Effects of bleomycin A5 combined with calmodulin inhibitor on the proliferation of S-180 cellsin vitro

The effects of bleomycin A5 (BLM A5) alone and combined with calmodulin inhibitor N-(4-aminobutyl)-5-chloro-2-naphthalene sulfonamide (W-13) on the proliferation on S-180 cellsin vitro were studied. IC₅₀ of BLM used alone for the cells was about 2.63 μg/ml, but it was reduced to 1/3.8 and 1/9.5 of 2.63 μg/ml when plus W-13 1, 5 μg/ml respectively. The results indicated that nontoxic doses of W-13 enhanced the hinibition of cell proliferation under the condition of BLM 0.5–2.5 μg/ml. In colony forming test, the survival fraction of S-180 cells treated with BLM plus W-13 was decreased to 1/87–240 of that of the cells treated with BLM alone. The results suggest that W-13 can enhance antitumor activity of BLMin vitro and may be used as an synergist of BLM A5in vivo.