Evaluation of the activity of some water‐soluble ferrocene and ferricenium compounds against carcinoma of the lung by the human tumor clonogenic assay

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Abstract
The two ferrocene compounds, ferrocenylacetic acid (3) and ferrocylthiomalic acid (4), as well as the ferricenium salts, ferricenium tetrachloroferrate (III) (1) and ferricenium trichloroacetate–trichloroacetic acid solvate (2), were investigated by the in vitro human tumor clonogenic assay for their inhibiting effects, in continuous exposure in a double‐layer medium, on the colony formation of single‐cell suspensions prepared from 30 selected fresh specimens of human adenocarcinoma, squamous cell carcinoma and large‐cell carcinoma of the lung. At the high drug concentration level of 100 μg cm −3, good response ratios were observed for 3 (79%) and 4 (72%), followed by 1 (67%) and 2 (52%). At the low concentration level of 10 μg cm−3 response ratios were below 25% for all compounds, best performance (24%) being shown by 1. In vitro experiments probing the schedule dependencies of the compounds' inhibiting effects against the lung carcinoma cell line PC‐9 were also performed, as were experiments involving the combination of the ferricenium salt 1 and cisplatin, which showed the combination effect to be additive in both one‐hour and continuous‐exposure tests.