amrubicin as a single agent was active in human lung tumors. To survey which antitumor agent available for clinical use produces a synergistic interaction with amrubicin, we examined the effects in combinations with amrubicinol, an active metabolite of amrubicin, of several chemotherapeutic agents in vitro using five human cancer cell lines using the combination index (CI) method of Chou and Talalay. Synergistic effects were obtained on the simultaneous use of amrubicinol with cisplatin, irinotecan, gefitinib and trastuzumab, with CI values after 3 days of exposure being <1. Additive effect was observed with the combination containing vinorelbine with CI values indistinguishable from 1, while the combination of amrubicinol with gemcitabine was antagonistic. All combinations tested in vivo were well tolerated. The combinations of cisplatin, irinotecan, vinorelbine, trastuzumab, tegafur/uracil, and to a lesser extent, gemcitabine with amrubicin caused significant growth inhibition of human tumor xenografts without pronouncedly enhancing body weight loss, compared with treatment using amrubicin alone at the maximum tolerated dose. Growth inhibition of tumors by gefitinib was not antagonized by amrubicin. These results suggest that amrubicin appears to be a possible candidate for combined use with cisplatin, irinotecan, vinorelbine, gemcitabine, tegafur/uracil or trastuzumab.

Figure 1

Effects of amrubicin and doxorubicin on the tumor growth and body weight change in human small‐cell lung cancer (SCLC) or non‐small‐cell lung cancer (NSCLC) xenograft models. Female mice bearing tumors were randomly allocated into groups of six to eight animals. Amrubicin and doxorubicin were administered i.v. on day 0 at doses of 25 mg/kg and 12.5 mg/kg, respectively. ○; control, •; amrubicin, ▴; doxorubicin. Results are given as mean ± standard deviation (SD).

Figure 2

Combination index values for amrubicinol with chemotherapeutic agents. Cells were simultaneously exposed to two agents at fixed ratios for 3 days at 37°C in 5% CO₂. Results are given as means of three separate experiments and bars indicates 95% confidence intervals (CI). CI < 1, = 1 and > 1 indicate synergism, addition and antagonism, respectively.

Figure 3

Effects of amrubicin, chemotherapeutic agents and their combination on the tumor growth and body weight change in human small‐cell lung cancer (SCLC) or non‐small‐cell lung cancer (NSCLC) xenograft models. Female mice bearing tumors were randomly allocated into groups of six animals Amrubicin was administered i.v. on day 0 at a dose of 25 mg/kg approximately 1 h before an administration of the other chemotherapeutic agents in every experiment. All results are given as the mean ± standard deviation (SD). (a) LX‐1; cisplatin was administered i.v. on day 0 at a dose of 10 mg/kg. ○; control, •; amrubicin, □; cisplatin, ▴; amrubicin + cisplatin. (b) LX‐1; irinotecan was administered i.v. on day 0 at a dose of 120 mg/kg. ○; control, •; amrubicin, □; irinotecan, ▴; amrubicin + irinotecan. (c) LX‐1; gemcitabine was administered i.p. on day 0 and 7 at a dose of 300 mg/kg per day. ○; control, •; amrubicin, □; gemcitabine, ▴; amrubicin + gemcitabine. (d) QG‐56; vinorelbine was administered i.v. on day 0 at a dose of 16 mg/kg. ○; control, •; amrubicin, □; vinorelbine, ▴; amrubicin + vinorelbine.

Figure 4

Effects of amrubicin, chemotherapeutic agents and their combination on the tumor growth and body weight change in human tumor xenograft models. Female mice bearing tumors were randomly allocated into groups of six animals. Amrubicin was administered i.v. on day 0 at a dose of 25 mg/kg approximately 1 h before an administration of the other chemotherapeutic agents in every experiment. All results are given as the mean ± standard deviation (SD). (a) 4‐1ST; trastuzumab was administered i.p. twice per week for 2 weeks at a dose of 100 mg/kg per day. ○; control, •; amrubicin, □; trastuzumab, ▴; amrubicin + trastuzumab. (b) SC‐6; tegafur/uracil was administered p.o. 5qd at a dose of 28 mg/kg per day. ○; control, •; amrubicin, □; tegafur/uracil, ▴; amrubicin + tegafur/uracil. (c) A431; gefitinib was administered p.o. 5qd at a dose of 150 mg/kg per day. ○; control, •; amrubicin, □; gefitinib, ▴; amrubicin + gefitinib.