Cell‐killing Activity and Kinetic Analysis of a Novel Antitumor Compound NC‐190, a Benzo[a]phenazine Derivative

A novel antitumor compound, N‐β‐dimethylaminoethyl 9‐carboxy‐5‐hydroxy‐10‐methoxybenzo[a]‐phenazine‐6‐carboxamide sodium salt (NC‐190), was evaluated for antitumor activity in vitro against cultured tumor cell lines, and the kinetics of cell killing was elucidated. NC‐190 strongly inhibited the growth of all of 3 murine tumor cell lines, 7 human tumor cell lines and 2 normal cell lines. With continuous exposure, the 50% inhibition concentrations were in the range of 0.005–0.06 μg/ml, except for KATO‐III (2.15 μ g/ml). By colony‐forming assay, concentrations of NC‐190 giving 90% cell kill (IC(90)) at various exposure times were obtained with HeLa S3 cells. The plot of IC(90)exposure time on a log‐log scale was linear for NC‐190 with a slope of ‐1, which is typical for cell cycle phase‐nonspecific agents. A 2 h treatment with NC‐190 induced a rapid reduction in cell viability at doses of more than 3 μ g/ml. At the dose where colony formation was completely inhibited, cell viability was persistently reduced to below 20% during the cell culture period. NC‐190 cauced a dose‐ and time‐dependent reduction in DNA synthesis. The inhibitions of RNA and protein synthesis were less than that of DNA synthesis. Spectroscopic studies of NC‐190 mixed with calf thymus DNA demonstrated that NC‐190 was capable of interacting with DNA. However, DNA thermal denaturation studies suggested that intercalation of NC‐190 was weak in comparison with those of classical intercalating drugs.